lagoonal deposits in the upper cretaceous rock springs formation mesaverde group southwest wyoming abstract most paleogeographic reconstructions of the rock springs formation show shorelines having lobate to arcuate deltas these shorelines are oriented ne sw with the sea to the southeast brackish water bodies are usually shown in interdistributary areas or associated with abandoned delta lobes and are open to the sea in this study a sedimentary sequence 30 50 m thick is interpreted as interdeltaic deposits brackish water deposits within the sequence are interpreted as interdeltaic lagoons rather than interdistributary bays three facies associations units are recognized in nine measured sections of the study interval unit a consists of interbedded sandstone mudrock and coal which occur in both fining and coarsening upward sequences less than 10 m thick fining upward sequences decrease in thickness and frequency upwards in unit a and are interpreted as distributary channels coarsening upward sequences associated with the channels are interpreted as crevasse splays that filled lakes or interdistributary bays in the upper part of the unit where only minor channels are present the coarsening upward sequences are interpreted as bay deltas unit b consists of fossiliferous silty shale and bioturbated sandy siltstone a low diversity fauna of bivalves gastropods ostracods and foraminifers indicates that brackish water conditions existed unit b intertongues with unit a to the northwest and with unit c to the southeast and is interpreted as lagoonal deposits unit c consists of crossbedded and burrowed sandstone in beds 0 5 9 m thick sandstones are laterally continuous in the southeast but become tabular bodies enclosed within unit b to the northwest laterally continuous sandstones are interpreted as shoreface deposits on the basis of multidirectional crossbeds marine trace fossils and continuity tabular sandstones are interpreted as flood tidal deltas on the basis of nw oriented crossbeds pinchouts to the northwest and enclosure within unit b scoured surfaces and rip up clasts within unit c indicate the presence of tidal channels or inlets interpreting unit b as an interdeltaic lagoon rather than an interdistributary bay is dependent on understanding its enclosing strata the distributary channels of unit a supplied the majority of the sediment in the lower part of the sequence however after the lagoon formed tidal channels and inlets of unit c supplied more sediment to the area than channels of unit a the shift in sedimentation from a landward to a seaward source reflects the change from a delta plain to an interdeltaic lagoon following abandonment of distributary channels

relationship between the equatorial and meridional modes of climatic variability in the tropical atlantic the tropical atlantic ocean exhibits two primary modes of interannual climate variability an equatorial mode analogous to but weaker than the pacific el nino phenomenon and a meridional mode that does not have a pacific counterpart the equatorial mode is responsible for warm and cold sea surface temperature sst events mainly in the gulf of guinea and is identifiable by abnormal changes in the equatorial thermocline slope resulting from zonal wind anomalies in the western tropical atlantic the meridional mode is characterized by a north south interhemispheric gradient of sst anomalies here it is shown using observed surface and subsurface oceanic temperatures that the meridional mode is linked to the equatorial mode at both decadal and short interannual 1 2 years time scales both modes involve north south displacements of the itcz as in the annual response

mapping climatological seasonal variations of surface currents in the tropical atlantic using ship drifts the seasonal variability of current velocities in the tropical atlantic was studied by grouping ship drift velocity observations into 2 5 boxes and calculating monthly mean velocity values these values were used to calculate and map the annual mean velocity the seasonal variation about the mean the annual and semiannual harmonics and the first two empirical orthogonal functions eofs the seasonal variation is primarily zonal in the equatorial band and in the north equatorial countercurrent necc and primarily alongshore near the coast of south america maxima of seasonal variation of 23 cm s are centered in the necc near 6 n 42 5 w and in the gulf of guinea near 2 n 7 5 w most 80 of the variance in the necc and along the western boundary of the area studied has an annual period most of the variance along the equator in the mid atlantic has a semiannual period over the whole region 49 of the seasonal variance is explained by the annual harmonic and 69 is explained by a combination of the annual and semiannual harmonics the second eof contains 29 of the variance of the data set and shows a simultaneous speeding slowing of the major equatorial currents the south equatorial current sec the north brazil current the necc and the guinea current along their principal axes of variation with a concurrent slowing speeding of the guyana current and the brazil current the pattern of variation resembles a large equatorial gyre centered along 4 n that flows clockwise from may to september and counterclockwise most of the rest of the year the first eof accounts for 35 of the variance and shows a simultaneous speeding slowing of eastward velocity from 5 s to 10 n except in the western sec the western end of the north brazil current and the guinea current the out of phase fluctuations apparent in the western sec near the equator are explained by the slowing and reversal of the south equatorial current near 2 n 40 w between april and june this slowing of the sec is associated with the start up of the necc which accelerates eastward in may june and july and flows eastward across the atlantic from july through december the sec divides seasonally near the eastern tip of brazil where residual alongshore velocities are northward for half the year peaking during may and june and southward for the other half of the year a second division can be seen north of the amazon where the north brazil current continues up the coast into the guyana current during the first half of the year but partially retroflects into the necc during the last half of the year a fast eastward flow in the necc coincides with below average velocities in the guyana current and above average velocities in the western sections of the north brazil current and the sec north of the equator

respective roles of the guinea current and local winds on the coastal upwelling in the northern gulf of guinea abstractthe northern gulf of guinea is a part of the eastern tropical atlantic where oceanic conditions due to the presence of coastal upwelling may influence the regional climate and fisheries the dynamics of this coastal upwelling is still poorly understood a sensitivity experiment based on the regional oceanic modeling system roms is carried out to assess the role of the detachment of the guinea current as a potential mechanism for coastal upwelling this idealized experiment is performed by canceling the inertia terms responsible for the advection of momentum in the equations and comparing with a realistic experiment the results exhibit two major differences first the guinea current is found to be highly sensitive to inertia as it is no longer detached from the coast in the idealized experiment the guinea current adjusts on an inertial boundary layer the inertial terms defining its lateral extension second the upwelling east of cape palmas disappears in absence of the guinea current detach

assessment of nutrients and heavy metals in the surface sediments of the artificially lake water reservoir karla thessaly greece in this research the sediment quality of the recently reconstructed lake karla central greece was evaluated by monitoring the nutrient loadings and heavy metal concentrations in 16 sites during the initial period of the lake s rehabilitation the results indicated that lake sediments exhibited a high nutrient status as manifested by the high loadings of organic carbon oc total nitrogen tn and available phosphorus ap comparison of metal ni cr co zn cu and pb levels with sediment quality guidelines showed that ni and cr were found in concentrations well above the pel probable effect level values no correlations were found between the nutrients and the measured heavy metals multivariate analysis results implied that ni cr co cu and zn were controlled by natural geological sources whereas pb might have an anthropogenic origin the bioavailability ratios of metals followed a decreasing order of pb cu co zn ni cr based on results obtained by a single 0 5 m hcl leach total and bioavailable concentrations of metals demonstrated significant seasonal variations but trends could not be generalized for all the elements on the contrary the nutrients did not show significant seasonal differences indicating that the lake sediments record the history of contamination with regard to nutrient status

the california current system in the southern california bight and the santa barbara channel recent observations in the santa barbara channel and over the california cooperative oceanic fisheries investigations calcofi southern california grid are used to examine seasonal circulation patterns in and near the southern california bight defined as the region east of the santa rosa ridge and including the santa barbara channel poleward flow relative to 500 m is found throughout the bight in all seasons except for spring and all subregions except the western part of the santa barbara channel in spring there is equatorward flow throughout the bight at all depths to 500 m though it tends to be surface or midcolumn intensified equatorward flow offshore of the bight present in all seasons narrows and accelerates into a jet like feature and simultaneously moves close to the santa rosa ridge in summer current meter data from the eastern entrance to the santa barbara channel are consistent with the seasonal results from the calcofi data and further show an upward propagation of phase at annual period with a phase speed of 1 to 2 m d 1 comparison with the calcofi ship winds suggests that poleward flow in the bight may be the result of positive wind stress curl through a sverdrup balance though the observed transport is only about 75 of that expected from the curl amplitude equatorward flow in the bight may be the result of coastal upwelling though the transport is larger than expected from the relatively weak winds in the bight and the offshore extent of the equatorward flow is about 10 rossby radii farther than might be expected for linearized coastal upwelling equatorward flow outside the bight cannot be explained as a sverdrup flow because the wind stress curl is positive throughout most of the region upward propagation of phase and downward propagation of energy may be indicative of forcing by remote wind equatorward of the bight given the complexity of possible forcing mechanisms for circulation in and near the bight a model that includes effects of remote wind forcing ekman pumping and topography is needed to explain the observations in a satisfactory way

spatial and temporal patterns of benthic macrofaunal communities on the deep continental margin in the gulf of guinea abstract density taxonomic composition at higher taxon level and vertical distribution of benthic macrofaunal communities and sediment characteristics pore water nitrogen organic carbon sulfur c n ratio n alcohol biomarkers were examined at three deep sites on the congo gabon continental margin this study was part of the multidisciplinary biozaire project that aimed at studying the deep benthic ecosystems in the gulf of guinea sampling of macrofaunal communities and of sediment was conducted during three cruises january 2001 december 2001 and december 2003 at two downslope sites 4000 m depth one located near the congo submarine channel 15 km in the south and the other one far from the channel 150 km in the south the third area located 8 km north of the congo channel in the surroundings of a giant pockmark at 3160 m depth was sampled during one cruise in december 2003 at these three locations the macrofaunal communities presented relatively high densities 327 987 ind 0 25 m 2 compared with macrofaunal communities at similar depths that is due to high levels of food input related to the congo river and submarine system activities that affect the whole study area the communities were different from each other in terms of taxonomic composition at higher taxon level phylum class order for all the groups except for the polychaetes classified into families the polychaetes dominated the communities and were responsible for the increase in densities observed at both deep sites 4000 m between january 2001 and december 2003 whereas the tanaidaceans the isopods and the bivalves were the other most abundant taxa responsible for the spatial differences between these sites the community at 3150 m differed from the two deep communities by higher abundances in bivalves nemerteans and holothuroids the composition of the polychaete community also differed among sites in the vicinity of the congo channel the expected positive effect of the additional organic matter transported through the turbiditic currents on to the surrounding benthic communities was not observed as the increase in densities during the study period was higher at the site located away from the congo channel than near the channel 80 vs 30 that may be due to the low food value of the organic matter of terrestrial origin carried through the turbidites and or to the disturbance caused by these turbidites conversely far from the channel the macrofaunal communities benefit from organic matter of higher energetic value originating mainly from marine sources but also from continental sources carried by the congo plume or by near bed currents across or along the continental slope spatial and temporal variability in trophic and physical characteristics of the sediment habitat at both deep sites also affected the vertical distribution of the macrofaunal communities the activities of the very active congo system structure the deep macrofaunal communities on a large area in terms of densities composition and vertical distribution the food input is enhanced at regional scale as well as the heterogeneity of the sediment characteristics mainly in terms of organic matter quality marine vs terrigenous in turn the densities are enhanced as well as the regional diversity of the macrofaunal communities in terms of taxonomic composition and distribution

distribution and origin of lead in stream sediments from small agricultural catchments draining miocene molassic deposits sw france total pb concentrations and isotopic composition were determined in stream bed sediments and bedrock from 29 small agricultural or forested catchments in the gascogne area sw france the contribution of pb from various natural and anthropogenic sources was investigated in this rural area which is very weakly impacted by industrial or urban emissions environmental parameters in catchments importance of forest cover organic matter and oxide content in sediments were considered a combination of geochemical enrichment calculation sequential extraction and isotopic investigations was performed to constrain the origin of pb and the distribution of anthropogenic pb in sediments most of the sediments have low total pb content compared to other agricultural regions more impacted by industrial or urban emissions the results indicated a moderate but significant pb enrichment particularly for catchments draining forested areas this enrichment was positively related to organic c content in sediment and catchment forest cover whereas in entirely cultivated catchments it was related to fe oxide content an average anthropogenic end member was determined using pb isotopes and was supposed to be representative of background atmospheric pb pollution with a weak influence of pb from recent gasoline and local fertiliser spreading the amount of anthropogenic pb pbanthr in sediments estimated using a geochemical approach mean 63 7 20 4 was higher than that estimated using an isotopic approach mean 36 6 17 8 but the same trend was observed among the samples except for low anthropogenic contributions the distribution of pbanthr in sediments from weakly forested catchments indicated a strong affinity for carbonates and fe oxides amorphous fe oxides became preferential trapping compounds as soon as pb enrichment increased and carbonate content decreased finally in cultivated catchments organic c was not a main trapping component for pbanthr in sediments

oceanic kelvin waves and tropical atlantic intraseasonal variability 1 kelvin wave characterization 1 oceanic kelvin waves from the equator to the west african coast are investigated in the framework of tropical atlantic intraseasonal variability in order to better highlight the wave propagations a 25 95 day band pass filter was applied to the sea surface height ssh product derived from the topex poseidon altimeter and an ocean general circulation model simulation for the 1993 2000 period in addition to equatorial eastward propagations our analysis reveals recurrent and continuous propagations distinguishable over thousands of kilometers poleward along the coasts as far as about 10 15 latitude a novel result with altimeter data the variance of the filtered ssh signal goes from 1 cm at the equator to 2 cm at the african coast estimates of the phase speed range from 1 5 to 2 1 m s along the equator and the west african coastline such values are very close to those of equatorial kelvin wave propagations likely dominated by the first two baroclinic modes supporting the fact that the coastal propagations are coastally trapped kelvin waves in order to simplify the description of these kelvin waves we present an intraseasonal climatology which reveals regular boreal autumn winter equator to coast propagations an improved description is achieved thanks to the computation of an extended empirical orthogonal function for the boreal autumn winter propagations lag correlation of ssh signals allows for a twofold quantification the phase speed and the importance of remote forcing along the coast the remote forcing effect of intraseasonal kelvin waves is clearly evidenced over coastal upwelling regions as far as 10 15 latitude the physical mechanism associated with the forcing of the kelvin waves and its impacts will be investigated in a future paper

ocean climate of the south east atlantic observed from satellite data and wind models the near coastal south east atlantic ocean off africa is a unique and highly dynamic environment comprising the cool benguela current warm angola current and warm agulhas current strong coastal upwelling and the congo river strongly influence primary production much of the present knowledge of the south east atlantic has been derived from ship borne measurements and in situ sensors which cannot generally provide extensive spatial and temporal coverage similarly previous satellite studies of the region have often focused on small spatial areas and limited time periods this paper provides an improved understanding of seasonal and interannual variability in ocean dynamics along the south east atlantic coast of africa using time series of satellite and model derived data products eighteen years of satellite sea surface temperature data are complimented by 7 years of sea level data three years of chlorophyll a data illustrate the seasonal biological response but the time series is not of sufficient length for investigating interannual variability in chlorophyll biomass modelled wind fields are used to describe atmospheric forcing of the surface ocean this is the first synoptic scale description of the south east atlantic from a suite of large spatial coverage long time series products previous studies of seasonal and interannual variability in the region are reviewed and used to interpret key oceanographic features and processes identified in the satellite data key findings of this study are 1 descriptions of seasonal and interannual variability from these data show climate forcing of the south east atlantic coast of africa from both the northern and southern boundaries bimodal seasonal signals of equatorial origin propagate poleward along the angolan coast while the trade winds and events in the agulhas region dominate the agulhas bank and southern benguela the northern benguela is a mixed regime under the influence of forcing from both directions 2 the benguela nino years of 1984 and 1995 are clearly observed in sea surface temperature and sea level anomalies and correspond to anomalously weak southerly winds at the equator these conditions were also observed in 1999 suggesting this too may have been a benguela nino year 3 consideration of putative nino type events in the equatorial atlantic from this and other studies suggests that the frequency of these events is much higher than previously estimated and may be similar to the frequency of el nino southern oscillation enso events in the pacific ocean furthermore years of anomalously strong southerly winds at the equator occur during pacific enso years c 2003 elsevier ltd all rights reserved

evidence of remote forcing in the equatorial atlantic ocean abstract an analysis of sea surface temperature sst and surface winds in selected areas of the tropical atlantic indicates that the nonseasonal variability of sst in the eastern equatorial atlantic gulf of guinea is highly correlated with the nonseasonal variability of the zonal wind stress in the western equatorial atlantic a negative positive anomaly of the zonal wind stress near the north brazilian coast is followed by a positive negative sst anomaly in the gulf of guinea about one month later furthermore the correlation between the local wind stress anomaly and sst anomaly in the gulf of guinea is considerably smaller these preliminary results indicate that remote forcing in the western equatorial atlantic ocean is an important factor affecting the eastern equatorial atlantic sea surface temperature recent equatorial theories are consistent with these observations

isopycnal and diapycnal circulation of the upper equatorial atlantic ocean in 1983 1984 isopycnal circulation and diapycnal processes in the equatorial atlantic ocean are investigated using eight cruises from november 1982 to july 1984 an eastward decrease of the transport of the equatorial undercurrent is observed averaging 18 2 106 m3 s 1 at 35 w to 10 2 106 m3 s 1 at 4 w there is also a meridional convergence at the undercurrent level and a larger meridional divergence in the surface layer of 15 106 m3 s 1 between 35 w and 4 w in the eastern equatorial atlantic the undercurrent core density as well as the salinity above the undercurrent experience a large seasonal cycle during the season where the eastern atlantic thermocline is closest to the surface and surface waters are coldest the current peaks in denser waters and subsurface salinity maximum are weaker an analysis of the salinity on isopycnal surfaces indicates that there is significant diapycnal mixing in the upper thermocline in the eastern atlantic the upper thermocline vertical heat diffusivity coefficient scaled over 1 of latitude varies between 3 cm2 s 1 during the upwelling season and nearly 0 early in the year this seasonal mixing is an important element of undercurrent dynamics the turbulent heat flux at the base of the surface layer averages 50 w m 2 between 1 5 n and 1 5 s the surface layer heat budget implies an average oceanic gain of 60 w m 2 between 1 5 n and 1 5 s which could result from exchanges with the atmosphere the heat flux and fresh water seasonal cycles needed to close the budgets are not realistic however the eastern equatorial atlantic thermocline seasonal upwelling is associated with a large inflow into the surface layer over the two years this flow averaging 11 12 106 m3 s 1 originates from the upper thermocline and diapycnal transports near the core of the undercurrent or below are found to be small below the core of the undercurrent we also find that mixing is not intense for instance at 26 5 in the upper part of the thermostad vertical heat diffusivity is only 0 6 cm2 s 1 assuming that mixing takes place over 1 of latitude the uncertainties on these budgets are however large and assumptions on the dynamics that were used could not be checked

seasonal variation of the gulf of guinea thermal structure data from 6 temperature sections are combined with other sequal focal data along 4 w from the coast 5 n to 3 s to study the seasonal variation of the temperature field in the gulf of guinea during 1983 the equatorial upwelling begins during mid april approximately 1 1 2 months before the climatic mean but has a normal amplitude and duration the upwelling on the coast at abidjan occurs approximately 1 1 2 months after the equatorial upwelling and precedes its climatic mean by 2 weeks at the equator vertical displacements of isotherms within the thermostad are complicated by an anomalous warming of the thermostad in may between the thermostad and the deeper thermocline at 230 m the seasonal isotherm displacement amplitude has a minimum at greater depths it increases again in all respects the fluctuation of the thermal field at the equator is similar to the climatic mean but displaced forward in time by 1 1 2 months

observation of the marine atmospheric boundary layer in the gulf of guinea during the 2006 boreal spring in situ satellite and model analyses data in april july 2006 are used to investigate the links between sea surface temperature sst and the marine atmospheric boundary layer mabl in the gulf of guinea the study region between 10 w and 6 e is divided into three areas with different characteristics the north area 4 5 n to 1 n with the wettest atmosphere and the warmest sst the upwelling area 1 n to 4 s with the strongest sst decrease and the south area 4 s to 8 s with a drier atmosphere and a more slowly decreasing sst than in the upwelling area the key zone of the air sea interactions in this region seems to be the sst front between north and upwelling areas on the one hand the study of the mabl on either side of the front shows a well mixed layer between the surface and about 500 m high sensitive to surface variations which gets shallower deeper when the sst decreases increases the mabl height about 1500 m follows the same variations but is not exactly collocated with the sst variations on the other hand the observation of the mabl across the sst front shows a strengthening of southeasterlies in the south area coinciding with a strong sst decrease in the upwelling area in the latter the wind weakens above the colder sst besides in the north area the wind strengthens above the warmer sst however the wind acceleration spans from the equator to 2 n in april and as far as 4 n in june a convergence zone is observed in the vicinity of 2 n in april suggesting a convection activity there favoured by the sst front copyright 2011 royal meteorological society

geologic controls on transgressive regressive cycles in the upper pictured cliffs sandstone and coal geometry in the lower fruitland formation northern san juan basin new mexico and colorado three upper pictured cliffs sandstone tongues in the northern part of the san juan basin record high frequency transgressive episodes during the late cretaceous and are inferred to have been caused by eustatic sea level rise coincident with differential subsidence outcrop and subsurface studies show that each tongue is an amalgamated barrier strand plain unit up to 100 ft 30 m thick successive upper pictured cliffs tongues display an imbricate relation and are offset basinward reflecting net shoreline progradation northeastward upper pictured cliffs barrier strand plain sandstones underlie and bound thickest fruitland coal seams on the seaward side controls on fruitland coal seam thickness and continuity are a function of local facies distribution in a coastal plain setting shoreline positions related to transgressive regressive cycles and basin subsidence during periods of relative sea level rise the pictured cliffs shoreline was temporarily stabilized allowing thick coastal plain peats to accumulate although some coal seams in the lower fruitland tongue override abandoned pictured cliffs shoreline deposits many pinch out against them differences in the degree of continuity of these coal seams relative to coeval shoreline sandstones are attributed to either differential subsidence in the northern part of the basin multiple episodes of sea level rise local variations in accommodation and progradation stabilization of the shoreline by aggrading peat deposits or a combination of these factors fruitland coalbed methane resources and productivity are partly controlled by coal seam thickness other important factors include thermal maturity fracturing and overpressuring the dominant production trend occurs in the northern part of the basin and is oriented northwestward coinciding with the greatest fruitland net coal thickness similar relationships between trends of thick coal seams of coeval origin with stacked shoreface sandstones exist in other western interior basins in the united states and serve as models for coalbed methane exploration in other basins of the world

slope derived deposits from the cretaceous interior seaway northwestern colorado abstract two types of mass movement deposits are interbedded within the dark marine upper cretaceous mancos shale in outcrops exposed on and near the slopes of mount garfield 12 km east of grand junction colorado these deposits are inferred to have formed at or seaward of the shallow marine shelf edge about 200 km from the contemporaneous shoreline the first type is a thick tens of meters laterally restricted 200 400 m deposit composed of rip up clasts of mancos shale rare sandstone and siltstone blocks and a silty mudstone matrix these deposits overlie abrupt bedding parallel basal contacts and are interpreted to record submarine debris flows the second type of deposit consists of landward rotated blocks of mancos shale tens of meters in scale adjacent to a listric fault scar and overlying a similar sharp planar base these are interpreted as slump blocks an associated third type of deposit consists of one or more 4 to 5 m thick beds composed of laterally extensive centimeter scale sandstone shale laminations that are rippled and extensively burrowed and that may represent distal turbidite deposits the mass movement deposits are interpreted as rare examples of the sedimentary record of the offshore slope environment in the cretaceous interior seaway a twice repeated vertical succession with basal sandstones intermediate mudstones and overlying slump blocks or debris flow deposits records fluctuations in relative sea level tectonism and sedimentation rate during the claggett transgression

deltaic coals of ferron sandstone member of mancos shale predictive model for cretaceous coal bearing strata of western interior the upper cretaceous ferron sandstone member of the mancos shale the coal bearing unit of the emery coalfield in central utah shows accumulation of clastic sediments in a lobate river dominated deltaic system that existed along the western shoreline of the interior cretaceous seaway during late turonian time five cycles of deltaic sedimentation each containing one major coal bed or coal zone are represented a clear genetic relationship exists between the geometries of the major coal beds of the emery field and the geometries of the delta front sandstone units with which they are associated the thicker part of each coal bed extends from the vicinity of the landward pinch out of the associated delta front sandstone landward to a distance of about 10 km this genetic relation forms the basis of a predictive model that can be used in designing more cost effective exploration programs in coal bearing strata of cretaceous age in the western interior

seasonal modes of surface cooling in the gulf of guinea a numerical simulation of the tropical atlantic ocean indicates that surface cooling in upwelling zones of the gulf of guinea is mostly due to vertical mixing at the seasonal scale the spatial structure and the time variability of the northern and southern branches of the south equatorial current sec and of the guinea current are correlated with the timing and distribution of turbulent heat fluxes in the gulf of guinea through modulation of the velocity shear at the subsurface these surface currents control the vertical turbulent exchanges bringing cold and nutrient rich waters to the surface this mechanism explains the seasonality and spatial distribution of surface chlorophyll concentrations better than the generally accepted hypothesis that thermocline movements control the nutrient flux the position of the southern sec explains why the cold tongue and high chlorophyll concentrations extend from the equator to 4 s in the southeastern part of the basin

warming and cooling the medieval climate anomaly in africa and arabia the medieval climate anomaly mca is a well recognized climate perturbation in many parts of the world with a core period of 1000 1200 common era here we present a palaeotemperature synthesis for the mca in africa and arabia based on 44 published localities the data sets have been thoroughly correlated and the mca trends palaeoclimatologically mapped the vast majority of available afro arabian onshore sites suggest a warm mca with the exception of the southern levant where the mca appears to have been cold mca cooling has also been documented in many segments of the circum africa arabian upwelling systems as a result of changes in the wind systems which were leading to an intensification of cold water upwelling offshore cores from outside upwelling systems mostly show warm mca conditions the most likely key drivers of the observed medieval climate change are solar forcing and ocean cycles conspicuous cold spikes during the earliest and latest mca may help to discriminate between solar oort minimum and ocean cycle atlantic multidecadal oscillation amo influence compared to its large share of nearly one quarter of the world s landmass data from africa and arabia are significantly underrepresented in global temperature reconstructions of the past 2 000 years onshore data are still absent for most regions in africa and arabia except for regional data clusters in morocco south africa the east african rift and the levant coast in order to reconstruct land palaeotemperatures more robustly over africa and arabia a systematic research program is needed

biological and physical signatures in the tropical and subtropical atlantic the variability of sea surface chlorophyll concentration in the tropical and subtropical atlantic during the first year of sea viewing wide field of view sensor seawifs imagery is examined an ocean general circulation model ogcm is used along with topex poseidon dynamic height observations and global gridded wind stress data sets to explain the physical forcing of surface ocean color signals regions of high surface chlorophyll are strongly correlated with mesoscale and large scale physical processes such as the strong upwelling off the west coast of africa the relatively high oceanic production within the guinea dome region and the generation and propagation of large anticyclonic eddies along the coast of south america north of the equator the major river outflows amazon orinoco and congo have strong signatures with plumes of apparently high chl a in excess of 10 mg m 3 near their deltas the fall bloom in the eastern tropical atlantic observed by the coastal zone color scanner czcs was absent in 1997 whereas a bloom was observed in this region in july september 1995 which was not observed by the czcs we attribute these apparent anomalies to the projection of the 1997 1998 el nino event into the tropical atlantic basin these signals are correlated with sea surface temperature anomalies known to be associated with enso the seawifs images show that there are seasonal blooms within the hydrographic provinces of the guinea and angola domes these hydrographic provinces are characterized by the dynamic uplift of the thermocline at the north equatorial current southern boundary guinea dome and the benguela current eastern boundary angola dome within these domes the ekman pumping and transport are significant due to the strong trade winds at the surface the ekman drift plays a major role in the spreading of surface blooms the spreading of the oceanic bloom at 12 n 30 w the congo river plume and the areal extent of the upwelling blooms off the coast of africa parallels the strength and extent of the ekman surface drift upwelling when broadly defined to include large scale vertical excursions of the thermocline explains virtually all of the surface chlorophyll observations in excess of 0 5 mg m 3 except in the river plumes i

seasonal cycle in the upper equatorial atlantic ocean the dynamics of the seasonal cycle in the upper equatorial atlantic ocean are studied using observations and a hierarchy of ocean models distinctive features of the seasonal cycle are strong annual and semiannual components eastward westward propagating sea surface height ssh and thermocline depth at the equator off the equator and westward propagating surface zonal currents at the equator modelling results show that linear theory can explain the seasonal cycle in thermocline depth and ssh while first order linear theory can also explain the structure of the seasonal cycle of surface zonal currents at the equator nonlinear terms are required they weaken the variability and improve its phase and zonal extent the important terms are meridional and vertical advection and vertical diffusion of zonal momentum the linear solution is essentially determined by the four gravest baroclinic modes and kelvin and first meridional mode rossby waves the eastward propagation in thermocline depth at the equator results from the kelvin wave contribution while the westward propagation in thermocline depth off the equator and surface zonal currents at the equator result from the first meridional mode rossby wave the contribution of kelvin and rossby waves generated by boundary reflections equals that of the directly forced waves the semiannual cycle in zonal winds although much weaker than the annual component forces a strong semiannual component in ssh and surface zonal currents because it excites the basin mode of the second baroclinc mode this explains the observed feature in the seasonal cycle from march to august

intraseasonal modulation of the surface cooling in the gulf of guinea abstracta regional numerical model of the tropical atlantic ocean and observations are analyzed to investigate the intraseasonal fluctuations of the sea surface temperature at the equator in the gulf of guinea results indicate that the seasonal cooling in this region is significantly shaped by short duration cooling events caused by wind forced equatorial waves mixed rossby gravity waves within the 12 20 day period band inertia gravity waves with periods below 11 days and equatorially trapped kelvin waves with periods between 25 and 40 days in these different ranges of frequencies it is shown that the wave induced horizontal oscillations of the northern front of the mean cold tongue dominate the variations of mixed layer temperature near the equator but the model mixed layer heat budget also shows that the equatorial waves make a significant contribution to the mixed layer heat budget through modulation of the turbulent cooling especially above the core of the equatorial undercurrent euc the tu

temperature variations in the equatorial atlantic as revealed by drifting buoys from may through september 1983 surface buoys deployed as a component of the focal experiment programme francais ocean et climat dans l atlantique equatorial drifted in the cold waters of the south equatorial current in the equatorial atlantic ocean the surface temperature sst is analysed along the buoy tracks in late may the strong temperature drop near 4 w and 3 s is associated with vertical mixing as cold patches appear near the equator horizontal advection is important in june and july as the cold water tongue expands southwards and westwards it is also important later in the western atlantic south of the equator where the cooling by advection is balanced primarily by heating from the atmosphere

sedimentological and petrographical characteristics of cretaceous strandplain coals a model for coal accumulation from the north american western interior seaway abstract coal seams formed on many cretaceous wave dominated strandplain sediments in north america are characterized by great lateral continuity tens to hundreds of kilometres substantial thicknesses up to 12 m relatively low ash and sulphur contents the coals formed behind an active shoreline in areas undergoing subsidence due to shale compaction and dewatering the zone of peat accumulation was remote from the shoreline and storm tidal inundations and generally protected from fluvial flooding if the rate of subsidence was too great lakes formed and peat did not accumulate statistical evaluation of petrographic properties by correspondence analysis of the lower cretaceous coals show that the strandplain coals form distinctive petrographic groups that are characterized by relatively low vitrinite contents and high inertinite contents semifusinite and inertodetrinite dominate in the inertinite maceral group liptinite contents are negligible tissue preservation indices and gelification indices indicate for the strandplain coals a forest type paleodepositional environment in which a relatively low water table allowed the accumulation of oxidized and partly oxidized components fusinite and semifusinite significant amounts of detrital components such as inertodetrinite and vitrinite b are diagnostic that some transportation of the organic material took place prior to deposition comparison of coal facies and depositional environments from permian coals of australian show that the lower cretaceous strandplain coals have petrographic similarities to coals that were formed under regressive back barrier conditions in the permian due to differences in nomenclature previously interpreted regressive back barrier environments may be similar to the strandplain environments discussed here

main processes of the atlantic cold tongue interannual variability the interannual variability of the atlantic cold tongue act is studied by means of a mixed layer heat budget analysis a method to classify extreme cold and warm act events is proposed and applied to ten various analysis and reanalysis products this classification allows 5 cold and 5 warm act events to be selected over the period 1982 2007 cold warm act events are defined by the presence of negative positive sea surface temperature sst anomalies at the center of the equatorial atlantic in late boreal spring preceded by negative positive zonal wind stress anomalies in the western equatorial atlantic an ocean general circulation model capable of reconstructing the interannual variability of the act correctly is used to demonstrate that cold act events develop rapidly from may to june mainly due to intense cooling by vertical mixing and horizontal advection the simulated cooling at the center of the basin is the result of the combined effects of non local and local processes the non local process is an upwelling associated with an eastward propagating kelvin wave which makes the mixed layer more shallow and preconditions the upper layers to be cooled by an intense heat loss at the base of the mixed layer which is amplified by a stronger local injection of energy from the atmosphere the early cooling by vertical mixing in march is also shown to be a good predictor of june cooling in july horizontal advection starts to warm the mixed layer abnormally and damps sst anomalies the advection anomalies which result from changes in the horizontal temperature gradient are associated in some cases with the propagation of rossby waves along the equator during warm act events processes are reversed generating positive sst anomalies a downwelling kelvin wave triggers stratification anomalies and mixed layer depth anomalies amplified by a weaker injection of energy from the atmosphere in may june in july warm act events are abnormally cooled due to negative horizontal advection anomalies resulting from processes similar to those that occur during cold act events this additional cooling process extends the period of cooling of the act reducing sst anomalies

comparison of mg ca and alkenone based sea surface temperature estimates in the fresh water influenced gulf of guinea eastern equatorial atlantic this study presents a comparison of sea surface temperature sst estimates based on mg ca ratios of globigerinoides ruber and alkenone unsaturation index u37 k in core sediment recovered from the gulf of guinea eastern equatorial atlantic mg ca and u37 k based sst estimates yield fairly comparable results for the time interval 21 000 14 500 years and for the late holocene the early and middle holocene however are largely characterized by a discrepant trend with warm mg ca and cold u37 k based sst estimates this discrepant sst trend is accompanied by low sea surface salinity estimates high riverine runoff and biogenic sediment which is characterized by high biogenic opal content low carbonate content and relatively low alkenone concentration we hypothesize that the discrepancy in the reconstructed ssts during the middle and early holocene presumably suggests a period of elevated riverine input of dissolved silica and dominantly siliceous phytoplankton bloom in a low saline and warm surface water while alkenone producers were likely prevalent in a season of cold sst and low riverine silica input this study suggests that changes in the local hydrography and nutrient input have strong influence on the u37 k based sst estimate that may be unraveled by combining different sst proxies

accumulation of heavy metals in the lacustrine sediment of longgan lake middle reaches of yangtze river china spatial and temporal distribution of heavy metals chromium copper nickel lead and zinc in the sediment of longgan lake middle reaches of yangtze river china were analyzed to discuss their enrichment characteristics and history in combination with geochronological data and to identify anthropogenic effects the results showed that the enrichment state of heavy metals was higher in the western versus eastern lake area although their concentrations behave in the opposite case which demonstrated that stronger human activities existed in the western lake catchment the enrichment history of heavy metals pointed out that prior to 1950 the enrichment state was lower in the ambient lake areas illustrating the natural effect on the lake thereafter the human activities in the catchment enhanced markedly causing an increasing heavy metal enrichment the increase of heavy metal enrichment in the 1970s occurred in the central lake areas the temporal difference between the ambient and central areas elucidated that the heavy metal accumulation might be buffered by the lake before they entered the sediment correlation analysis revealed that there was a significant correlation between heavy metals in the sediment suggesting their similar sources heavy metals were distinctly related to aluminum calcium lithium iron and organic matters which could denote their forms in the sediment

transport of terrestrial organic matter in the ogooue deep sea turbidite system gabon abstract in order to define the nature and distribution of the organic matter om preserved in the modern ogooue deep sea turbidite system gabon bulk geochemical techniques rock eval pyrolysis elemental and isotopic analyses and palynofacies were applied to three piston cores collected in the cape lopez canyon and lobe and on the continental slope north of the canyon the hemipelagic sedimentation in the study area is characterized by high accumulations of well preserved om 2 3 wt toc bulk geochemical and palynofacies analysis indicate both a marine and terrestrial origin of the om contribution of the marine source is higher on the slope than in the canyon and lobe om accumulation in turbidites is strongly controlled by the combined influence of the cape lopez canyon and littoral drift in the canyon and lobe turbidites show generally low toc content 0 5 wt and om is oxidized the origin of the om is interpreted as both marine and terrestrial with a higher contribution of continental source versus marine source the low toc contents are due to the large siliciclastic fraction transported by the littoral drift and diverted in the cape lopez canyon during high energy processes e g storms which tend to dilute the om in the turbidites transport by long shore currents and or turbiditic flows leads to oxidation of the om on the continental slope located north of the cape lopez canyon large amounts of om are deposited in turbidites up to 14 wt the om is predominantly derived from terrestrial land plants and has not been subjected to intense oxidation these deposits are characterized by high hydrocarbon potential up to 27 kg hc t rock indicating a good potential as gas prone source rock because cape lopez canyon captures a significant part of the sediment transported by the littoral drift the siliciclastic sedimentary flux is reduced north of the canyon om is thus concentrated in the turbidites variation in toc content within turbidite laminae can be explained by the burst and sweep deposition process affecting the boundary layer of the turbulent flow this study confirms that gravity flows play a preponderant role in the accumulation and preservation of om in deep water and that deep sea turbidite systems could be regarded as an environment where organic sedimentation occurs

why were sea surface temperatures so different in the eastern equatorial atlantic in june 2005 and 2006 abstract a comparison of june 2005 and june 2006 sea surface temperatures in the eastern equatorial atlantic exhibits large variability in the properties of the equatorial cold tongue with far colder temperatures in 2005 than in 2006 this difference is found to result mainly from a time shift in the development of the cold tongue between the two years easterlies were observed to be stronger in the western tropical atlantic in april may 2005 than in april may 2006 and these winds favorably preconditioned oceanic subsurface conditions in the eastern atlantic however it is also shown that a stronger than usual intraseasonal intensification of the southeastern trades was responsible for the rapid and early intense cooling of the sea surface temperatures in mid may 2005 over a broad region extending from 20 w to the african coast and from 6 s to the equator this particular event underscores the ability of local intraseasonal wind stress variability in the gulf of guinea to initiate the cold tongue seaso

new insights on the upper layer circulation north of the gulf of guinea the oceanic circulation in the upper layers of the north of the gulf of guinea is analyzed as inferred from in situ observations and numerical simulations this particular region in spite of the presence of a coastal upwelling and its impact on resources and regional climate is still poorly documented cruises carried out in the framework of different international programs e g egee amma pirata allowed to show the existence of an eastward flowing undercurrent found under the guinea current named the guinea undercurrent guc numerical results from high resolution simulation allowed the description of the seasonal variability of this current it appears that the guc is stronger in spring and reverses westward in august september we also depict the fate and the sources of the guc based on selected trajectories from numerical particle tracking the simulated trajectories reveal i a preferred route of the guc along 4 n from cape palmas to cape three points and following the coast east of cape three points ii strong recirculations in the most eastern part of the gulf of guinea and off cape palmas including warm and salty waters of the south equatorial current iv a weak inflow from northern latitudes through a subsurface current flowing southward along the west african coast in addition lagrangian experiments show that the guc is not an extension of the north equatorial undercurrent and confirm that this current does not penetrate into the gulf of guinea this article is protected by copyright all rights reserved

a review of wave dominated clastic shoreline deposits abstract barrier islands beaches wave dominated deltas and chenier plains probably form more than one fifth of present coasts and constitute an even larger proportion of the subsiding lowland coasts likely to be preserved in the stratigraphic record the geometry vertical sequences and composition of their deposits are the result of 1 shoreline behaviour whether transgressive regressive or stable 2 physical processes particularly the relative intensities of waves and tides 3 climate 4 global tectonic setting and 5 topography of underlying deposits published interpretations indicate that equivalent deposits are abundant in the geological record sandstones are mostly quartzose cemented by carbonates and quartz and have sheet or linear geometries ancient deposits can provide evidence of palaeogeography and some are economically significant particularly as hydrocarbon reservoir rocks four end member sedimentation models are proposed for the interpretation of ancient deposits 1 transgressive sheet sands associated with deltas 2 non deltaic transgressive sheet sands 3 regressive sheet sands and 4 linear sand bodies probable depositional settings geometries characteristics of deposits and palaeocurrent patterns are discussed

sedimentology of the coal bearing mist mountain formation line creek southern canadian cordillera relationships to coal quality abstract a detailed sedimentological investigation of the jurassic cretaceous mist mountain formation in the southern canadian cordillera was undertaken to determine what if any sedimentological factors control coal quality and seam geometry in the line creek area the mist mountain formation is divisible into two units based on abundance and lateral continuity of facies the lower unit consists of alternating laterally extensive coal seams and thick widespread channel sandstones interspersed with crevasse splay and flood plain facies sediments the lower unit was deposited in an interdeltaic coastal plain environment protected from marine incursion by the beach ridge dune sandstones of the underlying morrissey formation the upper unit of the mist mountain formation was deposited in a distal alluvial fluvial flood plain environment and has similar facies to the lower unit but coal seams and channel sandstones are less laterally continuous and thinner than in the lower unit channel sandstones decrease in number and thickness up section and are replaced by an increasing abundance of coal seams flood plain and crevasse splay facies sediments seam geometry and ash data indicate that clastic sedimentation had only limited influence on peat coal accumulation in the mist mountain formation while the geometry of the seams reflects the proximity of under and overlying channel sandstones neither abundance nor mineralogy of the coal ash reflects changes in surrounding clastic sediments the mist mountain formation peat mires were thus not obviously influenced by coeval fluvial activity characteristics of the lower unit suggest peat mires developed only during hiatus in clastic deposition whereas upper unit coals appear to have formed in at least partially domed mires contemporaneous with clastic sedimentation the vitrinite content of the coal increases up section at the expense of semifusinite possibly reflecting an increase in the proportion of arborescent vegetation in the mire with time and a lower susceptibility to fires

depositional model for understanding geometry of cretaceous coals major coal seams rock springs formation green river basin wyoming the upper cretaceous rock springs formation of the green river basin ranges from marine strata of prodelta origin to marginal marine and nonmarine equivalents of delta front and delta plain fluvial strata coal exploration drill holes measured sections and underground mine data have been analyzed to reconstruct the depositional setting of the rock springs formation extensive sheet sandstones are inferred to be delta front deposits reflecting the cuspate to arcuate geometry of wave dominated deltaic deposits extensive coal deposits up to 22 ft 6 7 m thick that developed on top of delta front sandstones extend for 15 mi 24 1 km along depositional dip and 36 mi 58 km along depositional strike these coal deposits are referred to as type a coal seams coal deposits 1 17 ft 0 3 5 2 m thick that developed in upper delta plain fluvial environments are less than 20 mi 32 2 km in length these deposits are referred to as type b coal seams type c seams are persistent thin coal deposits 1 8 ft 0 3 2 4 m thick developed on top of delta plain fluvial deposits less than 25 mi 40 2 km in length and they mark the delta lobe abandonment phase approximately 15 major coal zones exist in the rock springs formation the geometry of types a b and c reflects a genetic relationship to both deltaic and fluvial units in the marginal marine and nonmarine components of the rock springs formation a model for predicting coal seam thickness and continuity is believed to be applicable to additional exploration in the green river basin and in other cretaceous coal bearing basins in the western interior

coastally trapped eddies in the north of the gulf of guinea cyclonic eddies generated downstream of cape palmas and cape three points have been suggested to contribute to the coastal upwelling along the northern coast of the gulf of guinea a numerical analysis using a high resolution model is used to investigate the mesoscale activity and the coastal upwelling generation processes an eddy detection and tracking tool is applied to altimeter and model data showing good agreement between these data sets about two cyclonic eddies per year with an average radius of 60 km were identified downstream of both capes these cyclonic eddies have an average lifetime of about 60 days during the major coastal upwelling period boreal summer and an eastward propagation these cyclonic eddies are shallow energetic their relative vorticity can reach 3 times the earth s rotation and dimensionless parameters show that they are in an eddy shedding regime mean flow interactions and barotropic instabilities associated with capes are their main generation processes an idealized experiment is conducted in order to analyze the effect of capes on eddy generation and on coastal upwelling it reveals that these cyclonic eddies generated downstream of capes are not the process responsible for this coastal upwelling this experiment also suggests that the cyclonic eddies are the cause of the westward and coastal guinea counter current that is associated with a transfer of energy from eddy kinetic to the mean flow

cyclic facies architecture as a key to depositional controls in a distal foredeep campanian mesaverde group wyoming usa the mesaverde group consists of a thick wedge of fluvial littoral deltaic and shallow marine clastics shed into the cretaceous western interior seaway of north america the western parts of the seaway lay within the strongly subsiding foredeep of the active sevier fold and thrust belt further to the west the study area is located east of the axis of maximum subsidence and is thus in a favourable position to record competing effects of eustasy sediment supply and thrust load induced subsidence facies and sequence analysis carried out on high quality outcrop and well log data led to the recognition of a complex depositional cycle hierarchy within the typical storm and wave dominated inner shelf shoreface strand plain and delta systems of the mesaverde

lagrangian sources of frontogenesis in the equatorial atlantic front estimating the processes that control the north equatorial sea surface temperature sst front on the northern edge of the cold tongue in the tropical atlantic is a key issue for understanding the dynamics of the oceanic equatorial atlantic and the west african monsoon diagnosis of the frontogenetic forcings on a realistic high resolution simulation was used to identify the processes involved in the formation and evolution of the equatorial sst front the turbulent forcing associated with the mixed layer turbulent heat flux was found to be systematically frontolytic while the dynamic forcing associated with currents was found to be frontogenetic for the equatorial sst front nevertheless the low frequency component of the turbulent forcing was frontogenetic and initiated the sst front which was then amplified and maintained by the leading dynamic forcing this forcing was mainly driven by the meridional convergence of the northern south equatorial current nsec and the guinea current which points out the essential role played by the circulation in the equatorial sst front evolution the quasi biweekly variability of the equatorial sst front and its forcings were found to be more strongly coupled to the wind energy flux wef than to the surface wind stress in fact the wef controlled the convergence divergence of the nsec and guinea current and thus the meridional component of the leading dynamic forcing the wef explains the equatorial sst front development better than the wind does because it is a coupled ocean atmosphere process

benthic foraminifera off west africa 1 n to 32 s do live assemblages from the topmost sediment reliably record environmental variability abstract recent benthic foraminifera 125 m were investigated from multicorer samples on a latitudinal transect of 20 stations between 1 n and 32 s along the upper slope off west africa samples were selected from a narrow water depth interval between 1200 and 1500 m so that changes in water masses are minimized but changes in surface productivity are important and the only significant environmental variable live rose bengal stained benthic foraminifera were counted from the surface sediment down to a maximum of 12 cm dead foraminifera were investigated in the top 5 cm of the sediment only five live and five dead benthic foraminiferal assemblages were identified using q mode principal component analysis matching distinct primary productivity provinces characterized by different systems of seasonal and permanent upwelling differences in seasonality quantity and quality of food supply are the main controlling parameters on species composition and distribution of the benthic foraminiferal faunas to test the sensitivity of foraminiferal studies based on the uppermost centimeter of sediment only a comparative q mode principal component analysis was conducted on live and dead foraminiferal data from the top 1 cm of sediment it has been demonstrated that on the upper slope off west africa most of the environmental signals as recorded by species composition and distribution of the total live and dead assemblages i e including live and dead foraminifera from the surface sediment down to 12 cm and 5 cm respectively can be extracted from the assemblages in the top centimeter of sediment only on the contrary subsurface abundance maxima of live foraminifera and dissolution of empty tests strongly bias quantitative approaches based on the calculation of standing stocks and foraminiferal numbers in the topmost centimeter

variability of the mixed layer heat budget in the eastern equatorial atlantic during 2005 2007 as inferred using argo floats we examine the variability of the sea surface temperatures in the eastern equatorial atlantic during 2005 2007 by using argo profiling floats prediction and research moored array in the atlantic buoys and satellite in situ and atmospheric data sets the eastern equatorial atlantic characterized by shallow mixed layers all yearlong is divided into nine boxes of nearly equal surface area with respect to the dynamics and thermodynamics in this region monthly mixed layer heat budgets are computed in each box from 10 day argo profiles in all the boxes the net surface heat flux is one of the main causes of the seasonal evolution of sea surface temperatures for the 3 studied years the amount of short wave radiation penetrating through the base of the mixed layer and horizontal heat advection may locally contribute to the temperature variability while entrainment has a weaker contribution to balance the heat budget a residual term exists which includes all processes that cannot be calculated with observations as well as the possible errors in the other terms this residual is more intense in the cold tongue and the northern region and exhibits a clear seasonal cycle with minimum negative values in boreal summer and maximum values in winter this residual compares well with available observations of vertical turbulent mixing collected during etude de la circulation oceanique et des echanges ocean atmosphere dans le golfe de guinee campaigns 2005 2007 in the eastern equatorial atlantic when assuming that the residual is mostly associated with vertical turbulent mixing it can be conjectured that turbulent mixing is a significant cooling source in the cold tongue and north of the equator

some overlooked features of tropical atlantic climate leading to a new nino like phenomenon abstract the atlantic nino an equatorial zonal mode akin to the pacific el nino southern oscillation enso is phase locked to boreal summer when the equatorial easterly winds intensify and the thermocline shoals in the gulf of guinea a suite of satellite and in situ observations reveals a new mode of tropical atlantic variability that displays many characteristics of the zonal mode but instead peaks in november december nd this new mode is found to be statistically independent from both the atlantic nino in the preceding summer and the pacific enso the origin of this nd zonal mode lies in an overlooked aspect of the seasonal cycle in the equatorial atlantic in november the equatorial easterly winds intensify for the second time increasing upwelling and lifting the thermocline in the gulf of guinea an analysis of high resolution climatological data shows that these dynamical changes induce a noticeable sst cooling in the central equatorial atlantic the shoaling thermocline and increased upwelli

turbidity events observed in situ along the congo submarine channel abstract as part of the multidisciplinary programme biozaire devoted to studying deep sea benthic ecosystems in the gulf of guinea particulate input and its relationship with near bottom hydrodynamics were monitored using long term moorings from 2000 to early 2005 particular attention was given to material input through the congo ex zaire submarine channel that extends 760 km from the congo river mouth to the abyssal plain 5100 m near 6 s due to its direct connection to the congo river the congo canyon and channel system are characterised by particularly active recent sediment transport during this first in situ long term monitoring along the channel an energetic turbidity event was observed in january 2004 at three locations along the channel from 3420 to 4790 m in depth this event tilted and displaced the moorings installed at 3420 m site zr and 4070 m site zd and resulted in high sediment deposition at all three mooring sites the event moved at an average velocity of 3 5 m s 1 along the numerous channel meanders between 3420 and 4070 m then at 0 7 m s 1 between 4070 m and the end of the channel at 4790 m the particle cloud rose above the top of the valley at 4070 m site zd but not at 3420 m site zr where the channel was too deep lastly the mooring line broke at site zd in october 2004 probably due to a strong event like that of 2001 previously described by khripounoff et al khripounoff a vangriesheim a babonneau n crassous p denniellou b savoye b 2003 direct observation of intense turbidity activity in the zaire submarine valley at 4000 m water depth marine geology 194 151 158 between these strong events several peaks of high turbidity and particle flux occurred but without noticeable current increases these events were probably due to local sliding of sediment accumulated on the walls or terraces on the side of the channel the area near 4000 m depth and the lobe appear to be the main depocentres of particulate input rich in organic matter derived from the congo river

a numerical model for low frequency equatorial dynamics a f st efficient numerical procedure for modeling the linear low frequency motions on an equatorial beta plane is develo the model is capable of simulating the seasonal and interannual variability in realistically shaped ocean basins forc d by realistic winds the timestep allowed is the order of days rather than hours as allowed by more conventional schemes the numerical method is designed around the special characteristics f low frequency equato al waves a crucial element is the formulation of proper boundary conditions including those for a partial boundary such as the western end of the gulf of guinea the resp nse of an a i ntic shaped basin to a periodic wind is compared with the analytic results of cane and sarachlk for a mendlonally unbounded ocean the response along the equator is essentially the same narrow boundary layer forms along the guinea coast too narrow to be a single coastally trapped wave it is the sum of many modes the near lack of phase variation along the coast and the smallness of the phase difference be ween the equator and the coast are additional contrasts to the results for an initial value probl m studied by moore and others the implication is that the annually recurring upwelling in the gulf of guinea cannot be adequately modeled as the response to an impulsively applied wind stress

numerical simulation of the observed near surface east india coastal current on the continental slope we simulate the east india coastal current eicc using two numerical models resolution 0 1 circ times 0 1 circ an oceanic general circulation model ogcm called modular ocean model and a simpler linear continuously stratified lcs model and compare the simulated current with observations from moorings equipped with acoustic doppler current profilers deployed on the continental slope in the western bay of bengal bob we also carry out numerical experiments to analyse the processes both models simulate well the annual cycle of the eicc but the performance degrades for the intra annual and intraseasonal components in a model resolution experiment both models run at a coarser resolution of 0 25 circ times 0 25 circ simulate well the currents in the equatorial indian ocean eio but the performance of the high resolution lcs model as well as the coarse resolution ogcm which is good in the eicc regime degrades in the eastern and northern bob an experiment on forcing mechanisms shows that the annual eicc is largely forced by the local alongshore winds in the western bob and remote forcing due to ekman pumping over the bob but forcing from the eio has a strong impact on the intra annual eicc at intraseasonal periods local equatorial forcing dominates in the south north because the kelvin wave propagates equatorward in the western bob a stratification experiment with the lcs model shows that changing the background stratification from eio to bob leads to a stronger surface eicc owing to strong coupling of higher order vertical modes with wind forcing for the bob profiles these high order modes which lead to energy propagating down into the ocean in the form of beams are important only for the current and do not contribute significantly to the sea level

depositional environment sediment provenance and oxygen isotope paleoaltimetry of the early paleogene greater green river basin southwestern wyoming u s a depositional process sediment provenance and paleotopography are critical to paleogeographic reconstruction during the coeval laramide and sevier orogenies in the cordillera orogenic system here we conduct lithofacies analysis sediment provenance and paleoelevation studies in the fluvial lower paleogene fort union and the main body of the wasatch formations in the center of the greater green river basin in order to reconstruct paleogeography the depositional environment changed from low energy floodplains and associated meandering river during the paleocene to braided rivers during the earliest eocene the lowermost eocene strata have more precambrian basement derived feldspar grains compared to the paleocene strata this change in sediment provenance was associated with the change to dominant northwestward paleoflow direction suggesting major uplift of the laramide uinta mountains during the earliest eocene the 18o values of authigenic carbonates were stable during the early paleocene but decreased gradually from 10 permil during the late paleocene to 18 permil during the earliest eocene suggesting the lack of highland precipitation in the basin catchment during the early paleocene and significant surface uplift and arrival of highland precipitation from the uinta mountains during the earliest eocene the reconstructed paleoelevation of the uinta mountains was at least 3 km possibly greater than 3 5 km and the paleoelevation of the greater green river basin floor was at most 1 km and the paleorelief between the greater green river basin and uinta mountains was 2 km during the earliest eocene our record of the earliest eocene establishment of high topography of the uinta mountains through renewed uplift is 4 to 6 myr older than previously thought if the carbonate cements in the fort union formation record the isotope compositions of surface water from the sevier orogen their high 18o values likely suggest that the sevier orogen had rugged topography during the paleocene

propagation of the seasonal upwelling in the eastern equatorial atlantic abstract several mechanisms have been proposed to explain the coastal and equatorial upwelling in the eastern atlantic guinea gulf the most controversial is the mechanism of remote wind forcing in the western equatorial atlantic suggested by moore et al 1978 most of the possible explanations for the upwelling and their relative importance are discussed in view of recent observations detailed analysis of daily sea surface temperature sst collected at 16 coastal stations along the northern coast of the guinea gulf reveals that the upwelling event propagates westward along this coast at a mean speed of 0 7 m s 1 similar analysis of historical monthly mean sst data shows that the coastal upwelling event propagates poleward from 1 s to at least 13 s at the same phase speed furthermore the northern hemisphere and southern hemisphere coastal upwelling signals seem to start at the same time from the equator the same kind of analysis applied to hydrographic data from a station situated 41 km off abid

a composite tectonic eustatic origin for shelf sandstones at the cambrian ordovician boundary in north greenland shelf sandstones deposited at the cambrian ordovician boundary in central and western north greenland have a sheet like large scale geometry and extend for over 300 km along strike within a shallow marine carbonate dominated platform sequence conodont faunas from units above and below the most extensive sand sheet the kap coppinger member of the cass fjord formation and the permin land formation indicate that deposition of the sands spanned the proavus intermedius and lindstromi conodont biozones sand was derived by reworking of older quartzite dominated formations following the uplift and unroofing of a platform bulge to the east during the cambrian this sediment was transported northwards from the uplifted area across an unstable platform into a deep water trough however during sea level lowstands within the cambrian ordovician boundary interval this clastic material was deflected westwards and transported across the stable platform by progradation of tide and storm dominated shorelines facies sequences in the thickest part of the permin land formation suggest at least three such regressive cycles combined to form a composite sand body each regressive cycle comprises a shallowing upward transition from tide and storm deposited marine sediments to clean sandstones of marine or terrestrial origin the cycles are separated by thin but laterally extensive dolomites interpreted to represent drowning events thinner sequences further to the east are attributed to reduced accommodation space as a consequence of lower subsidence rates close to the uplifted source area whilst thin sequences in the west are ascribed to the effect of increasing distance from the sediment source so that only the youngest of the three regressive cycles is present

paleoclimate of the kimmeridgian tithonian late jurassic world i results using a general circulation model abstract the kimmeridgian tithonian 154 7 145 6 ma middle and late late jurassic was a time of expanded continental rifting increased sea floor spreading and a relatively high eustatic sea level stand these processes collectively caused the fragmentation and flooding of the megacontinent pangea as well as the alteration of the global paleoclimate using a version of the community climate model ccm from the national center for atmospheric research we report two kimmeridgian tithonian paleoclimate seasonal simulations with geologically inferred paleotopography one using a co 2 concentration of 280 ppm pre industrial level and the other 1120 ppm increasing the co 2 four fold warms virtually the entire planet the greatest warming occurs over the higher latitude oceans and the least over the equatorial and subtropical regions simulation of a warmer planet with an elevated greenhouse effect fits the distribution of paleoclimatically sensitive faunas floras and sedimentary rocks model results indicate that sea ice was restricted to the high latitudes of the boreal and austral seas making landfall only in restricted areas the trade winds bring heavy rainfall in december january february to eastern gondwana and in june july august to the tethys sea margins a strong june july august monsoon occurs over southeast asia the distribution of coals correlates to precipitation sufficient to maintain gymnosperm forests and coastal areas where water saturated sediments are a result of eustatic high stands of sea level evaporites are localized to areas of negative precipitation evaporation runoff is restricted to regions of intense precipitation overall the 1120 ppm co 2 simulation provides a reasonable paleoclimate for the kimmeridgian tithonian and provides a standard until a ccm with oceanic heat transport a coupled atmospheric oceanic model or one with a finer grid cell configuration is available the results need further scrutiny in areas with more detailed geologic information

on the response of the equatorial thermocline in the atlantic ocean to the seasonally varying trade winds measurements made during the seasonal response of the equatorial atlantic experiment in 1983 when the easterly trade winds near the equator ceased and then intensified as part of their annual cycle show a sequence of events leading to an adjusted thermocline both the duration and extent of the downwelling and upwelling associated with the adjustment process were zonally inhomogeneous along the equator an analytical reduced gravity model was driven by a hierarchy of easterly wind stress forcing functions representative of the atlantic to compare the integral nature of the forced long wave responses with the observations qualitative agreement was found with upwelling and downwelling sequences within the forced region increasing to the east as observed apparent model propagation speeds differed significantly from the prescribed model wave speeds within the forced region owing to the growth parameters of the winds and boundary reflections distorted the responses to the east of the forced region the resulting interference patterns tended to separate the region 0 10 w along the equator from the african coast as one of maximum upwelling

cross equatorial structure and temporal modulation of intraseasonal variability at the surface of the tropical atlantic ocean intraseasonal variability 10 50 days in the equatorial atlantic ocean is analyzed from multiyear 1999 2005 satellite gridded products of sea level anomalies sla and sea surface temperature sst two regions with distinct intraseasonal variability have been identified the first one west of 10 degrees w is dominated by westward propagating anomalies with maximum values in sla along 5 degrees n and in sst along 2 degrees n they occur in boreal summer with periods of 25 50 days and are known to correspond to tropical instability waves tiws we show that tiws have also a signature though weaker south of the equator especially along 5 degrees s in sla northern and southern anomalies propagate together westward being mostly out of phase suggesting that equatorial wave dynamics is involved in tiws variability an sst signature of tiws is also observed near 2 degrees s in quadrature with sst anomalies detected in the northern hemisphere the interannual modulations of the tiw signature in sla and sst are compared and discussed the second dominant intraseasonal signal is only seen east of 10 degrees w in sst and corresponds to an equatorially trapped variability confined to the gulf of guinea with periods between 10 and 20 days this signal is present in boreal summer when an intense sst front is observed just north of the equator intraseasonal variability with comparable periods is also observed in the meridional wind stress throughout the year comparison of sst and meridional wind stress anomalies suggests that the 10 to 20 day variability in sst is forced by the wind stress but seasonally modulated by the presence of the sst front

on the north brazilian eddy field abstract the region of large eddies occurring off the coast of brazil between approximately 3 n 10 n is revealed in some detail by repeated temperature observations on the along shore sea lane by ships of opportunity augmented by one airborne xbt expendable bathythermograph survey the general pattern of the circulation implied by the temperature structure is similar to that indicated by past hydrographic measurements and drifter tracks in general a large anticyclonic eddy to the north 7 n 10 n as well as a southern eddy like feature 3 n 6 n appear to be permanent patterns of the western north equatorial circulation this pattern somewhat resembles that found in the somali basin during the southwest monsoon

coupling between the atlantic cold tongue and the west african monsoon in boreal spring and summer 1 the formation of the atlantic cold tongue act is the dominant seasonal sea surface temperature signal in the eastern equatorial atlantic eea a comprehensive analysis of variability in its spatial extent temperature and onset is presented then the physical mechanisms which initiate act onset as well as the feedbacks from the act to the maritime boundary layer and how the act influences the onset of the west african monsoon wam are discussed we argue that in the eea the air sea coupling between the act and wam occurs in two phases from march to mid june the act results from the intensification of the southeastern trades associated with the st helena anticyclone steering of surface winds by the basin shape of the eea imparts optimal wind stress for generating the maximum upwelling south of the equator during the second phase mid june august wind speeds north of the equator increase as a result of the northward progression of the intensifying trades and as a result of significant surface heat flux gradients produced by the differential cooling between the act and the tropical waters circulating in the gulf of guinea gg it is anticipated that the atmospheric divergence induced at low levels north of the equator reduces convection over the gg and that increased northward winds shift convection over land correlations between the act and the wam onset dates over the last 26 years 1982 2007 measure as much as 0 8 this suggests that the act plays a key role in the wam onset

intraseasonal mixed layer heat budget in the equatorial atlantic during the cold tongue development in 2006 1 estimating the mixed layer heat budget is a key issue for understanding the cold tongue development in the eastern equatorial atlantic a high resolution ocean regional model is used to diagnose the mixed layer heat budget online during the egee 3 experiment from may to august 2006 the heat budget shows the major role of the horizontal advection and turbulent mixing in the mixed layer temperature balance in the cold tongue the surface net heat flux and entrainment processes play a minor role the equatorial cooling is mainly induced by low frequency advection which is balanced by high frequency zonal and meridional advections the high frequency advections are organized in patterns along the northern edge of the cold tongue where they are associated with strong sea surface temperature gradients and well developed tropical instability waves in the western atlantic special attention is paid to the wind energy flux which controls horizontal advection and turbulent mixing we suggest that the wind energy flux drives the vertical velocity which in turn adjusts the mixed layer depth its stratification and the vertical shear of the horizontal current although vertical advection is not essential in providing cold water in the atlantic cold tongue it is shown that the vertical velocity plays a central role in preconditioning the mixed layer and maximizes the turbulent mixing