calculated mineral equilibria for eclogites in cao na2o feo mgo al2o3 sio2 h2o application to the pouebo terrane pam peninsula new caledonia the high p medium t pouebo terrane of the pam peninsula northern new caledonia includes barroisite and glaucophane bearing eclogite and variably rehydrated equivalents the metamorphic evolution of the pouebo terrane is inferred from calculated p t and p t xh2o pseudosections for bulk compositions appropriate to these rocks in the model system cao na2o feo mgo al2o3 sio2 h2o the eclogites experienced a clockwise p t path that reached p 19 kbar and t 600 c the eclogitic mineral assemblages are preserved because reaction consequent upon decompression consumed the rocks fluid extensive reaction occurred only in rocks with fluid influx during decompression of the pouebo terrane

salinity driven thermocline transients in a wind and thermohaline forced isopycnic coordinate model of the north atlantic abstract an isopycnic coordinate oceanic circulation model formulated with the aim of simulating thermodynamically and mechanically driven flow in realistic basins is presented special emphasis is placed on the handling of diabatic surface processes and on thermocline ventilation the model performance is illustrated by a 30 year spinup run with coarse horizontal resolution 2 mesh in a domain with north atlantic topography extending from 10 to 60 n latitude the vertical structure encompasses 10 isopycnic layers in steps of 0 2 units capped by a thermodynamically active mixed layer from an initially isohaline state with isopycnals prescribed by zonally averaged climatology the model is forced by seasonally varying wind stress radiative and freshwater fluxes and by a thermal relaxation process at the surface after a mechanical spinup time of about 15 years a quasi stationary pattern of mean circulation and annual variability ensues characterized by pronounced subtropical mode water formation

global adjustment of the thermocline in response to deepwater formation the global adjustment of the thermocline in response to deepwater formation is studied in a single mode model on a beta plane the signal is carried from ocean to ocean by kelvin waves which travel equatorward along western boundaries eastward across the equator poleward at the eastern boundaries and then eastward around the southern tip of continents into the next ocean basin the interior is filled by rossby waves emanating from eastern boundaries stronger weaker deepwater formation induces an upward downward motion of the main thermocline in the world oceans the adjustment is completed on centennial time scales

permian outliers in western kentucky abstract two small down faulted outliers of latest pennsylvanian to early permian rocks occur in western kentucky these are the youngest paleozoic rocks in the illinois basin and are approximately 550 and 750 km respectively from strata of comparable age in the dunkard basin and midcontinent a continuous core gil 30 was drilled in the eastern cap mauzy outlier fusulinids leptotriticies beardi from a depth of 59 4 m were originally used as evidence for permian age although this species is now considered to be latest pennsylvanian ostracods from above the fusulinids support a permian age the upper 103 6 m of gil 30 is assigned to the mauzy formation and contains intervals of bedded micritic nodular to brecciated limestone of probable lacustrine origin alternating with marine to brackish water clastic intervals that tend to coarsen upward a single upward fining sandstone interval and a single 2 cm thick coal layer older strata contain much more coal and almost no bedded non marine limestone the grove center graben 18 km west of gil 30 is identified on the basis of an oil test hole electric log and coal test holes no core samples are available but log comparison indicates that the grove center outlier contains at least an additional 67 m of younger strata than gil 30 and is a prime target for further study regional coalification and oil maturation trends along with lack of evidence for syndepositional tectonic activity in gil 30 indicate that the permian rocks preserved in gil 30 and by extension the grove center graben are likely representative of strata that once occupied much of the illinois basin probably in continuity with the midcontinent the kentucky outliers therefore provide a link between the midcontinent and dunkard basins and may be important in addressing long standing problems such as the age of the dunkard and paleoclimate reconstructions

lawsonite omphacite bearing metabasites of the pam peninsula ne new caledonia evidence for disrupted blueschist to eclogite facies conditions

fractionation of bulk rock composition due to porphyroblast growth effects on eclogite facies mineral equilibria pam peninsula new caledonia chemically zoned porphyroblasts in metamorphic rocks indicate that diffusional processes could not maintain equilibrium conditions on a grain scale during porphyroblast growth or establish it afterwards an effect of this inability to maintain equilibrium is the progressive removal of elements forming garnet cores from any metamorphic reaction that occurs at the porphyroblast boundaries or in the matrix of the rock to examine this effect on mineral assemblages the bence albee matrix correction was applied to x ray intensity maps collected using eclogite samples from northern new caledonia in order to determine the chemical composition of all parts of the sample the manipulation of these element maps allows a quantitative analysis of the fractionation of the bulk rock composition between garnet cores and the matrix a series of calculated equilibrium volume compositions represents the change in matrix chemistry with progressive elemental fractionation as a consequence of prograde garnet growth under high p conditions pressure temperature pseudosections are calculated for these compositions in the cao na2o feo mgo al2o3 sio2 h2o system assemblages modal proportions and mineral textures observed in the new caledonian eclogites can be closely modelled by progressively removing elements forming garnet cores from the bulk rock composition the pseudosections demonstrate how chemical fractionation effects the peak metamorphic assemblage prograde textures and the development of retrograde assemblages

simulated variability of the atlantic meridional overturning circulation to examine the multi annual to decadal scale variability of the atlantic meridional overturning circulation amoc we conducted a four member ensemble with a daily reanalysis forced medium resolution global version of the isopycnic coordinate ocean model micom and a 300 years integration with the fully coupled bergen climate model bcm the simulations of the amoc with both model systems yield a long term mean value of 18 sv and decadal variability with an amplitude of 1 3 sv the power spectrum of the inter annual to decadal scale variability of the amoc in bcm generally follows the theoretical red noise spectrum with indications of increased power near the 20 years period comparison with observational proxy indices for the amoc e g the thickness of the labrador sea water the strength of the baroclinic gyre circulation in the north atlantic ocean and the surface temperature anomalies along the mean path of the gulf stream shows similar trends and phasing of the variability indicating that the simulated amoc variability is robust and real mixing indices have been constructed for the labrador the irminger and the greenland iceland norwegian gin seas while convective mixing in the labrador and the gin seas are in opposite phase and linked to the nao as observations suggest the convective mixing in the irminger sea is in phase with or leads the labrador sea newly formed deep water is seen as a slow anomalous cold and fresh plume flowing southward along the western continental slope of the atlantic ocean with a return flow of warm and saline water on the surface in addition fast travelling topographically trapped waves propagate southward along the continental slope towards equator where they go east and continue along the eastern rim of the atlantic for both types of experiments the northern hemisphere sea level pressure and 2 m temperature anomaly patterns computed based on the difference between climate states with strong and weak amoc yields a nao like pattern with intensified icelandic low and azores high and a warming of 0 25 0 5 c of the central north atlantic sea surface temperature sst the reanalysis forced simulations indicate a coupling between the labrador sea water production rate and an equatorial atlantic sst index in accordance with observations this coupling is not identified in the coupled simulation

circulation and deep water export at the western exit of the subpolar north atlantic the current system east of the grand banks was intensely observed by world ocean circulation experiment woce array acm 6 during 1993 95 with eight moorings reaching about 500 km out from the shelf edge and covering the water column from about 400 m depth to the bottom more recently a reduced array by the institut fur meerskunde ifm at kiel germany of four moorings was deployed during 1999 2001 focusing on the deep water flow near the western continental slope both sets of moored time series each about 22 months long are combined here for a mean current boundary section and both arrays are analyzed for the variability of currents and transports a mean hydrographic section is derived from seven ship surveys and is used for geostrophic upper layer extrapolation and isopycnal subdivision of the mean transports into deep water classes the offshore part of the combined section is dominated by the deep reaching north atlantic current nac with currents still at 10 cm s 1 near the bottom and a total northward transport of about 140 sv sv 106 m3 s 1 with the details depending on the method of surface extrapolation used the mean flow along the western boundary was southward with the section mean north atlantic deep water outflow determined to be 12 sv below the 27 74 kg m 3 isopycnal however east of the deep western boundary current dwbc the deep nac carries a transport of 51 sv northward below 27 74 kg m 3 resulting in a large net northward flow in the western part of the basin from watermass signatures it is concluded that the deep nac is not a direct recirculation of dwbc water masses transport time series for the dwbc variability are derived for both arrays the variance is concentrated in the period range from 2 weeks to 2 months but there are also variations at interannual and longer periods with much of the dwbc variability being related to fluctuations and meandering of the nac a significant annual cycle is not recognizable in the combined current and transport time series of both arrays the moored array results are compared with other evidence on deep outflow and recirculation including recent models of different types and complexity

observations inferences and mechanisms of the atlantic meridional overturning circulation a review this is a review about the atlantic meridional overturning circulation amoc its mean structure temporal variability controlling mechanisms and role in the coupled climate system the amoc plays a central role in climate through its heat and freshwater transports northward ocean heat transport achieved by the amoc is responsible for the relative warmth of the northern hemisphere compared to the southern hemisphere and is thought to play a role in setting the mean position of the intertropical convergence zone north of the equator the amoc is a key means by which heat anomalies are sequestered into the ocean s interior and thus modulates the trajectory of climate change fluctuations in the amoc have been linked to low frequency variability of atlantic sea surface temperatures with a host of implications for climate variability over surrounding landmasses on intra annual timescales variability in amoc is large and primarily reflects the response to local wind forcing meridional coherence of anomalies is limited to that of the wind field on interannual to decadal timescales amoc changes are primarily geostrophic and related to buoyancy anomalies on the western boundary a pacemaker region for decadal amoc changes is located in a western transition zone along the boundary between the subtropical and subpolar gyres decadal amoc anomalies are communicated meridionally from this region amoc observations as well as the expanded ocean observational network provided by the argo array and satellite altimetry are inspiring efforts to develop decadal predictability systems using coupled atmosphere ocean models initialized by ocean data

hydration of eclogite pam peninsula new caledonia garnet glaucophanite and greenschist facies assemblages were formed by the recrystallization of barroisite bearing eclogite facies metabasites in northern new caledonia the mineralogical evolution can be modelled by calculated p t and p xh2o diagrams for appropriate bulk rock compositions in the model system cao na2o feo mgo al2o3 sio2 h2o the eclogites having developed in a clockwise p t path that reached p 19 kbar and t 590 c underwent decompression with the consumption of free h2o as the volume of hydrous minerals increased eclogite is preserved in domains that experienced no fluid influx following the loss of this fluid garnet glaucophanite formed at p 16 kbar during semi pervasive fluid influx fluid influx after further isothermal decompression was focused in shear zones and resulted in chlorite albite bearing greenschist facies mineral assemblages that reflect p 9 kbar

comparison of fluid geochemistry and microbiology of multiple organic rich reservoirs in the illinois basin usa evidence for controls on methanogenesis and microbial transport abstract microbial methane in sedimentary basins comprises approximately 20 of global natural gas resources yet little is known about the environmental requirements and metabolic rates of these subsurface microbial communities the illinois basin located in the midcontinent of the united states is an ideal location to investigate hydrogeochemical factors controlling methanogenesis as microbial methane accumulations occur 1 in three organic rich reservoirs of different geologic ages and organic matter types upper devonian new albany shale up to 900 m depth pennsylvanian coals up to 600 m depth and quaternary glacial sediments shallow aquifers 2 across steep salinity gradients and 3 with variable concentrations of so 4 2 for all three organic rich reservoirs aqueous geochemical conditions are favorable for microbial methanogenesis with near neutral ph so 4 2 concentrations 80 c in nutrient poor environments necessitating the re introduction of microbes into the subsurface via groundwater transport

oceanic teleconnections remote response to decadal wind forcing abstract the transhemispheric and interbasin response to time dependent wind forcing localized in the northern hemisphere of a single basin is examined using the reduced gravity shallow water equations in domains of simple geometry on decadal timescales the pressure on the eastern boundary fluctuates synchronously in both hemispheres and thus communicates a signal to latitudes distant from the forcing the signal then penetrates into the interior through westward radiation of rossby waves associated with the eastern boundary pressure fluctuation is a time dependent mass flux across the equator that in a single basin is balanced by a storage of mass in the unforced hemisphere two oceanic basins connected by a reentrant channel at the high latitude edge of the southern hemisphere are then considered again the forcing is confined to the northern hemisphere of one basin only in this geometry the time dependent mass flux across the equator of the forced basin is not entirely balanced within the same ba

sulfide evolution in high temperature to ultrahigh temperature metamorphic rocks from lutzow holm complex east antarctica the high temperature ht to ultrahigh temperature uht metamorphic rocks from lutzow holm complex east antarctica show a systematic difference between sulfide assemblages in the rock matrix and those found as inclusions in the silicates stable in high temperatures matrix sulfides are commonly pyrite with or without pentlandite and chalcopyrite on the other hand inclusion sulfides are pyrrhotite with or without pentlandite and chalcopyrite lamellae when recalculated into integrated single phase sulfide compositions inclusion sulfides from the uht region showed a wider range of solid solution composition than the inclusion sulfides from the ht region the host minerals of the sulfides with extreme solid solution compositions are those stable at the peak of metamorphism such as orthopyroxene and garnet one of the most extreme ones is included in orthopyroxene coexisting with sillimanite quartz which is the diagnostic mineral assemblage of uht metamorphism these observations suggest that sulfide inclusions preserve their peak metamorphic compositions pyrrhotite did not revert to pyrite because of the closed system behavior of sulfur in inclusion sulfides on the other hand in the rock matrix where the open system behavior of sulfur is permitted original sulfides were partly to completely altered by the later fluid activity

origin of illite in the lower paleozoic of the illinois basin evidence for brine migrations in the lower paleozoic of the illinois basin three illite polytypes are found 2m 1 of detrital origin and 1m d and 1m of diagenetic origin illite polytype quantification of detrital 2m 1 illite and diagenetic 1m d and 1m illite combined with k ar age dating allows extrapolation to apparent detrital and diagenetic illite ages kinetic modeling of smectite illitization combined with the calculated age of illitization can evaluate different origins of illite the diagenetic illite in the lower paleozoic of the illinois basin is interpreted not to have formed solely by burial diagenesis but mainly during multiple brine events the upper ordovician maquoketa group contains diagenetic illite dominantly 1m d with minor 1m with an extrapolated age of 360 m y 356 377 m y and formed from smectite at temperatures of 50 100 c this age falls within the span of dates for illite smectite i s in k bentonites from the upper mississippi valley and is interpreted to be a combined result of illitization by burial diagenesis and either a hydrothermal brine from the southern and deeper part of the basin or a k rich brine from the michigan basin upper mississippi valley area or forest city basin in ordovician and cambrian shale partings and sandstone older than the maquoketa group the diagenetic illite 1m d in shale and 1m in sandstone has an age of 300 m y and formed at temperatures 140 c this late paleozoic age falls within the range of illites from sandstone in the upper mississippi valley and k bentonites of the appalachian basin it coincides with the alleghany orogeny and is interpreted as having formed by gravity driven flow from the uplifted alleghanian ouachita orogenic belt that drove hot 140 c fluids through the illinois basin

is ocean thermohaline circulation linked to abrupt stadial interstadial transitions abstract are the abrupt stadial interstadial s is climate transitions observed in the greenland ice cores also seen in marine climate records literature which shows that the s is events have a large footprint in ocean surface marine properties encompassing the entire northern hemisphere has been reviewed whether this influence extends to the deep circulation is more equivocal on most recent evidence several of the heinrich ice rafting debris events are clearly associated with elimination of north atlantic source waters from the deep atlantic but most cores studied do not resolve the other s is events except for one new record from the bermuda rise which shows all of the major s is cycles in benthic foraminiferal deep sea corals can tell us how rapid these events are in the deep sea

mechanisms of multidecadal atlantic meridional overturning circulation variability diagnosed in depth versus density space abstractmultidecadal variability of the atlantic meridional overturning circulation amoc is examined based on a comparison of the amoc streamfunctions in depth and in density space in a 700 yr present day control integration of the fully coupled community climate system model version 3 the commonly used depth coordinate amoc primarily exhibits the variability associated with the deep equatorward transport that follows the changes in the labrador sea deep water formation on the other hand the density based amoc emphasizes the variability associated with the subpolar gyre circulation in the upper ocean leading to the changes in the labrador sea convection combining the two representations indicates that the 20 yr periodicity of the amoc variability in the first half of the simulation is primarily due to an ocean only mode resulting from the coupling of the deep equatorward flow and the upper ocean gyre circulation near the gulf stream and north atlantic current in addition the density based amoc

large scale structure of the eclogite blueschist belt of new caledonia abstract this paper considers the large scale geometry of the northern part of the eclogite blueschist belt of new caledonia based largely on classical style structural analysis but in consideration of modern concepts regarding crustal extension exhumation of high pressure rocks and uplift shear zones played an important role in the evolution of the region early shear zones and high pressure metamorphism appear to be associated with overthrusting of an ultramafic sheet middle stage shear zones are associated with large scale continental extension during which the high pressure rocks were exhumed the extended crust was subsequently folded during renewed compression producing an orogen scale antiform throughout the high pressure belt that folds all previously formed structures late stage shear zones formed when the orogen was once again thrown into extension relatively youthful normal faults caused late block faulting uplifting a regional peneplain and producing the present geomorphology previously published interpretations of the structure and geometry of the belt have suggested that the high pressure rocks are found in the core of a regionally developed antiform interpreted as a metamorphic core complex our structural mapping shows that allochthonous slices of high pressure rocks are draped over a younger unrelated foliation antiform lower grade retrogressed equivalent rocks are found within the core of the antiform thus the metamorphic core complex model is rejected

baroclinic rossby waves in a square basin abstract the properties of forced baroclinic quasigeostrophic rossby waves in an ocean basin are discussed with emphasis on the apparent phase speed the response to a traveling wave wind stress curl consists of three parts two of which propagate westward and one that tracks the wind the apparent phase speed in the basin interior depends on the relative sizes of the amplitudes of these three terms which vary with forcing frequency and scale and with the size of the deformation radius with low frequency large scale forcing one westward wave dominates and its phase speed is the long baroclinic rossby wave speed with smaller forcing scales the component that tracks the wind is comparably strong and the superposition with the dominant westward wave can produce augmented apparent phase speeds at frequencies larger than the maximum free wave frequency proportional to the deformation radius the westward waves are trapped in deformation scale boundary layers yielding a weak directly forced interi

interdecadal variations of the thermohaline circulation in a coupled ocean atmosphere model abstract a fully coupled ocean atmosphere model is shown to have irregular oscillations of the thermohaline circulation in the north atlantic ocean with a time scale of approximately 50 years the irregular oscillation appears to be driven by density anomalies in the sinking region of the thermohaline circulation approximately 52 n to 72 n combined with much smaller density anomalies of opposite sign in the broad rising region the spatial pattern of see surface temperature anomalies associated with this irregular oscillation bears an encouraging resemblance to a pattern of observed interdecadal variability in the north atlantic the anomalies of sea surface temperature induce model surface air temperature anomalies over the northern north atlantic arctic and northwestern europe

topographic coupling of the atlantic overturning and gyre circulations abstractthe vorticity dynamics associated with the mean and time varying gyre and overturning circulations of the atlantic ocean are examined in a realistic ocean model hindcast simulation of the late twentieth century abyssal flow interaction with sloping bottom bathymetry gives rise to the bottom pressure torque bpt term of the vertically integrated vorticity equation the dominance of this term in the closure of the barotropic gyre circulation noted in previous studies is corroborated here for both non eddy resolving and eddy resolving versions of the parallel ocean program pop model this study shows that bpt is also a dominant term in the vorticity balance of the atlantic meridional overturning circulation amoc and therefore represents a key dynamical link between the overturning and gyre streamfunctions the interannual variability of the atlantic circulation over the last several decades viewed in terms of time varying integral vorticity balances demonstrates the fundamental role played by

diagenesis of the purington shale in the illinois basin and implications for the diagenetic state of sedimentary rocks of shallow paleozoic basins abstract the clay minerals micas and feldspars of the pennsylvanian age purington shale have been more diagenetically active than generally recognized they have undergone diagenetic changes comparable to those of cenozoic and mesozoic sedimentary rocks buried three to four times as deeply and heated to approximately twice the temperature the purington shale on the western shelf of the illinois basin has experienced maximum burial of 1 0 km and was never heated to more than 60 c except for a very brief time at about 80 c the illite smectite i s of the purington shale has 90 illite the chemical compositions of the feldspar assemblage in the 0 09 0 063 mm fraction differ from most modern detrital suites of feldspars but are similar to diagenetic sequences described by others from much greater burial depths and are extensively but not completely albitized the simplest interpretation of the apparently advanced stage of diagenesis is that the diagenetic processes have been operating at less press

regional implications of u pb shrimp age constraints on the tectonic evolution of new caledonia abstract u pb shrimp ages for zircons from plagiogranites indicate a late carboniferous age of formation for ophiolitic basement of the koh terrane in the central chain mountains of new caledonia samples from ophiolites at koh and koua yielded ages of 302 7 ma and 290 5 ma respectively the similarity of these ages to those of plagiogranites in the dun mountain ophiolite belt maitai terrane of new zealand and the comparable structural positions of the two terranes potentially constrain reconstructions of the cretaceous sw pacific margin detrital zircons from late mesozoic sediments that overlap the koh terrane also provide potential constraints on the location of new caledonia prior to its break up and dispersal from eastern australia

variability of deep ocean mass transport spectral shapes and spatial scales abstract this paper studies the variability of deep ocean mass transport using four 1000 yr integrations performed with coupled general circulation models statistics describing the spectral and spatial features are considered it is shown that these features depend crucially on the time mean state for the transport of tropical and subtropical water masses in three of the integrations the spectral levels continually increase with decreasing frequency and do not show isolated peaks at low frequencies the slope of the low frequency spectrum in a log log plot changes with increasing depth it has values of about 0 near the surface about 1 at intermediate depth and about 2 at or near the bottom the result indicates that the maximal memory timescale for deep ocean mass transport is longer than a few centuries the situation is different in the fourth integration which has a different mean circulation pattern in this case the low frequency spectrum is more or less flat in the tropical and subtropic

the north atlantic current and surrounding waters at the crossroads the north atlantic current is a well defined western boundary current that flows north along the east side of the grand banks from 40 to 51 n where it turns sharply to the east and begins its journey across the ocean the current is unique in transporting warm tropical waters to much higher latitudes than any other western boundary current and thus plays a crucial role in ameliorating the climate of the european subcontinent the north atlantic current originates in the gulf stream when the latter curves north around the southeast newfoundland rise a major submarine ridge that stretches se from the grand banks a well defined front delineates the path of the current as long as it flows north as a western boundary current after the current turns east in the north it broadens into a widening band of eastward drift without a sharp or permanent front in the sense of the eastward flowing gulf stream after it separates from cape hatteras the north atlantic current transports more than 40 sv 1 sv 106 m s 1 in the south and about 20 sv by the time it flows east across the mid atlantic ridge the currents along the northward flowing front are quite swift with typical maximum average speeds in the upper 300 m near 1 m s 1 2 knots the current meanders almost as wildly as a snaking river but unlike steep meanders in the gulf stream these meanders appear to be stable and with one exception have not been observed to break off to form pools of warm and or cold waters as frequently occurs in the gulf stream the meanders appear to be induced by major topographic features along the path of the current namely the southeast newfoundland rise the newfoundland seamounts and flemish cap strong recirculations develop on the concave side of the meanders one of these the mann eddy at the first meander crest of the north atlantic current should be regarded as a permanent feature of the north atlantic circulation other meanders also contain recirculations that can persist for months under certain conditions these can merge together to form an extended sw flow recirculation just east of the north atlantic current

wintertime atmospheric response to north atlantic ocean circulation variability in a climate model abstractmaximum covariance analysis of a preindustrial control simulation of the ncar community climate system model version 4 ccsm4 shows that a barotropic signal in winter broadly resembling a negative phase of the north atlantic oscillation nao follows an intensification of the atlantic meridional overturning circulation amoc by about 7 yr the delay is due to the cyclonic propagation along the north atlantic current nac and the subpolar gyre of a sst warming linked to a northward shift and intensification of the nac together with an increasing sst cooling linked to increasing southward advection of subpolar water along the western boundary and a southward shift of the gulf stream gs these changes result in a meridional sst dipole which follows the amoc intensification after 6 or 7 yr the sst changes were initiated by the strengthening of the western subpolar gyre and by bottom torque at the crossover of the deep branches of the amoc with the nac on the western flank of the mid atlantic

a study of the interaction of the north atlantic oscillation with ocean circulation observed patterns of wind stress curl and air sea heat flux associated with the north atlantic oscillation nao are used to discuss the response of ocean gyres and thermohaline circulation to nao forcing and their possible feedback on the nao the observations motivate and are interpreted in the framework of a simple mathematical model that couples ekman layers ocean gyres and thermohaline circulation to the atmospheric jet stream meridional shifts in the zero wind stress curl line are invoked to drive anomalies in ocean gyres and north south dipoles in air sea flux drive anomalous thermohaline circulation both gyres and thermohaline circulation play a role in modulating sea surface temperature anomalies and hence through air sea interaction the overlying jet stream the model which can be expressed in the form of a delayed oscillator with ocean gyres and or thermohaline circulation providing the delay identifies key nondimensional parameters that control whether the ocean responds passively to nao forcing or actively couples it suggests that both thermohaline circulation and ocean gyres can play a role in coupled interactions on decadal timescales

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

eocene arc continent collision in new caledonia and implications for regional southwest pacific tectonic evolution new caledonia preserves evidence that constrains models for the tectonic evolution of the southwest pacific region onland geology reflects four main tectonic phases 1 early mesozoic development of subduction related terranes and their accretion to the gondwana margin 2 cretaceous passive margin development and sea floor spreading during the gondwana breakup 3 foundering of an oceanic basin and the eocene arrival of thinned gondwana margin crust at a southwest facing subduction zone resulting in collisional orogenesis and obduction of an ophiolitic nappe from the northeast and 4 detachment faulting during extensional collapse resulting in unroofing of metamorphic core complexes the last phase explains supposedly anomalous metamorphic gradients in the northeast of the island

influence of the meridional shifts of the kuroshio and the oyashio extensions on the atmospheric circulation abstract the meridional shifts of the oyashio extension oe and of the kuroshio extension ke as derived from high resolution monthly sea surface temperature sst anomalies in 1982 2008 and historical temperature profiles in 1979 2007 respectively are shown based on lagged regression analysis to significantly influence the large scale atmospheric circulation the signals are independent from the enso teleconnections which were removed by seasonally varying asymmetric regression onto the first three principal components of the tropical pacific sst anomalies the response to the meridional shifts of the oe front is equivalent barotropic and broadly resembles the north pacific oscillation western pacific pattern in a positive phase for a northward frontal displacement the response may reach 35 m at 250 hpa for a typical oe shift a strong sensitivity since the associated sst anomaly is 0 5 k however the amplitude but not the pattern or statistical significance strongly depends on the lag and an

localization of abrupt change in the north atlantic thermohaline circulation 1 recent climate model experiments as well as paleoclimate records suggest that the meridional overturning circulation or thermohaline circulation in the atlantic ocean could change abruptly as a result of global warming and that this could have a significant impact on european climate we use a reduced gravity model to investigate the response of the atlantic overturning circulation to changes in forcing we find that variability at decadal and higher frequencies is confined to a single hemisphere this implies that a overturning variability resulting from high frequency changes in buoyancy forcing in the labrador and greenland seas will be limited to the north atlantic and b any observed decadal and higher frequency fluctuations in north atlantic overturning can only result from changes in the surface fluxes within the north atlantic basin itself these results suggest that southern ocean wind forcing is not important for north atlantic overturning on decadal and shorter timescales

observed impact of atlantic sst anomalies on the north atlantic oscillation the large scale patterns of covariability between monthly sea surface temperature sst and 500 mb height anomalies z500 in the atlantic sector are investigated as a function of time lag in the ncep ncar reanalysis 1958 97 in agreement with previous studies the dominant signal is the atmospheric forcing of sst anomalies but statistically significant covariances are also found when sst leads z500 by several months in winter a panatlantic sst pattern precedes the north atlantic oscillation nao by up to 6 months such long lead time covariance is interpreted in the framework of the stochastic climate model reflecting the forcing of the nao by persistent atlantic sst anomalies a separate analysis of midlatitudes 208 708n and tropical 208s 208n sst anomalies reveals that the bulk of the nao signal comes from the midlatitudes a dipolar anomaly with warm sst southeast of newfoundland and cold sst to the northeast and southeast precedes a positive phase of the nao and it should provide a prediction of up to 15 of its monthly variance several months in advance since the forcing sst pattern projects significantly onto the tripole pattern generated by the nao these results indicate a positive feedback between the sst tripole and the nao with a strength of up to 25 mk 21 at 500 mb or 2 3 mb k21 at sea level additionally a warming of the tropical atlantic 208s 208n roughly symmetric about the equator induces a negative nao phase in early winter this tropical forcing of the nao is nearly uncorrelated with and weaker than that resulting from the midlatitudes and is associated with shorter lead times and reduced predictive skill

eclogites and blueschists of the pam peninsula ne new caledonia a reappraisal high p rocks of the pam peninsula ne new caledonia are divided into three zones 1 an uppermost ferroglaucophane lawsonite zone of cretaceous to eocene metasediments and metavolcanics of the diahot terrane that experienced peak conditions involving p 7 9 kbar and t 400 58 c 2 albite epidote omphacite zone diahot terrane rocks that experienced blueschist facies conditions of p 12 6 1 2 kbar and t 570 36 c 3 lowermost metabasic eclogites of uncertain age that form the pouebo terrane which experienced high p conditions of p 23 9 3 0 kbar and t 600 c eclogite occurs as metre to kilometre scale pods in coarse grained hydrous mineral rich glaucophanite formed during hydration and decompression of the pouebo terrane metamorphism and deformation were consequent to 44 51 ma eocene convergence when sedimentary and ophiolitic nappes were thrust over the eclogites in a sw direction white mica ages constrain metamorphism to have ended by 37 1 ma large steps in metamorphic grade are coincident with sw dipping and ne dipping faults that separate the three zones and were formed during two stages 1 comparatively slow uplift and hydration of the pouebo terrane before it was juxtaposed with the albite epidote omphacite zone at p 14 kbar 2 comparatively rapid uplift of both the pouebo terrane and the albite epidote omphacite zone to form a domal core of eclogite flanked by significantly lower grade rocks to the sw and ne

formation waters from mississippian pennsylvanian reservoirs illinois basin usa chemical and isotopic constraints on evolution and migration we have analyzed a suite of seventy four formation water samples from mississippian and pennsylvanian carbonate and siliciclastic strata in the illinois basin for major minor and trace element concentrations and for strontium isotopic composition a subset of these samples was also analyzed for boron isotopic composition data are used to interpret origin of salinity and chemical and sr isotopic evolution of the brines and in comparison with a similar data set from an earlier study of basin formation waters from silurian devonian reservoirs systematics of cl br na show that present mississippian pennsylvanian brine salinity can be explained by a combination of subaerial seawater evaporation short of halite saturation and subsurface dissolution of halite from an evaporite zone in the middle mississippian st louis limestone along with extensive dilution by mixing with meteoric waters additional diagenetic modifications in the subsurface interpreted from cation br ratios include k depletion through interaction with clay minerals ca enrichment and mg depletion by dolomitization and sr enrichment through caco3 recrystallization and dolomitization ste genevieve limestone middle mississippian formation waters show 87sr86sr ratios in the range 0 70782 0 70900 whereas waters from the siliciclastic reservoirs are in the range 0 70900 0 71052 inverse correlations between 87sr86sr and b li and mg concentrations suggest that the brines acquired radiogenic 87sr through interaction with siliciclastic minerals completely unsystematic relations between 87sr86sr and 1 sr are observed sr concentrations in ste genevieve and aux vases middle mississippian waters appear to be buffered by equilibrium with respect to srso4 although there are many similarities in their origin and evolution these formation waters are distinguished from silurian devonian brines in the basin by elevated clbr and nabr ratios and by unsystematic sr isotope relationships thus waters from these two major segments of the illinois basin stratigraphic column form distinct geochemical regimes which are separated by the new albany shale group devonian mississippian regional aquitard geochemical evolution appears to have been influenced significantly by paleozoic and mesozoic hydrologic flow systems in the basin

influence of the north atlantic sst variability on the atmospheric circulation during the twentieth century the ocean atmosphere coupling in the north atlantic is investigated during the twentieth century using maximum covariance analysis of sea surface temperature sst and 500 hpa geopotential height analyses and performing regressions on dynamical diagnostics such as eady growth rate wave activity flux and velocity potential the north atlantic oscillation nao generates the so called sst anomaly tripole a rather similar sst anomaly tripole with the subpolar anomaly displaced to the east and a more contracted subtropical anomaly which is referred to as the north atlantic horseshoe pattern in turn influences the atmosphere in the fall and early winter the response is nao like and primarily results from subpolar forcing centered over the labrador sea and off newfoundland in summer the largest atmospheric response to sst resembles the east atlantic pattern and results from a combination of subpolar and tropical forcing to emphasize the interannual to multidecadal variability the same analysis is repeated after low pass filtering the sst influence is dominated by the atlantic multidecadal oscillation amo which also has a horseshoe shape but with larger amplitude in the subpolar basin a warm amo phase leads to an atmospheric warming limited to the lower troposphere in summer while it leads to a negative phase of the nao in winter the winter influence of the amo is suggested to be primarily forced by the atlantic ssts in the northern sub tropics such influence of the amo is found in winter instead of early winter because the winter sst anomalies have a larger persistence presumably because of sst reemergence

the persistence of winter sea surface temperature in the north atlantic abstract the impact of the seasonal variations of the mixed layer depth on the persistence of sea surface temperature sst anomalies is studied in the north atlantic using observations a significant recurrence of winter sst anomalies during the following winter occurs in most of the basin but not in the subtropical area of strong subduction when taking reemergence into account the e folding timescale of winter sst anomalies generally exceeds 1 yr and is about 16 months for the dominant sst anomaly tripole the influence of advection by the mean oceanic currents is investigated by allowing for a displacement of the maximum recurrent correlation and alternatively by considering the sst anomaly evolution along realistic mean displacement paths taking into account the nonlocality of the reemergence generally increases the wintertime persistence most notably in the northern part of the domain the passive response of the mixed layer to the atmospheric forcing thus has a red spectrum down to near dec

open ocean convection observations theory and models we review what is known about the convective process in the open ocean in which the properties of large volumes of water are changed by intermittent deep reaching convection triggered by winter storms observational laboratory and modeling studies reveal a fascinating and complex interplay of convective and geostrophic scales the large scale circulation of the ocean and the prevailing meteorology two aspects make ocean convection interesting from a theoretical point of view first the timescales of the convective process in the ocean are sufficiently long that it may be modified by the earth s rotation second the convective process is localized in space so that vertical buoyancy transfer by upright convection can give way to slantwise transfer by baroclinic instability moreover the convective and geostrophic scales are not very disparate from one another detailed observations of the process in the labrador greenland and mediterranean seas are described which were made possible by new observing technology when interpreted in terms of underlying dynamics and theory and the context provided by laboratory and numerical experiments of rotating convection great progress in our description and understanding of the processes at work is being made

the origins of late twentieth century variations in the large scale north atlantic circulation abstractsurface forcing perturbation experiments are examined to identify the key forcing elements associated with late twentieth century interannual to decadal atlantic circulation variability as simulated in an ocean sea ice hindcast configuration of the community earth system model version 1 cesm1 buoyancy forcing accounts for most of the decadal variability in both the atlantic meridional overturning circulation amoc and the subpolar gyre circulation and the key drivers of these basin scale circulation changes are found to be the turbulent buoyancy fluxes evaporation as well as the latent and sensible heat fluxes these three fluxes account for almost all of the decadal amoc variability in the north atlantic even when applied only over the labrador sea region year to year changes in surface momentum forcing explain most of the interannual amoc variability at all latitudes as well as most of the decadal variability south of the equator the observed strengthening of southern ocean westerly wi

comparison of the high pressure schist belts of new caledonia and sanbagawa japan the high pressure schist terranes of new caledonia and sanbagawa were developed along the oceanic sides of sialic forelands by tectonic burial metamorphism the parent rocks were chemically similar as volcanic sedimentary trough or trench sequences and metamorphic temperatures in both belts were 250 to 600 c from phase equilibria curves total pressures were higher for new caledonia 6 15 kb than for sanbagawa 5 11 kb and the estimated thermal gradients were 7 10 c km and 15 c km respectively pt paths identify the higher pressure in new caledonia p differences 2 kb at 300 c and 4 kb at 550 c with consequent contrast in progressive regional metamorphic zonation for pelites in the two areas lawsonite epidote omphacite new caledonia and chlorite garnet biotite sanbagawa in new caledonia the na amphibole is dominantly glaucophane and na pyroxenes associated with quartz are jadeite jd95 100 and omphacite in sanbagawa the amphibole is crossite or riebeckite and the pyroxene is omphacite jd50 for both areas garnet rims show increase in pyrope content with advancing grade but sanbagawa garnets are richer in almandine progressive assemblages within the two belts can be equated by such reactions as new caledonia sanbagawa glaucophane paragonite h2o albite chlorite quartz glaucophane epidote h2o albite chlorite actinolite and the lower pressure japanese associations appear as retrogressive phases in the new caledonia epidote and omphacite zones

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

nukundamite cu3 38fe0 62s4 bearing copper ore in the bingham porphyry deposit utah result of upflow through quartzite nukundamite is an important ore mineral in a geologic resource of approximately 90 million metric tons mt of 0 8 wt percent cu in quartzite on the northeast contact of the bingham stock in contrast with other deposits where nukundamite occurs as a minor phase in relatively low temperature sericitic assemblages nukundamite at bingham is widespread in higher temperature potassic assemblages the coexistence of this high sulfidation sulfide with potassic assemblages suggests an unusual evolutionary path for magmatic hydrothermal fluids in quartzite wall rocks nukundamite bearing copper ore restricted to a 240 m thick quartzite unit of the pennsylvanian bingham mine formation extends 170 m from the northeast margin of the mineralized stock along the strike of beds and plunges 1 km down the dip of beds 30 nnw the quartzite unit is cut off at depth by a thrust fault below which beds of the bingham mine formation are vertical and cut by abundant northeast striking steeply dipping faults dikes and isoclinal folds the fortuna zone ore forming hydrothermal assemblages in quartzite can be classified as main and late stage main stage minerals are predominantly disseminated quartz phlogopite k feldspar with nukundamite replaced by chalcopyrite and bornite and no pyrite replacement of nukundamite by chalcopyrite and bornite reduced its abundance from possibly as high as 90 to 10 vol percent of total sulfides at the end of the main stage late stage assemblages consist of quartz sericite kaolinite with abundant pyrite lesser amounts of bornite digenite enargite and traces of nukundamite based on experimental data and retrieved thermodynamic properties nukundamite is stable within a highly limited range of a fe 2 a h 2 f s2 and f o2 at temperatures between 501 and 223 c at very high sulfidation states values of a fe 2 a h 2 in the nukundamite field are also appropriate for the stable assemblages chalcopyrite bornite and chalcopyrite pyrite but nukundamite requires higher values of f s2 and f o2 than the latter more common assemblages phase equilibria indicate that nukundamite bearing sulfide assemblages of the main stage are metastable supersaturated with respect to pyrite we hypothesize that early brine and vapor known to be of magmatic origin on the basis of isotopic and fluid inclusion evidence traveled upward through several kilometers of quartzite along the stock contact and the fortuna zone and then up to the south southeast along bedding at its source region the brine had so2 g h2s g 1 typical of degassing magmas of intermediate composition on cooling and due to lack of redox buffers in quartzite the brine became increasingly oxidized and evolved to so2 g h2s g 0 1 at 450 c at constant f s2 precipitation of nukundamite with k feldspar phlogopite at temperatures below 400 c so2 g h2s g 0 01 was possible due to relatively high concentrations of s and k in the brine s aq 0 2 m k 0 5 m also resulting from lack of exchange reactions with quartzite subsequent replacement of nukundamite by bornite chalcopyrite during the late main stage required a different fluid at lower sulfidation and oxidation states and slightly higher a fe 2 a h 2 we suggest that this late main stage fluid rising within the faulted northeast margin of the stock had been enriched in iron and depleted in sulfur during main stage potassic alteration and ore deposition in the stock

storms consolidated field illinois basin identifying new reserves in a mature area discovered in 1939 storms consolidated field in the central illinois basin has produced approximately 24 5 million bbl oil mainly from mississippian sandstone reservoirs yet may contain significant remaining reserves the field produces from a combination structural stratigraphic trap along the upthrown side of a major normal fault trend although the principal reservoir zone the waltersburg sandstone is mostly depleted another important interval the aux vases sandstone appears underexploited in many parts of the field description and analysis of the only continuous core through the aux vases has led to the identification of major lithofacies and their characterization in terms of reservoir quality the aux vases appears to represent a series of shallow marine bars separated by nonreservoir areas of siltstone shale and shaly sandstone log based mapping of reservoir distribution plus production and pressure data indicates significant lateral and vertical compartmentalization of the reservoir although insufficient data exist for full scale integrated reservoir characterization studies a trend surface analysis was performed on structural information across the field the results of this analysis were compared with reservoir distribution maps to identify areas for future drilling or recompletion

impact of enso on the atmospheric variability over the north atlantic in late winter role of transient eddies abstractthe dynamical mechanism for the late winter teleconnection between el nino southern oscillation enso and the north atlantic oscillation nao is examined using the output from a 2000 yr integration of a coupled general circulation model gcm the coupled model captures many salient features of the observed behavior of both enso and nao as well as their impact on the surface climate in late winter both the observational and model data indicate more occurrences of negative phase of nao in late winter during el nino events and positive nao in la nina episodes the potential role of high frequency transient eddies in the above teleconnection is diagnosed during el nino winters the intensified transient disturbances along the equatorward shifted north pacific storm track extend their influences farther downstream the eddy induced negative height tendencies are found to be more coherent and stronger over north atlantic than that over north pacific these negative height tendencies over the north

stochastically driven multidecadal variability of the atlantic meridional overturning circulation in ccsm3 the atlantic meridional overturning circulation amoc in the last 250 years of the 700 year long present day control integration of the community climate system model version 3 with t85 atmospheric resolution exhibits a red noise like irregular multi decadal variability with a persistence longer than 10 years which markedly contrasts with the preceding 300 years of very regular and stronger amoc variability with 20 year periodicity the red noise like multi decadal amoc variability is primarily forced by the surface fluxes associated with stochastic changes in the north atlantic oscillation nao that intensify and shift northward the deep convection in the labrador sea however the persistence of the amoc and the associated oceanic anomalies that are directly forced by the nao forcing does not exceed about 5 years the additional persistence originates from anomalous horizontal advection and vertical mixing which generate density anomalies on the continental shelf along the eastern boundary of the subpolar gyre these anomalies are subsequently advected by the mean boundary current into the northern part of the labrador sea convection region reinforcing the density changes directly forced by the nao as no evidence was found of a clear two way coupling with the atmosphere the multi decadal amoc variability in the last 250 years of the integration is an ocean only response to stochastic nao forcing with a delayed positive feedback caused by the changes in the horizontal ocean circulation

the forcing of the pacific decadal oscillation the pacific decadal oscillation pdo defined as the leading empirical orthogonal function of north pacific sea surface temperature anomalies is a widely used index for decadal variability it is shown that the pdo can be recovered from a reconstruction of north pacific sea surface temperature anomalies based on a first order autoregressive model and forcing by variability of the aleutian low el nino southern oscillation enso and oceanic zonal advection anomalies in the kuroshio oyashio extension the latter results from oceanic rossby waves that are forced by north pacific ekman pumping the sst response patterns to these processes are not orthogonal and they determine the spatial characteristics of the pdo the importance of the different forcing processes is frequency dependent at interannual time scales forcing from enso and the aleutian low determines the response in equal parts at decadal time scales zonal advection in the kuroshio oyashio extension enso and anomalies of the aleutian low each account for similar amounts of the pdo variance these results support the hypothesis that the pdo is not a dynamical mode but arises from the superposition of sea surface temperature fluctuations with different dynamical origins

experimentally based water budgets for dehydrating slabs and consequences for arc magma generation phase diagrams of hydrous mid ocean ridge mor basalts to 330 km depth and of hydrous peridotites to 250 km depth are compiled for conditions characteristic for subduction zones a synthesis of our experimentally determined phase relations of chlorite lawsonite epidote zoisite amphibole paragonite chloritoid talc and phengite in basalts and of phase relations from the literature of serpentine talc chlorite amphibole and phase a in ultramafics permits calculation of h2o contents in hydrous phase assemblages that occur in natural compositions this yields the information necessary to calculate water budgets for descending slabs starting from low grade blueschist conditions 10 20 km depth with h2o contents between 5 and 6 wt for hydrated oceanic crust complete dehydration is achieved between 70 and 300 km depth as a function of individual slab geotherms hydrous phases which decompose at depth below volcanic arcs are lawsonite zoisite chloritoid and talc phengite in mafic compositions and chlorite and serpentine in peridotite approximately 15 35 of the initially subducted h2o are released below volcanic arcs the contribution of amphibole dehydration to the water budget is small 5 20 and occurs at relatively shallow depth 65 90 km in any predicted thermal structure dehydration is a combination of a stepwise and a continuous process through many different reactions which occur simultaneously in the different portions of the descending slab such a dehydration characteristic is incompatible with single phase dehydration models which focus fluid flow through a unique major dehydration event in order to explain volcanic fronts as a consequence of continuously progressing dehydration water ascending from the slab will be generally available to depth of ca 150 200 km the fluid rising from the subducting lithosphere will cause partial melting in the hot portion of the mantle wedge we propose that the volcanic front simply forms above the mantle wedge isotherm where the extent of melting is sufficient to allow for the mechanical extraction of parental arc magmas thermal models show that such an isotherm ca 1300oc locates below volcanic fronts slab surface depths below such an isotherm are compatible with the observed depths of the slab surface below volcanic fronts 1998 elsevier science b v all rights reserved

gulf stream variability and ocean atmosphere interactions abstract time series of gulf stream position derived from the topex poseidon altimeter from october 1992 to november 1998 are used to investigate the lead and lag relation between the gulf stream path as it leaves the continental shelf and the changes in sea level pressure surface wind stress and sea surface temperature sst as given by the ncep reanalysis the dominant signal is a northward southward displacement of gulf stream axis 11 to 18 months after the north atlantic oscillation nao reaches positive negative extrema a sst warming cooling peaking north of the gulf stream is also seen to precede the latitudinal shifts but it is a part of the large scale sst anomaly tripole that is generated by the nao fluctuations there is no evidence that the gulf stream shifts have a direct impact onto the large scale atmospheric circulation a fast passive response of the gulf stream to nao forcing is also suggested by a corresponding analysis of the yearly mean gulf stream position estimated from

tectonic accretion and underplating of mafic terranes in the late eocene intraoceanic fore arc of new caledonia southwest pacific geodynamic implications this paper deals with the tectonic events that result in the accretion of mafic terranes in the fore arc region and a close juxtaposition of ultramafic rocks low grade and high grade mafic terranes in many collisional orogens the example is taken from new caledonia where tectonic accretion subduction underplating and obduction of mafic terranes took place during the late eocene in an intra oceanic forearc setting the late eocene tectonic complex comprised three major terranes an overlying ultramafic mainly harzburgitic allochthon named the ophiolitic nappe an intermediate mafic mainly basaltic off scraped melange composed of kilometre scale slices of oceanic upper crust called the poya terrane parts of which have been metamorphosed into an eclogite blueschist facies complex the pouebo terrane and a lower continental basement formed by the norkolk ridge terranes based upon exhaustive sampling of the mafic terranes and field surveys our tectonic micropaleontologic and geochemical data reveal that poya and pouebo terranes rocks originally formed within one single campanian to late paleocene oceanic basin floored by tholeiitic basalt associated with some minor seamount related intraplate alkali basalt the tholeiitic basalt displays a continuous range of compositions spanning between undepleted and depleted end members the former being volumetrically predominant the overall geochemical and isotopic features indicate an origin from a prominently heterogeneous mantle source during the opening of a marginal basin the south loyalty basin which almost completely disappeared during eocene convergence the opening of this basin originally located to the east of the norfolk ridge was synchronous with that of tasman sea basin as a consequence of oceanward migration of the west dipping pacific subduction zone establishing the origin of the ultramafic ophiolitic nappe is beyond the scope of this paper however it appears to be genetically unrelated to the mafic poya and pouebo terranes although it was located in the late eocene fore arc the ophiolitic nappe and the corresponding oceanic lithosphere originated before the late cretaceous to the east of the south loyalty basin in a back arc setting or alternatively in a much older trapped basin for reasons that remain unclear a new east dipping subduction started in the eocene and consumed most of the south loyalty basin forming the intra oceanic loyalty arc due to a changing subduction regime underplating of the diahot terrane the mafic slices that now form the poya terrane were tectonically accreted in the loyalty fore arc region and remained under low pressure low temperature conditions possibly at the subsurface until the norfolk ridge reached the subduction zone diachronously this resulted in the final obduction of the fore arc area the two step obduction involved first the mafic complex forming the poya terrane and thereafter the lithospheric mantle that now forms the ophiolitic nappe in contrast pieces of the accretionnary complex were dragged down into the subduction zone underplated at depth ca 70 km and metamorphosed into high temperature eclogite to form the pouebo terrane metamorphics that display the same geochemical features as the poya terrane basalt a mid to late eocene syntectonic piggy back sedimentary basin the nepoui flysch basin mainly filled with mafic clastic material and shallow water carbonates that record the progressive uplift of the fore arc region due to the accretion and underplating of mafic ocean related and other material in contrast a slightly younger foreland basin located upon the norfolk ridge the priabonian bourail flysch basin received a massive input of detrital material derived from the norfolk ridge itself and a time increasing amount of mafic poya derived material that recorded the first step of obduction thereafter the bourail flysch was overthrust by the poya terrane and finally by the ophiolitic nappe at the same time buoyancy driven uplift and exhumation of the high pressure metamorphic complex occurred as a consequence of the diachronous blocking of the subduction zone finally for a short time a new subduction started along the west coast of new caledonia and generated small amounts of active margin related magmas these events have resulted in the close juxtaposition of unmetamorphosed and highly metamorphosed mafic and ultramafic terranes that may represent a good pre collision analogue of mafic ultramafic belts found in many collisional mountain ranges

constraining the timing of microbial methane generation in an organic rich shale using noble gases illinois basin usa abstract at least 20 of the world s natural gas originates from methanogens subsisting on organic rich coals and shales however in situ microbial methane production rates are unknown methanogens in the upper devonian new albany shale in the illinois basin extract hydrogen from low salinity formation water to form economic quantities of natural gas because of this association constraining the source and timing of groundwater recharge will enable estimation of minimum in situ metabolic rates thirty four formation water and gas samples were analyzed for stable isotopes oxygen and hydrogen chloride tritium 14 c and noble gases chloride and 18 o spatial patterns reveal a plume of water with low salinity 0 7 to 2154 mm and 18 o values 0 14 to 7 25 penetrating 1 km depth into evapo concentrated brines parallel to terminal moraines of the laurentide ice sheet suggesting glacial mediated recharge however isotopic mixing trends indicate that the recharge endmember 7 18 o is higher than the assumed bulk ice sheet value 18 o and similar to modern local precipitation 7 5 to 4 5 18 o continental paleoprecipitation records reveal that throughout the pleistocene 18 o of precipitation in the region ranged from 10 to 5 suggesting that the dilute groundwater was primarily sourced from paleoprecipitation with minor contributions from glacial meltwater for the majority of samples the atmosphere derived 4 he contribution is negligible and the 4 he is dominated by a crustal radiogenic source with near complete transfer of dissolved noble gases to the gas phase in addition mantle derived helium is negligible for all samples 18 o data however all groundwater in the study area was influenced by pleistocene recharge estimated in situ microbial methane production rates range from 10 to 1000 tcf ma 10 4 to 10 6 times slower than average laboratory rates from coals findings from this study have implications for targeting undeveloped microbial gas accumulations improving natural gas reservoir estimates the potential of in situ methanogen stimulation and understanding biologic cycling of carbon in subsurface reservoirs

prograde sulfide metamorphism in blueschist and eclogite new caledonia in new caledonia blueschist and eclogite preserve as inclusions in porphyroblastic minerals a record of sulfide present during prograde subduction processes sulfide inclusions in prograde garnet and lawsonite became chemically isolated from the matrix whereas sulfide minerals in the matrix continued to equilibrate with matrix fluids or grew later during retrogression cu fe sulfide mineral inclusions have been found across metamorphic grade within silicate defined metamorphic mineral zones spanning a crustal profile of 30 km bulk area scans of sulfide inclusions provide compositions that represent mixtures of the solid sulfide that were included as the host silicate minerals grew in general single sulfide inclusion compositions and aggregate sulfide assemblages are distinct from those of matrix phases high cu contents in sulfide inclusions are interpreted to be a consequence of fe lost from sulfide to growing garnet rather than the result of intrinsically high cu in the bulk rock the distribution of sulfide inclusion compositions across metamorphic grade considered together with the available thermodynamic data suggests that covellite nukundamite bearing inclusions in lawsonite high in both cu and s disappear at higher grades as these sulfide minerals are no longer stable similarly clustering near the ratio fe cu 1 1 may cease with increasing grade owing to the replacement of chalcopyrite intermediate solid solution iss by the denser assemblage pyrite pyrrhotite bornite digenite

oxygen and hydrogen isotope compositions of paleosol phyllosilicates differential burial histories and determination of middle late pennsylvanian low latitude terrestrial paleotemperatures abstract the clay mineralogy chemistry and stable hydrogen and oxygen isotope compositions were measured from 20 phyllosilicate samples representing 11 pennsylvanian age paleosol profiles taken from three cores in the illinois basin in order to assess their utility as proxies of low latitude terrestrial paleotemperatures the majority of the samples are mineralogical mixtures of illite smectite i s kaolinite and rarely discrete illite samples from a shallowly buried locality in the northern part of the basin are dominantly composed of smectite rich i s with variable amounts of kaolinite and no discrete illite samples from deeply buried interior parts of the basin are composed of illite rich i s variable amounts of kaolinite and discrete illite these phyllosilicate mixtures have 18 o v smow and d v smow values that range from 17 2 to 23 0 and 56 to 27 respectively assuming that the phyllosilicates preserve a record of isotopic equilibrium with pennsylvanian meteoric waters these oxygen and hydrogen isotope values correspond to crystallization temperatures ranging from 22 3 c to 55 3 c the clay mineralogy phyllosilicate 18 o and d values and calculated crystallization temperatures of 44 c to 55 c from deeply buried localities in the interior of the basin are not consistent with a pedogenic origin instead these trends are considered to be the result of diagenetic recrystallization of pedogenic minerals in response to greater depths of burial by 1 5 to 3 km in the southerly basin center localities as well as an interval of middle permian elevated heat flow associated with magmatic intrusions in the southern part of the basin phyllosilicate mineralogy 18 o and d values and calculated phyllosilicate crystallization temperatures from a shallowly buried northern locality in the illinois basin are consistent with a pedogenic origin and reveal a long term warming trend from an average temperature of 23 3 c in the lower desmoinesian to an average temperature of 32 3 c in the missourian this temperature change is coincident with a significant change in the composition of wetland vegetation in euramerica which has been attributed to a shift in low latitude pennsylvanian climate towards warmer and drier conditions in the late pennsylvanian this study reveals the presence of a dynamic late paleozoic paleoequatorial icehouse climate characterized by significant low latitude temperature variability unprecedented on modern earth

global teleconnections of meridional overturning circulation anomalies there is a wide range of evidence from both models and palaeoclimatic data that indicates the possibility of abrupt changes in the oceanic meridional overturning circulation moc however much of our dynamical understanding of the moc comes from steady state models that rely upon the assumption of thermodynamic equilibrium and are therefore only valid on millennial time scales here a dynamical model for the global teleconnections of moc anomalies on annual to multidecadal time scales is developed it is based on a linear theory for the propagation of zonally integrated meridional transport anomalies in a reduced gravity ocean and allows for multiple ocean basins connected by a circumpolar channel to the south the theory demonstrates that the equator acts as a low pass filter to moc anomalies as a consequence moc anomalies on decadal and shorter time scales are confined to the hemispheric basin in which they are generated and have little impact on the remainder of the global ocean the linear theory is compared with the results of a global nonlinear numerical integration which it reproduces to a good approximation

atmospheric response to the north atlantic ocean variability on seasonal to decadal time scales the ncep twentieth century reanalyis and a 500 year control simulation with the ipsl cm5 climate model are used to assess the influence of ocean atmosphere coupling in the north atlantic region at seasonal to decadal time scales at the seasonal scale the air sea interaction patterns are similar in the model and observations in both a statistically significant summer sea surface temperature sst anomaly with a horseshoe shape leads an atmospheric signal that resembles the north atlantic oscillation nao during the winter the air sea interactions in the model thus seem realistic although the amplitude of the atmospheric signal is half that observed and it is detected throughout the cold season while it is significant only in late fall and early winter in the observations in both model and observations the north atlantic horseshoe sst anomaly pattern is in part generated by the spring and summer internal atmospheric variability in the model the influence of the ocean dynamics can be assessed and is found to contribute to the sst anomaly in particular at the decadal scale indeed the north atlantic sst anomalies that follow an intensification of the atlantic meridional overturning circulation amoc by about 9 years or an intensification of a clockwise intergyre gyre in the atlantic ocean by 6 years resemble the horseshoe pattern and are also similar to the model atlantic multidecadal oscillation amo as the amoc is shown to have a significant impact on the winter nao most strongly when it leads by 9 years the decadal interactions in the model are consistent with the seasonal analysis in the observations there is also a strong correlation between the amo and the sst horseshoe pattern that influences the nao the analogy with the coupled model suggests that the natural variability of the amoc and the gyre circulation might influence the climate of the north atlantic region at the decadal scale

evaluation of coalbed gas potential of the seelyville coal member indiana usa abstract the seelyville coal member of the linton formation in indiana potentially contains 0 03 trillion m3 1 1 tcf of coalbed gas the gas content determined by canister desorption technique ranges from 0 5 to 5 7 cm3 g on dry ash free basis 15 4 to 182 2 scf ton the controls on gas content distribution are complex and cannot be explained by the coal rank alone ash content and the lithology of the overlying strata among other factors may influence this distribution

the instability of rossby basin modes and the oceanic eddy field abstract low frequency large scale baroclinic rossby basin modes resistant to scale dependent dissipation have been recently theoretically analyzed and discussed as possible efficient coupling agents with the atmosphere for interactions on decadal time scales such modes are also consistent with evidence of the westward phase propagation in satellite altimetry data in both the theory and the observations the scale of the waves is large in comparison with the rossby radius of deformation and the orientation of fluid motion in the waves is predominantly meridional these two facts suggest that the waves are vulnerable to baroclinic instability on the scale of the deformation radius the key dynamical parameter is the ratio z of the transit time of the long rossby wave to the e folding time of the instability when this parameter is small the wave easily crosses the basin largely undisturbed by the instability if z is large the wave succumbs to the instability and is largely destroyed before making a c

locally and remotely forced subtropical amoc variability a matter of time scales mechanisms driving the north atlantic meridional overturning circulation amoc variability at low frequency are of central interest for accurate climate predictions although the subpolar gyre region has been identified as a preferred place for generating climate timescale signals their southward propagation remains under consideration complicating the interpretation of the observed time series provided by the rapid climate change meridional overturning circulation and heatflux array western boundary time series rapid mocha wbts program in this study we aim at disentangling the respective contribution of the local atmospheric forcing from signals of remote origin for the subtropical low frequency amoc variability we analyze for this a set of four ensembles of a regional 208s 558n eddy resolving 1 128 north atlantic oceanic configuration where surface forcing and open boundary conditions are alternatively permuted from fully varying realistic to yearly repeating signals their analysis reveals the predominance of local atmospherically forced signal at interannual time scales 2 10 years whereas signals imposed by the boundaries are responsible for the decadal 10 30 years part of the spectrum due to this marked timescale separation we show that although the intergyre region exhibits peculiarities most of the subtropical amoc variability can be understood as a linear superposition of these two signals finally we find that the decadal scale boundary forced amoc variability has both northern and southern origins although the former dominates over the latter including at the site of the rapid array 26 58n

sulfides oxides and sphene in high pressure schists from new caledonia in the new caledonia high pressure schists pyrite pyrrhotite chalcopyrite rutile and sphene are common phases while hematite and ilmenite are rare and magnetite is absent the parageneses of these minerals were clarified from their occurrence as inclusions in garnet from phase relations in the cu fe s and fe ti o s systems and from phase rule considerations for the multi component system the sulfur fugacity estimated for pelites and basites containing pyrrhotite pyrite and rutile increased with increasing metamorphic grade the oxygen fugacity in these schists was less than 10 27 6 bars at 400 c 10 kb and 10 22 3 bars at 500 c 11 kb among the other components of the metamorphic fluid in pelites h2o was major ch4 co2 and h2s minor and h2 co cos and so2 rare the fluid composition altered with advancing metamorphic grade such that h2o decreased while co2 ch4 and h2s increased and this change was linked to concurrent massive decarbonization in the rock matrices

coherent surface subsurface fingerprint of the atlantic meridional overturning circulation 1 satellite altimeter data shows a weakening of the north atlantic subpolar gyre during the 1990s which is thought as an indicator of a slowdown of the atlantic meridional overturning circulation amoc however whether the recent slowing subpolar gyre is a decadal variation or a long term trend remains unclear here i show that altimeter data is highly correlated with instrumental subsurface ocean temperature data in the north atlantic and both show opposite signs between the subpolar gyre and the gulf stream path such a dipole pattern is a distinctive fingerprint of amoc variability as shown for the first time by a 1000 year coupled ocean atmosphere model simulation the results suggest that contrary to previous interpretations the recent slowdown of the subpolar gyre is a part of a multidecadal variation and suggests a strengthening of the amoc the ongoing satellite and subsurface temperature measurements could be used to monitor future amoc variations sensitively

preservation of re os isotope signatures in pyrite throughout low t high p eclogite facies metamorphism pyrite in lt hp eclogites from the western tianshan orogenic belt yields a re os age of 378 1 8 9 ma which is 30 70 ma older than ages previously obtained for the same rocks using the rb sr sm nd ar ar u pb and lu hf isotope systems the tianshan lt hp eclogite experienced temperatures of up to 570 c combined with pressures of up to 2 1 gpa during metamorphism these conditions are below the transition of pyrite to pyrrhotite which defines both pyrite stability and possibly its closure temperature for re os pyrite can preserve re os signatures through eclogite facies peak metamorphic conditions and thus allow determination of the formation age of pyrite in the protolith

a mechanism for the recurrence of wintertime midlatitude sst anomalies abstract in the early 1970s namias and born speculated that ocean temperature anomalies created over the deep mixed layer in winter could be preserved in the summer thermocline and reappear at the surface in the following fall or winter this hypothesis is examined using upper ocean temperature observations and simulations with a mixed layer model the data were collected at six ocean weather stations in the north atlantic and north pacific concurrent and lead lag correlations are used to investigate temperature variations associated with the seasonal cycle in both the observations and the model simulations concurrent correlations between the surface and subsurface temperature anomalies in both the data and the model indicate that the penetration of temperature anomalies into the ocean is closely tied to the seasonal cycle in mixed layer depth high correlations extend to relatively deep shallow depths in winter summer lead lag correlations in both the data and the model at some of the stations

long rossby wave basin crossing time and the resonance of low frequency basin modes the ability of long wave low frequency basin modes to be resonantly excited depends on the efficiency with which energy fluxed onto the western boundary can be transmitted back to the eastern boundary this efficiency is greatly reduced for basins in which the long rossby wave basin crossing time is latitude dependent in the singular case where the basin crossing time is independent of latitude the amplitude of resonantly excited long wave basin modes grows without bound except for the effects of friction the speed of long rossby waves is independent of latitude for quasigeostrophic dynamics and the rectangular basin geometry often used for theoretical studies of the wind driven ocean circulation is such a singular case for quasigeostrophic dynamics for more realistic basin geometries where only a fraction of the energy incident on the western boundary can be transmitted back to the eastern boundary the modes have a finite decay rate that in the limit of weak friction is independent of the choice of frictional parameters explicit eigenmode computations for a basin geometry similar to the north pacific but closed along the equator yield basin modes sufficiently weakly damped that they could be resonantly excited

extent and limits of biodegradation by in situ methanogenic consortia in shale and formation fluids abstract consortia of microbes degrade recalcitrant organic matter in deep subsurface reservoirs such as shales and coals under anaerobic conditions into simple c molecules such as co 2 and acetate these substrates are subsequently metabolized by methanogens into economic quantities of natural gas in sedimentary basins world wide this study explores organic matter in the devonian new albany shale illinois basin usa and associated fluids to investigate the extent of organic matter biodegradation and evaluate the potential for stimulating in situ gas production identification of labile compound classes such as n alkanes fatty acids and phenols in produced waters of the new albany shale and low biodegradation indices in the shale core samples indicate limited biodegradation together with detectable acetate concentrations up to 225 1 m these observations suggest that both the supporting microbial consortia and methanogens are limited in extent and activity by comparison the new albany shale is much less biodegraded than the microbial ch 4 producing michigan basin antrim shale powder river basin coals or san juan basin coals in the new albany shale the extent of biodegradation generally becomes more varied with higher salinities suggesting diverse microbial adaptations to degrade om at high salinities enhancement of in situ ch 4 production may be most effective if targeted at stimulating production of the supporting microbial consortia as well as methanogens

on the existence of storm tracks abstract given that middle latitude weather systems transport heat in a manner such as to weaken the baroclinicity that is thought to be crucial to their growth it is perhaps surprising that concentrated regions of such eddy activity i e storm tracks are found in the northern hemisphere winter the existence and possible self maintenance of storm tracks is investigated using a linear stationary wave model with storm track region forcings taken from data averaged over a number of winters it is found that the direct thermal effect of the eddies does indeed act against the existence of the storm track their vorticity fluxes lead to some reduction of this effect it is argued that the mean diabatic heating in the storm track region is an indirect eddy effect this heating is found to maintain the mean maximum in baroclinicity in the region further the mean low level flow induced by the eddy effects is such as to enhance the warm western oceanic boundary currents that are crucial to the existence of t

a theory for the surface atlantic response to thermohaline variability abstract the response of the upper warm limb of the thermohaline circulation in the north atlantic to a rapid change in deep water formation at high latitudes is investigated using a reduced gravity ocean model changes in deep water formation rate initiate kelvin waves that propagate along the western boundary to the equator on a timescale of months the response in the north atlantic is therefore rapid the southern hemisphere response is much slower limited by a mechanism here termed the ldquo uatorial buffer since to leading order the flow is in geostrophic balance the pressure anomaly decreases in magnitude as the kelvin wave moves equatorward where the coriolis parameter is lower together with the lack of sustained pressure gradients along the eastern boundary this limits the size of the pressure field response in the southern hemisphere interior adjustment is by the westward propagation of rossby waves but only a small fraction of the change in thermohaline circulation strength is commun

spectral characteristics of the response of the meridional overturning circulation to deep water formation abstract the response of the upper limb of the meridional overturning circulation to the variability of deep water formation is investigated analytically with a linear reduced gravity model in basins of simple geometry the spectral characteristics of the model response are first derived by prescribing white noise fluctuations in the meridional transport at the northern boundary although low frequency basin modes are solutions to the eigenproblem they are too dissipative to be significantly excited by the boundary forcing and the thermocline depth response has a red spectrum with no prevailing time scale other than that of a high frequency equatorial mode only flattening at the millennial time scale because of vertical diffusivity the meridional transport is asymmetric about the equator because the northern part of the basin is directly influenced by the boundary forcing while the southern part is mostly set in motion by long rossby waves this results in the equator acting as a low pass filter for

variability of the atlantic meridional overturning circulation in ccsm4 abstractatlantic meridional overturning circulation amoc variability is documented in the community climate system model version 4 ccsm4 preindustrial control simulation that uses nominal 1 horizontal resolution in all its components amoc shows a broad spectrum of low frequency variability covering the 50 200 yr range contrasting sharply with the multidecadal variability seen in the t85 1 resolution ccsm3 present day control simulation furthermore the amplitude of variability is much reduced in ccsm4 compared to that of ccsm3 similarities as well as differences in amoc variability mechanisms between ccsm3 and ccsm4 are discussed as in ccsm3 the ccsm4 amoc variability is primarily driven by the positive density anomalies at the labrador sea ls deep water formation site peaking 2 yr prior to an amoc maximum all processes including parameterized mesoscale and submesoscale eddies play a role in the creation of salinity anomalies that dominate these density anomalies high nordic sea densi

lopatin analysis of maturation and petroleum generation in the illinois basin a modified lopatin approach was used to evaluate the present day maturity of paleozoic source rock units across the illinois basin timing of generation regional porosity trends and basin paleostructure during major generative events ten cases were modeled at 100 locations to test assumed paleogeothermal gradients post pennsylvanian overburden thicknesses and rates of erosional stripping lopatin predicted maturities for the herrin number sign 6 coal and the new albany shale are in good agreement plus minus 0 02 r sub o with measured maturities if 500 3 000 ft of post middle pennsylvanian strata and were deposited and subsequently eroded between the permian and mid cretaceous and if paleogeothermal gradients were within a few degree c km of present day gradients predicted mean reflectance levels range from 1 0 to 4 0 r sub o at the base of the potsdam megagroup 0 7 to 3 5 at the base of the know megagroup and 0 6 to 1 3 at the base of the maquoketa shale excluding only a small high maturity area in southeastern illinois the knox and potsdam section attained oil generation 475 300 ma while the maquoketa and the younger new albany shale reached the oil window much later 300 250 ma because most significant structures in the basin formed after 300 ma any pre maquoketa source rocks were alreadymore within the gas zone and may have been largely spent by the time known structures formed any know or deeper traps in the basin will probably contain gas be restricted to old structures earlier than 300 ma or stratigraphic traps and will hold pre 300 ma generated hydrocarbons which subsequently cracked to gas less

evidence for stratigraphically controlled paleogeotherms in the illinois basin based on vitrinite reflectance analysis implications for interpreting coal rank anomalies coal rank reflects the temperature of coalification with higher rank coal forming at higher temperatures if the temperature of coalification depended only on the earth s geothermal gradient then the maximum rank of coal in a sedimentary basin should be directly proportional to the thickness of strata above the coal this association does not occur in the illinois basin a continental interior basin in the midwestern united states where the overall coal rank observed is higher than can be explained by past burial depth alone recognition of this anomaly has led many authors to suggest that hot groundwater flowing from south to north during a paleozoic basin scale groundwater migration event increased coal rank we analyzed vitrinite reflectance formula 1 a measure of rank as a function of depth in wells across the basin to determine how paleogeotherms representing variation in temperature with depth change with location our results show that the basin can be divided into three zones 1 in the southern zone the paleogeotherm varies irregularly with depth in strata above the sub absaroka unconformity the contact separating pennsylvanian and mississippian strata 2 in the central zone the paleogeotherm displays a distinct inflection at the unconformity for the rate of increase in formula 2 with depth is greater above the unconformity than below the unconformity and 3 the observed inflection in the paleogeotherm dies out northward until in the northern zone the paleogeotherm has the same slope both above and below the unconformity we propose that the inflection in the paleogeotherm of the central zone indicates that the hot groundwater responsible for causing an increase in coal rank flowed through a high permeability zone just below the sub absaroka unconformity this flow which advected heat into pennsylvanian strata above cooled as it moved northward so it did not influence the paleogeotherm in the northern zone preliminary studies of vein paragenesis stable isotope composition and fluid inclusions as well as computer modeling of flow related heat advection support this proposal 1 embed mml math 1 gif 2 embed mml math 2 gif

effect of latitudinal variations in low level baroclinicity on eddy life cycles and upper tropospheric wave breaking processes abstract an analysis of the potential vorticity gradient and the refractive index in quasigeostrophic qg flows on the sphere reveals that the absolute vorticity and the stretching parts have two contradictory effects on the horizontal shape of the baroclinic waves when the full variations of the coriolis parameter are taken into account in each term the absolute vorticity effect favors the anticyclonic southwest northeast tilt and anticyclonic wave breaking awb and is stronger in the upper troposphere in contrast the stretching effect promotes the cyclonic northwest southeast tilt and cyclonic wave breaking cwb and is more efficient at lower levels a positive eddy feedback acting on the latitudinal variations of the zonal winds is deduced because the absolute vorticity and the stretching effects are respectively more and less efficient with increasing latitude a more northward southward jet renders awb more less probable and cwb less more probable the jet is pushed or maintained mor

the variability of the atlantic meridional overturning circulation the north atlantic oscillation and the el nino southern oscillation in the bergen climate model abstract the link between the interannual to interdecadal variability of the atlantic meridional overturning circulation amoc and the atmospheric forcing is investigated using 200 yr of a control simulation of the bergen climate model where the mean circulation cell is rather realistic as is also the location of deep convection in the northern north atlantic the amoc variability has a slightly red frequency spectrum and is primarily forced by the atmosphere the maximum value of the amoc is mostly sensitive to the deep convection in the irminger sea which it lags by about 5 yr the latter is mostly forced by a succession of atmospheric patterns that induce anomalous northerly winds over the area the impact of the north atlantic oscillation on deep convection in the labrador and greenland seas is represented realistically but its influence on the amoc is limited to the interannual time scale and is primarily associated with wind forcing the tropical pacific shows a strong variability in the model

enigmatic formation of the norfolk basin sw pacific a plume influence on back arc extension 1 the norfolk basin is a small back arc basin in the sw pacific with an unknown age and origin for its formation moreover the process behind its formation as a back arc basin in a region of extensive volcanism has previously never been resolved we have conducted a detailed interpretation of recently acquired swath bathymetry gravity and magnetic data from the northern norfolk basin faust 2 survey together with existing data from the region to address the age and origin of the norfolk basin and propose a new model for basin evolution the norfolk basin is characterized by complex bathymetry which formed during three distinct tectonic phases 1 regions of elevated topography termed plateaus show characteristics of thickened oceanic crust formed during the cretaceous normal superchron in either a back arc basin environment or as a trapped piece of pacific phoenix oceanic crust 2 regions of deep bathymetry termed basins separate the cretaceous plateaus and show basement textured by seafloor spreading fabric of miocene age 3 widespread intraplate plume related volcanic activity post dating the formation of the plateaus but predating the formation of the basins a miocene model for the formation of the basin regions in the norfolk basin requires a 700 km landward jump in the location of back arc spreading even with continued subduction at the tonga kermadec trench and the seaward migration of the subduction hinge the cessation of spreading in the basin regions would have been followed by an eastward jump of back arc spreading by about 1000 km into the current lau basin we propose that the driving force for such an enormous landward jump in back arc spreading is active rifting driven by a mantle plume this scenario is supported by the extensive miocene intraplate volcanism observed in the norfolk basin and the elevated bathymetry of the entire region in this model mantle driven uplift and excess volcanism would have favored back arc rifting landward rather than seaward of the existing south fiji basin in an extensional regime on the over riding plate caused by the continued roll back of the subduction hinge this scenario is supported by the numerous miocene volcanic cones in the norfolk basin which are mainly located on the preexisting plateaus probably predating the formation of the basins as well as their plume melt signature the norfolk basin appears to be the first known example of a major back arc basin whose position relative to the slab was not controlled by subduction driven mantle flow and melting but by plume tectonics this requires a re evaluation of the traditional back arc basin theory in supra subduction zones

multiple equilibria and low frequency variability of the wind driven ocean circulation abstract the link between low frequency time dependent variability and the existence of multiple unstable steady state solutions in a reduced gravity quasigeostrophic ocean model for the midlatitude wind driven circulation is investigated it is shown that a sequence of successive symmetry breaking pitchfork bifurcations lead to multiple equilibria that differ from each other primarily in the elongation of the recirculation cell in the amount of meandering present in the intergyre jet and in a north south shift in the eastward jet the elongation of the recirculation cells and the meandering of the jet play compensating roles in the establishment of the global energy and vorticity balance the solutions also have distinct energy levels but general agreement between them and the bumps in a histogram of the total energy obtained from a 1200 yr time dependent simulation is not found nevertheless a substantial fraction of the variance 30 can be accounted for by four coherent structures that capture th

response of circulation and heat transport in the north atlantic to changes in thermohaline forcing in northern latitudes a model study to avoid an explicit simulation of the overflows across the greenland scotland ridge many models of the large scale ocean circulation seek to include the net effect of the inflowing dense water masses by restoring temperature and salinity near the ridge to observed conditions in this paper the authors examine the effect of different datasets for the northern restoring condition in two versions eddy resolving and non eddy resolving of the model of the north and equatorial atlantic that has been developed in recent years as a community modeling effort for woce it is shown that the use of smoothed climatological fields of temperature and salinity south of the denmark strait leads to strong deficiencies in the simulation of the deep flow field in the basin a switch to actual hydrographic data from the denmark strait ignites a rapid dynamic response throughout the north atlantic affecting the transport and vertical structure of the deep western boundary current and by virtue of the jebar efffect the transport of the horizontal gyres meridional overturning and northward heat transport too weak in the cases with climatological boundary conditions increase to more realistic levels in the subtropical north atlantic the initial response to switches in the high latitude thermohaline forcing is mediated by fast waves along the westurn boundary leading to changes in the deep western boundary current in low latitudes after about two years in the non eddy resolving cast the initial timescale depends on the horizontal grid spacing of the model in the high resolution case the first signal reaches the equator in a few months the adjustment to a new dynamic quasi equilibrium involves kelvin waves along the equator and rossby wave in the interior and is attained in less than two decades throughout the north atlantic it is suggested that these fast dynamic adjustment processes could play an important role in possible fluctuations of the thermohaline circulation or transitions between different equilibrium states of the coupled ocean atmosphere system and may have determined the timescale of the observed climatic transitions before and during the last deglaciation