late pleistocene glacial evolutionary stages in the gredos mountains iberian central system during the last glacial period late pleistocene the summits of the gredos mountains iberian central system were covered by plateau glaciers and later evolved into valley and slope glaciers the evolutionary sequence of these paleoglaciers has been obtained using geomorphological indicators and taking the principal moraine as reference these moraines show the limit between the glaciation and deglaciation periods in the glaciation period g four chronologically sequenced stages have been identified the local glacial maximum or maximum ice extent gm limited retreat lr re advance ra and finally major stabilization the steady state stage of greatest glacial stability ms in the deglaciation period d six chronologically sequenced stages have been identified an absolute retreat which involved regression and stabilization d1 two major retreat periods d2 and d4 and two stabilization periods d3 and d5 finally the last stage represents the complete disappearance of the glaciers d6 this evolutionary sequence allows more precise studies of the ages assigned through numerical dating procedures and of the correlation of the paleoglaciers in the gredos mountains with those of other regions

tectonic classification of cenozoic iberian foreland basins abstract the iberian microcontinent stands out because of its intense alpine intraplate deformation this is reflected in a large number of cenozoic basins of very different sizes most of the contacts between topographic highs and basins are thrust or strike slip faults all these basins seem to have undergone a common sedimentary evolution comprising four stages initiation of sedimentation intense syn tectonic infilling change from endorheic to exorheic drainage and accelerated erosion related to fluvial incision this simple evolutionary model shows a migration from east to west in which basins are still tectonically active at the atlantic margin of iberia this common evolution is also found in a series of geometrical characteristics such as the ratio r of length of strike slip fault and length of thrust fault that are very similar in both types of basin border settings thrust related basins are mainly associated with segmented pop downs whereas the main basins have the characteristics of open ramp basins strike slip related basins are mostly transpressive structures although small pull apart basins are usual along the vilarica and messejana faults for basin areas larger than 100 1000 km 2 a constant r value of 0 6 is found including the ebro duero madrid lower tagus and badajoz basins within the iberian microcontinent the total amount of cenozoic contractional deformation was distributed between strike slip and thrust faults with an r ratio close to 0 6 however for small basins this parameter seems to depend on the type of fault range or deformation belt pure strike slip transtension transpression and pop up independently of its local tectonic development

a direct method for assimilating sea surface height data into ocean models with adjustments to the deep circulation abstract there is as yet no consensus an the best method for inserting surface data into ocean models so that appropriate information is transmitted to the deeper layers in a rapid and efficient manner first we consider the correlation of sea surface pressure which is related to sea surface height as measured by altimeters and the surface and subsurface currents within the framework or a four layer quasi geostrophic model we begin by suggesting that the homogenization of potential vorticity q in the unforced layers discussed by rhines and young ensures that the potential vorticity anomalies in the deep ocean are weak it follows that instantaneous q information from thew deep layers may not need to be accurately known in order to reconstruct the deep eddy currents i e climatological q information may be sufficient taking the fields from the model we use the instantaneous surface streamfunction 1 data along with various approximate subsurface q climatologies and attempt to reconstruct the low

structural tectonic and glaciological controls on the evolution of fjord landscapes abstract the fjord landscape of south america stretching 1500 km between golfo corcovado 43 s and tierra del fuego 56 s is the largest continuous fjord landscape on earth this paper presents the results of new structural geological and geomorphological mapping of this landscape using optical satellite images and digital elevation models first order geological structures are represented by strike slip faults forming lineaments up to hundreds of kilometres long the strike slip faulting has been active since late cretaceous times and is responsible for the presence of a conspicuous structural cleavage visible as lineaments up to 10 km long a detailed analysis of these second order lineaments from digital image data was carried out in three sectors in sector 1 located northwest of the north patagonian icefield there are three distinct mean orientations characterized by a main nearly orogen parallel orientation az 145 and two orogen oblique secondary orientations az 20 and az 65 in sector 2 located west of the south patagonian icefield there are also three separate mean orientations with most of the lineaments concentrated between azimuths 0 and 80 mean at 36 and two other orogen oblique means at azimuth 122 and 163 in sector 3 around the cordillera darwin there is a single main orogen parallel mean at 100 115 in all three sectors mapped fjord orientations bear a striking similarity to the structural data with fjords orientated preferentially in the same direction as structural lineaments we infer that successive glaciations followed the same ice discharge routes widening and deepening pre existing geological structures at the expense of the surrounding terrain to create the fjord landscape this study has broader implications for ice sheet reconstructions and landscape evolution beneath ice sheets because we demonstrate that the primary control on fjord development in glaciated areas is geological and not glaciological

early holocene vegetation in the ayllon massif central system range spain based on macroremains a paleoecological approach abstract we present a palaeoecological study of well preserved vegetal macroremains in spain which age range 10 025 5371 cal yr bp confers it an outstanding interest because for the first half of the holocene palaeobotanical data are extremely scarce in the iberian central system range we found for the first time in the easternmost zone of the central system range macroremains belonging to the genus pinus these have specifically been identified as pinus cf sylvestris and pinus gr sylvestris these findings provide valuable information on the role of the genus pinus regarding the natural character of these pine forests in this relatively unknown region in the larger wood samples we measured tree rings and cross dated growth series which represent a 75 increase in the number of floating fossil chronologies and increase the time span by almost 1750 years in the centre of the iberian peninsula remarkably this is the first time in spain and in southern europe that some of the floating chronologies have been successfully crossdated creating four composite chronologies furthermore we discuss some palaeoclimatic inferences comparing with different sites in southern europe and provide new data for best knowing the palaeoecological characteristics of the first half of the holocene in spain likewise we found two bones belonging to aurochs bos primigenius one of these also dating from the first half of the holocene with valdojos constituting the only site with this taxon for this period in the central system range and surrounding areas

evidence for coupled reverse and normal active faulting in w iberia the vidigueira moura and alqueva faults se portugal abstract the vidigueira moura fault vmf is a 65 km long e w trending n dipping reverse left lateral late variscan structure located in se portugal w iberia which has been reactivated during the cenozoic with reverse right lateral slip it is intersected by and interferes with the ne sw trending alentejo plasencia fault east of this intersection for a length of 40 km the vmf borders an intracratonic tectonic basin on its northern side thrusting paleozoic schists meta volcanics and granites on the north over cenozoic continental sediments preserved in the basin on the south west of the faults intersection evidence of cenozoic reactivation is scarce in the eastern sector plio quaternary vmf reactivation is indicated by geomorphologic stratigraphic and structural data showing reverse movement with a right lateral strike slip component in response to a nw se trending compressive stress an average vertical displacement rate of 0 06 to 0 08 mm yr since late pliocene roughly the last 2 5 ma is estimated the alqueva fault af is a subparallel northward dipping 7 5 km long anastomosing fault zone that affects palaeozoic basement rocks and is located 2 5 km north and on the hanging block of the vmf the af is also a reverse left lateral late variscan structure which has been reactivated during the tertiary with reverse right lateral slip however plio quaternary reactivation was normal left lateral as shown by abundant kinematical criteria slickensides and geomorphic evidence it shows an average displacement rate of 0 02 mm yr for the vertical component of movement in the approximately last 2 5 ma it is proposed that the normal displacements on the af result from tangential longitudinal strain on the upthrown block of the vmf above a convex ramp of this main reverse structure according to this model of faults interaction the af is interpreted to work as a bending moment fault sited above the vmf thrust ramp consequently it is expected that the displacements on the af increase towards the topographic surface with the increase in the imposed extension declining downwards until they vanish above or at the vmf ramp in order to constrain the proposed scheme numerical modeling was performed aiming at the reproduction of the present topography across the faults using different geodynamic models and fault geometries and displacements

far field effects of alpine plate tectonism in the iberian microplate recorded by fault related denudation in the spanish central system abstract apatite fission track analysis was performed on 56 samples from central spain to unravel the far field effects of the alpine plate tectonic history of iberia the modelled thermal histories reveal complex cooling in the cenozoic indicative of intermittent denudation accelerated cooling events occurred across the spanish central system scs from the middle eocene to recent these accelerated cooling events resulted in up to 2 8 0 9 km of denudation in the western sierra de gredos and 3 6 1 0 km in the central and eastern gredos assuming a paleogeothermal gradient of 28 5 c and a surface temperature of 10 c the greatest amount of denudation 5 0 1 6 km occurred in the sierra de guadarrama accompanying rock uplift was 4 7 1 0 and 5 9 1 6 km in the eastern gredos and guadarrama respectively most denudation in the gredos occurred from the middle eocene to the early miocene and can be related to the n s stress field induced by the pyrenean compression in the guadarrama the greatest denudation was pliocene to recent of age and seems related to the ongoing nw se betic compression the fact that the formation of the e w trending gredos coincides with the n s pyrenean compression and the creation of the present day morphology of the ne sw trending guadarrama with the younger nw se betic compression indicates that they record the far field effects of alpine plate tectonics on iberia the trend of pre existing lineaments was of major importance in influencing the style and magnitude of these of far field effects

late glacial and post glacial deposits of the navamuno peatbog iberian central system chronology and paleoenvironmental implications abstract the navamuno peatbog sierra de bejar western spain is a 14 ha pseudo endorheic depression with boundaries defined by a lateral moraine of the cuerpo de hombre paleoglacier and fault line scarps on granite bedrock the stratigraphy of the navamuno peatbog system is characterized here using borehole data to a depth of 20 m an integrated interpretation from direct push coring dynamic probing boreholes and handheld auger drillings advances our knowledge of the navamuno polygenetic infill correlating this data with those obtained in other studies of the chronology and evolutionary sequence of the cuerpo de hombre paleoglacier has enabled us to establish the sequence of the hydrological system in the navamuno depression during the late pleistocene mis2 the depression was dammed by the cuerpo de hombre glacier and fed by its lateral meltwaters and was filled with glaciolacustrine deposits the onset of the holocene in navamuno is linked to a flat fluviotorrential plain with episodes of local shallow pond peat bog sedimentation this evolutionary sequence is congruent with the age model obtained from available radiocarbon dating obtaining 19 ages from 800 cal yr bp at depth 1 11 m to 16800 cal yr bp at depth 15 90 16 0 m finally the sedimentary record enabled interpretation of the environmental changes occurring in this zone during the late glacial from the older dryas to the younger dryas and postglacial holocene stages placing them within the paleoclimatic context of the iberian peninsula and mediterranean regions

ice surface morphology and flow on malaspina glacier alaska implications for regional tectonics in the saint elias orogen the saint elias mountains in southern alaska are located at a structural syntaxis where the coastal thrust and fold belt of the fairweather plate boundary intersects thrust faults and folds generated by collision of the yakutat terrane the axial trace of this syntaxis extends southeastward out of the saint elias mountains and beneath malaspina glacier where it is hidden from view and cannot be mapped using conventional methods here we examine the surface morphology and flow patterns of malaspina glacier to infer characteristics of the bedrock topography and organization of the syntaxis faults and folds beneath the eastern part of the glacier trend northwest and reflect dextral transpression near the terminus of the fairweather fault system those beneath the western part of the glacier trend northeast and accommodate folding and thrust faulting during collision and accretion of the yakutat terrane mapping the location and geometry of the structural syntaxis provides important constraints on spatial variations in seismicity fault kinematics and crustal shortening beneath malaspina glacier as well as the position of the collisional deformation front within the yakutat terrane we also speculate that the geometrical complexity of intersecting faults within the syntaxis formed a barrier to rupture propagation during two regional mw 8 1 earthquakes in september 1899

global climate and tectonic controls on the denudation of glaciated mountains abstract significant uncertainty exists concerning the efficiency of alpine glacial erosion relative to fluvial and hillslope processes latitudinal variations in temperature are important for determining the extent of glaciers as are the rates of tectonic uplift that influence the elevation and hence temperatures that glaciers can form the acute sensitivity of glacial erosion to temperature has complicated previous interpretations because temperatures must be cool enough to maintain ice yet warm enough to allow glacial sliding here we quantify the influence of climate and tectonics on glacial landscape evolution with a coupled glacial fluvial and hillslope landscape evolution model that systematically explores variations in rock uplift rate and periodic variations in climate i e glacial interglacial periods over million year time scales emphasis is placed on understanding when a particular climate is either more e g buzzsaw conditions or less erosive than its preglacial landscape results indicate that the erosional efficiency of glaciers varies as a function of latitudinal controlled temperature and rock uplift rate an order of magnitude increase in erosion rates occurs in some scenarios for both localized valley bottom erosion and short term one glacial period durations of glaciation however when averaged over the entire landscape for 2 ma increases in glacial erosion are typically less than double that of the preglacial landscape in some scenarios average glacial erosion rates are less than preglacial rates due to either small inefficient glaciers or extensive cold based glaciation model predictions are compared with a compilation of long term denudation rates from glaciated mountain ranges and indicate models perform well at explaining patterns of glacial erosion efficiency the findings presented here have clear implications for the impact of glaciations on the evolution of landscapes including 1 the climatic window in which glaciers are more erosive compared to pre glacial rates 2 spatial and temporal variations in denudation that can lead to pulses of erosion and 3 predictions of glacial erosional efficiency at different latitudes we conclude that latitudinal and elevation dependent variations in temperature control the efficiency of glacial denudation and explain discrepancies between previous studies

oblique strain partitioning and transpression on an inverted rift the castilian branch of the iberian chain the iberian chain is a wide intraplate deformation zone formed by the tectonic inversion during the pyrenean orogeny of a permian mesozoic basin developed in the eastern part of the iberian massif the n s convergence between iberia and eurasia from the late cretaceous to the lower miocene times produced significant intraplate deformation the nw se oriented castilian branch of the iberian chain can be considered as a key zone where the proposed models for the cenozoic tectonic evolution of the iberian chain can be tested structural style of basin inversion suggests mainly strike slip displacements along previous nw se normal faults developed mostly during the mesozoic to confirm this hypothesis structural and basin evolution analysis macrostructural bouguer gravity anomaly analysis detailed mapping and paleostress inversions have been used to prove the important role of strike slip deformation in addition we demonstrate that two main folding trends almost perpendicular ne sw to e w and nw se were simultaneously active in a wide transpressive zone the two fold trends were generated by different mechanical behaviour including buckling and bending under constrictive strain conditions we propose that strain partitioning occurred with oblique compression and transpression during the cenozoic 2008 elsevier b v all rights reserved

palaeoweathering profiles developed on the iberian hercynian basement and their relationship to the oldest tertiary surface in central and western spain

adjoint assimilation of altimetric surface drifter and hydrographic data in a quasi geostrophic model of the azores current the flow characteristics in the region of the azores current are investigated by assimilating topex poseidon and ers 1 altimeter data into the multilevel harvard quasigeostrophic qg model with open boundaries miller et al 1983 using an adjoint variational scheme moore 1991 the study site lies in the path of the azores current where a branch retroflects to the south in the vicinity of the madeira rise the region was the site of an intensive field program in 1993 semaphore we had two main aims in this adjoint assimilation project the first was to see whether the adjoint method could be applied locally to optimize an initial guess field derived from the continous assimilation of altimetry data using optimal interpolation oi the second aim was to assimilate a variety of different data sets and evaluate their importance in constraining our qg model the adjoint assimilation of surface data was effective in optimizing the initial conditions from oi after 20 iterations the cost function was generally reduced by 50 80 depending on the chosen data constraints the primary adjustment process was via the barotropic mode altimetry proved to be a good constraint on the variable flow field in particular for constraining the barotropic field the excellent data quality of the topex poseidon t p altimeter data provided smooth and reliable forcing but for our mesoscale study in a region of long decorrelation times o 30 days the spatial coverage from the combined t p and ers 1 data sets was more important for constraining the solution and providing stable flow at all levels surface drifters provided an excellent constraint on both the barotropic and baroclinic model fields more importantly the drifters provided a reliable measure of the mean field hydrographic data were also applied as a constraint in general hydrography provided a weak but effective constraint on the vertical rossby modes in the model finally forecasts run over a 2 month period indicate that the initial conditions optimized by the 20 day adjoint assimilation provide more stable longer term forecasts

two dimensional geomorphological characterization of a filled abandoned meander using geophysical methods and soil sampling abstract using geophysical methods for the geomorphological characterization of subsurface features has numerous advantages over traditional exploration methods because of their noninvasive and rapid nature in this study we compared the results of four geophysical methods with each other we also discuss their possibilities and limitations in a geomorphological investigation electrical resistivity tomography ert refraction seismic rs ground penetrating radar gpr and multichannel analysis of surface waves masw methods were applied at an abandoned meander in northern saxony to map a predefined structure by combining these methods we were able to characterize and delineate subsurface features of the abandoned meander including a point bar a channel and a cutbank core samples obtained from sonic drilling were used to validate the findings of both seismic methods however we found that electrical resistivity tomography and ground penetrating radar lacked penetration depth and could only be used to resolve shallower subsurface layers the ert gpr rs and masw can be used to gather images of subsurface structures the masw in particular provides supplementary information about the channel s internal structure with respect to lateral and vertical resolution besides fluvial morphological features we also detected inverse velocity structures within the channel this allowed us to characterize the abandoned meander using information about its layer distribution and material composition however we were only able to characterize and delineate the subsurface features of the abandoned meander by combining all of the aforementioned methods

the eddy field associated with the azores front east of the mid atlantic ridge as observed by the geosat altimeter two years of geosat data november 1986 to december 1988 for the azores madeira region of the north atlantic are analyzed the objective is to study the eddy field associated with the terminal retroflection of the azores current the rms variability of sea level anomaly is 4 to 8 cm with maximum values between 33 degrees and 35 degrees n being associated with the azores current and located on its northern flank higher energy is observed during winter and during the year november 1987 to november 1988 analysis of velocities at crossovers reveals anisotropy with larger meridional velocity variances this is the signature of meanders and or eddies elongated in the north south direction the eddy mean flow interaction is studied through the analysis of the reynolds tensor meridional and zonal accelerations of the mean by the eddy field are consistent with retroflection of the azores current to the south and to the west spectral analyses show that the dominant signals have periods and wavelengths larger than 100 days and 300 km respectively propagation velocities are westward but slow 1 5 km d synoptic mapping of the eddy field shows the wavelike structure of the variability on the northern flank of the current it is likely that the wave generation is not directly due to an instability of the azores current but is attributable to a cause more to the east once formed the wave interacts with the current in winter and forms meanders seasonal variations of the surface circulation are finally analyzed from the 2 year long time series of synoptic maps there is a clear seasonality in the surface circulation which generally appears to be consistent with historical in situ measurements in winter there is a strong meandering and a southward branching while in summer the mean front is narrower and penetrates further to the east

sequence and chronology of the cuerpo de hombre paleoglacier iberian central system during the last glacial cycle abstract the cuerpo de hombre paleoglacier occupies the upper sector of the cuerpo de hombre river basin located on the northwest slope of the sierra de bejar mountains iberian central system at the stage of the maximum ice extent during the last glacial cycle this paleoglacier was one of the longest tongues emerging from the sierra de bejar plateau glacier the study of the morphostratigraphic succession and the geometric and genetic relations between the geomorphological indicators of this paleoglacier has revealed its evolutionary sequence during the last glacial cycle the comparison between this sequence and the one previously established by a regional evolutionary pattern shows that although they both coincide in general terms some stages substages of this pattern must be corrected or more clearly defined the absolute chronology of the different stages was obtained using terrestrial cosmogenic nuclides 10 be the maximum ice extent of cuerpo de hombre paleoglacier has been dated to 25 0 ka mis2 and concurrent with the lgm this chronology coincides with date obtained for other paleoglaciers in the iberian central system but is slightly more modern than the regional chronology estimated as most likely for the maximum ice extent in these areas subsequent to reaching the maximum extent the glacier had a retreat minimum age 20 6 ka followed by another stage of expansion or readvance after which it stabilised until the start of the deglaciation stage 17 8 ka in all previous work the deglaciation stages in the iberian central system have been described as one continuous recession process however in the cuerpo de hombre paleoglacier all the data point to stabilisations of considerable magnitude and particularly to another stage of readvance of the glacier based on its chronology minimum age 11 1 ka and its evolutionary significance this new readvance has been correlated with the older dryas stadial finally the evolutionary context marked by the indicators and its chronology confirm that the whole of the late glacial sequence identified in cuerpo de hombre can be correlated with the traditionally established in northern europe climatic periods or stadials and interstadials oldest dryas bolling older dryas allerod younger dryas the minimum ages obtained for the cold periods stadials in this sequence in the cuerpo de hombre paleoglacier are respectively 17 5 ka 13 9 ka and 11 1 ka this complete sequence of the late glacial period including the stadials older and younger dryas had not been previously identified in any of the paleoglaciers in the iberian central system

assimilation of altimeter eddy fields in a limited area quasi geostrophic model abstract techniques for the synoptic analysis vertical inference dynamical adjustment and forecast of altimetric and deeper in situ data are presented as a first step towards the design of continuous assimilation schemes in limited area oceanic domains a year long time series of streamfunction maps denoted mark 2 drawn in the polymode area of the western north atlantic is used as a benchmark for various tests and simulations an original projection extension scheme using empirical modes of density and or pressure anomalies is used to obtain a first guess of the three dimensional structure of the currents starting from surface topography only in the mark 2 domain this technique works well since the first empirical mode is surface intensified and largely dominant an alternative approach is to incorporate deeper data e g float trajectories below the main thermocline the first guess currents are specified as initial and boundary condition of the harvard 6 level quasi geostrophic open ocean mode

data assimilation in a quasi geostrophic open ocean model of the gulf stream region using the adjoint method abstract the method of adjoint data assimilation is applied in a quasi geostrophic qg open ocean model of the gulf stream region the results of data assimilation experiments are presented in which simulated axbt and satellite altimeter observations are assimilated into the qg model the adjoint data assimilation scheme has the ability to correct for large errors in the speed and position of the gulf stream jet these experiments provide valuable insight into the dynamics of the assimilation procedure and highlight the limitations of the adjoint method in the gulf stream region the adjoint variables of the linearized qg model are approximations of the green s functions of the adjoint equations by examining maps of the adjoint variables one can determine the domain of influence of individual observations the results of assimilation experiments in which geosat sea surface height observations are assimilated into the qg model are also presented the results of the geosat assimilation experiments can b

rapid least squares inversion of apparent resistivity pseudosections by a quasi newton method1 a fast inversion technique for the interpretation of data from resistivity tomography surveys has been developed for operation on a microcomputer this technique is based on the smoothness constrained least squares method and it produces a two dimensional subsurface model from the apparent resistivity pseudosection in the first iteration a homogeneous earth model is used as the starting model for which the apparent resistivity partial derivative values can be calculated analytically for subsequent iterations a quasi newton method is used to estimate the partial derivatives which reduces the computer time and memory space required by about eight and twelve times respectively compared to the conventional least squares method tests with a variety of computer models and data from field surveys show that this technique is insensitive to random noise and converges rapidly this technique takes about one minute to invert a single data set on an 80486dx microcomputer

characterization of seasonal local recharge using electrical resistivity tomography and magnetic resonance sounding a groundwater recharge process of heterogeneous hard rock aquifer in the moole hole experimental watershed south india is being studied to understand the groundwater flow behaviour significant seasonal variations in groundwater level are observed in boreholes located at the outlet area indicating that the recharge process is probably taking place below intermittent streams in order to localize groundwater recharge zones and to optimize implementation of boreholes a geophysical survey was carried out during and after the 2004 monsoon across the outlet zone magnetic resonance soundings mrs have been performed to characterize the aquifer and measure groundwater level depletion the results of mrs are consistent with the observation in boreholes but it suffers from degraded lateral resolution a better resolution of the regolith bedrock interface is achieved using electrical resistivity tomography ert ert results are confirmed by resistivity logging in the boreholes ert surveys have been carried out twice before and during the monsoon across the stream area the major feature of recharge is revealed below the stream with a decrease by 80 of the calculated resistivity the time lapse ert also shows unexpected variations at a depth of 20 m below the slopes that could have been interpreted as a consequence of a deep seasonal water flow however in this area time lapse ert does not match with borehole data numerical modelling shows that in the presence of a shallow water infiltration an inversion artefact may take place thus limiting the reliability of time lapse ert a combination of ert with mrs provides valuable information on structure and aquifer properties respectively giving a clue for a conceptual model of the recharge process infiltration takes place in the conductive fractured fissured part of the bedrock underlying the stream and clayey material present on both sides slows down its lateral dissipation

assimilation of geosat altimetric data in a nonlinear reduced gravity model of the indian ocean part 1 adjoint approach and model data consistency abstract geosat sea level variations are assimilated into a nonlinear shallow water model of the indian ocean after spinup the model forced by observed winds over 1985 1988 provides a first guess for initial conditions on november 1986 and a mean thermocline depth used as a reference surface for altimetric observations data are assimilated during one year and north of 20 s the model data misfit is minimized using the adjoint model with respect to the initial conditions and the reference surface the assimilation algorithm converges fast and steadily the monthly rms difference between model and data is reduced from 21 to 16 m the optimal thermocline surface is significantly affected by assimilation large changes occur along the paths of the throughflow and south equatorial current it is found that the optimal mean state is valid only for the period of assimilation it degrades the agreement between observations and simulations for the following year because of the large interannual event that took

can meddies be detected by satellite altimetry geosat exact repeat mission altimeter data have been used to estimate the sea surface height anomaly relative to a 2 year mean reference surface in the eastern north atlantic ocean horizontal maps of the sea surface height anomaly for various periods were constructed by means of an objective analysis procedure the mean sea level was approximated by the dynamic topography from climatological hydrographic data results were compared to the dynamic topography calculated from hydrographic ground truth data sampled during march 1988 on an eddy resolving station network in the iberian basin despite the low signal to noise ratio of the altimeter data in this part of the ocean the agreement of the altimeter signal with hydrographic measurements is found to be significant individual cyclonic and anticyclonic eddies in the mediterranean outflow are identified in the altimetric maps the information visible in the sea surface height is significantly correlated with the dynamic topography of the layer 500 3000 dbar containing the core of the mediterranean outflow and maximum velocities of the baroclinic eddies the successive development of the identified eddies as studied from a sequence of sea surface height maps indicates a slight westward drift of the most pronounced feature with approximately 1 9 cm s propagation velocity the inferred path of that feature is consistent with additional information from moored current meter data

vegetation history climate and human impact in the spanish central system over the last 9000 years abstract in this paper we present a review of the available holocene pollen records from the spanish central system 113 sites and 150 14 c dates palynological data obtained from pollen analyses of peat bogs lakes and archaeological sites as well as radiocarbon dating were used to infer the human impact on vegetation and landscape during the last 9 millennia the neolithic contribution to the configuration of landscape is scarce limited to the valleys while chalcolithic settlements and their related activities agriculture and grazing represent the first evidence of significant human impact on the high mountains the pollen record has allowed us to relate two cultural periods of changing the copper age early bronze age and late bronze age early iron age transitions to abrupt climate disruptions the so called 4 2 and 2 8 ka cal bp events respectively from the iron age to the early middle ages anthropic activities were still sporadic mainly located in the lowlands but from the feudal period onwards when la mesta transhumance system takes place high mountain landscapes changed dramatically late modern period brings a further intensification of human pressure especially related to forestry with widespread pinewood afforestation

the significance of rock structure lithology and pre glacial deep weathering for the shape of intermediate scale glacial erosional landforms the main landforms within the glacially scoured precambrian rocks of the swedish west coast are closely connected to the principal structural pattern and have lately been explained as mainly a result of etch processes probably during the mesozoic and with a possible second period of etching during the neogene to explore the effect of multiple glacial erosion on the rock surfaces an island with two different lithologies and with striae from different directions was selected for a detailed study focusing on the shape of roches moutonnees air photo interpretation of bedrock lineaments and roches moutonnees combined with detailed field mapping and striae measurements are used to interpret the structural and lithological control on the resulting shape the study reveals a significant difference in shape between roches moutonnees in augen granite and orthogneiss low elongated and streamlined roches moutonnees occur in the gneiss area striated by a late weichselian ice flow from the ne this ice flow is subparallel with both the local dominant trend of topographically well expressed joints and the schistosity of the gneiss frequently there are no signs of quarrying on the lee sides of the gneiss roches moutonnees and hence they resemble the shape of whalebacks or ruwares as typically associated with the exposed basal weathering surface found in tropical areas the granite roches moutonnees were formed by an older ice flow from the ese which closely followed the etched wnw ese joint system of the granite late weichselian ice flow from the ne caused only minor changes of the landforms on the contrary marks of the early ese ice flow are poorly preserved in the gneiss area where it probably never had any large effect as the flow was perpendicular to both schistosity and structures and accordingly also to the pre glacial relief the study demonstrates that coincidence between ice flow direction and pre glacially etched structures is most likely to determine the effects of glacial erosion copyright 2002 john wiley sons ltd

palaeoenvironmental studies in nw iberia cantabrian range vegetation history and synthetic approach of the last deglaciation phases in the western mediterranean abstract at the north western limit of the mediterranean basin in the mediterranean oceanic transition zone the multidisciplinary study of two palaeolakes villaseca and la mata province of leon provides data on the last deglaciation the juxtaglacial lakes were formed during a deglaciation phase of the last cold stage weichselian wurm estimated from the regional and pyrenean chronological data between circa 48 ka and 32 ka ka 1000 years ago their drainage occurred circa 17 ka and 15 ka respectively during the definitive glacial retreat phases these results provide evidence for a glacial maximum extension preceding the global last glacial maximum lgm and an early deglaciation comparisons with the pyrenean data show that in the most important glacial basins of the pyrenean cantabrian range glaciers were still present at middle elevation circa 18 20 ka the final deglaciation did not happen until around 16 ka during the period 48 13 3 ka along the pyrenean cantabrian range three stages can be distinguished in the deglacial processes between circa 48 and 32 ka the deglacial retreats were contemporaneous with d o events 12 to 6 between circa 32 ka and 18 ka major sedimentary modifications were rare two of them are synchronous with d o 4 and 3 a glacial readvance also occurred during this period along the pyrenean cantabrian range between 18 and 17 ka major sedimentary changes and an increase in the 18o records of the ngrip ice core record are synchronous between 15 and 13 3 ka glacial retreats and sedimentary changes are synchronous with the climatic improvement observed from the end of the oldest dryas to the end of the bolling allerod period these correspondencies suggest relationships between the deglacial processes in the western mediterranean and the palaeoenvironmental events in the north atlantic region during the last glacial interglacial transition during the full glacial period the pollen data indicates dominant steppic environments the oldest dryas was not a constant cooling phase and from around 15 5 ka the pollen data indicates a slight warming during the holocene until circa 2040 cal bp mixed oak forests developed and pine was a prominent component of the cantabrian landscape then the forests were destroyed due to mining agriculture and fire and this favoured the extension of heathland

a global oceanic data assimilation system abstract a global oceanic four dimensional data assimilation system has been developed for use in initializing coupled ocean atmosphere general circulation models and many other applications the data assimilation system uses a high resolution global ocean model to extrapolate the information forward in time the data inserted into the model currently consists only of conventional sea surface temperature observations and vertical temperature profiles the data are inserted continuously into the model by updating the model s temperature solution every timestep this update is created using a statistical interpolation routine applied to all data in a 30 day window centered on the present timestep large scale features in the sea surface temperature analyses are consistent with those from independent analyses subsurface fields created from the assimilation are much more realistic than those produced without the insertion of data furthermore information contained in the assimilation field is shown to be re

the plateau glacier in the sierra de bejar iberian central system during its maximum extent reconstruction and chronology abstract a detailed study of the glacial morphology in the sierra de bejar iberian central system provided a data set of geomorphic indicators to reconstruct the paleoglaciers developed in this mountain area during the last glacial cycle late pleistocene applying a physical based glacier model and using the geomorphic indicators a three dimensional reconstruction of the ice mass during the maximum extent of the glaciers has been carried out we used this reconstruction to project hypsometric curves over the former glaciers and to estimate the elas equilibrium line altitudes of the paleoglaciers for their stage of maximum extent at this stage the sierra de bejar hosted a plateau glacier considered as a dome shaped icecap around 57 km2 in area according to our estimations the maximum thickness of the ice was 211 m the minimum elevation of paleoglaciers 1210 m asl and the regional ela was at 2010 m asl during later stages reduction in ice mass due to deglaciation caused the icecap to evolve into an icefield and finally the main glacier was fragmented in valley and cirque glaciers the geochronological data obtained with 10be provides an age of 27 ka for the maximum extent of the glaciers gm whereas the global last glacial maximum lgm represents a younger stage of the sierra de bejar glacier evolution finally the new data obtained in the sierra de bejar allow evaluating the influence of some factors such as the continentality and latitudinal location in the development of glacial processes in these areas of the iberian central system

large lenses of highly saline mediterranean water isolated compact anticyclonic eddies or salt lenses were found in the canary basin hydrographic surveys of three such lenses show large anomalies of salinity and temperature 0 8 2 5 c they are centered at 1100 m have a vertical extent of up to 900 m and radii of 50 km current meter records indicate anticyclonic velocities up to 29 cm s 1 fine structure with vertical scales of 20 m and less possibly due to intrusive decay appears at the outer edges of the lenses whereas the centers are free of such structure the probability of finding a salt lens at any station in the canary basin is fairly high 0 08

near surface geophysical analysis of the navamuno depression sierra de bejar iberian central system geometry sedimentary infill and genetic implications of tectonic and glacial footprint the geometric and genetic characterization of the navamuno depression peatland system iberian central system is presented here using results from a geophysical survey this depression is a 30 ha pseudo endorheic flat basin over granitic bedrock three geophysical techniques were used to map the subsurface geology and identify and describe the infill sequence shallow seismic refraction sr magnetic resonance sounding mrs and electrical resistivity measurements ves and ert the three main geoelectrical layers g1 g2 g3 identified in previous research have also been identified in the present work using the data obtained in this new research we have been able to analyse these three geological layers in detail and reinterpret them they can be grouped genetically into two sedimentary units an ancient sedimentary body g3 of unknown age and type beneath an upper pleistocene g2 and holocene g1 sedimentary infill the facies distribution and geometry of the upper pleistocene was examined using the sequence stratigraphy method revealing that the navamuno depression was an ice dammed in the last glacial cycle resulting in glaciolacustrine sedimentation a highly permeable sedimentary layer or regolith exists beneath the glaciolacustrine deposits below 40 m depth water content falls dramatically down to a depth of 80 m where unweathered bedrock may be present the information obtained from geophysical geological and geomorphological studies carried out in this research enabled us to consider various hypotheses as to the origin of this depression according to these data the navamuno depression may be explained as the result of a transtensional process from the puerto de navamuno strike slip fault during the reactivation of the iberian central system paleogene lower miocene alpine orogeny and can be correlated with the pull apart type basins described in these areas the neotectonic activity of this fault and the icedammed processes in these areas during the last glacial cycle mis2 were the main causes of recent sedimentary infill in this depression

on the origin of the azores current the azores current south of the azores archipelago is part of the subtropical north atlantic gyre using an international hydrographic data set we analyze mean and seasonal geostrophic transport fields in the upper 800 m of the ocean in order to determine the origin of the azores current in the western basin and seasonal changes in the related flow geostrophic currents are obtained by using the method applied by stramma 1984 in the eastern basin the azores current is found to originate in the area of the southwest newfoundland rise figure 10 in winter an almost uniform current connects this region of origin with the azores current while a branching into two current bands is observed in summer with the southern band forming a marked cyclonic loop within the upper 800 m all of the transport in the northern band and about 70 of the transport in the southern band recirculates in the eastern basin additionally expendable bathythermograph data from the azores current region indicate an increase of eddy potential energy from winter to summer

study of paleoweathering on the spanish hercynian basement montes de toledo central spain summary the hercynian basement of the iberian peninsula consists of a series of late hercynian blocks that were unleveled by the alpine orogeny the montes de toledo range is found in one of the elevated blocks of the central zone and shows ancient alterations affecting different rocks which are fossilized by sediments of different ages two of these weathering profiles under the plio pleistocene sediments of rana formations are studied one is developed on granodiorite with some intercalated metamorphic rocks and the other on a slaty series in both profiles smectite is formed in a first weathering process a second weathering process yielding kaolinite and affecting rana sediments is superimposed on older one both processes seem to be widely spread in the western part of the iberian peninsula

improved groundwater vulnerability mapping for the karstic chalk aquifer of south east england abstract the cretaceous age chalk of south east england forms an important aquifer within chalk the storage and transmission of groundwater is enhanced by subsurface karstic weathering the case study presented in this paper demonstrates that current approaches to assessing groundwater vulnerability to pollution and delineating source protection zones are flawed as they do not take proper account of the karstic nature of chalk improved techniques based on understanding the geological and geomorphological controls of karst development in chalk are proposed to overcome the shortcomings of published groundwater vulnerability maps the results also demonstrate the inadequacies of current groundwater modelling approaches for defining source protection zones the techniques follow european commission research recommendations by taking account of recharge presence of overlying cover deposits the nature of chalk karst and the way in which it influences the flow of groundwater the approach described allows for better informed decisions to be made about chalk aquifer management to ensure adequate protection and conservation of groundwater for example the published groundwater vulnerability map shows lambeth group deposits classified as being a minor aquifer of low groundwater vulnerability in the chosen study area however by applying the new techniques they are classified as having an aquifer vulnerability rating of moderate to very high when taking the karstic development of the underlying chalk into account

large scale distributed deformation controlled topography along the western africa eurasia limit tectonic constraints in the interior of the iberian peninsula the main geomorphic features mountain ranges and basins seems to be arranged in several directions whose origin can be related to the n s plate convergence which occurred along the cantabro pyrenean border during the eocene lower miocene time span the iberian variscan basement accommodated part of this plate convergence in three e w trending crustal folds as well as in the reactivation of two left lateral nne ssw strike slip belts the rest of the convergence was assumed through the inversion of the iberian mesozoic rift to form the iberian chain this inversion gave rise to a process of oblique crustal shortening involving the development of two right lateral nw se shear zones crustal folds strike slip corridors and one inverted rift compose a tectonic mechanism of pure shear in which the shortening is solved vertically by the development of mountain ranges and related sedimentary basins this model can be expanded to nw africa up to the atlasic system where n s plate convergence seems also to be accommodated in several basement uplifts anti atlas and meseta and through the inversion of two mesozoic rifts high and middle atlas in this tectonic situation the microcontinent iberia used to be firmly attached to africa during most part of the tertiary in such a way that n s compressive stresses could be transmitted from the collision of the pyrenean boundary this tectonic scenario implies that most part of the tertiary eurasia africa convergence was not accommodated along the iberia africa interface but in the pyrenean plateboundary a broad zone of distributed deformation resulted from the transmission of compressive stresses from the collision at the pyrenean border this distributed intraplate deformation can be easily related to the topographic pattern of the africa eurasia interface at the longitude of the iberian peninsula shortening in the rif betics external zones and their related topographic features must be conversely related to more local driven mechanisms the westward displacement of the exotic alboran domain other than n s convergence the remaining nnw sse to nw se latest miocene up to present convergence is also being accommodated in this zone straddling iberia and morocco at the same time as a new ill defined plate boundary that is being developed between europe and africa

continuous assimilation in an open domain of the northeast atlantic 1 methodology and application to athena 88 a scheme to perform suboptimal intermittent assimilation in an open ocean quasi geostrophic model is presented and applied to the assimilation of altimeter data in a domain of the northeast atlantic west of ireland both simulated and real altimeter data are used three dimensional 3 d synoptic observation fields and error variance fields are derived from synoptic dynamic topography anomaly estimates using an empirical orthogonal mode eof vertical extension technique the 3 d estimates are suboptimally combined with the time dependent part of the forecast fields suboptimality here means that the combination does not directly use spatial correlations of errors however the 3 d synoptic observation estimates used in the combination do contain error spatial statistical information the resulting fields added to a mean model climatology are used as initial conditions for the model which is integrated until a new dynamic topography anomaly estimate is available locally the combination is optimal in the sense that it is based on the observational error variances which reflect the measurement noise and the space time distribution of data and that it minimizes the error variance of the results a similar combination scheme using past as well as future observations is used to update the boundaries during model integration simulated surface topography anomaly maps typical of the northeast atlantic are assimilated every 20 days for a 300 day period with different noise characteristics typical of altimetric sampling errors in a three level version of the model the assimilation fields especially the vorticity at deeper levels converge toward the reference fields the convergence is obtained after o 100 days regardless of the observational noise levels tested up to 2 db using a relevant observational error model seems to matter in particular the error level should not be underestimated in the case of an 80 day gap in the data inflow the model predictability limits the reliability of the forecast beyond 20 days the scheme makes the model converge back as soon as new observations are entered with limited convergence loss due to the gap the case of an unknown model climatology is also studied finally the scheme is applied to geosat altimeter data added to the robinson bauer and schroeder annual climatology in the athena 88 cruise area which is contained in the model box the assimilation results compare favorably with hydrographical data from the cruise and help the synoptic interpretation of the observed phenomena

did pyrenean glaciers dance to the beat of global climatic events evidence from the wurmian sequence stratigraphy of an ice dammed palaeolake depocentre in andorra the ice marginal depositional sequence of la massana provides a chronostratigraphic benchmark for reconstructing the wurmian glacial evolution of the valira catchment in andorra se pyrenees the sedimentary record of andorra confirms the asynchronous chronology of glacier fluctuations in different parts of the pyrenean mountain range a major ice recession occurred at the end of marine isotope stage mis 4 high magnitude valley glacier fluctuations during mis 3 constitute another important finding major readvances occurred toward the end of mis 3 whereas mis 2 in particular the global last glacial maximum or lgm featured sharp contrasts in ice recession rates between pyrenean valleys substantial distances separated mis 4 glacier fronts the wurmian maximum ice extent or mie from those reached during the global lgm in contrast to situations in the eastern pyrenees where wurmian mie and global lgm ice fronts nearly coincided overall the valira glaciers reveal patterns that are more similar to those recorded elsewhere in the western and central pyrenees than in the eastern pyrenees the rapid fluctuations recorded by andorran glaciers during the second half of the wurm also suggest a response to global forcing events such as heinrich events in the north atlantic

late glacial early holocene vegetation and environmental changes in the western iberian central system inferred from a key site the navamuno record bejar range spain abstract a new record from a long sediment core s3 in navamuno 1505 m asl western iberian central system provides the reconstruction of the vegetation history and environmental changes in the region between 15 6 and 10 6 ka cal bp namely during the late glacial and the early holocene using a multiproxy analysis pollen based vegetation and climate reconstruction sedimentary macrocharcoals loss on ignition magnetic susceptibility and x ray fluorescence xrf measurements the results are then compared with other sequences from the iberian central system and the whole iberian peninsula in order to better understand the past dynamics of the main forest constituents the pollen record shows a shift from open pine forests 15 6 14 7 ka cal bp oldest dryas to mixed open pine birch woodlands 14 7 14 0 ka cal bp bolling woodlands were succeeded by a steppe like landscape until 13 4 ka cal bp older dryas which was replaced again by high mountain pine forests and riparian woodlands 13 4 12 6 ka cal bp allerod a great development of cold steppe grasslands linked to the decline of birch woodlands is documented 12 6 11 7 ka cal bp younger dryas the early holocene 11 7 10 6 ka cal bp was characterized by a progressive reforestation of the study area by pine and birch forests in the highlands and oak woods in the lowlands temperate tree taxa carpinus betulus castanea sativa corylus avellana fraxinus juglans tilia and ulmus were also common but likely at lower elevations pollen of fagus sylvatica was already recorded during the late glacial and the early holocene the marked increasing local fire activity during the warmer and wetter allerod oscillation could be related to a rise in tree cover supporting the climatically driven character of these fires nevertheless the strong increase in fire activity during the younger dryas would probably be related to growing tree and shrub mortality as well as to the wet dry biphasic structure of this stadial the standard modern analogue technique has been also applied to the navamuno sequence to provide quantitative climate estimations for the late glacial and the early holocene periods this record is one of the few continental archives that show the climatic trend between the late glacial and the early holocene in central iberia agreeing with many other regional records from the western mediterranean