ostracodes and paleoenvironments of the late quaternary don and scarborough formations toronto ontario type section exposures at the don valley brickyard and scarborough bluffs were studied for ostracode occurrences in all 12 species were identified from the don formation with candona rawsoni and

successions of invertebrate microfossils and the late quaternary deglaciation of the central st lawrence lowland canada and united states abstract foraminiferal and ostracode assemblages in late glacial and early post glacial sediments of the central st lawrence lowland show that a proglacial lake glacial lake st lawrence preceded the champlain sea in some parts of the lowland and that the champlain sea was in contact with the laurentide ice sheet during deglaciation of other parts of the lowland glaciolacustrine and glaciomarine environments were followed by marine environments with salinity as high as 24 34 the higher salinity water in the champlain sea was part of a salt water wedge extending from the gulf of st lawrence into the central st lawrence lowland the beginning of the champlain sea is placed between 11 4 and 11 6 ka bp on the basis of radiocarbon ages for the arrival of the salt water wedge in the central st lawrence lowland the distribution of rhythmites associated with glacial lake st lawrence shows that subaqueous outwash fans in the ottawa area were deposited in glacial lake st lawrence rather than in the champlain sea

convection over tropical africa and the atlantic ocean during northern summer part ii modulation by easterly waves abstract using meteosat data and european centre for medium range weather forecast ecmwf analyses we examine easterly waves and their relation with the cloudiness over west africa and the tropical atlantic ocean for three summers june july august and september 1983 85 spectral analysis of the low level meridional wind in the 2 8 5 1 day band reveals maximum wave amplitude near the west african coast at 20 n during august and september the wave amplitude is larger than during june and july and a secondary maximum appears around 7 5 n composites of the mean structure of the wave and the associated cloud modulation reveal consistent relationship between observed cloudiness and ecmwf analyses the phase of the wave modulation of the cloudiness is strongly dependent on the geographical location in response to changes in the mean climatological conditions this phase varies however grossly in four large land and ocean regions centered at 7 5 and 17 5 n respectively for which we derive vertical cro

stratigraphy paleoecology and glacial history of the gillam area manitoba sections along the nelson river in northern manitoba outcropping upstream and downstream from limestone dam record a long succession of late quaternary events the oldest sediment exposed consists of sandy nonfossiliferous sundance till of northwestern provenance and related to a kansan or illinoian glaciation the paleosol developed in the sundance till is assigned to the yarmouthian or sangamon interglacial on its stratigraphic position and depth of weathering fossiliferous clayey amery till of eastern provenance overlies the sundance till and underlies the nonglacial nelson river sediments aspartic acid d l ratios of wood fragments from the nelson river sediments correlate with an aspartic acid d l ratio of similar wood from the missinaibi formation in ontario beetle analysis indicates the nelson river sediments were deposited north of the tree line under conditions more severe than those found in the area today the deposits are believed to be of latest sangamon or possibly mid wisconsinan age

thermoluminescence dating studies of glacial silts from ontario to develop procedures for the direct dating of glacially related silts by thermoluminescence tl i have applied previously proposed techniques to three polymineralic 4 11 m samples from the toronto area furthermore one of these samples was studied in detail by isolating some mineral fractions the principal conclusion is that the tl of the lodgment halton till from woodbridge was not significantly reset during deposition whereas the tl of the waterlaid upper thorncliffe silt from the scarborough bluffs was reset as was the tl of the third sample wc st a massive silt from woodbridge that has been generally correlated with the glaciolacustrine sunnybrook diamict at the bluffs this conclusion follows from the observation of feldspar tl apparent ages of 140 ka for the 12 ka bp halton till and of 36 and 66 ka for the upper thorncliffe and wc st samples respectively the four laboratory factors that contributed most to inaccuracies in the tl apparent ages were 1 anomalous fading in the felds

case study of a developing african easterly wave during namma an energetic point of view abstract the west african perturbation that subsequently evolved into hurricane helene 2006 during nasa s african monsoon multidisciplinary analysis namma 15 august 14 september 2006 and amma s third special observing period sop 3 15 29 september 2006 has been simulated with the nonhydrostatic meso nh model using parameterized convection the simulated disturbance evolved over west africa and the adjacent eastern tropical atlantic through interactions between different processes at the convective scale mesoscale and synoptic scale the aim of this paper is to quantify the energetics of the simulated disturbance a set of energy equations is first developed in the hydrostatic case to solve the limitations of lorenz s analysis when applied to a finite domain it is shown that this approach is also valid in the compressible and in the anelastic case in order to apply it to the meso nh results application to the simulated pre helene disturbance allows one to determine the most important terms in

energetics of east pacific easterly waves during intraseasonal events abstractthe background atmospheric state of the east pacific warm pool in which easterly waves develop varies dramatically on intraseasonal time scales east pacific intraseasonal variability is well known to modulate local convective and circulation patterns westerly easterly intraseasonal phases are associated with westerly easterly low level wind and positive negative convective anomalies this study investigates the perturbation available potential energy pape and perturbation kinetic energy pke budgets of easterly waves composited during westerly easterly and neutral intraseasonal phases respectively the mechanisms magnitudes locations and vertical structures of easterly waves are shown to strongly vary as a function of intraseasonal phase easterly waves draw energy from low level barotropic conversion regardless of phase although the location and magnitude of the conversion varies strongly during neutral and westerly intraseasonal phases the generation of pape associated with

paired isotope records of carbonate and organic matter from the middle ordovician of argentina intrabasinal variation and effects of the marine chemocline abstract we investigate the expression of the middle darriwilian isotope carbon excursion mdice across marine shelf environments in the argentine precordillera previous work identified the mdice in the las chacritas formation in argentina but did not recognize the expression of the mdice in time equivalent strata of the deeper water las aguaditas formation albanesi et al 2013 palaeogeography palaeoclimatology palaeoecology v 398 p 48 66 recent biostratigraphic investigations of these units have for the first time provided the opportunity for high resolution correlation which suggest that the mdice or at least the initiation of the mdice should be observed in both the las chacritas and las aguaditas formations here we present new paired carbon isotope data of carbonate and organic carbon from the las chacritas and las aguaditas formations we identify a 2 positive shift in the isotopic composition of marine carbonate in the las chacritas formation whereas values abruptly fall to

magnesium content of non marine ostracod shells a new palaeosalinometer and palaeothermometer abstract ostracods are microcrustaceans with calcitic carapaces each consisting of two valves or shells that grow by moulting and regeneration of sequentially larger valves up to nine times before reaching maturity the mg content of these valves is species dependent and is a function of their growth stage and the temperature salinity mg content and mg ca ratio of their host water newly formed partly calcified valves of the non marine nektic ostracod mytilocypris henricae have high mg contents 100 000 ppm mg in caco3 at individual shell weights of 2 g this relative mg content decreases as calcification proceeds until shell weights exceed 120 g whereupon the mg content is constant and useful as an indicator of the ostracod s environment mg ca ratios in individual ostracod valves from several species of the genera mytilocypris and australocypris from culture experiments and a series of australian lakes indicate that the valve s mg content increases as a function of increasing temperature and salinity within the range 11 25 c and for waters containing 24 2325 ppm mg the molar mg ca ratio in these ostracods fully calcified valves increases by 0 0015 or 370 ppm mg in caco3 per 1 c and per change of 125 ppm mg in solution for most mainland australian lakes a change in water composition of 125 ppm mg corresponds to a change of 3 5 in salinity for a given mg content of a lake the mg ca ratio of the water may vary within the range of common lacustrine values without significantly affecting mg uptake in the ostracod valves these relationships can provide palaeosalinities and or palaeotemperatures for ostracods recovered from continental sediments for mg partitioning an increase in temperature and salinity produce increased mg content in ostracods whereas for 18o fractionation in biogenic calcite an increase in temperature produces a decrease in 18o of the ostracod and an increase in salinity leads to an increase in 18o of the ostracod thus a combination of 18o and mg measurements on non marine ostracods should enable unique resolution of palaeotemperature and palaeosalinity variations

bentonite geochronology marine geochemistry and the great ordovician biodiversification event gobe abstract attribution of ordovician climate forcing to explosive volcanism and the potential global importance of volcanism in ordovician biodiversification suggest the necessity of evaluating the relationships between k bentonite deposition and increasingly high resolution records of marine biogeochemical change globally ordovician strata preserve an extensive record of explosive volcanism including the widely recognized lower to middle ordovician famatina k bentonite suite in argentina and the upper ordovician millbrig deicke kinnekulle suite of north america and europe here we present high resolution id tims u pb zircon ages of k bentonites from measured sections of the san juan formation talacasto and cerro la chilca section of the argentine precordillera k bentonites from the argentine precordillera provide stratigraphically consistent i e younging upward ages that range from 473 45 0 70 ma to 469 53 0 62 ma and constrain the age of a low magnitude 2 globally recorded negative carbon isotope excursion evaluation of the timing of k bentonite deposition in the argentina precordillera relative to marine biostratigraphic and biogeochemical records provides insight into relationships between explosive volcanism and regional to global environmental change from a regional standpoint these ages provide critical direct evidence for a dapingian to earliest darriwilian age of the upper san juan formation at sampled localities these ages are consistent with carbon isotope data suggesting that the san juan formation in the region of its type section is coeval with only the base of the often correlated table head group of western newfoundland this data thus highlights the difficulties in using regional biostratigraphic data particularly within erosionally truncated or otherwise diachronous units to define the timeframe of carbon isotope chemostratigraphy new geochronological data also indicate that a discrete negative carbon isotope excursion within the san juan and table head formations is correlative to a globally recognized pre mdice negative excursion and indicates that this aspect of the marine carbon isotope record can be used as a discrete chronologic marker san juan formation bentonites however cannot be discretely correlated with observed environmentally significant changes in the middle ordovician marine geochemical records of carbon sulfur strontium or sea surface temperature these results suggest that the extent of volcanism represented by the famatina bentonite suite was insufficient to affect global surface environments and that the relationship between explosive volcanism and environmental change may not be straightforward as previously suggested

monsoons itczs and the concept of the global monsoon earth s tropical and subtropical rainbands such as intertropical convergence zones itczs and monsoons are complex systems governed by both large scale constraints on the atmospheric general circulation and regional interactions with continents and orography and coupled to the ocean monsoons have historically been considered as regional large scale sea breeze circulations driven by land sea contrast more recently a perspective has emerged of a global monsoon a global scale solstitial mode that dominates the annual variation of tropical and subtropical precipitation this results from the seasonal variation of the global tropical atmospheric overturning and migration of the associated convergence zone regional subsystems are embedded in this global monsoon localized by surface boundary conditions parallel with this much theoretical progress has been made on the fundamental dynamics of the seasonal hadley cells and convergence zones via the use of hierarchical modeling approaches including aquaplanets here we review the theoretical progress made and explore the extent to which these advances can help synthesize theory with observations to better understand differing characteristics of regional monsoons and their responses to certain forcings after summarizing the dynamical and energetic balances that distinguish an itcz from a monsoon we show that this theoretical framework provides strong support for the migrating convergence zone picture and allows constraints on the circulation to be identified via the momentum and energy budgets limitations of current theories are discussed including the need for a better understanding of the influence of zonal asymmetries and transients on the large scale tropical circulation

the genesis of african easterly waves by upstream development abstracta genesis mechanism for african easterly waves aews is proposed in the same manner that new troughs and ridges in the midlatitudes form downstream of existing ones through a mechanism known as downstream development it is proposed that new aews can be generated upstream of existing aews a local eddy kinetic energy budget of the aew that ultimately became hurricane alberto 2000 demonstrates that upstream development explains its genesis more convincingly than previous theories of aew genesis the energetics and ageostrophic secondary circulation of a composite aew are consistent with a new aew forming as a result of this mechanism some strengths and weaknesses of upstream development as a paradigm for aew genesis are discussed with respect to other potential mechanisms

storm influenced deltas and ice scouring in a late pleistocene glacial lake this paper identifies the sedimentary record of storms and bottom scouring ice masses that is preserved in upper pleistocene glaciolacustrine delta sediments deltaic sedimentation occurred on the margin of an enlarged ice dammed ancestral lake ontario with a surface elevation at least 80 m above the modern level beds of amalgamated hummocky and swaley cross strata separated by fairweather muds represent delta front storm deposits and overlie laminated prodelta clays the central and thickest part of a 5 km long outcrop exposes variably cross stratified sand in multiple channels inset within tabular sheets of rippled sand this complex represents a broad distributary channel system about 1 6 km wide and 20 m deep cut into delta front storm sequences a large scour and related deformation structures are attributed to bottom dragging ice masses possibly pressure ridged lake ice the depositional setting outlined in this paper emphasizes the importance of storm waves in large continental glacial lakes and provides a contrast with better known low energy conditions in small glacial lake basins

convectively coupled kelvin waves over tropical africa during the boreal summer structure and variability the structure and variability of convectively coupled kelvin waves during the boreal summer are explored using satellite observed brightness temperature data and ecmwf reanalyses kelvin wave activity is most prominent between the central and eastern pacific across africa and the indian ocean composite analysis shows that over sub saharan africa kelvin wave convection is peaked north of the equator while the dynamical fields tend to be symmetric with respect to the equator convectively coupled kelvin waves propagate faster over the pacific and western atlantic 24 m s 1 and slow down over tropical africa 14 m s 1 consistent with stronger coupling between the dynamics and convection over tropical africa the kelvin waves observed over africa generally propagate into the region from anywhere between the eastern pacific and the atlantic and decay over the eastern indian ocean basin results show marked interannual variability of kelvin wave activity over africa anomalously high kelvin wave variance tends to occur during dry years while low variance occurs during wet years african kelvin wave activity is positively correlated with sst anomalies in the equatorial east pacific the same warm sst anomalies that are favorable for enhanced kelvin wave activity suppress the mean rainfall over tropical africa via a more slowly varying teleconnection and associated subsidence a brief analysis of an intense kelvin wave in august 1987 a dry year shows a clear impact of the wave on convective development and daily rainfall over tropical africa this kelvin wave was also associated with a series of easterly wave initiations over tropical africa

global mass wasting during the middle ordovician meteoritic trigger or plate tectonic environment abstract mass wasting at continental margins on a global scale during the middle ordovician has recently been related to high meteorite influx although a high meteorite influx during the ordovician should not be neglected we challenge the idea that mass wasting was mainly produced by meteorite impacts over a period of almost 10 ma having strong arguments against the impact related hypothesis we propose an alternative explanation which is based on a re evaluation of the mass wasting sites considering their plate tectonic distribution and the global sea level curve a striking and important feature is the distribution of most of the mass wasting sites along continental margins characterised by periods of magmatism terrane accretion and continental or back arc rifting respectively related to subduction of oceanic lithosphere such processes are commonly connected with seismic activity causing earthquakes which can cause downslope movement of sediment and rock considering all that it seems more likely that most of this mass wasting was triggered by earthquakes related to plate tectonic processes which caused destabilisation of continental margins resulting in megabreccias and debris flows moreover the period of mass wasting coincides with sea level drops during global sea level lowstand in some cases sea level drops can release pore water overpressure reducing sediment strength and hence promoting instability of sediment at continental margins reduced pore water overpressure can also destabilise gas hydrate bearing sediment causing slope failure and thus resulting in submarine mass wasting overall the global mass wasting during the middle ordovician does not need meteoritic trigger

sediment gravity flow deposits of an ordovician deep sea fan system western precordillera argentina abstract ordovician siliciclastic sequences of portezuelo del tontal formation ptf in the western precordillera argentina are interpreted to be deep sea deposits which formed on a passive continental margin several facies and layer divisions have been identified and interpreted as high and low density turbidites debrites and contourites hemipelagites outer and inner upper middle submarine fan subenvironments have been recognized outer fan associations consist of lobe and lobe fringe sequences inner fan associations are defined by coarse grained and channelized deposits the vertical arrangement of facies associations is interpreted in terms of progradational and retrogradational processes some sharp progradational and retrogradational transitions were controlled by allocyclic factors such as sea level changes and tectonics of the source areas the submarine fan model for the ptf is an intermediate type between the pelite rich and the sand rich fans it was formed in a narrow and elongate deep sea basin controlled by the contemporaneous evolution of an oceanic rift in the direction of progradation

structural evolution of the argentine precordillera the rio san juan section abstract the argentine precordillera ap represents a high level fold and thrust belt which was formed during the andean tertiary crustal shortening in a w e transect studied mostly e directed imbrications are combined with folding and involve a pile of cambrian to tertiary sediments the thrust belt is detached above a main decollement within the ordovician to lower devonian strata to the east it is bounded by a back thrust zone directed westwards restored sections allow an estimate of crustal shortening and also provide insight into the structural development during pre tertiary times carbonate platform sequences of cambrian to ordovician age grade into a volcani clastic succession with transitional melanges representing deposits along a western continental slope in the western and easternmost parts of the ap cambrian to silurian deposits are affected by a first folding which to the west is combined with a slight metamorphic overprint during carboniferous to permian times intensified mobility along the eastern rim and in the western parts of the ap leads to crustal extension which partly was triggered by the formation of synsedimentary normal faults in the central ap no angular unconformities at the base of carboniferous permian deposits were found there was no field evidence found to postulate a terrane boundary within the ap area and an onset of thrust tectonics during cretaceous to early tertiary times

quaternary sequences along the north shore of lake ontario oshawa port hope we describe six major stratigraphic units from the hitherto neglected quaternary sequences along the north shore of lake ontario between oshawa and port hope these units from the base upwards co

darriwilian middle ordovician delta c 13 carb chemostratigraphy in the precordillera of argentina documentation of the middle darriwilian isotope carbon excursion mdice and its use for intercontinental correlation although documented from estonia latvia sweden eastern north america and china the middle ordovician darriwilian positive delta c 13 excursion known as the mdice has previously not been recognized with certainty in south america the most promising region in south america for detailed middle ordovician carbon isotope research is the precordillera of western argentina where there are many excellent exposures of biostratigraphically well dated carbonate successions spaning the tremadocian through sandbian stratigraphic interval for this project we collected numerous isotope and conodont samples from the middle darriwilian las chacritas and aguaditas formations at their type localities which yielded important biostratigraphic data as well as informative delta c 13 carb values in the e pseudoplanus zone in the upper half of the las chacritas formation there is a relatively modest but distinct delta c 13 carb excursion because its stratigraphic position and magnitude closely agree with the mdice in other parts of the world we recognize it as the first firm record of this excursion in south america the fact that the delta c 13 carb curve from the las aguaditas formation shows no such excursion is due to the existence of a stratigraphic gap between the lower and middle members of this formation that cuts out the excursion interval the precordilleran mdice is used for detailed long range correlations with successions in baltoscandia newfoundland and china illustrating the usefulness of also this delta c 13 carb excursion as a global stratigraphic tool a recent proposal of a greatly extended chronostratigraphic range of the table head group on newfoundland is rejected based on well established biostratigraphic evidence c 2013 elsevier b v all rights reserved less

chronology of late wisconsinan glaciation in middle north america abstract we propose a chronology of late wisconsinan glacial fluctuations in middle north america from alberta to wisconsin based on radiocarbon dates derived solely from wood previous chronologies of the southwestern margin of the north american continental ice sheet have depended to a considerable degree on radiocarbon dates from fine grained organic sediment this material is commonly contaminated with older carbon resulting in chronologic confusion by using only dates from wood much of the confusion disappears however because of the scarcity of wood dates only four of the sixteen identified fluctuations are accurately dated an advance into iowa about 14 000 to 13 500 bp an advance into south dakota and iowa about 12 300 bp an advance into the lake michigan basin about 11 700 bp and an advance into the lake superior basin about 9900 bp in addition the beginning of late wisconsinan glaciation before 20 000 bp is fairly well documented none of the fluctuations in the western part of the region are accurately dated

synoptic scale disturbances near the equator abstract a spectral analysis of winds analyzed and initialized at the european centre for medium range weather forecasts reveals an abundance of power in the 850 mb meridional wind along the equator with periods near four days the power is mostly in the westward propagating component using high pass filtered data it is shown that the waves have westward phase and eastward group propagation relative to the mean wind the longest wavelengths are found over the pacific ocean while the shortest are found over the convectively variable regions of indonesia south america and africa mean phase speeds at 850 mb are positively correlated with the mean wind on the equator at 500 mb and below and negatively correlated with the mean wind above that level the effective advecting zonal wind of the disturbances seems to be the density weighted average of the lower troposphere the structure of the disturbances bears resemblance to the expected structure of an equatorially trapped mixed rossby gravity wave over t

easterly wave regimes and associated convection over west africa and tropical atlantic results from the ncep ncar and ecmwf reanalyses ncep ncar and ecmwf daily reanalyses are used to investigate the synoptic variability of easterly waves over west africa and tropical atlantic at 700 hpa in northern summer between 1979 1995 1979 1993 for ecmwf spectral analysis of the meridional wind component at 700 hpa highlighted two main periodicity bands between 3 and 5 days and 6 and 9 days the 3 5 day easterly wave regime has already been widely investigated but only on shorter datasets these waves grow both north and south of the african easterly jet aej the two main tracks noted over west africa at 5 n and 15 n converge over the atlantic on latitude 17 5 n these waves are more active in august september than in june july their average wavelength phase speed varies from about 3000 km 8 m s 1 north of the jet to 5000 km 12 m s 1 south of the jet rainfall convection and monsoon flux are significantly modulated by these waves convection in the inter tropical convergence zone itcz being enhanced in the trough and ahead of it with a wide meridional extension compared to the 3 5 day waves the 6 9 day regime is intermittent and the corresponding wind field pattern has both similar and contrasting characteristics the only main track is located north of the aej along 17 5 n both over west africa and the atlantic the mean wavelength is higher about 5000 km long and the average phase speed is about 7 m s 1 then the wind field perturbation is mostly evident at the aej latitude and north of it the perturbation structure is similar to that of 3 5 days in the north except that the more developed circulation centers moving more to the north lead to a large modulation of the jet zonal wind component south of the aej the wind field perturbation is weaker and quite different the zonal wind core of the jet appears to be an almost symmetric axis in the 6 9 day wind field pattern a clockwise circulation north of the aej being associated with a counter clockwise circulation south of the jet and vice versa these 6 9 day easterly waves also affect significantly rainfall convection and monsoon flux but in a different way inducing large zonal convective bands in the itcz mostly in the trough and behind it as opposed to the 3 5 day wave regime these rainfall anomalies are associated with anomalies of opposite sign over the guinea coast and the sahelian regions over the continent these waves are more active in june july and in august september over the ocean gate phase i gave an example of such an active 6 9 day wave pattern considered as a sequence of weak easterly wave activity this phase was also a sequence of high 6 9 day easterly wave activity we suggest that the 6 9 day regime results from an interaction between the 3 5 day easterly wave regime maintained by the barotropic baroclinic instability of the aej and the development of strong anticyclonic circulations north of the jet over west africa and both north and south of the jet over the atlantic significantly affecting the jet zonal wind component the permanent subtropical anticyclones azores libya st helena could help initiation and maintenance of such regime over west africa and tropical atlantic based on an a priori period band criterion our synoptic classification has enabled us to point out two statistical and meteorological easterly wave regimes over west africa and tropical atlantic ncep ncar and ecmwf reanalyses are in good agreement the main difference being a more developed easterly wave activity in the ncep ncar reanalyses especially for the 3 5 day regime over the atlantic

regional differences in the kinematic and thermodynamic structure of african easterly waves this study examines regional differences in the structure of african easterly waves aews at four locations between east africa and the east atlantic in a 12 yr 1998 2009 climatology we focus on the cold core convectively active portions of the aews which are typically found between 5 and 15 n african easterly wave composites are produced from three reanalyses using the tracks of synoptic scale middle tropospheric vorticity maxima the vertical structure of temperature and vorticity in the composite aews are related to regional differences in the climatological and vortex centred diabatic heating and diabatic potential vorticity pv generation profiles from the reanalyses in addition differences in aew structure and activity between the three reanalyses are related to differences in rainfall and diabatic heating between the reanalyses the climatological diabatic heating over east africa which is associated mostly with latent heating peaks at 450 hpa with diabatic cooling below 750 hpa in contrast the convectively active west african coast and the east atlantic have increased diabatic heating in the lower troposphere due to these regional differences in diabatic heating diabatic pv generation peaks near 700 hpa over the continent and below 800 hpa over the east atlantic moving westwards from east africa to the east atlantic aew composites have weaker lower tropospheric cold cores and significantly increased lower tropospheric vorticity within the convectively active troughs the shape of the diabatic heating and pv generation profiles within the trough of the regional aew composites are similar to the climatological profiles in each respective region this suggests that regional differences in moist convection particularly the land ocean contrast provide a strong constraint on the diabatic process within the aew trough and therefore the vertical structure of the aews

on the instability of the african easterly jet and the generation of african waves reversals of the potential vorticity gradient abstract the relationship between the generation of african easterly waves and instability growing in regions with reversed potential vorticity gradients is studied using a regional climate model results indicate that the convective generation of potential vorticity pv due to the meridional and vertical gradients of diabatic heating in the upper and lower troposphere causes a vertically elongated pv anomaly on the southern flank of the african easterly jet this pv maximum at 9 n in the midtroposphere together with a pv minimum near 15 n at lower levels because of dry convection over the sahara reverses the meridional pv gradient between 9 and 15 n which suggests that the zonal flow may be unstable in this region analysis of the seasonal mean eliassen palm flux for african waves indicates that wave energy generated convectively through baroclinic overturning in the upper troposphere propagates downward and triggers barotropic conversions south of the jet and baroclinic conversions below and north

biostratigraphy and palaeoecology of middle late ordovician conodont and graptolite faunas of the las chacritas river section precordillera of san juan argentina a conodont graptolite biostratigraphic study was carried out on the top strata of the san juan las chacritas and las aguaditas formations in the la trampa range precordillera of san juan in western argentina significant conodont records in the san juan and las chacritas formations allow for the recognition of the yangtzeplacognathus crassus eoplacognathus pseudoplanus microzarkodina hagetiana and m ozarkodella subzones and eoplacognathus suecicus zones of darriwilian age index species and co occurrences of graptolites and conodonts were recorded in the las aguaditas formation allowing the identification of the nemagraptus gracilis and the pygodus anserinus zones which represent the sandbian stage these data indicate a hiatus between the las chacritas and the las aguaditas formations corresponding to the pygodus serra zone and the pterograptus elegans and hustedograptus teretiusculus zones upper darriwilian a total of 7287 identifiable conodont elements were recorded from the study section the species frequency registered for each zone shows that periodon and paroistodus are the most abundant taxa which are indicative of open marine environments the records of particular conodont taxa such as histiodella periodon microzarkodina eoplacognathus and baltoniodus allow a precise global correlation with other regions such as south central china baltoscandia north america great britain southern australia and new zealand the graptolite fauna identified here are recognized worldwide in equivalent strata in the baltic region great britain north america china southern australia and new zealand the presence of graptolites in the ribbon limestones of the las chacritas formation is documented for the first time

anatomy of an observed african easterly wave in july 2006 the detailed structure of an african easterly wave aew observed during the amma field campaign is analysed the wave was present from 25 to 29 july 2006 a complex circulation pattern was observed the overall structure of convection and the positive vorticity of the trough region had an elongated inverted v appearance wrapped around an area of low winds and clear skies satellite imagery showed that the aew was a significant influence on the modulation of convection on the large scale the wave was identified initially through its strong signature on soil moisture and convection the aew structure observed was not anticipated and has not been discussed in previous literature in addition wave tracking using a hovmoller diagram of meridional winds did not detect the wave and a hovmoller of vorticity showed the wave moved at a slower speed than other aews in july new schematics explaining the structure are presented describing the case as observed by satellites and analysed by a limited area version of the met office unified model it is proposed that the positive vorticity branches of the inverted v can be regarded as analogous to atmospheric fronts with characteristic gradients in winds and thermodynamic properties acting as locations for enhanced convection the implications of the new case are discussed in relation to previous theory and it is suggested that the accepted model of an idealised aew is incomplete and should be extended to include more complex structures copyright 2011 royal meteorological society and british crown copyright the met office

three dimensional structure and dynamics of african easterly waves part iii genesis this paper promotes the view that african easterly waves aews are triggered by localized forcing most likely associated with latent heating upstream of the region of observed aew growth a primitive equation model is used to show that aews can be triggered by finite amplitude transient and localized latent heating on a zonally varying basic state that is linearly stable heating close to the entrance region of the african easterly jet aej is shown to initiate aews downstream the heating leads to an initial trough that reaches the west african coast about 5 7 days later depending on the nature of the heating profile after this a structure that projects strongly onto the leading linear normal mode of the basic state becomes established characterized by a number of westward propagating disturbances that strongly resemble aews the sensitivity of the forced aews to the nature and location of the heating profile is examined aews are most efficiently triggered by heating profiles that establish lower tropospheric circulations close to the entrance region of the aej in the present study this was best achieved by lower tropospheric heating from shallow convection or upper level heating and lower level cooling from a stratiform precipitation profile both profiles have significant heating gradients in the vertical in the mid to lower troposphere this triggering paradigm for the genesis of aews has consequences for the variability and predictability of aews at weather and climate time scales in addition to the nature of the aej often emphasized it is crucial to consider the nature and variability of upstream heating triggers

an analysis of west african dynamics using a linearized gcm abstract this study utilizes a linear primitive equation spherical model to study the development and propagation of easterly wave disturbances over west africa perturbations are started from an initial disturbance consisting of a barotropic vortex and the governing equations are integrated forward in time the perturbations are introduced into basic states corresponding to the observed dynamical and thermodynamical characteristics of two wet years in the sahel and two dry years the model simulations show consistent contrasts in wave activity between the wet and dry years the waves are markedly stronger in the wet years and show a barotropic structure throughout the troposphere the waves tend to extend throughout the troposphere to the level of the tropical easterly jet tej in the wet years but not in the dry years the upper tropospheric shear which is stronger in wet years appears to be a key factor in wave development this shear is dependent on the intensity of the tej suggesting that the t

the low level structure of african easterly waves in 1995 abstract the existence of african easterly waves aews north of the african easterly jet aej core with maximum amplitude at low levels has been confirmed and clarified using radiosonde data and the u k meteorological office global model analysis from the hurricane season of 1995 at bamako 12 5 n 8 0 w the aews were characterized mainly by maximum amplitudes at the level of the aej around 700 mb whereas at dakar 14 7 n 17 5 w the waves were characterized by maxima between 850 and 950 mb the low level waves to the north of the aej arise in association with baroclinic interactions between the negative meridional potential vorticity pv gradients in the jet core and the positive low level gradient of potential temperature enhanced by the presence of low static stability air north of the aej these waves follow the positive meridional gradients over northern africa in contrast to the jet level aews that follow the meridional pv gradients at the level of the aej cross correlation analysis

paleoecology of limnic ostracodes a review of some major topics abstract the paleoecology of limnic ostracodes is reviewd in the context of the evolution of their environment in order to understand why there is a rich ostracode fossil record we examine data such as the quantitative and qualitative distribution of living ostracode species and ostracode assemblages ways of describing and limitations importance of biological and physico chemical factors for the local accumulation of high numbers of ostracodes and diversified assemblages is emphasized we discuss the limits of extrapolations of information from ecology to paleocology we stress how paleontological knowledge can be applied to neontological studies the possibility of using holocene ostracodes as indicators of morphometric changes of lakes temperature salinity eutrophication and as a criterion of meromictic conditions is demonstrated relationships between ostracodes and the chemical environment and particularly the morphological response of the carapace are considered e g diversity and qualitative composition of assemblages and chemical stability types of carapace mineralization and ornamentation and chemistry of bottom waters these ideas developed from studies on recent material are tested for limnic cenozoic faunas in the mesozoic the main questions arising from the study of nonmarine ostracodes deal with the possible evaluation of paleosalinities in marginal lagoonal environments purbeck wealden and with evaluation of depth and hydrochemical and paleoclimatological regime in truly lacustrine intracratonic basins some peculiarities of paleozoic nonmarine ostracode assemblages are described the paleoecological cause of changes in diversity of several ostracode groups in the carboniferous and permian is emphasized

energy dispersion in african easterly waves the existence of an upstream eastward group velocity for african easterly waves aews is shown based on single point lag regressions using gridded reanalysis data from 1990 to 2010 the eastward energy dispersion is consistent with the direction of ageostrophic geopotential flux vectors a local eddy kinetic energy eke budget reveals that early in the life cycle of aews growth rate due to geopotential flux convergence exceeds baroclinic and barotropic growth rates later in the life cycle eke decay due to geopotential flux divergence cancels or exceeds baroclinic and barotropic growth a potential vorticity pv budget is used to diagnose tendencies related to group propagation although both upstream and downstream group speeds are possible because of the reversal in the mean meridional pv gradient upstream propagation associated with the positive poleward pv gradient dominates wave packet evolution analogous to the concept of downstream development of midlatitude baroclinic waves new aews develop preferentially upstream of the older ones thus providing a mechanism for seeding new waves it is suggested that these results are also relevant to aew intermittency and storm track structure

the west african monsoon dynamics part iii the quasi biweekly zonal dipole abstract this paper presents an investigation of the mechanisms giving rise to the main intraseasonal mode of convection in the african monsoon during northern summer here identified as the quasi biweekly zonal dipole qbzd the qbzd is primarily characterized by a quasi stationary zonal dipole of convection whose dimension is larger than the west african monsoon domain with its two poles centered along the guinean coast and between 30 and 60 w in the equatorial atlantic the qbzd dynamical processes within the atlantic africa domain are examined in some detail the qbzd has a dipole pattern associated with a walker type circulation in the near equatorial zonal plane it is controlled both by equatorial atmospheric dynamics through a kelvin wave like disturbance propagating eastward between its two poles and by land surface processes over africa inducing combined fluctuations in surface temperatures surface pressure and low level zonal winds off the coast of west africa when convection is at a min

origin age and movement of pore water in argillaceous quaternary deposits at four sites in southwestern ontario hydrogeologic information in the form of textural properties field and laboratory determined hydraulic conductivity values vertical hydraulic gradients from piezometer nests and major ion and isotopic contents 18o 2h 3h 13c 14c was obtained from four sites located in southwestern ontario on thick deposits of clayey till and glaciolacustrine clay at each site the piezometers were installed from the water table zone situated 1 4 m below the surface to a maximum depth between 20 and 35 m below the surface values of hydraulic conductivity determined in the laboratory by consolidometer and triaxial methods are in the order of 10 8 10 7 cm s and are similar to values calculated from rates of water level rise in piezometers mean values of average vertical groundwater velocity calculated with the measured values of hydraulic conductivity porosity and hydraulic gradient using the darcy equation for a saturated non fractured porous medium range from 0 13 to 0 26 cm yr tritiated pore waters only occur within 3 6 m of ground surface thereby indicating that groundwaters below this depth recharged prior to at least 1952 18o in the pore waters exhibit a distinctive regular shift with depth from water table values of 9 to 10 smow characteristic of present day precipitation to values between 14 and 17 at depths of 20 40 m which are characteristic of much cooler waters corrected 14c ages of the groundwater are greater than 8000 yr b p thereby suggesting that the groundwaters at depth entered these deposits during or after the formation of these deposits approximately 11 000 to 14 000 yr ago 18o 2h and cl concentration profiles were simulated with a one dimensional model for transport by advection and diffusion in a saturated porous medium reasonable agreement between the model and the field profiles was obtained with values of effective diffusion coefficients of 3 0 10 6 cm2 s for 18o 2h and cl and with groundwater velocities between 0 03 to 0 05 cm yr based on these results it is concluded that the pore water in these deposits is a mixture of late pleistocene and modern waters and that the distribution of 18c 2h and cl in these deposits is influenced predominantly by molecular diffusion apparently more so than by hydraulic flow

determination of the dissolved anion composition of ancient lakes from fossil ostracodes the mineralogy of evaporite and other precipitated minerals together with geochemical studies has provided traditional sources of information about the major dissolved ion composition solutes of ancient lakes the paleocompositional resolving power of these methods is generally greatest in high salinity lakes that precipitate numerous solute sensitive evaporite minerals as opposed to dilute saline lakes that precipitate only a few minerals ostracodes live in dilute saline lakes where a species occurrence is determined by the relative proportions of the lake s major dissolved anions so that each species describes specific areas on an anion trilinear diagram moreover the upper salinity tolerance of each species appears to depend upon the types of major anions in solution and is therefore anion specific knowledge about both anion and anion salinity tolerances of an ostracode may ultimately provide a means of estimating absolute anion concentrations in paleolakes because ostracodes are common fossils in lake sediments they provide an important new source of original paleocompositional information suitable for many geologic climatic geochemical and paleontologic studies

early paleozoic orogenic belt of the andes in southwestern south america result of laurentia gondwana collision the late precambrian to early paleozoic age rock units of the pampean ranges the puna and the north patagonian massif of southwestern south america constitute the famatinian orogenic belt they are interpreted as an ordovician collisional belt between the occidentalia terrane and the gondwana craton they include mafic and ultramafic belts of neoproterozoic to early paleozoic age an intense tectonothermal event resulted from the collision syntectonic granitoids represent crustal melting in that collision syntectonic to late tectonic foreland basins developed the recently proposed juxtaposition of laurentia and east antarctica australia in the neoproterozoic raises the possibility that laurentia and western south america were close together in the early paleozoic and therefore that the famatinian belt resulted from laurentia gondwana collision occidentalia which is bordered by a cambrian carbonate platform similar to that of eastern north america may be a sliver detached from laurentia during late ordovician time

sedimentation on the ross sea continental shelf antarctica abstract glacial marine sedimentation has prevailed throughout most of the early glacial history of the ross sea region however since late miocene to early pliocene time the west antarctic ice sheet has advanced onto the continental shelf perhaps several times glacial troughs of the western ross sea may also have formed at this time these glacial troughs border outlet glaciers of the east antarctic ice sheet a widespread lodgement till facies was deposited during this glacial advance holocene retreat of this expanded ice sheet left no conspicuous meltwater record so decoupling of the ice sheet from the seafloor rather than rapid melting is implied modern glacial sediment is far less prevalent than biogenic sediment and reworked glacial sediment except in coastal areas adjacent to small ice shelves and ice tongues little or no debris is being transported beyond the calving line of the ross ice shelf siliceous mud and ooze occurs in the western ross sea where surface circulation is most vigorous and warm deep waters up well this siliceous sediment along with terrigenous silt and clay blankets the seafloor below approximately 300 m water depth most of the ross sea continental shelf is deeper than this surface sediments on shallow banks and coastal platforms have clearly been reworked by marine currents the most vigorous bottom current activity occurs in those areas where geostrophic currents impinge onto the shelf debris flows and turbidity currents are also important in eroding and redistributing glacial sediments on the shelf terrigenous silt and clay are more abundant in surface sediment than basal till the source of this silt and clay is problematic the most plausible sources being onshore transport of suspended sediment by impinging currents and subglacial meltwater input

pleistocene glacio lacustrine deltaic deposits of the scarborough formation ontario canada abstract the late pleistocene scarborough formation of the lake ontario basin represents a lacustrine deltaic sequence strongly affected by a nearby glacier it shows gradual upward coarsening and thickening of layers from varve like clay rich rhythmites at the base to channelized cross bedded sands at the top thick lensing massive layers cm of silty sand are found interstratified with thin layers of silt and clay in the lower and middle parts of the sequence these massive layers were probably formed by subaqueous gravity flows of material in part derived directly from a glacier absence of pebbles and of other features such as glacial silt pellets suggests dispersal away from the foot of the glacier rather than deposition under floating ice varve like rhythmites pollen and insect fauna indicate subarctic to arctic climatic conditions at the time of sediment deposition the large amount of sand in the upper part of the formation is best explained as derived from active outwash fans similar fans were formed during the last deglaciation in southern ontario and can be observed on the landscape

observations of seven african easterly waves in the east atlantic during 2006 abstract the african monsoon multidisciplinary analyses amma experiment and its downstream nasa extension namma provide an unprecedented detailed look at the vertical structure of consecutive african easterly waves during august and september 2006 seven easterly waves passed through the namma domain two waves developed into tropical cyclones debby and helene two waves did not develop and three waves were questionable in their role in the development of ernesto florence and gordon ncep global data assimilation system gdas analyses are used to describe the track of both the vorticity maxima and midlevel wave trough associated with each of the seven easterly waves dropsonde data from namma research flights are used to describe the observed wind structure and as a tool to evaluate the accuracy of the gdas to resolve the structure of the wave finally satellite data are used to identify the relationship between convection and the organization of the wind structure results support a necessary d

the argentine precordillera its odyssey from the laurentian ouachita margin towards the sierras pampeanas of gondwana

two contrasting african easterly wave behaviors abstractthe dominant structural variability of african easterly waves aews is explored using an empirical orthogonal function eof approach the structure of aews is obtained by projecting the w

intraseasonal variability over tropical africa during northern summer abstract the intraseasonal variability over africa during northern summer was analyzed using 25 years of ncep ncar reanalysis and satellite data the dominant pattern of variability was one of enhanced deep convection over the whole african monsoon region it appeared to arise at least partly as a remote response to the intraseasonal madden julian oscillation over the warm pool sector twenty days prior to the maximum in convection over africa there was no signal over africa but convection was reduced over the equatorial warm pool an equatorial kelvin wave response to this change in warm pool convection propagated eastward and an equatorial rossby wave response propagated westward and between them they completed a circuit of the equator and met up 20 days later over africa where the negative midtropospheric temperature anomalies in the kelvin and rossby waves favored deep convection over west africa the kelvin wave component contained lower tropospheric westerly anomalies that acted to increase t

an assessment of analytical techniques for the size analysis of fine grained sediments abstract an evaluation of techniques for the size analysis of fine grained sediments revealed that the malvern laser sizer e3600 electrozone particle counter model 112 micromeritics sedigraph 5000e and hydrophotometer work well for the analysis of sorted silt differences in results may be attributed to the particle property being measured by each instrument the malvern laser sizer and electrozone particle counter are sizing techniques the hydrophotometer and sedigraph determine sedimentation diameter through particle settling there was less agreement among these instruments for unsorted natural sediments containing greater than 15 percent clay by weight clay content of less than or equal to 8 percent does not appear to decrease the resolution of silt sized particles

intermittent african easterly wave activity in a dry atmospheric model influence of the extratropics abstracta dynamical model is constructed of the northern summertime global circulation maintained by empirically derived forcing based on the same dynamical code that has recently been used to study african easterly waves aews as convectively triggered perturbations thorncroft et al leroux and hall in the configuration used here the model faithfully simulates the observed mean distributions of jets and transient disturbances and explicitly represents the interactions between them this simple gcm is used to investigate the origin and intraseasonal intermittency of aews in an artificially dry no convection context a long integration of the model produces a summertime climatology that includes a realistic african easterly jet and westward propagating 3 5 day disturbances over west africa these simulated waves display intraseasonal intermittency as the observed aews also do further experiments designed to discern the source of this intermittency in the model show that the simulated waves are

linking african easterly wave activity with equatorial waves and the influence of rossby waves from the southern hemisphere abstracta connection is found between african easterly waves aews equatorial westward moving mixed rossby gravity wmrg waves and equivalent barotropic rossby waves rws from the southern hemisphere sh the amplitude and phase of equatorial waves is calculated by projection of broadband filtered era interim data onto a horizontal structure basis obtained from equatorial wave theory mechanisms enabling interaction between the wave types are identified aews are dominated by a vorticity wave that tilts eastward below the african easterly jet and westward above the tilt necessary for baroclinic wave growth however a strong relationship is identified between amplifying vorticity centers within aews and equatorial wmrg waves although the waves do not phase lock positive vorticity centers amplify whenever the cross equatorial motion of the wmrg wave lies at the same longitude in the upper troposphere southward flow and east of this in the lower troposphere northward flow two mechanisms could

the sedimentary record of drifting ice early wisconsin sunnybrook deposit in an ancestral ice dammed lake ontario canada abstract outcrops of pebbly mud diamict at scarborough in southern ontario canada the so called sunnybrook till are associated with the earliest incursion of the laurentide ice sheet lis into mid continent north america some 45 000 years ago the sunnybrook is a blanket like deposit containing deepwater ostracodes and occurs conformably within a thick 100 m succession of deltaic and glaciolacustrine facies that record water depth changes in a large proglacial lake contextual evidence associated facies sedimentary structures deposit geometry and landforms indicates a low energy depositional setting in an ice dammed ancestral lake ontario in which scouring by floating ice masses was an important process u shaped iceberg cut scours with lateral berms up to 7 m deep occur on the upper surface of the sunnybrook and are underlain by sub scour structures that extend several meters below the scour base ice rafted concentrations of clasts clast layers grooved surfaces formed by floating ice glissading over a muddy lake floor soft sediment striations and melanges of sand and mud mixed by grounding ice keels ice keel turbates are present and are all well known from modern cold environments the wider significance of this depositional model is that the lis margin lay east of scarborough and did not overrun southern ontario this finding is in agreement with recent data from the erie basin of canada ohio and indiana where deposits formerly correlated with the sunnybrook and thus implying an extensive early wisconsin ice sheet are now regarded as illinoian a speculative hypothesis is proposed that relates deposition of the sunnybrook and two younger deposits of similar sedimentology to surge like instabilities of the southern lis margin

a climatological study of transient mean flow interactions over west africa a statistical study is made of the relationship between intraseasonal variations in mid tropospheric flow over west africa and transient eddy activity during the june september monsoon season in order to investigate the interaction between the african easterly jet aej african easterly waves aews and convection ncep2 reanalyses are used together with outgoing long wave radiation olr data from june september 1979 2007 intraseasonal variability in the 600 hpa zonal wind is isolated using a 10 120 day filter the leading empirical orthogonal function eof describes north south displacements of the jet axis episodes of aew activity over the continent are evaluated in terms of the perturbation kinetic energy pke of the less than six day high pass filtered wind at 700 and 850 hpa pke and olr are also filtered for the intraseasonal signal lag covariance analyses reveal a two way interaction between the aej and synoptic scale transients prior to episodes of enhanced transient activity the aej is strengthened in the jet entrance region during and following these episodes the aej is strengthened on the northern flank of the jet exit region e vector analysis shows that this displacement of the aej is consistent with forcing by transients that have an aew like structure analysis of olr shows that periods of enhanced transient activity over west africa are associated with enhanced convection over the region at intraseasonal time scales and are correlated with prior episodes of enhanced convection to the east in the convective trigger region identified by thorncroft et al copyright 2009 royal meteorological society

lacustrine ostracodes in the late pleistocene sunnybrook diamicton of southern ontario canada two opposing interpretations have been made on the depositional origin of the late pleistocene sunnybrook diamicton in the metro toronto region of southern ontario the traditional view holds this deposit to be a till but more recent arguments advocate a glaciolacustrine origin by suspension deposition and ice rafting the discovery of a low diversity ostracode fauna consisting of candona subtriangulata candona caudata and darwinula stevensoni in the sunnybrook diamicton suggests a lacustrine origin excellent preservation of thin fragile shells and a mixture of juveniles and adults in sediments of varying texture clayey silt to silty clay indicate that there has been little winnowing or selective sorting and that the ostracodes are in situ indications are that the sunnybrook diamicton was deposited in a large deep and cold lake these new palaeontological observations call for a reassessment of the quaternary stratigraphy of the ontario basin and suggest that the laurentide ice sheet in the eastern

darriwilian middle ordovician conodont biofacies from the central precordillera of argentina abstract conodont biofacies structure was recognized throughout detailed stratigraphic sampling at three localities from the central precordillera of argentina from north to south las aguaditas creek las chacritas river and cerro la chilca sections a total of 50 carbonate samples yielded over 9900 identified specimens including a new conodont species fahraeusodus jachalensis which is described due to its paleoecological connotations the yangtzeplacognathus crassus eoplacognathus pseudoplanus and periodon macrodentatus zones are dominated by the ubiquitous species periodon macrodentatus and paroistodus horridus at the three study areas this enables the recognition of the periodon paroistodus biofacies in the central precordillera numerical cluster methodology allowed the identification of conodont sub biofacies the protopanderodus semiacontiodus sub biofacies in the las aguaditas creek the protopanderodus parapaltodus sub biofacies in the las chacritas river the parapaltodus sub biofacies at the cerro la chilca and the fahraeusodus ansella sub biofacies in all of the study sections these sub biofacies present distinctive attributes which are correlative with changes in the depositional environment the diverse protopanderodus parapaltodus sub biofacies developed with a shallowing of the basin while the fahraeusodus ansella sub biofacies is characteristic of deep environments shallower water settings resulted in higher species richness diversity and evenness of conodont communities the eustatic change that led to the drowning of the carbonate platform produced a shift to deeper anoxic benthic conditions that in turn induced a change in the taxonomic composition of the fauna and affected the diversity of the conodont communities

a systematic comparison of tropical waves over northern africa part ii dynamics and thermodynamics abstractthis study presents the first systematic comparison of the dynamics and thermodynamics associated with all major tropical wave types causing rainfall modulation over northern tropical afric

glacimarine processes and inductive lithofacies modelling of ice shelf and tidewater glacier sediments based on quaternary examples abstract three variables control the type of glacial debris source and where and when debris is introduced to an ocean 1 type of glacial ice source ice sheet or valley glacier 2 condition of a grounded glacier melting freezing or frozen base and cold or warm internal ice and 3 type of glacier front ice shelf or tidewater using these variables in different combinations eight glacimarine regimes are postulated to exist by integrating information from holocene sediment and pleistocene glacimarine sequences with the eight inductive regimes lithofacies relationships are predicted and modelled the models show a complexity of glacimarine lithofacies the importance of recognizing this complexity lies in realistic interpretations of ancient sequences ice shelf sediment may be limited in the geologic record because of tectonic and climatic constraints required for ice shelf formation alternatively in some tidewater glacier regimes larger volumes of glacimarine sediment are produced than in ice shelf regimes ice proximal sediment is distinctive especially near subglacial meltwater stream effluxes ice shelves and tidewater glaciers may produce similar ice proximal lithofacies e g morainal bank associations and laminites in certain regimes however details of lithofacies may aid in distinguishing ice shelf from tidewater regimes ice shelf and tidewater iceberg zone sediment can be distinguished from each other if basal and high level englacial debris can be distinguished ice shelf zone sediment out from the grounding line has a basal debris source high level englacial debris is deposited in more distal ice shelf zones resulting in sediment by pass in corresponding positions of a tidewater glacier regime iceberg rafted debris comprises mixed basal and high level englacial debris deeper water zones receive large volumes of sediment when a melting freezing base grounding line is at the edge of a continental shelf when the grounding line retreats sediment supply may be drastically reduced because of a back sloping continental shelf and trapping by morainal banks cool water bioclastic carbonates may accumulate once a grounding line has retreated although ice shelf iceberg zones are more extensive than those in tidewater regimes ice shelf icebergs have low debris content and resulting ice rafted debris may be scarce the smallest volume of sediment is produced by a frozen base ice sheet ending as a tidewater front and the largest volume by a melting freezing base valley tidewater glacier glacimarine sediment has a relatively high preservation potential near continental interiors or margins however at continental margins mass flow olistostrome and tectonic melange deposits may be preserved with glacimarine diamictites these deposits may be difficult to distinguish from each other especially if metamorphosed such as at a convergent margin the models presented do not fully represent the glacimarine environment because many other variables are omitted however the principal concepts of generating glacimarine lithofacies associations are considered continued research will verify if each regime exists and will provide data on those regimes that exist today to compare and modify these models

lithofacies types and vertical profile models an alternative approach to the description and environmental interpretation of glacial diamict and diamictite sequences abstract increased knowledge of modern glacial depositional environments has resulted in rapidly evolving classifications of glacial tills these are based to a large degree on theoretical considerations of likely depositional processes the classifications are sophisticated and more advanced than the establishment of simple field criteria whereby individual till facies can be identified in quaternary and pre quaternary successions this situation is compounded in many quaternary terrains by the continued description of tills in terms of laboratory derived analytical data only reflecting a traditional interest in stratigraphic correlation rather than reconstruction of depositional environment detailed sedimentological logging of lithofacies is rarely undertaken there is thus considerable confusion as to what is being described or sampled when analytical data are presented for many pleistocene tills the same remarks apply to pre pleistocene tillites a lithofacies code is presented here for the rapid description and visual appraisal of field sequences or drill cores containing unconsolidated diamicts or lithified diamictites the term till is not used as it has a strict genetic definition referring to direct aggregation and deposition by glacier ice use of a four part code in conjunction with codes already published for fluvial sediments allows fundamental field properties to be depicted independent of genetic terminology and provides a firm basis for subsequent environmental interpretation and analytical work the value of this approach is illustrated by comparing a representative suite of vertical profiles of diamict assemblages deposited by modern grounded glaciers with a classic late pleistocene glacigenic sequence at scarborough bluffs ontario

a multi scale analysis of the extreme rain event of ouagadougou in 2009 this study presents a multi scale analysis of an extreme rain event that occurred in burkina faso on 1st september 2009 with an absolute record of 263 mm rainfall observed at ouagadougou this high impact weather system results from the combination of several favourable ingredients at different scales the sea surface temperature anomaly patterns in july august 2009 of both the atlantic cold tongue the tropical atlantic dipole and the mediterranean sea are favourable factors for the northward penetration of the west african monsoon the intense convective activity of the last 10 day period in august is associated with the crossing of a convectively coupled kelvin wave increasing the african easterly wave aew activity and of an equatorial rossby wave at the synoptic scale this event corresponds to the passage of a train of 3 aews with increasing magnitude behind the 1st aew trough axis an intense and deep southerly monsoon burst develops it contributes to the amplification of the 2nd aew and its breaking associated with the formation of an intense meso vortex on the southern flank of the african easterly jet compared to the fast moving squall line the dominant type of precipitating weather system over the sahel the ouagadougou precipitating system appears to be a moist vortex propagating slowly allowing rainfall accumulation without wind gusts or convective cold pools observed at the surface the main precipitation area is located about 2 longitude downshear westward due to the african easterly jet of the centre of this strong meso vortex

dynamics of the west african monsoon part iv analysis of 25 90 day variability of convection and the role of the indian monsoon this paper is part of a series of studies addressing the dynamics of the west african summer monsoon at intraseasonal time scales between 10 and 90 days the dominant mode of 25 90 day convective variability in the african monsoon was investigated starting from previous results involving the excitation of dry equatorial kelvin and rossby waves by a negative diabatic heat source located over the warm pool this evolution is consistent with a significant contribution by a convectively coupled equatorial rossby wave and the mjo on the other hand convectively coupled kelvin waves as well as the dry kelvin wave signal have a very weak impact however there is more to the global control of the african summer monsoon than convectively coupled wave dynamics the active break cycle of the indian monsoon controlled by a northward moving dipole of diabatic heating in the indian sector can also influence the african monsoon through atmospheric teleconnections simulations performed with a dry primitive equation model show that this influence may be transferred through the northern indian heat source which excites a rossby cyclonic circulation propagating westward over north africa that is cut off by the northward arrival of the equatorial indian heat source and the associated intrusion of an anticyclonic ridge low level westerly winds and moisture advection within the itcz consequently increase over africa the mean time lag between an active phase over india and over africa is about 15 20 days

did the taconic appalachians continue into southern south america the appalachian mountains now terminating abruptly at the gulf of mexico coastal plain may have formerly continued into southern south america rocks forming the basement of the argentine andes can be interpreted as remnants of an early paleozoic orogen the famatinian belt not unlike the taconic appalachians both orogens are bordered to the west present coordinates by lower paleozoic carbonate platforms bearing the olenellid trilobite fauna that is characteristic of laurentia paleomagnetic and geologic data indicate that they could have formed as one continuous mountain chain possibly extending into antarctica during ordovician closure of an ocean basin southern iapetus between laurentia and gondwana the taconic and famatinian segments of the chain may have been truncated during late ordovician separation of laurentia and gondwana along the preexisting late neoproterozoic to cambrian rift system that initiated formation of the ouachita embayment and the southern margin of north america

an account of the techniques using ostracodes in palaeolimnology in australia abstract ostracodes are common in australian waters especially in saline lakes where they are particularly diverse this makes them indispensable tools for australian palaeolimnological studies especially since many australian lakes are saline the following types of subjective information can be obtained from the study of australian fossil ostracode faunas without knowledge of the ecology or taxonomy of their living representatives the search for a life assemblage can lead to detection of the presence of water currents and the effects of reworking in addition to the identification of particular facies such as a lake shoreline or a desiccation phase rate of sedimentation can be estimated as well as the amount of sediment compaction of drying information on water oxygenation and acidification can be obtained and finally presence of seasonality affecting lakes can be identified with additional reference to the ecology of particular species permanency of lake water can be assessed and so can the variability of rainfall and even at times the detection of whether a lake was close to a summer winter rainfall boundary shell ornamentation can inform on water depth in addition salinity data can be obtained as well as some information on water chemistry and temperature the latter from trace elements mg sr and stable isotope 18 o studies of ostracode shells

depositional controls on the magnetic characteristics of lodgement tills and other glacial diamict facies genetic interpretation of massive unstructured diamict and diamictite facies is a commonly encountered problem faced by sedimentologists data are presented concerning the magnetic characteristics namely anisotropy of magnetic susceptibility ams and natural remanent magnetism nrm of facies deposited by 1 lodgement processes at a glacier base lodgement till and 2 subaqueously by pelagic mud deposition and ice rafting rain out diamicts lodgement tills have an nrm that is distorted around the geomagnetic pole position to form a girdle approximately 90 in length either transverse or parallel to ice flow direction this distension appears to be the result of subglacial shear processes because other diamicts deposited passively by melt out below stagnant ice and modelled by a laboratory experiment show a nondeformed nrm clustering around the geomagnetic pole the ams data show that lodgement tills have only a weakly orientated magnetic microfabric glaciolacustrine rain out diamicts show

the shape propagation and mean flow interaction of large scale weather systems abstract for a zonal average operator the eliassen palm flux provides a diagnostic of both eddy behavior and the feedback of the eddies onto the mean flow this paper addresses the diagnosis problem for other averaging operators and in particular for time averaging which has proved in recent years such a powerful means of viewing the three dimensional tropospheric flow the horizontal velocity correlation tensor gives a measure of the characteristic horizontal eddy shape at a point it also implies the direction of the group velocity relative to the mean flow in cases where such a concept is valid however the major emphasis here is on the mean flow feedback of eddies in this respect the eddy vorticity flux is determined by derivatives of the components of the anisotropic part of the tensor making a reasonable approximation allows the eddy vorticity flux convergence to be written in terms of e v 2 u 2 u v a simple interpretation of the mean flow feedback of eddies is then possible a sligh

analysis of the dominant mode of convectively coupled kelvin waves in the west african monsoon abstract the dominant mode of convectively coupled kelvin waves has been detected over the atlantic and africa during northern summer by performing composite analyses on observational fields based on an eof reconstructed convection index over west africa propagating eastward many waves originate from the pacific sector interact with deep convection of the marine itcz over the atlantic and the continental itcz over west and central africa and then weaken over east africa and the indian ocean it has been shown that they are able to modulate the life cycle and track of individual westward propagating convective systems their mean kinematic characteristics comprise a wavelength of 8000 km and a phase speed of 15 m s 1 leading to a period centered on 6 to 7 days the african kelvin wave activity displays large seasonal variability being highest outside of northern summer when the itcz is close to the equator facilitating the interactions between convection and these equatorially trapped waves the co

restricted regional extent of the laurentide ice sheet in the great lakes basins during early wisconsin glaciation it is conventional wisdom that the last continental ice sheet in north america extended beyond the southern margins of the great lakes basins during both early ca 75 ka and late 30 ka phases of wisconsin glaciation this model hinges on the presence of a regionally extensive diamict traditionally interpreted as a subglacial till exposed in the ontario basin at toronto between last interglacial lacustrine sediments and late wisconsin tills the discovery of an in situ lacustrine ostracode fauna confirms previous sedimentological and geophysical investigations which concluded that the early wisconsin diamict is not a subglacial deposit but a stony mud deposited on the floor of an extensive glacial lake the unit together with younger mid wisconsin sediments was only overridden by the laurentide ice sheet during the late wisconsin after 30 ka we argue that during the early phase of wisconsin glaciation the laurentide ice sheet was thin highly dynamic and of insufficient volume to extend fully across the great lakes basins a situation more closely in accordance with the marine 18o 16o record and other proxy climatic data that show maximum cooling and global ice volumes at about 20 ka

sedimentation in a large lake a reinterpretation of the late pleistocene stratigraphy at scarborough bluffs ontario canada a lithofacies code developed for diamicts emphasizes facies variability in the classic upper pleistocene glaciogenic sequence at scarborough bluffs ontario canada lithological breaks along the bluffs are traditionally assigned to incursions of grounded ice margins and to interstadial lakes formed during ice retreat during the early and middle wisconsin detailed sedimentological logging through three diamict units previously formalized as sunnybrook seminary and meadowcliffe tills and intervening sandy lithofacies shows absence of glaciotectonic structures and diamicts associated with grounded glacier ice traction current activity during diamict accumulation postdepositional resedimentation of diamicts into topographic lows accompanied by turbidite activity a subaqueous deltaic origin for intervening sandy lithofacies and loaded transitional and interbedded contacts between sand and diamict the scarborough bluffs sequence may be the preserved bottom stratigraphy of a large lake the bottom stratigraphy results from repeated basinward progradation of deltaic sandy lithofacies over glaciolacustrine diamicts deposited below floating ice whether ice shelf ramp bergs or lake ice a facies model is presented for glaciolacustrine diamict deposition on the floors of enlarged pleistocene lakes trapping substantial volumes of fine grained suspended sediment

the west african monsoon dynamics part ii the preonset and onset of the summer monsoon the arrival of the summer monsoon over west africa has been documented by using daily gridded rainfall data and ncep ncar reanalyses during the period 1968 90 and olr data over the period 1979 90 two steps have been characterized through a composite approach the preonset and the onset of the summer monsoon the preonset stage corresponds to the arrival in the intertropical front itf at 15 8n that is the confluence line between moist southwesterly monsoon winds and dry northeasterly harmattan bringing sufficient moisture for isolated convective systems to develop in the sudano sahelian zone while the intertropical convergence zone itcz is centered at 58n the mean date for the preonset occurrence is 14 may and its standard deviation is 9 5 days during the period 1968 90 this leads to a first clear increase of the positive rainfall slope corresponding to the beginning of the rainy season over this sudano sahelian area the onset stage of the summer monsoon over west africa is linked to an abrupt latitudinal shift of the itcz from a quasi stationary location at 58n in may june to another quasi stationary location at 108n in july august the mean date for the onset occurrence is 24 june and its standard deviation is 8 days during the period 1968 90 this leads to a second increase of the positive rainfall slope over the sudano sahelian zone signing the northernmost location of the itcz and the beginning of the monsoon season this abrupt shift occurs mostly between 108w and 58e where a meridional land sea contrast exists and it is characterized by a temporary rainfall and convection decrease over west africa preonset dates onset dates and summer rainfall amount over the sahel are uncorrelated during the period 1968 90 the atmospheric dynamics associated with the abrupt itcz shift has been investigated between the preonset and the onset stages the heat low dynamics associated with the itf controls the circulation in the low and midlevels its meridional circulation intensity is the highest at the beginning of the monsoon onset this can lead to 1 increased convective inhibition in the itcz through intrusion of dry and subsiding air from the north and 2 increased potential instability through a greater inland moisture advection and a higher monsoon depth induced by a stronger cyclonic circulation in the low levels through higher vertical wind shear due to westerly monsoon wind and midlevel african easterly jet aej increases through enhancement of the instability character of the aej and through increased shortwave radiation received at the surface during the monsoon onset once the rainfall minimum occurred due to the convective inhibition the accumulated potential instability breaks the convective inhibition the inertial instability of the monsoon circulation is released and the associated regionalscale circulation increases leading to the abrupt shift of the itcz then the itcz moves north up to 108n where thermodynamical conditions are favorable it is suggested by the authors that the abrupt shift of the itcz initiated by the amplification of the heat low dynamics could be due to an interaction with the northern orography of the atlas ahaggar mountains subsidence over and north of this orography due to both the northern branches of the heat low and of the northern hadleytype cell contributes to enhance the high geopotentials north of these mountains and the associated northeasterly winds this leads to the development of a leeward trough that reinforces the heat low dynamics maintaining an active convective itcz through enhanced moist air advection from the ocean increasing the northern hadley circulation which reinforces the high geopotentials and the interaction with the orography through a positive feedback the fact that an abrupt shift of the itcz is only observed on the western part of west africa may result from the enhancement of moisture advection which comes from the west and has a stronger impact west of the greenwich meridian the northwest southeast orientation of the atlas ahaggar crest can induce the interaction with the heat low first in the east where the mountains are nearer to the itf than in the west and second in the west another consequence of the possible orography induced interaction with the atmospheric circulation is that the induced leeward trough increasing the cyclonic vorticity in the heat low may stimulate moisture convergence in the oceanic itcz near the western coast of west africa

a systematic comparison of tropical waves over northern africa part i influence on rainfall abstractlow latitude rainfall variability on the daily to intraseasonal time scale is often related to tropical waves including convectively coupled equatorial waves the madden julian oscillation

african easterly waves and convection part i linear simulations abstract a linearized version of a nonhydrostatic model is used to study the normal mode selection and the structure of the african easterly waves in dry and moist environments associated with an idealized african easterly jet structure the dry mode reproduces the principal observed characteristics of the lower troposphere in particular the low level ascent and convergence in the trough a simple cisk type parameterization improves the upper level circulation a budget of kinetic energy shows barotropic and baroclinic contributions and adequately reproduces the analysis of norquist et al the scale selection and the structure of the most unstable mode appears sensitive to the jet structure in particular to the meridional and vertical shear several discrepancies between observations and these linear modes emphasize the importance of an accurate description of convection

late pleistocene depositional systems of metropolitan toronto and their engineering and glacial geological significance the municipality of metropolitan toronto area 480 km2 population 2 15 million is centrally located on the late pleistocene sedimentary infill of the laurentian channel a broad bedrock low up to 115 km wide connecting the huron and ontario basins this channel forms part of a relict late tertiary drainage network the laurentian river modified by pleistocene glacial erosion and infilled by over 100 m of glacial and interglacial sediments the subsurface stratigraphy of the channel fill below metropolitan toronto has been established from many different data sources and is depicted in this paper as a series of cross sections with a total length of nearly 105 km the subsurface stratigraphy has been divided provisionally into five depositional complexes which have been mapped in the subsurface along several transects these are 1 a glacial complex of illinoian age 2 a lacustrine complex of sangamon interglacial and earliest wisconsinan sediments 120 000 75 000 bp 3 a glaciolacust

case study of an intense african easterly wave abstract the life cycle of an intense african easterly wave aew over the african continent is examined using european centre for medium range weather forecasts ecmwf operational analyses meteosat satellite images and synoptic observations this system the strongest aew of 2000 can be tracked from central north africa into the eastern atlantic ocean where it is associated with the genesis of hurricane alberto synoptic analysis of the kinematic and thermodynamic fields is supplemented by analysis of potential vorticity pv allowing exploration at the role of multiple scales in the evolution of this aew the authors analysis promotes the division of the aew life cycle into three distinctive phases i initiation the aew development is preceded by a large convective event composed of several mesoscale convective systems over elevated terrain in sudan this convection provides a forcing on the baroclinically and barotropically unstable state that exists over tropical north africa ii baroclini

a study of the energetics of african easterly waves using a regional climate model abstract the evolution and spatial distribution of the energetics of african waves are studied complete eddy energy equations for an open system are derived for the computation of energy transformations during wave generation and dissipation it is found that baroclinic overturning is the dominant energy source although barotropic conversions can be almost equally important when there is concentrated moist convection south of the jet or shallow cumulus convection beneath the jet the generation of active waves usually results from the nearly in phase evolution of baroclinic and barotropic conversions which are associated with significant rainfall over africa significant barotropic instability associated with the horizontal shear is usually induced by concentrated deep convection on the southern flank of the jet barotropic conversions associated with the vertical wind shear may attain even greater magnitudes than that associated with the horizontal shear when shallow cumulus convection beneath the jet

sedimentology of middle ordovician carbonates in the argentine precordillera evidence of regional relative sea level changes the las aguaditas formation in the argentine precordillera of san juan is the only ordovician carbonate sequence deposited on a slope spiculites mudstones and calcisiltites represent the autochthonous sediments characterized by a fine lamination rare fossils and their dark colour the pelagic fauna consists of rare radiolarians calcispheres trinucleid trilobites graptolites and conodonts the latter are typical of an open marine environment and proved a llanvirn llandeilo age for the las aguaditas formation

relationship of two lacustrine ostracode species to solute composition and salinity implications for paleohydrochemistry nonmarine ostracode species are indicative of the physical and chemical nature of lacustrine environments although salinity has traditionally been regarded as one of the more important parameters that affect the occurrence patterns of lacustrine ostracodes examination of the solute composition and salinities of the lakes where limnocythere sappaensis and l staplini live reveals that solute composition and not salinity is the most critical factor that controls their occurrence the occurrence of these taxa in the modern world is mutually exclusive l sappaensis lives in water that is enriched in na hco 3 and depleted in ca 2 l staplini lives in water that is enriched in various combinations of na mg 2 ca 2 cl and is depleted in hco 3 these solute compositions are the product of the mineral fractionation processes described by eugster and hardie the positive correlation between these two species occurrences and the mineralogic fractionation processes suggests that these taxa may be used as reliable paleohydrochemical indicators studies in progress dealing with other ostracode taxa suggest that saline lacustrine ostracodes can provide a precise method for reconstructing paleohydrochemistry

the west african monsoon dynamics part i documentation of intraseasonal variability intraseasonal variability in the west african monsoon is documented by using daily gridded datasets of rainfall and convection and reanalyzed atmospheric fields over the period 1968 90 rainfall and convection over west africa are significantly modulated at two intraseasonal timescales 10 25 and 25 60 day leading to variations of more than 30 of the seasonal signal a composite analysis based on the dates of the maximum minimum of a regional rainfall index in wet dry sequences shows that these sequences last on average 9 days and belong to a main quasiperiodic signal of about 15 days a secondary periodicity of 38 days is present but leads to a weaker modulation during a wet dry sequence convection in the itcz is enhanced weakened and its northern boundary moves to the north south while the speed of the african easterly jet decreases increases the speed of the tropical easterly jet increases decreases and the monsoon flow becomes stronger weaker all these features being similar to the ones associated with interannual variability characterizing wet and dry years this modulation of convection at intraseasonal timescales is not limited to west africa but corresponds to a westward propagating signal from eastern africa to the western tropical atlantic an enhanced monsoon phase is associated with stronger cyclonic activity in the low levels over the sahel associated with stronger moisture advection over west africa five days before the full development of the wet phase a stronger cyclonic circulation at 20 e induces enhanced southerly winds along 25 e where convection enhances while another westwardpropagating cyclonic circulation is located at 0 this atmospheric pattern is linked to the enhancement of the subsiding branch of the northern hadley cell at 35 n northerly advection of drier air over west africa and to increased dry convection in the heat low at 20 n it propagates westward leading to a zonally extended area of enhanced monsoon winds over west africa consistent with the occurrence of the wet phase

spatial and temporal variability of the three dimensional flow around african easterly waves abstractthis study presents a large scale trajectory analysis of african easterly waves aews across west africa and the eastern atlantic back trajectories were initialized at multiple pressure levels from in and around the vortex center of the aew troughs to reveal the source regions of environmental inflow the trajectory analysis highlights a changing influence of environmental air on aew troughs over west africa monsoonal flow dominates with source regions of air from the southwest and east to northeast influencing the trough as the aew troughs leave west africa flow from the northwest becomes increasingly important cluster analysis highlighted that the contribution of trajectories from the northwest increased as the aew troughs move westward and that this cluster also had high variability in environmental characteristics correlation analysis of outgoing longwave radiation around the troughs with environmental characteristics 72 h earlier was conducted on 443 aews this analysis reveals that th

laurentide ice sheet extent inferred from stable isotopic composition o c of ostracodes at toronto canada abstract early and middle wisconsin glaciolacustrine sediments exposed at scarborough bluffs toronto canada contain a low diversity benthic ostracode fauna dominated by candona subtringulata and c caudata we have studied the oxygen and carbon isotopic compositions of the two ostracode species from the base of the scarborough section to its top immediately below a late wisconsin till we find an upward decrease in 18 o in both species that is more marked in c caudata the shift in 18 o of ostracode calcite from interglacial values of 6 to 8 to values of 17 immediately below the late wisconsin till is the result of 1 lowering of 18 o of the lake as a result of addition of isotopically light meltwater from an advancing and thickening laurentide ice sheet combined with 2 lowering of 18 o of local precipitation entering the lake due to falling temperatures in the last stages of the lake 18 o of the lake water was between 17 and 21 corresponding to a lake body composed of between 35 and 55 glacial meltwater the lake appears to have been isotopically and thermally stratified for part of its history differences in 13 c values between c caudata and c subtriangulata increase upward in the stratigraphic section this may record enhanced partitioning of carbon isotopes between surface and bottom waters as a result of increased water depths photosynthesis by algae and changes in the input of dissolved organic carbon from the oxidation of organic matter if the age assessments of these sediments are correct then these data provide valuable information regarding the isotopic composition of ancestral lake ontario and also confirm that the basin was only fully glaciated during the late wisconsin

three dimensional structure and dynamics of african easterly waves part i observations the mean structure of african easterly waves aews over west africa and the adjacent atlantic is isolated by projecting dynamical fields from reanalysis and radiosonde data onto space time filtered satellite derived outgoing longwave radiation these results are compared with previous studies and an idealized modeling study in a companion paper which provides evidence that the waves bear a close structural resemblance to the fastest growing linear normal mode of the summertime basic state flow over africa there is a significant evolution in the three dimensional structure of aews as they propagate along 10 n across west africa at this latitude convection occurs in northerly flow to the east of the greenwich meridian then shifts into the wave trough and finally into southerly flow as the waves propagate offshore into the atlantic itcz in contrast to the north of the african easterly jet along 15 n convection remains in southerly flow throughout the waves trajectory along 10 n over west africa the location of convection is consistent with the adiabatic dynamical forcing implied by the advection of perturbation vorticity by the mean thermal wind in the zonal direction as in the companion paper offshore and along 15 n the relationship between the convection and dynamics is more complex and not as easily explained in terms of dynamical forcing alone

analysis of convection and its association with african easterly waves abstract the association between convection and african easterly wave aew activity over tropical africa and the tropical atlantic during the boreal summer is examined using satellite brightness temperature tb and ecmwf reanalysis datasets spectral analysis using 18 yr of tb data shows significant variance in the 2 6 day range across most of the region within the regions of deep convection this time scale accounts for about 25 35 of the total variance the 2 6 day convective variance has similar amplitudes over western and eastern africa while dynamic measures of aew activity show stronger amplitudes in the west this study suggests that weak aew activity in the east is consistent with initial wave development there and indicates that convection triggered on the western side of the mountains over central and eastern africa near darfur western sudan and ethiopia has a role in initiating aews westward the subsequent development and growth of aews in west africa is associated with stronger cohe

ostracod faunas in a large late pleistocene ice dammed lake southern ontario canada abstract in the lake ontario basin of mid continent north america near toronto canada a low diversity micro crustacean ostracod community dominated by candona caudata and candona subtriangulata occurs in several poorly sorted pebbly mud diamicts units sunnybrook seminary and meadowcliffe tills the diamicts were deposited in an ancestral ice dammed lake ontario with a level at least 90 m above the modern lake during the early and middle phases of the wisconsin glaciation 25 000 75 000 yr b p poorly sorted sediments accumulated by ice rafting and mud deposition from meltwater plumes and are separated by shallower water deltaic facies comparison of the modern habitat ranges of ostracods specifically their water depth temperature and dissolved oxygen preferences provides important palaeolimnological data regarding late pleistocene ice dammed lakes

mean state and wave disturbances during phases i ii and iii of gate based on era 40 abstract using ecmwf s second generation reanalysis era 40 the large scale mean state and synoptic scale features associated with african easterly wave disturbances aews are examined over west africa and the adjacent eastern atlantic ocean during the three 21 day observing periods of the global atmospheric research program garp atlantic tropical experiment gate in 1974 phase i 26 june 16 july phase ii 28 july 17 august phase iii 30 august 19 september results are partitioned into four geographical boxes in order to highlight differences among the aew vortices as they propagate westward along two tracks northern and southern over west africa land and the adjacent eastern atlantic ocean water this marks the first time that a detailed diagnosis of the northerly track aews has been conducted results are also compared to previous gate studies and a 30 yr climatology is extracted from era 40 in general the subjectively analyzed wind fields presented in earlier studies compare favorabl

rhythmically bedded glaciomarine sediments on whidbey island washington abstract several facies of late pleistocene glaciomarine sediments on whidbey island washington are rhythmically bedded the first consists of stratified silty sand which fines upward transitionally into pebbly mud several successions each approximately 0 6 m thick comprise a proximal meltwater facies thought to have been deposited in a shallow 10 m submarine fan environment both the positive lobe shape morphology of the exposure and the inferred depositional processes support this view underflow currents either high concentration turbidity currents or grain flows are thought to have deposited the silty sand while flocculation settling from turbid overflow and or interflow plumes and ice rafting were responsible for pebbly mud deposition such inferences are based on text ral analysis and observations of sedimentary structures the rhythmic interbedding is explained by invoking seasonal fluctuations of meltwater discharge this caused a variation of depositional process in areas proximal to meltwater input into the basin rhythmic interbedding is also observed within a channelized sequence of gravel sand and mud which comprise a fining upwards succession that includes turbidites laminations of sand and silt found in the upper portion of this section closely resemble the type of varved bedding commonly reported from glaciolacustrine sequences

on the relationship between african easterly waves and the african easterly jet this idealized modeling study investigates how convectively triggered african easterly waves aews are influenced by the intraseasonal variability of the african easterly jet aej a set of 10 day averaged zonally varying basic states is constructed with the ncep 2 reanalysis 1979 2006 a primitive equation model is used to simulate linear aews on each of these basic states using the same idealized convective heating localized over the darfur mountains as an initial trigger it is shown that the transient response depends strongly on the basic state with the same trigger many configurations of the aej fail to produce a wave disturbance while others produce strong easterly wave structures necessary conditions for the development of strong waves can be characterized by a strong jet a strong vertical shear or a strong and extended potential vorticity reversal in strong wave cases the jet is extended to the south and west and the jet core is aligned with the maximum of surface westerlies maximizing the vertical shear the pattern that is optimal for generating easterly waves also closely resembles the dominant mode of variation of the aej revealed by an empirical orthogonal function eof analysis of the set of basic states

the impact of moist processes on the african easterly jet african easterly wave system the african easterly jet easterly wave aej aew system was explored in an idealised model prescribed zonally symmetric surface temperature and moisture profiles determine the aej which becomes established through meridional contrasts in dry and moist convection as in previous studies a realistic aej developed with only dry convection including moist processes increased its development rate but reduced its speed and meridional extent aews grew through barotropic baroclinic conversions negative meridional potential vorticity pv gradients arose in the zonally symmetric state through the intrusion of the low pv saharan boundary layer since moist processes strengthened this significantly through diabatically generated pv in the intertropical convergence zone moist aews were three times stronger larger barotropic conversions and faster aej development increased the moist wave growth rate jet level and northerly low level amplitudes grew but in the moist case the low level amplitudes weakened as the aew interacted with convection consistent with their absence from observations during the peak monsoon striking dependencies between the aej aew and rainfall existed two time scales governed their evolution depending on the transfer coefficients 1 the aej s replenishment rate influenced by heat fluxes and 2 the wave growth rate by damping and the slower jet development rate moist aews were characterized by intermittent growth decay with growth preceded by increased mean rainfall and later weakening aejs these dependencies established an internal 8 10 day variability consistent with intra seasonal observations of 9 day rainy sequences this internal variability offers an alternative explanation to the previously proposed external forcing and a new view of the moist aew life cycle copyright 2009 royal meteorological society