a simple multicloud parameterization for convectively coupled tropical waves part i linear analysis abstract recent observational analysis reveals the central role of three multicloud types congestus stratiform and deep convective cumulus clouds in the dynamics of large scale convectively coupled kelvin waves westward propagating two day waves and the madden julian oscillation a systematic model convective parameterization highlighting the dynamic role of the three cloud types is developed here through two baroclinic modes of vertical structure a deep convective heating mode and a second mode with low level heating and cooling corresponding respectively to congestus and stratiform clouds a systematic moisture equation is developed where the lower troposphere moisture increases through detrainment of shallow cumulus clouds evaporation of stratiform rain and moisture convergence and decreases through deep convective precipitation a nonlinear switch is developed that favors either deep or congestus convection depending on the relative dryness of the troposphere in particular a dry troposphere

a multiscale model for tropical intraseasonal oscillations the tropical intraseasonal 40 to 50 day oscillation tio is the dominant component of variability in the tropical atmosphere with remarkable planetary scale circulation generated as envelopes of complex multiscale processes a new multiscale model is developed here that clearly demonstrates the fashion in which planetary scale circulations sharing many features in common with the observational record for the tio are generated on intraseasonal time scales through the upscale transfer of kinetic and thermal energy generated by wave trains of organized synoptic scale circulations having features in common with observed superclusters the appeal of the multiscale models developed below is their firm mathematical underpinnings simplicity and analytic tractability while remaining self consistent with key features of the observational record the results below demonstrate in a transparent fashion the central role of organized vertically tilted synoptic scale circulations in generating a planetary circulation resembling the tio

the indian monsoon and its variability for over 300 years the monsoon has been viewed as a gigantic land sea breeze it is shown in this paper that satellite and conventional observations support an alternative hypothesis which considers the monsoon as a manifestation of seasonal migration of the intertropical convergence zone itcz with the focus on the indian monsoon the mean seasonal pattern is described and why it is difficult to simulate it is discussed some facets of the intraseasonal variation such as active weak cycles break monsoon and a special feature of intraseasonal variation over the region namely poleward propagations of the itcz at intervals of 2 6 weeks are considered vertical moist stability is shown to be a key parameter in the variation of monthly convection over ocean and land as well as poleward propagations special features of the bay of bengal and the monsoon brought out by observations during a national observational experiment in 1999 are briefly described

2 5 b y of punctuated earth history as recorded in a single rock deciphering the absolute chronology of ancient crustal rocks is often problematical because of isotopic reequilibration and or mixing during multiple geologic events ion probe u pb age data from texturally distinct zircon crystal domains in a single sample of high grade gneiss from the nimrod group in antarctica reflect successive resorption and crystallization under disequilibrium conditions our data indicate that archean crust of the east antarctic shield initially formed from juvenile magmas ca 3000 ma extends to the central transantarctic mountains successive zircon growth ca 2955 1720 and 530 ma records a sequence of distinct widely spaced high temperature metamorphic and or anatectic events related to archean paleoproterozoic and eocambrian orogenesis

structure related geochemical ree and isotopic k ar rb sr δ18o characteristics of clay minerals from rotliegend sandstone reservoirs permian northern germany abstract euhedral illite cementing the gas bearing sandstone reservoirs of the rotliegend in the niedersachsische rift system northern germany was studied along a horst to graben cross section to examine its chemical and isotopic characteristics the data show that differentiated illite particles grew during a tectono thermal event marked by distinct episodic hydrothermal activities along fault drains and in the poral space of sandstones at 210 ma and at 195 to 190 ma in horst positions at 185 to 175 ma in the nearby graben and at 170 to 165 ma in both the horst and graben varied ree distribution patterns and initial 87sr 86sr ratios from 0 7124 to 0 7142 relative to illite particle size outline a high chemical variability of the fluids during illite growth the 18o values of illite range from 20 0 to 12 4 and those of chlorite from 12 0 to 6 9 the changing 18o values of the minerals most likely relate to varied 18o values of the fluids or to different water rock ratios during crystallization differences among the ree and 87sr 86sr tracers and the 18o values of different generations of illite also suggest a changing fluid chemistry relative to time significant positive eu anomalies and negative ce anomalies in the ree distributions of illite suggest feldspar alteration by the migrating fluids in oxidizing environments

two massive rapid releases of carbon during the onset of the palaeocene eocene thermal maximum the release of massive amounts of carbon led to abrupt warming 55 5 million years ago an analysis of soil carbonates shows two distinct carbon injections at the event onset each releasing over 0 9 petagrams of carbon per year over hundreds to thousands of years

high pressure and ultrahigh temperature metamorphism at komateri northern madurai block southern india we report for the first time the evidence for prograde high pressure hp metamorphism preceding a peak ultrahigh temperature uht event in the northernmost part of the madurai block in southern india mg al rich grt ged rocks from komateri in karur district contain poikiloblastic garnet with numerous multi phase inclusions although most of the inclusion assemblages are composed of gedrite quartz and secondary biotite rare staurolite sapphirine and spinel quartz are also present the xmg mg fe mg of staurolite 0 45 0 49 is almost consistent with that reported previously from namakkal district in the palghat cauvery shear zone system xmg 0 51 0 52 north of the madurai block the hp event was followed by peak uht metamorphism at t 880 1040 c and p 9 8 12 5 kbar as indicated by thermobarometric computations in the grt ged rock and associated mafic granulite symplectic intergrowth of spinel xmg 0 50 0 59 zno 1 7 wt and quartz a diagnostic indicator of uht metamorphism probably formed by decompression at uht conditions the rocks subsequently underwent retrograde metamorphism at t 720 760 c and p 4 2 5 1 kbar the p t conditions and clockwise exhumation trajectory of the komateri rocks comparable to similar features recorded from the palghat cauvery shear zone system suggest that the madurai block and the palghat cauvery shear zone system underwent similar hp and uht metamorphic history probably related to the continent continent collision during the final stage of amalgamation of gondwana supercontinent

a blast of gas in the latest paleocene simulating first order effects of massive dissociation of oceanic methane hydrate carbonate and organic matter deposited during the latest paleocene thermal maximum is characterized by a remarkable 2 5 excursion in delta 13c that occurred over approximately 10 4 yr and returned to near initial values in an exponential pattern over approximately 2 x 10 5 yr it has been hypothesized that this excursion signifies transfer of 1 4 to 2 8 x 10 18 g of ch4 from oceanic hydrates to the combined ocean atmosphere inorganic carbon reservoir a scenario with 1 12 x 10 18 g of ch4 is numerically simulated here within the framework of the present day global carbon cycle to test the plausibility of the hypothesis we find that 1 the delta 13c of the deep ocean shallow ocean and atmosphere decreases by 2 3 over 10 4 yr and returns to initial values in an exponential pattern over approximately 2 x 10 5 yr 2 the depth of the lysocline shoals by up to 400 m over 10 4 yr and this rise is most pronounced in one ocean region and 3 global surface temperature increases by approximately 2 degrees c over 10 4 yr and returns to initial values over approximately 2 x 10 6 yr the first effect is quantitatively consistent with the geologic record the latter two effects are qualitatively consistent with observations thus significant ch4 release from oceanic hydrates is a plausible explanation for observed carbon cycle perturbations during the thermal maximum this conclusion is of broad interest because the flux of ch4 invoked during the maximum is of similar magnitude to that released to the atmosphere from present day anthropogenic ch4 sources

role of horizontal advection of seasonal mean moisture in the madden julian oscillation a theoretical model analysis abstractthe impact of horizontal advection of seasonal mean moisture smm on madden julian oscillation mjo dynamics is investigated here using a theoretical model that includes moisture advection processes the zonal advection of smm with an eastward gradient is found to produce planetary scale instability and promote slow eastward propagation corresponding to an intraseasonal periodicity this is because the smm advection by an anomalous easterly of the kelvin waves generates a moisture source to the east of precipitation which favors eastward propagation and unstable growth on the other hand the advection of smm with a westward gradient results in a westward propagating unstable mode for a realistic smm distribution the simulated eastward propagation is enhanced over the indo pacific warm pool while the westward propagation prevails over the central eastern pacific in contrast to the zonal advection of smm the meridional advection of smm only affects short waves and leaves planetary waves nea

a frictional skeleton model for the madden julian oscillation abstractthe madden julian oscillation mjo is a multiscale system a skeleton model developed by majda and stechmann can capture some of planetary scale aspects of observed features such as slow eastward propagation nondispersive behavior and quadrupole vortex structure however the majda stechmann model cannot explain the source of instability and the preferred planetary scale of the mjo since the mjo major convection region is leaded by its planetary boundary layer pbl moisture convergence here a frictional skeleton model is built by implementing a slab pbl into the neutral skeleton model as a skeleton model allowing the scale interaction this model is only valid for large scale waves this study shows that the pbl frictional convergence provides a strong instability source for the long eastward modes although it also destabilizes very short westward modes for the long waves wavenumber less than 5 the pbl ekman pumping moistens the low troposphere to the east of the mjo convective envel

mesoarchean and paleoproterozoic history of the nimrod complex central transantarctic mountains antarctica stratigraphic revisions and relation to the mawson continent in east gondwana abstract high grade metamorphic and igneous rocks originally mapped as the nimrod group represent the only known crystalline basement of the east antarctic shield exposed in the transantarctic mountains shrimp u pb age data from zircon show that this assemblage preserves multiple geologic events spanning 2 5 b y of archean to early paleozoic history culminating in thermomechanical reworking and active margin magmatism during the ross orogeny new age data from igneous and metamorphic rocks as well as from detrital zircons in metasedimentary quartzites refine the mesoarchean to paleoproterozoic history and indicate the need to abandon the stratigraphic term nimrod group and its five formations in its place we redefine only the igneous and high grade gneissic parts of the assemblage as the nimrod complex and all other metasedimentary rocks exposed in the miller and geologists ranges are included in a newly defined argosy schist within the nimrod complex the oldest layered gneisses represent magmatic mesoarchean crust formed between about 3150 and 3050 ma correspondence of u pb zircon crystallization ages with whole rock sm nd model ages indicates formation from juvenile mantle melts magmatism at ca 3100 ma was followed closely by high temperature metamorphism recorded by zircon crystallization at 2955 2900 ma likely due to high advective heat transfer and or thermal insulation of newly stabilized crust metaigneous units with ages of ca 2500 ma indicate a late neoarchean period of anatexis and or magmatism although the geologic context for these events is uncertain gneissic eclogitic and metaigneous rocks record an important period of deep crustal metamorphism thickening and magmatism between 1730 and 1700 ma referred to as the nimrod orogeny that may have played an early role in assembly of east gondwana cratons a new lithodemic unit argosy schist consists of interlayered mica schist quartzite amphibolite and calc silicate schist quartzites from the schist unit have two distinctive detrital zircon provenance characteristics one type has populations that correlate with dated gneissic and metaigneous units of the nimrod complex indicating a proximal provenance whereas a second type has detrital zircon ages resembling those from neoproterozoic beardmore group sandstones indicating a common broader east antarctic shield provenance their maximum depositional ages range widely from about 2000 to 900 ma leaving unresolved their age and geologic relationship to either the nimrod complex or beardmore group yet they comprise a metasedimentary assemblage that is distinctive from the nimrod complex recent findings of mesoarchean gneisses in the gawler craton geochronology from terre adelie and our new age data from the nimrod complex thus highlight the importance of ca 3 1 2 5 and 1 7 ga events in formation of the composite east antarctic shield adjacent to the modern transantarctic mountains correlative crustal units may extend to the southern prince charles mountains and shackleton range collectively this extensive crustal province referred to as the mawson continent represents an elongate belt of primary mesoarchean crust that experienced major reworking at ca 2 5 and 1 7 ga the latter period includes both high and low p t petrologic signatures providing evidence of crustal thickening and magmatism that may signify collisional processes related to paleoproterozoic cratonal amalgamation during formation of the nuna supercontinent

fundamental causes of propagating and nonpropagating mjos in mjotf gass models abstractthis study investigates the fundamental causes of differences in the madden julian oscillation mjo eastward propagation among models that participated in a recent model intercomparison project these models are categorized into good and poor groups characterized by prominent eastward propagation and nonpropagation respectively column integrated moist static energy mse budgets are diagnosed for the good and the poor models it is found that a zonal asymmetry in the mse tendency characteristic of eastward mjo propagation occurs in the good group whereas such an asymmetry does not exist in the poor group the difference arises mainly from anomalous vertical and horizontal mse advection the former is attributed to the zonal asymmetry of upper midtropospheric vertical velocity anomalies acting on background mse vertical gradient the latter is mainly attributed to the asymmetric zonal distribution of low tropospheric meridional wind anomalies advecting background mse and moisture fields base

calcareous nannoplankton response to surface water acidification around oceanic anoxic event 1a ocean acidification induced by atmospheric co2 may be a major threat to marine ecosystems particularly to calcareous nannoplankton we show that during the aptian 120 million years ago oceanic anoxic event 1a which resulted from a massive addition of volcanic co2 the morphological features of calcareous nannofossils traced the biological response to acidified surface waters we observe the demise of heavily calcified nannoconids and reduced calcite paleofluxes at the beginning of a pre anoxia calcification crisis ephemeral coccolith dwarfism and malformation represent species specific adjustments to survive lower ph whereas later abundance peaks indicate intermittent alkalinity recovery deepwater acidification occurred with a delay of 25 000 to 30 000 years after the dissolution climax nannoplankton and carbonate recovery developed over 160 000 years under persisting global dysoxia anoxia

analytic representation of the large scale organization of tropical convection the pivotal role of mesoscale organization on the large scale coherence of tropical convection is represented by a nonlinear dynamical model the general model consists of two interlocked systems a mesoscale parameterization of organized convection and a two layer model of large scale equatorial dynamics the lower layer dynamics is rossby gyre like whereas outflow from organized convection maintains the upper layer circulation the transports of zonal momentum in the vertical and meridional directions are key processes an archetype of the general model in spite of being brutally simplified represents the convective organization momentum transport and equatorial superrotation realized by the cloud resolving convection parameterization or superparameterization explicit approach developed by grabowski the mesoscale parameterization is an analytic equivalent of the cloud system resolving models used in this computational approach finally issues in parameterizing convective organization are discussed

biochronological continuity of the paleogene sediments of the himalayan foreland basin paleontological and other evidences abstract the paleontological and field evidences presented in the paper demonstrate a biochronological continuity from the marine subathu late thanetian to middle lutetian through the passage beds late lutetian to middle bartonian to the dagshai and equivalent formations late bartonian to rupelian of the himalayan foreland basin east of hazara kashmir syntaxis a similar continuity has also been demonstrated in the sulaiman range based on an assignment of oligocene age to the bugti vertebrate fauna hitherto considered to be of early miocene age thus the concept of a 10 ma hiatus in the foreland basin based on 40 ar 39 ar dates of single detrital muscovite grains from the supposed basal dagshai arenite is no longer tenable while the occurrence of cr spinel and k t boundary nannoplanktons in the subathu formation and passage beds indicate a westerly northwesterly provenance that of the radiolarian chert in the dagshai and coeval formations indicates a northerly provenance from the indus suture zone coinciding with the first influx of the himalayan detritus around 40 ma

the influence of sea surface temperature on the tropical intraseasonal oscillation a numerical study abstract the development and movement of the tropical intraseasonal system tis exhibit remarkable annual variations it was hypothesized that spatial and temporal variation in sea surface temperature sst is one of the primary climatic factors that are responsible for the annual variation of tiss this paper examines possible influences of sst on the tis through numerical experiments with a 2 5 layer atmospheric model on an equatorial plane in which sst affects atmospheric heating via control of the horizontal distribution of moist static energy and the degree of convective instability the gradient of the antisymmetric with respect to the equator component of sst causes a southward propagation of the model tis toward northern australia in boreal winter and a northward propagation over the indian and western pacific oceans in boreal summer the phase speed of the meridional propagation increases with the magnitude of antisymmetric sst gradients the poleward propagation of the equatorial disturba

madden julian oscillation analog and intraseasonal variability in a multicloud model above the equator the madden julian oscillation mjo is the dominant component of tropical intraseasonal variability and a theory explaining its structure and successful numerical simulation remains a major challenge a successful model for the mjo should have a propagation speed of 4 7 m s predicted by theory a wavenumber 2 or 3 structure for the planetary scale low frequency envelope with distinct active and inactive phases of deep convection an intermittent turbulent chaotic multiscale structure within the planetary envelope involving embedded westward and eastward propagating deep convection events and qualitative features of the low frequency envelope from the observational record regarding e g its zonal flow structure and heating here such an mjo analog is produced by using the recent multicloud model of khouider and majda in an appropriate intraseasonal parameter regime for flows above the equator so that rotation is ignored key features of the multicloud model are i systematic low level moisture convergence with retained conservation of vertically integrated moist static energy and ii the use of three cumulus cloud types congestus stratiform and deep convective together with their differing vertical heating structures besides all of the above structure in the mjo analog waves there are accurate predictions of the phase speed from linear theory and transitions from weak regular mjo analog waves to strong multiscale mjo analog waves as climatological parameters vary with all of this structure in a simplified context these models should be useful for mjo predictability studies in a fashion akin to the lorenz 96 model for the midlatitude atmosphere

high magnesium staurolite in a sapphirine garnet rock from the limpopo belt southern africa unusually mg rich staurolite with f fe fe mg 0 51 occurs in a peraluminous silica deficient sapphirine garnet gedrite spinel corundum phlogopite rock as relic inclusions within pyrope almandine garnet f 0 43 0 48 from which it is generally separated by sapphirine f 0 19 gedrite has f 0 24 0 27 phlogopite 0 19 and spinel 0 43 the gradual disappearance of staurolite is due to a shift of the 3 phase afm assemblage staurolite garnetsapphirine to more fe rich compositions according to probably prograde reactions between staurolite and garnet to form sapphirine together with either quartz or gedrite thus still more mg rich staurolite seems to have existed in the rock at earlier stages of metamorphism characterized by lower temperatures and perhaps higher pressures the local equilibria now frozen in indicate minimum pressures of 7 8 kbar and temperatures in excess of about 800 c

propagation and the vertical structure of the madden julian oscillation abstract the madden julian oscillation mjo dominates tropical variability on time scales of 30 70 days during the boreal winter spring it is manifested as an eastward propagating disturbance with a strong convective signature over the eastern hemisphere the space time structure of the mjo is described using the national centers for environmental prediction national center for atmospheric research reanalysis advanced very high resolution radiometer outgoing longwave radiation observed sea surface temperature and the climate prediction center merged analysis of precipitation empirical orthogonal function analysis is used to identify the convective signature of the mjo and regression is used to identify key relationships with the convection compared to analyzing successive years of data the selection of years of strong mjo activity results in a more robust lead lag structure and an increase in explained variance the mjo exhibits a rich vertical structure with low level moisture convergence bein

global dinoflagellate event associated with the late paleocene thermal maximum the late paleocene thermal maximum or lptm ca 55 ma represents a geologically brief time interval 220 k y characterized by profound global warming and associated environmental change the lptm is marked by a prominent negative carbon isotope excursion cie interpreted to reflect a massive and abrupt input of 12 c enriched carbon to the ocean atmosphere reservoir possibly as a result of catastrophic gas hydrate release on time scales equivalent to present day rates of anthropogenic carbon input the lptm corresponds to important changes in the global distribution of biota including mass extinction of marine benthic organisms the dinoflagellate cyst record indicates that surface dwelling marine plankton in marginal seas also underwent significant perturbations during the lptm we report on the dramatic response of representatives of the genus apectodinium from two upper paleocene lower eocene sections in the southern new zealand and northern austria hemispheres where the dinoflagellate records are directly correlated with the cie benthic foraminifera extinction event and calcareous nannofossil zonation the results indicate that the inception of apectodinium dominated assemblages appears to be synchronous on a global scale and that the event is precisely coincident with the beginning of the lptm apectodinium markedly declined in abundance near the end of the lptm this apectodinium event may be associated with 1 exceptionally high global sea surface temperatures and or 2 a significant increase in marginal marine surface water productivity such a globally synchronous acme of dinoflagellate cysts is unprecedented within the dinoflagellate cyst fossil record

high resolution records of the late paleocene thermal maximum and circum caribbean volcanism is there a causal link two recently drilled caribbean sites contain expanded sedimentary records of the late paleocene thermal maximum a dramatic global warming event that occurred at ca 55 ma the records document significant environmental changes including deep water oxygen deficiency and a mass extinction of deep sea fauna intertwined with evidence for a major episode of explosive volcanism we postulate that this volcanism initiated a reordering of ocean circulation that resulted in rapid global warming and dramatic changes in the earth s environment

role of the boundary layer moisture asymmetry in causing the eastward propagation of the madden julian oscillation the moisture budget associated with the eastward propagating madden julian oscillation mjo was diagnosed using 1979 2001 40 yr ecmwf re analysis era 40 data a marked zonal asymmetry of the moisture relative to the mjo convection appears in the planetary boundary layer pbl below 700 hpa creatingapotentiallymoreunstablestratificationtotheeastofthemjoconvectionandfavoringtheeastward propagation of mjo the pbl integrated moisture budget diagnosis indicates that the vertical advection of moisture dominates the low level moistening ahead of the convection a further diagnosis indicates that the leading term in the vertical moisture advection is the advection of the background moisture by the mjo ascending flow associated with pbl convergence the cause of the zonally asymmetric pbl convergence is further examined it is found that heating induced free atmospheric wave dynamics account for 75 90 of the total pbl convergence while the warm sst anomaly induced by air sea interaction contributes 10 25 of the total pbl convergence the horizontal moisture advection also plays a role in contributing to the pbl moistening ahead of the mjo convection the leadingterm in the moistureadvectionis the advectionacross the backgroundmoisture gradient by the mjo flow in the western indian ocean maritime continent and western pacific the meridional moisture advection by the mjo northerly flow dominates while in the eastern indian ocean the zonal moisture advection is greater the contribution of the moisture advection by synoptic eddies is in generalsmall ithas a negativeeffect overthetropicalindianoceanand westernpacificandbecomespositive in the maritime continent region

magnesium staurolite and green chromian staurolite from fiordland new zealand staurolite with up to 6 5 mgo and magnesium as the dominant divalent cation is recorded from an incompletely reconstituted metatroctolite from fiordland new zealand it occurs in complex assemblages including pyrope hornblende spinel and corundum and is estimated to have crystallized at about 12 kbar and 750 degrees c the a cell edge of this staurolite 7 891 a o is markedly larger than that of other natural staurolites which may be attributed to substantial substitution of mg for al in the kyanite layer of the staurolite structure a green staurolite with 2 cr 2 o 3 is also recorded from a mafic metatuff from fiordland

black shale formation during the latest danian event and the paleocene eocene thermal maximum in central egypt two of a kind abstract the paleocene eocene thermal maximum petm 55 8 ma is considered as the most severe of a series of transient warming events hyperthermals that occurred during the early paleogene however the extent and magnitude of environmental changes during the short lived warming events pre and post dating the petm are still poorly constrained in this study we focus on the latest danian event lde 61 7 ma and compare it to the petm we present high resolution micropaleontological geochemical and mineralogical data of the petm and the lde in two adjacent sections from the gebel qreiya area in egypt there both events are characterized by a distinct set of event beds overlying an unconformity they are associated with intense carbonate dissolution and substantial changes in the benthic foraminifera fauna moreover both show an abrupt drop of siliciclastic input sediment starvation correlative to the onset of black shale formation and a strong enrichment in redox sensitive trace elements the evidence for enhanced detrital input during the onset of the petm and a longer recovery phase with enhanced phosphorus sedimentation during the petm attests a stronger environmental impact of this event compared to the lde according to rock eval and elemental analysis the petm as well as the lde event beds have up to 4 wt organic carbon small amounts of volatile hydrocarbons but high amounts of highly weathered and inert organic matter black carbon during pyrolysis the extremely high temperatures for the maximum release of hydrocarbons of the petm and lde samples correspond to thermal heating of 170 c which is incompatible with the sediment burial history therefore we suggest that the organic matter in both event deposits does not reflect well preserved marine biomass but predominantly represents a mixture of heavily weathered autochthonous marine material and allochthonous combustion residues differences in preservation and or type of organic matter are also likely to account for the divergent stable isotope anomalies of organic carbon the well known negative carbon isotope anomaly at the petm and a positive anomaly at the lde although warming water column stratification and enhanced nutrient input may have promoted anoxic conditions on the shelf during the lde as well as during petm our results support rapid sea level rise and clastic starvation as one important mechanism for black shale formation and carbon sequestration for both events this result underlines the similarity of both hyperthermal events in terms of environmental changes recorded on the southern tethyan margin with the petm showing an additional early phase of strong detrital input not revealed at the lde

an air sea coupled skeleton model for the madden julian oscillation this work is an extension and improvement of the minimal madden julian oscillation mjo skeleton model developed by majda and stechmann which can capture some important features of the mjo slow eastward propagation quadrupole vortex structure and independence of frequency on wavelength but is unable to produce unstable growth and selection of eastward propagating planetary waves with the addition of planetary boundary layer frictional moisture convergence these deficiencies can be remedied the frictional boundary layer selects the planetary scale eastward propagation as the most unstable mode but the dynamics remains confined to atmospheric processes only here the authors study the role of air sea interaction by implementing an oceanic mixed layer ml model of wang and xie into the mjo skeleton model in this new air sea coupled skeleton model the features of the original skeleton model remain additionally the air sea interaction under mean westerly winds is shown to produce a strong instability that selectively destabilizes the eastward propagating planetary scale waves although the cloud shortwave radiation seasurfacetemperature crs feedbackdestabilizesbotheastwardand westward modes theair sea feedback associated with the evaporation and oceanic entrainment favors planetary scale eastward modes over the western hemisphere where easterly background winds prevail the evaporation and entrainment feedbacks yield damped modes indicating that longitudinal variation of the mean surface winds plays an important role in regulation of the mjo intensity in addition to the longitudinal variation of the mean sea surface temperature or mean moist static stability this theoretical analysis suggests that accurate simulation of the climatological mean state is critical for capturing the realistic air sea interaction and thus the mjo

changes in the hydrological cycle in tropical east africa during the paleocene eocene thermal maximum the paleocene eocene thermal maximum petm at ca 55 8 ma is one of the most studied instances of past greenhouse gas induced global warming as such it provides a rich opportunity to examine the impact of such global change on local climates the effects of increased continental and sea surface temperatures on local precipitation and humidity during the petm remain poorly constrained and studies reveal complex regional differences whilst some localities appear to experience a net increase in humidity others exhibit the opposite crucially there are few records of hydrological change from tropical regions recent onshore drilling expeditions in tanzania have yielded expanded sedimentary sections deposited in a marine environment that span much of the late cretaceous and paleogene and show exceptionally good preservation of both calcareous microfossils and organic matter the petm interval has previously been constrained by both biostratigraphy and carbon isotopic records and spans ca 7 m of section lipid distributions including various terrestrial marine and bacterial biomarkers and their hydrogen isotopic compositions as well as mineralogy were used to examine east african vegetation and hydrological responses to the global change occurring at the petm although total organic carbon contents decrease the concentrations of both higher plant n alkanes n alkanoic acids and soil bacterial glycerol dialkyl glycerol tetraethers biomarkers increase dramatically at the onset of the petm negative carbon isotope excursion cie suggesting an increased discharge of fluvial sedimentary organic matter similarly mineralogical indicators of terrestrial input including ti al and si al ratios quartz contents and notably the proportion of kaolinite also increase at the onset of the cie however higher plant leaf wax n alkanes c27 c29 and c31 become more deuterium enriched throughout the same interval suggesting a more arid and or hotter rather than a more humid environment this evidence collectively suggests an east african early petm climate characterised by overall hot and arid conditions punctuated by intense perhaps seasonal precipitation events these data match observations from other locations at mid latitudes suggesting that the humid climate often suggested for the petm was not globally widespread

antecedents and self induction of active break south asian monsoon unraveled by satellites 1 understanding the origin and perpetuation of the monsoon cycle has eluded scientists for decades using a suite of unprecedented satellite measurements we show that the antecedents of the active break monsoon emerge in the western equatorial indian ocean eio the initiation of a new rainy phase in the western eio is preceded by in situ surface wind convergence and central eio warming both are induced by the subdued condition over the eastern eio set up in the previous cycle thus a self induction mechanism appears to be operating in maintenance of the indian monsoon intraseasonal oscillation the finding here offers a focus for prediction of the active break indian monsoon with potential predictability about four weeks in advance

on the duration of the paleocene eocene thermal maximum petm 1 the paleocene eocene thermal maximum petm is one of the best known examples of a transient climate perturbation associated with a brief but intense interval of global warming and a massive perturbation of the global carbon cycle from injection of isotopically light carbon into the ocean atmosphere system one key to quantifying the mass of carbon released identifying the source s and understanding the ultimate fate of this carbon is to develop high resolution age models two independent strategies have been employed cycle stratigraphy and analysis of extraterrestrial helium heet both of which were first tested on ocean drilling program odp site 690 these two methods are in agreement for the onset of the petm and initial recovery or the clay layer main body but seem to differ in the final recovery phase of the event above the clay layer where the carbonate contents rise and carbon isotope values return toward background values here we present a state of the art age model for the petm derived from a new orbital chronology developed with cycle stratigraphic records from sites drilled during odp leg 208 walvis ridge southeastern atlantic integrated with published records from site 690 weddell sea southern ocean odp leg 113 during leg 208 five paleocene eocene p e boundary sections sites 1262 to 1267 were recovered in multiple holes over a depth transect of more than 2200 m at the walvis ridge yielding the first stratigraphically complete p e deep sea sequence with moderate to relatively high sedimentation rates 1 to 3 cm ka where a is years a detailed chronology was developed with nondestructive x ray fluorescence xrf core scanning records on the scale of precession cycles with a total duration of the petm now estimated to be 170 ka the revised cycle stratigraphic record confirms original estimates for the duration of the onset and initial recovery but suggests a new duration for the final recovery that is intermediate to the previous estimates by cycle stratigraphy and heet

global decline in ocean ventilation oxygenation and productivity during the paleocene eocene thermal maximum implications for the benthic extinction the prominent global warming event at the paleocene eocene boundary 55 ma referred to as the paleocene eocene thermal maximum petm was characterized by rapid temperature increase and changes in the global carbon cycle in

sapphirine quartz corona around magnesian xmg 0 58 staurolite from the palghat cauvery suture zone southern india evidence for high pressure and ultrahigh temperature metamorphism within the gondwana suture abstract we report the first finding of equilibrium sapphirine quartz assemblage from the palghat cauvery suture zone pcsz in southern india providing unequivocal evidence for extreme crustal metamorphism at ultrahigh temperature uht conditions associated with the collisional assembly of the gondwana supercontinent in the late neoproterozoic cambrian the sapphirine and quartz occur as coronas around mg rich x mg 0 58 staurolite within poikiloblastic garnet in an mg al rich rock suggesting the progress of the prograde dehydration reaction staurolite garnet sapphirine quartz h 2 o although the occurrence of mg rich staurolite was previously noted from some localities in the pcsz no sapphirine quartz direct association has yet been reported the available experimental studies on mg rich staurolite indicate that the mineral is stable at p 15 kbar and suggest that the complex texture that we report here might correspond to a peak high pressure regime prior to the uht event the symplectic sapphirine quartz around staurolite probably implies decompression from p 15 kbar toward the stability of sapphirine quartz at temperatures of c 1000 c along a clockwise p t path the prograde high pressure metamorphism and following uht event correlate with the subduction collision tectonics associated with the final stage of amalgamation of gondwana supercontinent

astronomical climate control on paleosol stacking patterns in the upper paleocene lower eocene willwood formation bighorn basin wyoming the willwood formation of the bighorn basin wyoming usa is a thick succession of upper paleocene and lower eocene fluvial floodplain sandstones and mudstones reddish paleosols formed on the floodplain mudstones alternate rhythmically on various scales with heterolithic intervals of small channel sandstones and mudstones showing weak pedogenesis spectral analysis of redness in the willwood successions at polecat bench and red butte reveals significant spectral peaks corresponding to cycle thicknesses of 8 and 3 m the 8 m cycle reflects distinct clusters of 3 5 paleosols age constraints show that the period of this cycle closely matches the 21 k y climatic precession cycle the 3 m cycle corresponds to individual paleosols with a period of 7 8 k y this period is similar to millennial scale sub milankovitch cycles found in marine and lacustrine successions of pliocene pleistocene age precession and millennial scale climate variations probably affected paleosol development through cyclic changes from predominantly overbank to predominantly channel avulsion deposition with the latter periodically halting soil formation because of high sediment accumulation a new age model was developed for the paleocene eocene carbon isotope excursion cie at polecat bench based on the precessional origin of paleosol clusters the main body of the cie spans 5 5 precession cycles or 115 k y and the recovery tail of the cie spans 2 precession cycles or 42 k y this outcome is consistent with and independently confirms recent estimates of cie duration based on deep sea cores

quantification of loss of calcite pyrite and organic matter due to weathering of toarcian black shales and effects on kerogen and bitumen characteristics abstract comparison of geochemical data on posidonia shale early toarcian from a shallow unweathered core and from adjacent weathered exposures of the same fades was performed results revealed that quantitatively the most affected petrographic constituent is pyrite and that organic matter and carbonate were also altered by weathering due to this process of weathering the bulk composition of organic matter especially the molecular composition of soluble organic matter and the fluorescence colour of organic particles are changed estimates of weathering rates reveal that the annual release of sulphur and organic carbon from black shales may significantly add to anthropogenic pollution

a climatology of waves in the equatorial region abstract propagating anomalies of moisture and moist deep convection in the tropics are organized into a variety of large scale modes these include but are not limited to the so called intraseasonal oscillations convectively coupled waves similar to those predicted by shallow water theory on the equatorial beta plane and tropical depression type disturbances along with the annual and diurnal cycles these modes act and interact to control much of the variance of tropical convection analyses of 10 yr of outgoing longwave radiation olr and precipitable water pw data are carried out to develop comparative climatologies of these wavelike modes the analysis relaxes the commonly used cross equatorial symmetry constraints which allows study of the portions of the wavelike processes that are asymmetric across the equator mean background states are found for olr and for pw as functions of day of the year examination of anomalies together with the background reveals much about how the waves are affec

an osmium isotope excursion associated with the late paleocene thermal maximum evidence of intensified chemical weathering in the latest paleocene an abrupt shift to more negative 13c values has been documented at numerous marine and terrestrial sites bralower et al 1997 cramer et al 1999 kaiho et al 1996 kennett and stott 1991 koch et al 1992 stott et al 1996 thomas and shackleton 1996 zachos et al 1993 this carbon isotope event cie is coincident with oxygen isotope data that indicate warming of surface waters at high latitudes of nearly 4 6 c kennett and stott 1991 and more moderate warming in the subtropics thomas et al 1999 here we report 187os 188os isotope records from the north atlantic and indian oceans which demonstrate a 10 increase in the 187os 188os ratio of seawater coincident with the late paleocene cie this excursion to higher 187os 188os ratios is consistent with a global increase in weathering rates the inference of increased chemical weathering during this interval of unusual warmth is significant because it provides empirical evidence supporting the operation of a feedback between chemical weathering rates and warm global climate which acts to stabilize earth s climate walker et al 1981 estimates of the duration of late paleocene cie bains et al 1999 bralower et al 1997 norris and rohl 1999 rohl et al 2000 in conjunction with the os isotope data imply that intensified chemical weathering in response to warm humid climates can occur on timescales of 104 105 years this interpretation requires that the late paleocene thermal maximum os isotope excursion be produced mainly by increased os flux to the ocean rather than a transient excursion to higher 187os 188os ratios in river runoff although we argue that the former is more likely than the latter we cannot rule out significant changes in the 187os 188os ratio of rivers

a staurolite talc assemblage in tourmaline phlogopite chlorite schist from northern victoria land antarctica and its petrogenetic significance staurolite and corundum are found as inclusions in tourmaline in a talc phlogopite chlorite albite chist near mount bernstein 71 37 s 163 07 e northern victoria land antarctica these inclusions are interpreted as relics of a staurolite talc corundum chlorite assemblage that was stable during an early stage in the metamorphic cycle and subsequently armored by tourmaline probably during the middle stage pressures and temperatures during the middle stage are estimated to be 650 700 c and 5 5 6 4 kbar the transition from the early to the middle stage represents a roughly isothermal decrease in pressure of 2 3 kbar during a late retrograde stage t 300 370 c p 3 5 kbar staurolite was partly replaced by a muscovitic aggregate containing clinozoisite pumpellyite and margarite

eclogite facies metamorphism preserved in tectonic blocks from a lower crustal shear zone central transantarctic mountains antarctica in the geologists and miller ranges of the central transantarctic mountains mafic and ultramafic tectonic blocks occur in an early cambrian amphibolite to granulite facies lower crustal transpressional shear zone mafic blocks consist of garnet clinopyroxene symplectite hornblende plagioclase quartz ilmenite orthopyroxene biotite mineral compositions in these blocks generally reflect equilibration under upper amphibolite to lower granulite facies conditions t 700 c p 8 12 kbar these conditions are the same as those indicated by peak syn kinematic assemblages in the enclosing shear zone tectonites mineral and textural evidence for an earlier higher pressure p 12 25 kbar eclogite facies metamorphism includes 1 plagioclase reaction rims around anhedral garnet 2 complex clinopyroxene intergrowths consisting of augite plagioclase quartz hornblende orthopyroxene interpreted as exsolved na rich clinopyroxene omphacite and 3 unusual magnesian staurolite atomic mg mg fe 0 58 inclusions in pyrope almandine garnet we suggest that the relict eclogite facies metamorphism records an earlier period of crustal thickening that occurred prior to formation of the transpressional shear zone perhaps as an early stage in ross orogenesis

frictional moisture convergence in a composite life cycle of the madden julian oscillation abstract a composite life cycle of the madden julian oscillation mjo is constructed using an index based on the first two eofs of the bandpass filtered 20 80 days 850 mb zonal wind averaged from 5 n to 5 s every 2 5 around the equator precipitation 1000 mb convergence 850 mb wind and 200 mb wind are composited for the period 1979 95 water vapor integrated from the surface to 300 mb is composited for the period 1988 92 frictional moisture convergence at the equator is shown to play an important role in the life cycle of the madden julian oscillation mjo regions of boundary layer convergence foster growth of positive water vapor anomalies to the east of convection this convergence coincides with 850 mb easterly wind anomalies as is consistent with kelvin wave dynamics drying of the atmosphere occurs rapidly after the passage of convection with the onset of 850 mb westerly perturbations possible mechanisms for this drying include boundary layer divergence and subsidence or horizontal advect

fluvial discharge and sea level changes controlling black shale deposition during the paleocene eocene thermal maximum in the dababiya quarry section egypt abstract the formation of black shales along the tethyan margins at the paleocene eocene thermal maximum petm 55 ma may have been an important feedback mechanism to reduce the warming by excess carbon burial however the detailed evolution of sediment redox conditions during this event is still poorly constrained we address this issue by a high resolution mineralogical and geochemical investigation of the outer neritic dababiya quarry petm section in central egypt which serves as the global boundary stratotype section and point for the base of the eocene there the base of the petm beds corresponds to the onset of sediment lamination indicative of oxygen deficiency at the seafloor the absence of calcium carbonate and a major increase in phyllosilicate abundance and change in detritus sensitive trace elements is indicative of severe carbonate dissolution in addition to enhanced fluvial input erosion of coastal low lands and deposition during low or slightly rising sea level subsequently fully anoxic conditions were established for a short period during the peak phase of the petm as recorded by the strong relative enrichment of redox sensitive trace elements and organic carbon compared to background sediments the decoupling of the fe and mo contents from the detrital fraction may even indicate that euxinic conditions existed with free hydrogen sulfide in the water column concurrent to the onset of anoxia high carbonate and quartz contents as well as high elemental ratios of si al suggest a major drop of siliciclastic sediment supply sediment starvation most likely caused by a rapid sea level rise the final recovery phase of the petm is associated with a progressive restoration of the pre petm siliciclastic sedimentation temporary seasonal anoxic to dysoxic conditions and high phosphorus enrichment followed by carbonate dominated sedimentation and the return to well oxygenated conditions we conclude that after a period of strong fluvial discharge several parameters inherent to the petm e g warming water column stratification and enhanced fluvial discharge may have contributed to the development of anoxia and increased the burial efficiency of organic carbon by reducing water column oxygenation the temporal coincidence of sediment starvation and onset of black shale deposition during the petm suggests that a rapid sea level rise was an additional important triggering factor therefore our results support not only current views that tethyan continental shelf areas may have acted as large carbon sinks during the petm but also indicate that transgressions may have provided an important feedback mechanism for organic carbon drawdown during hyperthermal events

paleoproterozoic oceanic subduction in the north china craton insights from the metamorphic p t t paths of the chicheng melange in the hongqiyingzi complex abstract how and when modern style plate tectonics started in the earth s history is one of the most important scientific issues the chicheng melange in the north margin of north china craton ncc presents a new insight into the paleoproterozoic cold oceanic subduction and the beginning of modern style plate tectonic regime the melange comprises blocks of retrograde eclogites amphibolites and peridotites in a matrix of metasediments the retrograde eclogites mainly contain garnet amphibole and symplectites consisting of fine grained plagioclase clinopyroxene and amphibole three metamorphic stages were derived involving the prograde peak and post peak decompression stages the p t conditions for the prograde and peak stages range from 17 kbar 660 c to 22 750 c kbar based on mineral composition isopleths in p t pseudosections involving core to mantle increasing pyrope and decreasing grossular in garnet and ti content in amphibole the post peak decompression is proposed to be isothermal under melt fluid absent conditions recorded a pressure of 8 11 kbar on the basis of symplectite assemblages for the amphibolites pre peak heating peak temperature and post peak cooling metamorphic stages were derived they experienced anataxis during this overprinting metamorphism when heated to above the solidus the peak temperature conditions are constrained to be 5 7 kbar 780 830 c on the basis of the contours of the maximum ti in amphibole and anorthite of plagioclase in p t pseudosections zircon u pb dating for the selected samples and a summary of published age data reveal that the eclogite facies metamorphism may have occurred at 1 85 1 80 ga and the eclogitic rocks exhumed to a lower crust level during or after subduction to be overprinted by multi phase thermal events at 1 66 ga and 460 420 ma with undefined conditions and at 360 270 ma under amphibolite facies the eclogite facies metamorphism from the chicheng melange shows a geothermal gradient of 9 c km pointing to a cold oceanic subduction at late paleoproterozoic that occurred along the northern margin of the ncc the overprinting metamorphism with anataxis recognized from the amphibolites represents a low pressure type with a geothermal gradient of 35 c km which was interpreted to occur at 360 270 ma governed by extension

a model for the boreal summer intraseasonal oscillation abstract the tropical intraseasonal oscillation iso exhibits pronounced seasonality the boreal summer iso is more complex than its winter counterpart due to the coexistence of equatorial eastward off equatorial westward and northward propagating low frequency modes and their interactions based on observational evidence and results obtained from numerical experiments a mechanism is proposed for the boreal summer iso in which the northern hemisphere summer monsoon nhsm circulation and moist static energy distribution play essential roles with a climatological july mean basic state the life cycle of model low frequency waves consists of four processes an equatorial eastward propagation of a coupled kelvin rossby wave packet an emanation of moist rossby waves in the western pacific a westward propagation and amplification of the rossby waves in south asian monsoon regions and a reinitiation of the equatorial disturbances over the central indian ocean the life cycle spans about one month and p

from greenhouse to icehouse organic walled dinoflagellate cysts as paleoenvironmental indicators in the paleogene abstract dinoflagellates are an important component of the extant eukaryotic plankton their organic walled hypnozygotic cysts dinocysts provide a rich albeit incomplete history of the group in ancient sediments building on pioneering studies of the late 1970s and 1980s recent drilling in the southern ocean has provided a wealth of new dinocyst data spanning the entire paleogene such multidisciplinary studies have been instrumental in refining existing and furnishing new concepts of paleogene paleoenvironmental and paleoclimatic reconstructions by means of dinocysts because dinocysts notably exhibit high abundances in neritic settings dinocyst based environmental and paleoclimatic information is important and complementary to the data derived from typically more offshore groups as planktonic foraminifera coccolithophorids diatoms and radiolaria by presenting case studies from around the globe this contribution provides a concise review of our present understanding of the paleoenvironmental significance of dinocysts in the paleogene 65 25 ma representing earth s greenhouse icehouse transition this episode holds the key to the understanding of extreme transient climatic change we discuss the potential of dinocysts for the reconstruction of paleogene sea surface productivity temperature salinity stratification and paleo oxygenation along with their application in sequence stratigraphy oceanic circulation and general watermass reconstructions

enhanced terrestrial weathering runoff and surface ocean carbonate production during the recovery stages of the paleocene eocene thermal maximum 1 the carbonate saturation profile of the oceans shoaled markedly during a transient global warming event known as the paleocene eocene thermal maximum petm circa 55 ma the rapid release of large quantities of carbon into the ocean atmosphere system is believed to have triggered this intense episode of dissolution along with a negative carbon isotope excursion cie the brevity 120 220 kyr of the petm reflects the rapid enhancement of negative feedback mechanisms within earth s exogenic carbon cycle that served the dual function of buffering ocean ph and reducing atmospheric greenhouse gas levels detailed study of the petm stratigraphy from ocean drilling program site 690 weddell sea reveals that the cie recovery period which postdates the cie onset by 80 kyr is represented by an expanded 2 5 m thick interval containing a unique planktic foraminiferal assemblage strongly diluted by coccolithophore carbonate collectively the micropaleontological and sedimentological changes preserved within the cie recovery interval reflect a transient state when ocean atmosphere chemistry fostered prolific coccolithophore blooms that suppressed the local lysocline to relatively deeper depths a prominent peak in the abundance of the clay mineral kaolinite is associated with the cie recovery interval indicating that continental weathering runoff intensified at this time as well robert and kennett 1994 such parallel stratigraphic changes are generally consonant with the hypothesis that enhanced continental weathering runoff and carbonate precipitation helped sequester carbon during the petm recovery period e g dickens et al 1997 zachos et al 2005

late palaeocene early eocene dinoflagellate cysts from the turgay strait kazakhstan correlations across ancient seaways abstract the results of a quantitative palynological analysis emphasizing organic walled dinoflagellate cysts dinocysts of palaeocene eocene deposits exposed in the sokolovsky quarry turgay trough northern kazakhstan are presented here located in the ancient turgay strait a former seaway presumed to have connected the tethyan and boreal oceans and seas in the early palaeogene the sokolovsky quarry outcrop occupies a key position for the analysis of connections between these realms in general the dinocyst succession of sokolovsky closely resembles coeval arctic ocean north sea basin counterparts only in one interval endemic and or possibly tethyan species co occur the successive dinocyst assemblages allow recognition of the late palaeocene early eocene p5a p5b p6a p6b and e2 zones established in the north sea basin the succession is interpreted to represent parts of several third order sea level cycles correlative with those recognised in the north sea basin detailed comparison with similar studies from southeastern england allows the recognition of parts of third order cycles thanetian 1 tht 1 2 4 5 and ypresian ypr 3 in addition two important stratigraphic gaps within the palaeocene eocene succession are recognised possibly reflecting times of sea level lowering these gaps are inferred from 1 the absence of a complete p5b p6a transition 2 the absence of zone e1 and 3 bio sequence stratigraphy combined results indicate that the turgay strait flooded from the north between 57 8 and 57 1 ma cycles tht 1 and 2 in part with a minor missing section during the second phase of turgay flooding 56 4 55 3 ma evidence may be taken to indicate increased influence from the tethyan ocean and or warmer conditions deposits reflecting the late palaeocene thermal maximum associated with this interval are present at sokolovsky quarry this interval is marked by abundant apectodinium spp including a augustum and organic rich layers a third flooding is correlative to the london clay transgression from 54 5 ma from our study no decisive evidence has become available that confirms that a connection between the arctic and tethyan oceans via the turgay strait in the early palaeogene existed nevertheless during intervals of major sea level fall the turgay strait depression may be regarded to have been an important feature for migrating terrestrial biota four new wetzeliellioid taxa apectodinium sp a apectodinium sp b wilsonidium sp a and wilsonidium sp b are described from the palaeocene part of the section

a new multiscale model for the madden julian oscillation abstract a multiscale model of the mjo is developed here that accounts in a simplified fashion for both the upscale transfer from synoptic to planetary scales of momentum and temperature from wave trains of thermally driven equatorial synoptic scale circulations in a moving convective envelope as well as direct mean heating on planetary scales this model involves idealized thermally driven congestus synoptic scale fluctuations in the eastern part of the moving wave envelope and convective superclusters in the western part of the envelope the model self consistently reproduces qualitatively many of the detailed structural features of the planetary circulation in the observations of the mjo including the vertical structure in both the westerly onset region and the strong westerly wind burst region as well as the horizontal quadrupole planetary vortex structure the westerly midlevel inflow in the strong westerly region and the quadrupole vortex are largely produced in the model by the upscale transpor

dissociation of oceanic methane hydrate as a cause of the carbon isotope excursion at the end of the paleocene isotopic records across the latest paleocene thermal maximum lptm indicate that bottom water temperature increased by more than 4 c during a brief time interval 104 years of the latest paleocene 55 6 ma there also was a coeval 2 to 3 excursion in the 13c of the ocean atmosphere inorganic carbon reservoir given the large mass of this reservoir a rapid 13c shift of this magnitude is difficult to explain within the context of conventional hypotheses for changing the mean carbon isotope composition of the ocean and atmosphere however a direct consequence of warming bottom water temperature from 11 to 15 c over 104 years would be a significant change in sediment thermal gradients and dissociation of oceanic ch4 hydrate at locations with intermediate water depths in terms of the present day oceanic ch4 hydrate reservoir thermal dissociation of oceanic ch4 hydrate during the lptm could have released greater than 1 1 to 2 1 1018 g of carbon with a 13c of approximately 60 the release and subsequent oxidation of this amount of carbon is sufficient to explain a 2 to 3 excursion in 13c across the lptm fate of ch4 in oceanic hydrates must be considered in developing models of the climatic and paleoceanographic regimes that operated during the lptm

precursors of the paleocene eocene thermal maximum petm in the subathu group nw sub himalaya india abstract the paleocene eocene thermal maximum petm is one of the most pronounced and widely documented global warming events in the geological history that occurred at the beginning of the eocene 56 ma causing substantial changes in biota and geochemistry it is marked worldwide by a negative isotopic excursion of 13c the biotic changes associated with the petm in marine realm include bloom of the dinoflagellate apectodinium turnover of larger foraminiferids diversification of planktic foraminiferids and carbonate dissolution of calcareous test shells etc while the geochemical changes include decrease in carbonates and increase in abundance of silicates and phyllosilicates etc conspicuously there has been no attempt to identify the petm in the himalaya even though some himalayan sections are known to have paleocene eocene transition beds to fill this lacuna we investigated the basal part of the late paleocene middle eocene subathu group exposed at the village kurla near subathu in himachal pradesh nw sub himalaya for biotic mineralogical and geochemical signatures of this abrupt warming event the significant results of this study include carbon isotope excursion cie of 3 4 occurrence of index dinoflagellate genus apectodinium and carbonate dissolution of the larger benthic foraminiferids the mineralogical changes noted across the paleocene eocene transition include increase in quartz and phyllosilicates and decrease in carbonates the geochemical changes include i increase in sio2 al2o3 k2o and fe2o3 ii decrease in caco3 iii decreasing trend of si al fe al and mg al ratios iv increasing trend of k al ti al and zr al ratios v changes in trace element abundance vi maximum chemical index of alteration cia of 85 89 and vii increase in abundance of rare earth elements the aforementioned dataset is clearly very close to the petm and even reflects its probable onset and peak phases however it is insufficient to definitively identify the petm in the studied section nevertheless since this study is the first from a himalayan section and brings out considerable new information all results and interpretations are presented and discussed here

high pressure metamorphism during the llano orogeny inferred from proterozoic eclogite remnants mineral chemistries and textures in mafic garnet pyroxene rock within the lost creek gneiss in the purdy hill quadrangle mason county texas record three distinct p t events two of them at pressures higher than any previously documented for these grenville age rocks the earliest metamorphic episode produced an eclogitic assemblage of pyrope rich almandine sodian augite orthopyroxene pargasitic amphibole some orthopyroxene cores record pressures greater than 15 kbar even for the most conservative estimated temperature of 500 c garnet and orthopyroxene rims and matrix clinopyroxene and amphibole record a second event at 750 c and 8 kbar symplectites of clinopyroxene plagioclase and coronas around garnet of plagioclase amphibole magnetite formed in response to reheating and hydration associated with postkinematic intrusion at the amphibolite facies conditions 600 650 c 3 5 5 kbar commonly recorded in the region recognition of early high pressure metamorphic episodes markedly strengthens the correlation between these rocks and other grenville age exposures along the continental margin and provides petrologic support for models invoking proterozoic subduction accompanying the llano orogeny

the importance of blueschist eclogite dehydration reactions in subducting oceanic crust the metamorphic evolution and dehydration of subducting oceanic crust may be predicted by combining calculated pressure temperature p t paths with a model of metabasalt phase equilibria in steady state subduction zones with high rates of shear heating the upper parts of the subducting oceanic crust progress through the greenschist amphibolite granulite eclogite facies whereas lower parts of the subducting oceanic crust progress through the blueschist eclogite facies in steady state subduction zones with moderate rates of shear heating most of the subducting oceanic crust passes through the blueschist eclogite transition in steady state subduction zones with low rates of shear heating the entire subducting oceanic crust lies within the blueschist facies to depths greater than 70 km for oceanic crust containing 1 2 wt h 2 o dehydration will not begin until the onset of eclogite or amphibolite facies metamorphism depending on the p t path for many subduction zones the most important dehydration reactions in the subducting oceanic crust occur at the blueschist eclogite facies transition associated with the breakdown of lawsonite or clinozoisite glaucophane and chlorite large amounts of h 2 o released by blueschist eclogite dehydration reactions could trigger partial melting in the overlying mantle wedge and may play a crucial role in the generation of arc magmas

spatiotemporal patterns of carbonate sedimentation in the south atlantic implications for carbon cycling during the paleocene eocene thermal maximum abstract rapid carbon input into the ocean atmosphere system caused a dramatic shoaling of the lysocline during the paleocene eocene thermal maximum petm a transient 170 kyr global warming event that occurred roughly 55 ma carbon cycle models invoking an accelerated carbonate silicate feedback mechanism to neutralize ocean acidification predict that the lysocline would subsequently deepen to depths below its original position as the marine carbonate system recovered from such a perturbation to test this hypothesis records of carbonate sedimentation and preservation for petm sections in the weddell sea odp site 690 and along the walvis ridge depth transect odp sites 1262 1263 and 1266 were assembled within the context of a unified chronostratigraphy the meridional gradient of undersaturation delimited by these records shows that dissolution was more severe in the subtropical south atlantic than in the weddell sea during the petm a spatiotemporal pattern inconsistent with the view that atlantic overturning circulation underwent a transient reversal deepening of the lysocline following its initial ascent is signaled by increases in caco3 and coarse fraction content at all sites carbonate preservation during the recovery period is appreciably better than that seen prior to carbon input with carbonate sedimentation becoming remarkably uniform over a broad spectrum of geographic and bathymetric settings these congruent patterns of carbonate sedimentation confirm that the lysocline was suppressed below the depth it occupied prior to carbon input and are consistent with the view that an accelerated carbonate silicate geochemical cycle played an important role in arresting petm conditions

palaeoenvironmental and climatic changes during the palaeocene eocene thermal maximum petm at the wadi nukhul section sinai egypt the palaeocene eocene thermal maximum petm interval at the wadi nukhul section sinai egypt is represented by a 10 cm thick condensed clay rich layer corresponding to the np9a np9b nannofossil subzone boundary the wadi nukhul palaeocene eocene boundary peb is characterized by 1 an abrupt negative excursion in carbonate and organic carbon isotope ratios 6 in 13 c carb and 2 13 c org 2 an abrupt persistent negative shift in organic nitrogen isotope values 15 n org 3 a significant increase in phosphorus concentrations just above the carbon isotope excursion 4 a decrease in carbonate content and significant increase in kaolinite and 5 high vanadium and low manganese contents coincident with the occurrence of framboidal pyrite the abrupt correlative isotopic excursions of 13 c carb 13 c org and 15 n suggest that the lowermost part of the petm is missing the decrease in carbonate content indicates dilution by high detrital input triggered by acid weathering and carbonate dissolution in response to increased atmospheric co 2 resulting from the oxidation of methane the sudden increase in kaolinite content reflects a short lived change to humid conditions the 15 n values close to 0 above the peb suggest a bloom of n 2 fixing cyanobacteria increased bacterial activity may be either the cause or the result of the anoxia locally associated with the petm

a simple multicloud parameterization for convectively coupled tropical waves part ii nonlinear simulations observations in the tropics point to the important role of three cloud types congestus stratiform and deep convective clouds besides ubiquitous shallow boundary layer clouds for both the climatology and large scale organized anomalies such as convectively coupled kelvin waves two day waves and the madden julian oscillation recently the authors have developed a systematic model convective parameterization highlighting the dynamic role of the three cloud types through two baroclinic modes of vertical structure a deep convective heating mode and a second mode with lower troposphere heating and cooling corresponding respectively to congestus and stratiform clouds the model includes both a systematic moisture equation where the lower troposphere moisture increases through detrainment of shallow cumulus clouds evaporation of stratiform rain and moisture convergence and decreases through deep convective precipitation and also a nonlinear switch that favors either deep or congestus convection depending on whether the lower middle troposphere is moist or dry here these model convective parameterizations are applied to a 40 000 km periodic equatorial ring without rotation with a background sea surface temperature sst gradient and realistic radiative cooling mimicking a tropical warm pool both the emerging walker cell climatology and the convectively coupled wave fluctuations are analyzed here while various parameters in the model are varied the model exhibits weak congestus moisture coupled waves outside the warm pool in a turbulent bath that intermittently amplify in the warm pool generating convectively coupled moist gravity wave trains propagating at speeds ranging from 15 to 20 m s 1 over the warm pool while retaining a classical walker cell in the mean climatology the envelope of the deep convective events in these convectively coupled wave trains often exhibits large scale organization with a slower propagation speed of 3 5 m s 1 over the warm pool and adjacent region occasional much rarer intermittent deep convection also occurs outside the warm pool the realistic parameter regimes in the multicloud model are identified as those with linearized growth rates for large scale instabilities roughly in the range of 0 5 k day 1

organization of convection within the madden julian oscillation convection associated with the madden julian oscillation mjo is organized over a broad range of time and space scales within a large scale envelope of activity the large scale envelope of convection is characterized as an eastward propagating disturbance predominantly of zonal wavenumber 2 which is confined over the warmest waters of the indian and western pacific oceans large scale convection is shifted toward the disturbance s temperature anomaly which appears to result from frictional effects in the boundary layer synoptic and mesoscale convective activity is enhanced within the wet phase of the large scale envelope the increase at synoptic scales occurs uniformly over all scales but little difference in the character of the variability is observed between dry and wet phases the enhanced mesoscale activity within the wet phases exhibits a marked tendency to be organized into westward propagating clusters with periods near 2 days and half wavelengths of about 1000 km the role of these modes for the evolution of the mjo is discussed

phase relations of epidote blueschists phase diagrams have been computed for minerals in the system ncmash using the optimised thermodynamic data base of berman 1988 augmented by data on glaucophane and pumpellyite to illustrate the relationships between rocks containing epidote and sodic amphibole and those containing assemblages characteristic of neighbouring metamorphic facies the stoichiometries of stable bounding equilibria yield a simple list of mineral parageneses that serves to define an epidote blueschist facies and surrounding metamorphic facies the calculations suggest that when iron free the pairs zoisite glaucophane and clinozoisite glaucophane do not possess a stability field the natural fe bearing paragenesis of epidote sodic amphibole occupies a closed field in the pt diagram whose size increases dramatically as the ratio fe3 al in the minerals is increased where garnet is involved in bounding reactions such as with respect to eclogite and garnet bearing albite epidote amphibolite the epidote blueschist field decreases in size as the ratio fe2 mg is increased the classic blueschist to greenschist transition reaction is best developed in rocks with large fe3 and fe2 contents and is possibly metastable in mgal rich rocks in the latter a wedge of albite epidote actinolite barroisite amphibolite separates the epidote blueschist from the greenschits paragenesis field a first occurrence of garnet divides the epidote blueschist field into a lower temperature garnet free zone and a higher temperature garnet bearing zone although the temperatures calculated for this garnet isograd seem high the locations of all the facies boundaries are influenced by h2o activity however even minor amounts of co2 in the fluid phase x co2 0 005 render the epidote sodic amphibole paragenesis metastable so that facies boundaries cannot be shifted by varying the co2 content of the fluid phase below 600 c no mutual boundaries exist between the amphibolite facies and the epidote blueschist and eclogite facies respectively the calculated low pressure limit for the eclogite paragenesis pyralspite omphacite jd 50 quartz typical metabasite compositions is 12 to 14 kbars with h2o activity 0 9 or 1 5 to 2 kbar lower for jd 30

roles of barotropic convective momentum transport in the intraseasonal oscillation both observational data analysis and model simulations suggest that convective momentum transport cmt by cumulus convection may play a significant role in the intraseasonal oscillations iso by redistributing atmospheric momentum vertically through fast convective mixing process the authors present a simple theoretical model for the iso by parameterizing the cumulus momentum transport process in which the cmt tends to produce barotropic wind anomalies that will affect the frictional planetary boundary layer pbl in the model with equatorial easterly vertical wind shear vws it is found that the barotropic cmt tends to select most unstable planetary scale waves because cmt suppresses the equatorial ekman pumping of short waves which reduces the shortwave instability from the pbl moisture convergence and accelerates the shortwave propagation the model with subtropical easterly vws has behavior that can be qualitatively different from the model with equatorial easterly vws and has robust northward propagation the basic mechanism of this northward propagation is that the cmt accelerates the barotropic cyclonic wind to the north of iso which will enhance the precipitation by pbl ekman pumping and favor the northward propagation the simulated northward propagation is sensitive to the strength and location of the seasonal mean easterly vws these results suggest that accurate simulation of the climatological mean state is critical for reproducing the realistic iso in general circulation models

a high resolution north sea eocene dinocyst zonation abundant dinoflagellate cysts dinocysts from eocene strata of the north sea exhibit a consistent succession of events based on the analysis of 120 wells from quadrant 3 in the north to quadrants 21 and 22 in the south these events have a constant relationship with stratigraphic sequences and subsequences throughout the area eight eocene dinocyst zones and 23 subzones and the uppermost palaeocene apectodinium augustum biozone are defined by last occurrence or abundance events the north sea dinocyst succession is similar to that in denmark northwest germany belgium the netherlands and southern england permitting correlation with calcareous nannoplankton zones for sections in these areas and hence allowing correlation of north sea stratigraphy with northwest european and worldwide events

what caused the long duration of the paleocene eocene thermal maximum 1 paleorecords show that the paleocene eocene thermal maximum petm 56 ma was associated with a large carbon cycle anomaly and global warming 5 k which persisted for at least 50 kyr conventional carbon cycle climate models that include a single initial carbon input pulse over 10 kyr fail to reproduce the long duration of the petm without invoking additional slow carbon release over more than 50 kyr hereafter referred to as bleeding however a potential carbon source for the bleeding as well as its release mechanism has hitherto remained elusive here i present first principle calculations of heat transfer in marine sediments which demonstrate that a bottom water temperature anomaly as generated during the petm takes tens of thousands of years to penetrate the top few hundred meters of deep sea sediments while the initial temperature rise has been suggested to cause dissociation of the majority of oceanic methane hydrate within 10 kyr my calculations reveal a long tail of hydrate dissociation causing smaller but continued carbon release substantially beyond 10 kyr in addition i suggest that temperature enhanced metabolic processes in marine sediments and the absence of methane hydrate deposition during the petm contributed to prolonged carbon input during the event enhanced fluxes of methane over this time scale would have sustained the carbon isotope excursion and amplified long term greenhouse warming by elevating atmospheric concentrations of steady state ch4 or in oxidized form co2

a transient rise in tropical sea surface temperature during the paleocene eocene thermal maximum the paleocene eocene thermal maximum petm has been attributed to a rapid rise in greenhouse gas levels if so warming should have occurred at all latitudes although amplified toward the poles existing records reveal an increase in high latitude sea surface temperatures ssts 8 to 10 c and in bottom water temperatures 4 to 5 c to date however the character of the tropical sst response during this event remains unconstrained here we address this deficiency by using paired oxygen isotope and minor element magnesium calcium ratios of planktonic foraminifera from a tropical pacific core to estimate changes in sst using mixed layer foraminifera we found that the combined proxies imply a 4 to 5 c rise in pacific sst during the petm these results would necessitate a rise in atmospheric pco 2 to levels three to four times as high as those estimated for the late paleocene

a petrogenetic grid for pelitic schists in the system sio 2 al 2 o 3 feo mgo k 2 o h 2 o a quantitative petrogenetic grid for pelitic schists in the system kfmash that includes the phases garnet chlorite biotite chloritoid cordierite staurolite talc kyanite andalusite sillimanite and pyrophyllite with quartz h2o and muscovite or k feldspar in excess is presented the grid is based on thermodynamic data of berman et al 1985 and berman 1988 for endmember kfash and kmash equilibria and natural fe mg partitioning for the kfmash system calculation of p t slopes and the change in fe fe mg along reactions in the kfmash system were made using the gibbs method in addition the effect on the grid of mno and cao is evaluated quantitatively the resulting grid is consistent with typical buchan and barrovian parageneses at medium to high grades at low grades the grid predicts an extensive stability field for the paragenesis chloritoid biotite which arises because of the unusual facing of the reaction chloritoid biotite quartz h2o garnet chlorite muscovite which proceeds to the right with increasing t in the kfmash system however the reaction proceeds to the left with increasing t in the mnkfash system so the assemblage chloritoid biotite is restricted to bulk compositions with high fe fe mg mn typical metapelites will therefore contain garnet chlorite at low grades rather than chloritoid biotite

40 ar 39 ar mineral age constraints on the paleozoic tectonothermal evolution of high grade basement rocks within the ross orogen central transantarctic mountains the precambrian to early paleozoic orogenic history of the central transantarctic mountains is obscured by uncertainties in the regional extent relative intensities and tectonic significance of three or more events the nimrod beardmore and ross orogenies significant problems exist in correlation of structural styles structural geometry and lithotectonic units across major tectonic boundaries as well as in conflicting geochronological results in an effort to resolve these disparities 40 ar 39 ar ages were determined for hornblende and muscovite from several lithotectonic subunits of the nimrod group exposed in the miller range including amphibolitic gneiss ca 1 7 ga orthogneiss and metasedimentary mica schist these rocks display ductile deformation fabrics that formed prior to intrusion of ca 500 ma post kinematic granitic plutons hornblende concentrates from eight gneiss samples in the miller range display internally discordant 40 ar 39 ar apparent age spectra due to va

environmental change across the paleocene eocene transition from eastern new zealand a marine palynological approach abstract recent improvements in the resolution and calibration of dinoflagellate cyst dinocyst bioevents across the paleocene eocene p e transition in new zealand allow better understanding of the relation between dinocyst variations and environmental change in southern mid high latitudes during this greenhouse climate combining information from land spore pollen assemblages with coeval dinocyst records allows evaluation of plant changes in a marine based timeframe palynological associations at tawanui and moeraki hampden eastern new zealand fluctuate across the p e transition and local palynological phases are recognized the onset of major fluctuations in dinocyst assemblages coincide with the intense warmth and excess carbon of the initial eocene thermal maximum ietm changes in sea surface temperature sst appear to have been the main environmental factor that affected dinoflagellates short lived intervals of higher ssts suggested by a high relative abundance of the apectodinium complex are seen during the ietm and lower eocene abundant cysts of probable heterotrophic dinoflagellates suggest surface waters remained relatively eutrophic for up to 0 5 myr after the onset of the ietm perhaps in response to enhanced terrigenous input related to changes in the character and pattern of continental weathering in contrast to dinocysts spore pollen assemblages suggest plant communities remained rather stable across the p e transition vegetation was dominated by a mesothermal conifer dominated multistratal rainforest and low latitude nypa mangroves were established by the uppermost paleocene plants in this region show no clear response to the ietm and the predominant vegetation change may have occurred at least 1 5 myr later characterized by an increase in mesothermal megathermal angiosperm plants

intraseasonal behavior of clouds temperature and motion in the tropics abstract the spectral character of tropical convection is investigated in an 11 yr record of outgoing longwave radiation from the advanced very high resolution radiometer to identify interaction with the tropical circulation along the equator in the eastern hemisphere the space time spectrum of convection possesses a broad peak at wave numbers 1 3 and eastward periods of 35 95 days significantly broader than the dynamical signal of the madden julian oscillation mjo this quasi discrete convective signal is associated with a large scale anomaly that propagates across and modulates time mean or climatological convection over the equatorial indian ocean and western pacific outside that region the convective signal is small even though under amplified conditions coherence can be found east of the date line and in the subtropics having a zonal scale of approximately wavenumber 2 anomalous convection propagates eastward at some 5 m s 1 and suppresses as well as reinforces climatological convection

the mjo and convectively coupled waves in a coarse resolution gcm with a simple multicloud parameterization abstract the adequate representation of the dominant intraseasonal and synoptic scale variability in the tropics characterized by the madden julian oscillation mjo and convectively coupled waves is still problematic in current operational general circulation models gcms here results are presented using the next generation ncar gcm the high order methods modeling environment homme as a dry dynamical core at a coarse resolution of about 167 km coupled to a simple multicloud parameterization the coupling is performed through a judicious choice of heating vertical profiles for the three cloud types congestus deep and stratiform that characterize organized tropical convection important control parameters that affect the types of waves that emerge are the background vertical gradient of the moisture and the stratiform fraction in the multicloud parameterization which set the strength of large scale moisture convergence and unsaturated downdrafts in the wake of deep convection respectively three

corundum quartz and mg staurolite bearing granulite from the limpopo belt southern africa implications for a p t path abstract a new occurrence of the rare corundum quartz assemblage and magnesian staurolite has been found in a gedrite garnet rock from the central zone of the neoarchean limpopo belt in zimbabwe poikiloblastic garnet in the sample contains numerous inclusions of corundum quartz sillimanite magnesian staurolite sapphirine orthopyroxene and sapphirine sillimanite assemblages as well as monophase inclusions corundum often containing subhedral to rounded quartz occurs as subhedral to euhedral inclusions in the garnet quartz and corundum occur in direct grain contact with no evidence of a reaction texture the textures and fe mg ratios of staurolite inclusions and the host garnet suggest a prograde dehydration reaction of st grt crn qtz h2o to give the corundum quartz assemblage peak conditions of 890 930 c at 9 10 kbar are obtained from orthopyroxene sapphirine and garnet staurolite assemblages a clockwise p t path is inferred with peak conditions being followed by retrograde conditions of 4 6 kbar and 500 570 c the presence of unusually magnesian staurolite mg fe mg 0 47 0 53 and corundum garnet assemblages provides evidence for early high pressure metamorphism in the central zone possibly close to eclogite facies the prograde high pressure event followed by high to ultrahigh temperature metamorphism and rapid uplifting of the limpopo belt could have occurred as a result of neoarchean collisional orogeny involving the zimbabwe and kaapvaal cratons

bolide summer the paleocene eocene thermal maximum as a response to an extraterrestrial trigger the standard paradigm that the paleocene eocene thermal maximum petm represents a threshold event intrinsic to earth s climate and connected in some way with long term warming has influenced interpretations of the geochemical climate and biological perturbations that occurred at this event as recent high resolution data have demonstrated that the onset of the event was geologically instantaneous attempts to account for the event solely through endogenous mechanisms have become increasingly strained the rapid onset of the event indicates that it was triggered by a catastrophic event which we suggest was most likely a bolide impact we discuss features of the petm that require explanation and argue that mechanisms that have previously been proposed either cannot explain all of these features or would require some sort of high energy trigger a bolide impact could provide such a trigger and in the event of a comet impact could contribute directly to the shape of the carbon isotope curve we introduce a carbon cycle model that would explain the petm by global warming following a bolide impact leading to the oxidation of terrestrial organic carbon stores built up during the late paleocene our intention is to encourage other researchers to seriously consider an impact trigger for the petm especially in the absence of plausible alternative mechanisms

planetary scale selection of the madden julian oscillation in an air sea coupled dynamic moisture model the authors present an air sea coupled dynamic moisture asdm model to explore the mechanism of preferred planetary scale of the madden julian oscillation mjo this asdm model extended from the original frictionally coupled dynamic moisture model and a mixed layer model can present a good simulation of planetary scale characteristics of the mjo including a slow eastward propagation of 5 m s 1 coupled rossby kelvin wave like structure and phase leading of convective center by warm sea surface temperature sst it is interesting that the planetary scale selection in terms of instability is only found in the nonlinear asdm model with the assumption of positive only heating such a scale selection however cannot be found in the asdm model with linear heating or in an uncoupled atmosphere model the essential mechanism for the scale selection is nonlinear positive only heating and the air sea interaction primarily provides an instability source to support this scale selection this scale selection is attributed to different phase speeds of coupled moist rossby kelvin waves and dry kelvin waves from short wave initial perturbations the easterly wind anomalies of eastward propagating dry kelvin waves from a stronger wave component will catch up with other weaker moist components and suppress their westerly wind anomalies resulting in weak sst gradient as well as reduced moisture convergence and precipitation for these suppressed components as a result the wavenumber one structure is selected the warm pool like mean state will select the stronger component among the initial short wave perturbations and accelerate this scale selection process these results provide new insight into mjo mechanism in terms of air sea interaction

zonal and vertical structure of the madden julian oscillation abstract a statistical study of the three dimensional structure of the madden julian oscillation mjo is carried out by projecting dynamical fields from reanalysis and radiosonde data onto space time filtered outgoing longwave radiation olr data mjo convection is generally preceded by low level convergence and upward motion in the lower troposphere while subsidence cooling and drying prevail aloft this leads to moistening of the boundary layer and the development of shallow convection followed by a gradual and then more rapid lofting of moisture into the middle troposphere at the onset of deep convection after the passage of the heaviest rainfall a westerly wind burst region is accompanied by stratiform precipitation where lower tropospheric subsidence and drying coincide with continuing upper tropospheric upward motion the evolution of the heating field leads to a temperature structure that favors the growth of the mjo the analysis also reveals distinct differences in the vertical structure

propagation mechanisms for the madden julian oscillation the madden julian oscillation mjo is examined using 20 years of outgoing long wave radiation and national centers for environmental prediction national center for atmospheric research re analysis data two mechanisms for the eastward propagation and regeneration of the convective anomalies are suggested the first is a local mechanism operating over the warm pool region at the phase of the mjo with a dipole structure to the convection anomalies there is enhanced tropical convection over the eastern indian ocean and reduced convection over the western pacific over the equatorial western indian ocean the equatorial rossby wave response to the west of the enhanced convection includes a region of anomalous surface divergence associated with the anomalous surface westerlies and pressure ridge this lends to suppress ascent in the boundary layer and shuts off the deep convection eventually leading to a convective anomaly of the opposite sign over the indonesian sector the equatorial kelvin wave response to the east of the enhanced convection includes a region of anomalous surface convergence into the anomalous equatorial surface easterlies and pressure trough which will tend to favour convection in this region the indonesian sector is also influenced by an equatorial rossby wave response of opposite sign to the west of die reduced convection over the western pacific which also has a region of anomalous surface convergence associated with its anomalous equatorial surface easterlies and pressure trough hence convective anomalies of either sign tend to erode themselves from the west and initiate a convective anomaly of opposite sign via their equatorial rossby wave response and expand to the east via their equatorial kelvin wave response the second mechanism is global involving an anomaly completing a circuit of the equator enhanced convection over the tropical western pacific excites a negative mean sea level pressure m s l p anomaly which radiates rapidly eastward as a dry equatorial kelvin wave at approximately 35 m s 1 over the eastern pacific it is blocked by the orographic barrier of the andes and central america for several days before propagating through the gap at panama after rapidly propagating as a dry equatorial kelvin wave over the atlantic the m s l p anomaly is delayed further by the east african highlands before it reaches the indian ocean and coincides with the development of enhanced convection at the start of the next mjo cycle

basaltic explosive volcanism but no comet impact at the paleocene eocene boundary high resolution chemical and isotopic records from egypt spain and denmark in the search for a triggering mechanism for the paleocene eocene p e boundary event 55 ma centimeter resolution chemical e g ir os pt and isotope e g os o 187 os 188 he 3 he 4 sr 87 sr 86 records across this boundary have been established for six uplifted marine sections in egypt spain and denmark the sections studied represent some of the stratigraphically most complete records across the onset of the carbon isotopic excursion cie and associated benthic foraminifera extinctions that mark the paleocene eocene boundary high sensitivity analyses failed to uncover evidence of extraterrestrial element or isotope enrichments in the six sections refuting the hypothesis of a major comet impact at the boundary preliminary searches for other impact indicative features such as spherules or shocked quartz also gave negative results in the danish section studied three basaltic ir rich ash layers occur at the paleocene eocene boundary but no similar ashes were found in egypt or spain the three ashes represent the earliest known manifestation of an unusual i to 2 million year long phase of explosive basaltic volcanism in the faero greenland region this volcanism is synchronous with major flood basalt effusions in east greenland and is associated with prominent paleogeographic changes in the high latitude north atlantic region discharge of mantle derived os to seawater during this volcanism may explain a small decrease in os o 187 os o 188 ratio at the paleocene eocene boundary in the zumaya section in spain the environmental perturbations at the paleocene eocene boundary appear to have been triggered by basaltic volcanism but any model for the detailed causal relation remains speculative c 2004 elsevier b v all rights reserved less

astronomical calibration of the paleocene time the first complete cyclic sedimentary successions for the early paleogene from drilling multiple holes have been retrieved during two odp expeditions leg 198 shatsky rise nw pacific ocean and leg 208 walvis ridge se atlantic ocean these new records allow us to construct a comprehensive astronomically calibrated stratigraphic framework with an unprecedented accuracy for both the atlantic and the pacific oceans covering the entire paleocene epoch based on the identification of the stable long eccentricity cycle 405 kyr high resolution x ray fluorescence xrf core scanner and non destructive core logging data from sites 1209 through 1211 leg 198 and sites 1262 1267 leg 208 are the basis for such a robust chronostratigraphy former investigated marine odp sites 1001 and 1051 and land based e g zumaia sections have been integrated as well the high fidelity chronology is the prerequisite for deciphering mechanisms in relation to prominent transient climatic events as well as completely new insights into greenhouse climate variability in the early paleogene we demonstrate that the paleocene epoch covers 24 long eccentricity cycles we also show that no definite absolute age datums for the k pg boundary or the paleocene eocene thermal maximum petm can be provided by now because of still existing uncertainties in orbital solutions and radiometric dating however we provide two options for tuning of the paleocene which are only offset by 405 kyr our orbitally calibrated integrated leg 208 magnetostratigraphy is used to revise the geomagnetic polarity time scale gpts for chron c29 to c25 we established a high resolution calcareous nannofossil biostratigraphy for the south atlantic which allows a much more detailed relative scaling of stages with biozones the re evaluation of the south atlantic spreading rate model features higher frequent oscillations in spreading rates for magnetochron c28r c27n and c26n

new chronology for the late paleocene thermal maximum and its environmental implications the late paleocene thermal maximum lptm is associated with a brief but intense interval of global warming and a massive perturbation of the global carbon cycle we have developed a new orbital chronology for ocean drilling program odp site 690 weddell sea southern ocean by using spectral analysis of high resolution geochemical records the lptm interval spans 11 precessional cycles yielding a duration of 210 to 220 k y the 13 c anomaly associated with the lptm has a magnitude of about 2 5 to 3 we show that about 2 of the excursion occurs within two steps that each were less than 1000 yr in duration the remainder developed through a series of steps over 52 k y the timing of these steps is consistent with a series of nearly catastrophic releases of methane from gas hydrates punctuated by intervals of relative equilibria between hydrate dissociation and carbon burial further we are able to correlate the records between odp sites 690 and 1051 western north atlantic on the scale of 21 k y cycles which demonstrates that the details of the 13 c excursion are recognizable between distant sites comparison of cycle records at sites 690 and 1051 suggests that sediment representing the interval 30 k y just prior to and at the onset of the lptm are missing in the latter location this unconformity probably resulted from slope failure accompanying methane hydrate dissociation within 10 k y of the start of the lptm

beyond methane towards a theory for the paleocene eocene thermal maximum abstract extreme global warmth and an abrupt negative carbon isotope excursion during the paleocene eocene thermal maximum petm have been attributed to a massive release of methane hydrate from sediments on the continental slope 1 however the magnitude of the warming 5 to 6 c 2 3 and rise in the depth of the ccd 2 km 4 indicate that the size of the carbon addition was larger than can be accounted for by the methane hydrate hypothesis additional carbon sources associated with methane hydrate release e g pore water venting and turbidite oxidation are also insufficient we find that the oxidation of at least 5000 gt c of organic carbon is the most likely explanation for the observed geochemical and climatic changes during the petm for which there are several potential mechanisms production of thermogenic ch4 and co2 during contact metamorphism associated with the intrusion of a large igneous province into organic rich sediments 5 is capable of supplying large amounts of carbon but is inconsistent with the lack of extensive carbon loss in metamorphosed sediments as well as the abrupt onset and termination of carbon release during the petm a global conflagration of paleocene peatlands 6 highlights a large terrestrial carbon source but massive carbon release by fire seems unlikely as it would require that all peatlands burn at once and then for only 10 to 30 ky in addition this hypothesis requires an order of magnitude increase in the amount of carbon stored in peat the isolation of a large epicontinental seaway by tectonic uplift associated with volcanism or continental collision followed by desiccation and bacterial respiration of the aerated organic matter is another potential mechanism for the rapid release of large amounts of co2 in addition to the oxidation of the underlying marine sediments the desiccation of a major epicontinental seaway would remove a large source of moisture for the continental interior resulting in the desiccation and bacterial oxidation of adjacent terrestrial wetlands

a case for a comet impact trigger for the paleocene eocene thermal maximum and carbon isotope excursion abstract we hypothesize that the rapid onset of the carbon isotope excursion cie at the paleocene eocene boundary 55 ma may have resulted from the accretion of a significant amount of 12c enriched carbon from the impact of a 10 km comet an event that would also trigger greenhouse warming leading to the paleocene eocene thermal maximum and possibly thermal dissociation of seafloor methane hydrate indirect evidence of an impact is the unusual abundance of magnetic nanoparticles in kaolinite rich shelf sediments that closely coincide with the onset and nadir of the cie at three drill sites on the atlantic coastal plain after considering various alternative mechanisms that could have produced the magnetic nanoparticle assemblage and by analogy with the reported detection of iron rich nanophase material at the cretaceous tertiary boundary we suggest that the cie occurrence was derived from an impact plume condensate the sudden increase in kaolinite is thus thought to represent the redeposition on the marine shelf of a rapidly weathered impact ejecta dust blanket published reports of a small but significant iridium anomaly at or close to the paleocene eocene boundary provide supportive evidence for an impact

convection over the pacific warm pool in relation to the atmospheric kelvin rossby wave abstract deep convection over the western tropical pacific warm pool is analyzed in terms of its relation to the atmospheric kelvin rossby wave which dominates the large scale flow during the austral summer the study uses doppler radar data collected by aircraft and ship radars during different time periods in the tropical ocean global atmosphere coupled ocean atmosphere response experiment to characterize the mesoscale circulations of organized convective cloud systems occurring throughout the season the study focuses on convection in two contrasting phases of the wave the westerly onset region just west of the point within the wave where low level easterlies change to westerlies and the strong westerly region or westerly wind burst lying between the large scale counterrotating gyres of the kelvin rossby wave in the westerly onset region the zonal wind component had midlevel easterlies overlying low level westerlies in the strong westerly region a deep layer of westerlies extended from the

convectively coupled equatorial waves 1 convectively coupled equatorial waves ccews control a substantial fraction of tropical rainfall variability their horizontal structures and dispersion characteristics correspond to matsuno s 1966 solutions of the shallow water equations on an equatorial beta plane namely kelvin equatorial rossby mixed rossby gravity and inertio gravity waves because of moist processes the tilted vertical structures of ccews are complex and their scales do not correspond to that expected from the linear theory of dry waves the dynamical structures and cloud morphology of ccews display a large degree of self similarity over a surprisingly wide range of scales with shallow convection at their leading edge followed by deep convection and then stratiform precipitation mirroring that of individual mesoscale convective complexes ccews have broad impacts within the tropics and their simulation in general circulation models is still problematic although progress has been made using simpler models a complete understanding of ccews remains a challenge in tropical meteorology

development characteristics and dynamic structure of tropical intraseasonal convection anomalies abstract the development and dynamical structure of intraseasonal low frequency convection anomalies in the equatorial region are investigated using 10 years 1975 85 of outgoing longwave radiation olr and 7 years 1979 85 of 200 and 850 mb wind data the composite olr anomalies for 36 cases show a four stage development process initiation over equatorial africa rapid intensification when passing through the indian ocean mature evolution characterized by a weakening in the maritime continent and redevelopment over the western pacific and dissipation near the date line in moderate events or emanation from the equator toward north america and southeastern pacific in strong events a noticeable feature in vertical structure is that the 850 mb convergence leads convection and midtropospheric upward motion by about 30 degrees longitude in both developing and mature phases equatorial upper lower level easterly westerly anomalies and associated twin anomalous anticyclonic cyclonic circulation an

crystal chemical evaluation of garnet and omphacite microprobe analyses its bearing on the classification of eclogites abstract the reliability of 920 clinopyroxene and 804 garnet microprobe analyses performed from 1964 through 1984 has been evaluated on the basis of crystal chemical constraints resulting from the latest structural investigations accepted were 343 pyroxenes and 28 garnets which were increased to 444 and 287 respectively after relaxation of some of the initial rigorous constraints so as to meet the number suitable for statistical processing the graphical portray of the accepted data permits the detection of the chemical elements significant in discriminating these eclogite minerals in three groups related to the geological settings of the enclosing rocks and therefore to their p t conditions of formation and to their small variations in bulk chemistry the best discriminant plots were found to be the ca mg na al vi na fe 3 triangle for clinopyroxenes essentially the di jd acm triangle and the ca mg fe 2 triangle for garnets essentially the gross pyr alm triangle their updated versions are reported in addition the data suggest that the p t regime acting during subduction metamorphism was remarkably constant in space and in time they hint for a future possible division of common regional metamorphic eclogites into three isofacial groups provided that the statistics will be increased and additional geological information becomes available finally they point out that the peculiar crystal chemistry of the minerals in kimberlite xenoliths may require reconsideration of the constraints inferred from crustal occurrences

release of methane from a volcanic basin as a mechanism for initial eocene global warming a 200 000 yr interval of extreme global warming marked the start of the eocene epoch about 55 million years ago negative carbon and oxygen isotope excursions in marine and terrestrial sediments show that this event was linked to a massive and rapid approximately 10 000 yr input of isotopically depleted carbon it has been suggested previously that extensive melting of gas hydrates buried in marine sediments may represent the carbon source and has caused the global climate change large scale hydrate melting however requires a hitherto unknown triggering mechanism here we present evidence for the presence of thousands of hydrothermal vent complexes identified on seismic reflection profiles from the voring and more basins in the norwegian sea we propose that intrusion of voluminous mantle derived melts in carbon rich sedimentary strata in the northeast atlantic may have caused an explosive release of methane transported to the ocean or atmosphere through the vent complexes close to the palaeocene eocene boundary similar volcanic and metamorphic processes may explain climate events associated with other large igneous provinces such as the siberian traps approximately 250 million years ago and the karoo igneous province approximately 183 million years ago