late weichselian and holocene sedimentary palaeoenvironment and glacial activity in the high arctic van keulenfjorden spitsbergen high arctic fjords for example van keulenfjorden on spitsbergen provide valuable palaeoenvironmental archives as they typically contain landforms and sediment sequences that document past changes in glacial activity with high temporal resolution van keulenfjorden was covered with a grounded glacier during the last glacial and it was deglaciated between c 11 8 and 11 3 cal ka bp the retreat of the ice front accelerated from approximately 80 to 190 m a during the deglaciation the maximum late holocene glacier extent occurred after surge like advances of the glacier nathorstbreen between 2790 and 2610 cal yr bp i e during a period with the coldest climatic conditions on svalbard this maximum extent was reached approximately 2600 years earlier than inferred for most fjords on svalbard suggesting that surge like glacier advances on svalbard can occur under variable climatic conditions the time interval between the advances of nathorstbreen around 2 7 ka bp was approximately 100 150 years this is comparable to the last and only historically known quiescent phase of nathorstbreen of c 120 years between the late 19th century and the most recent surge from 2003 to 2012

general circulation model study on the green sahara during the mid holocene an impact of convection originating above boundary layer 1 the mechanism maintaining widespread vegetation over the sahara 6000 years before present 6kbp is investigated with an atmospheric general circulation model gcm focusing on an impact of convection originating above the planetary boundary layer pbl the multiple cloud base arakawa schubert scheme mcb is implemented in the gcm and it is shown that mcb significantly strengthens the impact of vegetation over the sahara on precipitation in this region if it is assumed that the whole sahara was covered by vegetation at 6kbp the total precipitation is sufficient to maintain vegetation over the south and northwest sahara high valued moist static energy air ranges from surface to the middle troposphere over the northern half of intertropical convergence zone itcz in summer because of strong northward moisture transport in the lower troposphere convection originating above the pbl prevails in this region especially when the pbl top is lowered between night and early morning and strengthens the intrusion of the itcz into the sahara then moisture is further transported northward by the african wave disturbances enhancing precipitation over the northwestern sahara

mechanisms for precipitation variability of the eastern brazil sacz convective margin the present study examines the mechanisms for the connection between the precipitation variability in eastern brazil and the south atlantic convergence zone sacz convective margin eastern brazil sacz convective margin and the variability of low level inflow on interannual time scales during austral summer theauthors methodologyisbasedontheanalysisofobservationaldatasetsandsimulationsby theuniversity of california los angeles ucla atmospheric general circulation model agcm coupled to the simplified simple biosphere model it is demonstrated that the inflow variability is associated with the leading mode of wind variability over subtropicalsouth america andtheconnection isestablishedthroughthemechanismofananalyticprototype for convective margin shifts proposed in previous studies over the eastern brazil sacz convective margin the weaker stronger convection tends to occur together with stronger weaker low level inflows in reference to the mean easterly trades by changing the ventilation effect stronger weaker inflows with low moist static energy from the atlantic ocean suppress promote convection the causal relationship is verified by agcm mechanism testing experiments performed in perpetual february mode in which low level nondivergent wind perturbations are imposed in a region overlapping eastern brazil and the western atlantic ocean with solely the imposed wind perturbations acting on the moisture advection in the model equation the agcm can reproduce the precipitation variability in the eastern brazil sacz convective margin the capability of the agcm in capturing such precipitation sensitivity to the low level inflow variability also suggests that the mechanism can be applied to other regions of convective margins or to other time scales

a second order bulk boundary layer model abstract bulk mass flux models represent the large eddies that are primarily responsible for the turbulent fluxes in the planetary boundary layer as convective circulations with an associated convective mass flux in order for such models to be useful it is necessary to determine the fractional area covered by rising motion in the convective circulations this fraction can be used as an estimate of the cloud amount under certain conditions matching conditions have been developed that relate the convective mass flux to the ventilation and entrainment mass fluxes these are based on conservation equations for the scalar means and variances in the entrainment and ventilation layers methods are presented to determine both the fractional area covered by rising motion and the convective mass flux the requirement of variance balance is used to relax the well mixed assumption the vertical structures of the mean state and the turbulent fluxes are determined analytically several aspects of this simple m

emplacement and deformation of granitoids during volcanic arc construction in the foothills terrane central sierra nevada california abstract emplacement of a series of late jurassic to early cretaceous tonalites and diorites at depths of 4 to 9 km accompanied volcanic arc construction in the foothills terrane central sierra nevada california emplacement of these plutons occurred after initiation of faulting and rigid rotation of bedding and immediately before widespread cleavage development pluton emplacement occurred by permissive emplacement in the hinges of large anticlines or domes or as structurally controlled sill like bodies in a ductile shear zone and was accompanied by widespread mingling of magmas subsequent deformation rotated but did not internally deform one pluton strongly deformed several others and shortened the overlying volcanic and sedimentary sequences by 30 to 50 we suggest that deformation was active throughout volcanic arc construction but evolved from early more brittle deformation to ductile flow immediately after pluton emplacement and back to brittle deformation as the arc was uplifted and cooled at this location arc magmatism lasted at least 30 ma whereas deformation lasted at least 35 ma and possibly much longer the different emplacement mechanisms changing style of deformation and differences in viscosity contrast between plutons and wall rocks resulted in an impressive variety of structural characteristics and apparent timing relationships for the subvolcanic plutons

time transgressive deposits of repeated depositional sequences within interlobate glaciofluvial esker sediments in koylio sw finland abstract evidence of conspicuous repeated seasonal to annual deposition of glaciofluvial and glaciolacustrine sequences within a structurally complex interlobate esker segment in sw finland is presented the time transgressive overlapping depositional sequences consist of deposits from two successive melt seasons including three vertically stacked lithofacies associations 1 massive to stratified coarse gravels summer deposits 2 trough and ripple cross stratified fine grained deposits autumn to winter deposits and 3 sandy stratified beds spring deposits the depositional environment of each lithofacies association involves a transition from subglacial or submarginal tunnel to a subaqueous re entrant environment which then passes to a proglacial glaciolacustrine environment the study also presents evidence of headward extension of subglacial tunnel deposits related to the rapid shifting of a tunnel expansion point during the increasing spring discharge which occupied the old tunnel exit this mode of annual deposition has not been reported previously in esker studies the good preservation of the rhythmic lithofacies associations is suggested as resulting from interlobate depositional conditions associated with rapidly decaying icestreams therefore the depositional model may provide a key to recognizing time transgressive interlobate eskers that form an important geomorphological and sedimentological record of meltwater activity during the last deglaciation of the fennoscandian and laurentide ice sheets the identification of time transgressive interlobate eskers and associated palaeo icestream behaviour is an essential step forward for more accurate models of ice sheet behaviour and palaeoclimatic reconstructions

on the early response of the climate system to a meltwater input from greenland theearlyresponseoftheatmosphere oceansystemtomeltwaterrunofforiginatingfromthegreenlandice sheet is studied using a coupled atmosphere ocean general circulation model aogcm for this purpose aogcm ensemble simulations without and with associated ocean freshening around greenland are compared for freshwater perturbations initiated in northern winter the mean response for the first three months shows the emergence of negative sea surface temperature sst anomalies in the denmark strait in association with enhanced oceanic advection by the east greenland current the response also shows negative sst anomalies in the north atlantic associated with enhanced westerlies at the ocean surface additionally the baroclinic atmospheric cyclonic circulation east of greenland intensifies and anticyclonic circulations with equivalent barotropic structures develop over western europe and the north pacific ocean simulations by the atmospheric component of the aogcm indicate that atmosphere ocean interactions contribute significantly to enhance the response the sensitivity of the coupled system response to the timing of freshwater perturbation is also studied for freshwater perturbations initialized in northern summer the response during the following winter is similar but stronger in magnitude in the northern hemisphere the atmospheric response resembles the arctic oscillation ao mode of variability the association between anomalies in the denmark strait ssts and in the atmosphere east of greenland is consistent with that observedduring previous great salinityanomaly gsa events the results obtainedhighlight the importance ofatmosphere oceaninteractionintheearlyclimateresponsetogreenlandmelting theteleconnectionswith the north pacific and the contribution of gsa events to north atlantic oscillation nao variability

thin film channelized drainage or sheetfloods beneath a portion of the laurentide ice sheet an examination of glacial erosion forms northern new york state usa abstract morphologic analyses of characteristic bedrock erosion forms found in northern new york state usa were used to reconstruct the subglacial conditions under which they may have been produced observations from sites on wellesley island n y at point salubrious n y and at an open pit mine near balmat n y were combined with regional mapping of a diverse suite of glacial erosion forms in order to establish the areal extent and significance of subglacial drainage in northern new york results of these site specific and regional studies are the basis for discussion of the probable role of subglacial meltwater in the region bedrock erosion forms preserved at various locations in northern new york are interpreted as products of flow separation of localized subglacial meltwater during ice bed decoupling the regional distribution of these forms indicates that they are largely restricted to pre existing subglacially modified bedrock valleys that served as subglacial tunnel channels regionally extensive deep subglacial meltwater flow characterized as sheetfloods is not required to account for the erosional features described from specific sites in northern new york state

mesozoic evolution of exotic terranes and marginal seas western north america abstract regional terrane analysis has been combined with a global evaluation of plate kinematics to produce a new tectonic model for the mesozoic evolution of western north america and its associated marginal seas the model employs a two tiered data reliability ranking system to resolve conflicts within data sets the lower tier of the ranking system involves the assignment of a numerical rank to paleomagnetic and or paleobiogeographic data based on each data set s reliability the upper tier of the ranking system places the paleomagnetic and paleobiogeographic data in perspective by assigning a relative order of importance to different types of data the most reliable data are considered to be departure rift and arrival collision times that are tightly constrained by independent data sets evidence of subduction and or strike slip motion also ranks high in the master ranking system paleomagnetic and vertebrate paleobiogeographic data come next in the hierarchy followed by invertebrate and floral paleobiogeographic data application of this approach to a case study the baja british columbia controversy has resulted in a coherent model for the entire region results derived from the application of this modelling approach to the problem of the mesozoic assembly of western north america suggest that its evolution may be modeled using a minimum of 57 large terranes oblique convergence may have been the dominant tectonic process along the western north american margin during the mesozoic causing large scale latitudinal transport of many exotic terranes the motions of the terranes produced a number of marginal seas yukonia etc that were short lived but important components of western margin tectonics a combination of collision events side swiping episodes and changes in plate kinematics led to the initiation of several regional tectonic upheavals including the nevadan and sevier orogenies

glacial geomorphology of the central barents sea implications for the dynamic deglaciation of the barents sea ice sheet abstract contemporary climate change has resulted in great uncertainty in how glaciers and ice sheets around the earth might evolve it has long been appreciated that the contemporary west antarctic ice sheet wais shares many similarities with the former barents sea ice sheet bsis therefore an increasing number of studies have sought to investigate the barents sea glacial record to better understand marine based glaciation this paper reports the analysis of a new high resolution bathymetric survey covering 55 000 km2 in the central barents sea the relative chronologies of newly mapped glacial landforms such as mega scale glacial lineations grounding zone wedges moraines and crevasse squeeze ridges are used to reconstruct the ice sheet dynamics in the central barents sea our results show that the ice sheet responded dynamically with different periods of retreat advance and stagnation observed these new landform records have been integrated with other geomorphological records in order to reconstruct the retreat pattern of the bsis between 17 14 ka when the fennoscandian ice sheet is thought to have uncoupled from the bsis our data shows that the dynamic drawdown of the ice sheet saddle by ice streams was probably the primary mechanism in separating the two ice sheets after the ice sheets uncoupled the bsis is shown to have retreated episodically with several periods of relative stability geomorphological records such as those from the bsis can be used to constrain ice sheet modelling and will help to develop a clearer understanding of marine based glaciation and the role of ice streams in driving ice sheet evolution

structural chronology oroclinal deformation and tectonic evolution of the southeastern klamath mountains california devonian to jurassic volcanic sedimentary and minor intrusive rocks of the redding section rs accumulated in an intermittently active island arc setting general stratigraphic concordancy and the downsection continuity of metamorphic facies series indicate that these rocks shared a common postdepositional geologic history burial metamorphism produced secondary mineral assemblages of the zeolite prehnite pumpellyite pumpellyite actinolite and greenschist facies close correspondence between pressures calculated from existing stratigraphic overburden and those predicted from the observed metamorphic facies series indicates that less than 3 km of strata have been eroded from the presently exposed top of the early middle jurassic potem formation shortly after deposition of the potem formation compressional deformation f1 produced open to isoclinal folds foliations and small thrust faults k ar dates from post tectonic intrusions indicate that f1 deformation was completed before 168 ma this minimum age of f1 deformation is corroborated by a postfolding paleomagnetic overprint acquired at about 171 ma a second suite of intrusions dated at 120 130 ma provided a thermal pulse that variably reset the k ar system in f1 fabric defining celadonite and other relatively ar unretentive materials the nevadan orogeny late jurassic did not significantly deform rocks of the rs if at all nor is evidence for permo triassic sonoman deformation apparent the geometry of f1 structures varies systematically with location in the western bollibokka quadrangle bq f1 folds are upright with subvertical axial planes and associated foliations in the eastern bq f1 folds are overturned to the east with axial planes and associated foliations dipping as little as 40 to the west regional relationships suggest that f1 may have been a response to coeval tectonism in the western klamaths wherein crustal thickening during regional westward thrusting induced gravitational detachment of the rs from its partly serpentinized ophiolitic basement f1 structures subsequently were broadly warped about vertical axes producing variable paleomagnetic declination anomalies that range from 0 to greater than 100 clockwise the timing and cause of this f2 deformation event are as yet relatively unconstrained but were almost certainly post jurassic and may have been associated with development of the columbia embayment paleomagnetic data indicate north american paleolatitudes for the rs since at least the permian and apparently weigh against an allochthonous or exotic origin for this terrane paleontologic data indicate strong faunal similarities with north america and to a lesser extent with a tethyan province the significance of this apparent dual provinciality remains uncertain but extreme endemism of tethyan fusulinids corals brachiopods and pelecypods is questionable

simulations of the atmospheric response to south atlantic sea surface temperature anomalies abstract the sensitivity of the atmospheric circulation to sea surface temperature sst anomalies in the tropical and subtropical south atlantic ocean is studied by means of simulations with an atmospheric general circulation model gcm two types of prescribed sst anomalies are used motivated by previous analyses of data the first occurs during austral summers in association with a strengthening of the south atlantic convergence zone sacz and consists of cold sst anomalies over the subtropical south atlantic the second is the leading seasonally varying empirical orthogonal function of sst consisting of warm basin scale anomalies with maximum amplitude in the subtropics during january march and at the equator in june an ensemble of about 10 seasonal simulations is made using each type of anomaly focusing on the january march period in the first case and the january june seasonal evolution in the second during january march both experiments yield a statistically significant baroclinic response o

facies architecture within a regional glaciolacustrine basin copper river alaska abstract this paper defines the principal architectural elements present within the pleistocene glaciolacustrine basin fill of the copper river basin in alaska the copper river drains an intermontane basin via a single deeply incised trench through the chugach mountains to the gulf of alaska this trench was blocked by ice during the last glacial cycle and a large ice dammed lake referred to as lake atna filled much of the copper basin facies analysis within the basin floor allows a series of associations to be defined consistent with the basinward transport of sediment deposited along calving ice margins and at the basin edge basinward transport involves a continuum of gravity driven processes including slumping cohesive debris flow hyperconcentrated concentrated density flows and turbidity currents this basinward transport results in the deposition of a series of subaqueous fans of which two main types are recognised 1 large stratified basin floor fans which extend over at least 5 km and are exposed in the basin centre these fans are composed of multiple lobes incised by large mega channels giving fan architectures that are dominated by horizontal strata and large cross cutting channel fills individual lobes and channel fills consist of combinations of diamict derived from iceberg rainout and the ice marginal release of subglacial sediment multiple units of fining upward gravels which grade vertically into parallel laminated and rippled fine sands and silts deposited by a range of density flows and currents derived from the subaqueous discharge of meltwater and rhythmites grading vertically into diamicts deposited from a range of sediment density flows re mobilising sediment deposited by either iceberg rainout or the ice marginal release of sediment 2 small complex proximal fans which extend over less than 2 km and are exposed in the southern part of the basin these fans are composed of coalescing and prograding lobes of diamict and gravel deposited both directly by subaqueous meltwater and from sediment density flows these lobes are cross cut by a range of sand and gravel filled troughs and channels cut by subaqueous outwash and either overlie or are overlain by horizontal sheets of gravel and diamict deposited from a range of sediment density flows the fans are therefore characterised by a complex and laterally variable facies architecture water depth proglacial topography stability of meltwater portals and sediment supply may all be important in determining the type of subaqueous fan present at any one location we suggest that the copper river basin fill is dominated by packages of sediment containing multiple subaqueous fans with individual fans separated by units of diamict each sediment package is in turn separated from the next by a palaeo landsurface shaped by interstadial interglacial fluvial processes and by volcanic debris flows

deformation and metamorphism in the bard area of the sesia lanzo zone western alps during subduction and uplift the structure microstructure and petrology of a small area close to the village of bard in val d aosta italy has been studied in detail the area lies across the contact between the gneiss minuti gm and the eclogitic micaschist ems complexes of the lower element of the sesia portion of the sesia lanzo zone western alps both complexes have undergone high pressure metamorphism but the metamorphic assemblages indicate a sudden increase in pressure in going across the contact from the gm to the ems therefore we interpret the contact as a thrust dividing the lower element of the sesia into two sub elements this interpretation is supported by structural evidence the early alpine 90 70 ma metamorphic history is best preserved in the ems and is one of increasing pressure associated with thrusting the maximum p t recorded in the ems is 1500 mpa 15kbar and 550 c and in the gm is 1500 1300 mpa 15 13 kbar and 500 550 c we suggest that the rocks were probably in an active benioff zone during this time from then on the histories of the gm and ems are the same deformation continued and the thrust and thrust slices were folded during decreasing pressure we interpret the first postthrusting deformation in terms of uplift associated with continued shortening of the crust and underplating after the benioff zone had become inactive and a new benioff zone had developed further to the north west a still later deformation and the lepontine metamorphism 38 ma are related to continued uplift much of this deformation is characterized by structures indicative of vertical shortening and lateral spreading as the mountains rose above the general level of the surface

deformation partitioning and porphyroblast rotation in meta morphic rocks a radical reinterpretation abstract most porphyroblasts never rotate during ductile deformation provided they do not intern ally deform during subsequent events with the exception of relatively uncommon but spectacular examples of spiralling garnets instead the sur rounding foliation rotates and reactivates due to partitioning of the deformation around the porphyroblast consequently porphyroblasts commonly preserve the orientation of early foliations and stretching lineations within strain shadows or inclusion trails even where these structures have been rotated or obliterated in the matrix due to subsequent deformation these relationships can be readily used to help develop an understanding of the processes of foliation development and they demonstrate the prominent role of reactivation of old foliations during subse quent deformation they can also be used to determine the deformation history as porphyro blasts only rotate when the deformation cannot partition and involves progressive shearing with no combined bulk shortening component

mineral fabrics in high level intrusions recording crustal strain and volcano tectonic interactions the shellenbarger pluton sierra nevada california the minarets caldera is a volcano plutonic complex in the sierra nevada california that exemplifies complex interactions between volcanism and tectonic deformation in continental margin arcs caldera evolution commenced with emplacement of pre collapse rhyolitic ash flow tuff followed by collapse and deposition of volcanic breccia and rhyodacitic ash flow tuff subsequently the volcanic rocks were deformed along the regional bench canyon shear zone the caldera centre was then intruded by the resurgent c 100 ma steep sided shellenbarger granite pluton which steepened the shear zone foliation the pluton was overprinted by syn to post magmatic nne ssw horizontal shortening the same shortening was documented in several other late cretaceous syntectonic plutons in the sierra nevada and interpreted to record dextral transpression during convergence of the farallon and north american plates to explain the unusual tectonic fabric in the shallow level shellenbarger pluton we develop a general model for strain partitioning in syntectonic magma bodies emplaced at various crustal levels we propose that shallow intrusions isolated within stiff crust may tend to accommodate minor pure shear strain whereas simple shear dominates along weak faults and shear zones by contrast a rheological reversal is crossed deeper in the crust and magma bodies become the weakest simple shear dominated parts of the system supplementary material analytical methods and anisotropy of magnetic susceptibility and u th pb isotopic data are available at https doi org 10 6084 m9 figshare c 3582749

the influence of large ductile shear zones on the emplacement and deformation of the wyangala batholith se australia abstract the wyangala batholith consists of many small s and i type plutons most of which are elongate in a n s direction our studies of this batholith indicate that n s striking magmatic foliations exist in some of the individual plutons but are not strongly developed a few individual plutons show evidence of forceful emplacement but in general most do not intense post emplacement deformation occurs in a series of e directed thrusts that border the eastern edge of individual plutons or the batholith as a whole this thrusting formed gneissic layering mylonites and secondary foliations in the batholith and complex polyphase folding and cleavage development in the wall rocks we suggest that the batholith was emplaced as sheet like bodies possibly along steep reverse faults data presently available indicate that the pre emplacement deformation of the wall rocks is middle silurian that the batholith was emplaced in the late silurian and that post emplacement thrusting is late silurian to early carboniferous finally the close association of batholiths and regions of complex deformation in the lachlan fold belt suggest to us that these elements may represent shallow level equivalents of hollister crawford s surge tectonics geology 14 558 561 1986

sedimentation in an esker system influenced by bedrock topography near kingston ontario late wisconsinan sand and gravel deposits on the frontenac arch ontario record a major meltwater drainage system developed subglacially and subaqueously in one or more glacial lake phases of the lake ontario basin during retreat of the laurentide ice sheet factors influencing channel location morphology and sediment deposition are ice flow direction and the precambrian bedrock topography in turn dependent upon bedrock structure and composition meltwater drainage across the frontenac arch is localized within a broad depression oriented approximately parallel to glacial flow sediment deposition within the regional depression follows ice flow direction despite irregular bedrock relief indicating formation of the meltwater system and associated sediments in three stages i establishment of a continuous meltwater system subglacially under high hydrostatic pressure with minor erosion of underlying precambrian bedrock ii deposition of poorly sorted coarse grained sediment in cavities or channels associated with irregular bedrock topography and iii deposition of several coalescing subaqueous outwash fans at the ice margin as the glacier receded from the area the discontinuous nature of the deposits and the association of proximal to distal outwash fan facies within a deposit suggest that esker sedimentation occurred during periodic stabilization of the ice front during deglaciation

kinematic and metamorphic aspects of cleavage formation in very low grade metamorphic slates abstract fabric studies on first cleavages in very low grade metamorphic slates from the rheinisches schiefergebirge and other very low grade metamorphic fold belts reveal two types of slaty cleavage 1 1 cleavage without syntectonic phyllosilicate recrystallization these are generally crenulation cleavages 2 2 cleavage with syntectonic phyllosilicate recrystallization with increasing syntectonic metamorphism the crenulation fabric is modified by solution of grains along cleavage planes and precipitation of material within the cleavage lamellae with further increase of metamorphism the crenulation fabric is gradually obliterated the finite fabric results from progressive solution crystallization and recrystallization superimposed with bending kinking and internal rotation achieved by slip parallel to the basal planes of phyllosilicates

the depositional history of an esker near ottawa canada the 10 km long stittsville ridge trending parallel to the last direction of ice advance into the ottawa area is here classified as an esker the sediments of the ridge are interpreted as subaqueous outwash deposited from a subglacial or englacial meltwater conduit emptying into an inlet in the late wisconsin glacier front the ridge formed by the coalescence of subaqueous outwash fans as the ice retreated northward sedimentological variation along the ridge is attributed to a change in the morphology of the inlet as the ice front retreated from an initially narrow symmetrical shape to a broader and increasingly asymmetrical form

extent of the nevadan orogeny central sierra nevada california the late jurassic nevadan orogeny has long been considered responsible for much of the deformation that occurred in the central sierra nevada on the basis of our recent work and that of other workers we suggest that the intensity of nevadan deformation in the central sierra nevada decreases eastward within the foothills belt is restricted to domainal deformation in rocks between the melones fault zone and the batholith and is virtually absent in the continental volcanic arc along the east side of the range these data and interpretations suggest that in the central sierra nevada nevadan deformation does not represent as intense and widespread an orogeny as originally supposed

the depositional history of the bloomington complex an ice contact deposit in the oak ridges moraine southern ontario canada abstract the oak ridges moraine is a major physiographic feature of south central ontario canada that is made up of a number of distinct depositional elements one of these elements the bloomington complex is a body of sand gravel and diamict that was deposited largely within an east west trending interlobate lake basin that formed as the continental glacier split into two lobes a northern lobe termed the simcoe lobe and a southern lobe termed the ontario lobe the oldest exposed sediment in the bloomington complex is a sequence of stratified sand and gravel that is interpreted to have been deposited as coalesced subaqueous outwash fans that developed where several glacial meltwater conduits emptied into the proglacial lake these deposits are locally sharply incised by stratified sand and gravel that is interpreted as a glaciofluvial deposit laid down when the lake basin drained as ice margin retreat caused outlets to open along the niagara escarpment 60 km to the west the fan complex and glaciofluvial deposits are overlain in turn by stratified sand silt and clay that was deposited within the lake basin after the ice margins readvanced closing the drainage outlets and allowing the lake to rise the glaciolacustrine deposits pass gradationally upward into a heterogeneous deposit of sand silt clay and diamict that is interpreted as an ice marginal deposit of the last stages of closing of the lake basin as the northern and southern ice lobes converged finally a cap of diamict covers the area deposited as glacial ice advancing from the south over rode the study area the complete package of sediment that makes up the bloomington complex illustrates the effects of fluctuating ice margins on proglacial deposition in a glaciolacustrine setting

a glaciofluvial origin for drumlins of the livingstone lake area saskatchewan the livingstone lake drumlin field of northern saskatchewan is on the athabasca plains it is draped over high ground underlain by the precambrian athabasca sandstone the drumlins occur in spindle parabolic and transverse asymmetrical forms a map of individual drumlins shows that features of similar form occur together the drumlins are related on a regional scale to even larger landforms there is also an arrangement of drumlins in streams parallel to the assumed flow direction these patterns illustrate spatial organisation of the drumlin forming flows the livingstone lake drumlins are closely related to tunnel valleys large crescentic scours and eskers exposed bedrock reveals widespread scalloping and sichelwannen an argument is made that drumlins are related to these glaciofluvial forms but were created at different times and by different flows than those forming small scale flutings and other lodgment features sediments within the drumlins are mainly primary water sorted deposits some of wh

complex strain patterns developed at the frontal and lateral tips to shear zones and thrust zones abstract many of the complex strain patterns seen in shear zones and thrust zones such as variable fabric orientations refolded folds and fabrics together with folds with hinges almost parallel to the main transport direction can be explained in terms of differential movement within the shear zones these strains are developed at the frontal and lateral tips of the zones as they propagate examples are taken from the moine thrust zone of scotland which show variations in strains particularly at the lateral tips the form of differential movement described here may lead to complex strain paths and non plane strain ellipsoids and the spatial variations in finite strain may be used to delineate zones of extensional and compressional flow and differential movement in the shear zones or thrusts

the parameterization of the planetary boundary layer in the ucla general circulation model formulation and results abstract a planetary boundary layer pbl parameterization for general circulation models gcms is presented it uses a mixed layer approach in which the pbl is assumed to be capped by discontinuities in the mean profiles both clear and cloud topped boundary layers are parameterized particular emphasis is placed on the formulation of the coupling between the pbl and both the free atmosphere and cumulus convection for this purpose a modified coordinate is introduced in which the pbl top and the lower boundary are both coordinate surfaces the use of a bulk pbl formulation with this coordinate is extensively discussed results are presented from a july simulation produced by the ucla gcm pbl related variables are shown to illustrate the various regimes the parameterization is capable of simulating

post nevadan deformation along the bear mountains fault zone implications for the foothills terrane central sierra nevada california southern parts of the foothills terrane sierra nevada california consist of western and eastern sequences of volcanic rocks and overlying slate gray wacke units separated by a multiply deformed and lithologically chaotic central belt structural and strain studies suggest that the intensity of regional ductile deformation decreased from greater than 50 shortening in the western belt to less than 30 shortening in the eastern belt and that much of this ductile deformation is younger than the timing usually assumed for the nevadan orogeny these structures are in turn deformed by a large ductile shear zone representing the southern continuation of the bear mountains fault zone this shear zone separates the western and central belts has an oblique east over west sense of movement and deforms the western margin of the guadalupe igneous complex these observations suggest that the eastern and western volcanic sequences are pieces of arcs amalgamated along the bear mountains fault zone during and after nevadan deformation

strains and structures associated with a terrane bounding stretching fault the melones fault zone central sierra nevada california abstract an examination of the structures total strains and rock types across the melones fault zone indicates that in the central sierra nevada this fault separates and locally imbricates two distinct terranes east of the fault a widespread early jurassic cleavage displays west northwest to northwest strikes and is associated with moderate to high strain intensities these structures form in jura triassic metasedimentary rocks in part derived from a continental source a weak northwest striking cleavage and low strain intensities occur west of the fault in lower jurassic volcanic rocks and upper jurassic slates and sandstones the fault zone itself consists of steep east dipping ductile brittle shear zones or stretching faults along which the early jurassic structures are transposed parallel to the jura cretaceous and fault related structures large flattening type strains are common in the fault zone and may be the result of heterogeneous strains developed when the shear zones bend around resistant blocks or by volume losses total strains in the eastern hanging wall reflect the superposition of fault related on older strains therefore stretching lineations in this hanging wall do not reflect directions of fault motion stretching lineations in the footwall and fault zone kinematic indicators in the fault zone and a small eastward jump in metamorphic grade suggest an east over west or reverse sense of movement no evidence for significant strike slip or oblique slip motion was found removal of footwall strains indicates that the jura cretaceous shortening across the fault was responsible for both the transposition of older structures east of the fault and the rotation of the fault to its present steep dips thus the melones fault is a large ductile brittle shear zone along which the eastern hanging wall merced river terrane moved to the southwest over the western footwall eastern foothills terrane

macroforms large bedforms and rhythmic sedimentary sequences in subglacial eskers south central ontario implications for esker genesis and meltwater regime abstract eskers of south central ontario were deposited in closed subglacial conduits which were continuous main conduits this interpretation is supported by the intimate association of eskers with an anastomosing network of tunnel channels relatively continuous esker ridges minimal post formational disturbance of esker sediments intercalation of till and stratified sand and gravel diapiric folding at an esker core low variability in palaeocurrent direction and upslope flow paths down esker trends in clast lithology roundness and sphericity indicate continuous conduits with sediment supply by subglacial deformation of adjacent material into the conduits melt out of sediment from the conduit walls and fluvial resedimentation esker ridge morphology is attributed to synchronous erosion transportation and deposition along the main conduits such that ridge discontinuities are primarily explained as zones of non deposition during esker formation composite pseudoanticlinal and oblique accretion avalanche bed macroforms are identified gravel facies within these macroforms were deposited from fluidal flows or hyperconcentrated dispersions progradation of macroforms or migration of constituent large bedforms through the main conduits may have temporarily blocked constricted portions of those conduits and acted as possible internal autogenic controls on sediment availability and flow resistance the location of macroforms within conduits was primarily controlled by conduit geometry and sediment availability and later by feedback between macroform and conduit geometries sand and gravel units alternate rhythmically in vertical section rhythmicity is interpreted as a response to episodic flood flows controlled by seasonal changes in water supply but not necessarily representing annual events fans beads anabranched reaches and extended hummocky deposits are intimately associated with the main esker ridges they are interpreted in terms of subglacial cavities and localized flotation zones connected to the main conduits during flood events in phase wave structures are the products of hydraulic jumps in hyperconcentrated flood flows at flow expansions into swells within the main conduits into cavities connected to the main conduits or at a grounding line esker ridges record only the most powerful flood events whereas fans and beads record flow events in finer detail being primarily depositional reservoirs laterally fining deposits record the waning stages of conduit operation

a treatment for the stratocumulus to cumulus transition in gcms numerical models of climate have great difficulties with the simulation of marine low clouds in the subtropical pacific and atlantic oceans it has been especially difficult to reproduce the observed geographical distributions of the different cloud regimes in those regions the present study discusses mechanisms proposed in previous works for changing one regime into another one criterion is based on the theory of stratocumulus destruction through cloud top entrainment instability due to buoyancy reversal situations in which the mixture of two air parcels becomes denser than either of the original parcels due to evaporation of cloud water another criterion is based on the existence of decoupling in the boundary layer when decoupled the stratocumulus regime changes to another in which these clouds can still exist together with cumulus in a les study the authors have suggested that a combination of those two criteria can be used to diagnose whether at a location the cloud regime corresponds to a well mixed stratocumulus regime a shallow cumulus regime or to a transitional regime where the boundary layer is decoupled the concept is tested in the framework of an atmospheric general circulation model gcm it is found that several outstanding features of disagreement between simulation and observation can be interpreted as misrepresentations of the cloud regimes by the gcm a novel criterion for switching among regimes is proposed to alleviate the effects of these misrepresentations

a moist pbl parameterization for large scale models and its application to subtropical cloud topped marine boundary layers abstract a new general purpose boundary layer parameterization that permits realistic treatment of stratocumulus capped boundary layers scbls with coarse vertical resolution is described it combines a 1 5 order turbulent closure model with an entrainment closure at the boundary layer top three different implementations of the entrainment closure in which the boundary layer height is respectively prognosed reconstructed from thermodynamic values at the grid points or restricted to lie on a flux level of the host model grid are tested in a single column modeling framework at both fine and coarse vertical resolution the first two approaches permit a stratocumulus top and base to lie between grid levels and evolve continuously with time but are more complicated to implement in a three dimensional model the model performs very well in cases of dry convection whatever the inversion implementation and the vertical resolution with 15 mb or better vertical resolution all approaches properly simulate

sedimentary facies relationships in esker ridge esker fan complexes southeastern ontario canada application to the exploration for asphalt blending sand abstract in this paper we examine the viability of using sedimentological facies modelling techniques in the exploration for a specific aggregate mineral resource blending sand blending sand is a naturally occurring medium grained poorly sorted aggregate that is an integral component of asphalt mixes in canada and the northern united states and europe glacial outwash deposits are a common exploration target a glaciogenic complex in southeastern ontario that contains blending sand was examined in order to document the facies organization and origin of the complex as a whole and the blending sand deposits in particular in this study blending sand is located only within the proximal portion of the esker fans and can be characterised as a distinct facies that was formed by sustained high density underflows which deposited cross bedded medium sand periodic fluctuations in flow speed allowed interbeds of rippled fine sand to accumulate giving the facies its overall poor sorting a comparison with similar deposits elsewhere indicates that local facies associations have more widespread applicability therefore the surface morphology and the spatial arrangement of sediment facies within esker ridge esker fan complexes can be used as predictive exploration tools to locate blending sand in these types of deposits different facies models are needed for other deposit types and aggregate products

a method for determining equivalent depths of the atmospheric boundary layer over the oceans the concept of an equivalent depth of the atmospheric boundary layer is discussed in the framework of vertically integrated boundary layer equations a method is presented by which these depths may be computed from sea level pressure analyses and ocean surface wind speed measurements an explicit representation that yields a realistic value for the equivalent depth from the equator to the pole is given in terms of these parameters for this study the equivalent depths were calculated from 3 days of altimeter wind speed data taken from seasat this study shows that over the mid latitude and polar regions and in the range of surface wind speeds between 5 m s and 15 m s the equivalent depths are calculated to be about 700 800 m comparable to the heights of the atmospheric boundary layer in the polar region both scale heights are also quite comparable in values ranging between 200 and 600 m over the tropics however the conventional scale heights as is well known are unreasonably large whereas the calculated equivalent depths are quite realistic and well defined it is therefore concluded that the method presented in this study may be used to infer heights of the atmospheric boundary layer over the global oceans in addition the calculated equivalent depths together with the measured surface wind speeds provide an estimate of the spin up time for the boundary layer flows during the 3 day period the spin up times are found to vary between 4 5 hours in the polar regions to about 39 4 hours in the mid latitudes

the carstairs kames lanarkshire scotland morphology sedimentology and formation the carstairs kames have been the subject of debate for over 150 yr a synthesis of previous work along with new sedimentological data is used to reappraise this classic british esker locality three morphological elements are recognised i large sinuous and anastomosing ridges ii large irregular linear mounds and iii small low and irregular mounds the main ridge system is composed of a core of boulder gravel with sand pebble gravel above and adjacent to the core the large linear mounds contain a varied facies range which include glaciolacustrine sediments deltaic sequences laminites and dropstones debris flows and glaciofluvial channel systems all the deposits both in the main ridges and in the adjacent linear mounds contain syn and post depositional subsidence structures including normal faults synclinal folds and growth faults a range of potential origins for these landforms is reviewed and it is suggested that glaciofluvial sedimentation in a supraglacial environment controlled by a topography of ice cored ridges is the most appropriate depositional model 1997 john wiley sons ltd

regional structural and strain analyses of terranes in the western metamorphic belt central sierra nevada california abstract a comparison of total strains in 225 samples from the western metamorphic belt sierra nevada shows that strain types and intensities strongly depend on rock type greywackes and clast supported conglomerates are least strained whereas more intense strains occur in lapilli tuffs pebbly mudstones and slates large belts of volcanic rock record plane strain whereas nearby slate and greywacke sequences record flattening type strain suggesting that volume losses of 45 65 occurred in slates and 0 26 in greywackes lapilli tuffs record less than 11 volume loss the differences in volume loss and strain from one rock type to another require that discontinuities in total strain occur at most lithologic contacts independently of the lithologic control regional structural patterns and strain fields support the delineation of three terranes foothills merced river and northern sierra and two distinct domains western and eastern foothills terranes at these latitudes within the western metamorphic belt these terranes each bordered by large ductile shear zones differ in average strain intensity and orientation but not in strain type in the foothills terrane strain intensities decrease from moderate values in the western foothills terrane to low values in the eastern foothills terrane strain intensities in the study area are highest in the melones and bear mountains fault zones and in terranes east of the melones fault structures associated with regional deformation in each terrane do not extend far across terrane boundaries multiple generations of regionally developed structures are therefore rare in this part of the western metamorphic belt outside of fault zones we see one regionally developed cleavage in the foothills terrane a single but older cleavage in the merced river terrane and two still older cleavages in the northern sierra terrane however younger deformations may have reactivated and rotated older structures in adjacent terranes the timing and kinematics of the deformation in the foothills terrane suggest that faulting and rigid body rotations preceded pervasive shortening continued fault movement and rotation of faults to steep dips if orientations of ductile structures reflect plate motions structures in the merced river terrane suggest jurassic triassic orthogonal nne convergence whereas structures in the foothills terrane support late jurassic orthogonal ne convergence changing to oblique ene convergence about 150 ma ago

impacts of sst anomalies on the north atlantic atmospheric circulation a case study for the northern winter 1995 1996 the present paper selects the northern winter of december 1995 february 1996 for a case study on the impact of sea surface temperature sst anomalies on the atmospheric circulation over the north atlantic and western europe in the atlantic the selected winter was characterized by positive sst anomalies over the northern subtropics and east of newfoundland and negative anomalies along the us coast a weak la nina event developed in the pacific the north atlantic oscillation nao index was low precipitation over the iberian peninsula and northern africa was anomalously high and precipitation over northern europe was anomalously low the method of study consists of assessing the sensitivity of ensemble simulations by the ucla atmospheric general circulation model ucla agcm to sst anomalies from the observation which are prescribed either in the world oceans the atlantic ocean only or the subtropical north atlantic only the results obtained are compared with a control run that uses global time varying climatological sst the ensemble simulations with global and atlantic only sst anomalies both produce results that resemble the observations over the north atlantic and western europe it is suggested that the anomalous behavior of the atmosphere in the selected winter over those regions therefore was primarily determined by conditions within the atlantic basin the simulated fields in the tropical north atlantic show anomalous upward motion and lower upper level convergence divergence in the atmosphere overlying the positive sst anomalies consistently the subtropical jet intensifies and its core moves equatorward and precipitation increases over northern africa and southern europe the results also suggest that the sst anomalies in the tropical north atlantic only do not suffice to produce the atmospheric anomalies observed in the basin during the selected winter the extratropical sst anomalies would provide a key contribution through increased transient eddy activity which causes an extension of the subtropical jet eastward from the coast of north america

the development of folds and cleavages in slate belts by underplating in accretionary complexes a comparison of the kodiak formation alaska and the calaveras complex california the development of folds and cleavages in slate and graywacke belts is commonly attributed to arc continent or continent continent collisions however the kodiak formation of southern alaska and the calaveras complex of the western sierra nevada california are two slate and graywacke belts in which folds and slaty cleavages developed during simple underthrusting and underplating within accretionary wedges the maastrichtian kodiak formation is composed dominantly of coherent turbidites but includes lesser pebbly mudstone minor conglomerate and rare chert the kodiak formation is part of a large accretionary complex that youngs in age seaward but bedding tops generally show landward younging a progression of structures has been determined by crosscutting relationships and includes 1 syndeformational depositional features 2 broken formation 3 slaty cleavage folds and thrust faults 4 crenulations and crenulation cleavage 5 late brittle thrust faults and 6 right lateral strike slip faults broken formation slaty cleavage thrust faults and folds developed during underthrusting and underplating within an accretionary wedge crenulations and brittle thrust faults are related to subsequent intrawedge shortening based on peak metamorphism in the uppermost zeolite to prehnite pumpellyite facies underplating occurred at a minimum depth of 10 km the calaveras complex is composed of argillite chert graywacke pebbly mudstone limestone and volcanic rocks its age of deposition has a maximum range from permian to early jurassic overall the unit appears to young westward but local facing indicators show eastward younging of individual blocks the sequence of structures developed in the calaveras complex is 1 syn depositional olistostromes 2 broken formation 3 slaty cleavage folds and thrust faults and 4 younger jura triassic folds and crenulation cleavages broken formation and slaty cleavage developed during underthrusting and underplating in an accretionary wedge in an analogous fashion to the kodiak formation greenschist facies metemorphism during underplating suggests that the calaveras complex was accreted at deeper levels or in a wedge with a higher geothermal gradient than the kodiak formation some other probable examples of slate graywacke belts that became folded and well foliated during underplating include part of the dunnage zone newfoundland the southern uplands complex scotland the torlesse terrane new zealand part of the hamburg klippe pennsylvania and the taconic allochthons new york peak metamorphism in these belts indicates that they were accreted in accretionary wedges with geothermal gradients higher than usually assumed for such tectonic settings such wedges may have been fairly common features at convergent margins

collapse of sediment filled crevasses associated with floods and mass flows in the proximal zone of the pernunnummi sandurdelta iii salpausselka sw finland abstract we aim to explain the complex geomorphology and sedimentology of the proximal zone of the pernunnummi sandurdelta which forms the most prominent portion of the iii salpausselka ice marginal complex of the former scandinavian ice sheet in sw finland we focus on the sedimentology of distinct diamicton covered glaciofluvial and glaciolacustrine landforms kames making accurate interpretations of both proximal diamictons and related sedimentary facies a crucial approach in the reconstruction of the depositional history of ice marginal zones we propose that the build up of the sandurdelta was followed by the formation of a glaciofluvially dominated supraglacial landsystem within a stagnant ice zone which fringed a glacial embayment between sub lobes of different deglacial dynamics the role of an integrated meltwater system including a major subglacial tunnel and water filled crevasses was crucial in constructing the controlled topography of this supraglacial landsystem the stagnant ice zone contributed to the incremental retreat of the ice margin within a shallow water environment where growing end moraines and proglacial deposits led to the development of supra aquatic conditions our results also evoke temporary dammed water bodies which were supported by ice marginal frozen bed conditions within the baltic sea icestream the collapse of crevasses with ice contact glaciofluvial and glaciolacustrine sediments during the continued deglaciation led to outbursts of dammed meltwater accompanied by extensive mass flows that formed the diamictons partially covering the ice proximal zone because ice marginal and esker related glaciofluvially dominated landform complexes with disintegration topography are relatively common along the main ice marginal deposits of the last great ice sheets the interpreted sedimentary record must be more common than previously reported thus extensive surficial and proximal diamictons of the ice marginal complexes do not always indicate either a re advance or a major oscillation of the ice front this study promotes the understanding of deglacial icestream dynamics with no known modern analogues and hence helps to improve both palaeogeographic reconstructions and the future compilation of even more accurate ice sheet models

links between annual variations of peruvian stratocumulus clouds and of sst in the eastern equatorial pacific abstract the hypothesis that peruvian stratocumulus play an important role on both the annual mean and annual variations of sea surface temperature sst in the eastern equatorial pacific is examined the problem is addressed by performing sensitivity experiments using the university of california los angeles coupled atmosphere ocean gcm with different idealized temporal variations of stratocumulus in a region along the coast of peru the results obtained are consistent with the notion that peruvian stratocumulus are a key component of the interhemispherically asymmetric features that characterize the annual mean climate of the eastern equatorial pacific including the cold ssts off peru and the absence of a southern itcz the principal new finding of this study is that the annual variations i e deviations from the annual mean of peruvian stratocumulus are linked to the differences between the amplitude duration and westward propagation of the warm and cold phases of the equatorial cold tongue in

buoyancy reversal decoupling and the transition from stratocumulus to shallow cumulus topped marine boundary layers the transition in a marine boundary layer mbl from stratocumulus topped to shallow cumulus topped is investigated by using a large eddy simulation les model the experiments performed aim to examine the influence on the transition of 1 the probability of buoyancy reversal at the mbl top i e situations in which the mixture of two air parcels becomes denser than either of the original parcels due to phase change or other nonlinear processes involved in the mixing and 2 the degree of decoupling in the mbl i e the strength of a shallow stably stratified layer near cloud base our results suggest that a stratocumulus topped mbl is most likely to transit to a cumulus topped one when 1 there exists high probability of buoyancy reversal at the mbl top and 2 the mbl is decoupled due to large surface evaporation we argue that a parameterization that includes representation of those two effects combined has the potential to provide a simple way of predicting the mbl transition in climate models

multiply deformed terrains problems of correlation abstract the best tools available for carrying out a structural analysis in a complex area are overprinting style and patterns of orientation unfortunately all have limitations which are reviewed briefly and discussed in areas of continuous unfaulted outcrop the deformational history can be established purely on the basis of overprinting but even in such areas there can be problems since not all overprinting relationships are unambiguous most fold interference patterns are reliable overprinting relationships based on foliations however are commonly unreliable and various examples are cited and discussed even in areas where the sequence of deformational events can be established their temporal significance is unclear since the methods applied only determine local relative timing and absolute relationships must vary in space and time across an orogen

the partitioning of deformation in flowing rock masses abstract most geological structures owe their development to heterogeneous and or non steady flow flow partitioning refers to the division of the instantaneous velocity field into components related to translation strain and rotation flow partitioning during the development of a geological structure usually changes with time and different histories of flow are involved at different points in the developing structure heterogeneity leads to the development of flow domains with different characteristics notably the degree of non coaxiality of deformation and different partitionings of the rotational component of flow into shear induced vorticity and spin during non steady flow there is often continual repartitioning of vorticity between the spin and shear induced components spin is an important aspect of flow leading to the development of structure this paper discusses the partitioning of deformation in a flowing rock mass coaxial flow tends to occur in isotropic materials in regions near weakly constrained boundaries non coaxial flow is favoured by suitably oriented material anisotropy and or the presence of well defined boundary constraints involving parallel relative displacements a developing anisotropy e g a crystallographic fabric in a shear zone can induce a change from coaxial to non coaxial flow other effects are related to the scale of approximation for example bulk shear induced vorticity can be locally converted to spin flow in the crust and mantle of the earth produces geological structures on all scales and involves many different types of rheological response the factors that affect flow partitioning e g spin versus non coaxial deformation are therefore of interest

quasi stationary waves in the southern hemisphere part ii generation mechanisms abstract in this part ii the authors investigate the role that antarctic elevations the rest of the world orography thermal forcing from lower latitudes and the transient eddy component of the flow play on the generation of the quasi stationary wave field in the southern hemisphere an approach based on the ucla gcm is followed results from a control simulation with full orography and from experiments without the antarctic elevations and without the rest of the world orography suggest that the quasi stationary wave with zonal wavenumber 1 qs wave 1 around antarctica is primarily generated by mechanisms other than the antarctic elevations comparison of a three dimensional eliassen palm flux vector in the control simulation and those where the antarctic elevation and the rest of the world orography are removed suggests that wave activity propagates both from the subtropics and from polar latitudes although in qualitative agreement with results of part i the horizontal and vertical structure of t

alternative methods for specification of observed forcing in single column models and cloud system models we discuss alternative methods for prescribing advective tendencies in single column models scms and cloud system models these include revealed forcing in which the total advective tendency is prescribed from observations horizontal advective forcing in which the horizontal advective tendencies are prescribed together with the observed vertical motion which is combined with the predicted sounding to determine the tendencies due to vertical advection and relaxation forcing in which the horizontal advective tendencies are computed by relaxing the sounding toward the observed upstream sounding with a relaxation timescale determined by the time required for the wind to carry parcels across the grid column when relaxation forcing is used the horizontal advective tendencies can be diagnosed from the model output and compared with the corresponding observed tendencies we present scm results to illustrate these three forcing methods based on data from several field experiments in both the tropics and the midlatitudes each method is shown to have its strengths and weaknesses overall the results presented here do not show unambiguous differences between revealed forcing and horizontal advective forcing the two methods appear to be generally comparable revealed forcing may therefore be preferred for its simplicity relaxation forcing guarantees realistic soundings of the state variables but can produce large errors in parameterized processes which are driven by rates e g fluxes rather than states in particular relaxation forcing gives large errors in the precipitation rate in this model we demonstrate that relaxation forcing leads to unrealistically high low precipitation in versions of the model which tend to produce unrealistically dry humid soundings the observed horizontal advective tendencies in the tropics are so weak especially for temperature that small absolute errors in the diabatic tendencies diagnosed with relaxation forcing can lead to large relative errors in the diagnosed horizontal advective tendencies

deglacial meltwater drainage and glaciodynamics inferences from laurentide eskers canada abstract this paper evaluates current knowledge of laurentide eskers in canada in the light of developments in glacier hydrology and glacial sedimentology questions regarding the morpho sedimentary relations of eskers the synchroneity and operation of r channel systems the role of supraglacial meltwater input and proglacial water bodies the controls on esker pattern and the glaciodynamic condition of the ice sheet at the time of esker formation are discussed a morphologic classification of eskers is proposed five types of eskers are identified and investigated type i eskers likely formed in extensive synchronous dendritic r channel networks under regionally stagnant ice that terminated in standing water type ii eskers likely formed in short subaqueously terminating r channels or reentrants close to an ice front or grounding line that may have actively retreated during esker sedimentation type iii eskers plausibly formed in short r channels that drained either to interior lakes in or tunnel channels under regionally stagnant ice type iv eskers may have formed as time transgressive segments in short subaerially terminating r channels or reentrants that developed close to the ice margin as the ice front underwent stagnation zone retreat or downwasted and backwasted regionally stagnant ice however formation in synchronous r channels cannot be discounted on the basis of reported observations type v eskers may have formed in h channels that terminated subaerially the spatial distribution of these esker types is discussed the factors that determined laurentide r channel pattern and operation were likely a complex combination of i supraglacial meltwater discharge ii the number and location of sink holes iii the ice surface slope thickness and velocity and iv the permeability topography and rigidity of the bed these factors cause and respond to changes in ice dynamics and thermal regime over the glacial cycle

stretching normal to the regional thrust displacement in a thrust wrench shear zone rehamna massif morocco the hercynian rehamna massif of morocco is located in the meseta belt on the sheared boundary between the weakly strained western meseta coastal block and an intensely deformed carboniferous basin deformation may be related to three superposed phases the most important phases d1 and d2 result in a main composite s1 2 foliation and are related to westward thrusting d4 is contemporaneous with the emplacement of syn to late tectonic granitic plutons fold asymmetry and microstructures rotated garnets s c tectonites suggest a dominant westward thrusting in eastern rehamna in central rehamna along the thrust zone front stretching lineations are almost normal to the regional coeval thrust displacement direction and microstructures rotated garnets shear bands asymmetrical pressure shadows observed along the 1 direction stretching lineation direction suggest dextral reverse southward wrenching this particular strain pattern is interpreted as a product of thrust wrench shearing combining ductile thrusting and wrenching during the progressive synmetamorphic shortening of the area along the frontal tip of the central meseta thrust units

sequential porphyroblast growth and crenulation cleavage development during progressive deformation abstract six stages of crenulation cleavage development during a single deformation event d2 can be recognised in both matrix and porphyroblast inclusion trails in the robertson river formation n e australia these stages progress from undeformed to crenulation and differentiated crenulation of s1 through development of differentiated crenulation cleavage s2 and differentiated schistosity s2 to homogeneous foliation s2 these rocks underwent prograde metamorphism during d2 and chloritoid garnet staurolite andalusite and sillimanite isograds have been mapped most rocks are rich in porphyroblasts which commonly contain well defined inclusion trails the geometry of these trails varies from one mineral type to the next depending on the timing of porphyroblast growth relative to the stage of crenulation cleavage development in the schistose matrix the deformation history involved progressive bulk inhomogeneous shortening and the strain is very heterogeneous on all scales partly as a consequence of this hence each of the six stages of crenulation cleavage development formed locally at various times during d2 therefore if a porphyroblast grew late in the deformation it could overgrow all stages of crenulation cleavage development including the very early ones the temperature increased during metamorphism in any one locality and consequently some porphyroblasts overgrew others that were unstable in the new conditions preserving them from destruction hence the precise timing of mineralogical reactions deduced from isograds and mineral chemistry relative to the stages in schistosity development can also be determined in the andalusite zone the sequence of porphyroblasts in decreasing order of age is biotite garnet biotite staurolite andalusite dissolution of garnet occurred during growth of staurolite and especially andalusite and dissolution of staurolite accompanied andalusite growth

orographic influences on subtropical stratocumulus the impact of south american orography on subtropical stratocumulus clouds off the peruvian coast is investigated in the context of an atmospheric general circulation model it is found that stratocumulus incidence is significantly reduced when south american orography is removed key to this behavior is a decrease in lower tropospheric stability lts that allows for more frequent stratocumulus destruction through the model s cloud top entrainment instability mechanism the role of orography in enhancing peruvian stratocumulus is as follows within the pbl orography deflects the midlatitude westerly winds equatorward in association with cold air advection and blocking of the low level flow from the continent above the pbl the steep and high south american orography deflects a significant portion of the midlatitude westerlies equatorward this flow sinks along the equatorward sloping isentropes thus promoting subsidence both processes increase lts over the stratocumulus region in further agcm experiments the sensitivity of peruvian stratocumulus to the use of unsmoothed orographic boundary conditions is assessed the results show no significant differences to the control simulation which uses smoothed orography this suggests that in the context of gcms a representation of south american orography more detailed than is generally used has little potential for improving the performance of coupled ocean atmosphere models in the eastern tropical pacific

analysis and interpretation of composite foliations in areas of progressive deformation abstract in areas of progressive deformation where successive structures develop during a relatively continuous deformation within a geologically short time period traditional chronological notations of structural elements e g s 1 s 2 etc can give erroneous impressions of how large rock masses evolve in time and space we demonstrate from field examples that successive structures can develop which a are comparable in morphology and orientation but of different ages b are different in morphology but of comparable age and c show rapid morphological changes over short distances under such conditions correct identification of the relative age of structures is often difficult to impossible we consider the concepts of a composite foliation and of transposition cycles as vehicles to objectively evaluate the significance of different sets of structures in the evolution of larger rock masses we suggest that 1 structural elements be labeled using morphological notation adding numerical subscripts only when independent evidence is available 2 geologists more fully acknowledge and integrate the concept of deformation partitioning into their models and 3 when analyzing areas of multiple deformation more emphasis is placed on the relationship between domains of differing complexity integration of these three perspectives in the analysis will lead to a more realistic basis upon which to model the structural evolution of large rock masses

what determines the position and intensity of the south atlantic anticyclone in austral winter an agcm study abstract the south atlantic anticyclone is a major feature of the austral winter climatology an atmospheric general circulation model agcm is used to study the dynamics of the south atlantic anticyclone by means of control simulations and experiments to investigate sensitivity to prescribed orography sea surface temperatures and soil wetness the south atlantic anticyclone in the first control simulation is unrealistically zonally elongated and centered too far west errors typical of coupled ocean atmosphere gcms results of the sensitivity experiments suggest that these deficiencies are associated with another family of systematic model errors the overprediction of convection over the tropical land surfaces particularly over eastern tropical africa and india and the concurrent large scale westward shift in the divergence center at upper levels and the convergence center at lower levels the results also confirm the important role of south american and african orography in localizing the south atl

a thermal plume model for the convective boundary layer representation of cumulus clouds abstract the thermal plume model a mass flux scheme combined with a classical diffusive approach originally developed to represent turbulent transport in the dry convective boundary layer is extended here to the representation of cloud processes the modified parameterization is validated in a 1d configuration against results of large eddy simulations les as well as in a 3d configuration against in situ measurements for a series of cases of dry and cloudy convective boundary layers accounting for coherent structures of the mixed layer with the mass flux scheme improves the representation of the diurnal cycle of the boundary layer particularly its progressive deepening during the day and the associated near surface drying results also underline the role of the prescription of the mixing of air between the plume and its environment and of submean plume fluctuations

structures and fabrics in a crustal scale shear zone betic cordillera se spain abstract a broad zone of dominantly ductile high strain deformation lies beneath the aguilon nappe in the sierra alhamilla southern spain it forms part of a crustal scale movement zone traceable through much of the betic cordillera which separates the higher betic nappes from the underlying nevado filabride complex the zone is characterized in outcrop by a distinctive platy foliation and a strong nne trending stretching lineation microstructural characteristics include quartz ribbons mica fish augen of feldspar and other minerals in a matrix of dynamically recrystallized quartz and extensional crenulation cleavages narrow bands of ultramylonite and cataclasite occur within and on the margins of the movement zone deformation occurred under lower greenschist facies conditions and was accompanied by retrogression of earlier higher grade mineral assemblages structures in the movement zone developed in a temporal sequence beginning with isoclinal folding and transposition of older foliations this was followed by the formation of extensional crenulation cleavages and the progressive localization of strain into the ultramylonite bands mylonitic foliation in these bands is deformed by syn mylonite folds restricted to the bands all these structures were then deformed by s to se vergent small scale folds restricted to the movement zone as a whole cataclasis associated with alteration is localized along the ultramylonite bands and indicates a transition to late stage brittle deformation the lower boundary of the movement zone is gradational strain decreases recrystallized grainsize and the degree of recrystallization of quartz increases and pressure solution becomes the dominant deformation mechanism in mica schist asymmetric quartz fabrics in the movement zone indicate a nne sense of shear but variations in the degree of asymmetry suggest that flow was partitioned with the ultramylonite bands taking up much of the shear strain and the intervening rocks deforming more slowly and with a lower degree of non coaxiality diffuse fabrics in the fine grained ultramylonite bands may indicate a switch to a grainsize sensitive deformation mechanism and an overall downward increase in the opening angle of crossed girdle fabrics may reflect increased water activity at depth

factors influencing cloud area at the capping inversion for shallow cumulus clouds large eddy simulations of marine cumulus clouds are performed aspects of the simulations are varied in order to identify those parameters that play a role in determining when the cumulus clouds spread out under the capping inversion into stratocumulus these include the strength of the surface fluxes which also affects the strength of the cumulus mass transport the strength of the capping inversion the moisture content of the free atmosphere the strength of cloud top radiative cooling and whether there is significant precipitation or sedimentation of cloud drops tests are also performed to evaluate sensitivity to the model resolution as in previous studies having sufficient resolution at the capping inversion is found to be important for robust simulation of any stratiform cloud that forms there in addition the cloud cover is found to be sensitive to many of the physical processes investigated in the end though a clear and robust dependence emerges on the cloud top entrainment instability parameter for large a typical small shallow cumulus cloud cover is seen for below the threshold for buoyancy reversal the cumulus spreads into a solid sheet of stratocumulus beneath the inversion consistent with previous studies there is no abrupt transition and the cloud cover decreases smoothly as increases the conclusion is reached that varying other parameters in the simulations affects the cloud cover through their impact on the size of the jumps across the inversion and thence the implications for turbulent mixing parametrizations in general circulation models are discussed crown copyright 2009 reproduced with the permission of hmso published by john wiley sons ltd

a minimal three dimensional tropical cyclone model abstract a minimal 3d numerical model designed for basic studies of tropical cyclone behavior is described the model is formulated in coordinates on an f or plane and has three vertical levels one characterizing a shallow boundary layer and the other two representing the upper and lower troposphere respectively it has three options for treating cumulus convection on the subgrid scale and a simple scheme for the explicit release of latent heat on the grid scale the subgrid scale schemes are based on the mass flux models suggested by arakawa and ooyama in the late 1960s but modified to include the effects of precipitation cooled downdrafts they differ from one another in the closure that determines the cloud base mass flux one closure is based on the assumption of boundary layer quasi equilibrium proposed by raymond and emanuel it is shown that a realistic hurricane like vortex develops from a moderate strength initial vortex even when the initial environment is slightly stable to deep convect