the meridional temperature gradient in the eastern north atlantic during mis 11 and its link to the ocean atmosphere system temporal and spatial patterns in eastern north atlantic sea surface temperatures sst were reconstructed for marine isotope stage mis 11c using a submeridional transect of five sediment cores the sst reconstructions are based on planktic foraminiferal abundances and alkenone indices and are supported by benthic and planktic stable isotope measurements as well as by ice rafted debris content in polar and middle latitudes additionally the larger scale dynamics of the precipitation regime over northern africa and the western mediterranean region was evaluated from iron concentrations in marine sediments off nw africa and planktic 13c in combination with analysis of planktic foraminiferal abundances down to the species level in the mediterranean sea compared to the modern situation it is revealed that during entire mis 11c sensu stricto ss i e between 420 and 398 ka according to our age models a cold sst anomaly in the nordic seas co existed with a warm sst anomaly in the middle latitudes and the subtropics resulting in steeper meridional sst gradients than during the holocene such a sst pattern correlates well with a prevalence of a negative mode of the modern north atlantic oscillation we suggest that our scenario might partly explain the longer duration of wet conditions in the northern africa during mis 11c compared to the holocene

intraseasonal modulation of south american summer precipitation intraseasonal variation of convection over south america is examined using singular spectrum analysis ssa the dipole convection pattern with centers of action over the sacz and the subtropical plains is modulated by modes of different timescales both oscillatory modes with periods of 36 40 days mode 40 and 22 28 days mode 22 influence convection over the sacz with the faster mode mode 22 leading the variability over the subtropical plains mode 40 is related to the madden julian oscillation outgoing longwave radiation anomalies olra propagate eastward from the western pacific to the central pacific with a period of 40 48 days the 200 hpa streamfunction composites show a wavenumber 1 structure in the tropics and a wave train propagating downstream from the convective area in the tropical pacific the development of the dipole pattern is also contributed by mode 22 which features the meridional propagation of olra over south america from midlatitudes to the tropics the streamfunction composites for mode 22 show a wave train extending from the central pacific eastward to about 608s and curving toward the northeast over south america when the sacz is enhanced these two modes become meridionally aligned locally such episodes are characterized by a wave train propagating northeastward from southern south america toward the tropics composites based on the ssa decomposition indicate that the dominant periods of variability 22 and 40 days cancel out over the pacific region and reinforce each other over the sacz for times close to onset of the enhanced sacz episodes

ageostrophic geopotential fluxes in downstream and upstream development of baroclinic waves abstract with the use of a simple primitive equation model it is demonstrated that the convergence divergence of ageostrophic geopotential fluxes can be a major source sink of kinetic energy for both downstream and upstream development of baroclinic waves and can play a dominant role during the early stages of wave development it is also shown that both surface friction and effects lead to an asymmetry in the upstream versus downstream development with downstream development much stronger a total group velocity is defined based on ageostrophic fluxes and its relationship to the rate of wave packet spreading and to convective and absolute instability is discussed

spatial heterogeneities in a bioclastic shoal outcrop reservoir analogue architectural cyclical and diagenetic controls on lateral pore distribution abstract the distribution of pores in carbonate rocks is controlled by the synergy of different factors such as the initial sediment environment processes and diagenesis prediction of the texture related pore distribution to evaluate reservoir quality is still a challenging task in geothermal and hydrocarbon exploration in order to degrease these uncertainties 3d facies models are produced on the basis of facies types and their relationship to petrophysical properties however several studies have shown that these relationships are often rather controlled by diagenesis that is often described as a sequence for an entire reservoir two outcrops as part of the same bioclastic shoal reservoir analogue present two different architectural styles i layer cake architecture and ii high angle foreset architecture in order to identify petrophysical trends and related controlling factors both outcrops were mapped and studied in detail based on the investigation of 41 thin sections microfacies types were defined and diagenesis was analysed in addition permeability porosity was measured and pores were digitally characterized although both outcrop successions studied are associated with the same reservoir interval varied architecture leads to fundamental differences in the porosity permeability distribution petrophysical trends in the layer cake architecture are mainly controlled by cyclicity and channel features compared to layer cake architecture trends in the high angle foreset architecture are dominantly controlled by the depositional environment both outcrops show differences in their diagenesis while layer cake architecture suffered the entire sequence large parts of the high angle foreset architecture were not influenced by late burial and telogenetic processes as a consequence primary porosity is persevered within the high angle foreset architecture in addition results of this investigation indicate that primary porosity has a bigger influence on good permeability values compared to telogenetic associated vug enhancement this investigation therefore demonstrates that individual carbonate reservoirs can suffer different diagenetic pathways moreover the study highlights the potential of outcrop studies to improve the principal understanding of fundamental trends within potential subsurface reservoirs

sea surface water variability during the mid brunhes inferred from calcareous plankton in the western mediterranean odp site 975 abstract planktonic foraminifera and calcareous nannoplankton were analyzed in core ocean drilling program site 975 located in the western mediterranean in order to study their response to environmental changes across the mid brunhes interval and specifically through marine isotope stage mis 15 and 8 ca 650 230 ka multivariate analysis of assemblage composition revealed that the calcareous plankton dynamics were mainly driven by surface water temperatures both on glacial interglacial and stadial interstadial time scales throughout the studied interval foraminiferal and nannoplankton assemblages responded to environmental forcing in concert except during mis 15 when multiple environmental factors appear to have been superimposed on the otherwise dominating effect of temperature variability sea surface temperature sst has been estimated from planktonic foraminiferal assemblages using the artificial neural networks method pointing out relevant seasonal variations through the record our reconstructions reveal that calcareous plankton assemblages also responded to other environmental factors than temperature including modification in surface water stratification nutrient availability and detrital input specifically a more stable stratified water column seems to have accompanied the interval through mis 15 13 on the other hand across the mid brunhes interval from mis 12 onwards the enhanced glacial strength affected both planktonic foraminifera and calcareous nannofossils planktonic foraminifera indicate that mixed and productive surface waters developed during glacials and stadials accompanied by episodes of increased detrital input as suggested by calcareous nannoplankton assemblages enhanced food availability was likely driven by wind induced upwelling and or by continental coastal input during dry conditions persisting in the mediterranean region and over north africa finally spectral and wavelet analyses of calcareous plankton time series allowed to identify the pattern of periodic response of the plankton at milankovitch cycles and in some cases at millennial variability the dominant 100 kyr periodicity recorded in surface water temperature proxies clearly reflects a major response of the planktonic community to the global glacial interglacial climate pattern high frequency variation 5 8 11 13 ky of surface water temperature proxies and of selected taxa abundance highlights the occurrence of millennial scale instability superimposed on the paleoenvironmental modifications occurring through the mid brunhes interval climate transition this framework accounts for the occurrence of different surface water dynamics across the mid brunhes interval and is in favor of the hypothesis that the millennial scale surface water temperature variations are modulated by the harmonics of the precession forcing

revision of the early middle pleistocene calcareous nannofossil biochronology 1 75 0 85 ma the extant nannofossil biostratigraphic and biochronologic framework for the early middle pleistocene time interval has been tested through the micropaleontological analysis of globally distributed high quality low to mid latitude deep sea successions the quantitative temporal distribution patterns of relative abundances of selected taxa were reconstructed in critical intervals and the following biohorizons were defined first occurrence of medium sized gephyrocapsa spp last occurrence of calcidiscus macintyrei first occurrence of large gephyrocapsa spp last occurrence of large gephyrocapsa spp first occurrence of reticulofenestra asanoi re entrance of medium sized gephyrocapsa spp and last occurrence of reticulofenestra asanoi the detailed patterns of abundance change at these biohorizons were used to generate a detailed biostratigraphy and the biostratigraphic data were transformed into a precise biochronology by means of correlation to isotope stratigraphies and astronomical timescales the degree of isochrony or diachrony of the biohorizons was evaluated biohorizons and are isochronous occurring close to marine isotope stages mis 55 and mis 22 respectively and and are slightly diachronous on the order of 30 40 kyr whereas biohorizons and are confirmed as diachronous on the order of 100 80 and 60 kyr respectively some of the events are clearly controlled by environmental conditions e g the last occurrence of r asanoi related to significant environmental changes associated with the first large amplitude glaciation of the late quaternary mis 22

reactivated basement structures affecting the sedimentary facies in a tectonically quiescent epicontinental basin an example from nw switzerland abstract the jurassic deposits in the southern part of central europe accumulated in a shallow epicontinental sea and their deposition has usually been believed to have corresponded to a phase of tectonic quiescence neither on conventional seismic records nor in outcrops obvious indications of synsedimentary tectonics were found nonetheless subtle variations in lithofacies and thickness occur above faults in the crystalline basement in fact preexisting structures became reactivated in the jurassic during major extensional phases when the tethys and the north atlantic opened this reactivation led to differential subsidence and or to rotation of fault bounded blocks but the sediments were deformed mainly flexurally as vertical movements in the basement were dissipated by triassic salt thus the depositional area was morphologically differentiated into swells and depressions in siliciclastic muddy environments swells were characterized by hardbottoms and hiatus beds depressions were filled by distal tempestites and gravity deposits in carbonate settings reefs nucleated on swells marls and muds were deposited in depressions many of them gravity deposits reactivation of faults occurred only during short episodes and was not synchronous throughout the study area and reactivation of individual faults was episodic and probably controlled by the palaeostress field and the faults orientation reactivation of deep rooted faults is also documented by hydrothermal activity which led to vein mineralization and alteration of minerals today exposed in nearby basement units the chronostratigraphic ages of the hydrothermal processes coincide with phases of enhanced subsidence during the sinemurian aalenian bajocian bathonian and oxfordian in turn facies changes of the sedimentary cover should be useful to predict basement structures when no seismic records are available

sea surface temperatures did not control the first occurrence of hudson strait heinrich events during mis 16 1 hudson strait hs heinrich events ice rafting events in the north atlantic originating from the laurentide ice sheet lis are among the most dramatic examples of millennial scale climate variability and have a large influence on global climate however it is debated as to whether the occurrence of hs heinrich events in the eastern north atlantic in the geological record depends on greater ice discharge or simply from the longer survival of icebergs in cold waters using sediments from integrated ocean drilling program iodp site u1313 in the north atlantic spanning the period between 960 and 320 ka we show that sea surface temperatures ssts did not control the first occurrence of hs heinrich like events in the sedimentary record using mineralogy and organic geochemistry to determine the characteristics of ice rafting debris ird we detect the first hs heinrich like event in our record around 643 ka marine isotope stage mis 16 which is similar as previously reported for site u1308 however the accompanying high resolution alkenone based sst record demonstrates that the first hs heinrich like event did not coincide with low ssts thus the hs heinrich like events do indicate enhanced ice discharge from the lis at the end of the mid pleistocene transition not simply the survivability of icebergs due to cold conditions in the north atlantic

influence of the intraseasonal variability on heat waves in subtropical south america the influence of the intraseasonal variability on heat wave development over subtropical south america during austral summer is analyzed the role of the south atlantic convergence zone sacz on this development is documented results show that intraseasonal variability can explain on average at least 32 of summer temperature variance moreover 73 of the heat waves in subtropical south america develop in association with an active sacz the analysis of pentad maps shows that warm conditions in the region under study develop in association with the strengthening of an anticyclonic anomaly which is discernible over the subtropical regions at least 15 days before temperature peak occurrence that circulation anomaly is embedded in a large scale rossby wave train extending along the south pacific ocean that is linked to convection anomalies at the equatorial western and central pacific ocean in addition the development of the anticyclonic circulation over subtropical south america appears to be strengthened by the subsidence conditions promoted by the active sacz which result in temperature rise in the subtropical region under relatively dry conditions on the other hand during the last 2 days of evolution sacz activity weakens and the progressive temperature rise in the region is dominated by warmer and moister air being anomalously advected from the north results confirm the important role that sacz activity on intraseasonal time scales has in inducing persistent circulation anomalies at the subtropical regions that can result in the development of persistent heat waves and very extreme daily temperature

triassic climates state of the art and perspectives abstract the climate of the triassic period was characterized by a non zonal pattern dictated by a strong global monsoon system with effects that are most evident in the tethys realm this strong monsoonal regime is related to the aggregation of the pangaean supercontinent which by triassic time was already completed climate oscillations existed within this framework the harsh hot house climatic conditions that characterized the late permian and perhaps precipitated the end permian mass extinction were probably maintained during the early triassic and may account for the impoverished but distinctive faunal and floral lower triassic associations although metazoan reef builders were probably the most affected group carbonate production remained high at least in the western tethys realm the middle triassic was characterized locally by humid episodes although their geographical distribution has yet to be clarified the carnian pluvial event marks an episode of increased rainfall documented worldwide was the most distinctive climate change within the triassic different hypotheses have been proposed for its causes changes of atmospheric or ocean circulation driven by plate tectonics a peak of the global monsoon due to maximum continent aggregation or triggering by the eruption of a large igneous province subsequently the late carnian and norian seem to have been climatically stable although minor climatic changes have recently been described even from this time period finally the end triassic extinction event is also associated with climate change specifically warming and increased rainfall but this evidence comes mostly from the northern parts of the central atlantic magmatic province and the global pattern of climate change at the triassic jurassic boundary has still to be resolved many facets of triassic climate are intriguing and deserve further research however palaeoclimate studies on the triassic have so far been carried out only locally with different proxies those proxies will require inter calibration in order to depict correctly the temporal and geographical patterns of triassic climate

large amplitude short scale stationary rossby waves in the southern hemisphere observations and mechanistic experiments to determine their origin abstract studies by van loon and jenne van loon et al trenberth and others indicate that stationary waves in the southern hemisphere are dominated by planetary scales kalnay and halem reported the presence of large amplitude short scale stationary waves during the month of january 1979 in the lee of south america and their disappearance in february 1979 in this paper we present further observational evidence of the january waves we also perform two 15 day forecast experiments with the glas fourth order general circulation model and initial conditions corresponding to 5 january and 4 february 1979 these factors reproduce reasonably well the presence of the january waves and their absence in february several mechanistic experiments to determine the origin of the waves are then performed the principal conclusions are a large amplitude stationary rossby waves with zonal wavenumber 7 were present between 20 and 40 s both in the south pacific and east of south america during january 1979 they app

summer precipitation variability over south america on long and short intraseasonal timescales a dipole pattern in convection between the south atlantic convergence zone and the subtropical plains of southeastern south america characterizes summer intraseasonal variability over the region the dipole pattern presents two main bands of temporal variability with periods between 10 and 30 days and 30 and 90 days each influenced by different large scale dynamical forcings the dipole activity on the 30 90 day band is related to an eastward traveling wavenumber 1 structure in both olr and circulation anomalies in the tropics similar to that associated with the madden julian oscillation the dipole is also related to a teleconnection pattern extended along the south pacific between australia and south america conversely the dipole activity on the 10 30 day band does not seem to be associated with tropical convection anomalies the corresponding circulation anomalies exhibit in the extratropics the structure of rossby like wave trains although their sources are not completely clear

plankton biochronology for the last 772 000 years from the western south atlantic ocean abstract calcareous microfossils have potential in the biostratigraphy of pleistocene sediments and a clear relationship with paleoceanographic studies conversely there are few quantitative biostratigraphic studies of chronologically tuned events or sections in the western south atlantic in order to improve the stratigraphical framework for south atlantic paleoceanographic studies the present work attempts to review the last 772 000 years by carrying out a quantitative analysis of the calcareous nannofossil and planktonic foraminiferal assemblages by comparing them with a high resolution marine isotopic record 18 o this work is based on the analysis of two piston cores obtained from the continental slope of the santos basin in the santos drift southeastern brazilian continental margin twelve pleistocene calcareous nannofossil events and twenty planktonic foraminifera events calibrated with oxygen isotopes and correlated with literature stratigraphies are discussed this is the first calcareous plankton biochronology study for the last 772 kyr in the western south atlantic ocean more studies in this region will help to establish a more precise biochronology for these calcareous microfossils this study also presents six new biostratigraphic events of isotopically caibrated planktonic foraminifera which can be used as markers in the western south atlantic

integrated sequence stratigraphy facies stable isotope and palynofacies analysis in a deeper epicontinental carbonate ramp late jurassic sw germany abstract sequence stratigraphy in deeper water epicontinental carbonates such as in the upper jurassic of southern germany is difficult because the recognition of parasequences sequences and sequence boundaries is impeded by the paucity in diagnostic sedimentological criteria or stratal surfaces using the genetic stratigraphic approach and integrating facies stable isotope c o and palynofacies analysis two types of genetic depositional sequences can be discriminated small scale sequences are stacked into medium scale sequences which may record a 400 kyr milankovitch signal the medium scale sequences were correlated regionally using both gamma ray logs and stable isotope records regional correlations show that the depocentres are controlled by underlying palaeotectonic elements late palaeozoic troughs the rise fall turnarounds of medium scale sequences are marked by negative 18o peaks temperature maxima and reduced absolute palynoclast contents the fall rise turnarounds are marked by positive 18o peaks temperature minima and high absolute palynoclast contents the initiation and termination of sponge microbial mounds show characteristic patterns thrombolitic microbialites form during intervals of 1 reduced input of terrestrial palynomorphs interpreted as an increase in distality 2 decreasing 13c trends interpreted to be related to decreasing nutrient supply and 3 decreasing 18o values interpreted as phases of warming and rising relative sea level in contrast thrombolitic stromatolitic microbialites were found to occur during phases of 1 increasing input of terrestrial palynomorphs interpreted as an increase in proximality 2 increasing 13c values interpreted to reflect increasing terrestrial input and nutrient supply as well as increasing 18o values interpreted as phases of cooling and relative sea level falls isotopic and palynofacies evidence suggests that bioherms were terminated by sudden input of nutrients during relative sea level falls sedimentological criteria were clearly not sufficient to delineate a robust sequence stratigraphic framework

triassic monsoonal climate and its signature in ladinian carnian carbonate platforms southern alps italy abstract paleoclimatic general circulation models suggest the existence of a monsoonal climate during the permo triassic over wide parts of the megacontinent pangea and its adjacent oceans this paper discusses how ladinian carnian sedimentary successions outcropping in the southern alps record the signature of this climate sedimentological associations of tepees capped by terra rossa paleokarst braided fluvial sediments capped by caliche soils and evaporite beds alternating with clay rich delta deposits all indicate that net precipitation values changed substantially over short geological time scales early diagenetic features including episodes of dissolution in stratigraphies of meteoric calcite cements corrosion and hematitization of siliciclastic detritus prior to deposition early eu edral tectosilicate cementation and dolomitization from evaporation concentrated seawater record frequently changing paleohydrological conditions sedimentological and early diagenetic data recording highly variable seemingly conflicting paleoclimate information can best be attributed to fluctuations in net precipitation intensities controlled by monsoonal climate ranging from seasons to 106 yr d18o values in early meteoric cements 5 2 to 6 4 reflect the presence of strongly depleted meteoric waters which are not compatible with the southern alps paleolatitude or paleotopography in the triassic and can be directly related to precipitation intensities associated with a monsoonal climate strong precipitation could have also resulted in decreased surface water salinities and depleted d18o in surface waters d18o time series from marine rocks and early meteoric cements indicate a trend from middle triassic values generally deplet d with respect to the expected marine signature to less depleted late triassic values this is interpreted to represent an unusually wet episode high net precipitation transitionally grading in the late triassic into a relatively add period or low net precipitation despite the fact that several factors controlled the intensity of monsoonal precipitation the effects of its variations through time are evident at different time scales in the middle and upper triassic record of the southern alps

geological interpretation of dekorp 2 s a deep seismic reflection profile across the saxothuringian and possible implications for the late variscan structural evolution of central europe abstract a 250 km long deep seismic section the first of its kind in west germany s dekorp project is interpreted in terms of late variscan collisional tectonics the structural model used is based on the intracontinental thrust tectonics concept of modern collision orogens the crustal profile across the saxothuringian zone seems to indicate north facing ramps antiformal stacks and culminations within the crystalline basement of the internal mid european variscides that have been only partially overprinted by permo mesozoic crustal stretching

a review of calcareous nannofossil astrobiochronology encompassing the past 25 million years this paper presents a review of astrobiochronological calibration of recent to late oligocene calcareous nannofossil datum events biohorizons included in the paper are those of the widely used standard nannofossil zonations of martini e 1971 standard tertiary and quaternary calcareous nannoplankton zonation in farinacci a ed proceedings of the second international conference on planktonic microfossils roma rome ed tecnosci vol 2 pp 739 785 and okada h and bukry d 1980 supplementary modification and introduction of code numbers to the low latitude coccolith biostratigraphy zonation bukry 1973 1975 marine micropaleontology 51 321 325 as well as supplementary biohorizons proposed in the literature the biohorizons have been selected on the basis of the unambiguous taxonomy of the index taxa and their biostratigraphic usefulness we emphasise the application of rigorous methodology in nannofossil studies which permits an evaluation of biohorizons in terms of reliability and calibrates their potential correlatability astrochronological age estimates rely on the geologic timescale developed by the ics in 2004 with some new calibrations included we provide an overview of the relative position of biohorizons versus the astronomically calibrated ages of magnetic reversals and reference isotope stratigraphies surprisingly there are still few high resolution quantitative biostratigraphic studies of astrochronologically tuned sections in spite of the central role of such studies in addressing fundamental problems such as the tempo and mode of plankton evolution

subseasonal variations of rainfall in south america in the vicinity of the low level jet east of the andes and comparison to those in the south atlantic convergence zone abstract regional and large scale circulation anomalies associated with variations in rainfall downstream of the south american low level jet are identified and compared to those in the south atlantic convergence zone sacz composites of precipitation associated with strong jets reveal an approximate doubling of the quantities one would expect from climatology with an evolution of the rainfall pattern from south to north the occurrence of extreme precipitation events follows a similar pattern meridional cross sections of composite wind reveal a distinct low level jet near 20 s and a baroclinic development farther south that appears to force the jet geopotential height temperature and large scale wind composites suggest that this developing disturbance is tied to a wave train that originates in the midlatitude pacific and turns equatorward as it crosses the andes mountains similar composites based on sacz rainfall reveal similar features but of opposite sign suggesting that the phase of the wave

dolomite and dolomitization of the permian khuff c reservoir in ghawar field saudi arabia abstract the permian khuff c reservoir in saudi arabia is known for its lateral and vertical heterogeneity caused mainly by dolomitization detailed petrographic analysis of 600 thin sections from six cored wells revealed three main replacive dolomite fabrics 1 fabric preserving mimetic fpm 2 fabric preserving nonmimetic fpnm and 3 fabric destructive fd dolomites crystal sizes are mostly less than or equal to 20 m for fpm dolomite less than or equal to 50 m for fpnm dolomite and less than or equal to 100 m for fd dolomite the fpm dolomite decreases in abundance and fpnm dolomite increases in abundance with increasing grain content of the facies the 18 o values of dolostones although considered an obsolete term dolostone is used here to mean rock containing 80 dolomite indicate early dolomitization at low temperatures in permian seawater or evaporated seawater with landward facies mudstone and wackestone generally dolomitized by more evaporated waters and seaward grainy facies generally dolomitized by less evaporated more normal marine seawaters stratigraphic variations in the dolostones 18 o values track with facies variations through fourth order depositional sequences and indicate that different stratigraphic bodies of dolomite formed from seawaters with different degrees of evaporation the 13 c values of the dolostones exhibit temporal trends inherited from the precursor limestones variations in the lateral and vertical abundance of dolomite and dolomite fabrics in the propensity for each facies to be dolomitized and in the dolomites oxygen isotopic values all suggest that multiple dolomitization events occurred in the khuff c reservoir as depositional cycles accumulated with some dolostones overprinted by younger events average porosities of grain rich dolostones are greater than those of mud rich dolostones indicating that depositional facies preordained porosity distribution within the dolostones however the more evaporated the dolomitizing fluid the more likely dolomitization resulted in lower porosity regardless of facies

calcareous nannofossil bioevents and environmental control on temporal and spatial patterns at the early middle pleistocene quantitative distributions of calcareous nannofossils are analysed in the early middle pleistocene at the small gephyrocapsa and pseudoemiliania lacunosa zone transition in deep sea cores from the mediterranean sea and north atlantic ocean ocean drilling program odp sites 977 964 and 967 deep sea drilling project dsdp site 607 the temporal and spatial mode of occurrence of medium sized gephyrocapsids and reticulofenestrids has been examined to refine biostratigraphic constraints and evaluate possible relationships of stratigraphic patterns to environmental changes during a period of global climatic deterioration the timing of bioevents has been calibrated using high resolution sampling and correlation to the y 18 o record in chronologically well constrained sections newly identified events and ecostratigraphical signals enhance the stratigraphic resolution at the early middle pleistocene the first occurrence fo of intermediate morphotypes between pseudoemiliania and reticulofenestra reticulofenestra sp is proposed as a reliable event within marine isotope stage mis 35 or at the mis 35 34 transition the distribution of reticulofenestra asanoi is characterized by rare and scattered occurrences in its lowest range but the first common occurrence fco is consistently identified at mis 32 or 32 31 the last common occurrence lco of the species is a distinctive event at mis 23 in the studied interval gephyrocapsa omega dominates among medium sized gephyrocapsa the fo of g omega and contemporaneous re entry of medium sized gephyrocapsids at the lower middle pleistocene transition are diachronous between the atlantic ocean and mediterranean sea and from the western to eastern mediterranean in the mediterranean the lo of g omega falls at mis 15 insolation cycle 54 and is isochronous among the sites abundance fluctuations of g omega show notable relations to early middle pleistocene climate changes they considerably increase in abundance at the interglacial stages suggesting warm water preferences gephyrocapsa omega temporarily disappears during the glacial mis 22 and mis 20 above mis 20 an impoverishment in g omega and in the total abundance of medium sized gephyrocapsids occurs a decrease in abundance of g omega is observed between the western site 977 and the easternmost site 967 in the mediterranean sea as a possible response to high salinity and or low nutrient content possible environmental influences on the distribution of r asanoi and of reticulofenestra sp are discussed d 2004 elsevier b v all rights reserved

the paleogeography of paleozoic and mesozoic storm depositional systems present day hurricane belts are confined to 5 45 latitude along the western edges of oceans whereas winter storms occur ubiquitously above 25 latitude both hurricanes and winter storms occur between 25 and 45 latitude in some areas storm zones can be identified on global paleogeographic maps with the assumption that this latitudinal zonation of storm systems existed in the geological past evaluation of 69 previously recognized paleozoic and mesozoic storm depositional systems on such maps showed that only 70 of them occur in ancient hurricane mixed hurricane and winter storm and winter storm belts the remainder occur on the western sides of continents and or at low paleolatitudes and therefore well may be of different origin mesozoic storm depositional systems containing hummocky stratification tend to occur in counterpart paleo winter storm belts whereas hummocky stratification in suggested paleozoic examples occur in both winter storm and hurricane belts and in paleolatitudes where we in

quantitative analysis of quaternary nannoplankton in the subtropical northwestern pacific ocean abstract time progressive changes of nannoflora and biometry of coccoliths for the last 1 3 m y were investigated for a piston core recovered from the west mariana ridge the species compositions were quantitatively investigated under an electron microscope and six assemblages assemblages a through f were identified significant changes in relative abundances of various types of genus gephyrocapsa are the main cause for the stratigraphic change of the flora a dominant occurrence of gephyrocapsa protohuxleyi var a which can be identified only under an electron microscope was observed for the first time in a thin sequence which corresponds to the lowest part of the brunhes epoch 0 75 0 62 ma because of this characteristic occurrence assemblage d was further subdivided into three subassemblages the dominant occurrence of small gephyrocapsa which is well known in the small gephyrocapsa zone of the equatorial pacific ocean was not observed but the almost complete absence of medium to large gephyrocapsa during approximately 200k years of the middle pleistocene was confirmed a stratigraphically restricted occurrence of a large form of reticulogenestra was also confirmed by the biostratigraphic study under a light microscope and the last and first occurrences of the largest form reticulofenestra sp a 6 5 m were identified at 0 81 and 0 98 ma respectively in addition to these four events precise ages for another five well known evolutionary events were also calibrated these ages are generally in good agreement with previously reported ages from other world oceans and diachronism was not evident for most of these evolutionary events

climate of the supercontinent pangea numerous climate models predict that the geography of the supercontinent pangea was conducive to the establishment of a megamonsoonal circulation in general geologic evidence supports the hypothesis of a megamonsoon that reached maximum strength in the triassic pangea in the late carboniferous had widespread peat formation in what is now central and eastern north america and europe and relatively dry conditions on the colorado plateau the equatorial region of the continent became drier through the end of the carboniferous by the permian the equatorial region of pangea was dry and indicators of aridity and rainfall seasonality became more widespread wind directions from colorado plateau eolian sandstones are consistent with an increasing influence of monsoonal circulation at this time in the triassic climate in the colorado plateau region became relatively wet though still seasonal and the few eolian sandstones indicate a major shift in wind direction at that time in addition sedimentation

reactive transport modeling of brine reflux dolomitization anhydrite precipitation and porosity evolution abstract both geothermal convection and brine reflux drive circulation of sea water derived fluids through carbonate platforms during early burial but dynamic interactions between heat and solute transport and resulting diagenesis are at present poorly understood this paper describes high resolution reactive transport model rtm simulations that suggest that reflux of 85 ppt brines rapidly restricts geothermal convection to the platform margin with flow focused in the more permeable shallow carbonates in a baseline simulation involving an elongate 25 km wide grain dominated packstone platform brine reflux resulted in complete dolomitization beneath the 5 km wide brine pool in 335 ky the dolomite body then extends downward at c 22 m 100 ky into an underlying broad area of partial dolomitization this process enhances porosity at shallow depth but beneath the dolomite body precipitation of anhydrite occludes porosity and limits the depth of reflux in contrast geothermal convection at the platform margin forms a smaller partially dolomitized body over a longer time 60 dolomite after 1 my with very minor associated anhydrite cementation reflux diagenesis is sensitive to platform geometry with higher rates of fluid flow increasing the depth of alteration beneath the brine pool for a circular platform compared to the linear baseline fluid flow across thermal gradients enhances reaction rates and ignoring heat transport by 85 ppt brine reflux underestimates the extent of reflux dolomite by 25 and associated anhydrite by 90 the depth and rate of anhydritization is sensitive to the geothermal heat flux whereas platform top temperatures affect dolomitization rate reflux diagenesis is also sensitive to brine density which affects both fluid flow and reaction rates sediment permeability and reactive surface area rsa are key intrinsic controls on diagenesis where the permeability structure permits sufficient fluid flow diagenesis preferentially affects more reactive fine grained sediments however as flow rates decline reactions become focused in the more permeable but less reactive sediments simulations thus shed light on why in some settings reflux preferentially dolomitizes muddy sediments but elsewhere favors grainstones once active reflux ceases brines continue to flow in the subsurface but this latent reflux causes only minor dolomitization due to prior mg2 consumption at shallow depth

variability of surface water characteristics and heinrich like events in the pleistocene midlatitude north atlantic ocean biomarker and xrd records from iodp site u1313 mis 16 9 1 a reconstruction of milankovitch to millennial scale variability of sea surface temperature sst and sea surface productivity in the pleistocene midlatitude north atlantic ocean marine isotope stage mis 16 9 and its relationship to ice sheet instability was carried out on sediments from integrated ocean drilling program iodp site u1313 this reconstruction is based on alkenone and n alkane concentrations u37k index total organic carbon toc and carbonate contents x ray diffraction data magnetic susceptibility and accumulation rates increased input of ice rafted debris occurred during mis 16 12 and 10 characterized by high concentrations of dolomite quartz and feldspars and elevated accumulation rates of terrigenous matter minimum input values of terrigenous matter on the other hand were determined for mis 13 and 11 peak values of dolomite coinciding with quartz plagioclase and kalifeldspar peaks and maxima in long chain n alkanes indicative for land plants are interpreted as heinrich like events related to sudden instability of the laurentide ice sheet during early and late deglacial phases of the glacials the coincidence of increased toc values with elevated absolute concentrations of alkenones suggests increased glacial productivity probably due to a more southern position of the polar front alkenone based sst reached absolute maxima of about 19 c during mis 11 3 and absolute minima of 10 c during mis 12 and 10 within mis 11 prominent cooling events mis 11 22 and 11 24 occurred the absolute sst minima recorded directly before and after the glacial maxima mis 10 2 and 12 2 are related to heinrich like event meltwater pulses as supported by the coincidence of sst minima and maxima in c37 4 alkenones and dolomite these sudden meltwater pulses especially during terminations iv and v probably caused a collapse of phytoplankton productivity as indicated by the distinct drop in alkenone concentrations ice sheet disintegration and subsequent surges and outbursts of icebergs and meltwater discharge may have been triggered by increased insolation in the northern high latitudes

δ13c and δ18o values of triassic brachiopods and carbonate rocks as proxies for coeval seawater and palaeotemperature abstract a dataset of 160 isotope 13c and 18o values from anisian ladinian carnian and rhaetian articulate brachiopod shells complemented by 158 carbon and oxygen isotope values from whole rock carbonates define the first continuous stable isotope baseline trends for the triassic seawater the carbon isotope data suggest the existence of several short term high amplitude excursions in the early triassic followed by a predominance of values around 0 5 1 during the middle triassic a rise to 3 5 during the carnian plateau at this level during the late carnian to early norian and a 1 5 decline in the middle norian to values around 2 during the late norian rhaetian interval the causation scenarios for these rapid oscillations are at present equivocal but may in part reflect a biological instability of the carbon cycle following the recovery from the end permian extinction event and or an input of mantle derived co2 from enhanced volcanic activity the 18o values from well preserved brachiopods from the tethyan realm range from 3 9 to 0 6 v pdb these values require open marine triassic seawater 18o values close to 0 v smow for the calculated temperatures to be within the range of tolerance of the coexisting reef building corals a 2 18o increase within the uppermost cordevolian and early julian suggests either a distinct temperature decline in the southern alps during that time interval an increase in seawater salinity or their combination oxygen isotope values for the muschelkalk brachiopods range between 6 2 and 2 0 and likely reflect a strong influx of meteoric waters into the germanic basin that shifted the oxygen isotopes to more negative values

a middle pleistocene northeast atlantic coccolithophore record paleoclimatology and paleoproductivity aspects abstract changes in paleoclimate and paleoproductivity patterns have been identified by analysing in conjunction with other available proxy data the coccolithophore assemblages from core md03 2699 located in the portuguese margin in the time interval from the marine isotope stage mis 13 14 boundary to mis 9 535 to 300 ka during the mid brunhes event the assemblages associated with the eccentricity minima are characterised by higher nannoplankton accumulation rate nar values and by the blooming of the opportunistic genus gephyrocapsa changes in coccolithophore abundance are also related to glacial interglacial cycles higher nar and numbers of coccoliths g mainly occurred during the interglacial periods while these values decreased during the glacial periods superimposed on the glacial interglacial cycles climatic and paleoceanographic variability has been observed on precessional timescales the structure of the assemblages highlights the prevailing long term influence of the portugal pc and iberian poleward ipc currents following half and full precession harmonics related to the migration of the azores high ah pressure system small gephyrocapsa and coccolithus pelagicus braarudii are regarded as good indicators for periods of prevailing pc influence gephyrocapsa caribbeanica syracosphaera spp rhabdosphaera spp and umbilicosphaera sibogae denote periods of ipc influence our data also highlights the increased percentages of coccolithus pelagicus pelagicus during the occurrence of episodes of very cold and low salinity surface water probably related to abrupt climatic events and millennial scale oscillations of the ah icelandic low il system

ocean climate variability in the eastern north atlantic during interglacial marine isotope stage 11 a partial analogue to the holocene similar orbital geometry and greenhouse gas concentrations during marine isotope stage 11 mis 11 and the holocene make stage 11 perhaps the best geological analogue period for the natural development of the present interglacial climate results of a detailed study of core md01 2443 from the iberian margin suggest that sea surface conditions during stage 11 were not significantly different from those observed during the elapsed portion of the holocene peak interglacial conditions during stage 11 lasted nearly 18 kyr indicating a holocene unperturbed by human activity might last an additional 6 7 kyr a comparison of sea surface temperatures sst derived from planktonic foraminifera for all interglacial intervals of the last million years reveals that warm temperatures during peak interglacials mis 1 5e and 11 were higher on the iberian margin than during substage 7e and most of 9e the sst results are supported by heavier delta 18 o values particularly during 7e indicating colder ssts and a larger residual ice volume benthic delta 13 c results provide evidence of a strong influence of north atlantic deep water at greater depths than present during mis 11 the progressive ocean climate deterioration into the following glaciation is associated with an increase in local upwelling intensity interspersed by periodic cold episodes due to ice rafting events occurring in the north atlantic

calcareous nannofossil changes during the mid pleistocene revolution paleoecologic and paleoceanographic evidence from north atlantic site 980 981 abstract new quantitative data on calcareous nannofossil assemblages through 583 1138 thousand years ago kyr have been acquired in high sample resolution 2 3 ky at northern atlantic odp ocean drilling program site 980 981 assemblage composition reflects a temperate paleobioprovince suggesting significant influx of warm north atlantic current at the site location during the mid pleistocene transition between marine isotope stage mis 35 and 15 three intervals have been described based on changes in nannofossil composition and abundance fluctuations of taxa reticulofenestrids are abundant just in the first interval mis 35 22 which is also characterised by the absence of gephyrocapsa 4 m and c pelagicus s l the latter occurring in upper mis 24 only the second interval corresponds to the expanded warm mis 21 that is accompanied by high carbonate content absence of both nannofossil reworking and ice rafted debris ird higher abundance of c leptoporus 5 8 m and h carteri and absence of c pelagicus s l and medium gephyrocapsids the third interval mis 20 15 records the occurrence of c pelagicus s l and medium gephyrocapsa generally higher abundance and higher amplitude fluctuations of helicoliths and absence of reticulofenestrids the major changes in nannofossil assemblages seem to be the result of combined paleoenvironmental factors related to sea surface water features temperature and nutrient availability sea ice cover and possibly to deep and intermediate water production of both northern and southern hemisphere origin during glacial and interglacial phases complex inter relationships between environmental parameters and evolutionary ecological factors are inferred to explain the patterns of coccolithus pelagicus subspecies whose distribution and abundance fluctuations are compared with the available patterns of turborotalia quinqueloba and neogloboquadrina pachyderma left coiled at site 980 and with the c pelagicus subspecies patterns from north atlantic dsdp deep sea drilling project site 607 and south atlantic odp site 1090 data collected provide additional information on stratigraphic distribution of selected taxa the first occurrence fo of gephyrocapsa omega is confirmed as a diachronous event even in the atlantic ocean while the first and last common occurrence fco lco of r asanoi appear as diachronous and synchronous events respectively on a global scale

subpolar high anomaly preconditioning precipitation over south america abstract the mechanisms associated with the intraseasonal variability of precipitation over south america during the spring season are investigated with emphasis on the influence of a quasi stationary anomalous circulation over the southeastern south pacific ocean sep a spectral analysis performed to the bandpass filtered time series of daily precipitation anomalies for the la plata basin lpb and the south atlantic convergence zone sacz regions revealed several statistically relevant peaks corresponding to periods of roughly 23 days and 14 16 days with the lower higher frequency peaks more prevalent for the sacz lpb the large scale circulation patterns preconditioning precipitation variability over both regions were explored by means of a regression analysis performed on the daily 500 hpa geopotential anomaly field provided by the ncep ncar reanalysis dataset the most prominent feature of the regression fields is the presence of a quasi stationary anomalous anticyclonic cyclonic circulation

calcareous nannofossil changes in response to the spreading of the south china sea basin during eocene oligocene abstract numerous models have been proposed to constrain the process of the south china sea formation yet the paleogene paleoenvironmental researches are hindered by the paucity of long continuous well dated geological records in this work eocene to oligocene nannofossil biostratigraphy and assemblage changes in a sediment section from the northern south china sea were studied to shed light on these issues we established an age model to confine the studied section between 40 and 22 ma based on 17 calcareous nannofossil datum levels the age model enabled to date the most prominent seismic reflector t60 centered at 26 8 ma a regional tectonic event interpreted as corresponding to the ridge jump event in the early phase of south china sea spreading changes in nannofossil abundance and assemblage compositions imply continuous transgression and deepening of water depth from the late eocene to early miocene during the late eocene the studied area was a neritic sea with relatively eutrophic conditions supporting abundant r lockeri group and c pelagicus from 34 ma to 27 ma during the oligocene the earlier neritic environment was replaced by relative warm and oligotrophic conditions in a shallow sea as indicated by higher concentration of c floridanus sphenolithus spp and helicosphaera spp since 26 ma pelagic conditions prevailed small reticulofenestra

influence of subtle paleo tectonics on facies and reservoir distribution in epeiric carbonates integrating stratigraphic analysis and modelling u muschelkalk sw germany abstract the middle triassic upper muschelkalk carbonate ramp deposits in sw germany provide an excellent laboratory scale analogue for vast epeiric basin fills such as in the middle east the upper muschelkalk and the entire mesozoic overburden in sw germany were deposited on a complex mosaic of three major differentially subsiding variscan paleo tectonic blocks the rhenohercynian saxothuringian and moldanubian subtly influencing the depositional facies pattern for long periods of time this study is based on detailed sedimentological logs of 41 boreholes and surface outcrop sections and 39 gamma ray logs lithofacies analysis and a 1 d and 2 d sequence stratigraphic analysis leading to a regional correlation integrating sequence architecture and marker beds using the subsurface 3d modelling tool petrel two nested geocellular reservoir models were generated i a basin scale 201 5 325 km lithofacies associations lfa model based on truncated gaussian simulation tgs ii a field scale 50 50 km lithofacies types lft model based on sequential indicator simulation sis the integrated 3d facies models reveal landward facies retrogradation with patchy isolated shoal bodies during the transgressive hemisequence and basinward facies progradation with well connected large shoals within the regressive hemisequence models combined with structural maps show the influence of large variscan block segments and smaller scale internal structural elements on the distribution and the size of reservoir analogues both shoal and dolomite bodies this relationship offers a new tool for exploration in epeiric carbonates using deep seated paleo tectonic patterns for the prediction of both hydrocarbon and geothermal reservoirs

southern ocean pleistocene calcareous nannofossil events calibration with isotope and geomagnetic stratigraphies abstract several cores recovered from the northern belt of the southern ocean were analysed to study the pleistocene calcareous nannofossil records calcareous nannofossil events previously described in medium and low latitudes were identified and calibrated with the oxygen isotope and geomagnetic time scales although sedimentation rates hiatuses and degree of calcareous nannofossil preservation sometimes prevent the identification and or accurate calibration of some of these events a useful stratigraphic framework was obtained the possibility of using these calibrated events from high to low latitudes facilitates correlations and should facilitate isotope event identification in a region with low temperature where calcareous plankton stratigraphies are in general restricted in general pleistocene southern high latitude calcareous nannofossil events show synchronism with those observed in warm and temperate surficial waters small discrepancies in the assigned ages are sometimes related to low sampling resolution due to low sedimentation rates the first occurrence fo of emiliania huxleyi and the last occurrence lo of pseudoemiliania lacunosa are observed in marine isotope stages mis 8 and 12 respectively a reversal in abundance between gephyrocapsa muellerae and e huxleyi is observed close to the mis 4 5 boundary mis 6 is characterised by an increase in g muellerae and mis 7 features a dramatic decrease in the proportion of gephyrocapsa caribbeanica this latter species began to increase its proportions from the mis 13 14 boundary to mis13 showing diachronism between the different sites the lo of reticulofenestra asanoi is observed at mis 22 confirming this event as a global synchronous reference datum by contrast the fo of r asanoi occurs at mis 35 and is diachronous with the existing data from other oceanic regions a re entry of medium sized gephyrocapsa 3 5 m maximum diameters can be identified in some cores close to mis 25 although the low abundance of this taxon prevents an accurate calibration it may be concluded that this event is diachronous as compared with the existing low latitude data the lo of large morphotypes of gephyrocapsa is well correlated with mis 37 showing synchronism with other oceanic regions whereas the fo of this species is not well calibrated due to the absence of age control points

calcareous plankton and the mid brunhes climate variability in the alboran sea odp site 977 abstract quantitative calcareous plankton analyses have been performed at the ocean drilling program site 977 in the alboran sea through the mid brunhes interval 300 540 ka the results evidence orbital suborbital and millennial scale climate variability which primary reflects temperature change the patterns of increase decrease of coccolithophore and planktonic foraminifera warm water taxa reproduce the stage and substage climate variability in the planktonic 18o in good agreement with other planktonic isotope records from mediterranean sea and atlantic ocean variable conditions characterized by alternating cool nutrient rich or warm and stable sea surface waters occurred during interglacial marine isotope stage mis 13 in response to high amplitude oscillations of insolation during obliquity maximum and to north africa monsoon strength influencing distribution of taxa mis 13a resulted warmer than mis 13c based on the higher abundances of warm water taxa they increase just after insolation maxima suggesting a primary response of calcareous plankton to precessional orbital control following short term warm mis 11e and more humid mis 11d phases a climate optimum lasting about 16 kyr is recognized during mis 11c when major tropical subtropical water arrival into the alboran sea occurred as evidenced by the presence of trilobatus sacculifer mis 11c records unstable climate condition that persisted up to the late mis 11 indicating multiple pulses of southward migrations of subpolar front following the full interglacial mis 11c warm and oligotrophic conditions occurred during mis 9 as during mis 11 especially in mis 9e although without a climate optimum reduced abundance of warm water taxa and decrease of globorotalia inflata highlight colder surface water conditions and decreased atlantic mediterranean water exchange during glacials especially during the prominent sea level low stand of mis 12 short term prominent peaks of the polar subpolar neogloboquadrina pachyderma and coccolithus pelagicus ssp pelagicus and additional key taxa preferring fresher and turbid water together with minima in total nannofossil accumulation rate and enhanced coccolith reworking sustain a correlation with the north atlantic heinrich type ht events ht1 ht1a ht3 ht4 6 thus documenting the sensitiveness of the alboran sea in recording european and laurentide ice sheet dynamics the comparable chronology of most of these cold spells in the available balearic and ionian calcareous plankton records highlights that atlantic melt water entering alboran basin through gibraltar strait may have reached the central mediterranean preserving some of its original polar signature

a dynamic explanation for the origin of the western mediterranean organic rich layers the eastern mediterranean sapropels are among the most intensively investigated phenomena in the paleoceanographic record but relatively little has been written regarding the origin of the equivalent of the sapropels in the western mediterranean the organic rich layers orls orls are recognized as sediment layers containing enhanced total organic carbon that extend throughout the deep basins of the western mediterranean and are associated with enhanced total barium concentration and a reduced diversity dysoxic but not anoxic benthic foraminiferal assemblage consequently it has been suggested that orls represent periods of enhanced productivity coupled with reduced deep ventilation presumably related to increased continental runoff in close analogy to the sapropels we demonstrate that despite their superficial similarity the timing of the deposition of the most recent orl in the alboran sea is different than that of the approximately coincident sapropel indicating that there are important differences between their modes of formation we go on to demonstrate through physical arguments that a likely explanation for the origin of the alboran orls lies in the response of the western mediterranean basin to a strong reduction in surface water density and a shoaling of the interface between intermediate and deep water during the deglacial period furthermore we provide evidence that deep convection had already slowed by the time of heinrich event 1 and explore this event as a potential agent for preconditioning deep convection collapse important differences between heinrich like and deglacial like influences are highlighted giving new insights into the response of the western mediterranean system to external forcing

outcrop analog for an oolitic carbonate ramp reservoir a scale dependent geologic modeling approach based on stratigraphic hierarchy considerable effort has been devoted to the development of simulation algorithms for facies modeling whereas a discussion of how to combine those techniques has not existed the integration of multiple geologic data into a three dimensional model which requires the combination of simulation techniques is yet a current challenge for reservoir modeling this article presents a thought process that guides the acquisition and modeling of geologic data at various scales our work is based on outcrop data collected from a jurassic carbonate ramp located in the high atlas mountain range of morocco the study window is 1 km 0 6 mi wide and 100 m 328 1 ft thick we describe and model the spatial and hierarchical arrangement of carbonate bodies spanning from largest to smallest 1 stacking pattern of high frequency depositional sequences 2 facies association and 3 lithofacies five sequence boundaries were modeled using differential global position system mapping and light detection and ranging data the surface based model shows a low angle profile with modest paleotopographic relief at the inner to middle ramp transition facies associations were populated using truncated gaussian simulation to preserve ordered trends between the inner middle and outer ramps at the lithofacies scale field observations and statistical analysis show a mosaiclike distribution that was simulated using a fully stochastic approach with sequential indicator simulation this study observes that the use of one single simulation technique is unlikely to correctly model the natural patterns and variability of carbonate rocks the selection and implementation of different techniques customized for each level of the stratigraphic hierarchy will provide the essential computing flexibility to model carbonate settings this study demonstrates that a scale dependent modeling approach should be a common procedure when building subsurface and outcrop models

reconstruction of surface water dynamics in the north atlantic during the mid pleistocene 540 400 ka as inferred from coccolithophores and planktonic foraminifera abstract changes in paleoclimate and paleoproductivity patterns have been identified by analyzing the coccolithophore assemblages from the iodp site u1314 located in the subpolar north atlantic together with other proxy data available during the time interval from the marine isotope stages mis 14 to mis 11 ca 540 to 400 ka the comparison of this data with that of md03 2699 located off the iberian margin allowed us to study their common response to environmental changes in terms of paleoproductivity and temperature variability statistical analyses of the composition of coccolithophore assemblages revealed that the calcareous plankton dynamics were mainly driven by eccentricity which controlled the alternating migration of the polar front pf and the north atlantic current nac at glacial interglacial timescales the high frequency variability of paleoproductivity over imposed onto glacial interglacial variability at both sites were related to nac intensifications on a precessional timescale the northward southward migration of the pf caused a strengthening weakening of the nac which created an intensification weakening of the irminger current ic at site u1314 and the portugal current pc at md03 2699 furthermore low latitude processes have been shown to influence climate in the high latitude during the late pleistocene during mis 14 and 12 enhanced glacial strength affected both coccolithophores and planktonic foraminifera indicating a southward movement of the nac using the same proxies a northward movement of the nac is recorded during mis 13 and 11 alternatively the spectral analyses performed on calcareous plankton assemblages allowed the identification of a pattern of periodic response of the plankton at the orbital and in some cases millennial level as well as abrupt heinrich type time scale variability during termination v tv this was the most extreme event and was related to a massive iceberg discharge from high to mid latitudes

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

african monsoons an immediate climate response to orbital insolation the croll milankovitch astronomical theory of climate1 3 has received strong support from the evidence of a linear climatic forcing by obliquity and precession although nonlinearity had to be assumed for eccentricity4 5 moreover interglacials have appeared to be controlled by the orbital insolation6 although a phase shift of 6 000 5 000 yr is seen between an astronomical climate index and terrestrial climate indicators dominated by the northern ice sheet dynamics climate proxy data of low latitudes are less directly dependent on the ice sheets here it is shown that during the past 464 000 yr african monsoons signalled by the east mediterranean sapropels were heaviest always and only when a northern summer monsoon index computed from the orbital variation of insolation reached maximum values this occurred during all the interglacials but also twice during glacial periods thus tropical aridity is not the single climatic pattern of glacial periods an immediate terrestrial climate response to orbital variations of insolation is established

outcrop constrained hydrogeological simulations of brine reflux and early dolomitization of the permian san andres formation our hydrogeologic model tests the effectiveness of brine reflux as the mechanism for early dolomitization of the permian san andres formation brine circulation is constrained by sequence stratigraphic parameters and a heterogeneous distribution of petrophysical properties based on outcrop data the model simulates accumulation of the san andres platform and calculates fluid flow and solute transport in response to relative sea level fluctuations it tracks porosity loss caused by compaction and the concomitant permeability feedback the amount of dolomite potentially formed is calculated by means of a magnesium mass balance between brine and rock results show that 1 brine reflux is an effective mechanism to deliver magnesium to dolomitize large carbonate successions 2 relative sea level controlled transient boundary conditions result in intricate flow and salinity patterns that can generate irregular dolomite bodies with complex spatial distributions 3 pervasive dolomitization can result from several short lived reflux events by the amalgamation of brine plumes sourced in different locations and times and 4 the model successfully recreates the dolostone and limestone patterns observed in san andres outcrops

changes in calcareous nannofossil assemblages during the mid pleistocene revolution the distribution of calcareous nannofossils are quantitatively analysed in high resolution deep sea core samples from north atlantic dsdp site 607 and eastern mediterranean odp site 967 between marine oxygen isotope stage mis 35 and 15 in order to observe the response of calcareous nannofossils to the mid pleistocene revolution mpr nannofossil abundance patterns show major variations through mis 25 22 and distinct higher amplitude changes from mis 21 upward sometime clearly correlatable to glacial interglacial cycles high amplitude short term fluctuations of small placoliths and f profunda characterize the interval through mis 24 to 22 21 suggesting strong instability in nutricline dynamics and surface water productivity principal component analysis and shannon weaver indices diversity and dominance highlight significant shifts mainly related to variations in the characteristics of surface waters in both sites a minimum in diversity is recorded at mis 22 21 corresponding to a maximum in the dominance of reticulofenestra spp at site 607 and of pseudoemiliania lacunosa at site 967 above mis 21 the increase in abundance of various taxa c leptoporus umbilicosphaera spp syracosphaera spp rhabdosphaera spp oolithotus spp and a general increase in diversity are related to a distinct trend toward more stable and oligotrophic surface waters in contrast to the higher productivity and less stratified surface waters of the early pleistocene in addition power spectral analysis was performed on calcareous nannofossil abundances shannon index diversity values and factor 1 of principal component analysis these show significant peaks in the obliquity 41 kyr and eccentricity 100 kyr frequency bands indicating that the quasi periodic oscillations in the climate proxy data are controlled by these orbital parameters a relationship between changes in abundance of calcareous nannofossils and production of glacial north atlantic deep water is inferred

multiple scale facies and reservoir quality variations within a dolomite body outcrop analog study from the middle triassic sw german basin abstract this study focuses on a porous dolomite body in the proximal part of an epeiric carbonate ramp triassic muschelkalk south german basin analogous to hydrocarbon bearing dolomite reservoirs in the middle east e g khuff and arab formations the dolomite body is made up of shoal lagoonal and peritidal facies types and is built by a three fold hierarchy of cycles 3rd order to 5th order the best reservoir quality occurs in finely crystalline lagoonal dolo mudstones mean k 37 8 md 20 2 with micro intercrystalline and vuggy porosity coarsely crystalline shoal related dolo grainstones show variable reservoir potential mean k 30 1 md 4 4 due to late diagenetic modification reservoir quality significantly decreases in the non dolomitized foreshoal section mean k 4 5 md 3 6 stratigraphically the most porous dolomite occurs in the upper regressive portion of the 3rd order cycle reservoir quality progressively decreases towards the limy bottom of the section outcrop mapping showed high lateral continuity for the distribution of facies types and poroperm values on the scale of several 10s of meters within correlated 5th order cycles considerable facies and poroperm heterogeneity is already observed on the 100s of meters scale on a 1000s of meters scale the facies and lithology distribution is controlled by the geometry of a gently inclined carbonate ramp during regression a progradational pattern is recognized marked by a basinward migration of backshoal facies and a down dip decrease of dolomite body thickness lithology facies and poroperm data from outcrops and cores were used for 3d modeling with the software petrel the modeled variations in the poroperm distribution are consistent with the degree of heterogeneity expected for a combination of laterally persistent lithology and highly variable facies results of this study may help to better understand the reservoir heterogeneity of inner ramp dolomite bodies and can be applied to improve characterization and modeling of similar dolomite reservoirs

three dimensional facies modeling of carbonate sand bodies outcrop analog study in an epicontinental basin triassic southwest germany this article is the first part of an integrated study to characterize the anatomy and geometries of carbonate shoal reservoir bodies in epicontinental settings it is based on outcrop analog data from triassic layer cake carbonates in the south german basin which were deposited along an epicontinental very gently inclined carbonate ramp the database of this study consists of 56 measured sections supplemented by six shallow cores and wireline logs covering an area of 25 by 36 km 15 by 22 mi the potential reservoir bodies consist generally of midramp shoal and shoal fringe facies types which are composed of skeletal and oolitic carbonate packstones and grainstones with significant amounts of porosity the upper muschelkalk is composed of a lower transgressive and an upper regressive interval within these shoal bodies show not only similarities but also major differences in character geometry and distribution these reflect the conditions of an epeiric system which reacts strongly to small changes in accommodation the accommodation seems to be mainly triggered by the interaction of hierarchically organized large medium and small scale relative sea level changes and a subtle paleorelief at the level of medium scale cycles distinct two dimensional cyclicity styles can be differentiated which record the lateral facies distribution along the depositional gradient different styles of medium scale cycles include different types of shoal bodies 1 transgressive crinoidal shoal style shoal bodies mean width 21 km 13 mi mean length 37 km 23 mi mean thickness 4 2 m 13 7 ft with low facies differentiation deposited on top of subtle paleohighs 2 skeletal sheets style thin reservoir sheets mean width 5 1 km 3 1 mi mean length 11 1 km 6 8 mi mean thickness 0 3 m 0 9 ft of reservoir facies on top of the paleohighs 3 regressive oolitic shoal style shoal bodies mean width 14 6 km 9 0 mi mean length 20 8 km 12 9 mi mean thickness 0 69 m 2 2 ft with high facies differentiation on the flanks of paleohighs and 4 low accommodation style patchy and mosaic distribution of shoal bodies mean width 11 2 km 6 9 mi mean length 26 km 16 mi mean thickness 0 69 m 2 2 ft all data were loaded into three dimensional 3 d modeling software to distribute 14 facies types and model the 3 d stratigraphic architecture the resulting facies distribution implies that volume and dimensions of the shoal bodies are mainly controlled by the combination of stratigraphic cycles and a subtle paleorelief which is indicated by overall thickness changes of succession high energy shoal facies types occur only in and around areas with a reduced overall thickness whereas areas with a thicker development are dominated by low energy muddy facies types all observations combined point to the presence of a subtle paleorelief which could be induced by slight differential subsidence of inherited paleotectonic basement blocks on the kilometer to regional scale previous studies suggest simple layer cake stratal patterns however in the full 3 d view the apparent layer cake stratigraphy turned out to be a pseudolayer cake with very gentle 0 01 0 001 dip clinoform geometries these very subtle offlapping pinch out geometries may have been overlooked in epeiric reservoir systems elsewhere

middle triassic shallow water limestones from the upper muschelkalk of eastern france the origin and depositional environment of some early mesozoic fine grained limestones abstract we have analyzed the sedimentary structures depositional geometries and petrography of a middle triassic fine grained limestone succession from the upper muschelkalk in the intracratonic germanic basin the limestones occur in a unit several metres thick that extends over an area of at least 2500 km2 in eastern france the geometry of specific wave ripples and small channels filled by lateral accretion bedded limestones and the cyclic sedimentation of the upper muschelkalk in eastern france indicate deposition on a very shallow subtidal shelf commonly under the influence of relatively strong currents the limestones mostly consist of microspar with a few skeletal grains the formation of current ripples in the fine grained limestones appear to be incompatible with an originally muddy grain size the major part of the microsparite may thus have originated from the recrystallization of silt size carbonate grains e g calcispheres or peloids

sequence stratigraphy of middle triassic carbonates and terrigenous deposits muschelkalk and lower keuper in the sw germanic basin maximum flooding versus maximum depth in intracratonic basins abstract we analyze the sequence stratigraphy of the middle muschelkalk to the lower keuper strata middle triassic in the sw germanic basin the sequences are interpreted on the basis of a synthesis of facies in the neritic carbonates terrigenous sediments and evaporites along a basin margin to center transect continental sediments cs lower middle muschelkalk occur at the base of the middle upper muschelkalk sequence thick retrogradational marginal marine sediments overlain by open marine deposits middle middle muschelkalk to lower upper muschelkalk form the transgressive systems tract in the basin center only bathymetric criteria are available for recognition of this systems tract the maximum flooding surface mfs at the basin margin differs in age from the maximum depth interval in the basin center maximum depth surfaces or intervals mdi new term should be recognized in many deep basins where flooding is not recorded the highstand systems tract upper upper muschelkalk is strongly progradational the upper sequence boundary muschelkalk keuper boundary is characterized by subaerial exposure at the basin margin and submarine erosion in most other sections along this boundary the low paleo relief resulted in a lack of coarse grained clastic deposits in the basin center a strongly regressive succession lower lower keuper allows possibly for the first time in an intracratonic basin the distinction of an early or late lowstand systems tract elst or llst high frequency low amplitude sea level fluctuations resulted in parasequences in the open marine upper muschelkalk but in high frequency sequences in the coastal plain sediments of the overlying parts of the lower keuper

coccolithophores as proxy of seawater changes at orbital to millennial scale during middle pleistocene marine isotope stages 14 9 in north atlantic core md01 2446 quantitative coccolithophore analyses were performed in core md01 2446 located in the midlatitude north atlantic to reconstruct climatically induced sea surface water conditions throughout marine isotope stages mis 14 9 the data are compared to new and available paleoenvironmental proxies from the same site as well as other nearby north atlantic records that support the coccolithophore signature at glacial interglacial to millennial climate scale total coccolithophore absolute abundance increases during interglacials but abruptly drops during the colder glacial phases and deglaciations coccolithophore warm water taxa wwt indicate that mis11c and mis9e experienced warmer and more stable conditions throughout the whole photic zone compared to mis13 mis11 was a long lasting warmer and stable interglacial characterized by a climate optimum during mis11c when a more prominent influence of the subtropical front at the site is inferred the wwt pattern also suggests distinct interstadial and stadial events lasting about 4 10 kyr the glacial increases of gephyrocapsa margereli g muellerae 3 4 m along with higher values of corg additionally supported by the total alkenone abundance at site u1313 indicate more productive surface waters likely reflecting the migration of the polar front into the midlatitude north atlantic distinctive peaks of g margereli muellerae 4 m c pelagicus pelagicus neogloboquadrina pachyderma left coiling and reworked nannofossils combined with minima in total nannofossil accumulation rate are tracers of heinrich type events during mis12 and mis10 additional heinrich type events are suggested during mis12 and mis14 based on biotic proxies and we discuss possible iceberg sources at these times our results improve the understanding of mid brunhes paleoclimate and the impact on phytoplankton diversity in the midlatitude north atlantic region

pangaean climates megamonsoons of the megacontinent the climate for a highly idealized geographic representation of the megacontinent of pangaea corresponding to the period 250 200 m y ago is explored using a low resolution atmospheric general circulation model that is coupled to a static mixed layer ocean of constant depth with a provision for sea ice formation and decay soil moisture is included as a predicted variable on the continent because there are large uncertainties about key factors that might influence the pangaean climate sensitivity experiments are used to examine the climate for two different mean elevations 0 and 1000 m two different snowcover prescriptions and two different levels of implied greenhouse heating and solar luminosity modern co2 concentration and modern solar luminosity fivefold increase in modern co2 concentration and a 1 decrease in modern solar luminosity in all of the experiments the large bipolar land masses of laurasia and gondwanaland joined near the equator in the west and separated by the tethys sea in the east exhibit extreme continentality with hot summers cold winters and large scale summer and winter monsoon circulations year round or seasonal aridity is simulated for all but the eastern coastal regions the tropical western coast and the regions poleward of 40 latitude the simulated climate of the idealized pangaean continent has many features that correspond qualitatively with geologic evidence for tropical warmth and aridity in the late permian and triassic however the model results serve mainly to indicate the importance of various climate forming factors geography topography heating detailed comparisons will require new experiments with better models and more accurate geologic boundary conditions

transient behavior of the meridional moisture transport across south america and its relation to atmospheric circulation patterns the transient behavior of meridional moisture transport across the south american continent is examined with the reanalysis data provided by the european centre for medium range weather forecasts ecmwf the results show clearly the effects of the valley between the andes and the brazilian plateau in canalizing the southward moisture transport an intense jet is episodically formed in this valley the synoptic variability of this low level jet and its relation to the large scale atmospheric circulation are studied

paleoenvironmental conditions at core kc01b ionian sea through mis 13 9 evidence from calcareous nannofossil assemblages quantitative analyses on calcareous nannofossil assemblages on high temporal resolution 600e800 years have been carried out from core kc01b in the ionian sea eastern mediterranean throughout marine isotope stage mis 13e9 between 500 and 300 ka this is an interval of considerable climate changes known as the mid brunhes event which includes mis 11 considered as a possible analogue for future interglacial conditions in the mediterranean core the interval is characterized by the dominance of gephyrocapsaspp as also known fromocean records calcareous nannofossil abundance fluctuations have been interpreted in terms of modification of sea surface primary productivity water stratification and temperature specifically the increase in abundance of gephyrocapsa caribbeanica and small gephyrocapsa coupled with decreases of florisphaera profunda syracosphaera spp and rhabdosphaera spp suggests enhanced primary productivity mixed surface waters during interglacial stages and at the terminations which can be interpreted in terms of interaction between climate changes and mesoscale oceanographic circulation on the other hand distributions of calciosolenia spp oolithotus spp and umbilicosphaera sibogae which are inphase with d 18 o curve showing higher abundances at the lighter values of the marine

the ups and downs of tectonic quiescence recognizing differential subsidence in the epicontinental sea of the oxfordian in the swiss jura mountains abstract recent studies in northern switzerland have shown that epicontinental areas thought to have been tectonically stable during the mesozoic were not necessarily as rigid as presumed by comparing oxfordian facies boundaries and depocenters in their palinspastic position with known faults in the basement a direct relationship between the two can be demonstrated previously the lack of obvious synsedimentary tectonic features has lulled scientists into believing that the realm of the swiss jura was tectonically stable during the mesozoic however it can be shown that facies and sedimentary structures are largely influenced by tectonics subsurface data provide evidence for the presence of paleozoic troughs in the basement which apparently were prone to reactivation during the pan european stress field reorganization taking place in the late jurassic this led to differential subsidence along pre existing lineaments within the study area which can be recognized in the distribution of oxfordian epicontinental basins and their coeval shallow water counterparts eustatic sea level fluctuations played an important role in the development of shallow water facies patterns but a subordinate role in the control of accommodation space in basins while tectonic activity is often recorded in the sedimentary record in the form of platform break ups and associated sedimentary debris more subtle indicators may be overlooked or even misinterpreted sedimentary structures and isopach maps as well as subsurface data in the study area suggest that subtle synsedimentary tectonic movements led to the formation of two shallow diachronous epicontinental basins during the late jurassic it becomes possible to recognize and differentiate the combined effects of local and regional tectonism eustasy and sedimentation

early diagenesis driven by widespread meteoric infiltration of a central european carbonate ramp a reinterpretation of the upper muschelkalk abstract meteoric diagenesis of carbonate ramps is often difficult to interpret and can commonly be confused with other coinciding diagenetic processes the middle triassic upper muschelkalk of switzerland provides an insightful case in which the effects of several overprinting diagenetic environments including matrix dolomitization can be clearly unravelled previous studies suggested that diagenesis took place in connate marine waters with later meteoric waters being invoked to explain recrystallization of dolomite in this study diagenetic analyses c o stable isotope ratios thin section point counting cathodoluminescence and uv fluorescence microscopy of calcitic bioclastic samples have revealed that early diagenesis pre stylolitization and the accompanying porosity evolution did not occur exclusively in the presence of marine fluids five sequential stages of diagenesis have been identified marine shallow burial mixing zone meteoric and dolomitization marine diagenesis induced precipitation of bladed and inclusion rich syntaxial cements that fluoresce strongly under uv light both cements account for a mean 7 5 vol reduction in the porosity of bioclastic beds shallow burial diagenesis likely induced mouldic porosity and associated fluorescent dog tooth cementation based on light oxygen isotope and elevated strontium isotope ratios matrix aragonite calcite neomorphism is interpreted to have occurred in a mixture of marine and meteoric fluids the combination of shallow burial and mixing zone processes reduced porosity on average by 4 8 vol evidence for subsequent meteoric diagenesis is found in abundant dog tooth and blocky calcite cements that have mean 18 o vpdb of 9 36 and no signs of recrystallization these meteoric cements reduced porosity by a further 13 4 vol percolation of meteoric water through the ramp was driven by hydraulic gradients on an adjacent basement high which was exposed by a cycle of early ladinian regressions following meteoric diagenesis the upper muschelkalk was dolomitized by refluxing brines this complex history of diagenesis resulted in moderate porosities in dolomitized rocks up to 20 and low porosities

distribution of diatoms coccolithophores and planktic foraminifers along a trophic gradient during sw monsoon in the arabian sea the distribution of diatoms coccolithophores and planktic foraminifers mirrored the hydrographic and trophic conditions of the surface ocean 0 100 m across the upwelling area off the oman coast to the central arabian sea during may june 1997 and july august 1995 the number of diatoms was increased in waters with local temperature minimum and enhanced nutrient concentration nitrate phosphate silicate caused by upwelling vegetative cells of chaetoceros dominated the diatom assemblage in the coastal upwelling area towards the more nutrient depleted and stratified surface waters to the southeast the number of diatoms decreased coccolithophore and planktic foraminiferal numbers increased and floral and faunal composition changed in particular the transition between the eutrophic upwelling region off oman and the oligotrophic central arabian sea was marked by moderate nutrient concentration and high coccolithophore and foraminifer numbers florisphaera profunda previously often referred as a lower photic zone species was frequent in water depths as shallow as 20 m and at high nutrient concentration up to 14 mol no3 l 1 and 1 2 mol po4 l 1 to the oligotrophic southeast of the divergence cell densities of coccolithophores declined and umbellosphaera irregularis prevailed throughout the water column down to 100 m depth in general total coccolithophore numbers were limited by nutrient threshold concentration with low numbers 70 103 cells l 1 at low no3 and po4 the components of the complex microplankton succession diatoms coccoliths and planktic foraminifers and possibly others should ideally be used as a combined paleoceanographic proxy consequently models on plankton ecology should be resolved at least for the seasonality to account for the bias of paleoceanographic transfer calculations

the generation of global rotational flow by steady idealized tropical divergence abstract tropical convective heating is balanced on the large scale by the adiabatic cooling of ascent the horizontal divergence of the wind above this heating may be viewed as driving the upper tropospheric rotational wind field a vorticity equation model is used to diagnose this relationship it is shown that because of the advection of vorticity by the divergent component of the flow the rossby wave source can be very different from the simple fd source often used in particular an equatorial region of divergence situated in easterly winds can lead to a rossby wave source in the subtropical westerlies where it is extremely effective this part of the source can be relatively insensitive to the longitudinal position of the equatorial divergence a divergence field which is asymmetric about the equator can lead to a quite symmetric rossby wave source for a steady frictionless flow the rossby wave source averaged over regions within closed streamfunction or absolute vorticity contours is under cert

palynology of the circum mediterranean triassic phytogeographical and palaeoclimatological implications following a tentative evaluation of palynological information from ladinian and more particularly karnian successions there seems to be every indication that qualitative and quantitative compositional differences of palynological assemblages could well be applied in testing concepts of triassic phytogeography and palaeoclimatology

a paleoecological and paleobiogeographic evaluation of helicosphaera inversa gartner theodoridis and the diachrony of its first occurrence abstract the distribution pattern of helicosphaera inversa gartner theodoridis is examined from a mid latitude north atlantic core md01 2446 and two mediterranean cores ocean drilling program odp site 975 and core kc01b through marine isotope stage mis 13 to 9 the earliest rare occurrences are observed from the uppermost part of mis 12 while common and continuous abundances characterize mis 11 the paleoenvironmental framework of the study cores suggests that the taxon thrived in warm surface waters correlation with new data from planktonic foraminifera also suggests that h inversa may have only flourished within a limited salinity range comparison with previous findings highlights major diachrony in the fo of the taxon between low and mid latitude records it first occurred at lower latitude in the pacific as early as 0 8 ma while in the mid latitude north atlantic regions it is not recorded before 0 51 ma the distribution of the taxon in the north atlantic ocean also apparently varies in relation with surface water masses and hydrographic fronts the results suggest that the fo of h inversa is ecologically controlled and needs to be used with caution in worldwide stratigraphic correlation nevertheless the distribution of the species within the mediterranean basin can produce an invaluable ecostratigraphical signal

abrupt climate events 500 000 to 340 000 years ago evidence from subpolar north atlantic sediments subpolar north atlantic proxy records document millennial scale climate variations 500 000 to 340 000 years ago the cycles have an approximately constant pacing that is similar to that documented for the last glacial cycle these findings suggest that such climate variations are inherent to the late pleistocene regardless of glacial state sea surface temperature during the warm peak of marine isotope stage 11 mis 11 varied by 0 5 to 1 c less than the 4 to 4 5 c estimated during times of ice growth and the 3 c estimated for glacial maxima coherent deep ocean circulation changes were associated with glacial oscillations in sea surface temperature

revised tuning of ocean drilling program site 964 and kc01b mediterranean and implications for the δ18o tephra calcareous nannofossil and geomagnetic reversal chronologies of the past 1 1 myr 1 high resolution color reflectance records of kc01 and kc01b calabrian ridge ionian sea are presented and compared with a modified spliced high resolution color reflectance record of ocean drilling program odp site 964 this comparison revealed that kc01b is characterized by intensive deformation between 27 and 28 5 m piston depth and that some sapropels are tectonically reduced in thickness moreover the piston coring has caused considerable stretching in the top of kc01 and kc01b using a new splice of odp site 964 as guide previous astronomical tuned timescales of kc01b and odp site 964 were evaluated this evaluation resulted in a new sapropel based astronomical timescale for the last 1 1 myr the new timescale implies a much more uniform change in sedimentation rate for the ionian sea cores two prominent excursions to lighter values in the 18o record of the planktonic foraminiferal species globigerinoides ruber occur during marine isotopic stages 12 and 16 applying the new timescale these shifts correspond with maxima in obliquity and are punctuated by minima in the precession cycle they are absent in global ice volume records and are interpreted as reflecting a summer low salinity surface water lens that floats on top of extremely saline intermediate and deep waters at times of the very low sea levels during these glacial periods all biostratigraphic and magnetostratigraphic events found in kc01b and odp site 964 were re dated according to the new timescale and the ages of 33 tephra layers were reviewed the new ages for the calabrian ridge 2 and 3 magnetic events in the brunhes are concordant with minima in the global sint800 composite record derived from worldwide deep sea records of relative paleointensity and have been attributed to the big lost and la palma excursions respectively

the nature of a heat wave in eastern argentina occurring during salljex this note describes the physical processes associated with the occurrence of a heat wave over central argentina during the austral summer of 2002 03 during which the south american low level jet experiment salljex was carried out the salljex heat wave that lasted between 25 january and 2 february 2003 was punctuated by extreme conditions during its last 3 days with the highest temperature recorded over the last 35 yr at several stations of the region it was found that not only the activity of synoptic scale waves but also the intraseasonal oscillation variability had a strong impact on the temperature evolution during this summer during the weeks previous to the heat wave development an intensified south atlantic convergence zone sacz dominated the atmospheric conditions over tropical south america temperatures started to increase in the subtropics due to the subsidence and diabatic warming associated with the sacz as depicted by salljex upper air observations an extratropical anticyclone that evolved along southern south america further intensified subsidence conditions by the end of january the warming processes associated with sacz activity weakened while horizontal temperature advection began to dominate over central argentina due to the intensification of the south american low level jet this mechanism led to temperature extremes by 2 february with temperature anomalies at least two standard deviations larger than the climatological mean values intense solar heating favored by strong subsidence was responsible for the heat wave until 31 january after which horizontal temperature advection was the primary process associated with the temperature peak

mediterranean quaternary sapropels an immediate response of the african monsoon to variation of insolation abstract in the subsurface of the east mediterranean sea eleven discrete basin wide organic rich black sapropels were deposited during the last 465 000 years they are dated by oxygen isotopic chronostratigraphy the most recent sapropel has been shown to be the consequence of heavy nile river summer floods due to increased monsoonal summer precipitation over ethiopia and not of scandinavian ice sheet meltwater influx into the east mediterranean sea as was previously believed while most sapropels were deposited during interglacials two thick sapropels formed during glacial periods as shown by their position in the oxygen isotopic stratigraphy and by their pollen record in core rc9 181 the new evidence presented here is that the sapropel sequence in this core including the two glacial sapropels correlates on a one to one basis with the highest values of an index of insolation on top of the atmosphere the concept of this index derives from an analysis of the african monsoon process the index variation is computed for the last 465 000 years from the caloric northern summer insolation in the tropical latitudes controlled by variations of the earth s orbital parameters it is conjectured that this index might be linked through the climate system to the monsoonal precipitation which in africa produces the nile river summer flood

the south pacific convergence zone spcz a review abstract the circulation features associated with the south pacific convergence zone spcz and its accompanying cloud band are reviewed and discussed the paper focuses on the following topics location structure and characteristics of the spcz theories and observations concerning its existence the significance and scope of the spcz in global scale circulation patterns quasi periodic changes in its location and strength and synoptic scale features within its regional influence e g cyclones subtropical jets it concludes with some challenging problems for the future

review and new aspects concerning the formation of eastern mediterranean sapropels abstract in this paper it is proposed that the formation of eastern mediterranean sapropels occurred in an anti estuarine type of circulation which was to some degree weakened relative to the present in response to reduction of the eastern mediterranean excess of evaporation over freshwater input this reduction of excess evaporation would have been imposed by intensifications of 1 the indian ocean summer sw monsoon influencing the eastern mediterranean via increased nile discharge and 2 the system of mediterranean depressions an element of the westerly atlantic system causing increased precipitation and decreased evaporation both the indian ocean summer monsoon and the westerly atlantic system would be intensified in response to the occurrence of distinct minima in the cycle of precession it is demonstrated that reduced excess evaporation whether or not coinciding with global phases of deglaciation would lead to reduction of surface water salinities in the eastern mediterranean causing isolation of previously formed high salinity cooler deep water thus mixing was severely reduced possibly even restricted to eddy diffusion with only occasional convective events that because of the existing density gradient hardly ever would reach the deepest parts of the basin the consequently diminished oxygen advection down from a few hundred meters in the water column favoured preservation of the sinking organic matter this would however suffice only to enable the formation of sapropels with low organic carbon contents the high organic carbon contents observed in various sapropels are argued to reflect superimposed increases of export production the described scenario accounts for previously reported 1 increases of organic carbon content with increasing depth of deposition within individual sapropels and 2 asymmetrical sequences of sapropel deposition characterized by gradual build up and rather abrupt ending it is furthermore in agreement with 3 isotopic and faunal reconstructions of the history of exchange transports through both the strait of sicily and the strait of gibraltar and 4 faunal and floral reflections of the presence or absence of a distinct deep chlorophyll maximum with its associated increases in export production indicating the presence or absence of a shallow pycnocline within the euphotic layer moreover the described scenario 5 is in no way conflicting with the reports of sapropels in the western mediterranean and 6 seems to be endorsed by occasionally intercalated intervals suggestive of somewhat improved oxygenation amidst anoxic benthic desert levels a situation that has been observed in a few quaternary and pliocene sapropels