western mediterranean environmental changes evidences from fluvial archives abstract when dealing with current and past landscape evolution a key issue addresses responses of geomorphic systems to the large number of influencing variables identifying morphodynamic phases and revealing interrelations with specific driving forces are demanding tasks for quaternary research in this paper we present late pleistocene and holocene fluvial sedimentation patterns of three western mediterranean river catchments namely jarama river guadalete river and guadalquivir river that extent along a climatic transect from semi humid sw spain to semi arid central spain these studies are based on extensive fieldwork conducted on 36 exposures and 13 drillings in floodplain positions field data is supported by geochemical analyses while the chronological framework was obtained from the analyses of 70 radiocarbon samples results show distinct patterns of fluvial sedimentation as well as soil formation linked to floodplain stability for each river catchment on regional or catchment scale pollen stratigraphical correlation and comparison with lacustrine records show that fluvial dynamics have a strong reaction to climatic shifts with phases of high fragility characterized by catchment erosion and floodplain sedimentation in response to climatic aridification events and phases of climate change in general the comparison of the examined river systems reveals that periods of supra regional floodplain sedimentation in several catchments occurred from 8 0 to 7 0 5 0 to 3 8 2 2 to 1 5 and around 1 0 as well as 0 4 ka cal bp while we found periods of supra regional soil formation from 13 3 to 12 7 7 0 to 5 1 with a short interruption around 6 0 to 5 5 ka 2 8 to 2 3 ka 1 4 to 1 2 ka and 0 8 to 0 5 ka cal bp beside these consistencies we found deviating dynamic patterns that are apparently expressed in terms of differing onset and offset differing durations or even the lack of fluvial system response the main reasons for this can be seen in different regional climate condition and impacts of further influencing factors or in different levels of sensitivity of the river catchments that may be controlled by initial hydrological conditions catchment size or the degree of anthropogenic influence a larger scale assessment shows that fluvial dynamic patterns are hardly comparable across entire spain due to strong spatial heterogeneity of physiographic and climatic conditions on the iberian peninsula in particular when areas are influenced by different circulation systems e g regions influenced by the atlantic ocean vs regions influenced by the mediterranean sea however the consideration of north atlantic marine records reveals a certain coupling between north atlantic coolings atmospheric processes leading to arid climate over large parts of spain as well as increased landscape instability including strong fluvial sedimentation activity attendant atmospheric conditions are discussed

climatic change on the iberian peninsula recorded in a 30 000 yr pollen record from lake banyoles the banyoles lacustrine sequence shows that the vegetational history of the northeastern iberian peninsula during the last 30 000 yr follows the north atlantic pattern of climatic oscillations the banyoles pollen diagram supported by two calibrated 14c dates and nine u th dates shows a clear interstadial event between 30 000 and 27 000 yr b p a pleniglacial period with minor oscillations that ended abruptly ca 14 420 410 yr b p and a late glacial sequence that records the classical stages described in northern europe the bolling allerod interstade the younger dryas event at 12 000 yr b p u series age and a short warming phase between the younger dryas and the last cold event dated at 11 000 yr b p u series age

deglacial warming of the northeastern atlantic ocean correlation with the paleoclimatic evolution of the european continent abstract isotopic micropaleontologic and pollen analyses of deep sea cores from the bay of biscay and the northeastern atlantic ocean show that the deglacial warming of this oceanic area was closely correlated with the paleoclimatic evolution of the adjacent european continent temperatures were at least as warm as those of today in the bay of biscay between 13 300 and 11 000 b p coinciding with the combined bolling allerod warm continental events a major spread of polar water occurred between 11 000 and 10 000 b p during this event which coincides with the younger dryas continental cold event marine temperatures were almost as low as those of the last glacial maximum the final deglacial warming of the norteastern atlatntic ocean occurred during the following 3000 yr

late glacial and holocene palaeoclimatic record from sierra de cebollera northern iberian range spain abstract the study of a pollen sequence obtained from a peat deposit in hoyos de iregua iberian range north central spain has been carried out revealing new information about the vegetation dynamics and climate changes since late glacial times pollen zones have been defined corresponding to successive phases in vegetation history during the end of the late wurm oldest dryas late glacial interstadial younger dryas and the holocene during the oldest dryas event there was a sparse vegetation cover dominated by herbaceous taxa with pinus as the unique arboreal taxon with some importance the vegetation landscape during the late glacial interstadial 13 000 11 000 yr bp corresponded to coniferous forest and mixed forests including the presence of evergreen quercus between the late glacial and the holocene a brief cooler and drier phase occurred the younger dryas event 11 000 10 000 yr bp during this period an important reduction of the tree masses characterized the evolution of the landscape the holocene began with a period of increasing temperature that resulted in an expansion of the arboreal elements which reached their highest representation during the holocene climatic optimum from 5060 90 bp a change to more arid conditions occurred favouring the development of the mediterranean vegetation within the late holocene clear evidence of the human impact on the environment are detected being more accentuated towards the uppermost levels

flow and deformation of viscous silica oversaturated dispersions in low grade faults abstract cryptocrystalline silica veins occur along shear faults and in dilatational cracks in low grade cataclasites derived from leucocratic granitoids the silica minerals occur as radiate bladed quartz and as spherulitic and sheaf like clusters of neocrystallites that nucleated on crush fragments in a matrix of opaline and chalcedony this texture is indicative of rapid crystallization from a viscous oversaturated fluid the veins are clast loaded and typically demonstrate a banding defined by variation in the amount and size of feldspar crush fragments three types of veins are distinguished that differ in relative timing of viscous fluid flow deformation and crystallization type 1 veins are dilatational cracks in which static settling and crystallization took place an undisturbed planar layering is found which has no fixed orientation with respect to the vein wall this banding is commonly associated with a layering defined by periodic variations in hematite precipitates type 2 veins show a gradual decrease in grain size of the crush fragments from one vein wall to the other this banding shows pinch and swell structures micro boudinage and folding suggestive of flow type 3 veins occur in shear faults and demonstrate a banding which is asymmetric with respect to the vein walls apart from pinch and swell structures and folds the foliation shows sigmoidal deflection similar to that in shear bands in ductile mylonites it is proposed that the cryptocrystalline fragment loaded veins are formed by solidification of a silica sol or hydrogel that was formed by quenching of a hot fragment bearing solution during brittle failure the effect of a viscous fluid in fault rock is discussed in terms of rheology and of seismic periodicity

glacial stages in the pena negra valley iberian range northern iberian peninsula assessing the importance of the glacial record in small cirques in a marginal mountain area abstract the objective of this study was to assess whether it is possible to obtain a comprehensive record of the last deglaciation from the small pena negra glacial cirque in a marginal mountain range in the iberian range northern iberian peninsula the cirque is located in sierra cebollera at an elevation slightly over 2000 m a s l in the divide and has relatively low elevational difference between its uppermost and lowest parts the pena negra glacial cirque was selected because of the presence of several lateral moraines indicating the occurrence of a glacial tongue of 1 8 km length and a small rock glacier enabling identification of the main glacial stages that affected the paleo evolution of the glacier using cosmogenic exposure dating techniques and geomorphological mapping it was possible to reconstruct the historical pena negra glacier and to distinguish i the maximum ice extent mie at approximately 18 20 ka coinciding with the global last glacial maximum glgm although the occurrence of a previous stage was not ruled out ii a stage of glacial re advance at 16 17 ka coinciding with the oldest dryas followed by rapid ice melting iii the development of a rock glacier in a minor structural cirque near the headwall at 14 15 ka when paraglacial processes were probably dominant and iv evidence of ice melting in the uppermost cirque at 13 5 ka study of the pena negra glacier revealed the history of a minor valley glacier affected by distinct stages including the formation of a small rock glacier in the final phases of deglaciation no evidence of a younger dryas re advance was found

early holocene humidity patterns in the iberian peninsula reconstructed from lake pollen and speleothem records abstract comparison of selected well dated lacustrine speleothem and terrestrial pollen records spanning the holocene onset and the early holocene ca 11 7 8 cal kyrs bp in the iberian peninsula shows large hydrological fluctuations and landscape changes with a complex regional pattern in timing and intensity marine pollen records from alboran the mediterranean and off shore atlantic sites show a step wise increase in moisture and forest during this transition however available continental records point to two main patterns of spatial and temporal hydrological variability i atlantic influenced sites located at the northwestern areas enol sanabria lucenza prd 4 characterized by a gradual increase in humidity from the end of the younger dryas to the mid holocene similarly to most north atlantic records and ii continental and mediterranean influenced sites laguna grande villarquemado fuentillejo padul estanya banyoles salines with prolonged arid conditions of variable temporal extension after the younger dryas followed by an abrupt increase in moisture at 10 9 cal kyrs bp different local climate conditions influenced by topography or the variable sensitivity gradual versus threshold values of the proxies analyzed in each case are evaluated vegetation composition conifers versus mesothermophilous taxa and resilience would explain a subdued response of vegetation in central continental areas while in mediterranean sites insufficient summer moisture availability could not maintain high lake levels and promote mesophyte forest in contrast to atlantic influenced areas comparison with available climate models greenland ice cores north atlantic marine sequences and continental records from central and northern europe and the whole mediterranean region underlines the distinctive character of the hydrological changes occurred in inner iberia throughout the early holocene the persistent arid conditions might be explained by the intensification of the summer drought due to the high seasonality contrast at these latitudes caused by the orbital induced summer insolation maximum new records particularly from western and southernmost iberia and palaeoclimate models with higher spatial resolution would help to constrain these hypotheses

recent contributions to the climatology of the last glacial interglacial cycle based on french pollen sequences abstract new pollen data derived from three long french sequences and methodological improvements in the methods used to reconstruct past climates are summarized here after a short presentation of the study sites and pollen diagrams estimated climate parameters during the major episodes of the last 140 000 years are shown to be coherent between sites analysis of the seasonality variations provides much additional information in particular it is shown that the advection from the ocean has governed the last climatic cycle on the european continent

late pleistocene holocene palaeoenvironmental evolution of the anamaza river valley iberian range ne spain multidisciplinary approach on the study of carbonate fluvial systems abstract the uppermost pleistocene and holocene palaeoenvironmental evolution of the anamaza river valley iberian range ne spain is deduced using multidisciplinary approach including stratigraphical mineralogical palynological geochemical geophysical methods and drilling main changes were registered in distinct subenvironments of a carbonate fluvial system including the channelled zone and wetlands in the floodplain tufa barrages dominated although pools also existed geophysical survey and coring reveal tufa build ups and pool facies also in the subsoil lower water temperature and scarce evaporation are deduced for the pleistocene fluvial system that progressively changed through the holocene with more hydrologically closed areas and higher evaporation influence a general aggrading evolution during warm stages related with increasing base level and damming due to fast carbonate precipitation characterised the holocene detrital tufa indicates erosive high energy floods or colder stages when water level would decrease favouring erosion 14 c and 230 th 234 u dating reveal high sedimentation rates and three main discontinuities related with cold episodes younger dryas middle part of the holocene climate optimum and iron age epoch during the uppermost pleistocene tufa growth would be enhanced during warmer episodes as the bolling allerod in the younger dryas scarce vegetation favoured erosion of both slopes and tufa constructions subsequent warmer temperatures during the first part of the holocene favoured vegetated slopes enhanced tufa growing although interrupted in the middle part of the holocene climate optimum and development of wetlands with riparian vegetation in the floodplain where either siliciclastics or detrital tufa incoming alternated with low energy waters stages and mud settling progressive decline in tufa is deduced for the upper holocene but it is not possible to determine whether this and other palaeoenvironmental changes were related either to climate or increasing human activities during the roman and medieval warm periods more oxidizing conditions in the wetlands and increasing erosion prevailed probably conditioned by human activities the pollen record shows for the early holocene development of pinus forest with betula and expansion of deciduous quercus xerophilous and heliophilous grassland subsequent increasing moisture supported open forests with deciduous quercus ulmus corylus and evergreen quercus ilex pistacia species from ca 4000 yrbp a dominant deciduous quercus forest with groves of corylus ulmus acer fagus and taxus expanded and human activities grazing occurred from 1200 yrbp dry grassland expanded due to intensive land use agropastoral activities almost completely deforested plateaus surround the site today with slopes covered by patchy grass with junipers groves and screeds with little soil

human trace on the landscape during the holocene at el mirador cave sierra de atapuerca spain the palynological evidence the archaeological research focusing on el mirador cave sierra de atapuerca spain has revealed a succession of occupation levels in a dung layers context that span from the early neolithic to th

termination of the last glaciation in the iberian peninsula inferred from the pollen sequence of quintanar de la sierra abstract a 4 5 m thick late glacial pollen sequence supported by 17 ams14c dates has been investigated at the quintanar de la sierra marshland iberian cordillera north central spain pollen zones were defined that correspond to successive phases in vegetation history during the end of the late wurm late glacial interstade and younger dryas periods a transfer function approach has been adopted to derive quantitative climate estimates from the pollen assemblage data a first expansion ofjuniperusandhippophae about 13 50014c yr b p indicates the beginning of the late glacial interstade which is characterized by ajuniperus betula pinussuccession that suggests higher temperatures and moisture than during full glacial time the younger dryas interval is recorded by a 120 cm thick sediment unit that is dominated by herbaceous pollen transfer function estimates suggest that the climate during this period was cold with low precipitation during most of the year although not in summer the holocene arboreal recolonization in the area started about 10 00014c yr b p with a renewedjuniperus betula pinussuccession related to a strong increase in annual temperature and precipitation the start of this process was synchronous with mean sea surface temperature changes as recorded from the nearby su 81 18 marine core the strong affinity with other european late glacial pollen sequences demonstrates that the pattern of climatic changes during the last glacial interglacial transition was similar in both northwestern and southwestern europe

structural control of scarps in the rembrandt region of mercury lobate scarps thought to be the surface expression of large thrust faults are the most spectacular contractional tectonic features visible on mercury most lobate scarps follow a general and relatively simple pattern with a roughly arcuate or linear form in plan view and an asymmetric cross section characterized by a steeply rising scarp face and a gently declining back scarp in this work we study two peculiar and complex scarps in the rembrandt region of mercury through messenger imagery on the one hand the formation of these scarps resulted in the deformation of features such as impact craters fractures extensional faults and volcanic plains while on the other hand the deformed features partly influenced the formation of the scarps evidence for structural control on the formation of the scarps includes their orientation segmentation bifurcation change in structural trend and dip orientation and transition into high relief ridges or wrinkle ridge morphologies in some cases thus these two lobate scarps provide examples of complex geological relations among other features expanding the recognized richness of mercurian geology also the southern scarp records a complex history of contraction suggesting that the development of some mercurian lobate scarps may be more complex than usually thought

interpreting drivers of change in fluvial archives of the western mediterranean a critical view abstract fluvial archives in particular late glacial to holocene floodplain records may provide valuable information regarding past environmental conditions and stages of landscape evolution in view of the high significance of floodplain dynamics for the development of entire landscapes the number of studies that have been performed on floodplain sediments remains comparatively low especially regarding the western mediterranean region however one of the reasons could be seen in the high complexity and diversity of processes and factors that control and influence fluvial activity that often hampers a straightforward interpretation of floodplain dynamics therefore a basic demand on fluvial archive research is to address the complexity of the factors that control the characteristics of fluvial sequences in order to provide a robust basis for their interpretation as a starting point for discussion this paper aims to give an overview of fluvial dynamic patterns in the western mediterranean for the last 15 ka in order to examine their relevance for palaeoenvironmental reconstructions the basis for this is provided by previous investigations on four different river systems in spain and northern africa the results of which are herein synthesized in order to propose a regional late pleistocene and holocene fluvial history for the western mediterranean realm basic results are related to alluvial floodplain deposits and visible features within them such as alluvial soils incision marks and aggradation phenomena since fluvial systems are open systems we discuss our findings against the background of different influencing factors that could modify fluvial architecture and may restrict palaeoenvironmental reconstructions a more comprehensive interpretation focuses on signals that are common to each of the studied river systems in this respect we critically discuss the customary nature of cumulative probability functions for the identification of regional flooding episodes and point out the benefits of a stratigraphy supported approach for characterizing regional floodplain dynamics finally three alluvial soil formation periods were found in all settings a first phase after 15 ka ending with the younger dryas event a second one from 7 to 5 ka with a break between 6 5 and 5 5 ka and a third phase between 3 and 2 ka these soil formation periods were interrupted and framed by fluvial dynamic phases accompanied by channel aggradation floodplain deposition floodplain erosion and or river incision in particular after 5 ka around 1 6 and at 1 ka and during the little ice age lia floodplain aggradation affected river systems in iberia and northern africa as well a cautious assessment of these results and extensive comparisons with secondary archive information prompts us to relate the aggradation periods with climate forcing by means of a supra regional aridification that effected large areas of the western mediterranean in contrast the three mentioned soil formation periods can be linked with landscape stability most probably triggered by favorable climate conditions in the western mediterranean apart from these large scale patterns we discuss the reliability of information emerging from floodplain records against the background of individualistic river behavior and self organization regarding future work we want to emphasize the great potential of yet rarely applied system oriented approaches that also attach importance to sub catchment dynamics as a link between catchment slopes and the main river floodplain

the biogeographical role of pinus forest on the northern spanish meseta a new holocene sequence abstract the aim of this paper is to reconstruct the variation in the vegetation during the holocene on the northern meseta through pollen analysis in order to determine the roles played by pinus and quercus in the vegetation dynamics a new pollen sequence camporredondo in the centre of the duero river basin northern meseta spain is presented it covers the period from ca 11 250 to 1630 cal yr bp the camporredondo sequence suggests that a forested landscape existed from the start of the holocene with values of approximately 90 of arboreal pollen mainly derived from pine forests in the surroundings shortly after 8600 cal yr bp pine forests continued to dominate but the landscape became more open while stands of deciduous and evergreen quercus developed around 4500 years ago coinciding with the start of a period of less rainfall the lacustrine areas in these territories began to silt up favouring hydrophytic taxa such as salix or cyperaceae a comparison with other holocene pollen sequences from the central eastern part of the northern meseta confirms the presence of pine forests in the whole region since the early holocene we discuss the variations of the general vegetation pattern in terms of the local or regional conditions at each site throughout the holocene pinus forests dominated at least in the eastern half of the duero river basin the typical holocene substitution of conifers by broadleaf species as recorded in other parts of the iberian peninsula and europe never takes place in the study area the results of the present study suggest that the current view of the potential vegetation in the spanish northern meseta should be reviewed

interrelated continental sedimentary environments in the central iberian range spain facies characterization and main palaeoenvironmental changes during the holocene a complex holocene system in the central iberian range ne spain has been reconstructed on the basis of sediments recovered from cores and in situ observations small alluvial fans graded into a wide shallow lacustrine area anavieja lake that connected downstream with a carbonate fluvial system with associated vegetated zones the fluvial system was mainly characterized by the development of tufa barriers especially during the first part of the holocene that separated pools or small lakes oncolites detrital tufas calcarenites and marls were deposited in these pools adjacent vegetated areas were covered by macrophytes and were episodically reached by detrital tufa supplies indicating high flood stages high sedimentary rates existed in both the fluvial including the pools and vegetated areas suggesting that despite the common erosion of tufas a clear aggradating evolution existed by contrast very low sedimentary rates were registered in the anavieja lake all the environments but especially the vegetated areas registered the climate evolution during the holocene although the onset of the holocene was characterized by wide climate variability warm and humid conditions dominated during the first part and drier conditions during the second part a water level recovery seems to have been existed during the last millennium this is a good example of the potential of continental systems other than lakes to be useful for palaeoenvironmental and palaeoclimatic studies

the mode and mechanism of the last deglaciation oceanic evidence changes in ocean temperature carbonate productivity and ice rafted detritus in the north atlantic suggest that half of the northern hemisphere ice volume at the last glacial maximum had disappeared by 13 000 yr b p despite the still extensive limits of the ice sheets this early thinning of the ice sheets occurred during a time when summer insolation values were slowly rising but when pollen evidence south of the ice margins indicates cold dry air masses we infer that this rapid early ice disintegration 16 000 13 000 yr b p was caused by oceanic mechanisms 1 rising sea level causing increased calving along ice margins 2 the chilling of the sea surface by icebergs and meltwater reducing moisture extraction by the atmosphere and transport to the ice sheets and 3 winter freezing of the low salinity meltwater layer suppressing local moisture extraction and the regional influx of moisture bearing storms from lower latitudes in winter and hence starving the ice sheets these oceanic feedback mechanisms were strongest from 16 000 to 13 000 yr b p and weaker but still active from that date until the end of deglaciation at 6000 yr b p

abrupt climate change sea surface salinity and paleoproductivity in the western mediterranean sea gulf of lion during the last 28 kyr abstract the planktonic foraminiferal record of core md99 2346 gulf of lion shows a decrease of sea surface temperature sst at the time of heinrich event h2 24 23 5 cal kyr bp younger dryas and during the early to middle holocene these events were associated with a decrease of surface water salinity the salinity lowering events were similar and synchronous to those recorded in the north atlantic ocean during h1 h2 and the younger dryas they can be explained by a decrease in the salinity of the atlantic surface water entering the mediterranean through the strait of gibraltar this result indicates that the mediterranean sea remained a concentration basin and that its freshwater budget was not significantly different from the modern conditions at the time of these low salinity events higher abundances of the benthic foraminifer cibicidoides pachydermus at the time of heinrich events h2 and h1 may result from a seasonal and more pulsed supply of labile organic matter a high abundance of intermediate and deep infaunal taxa globobulimina spp during the warm bolling allerod period is interpreted as a result of an increased lateral advection of organic matter to the deeper environments of the gulf of lion surface water productivity as reflected by the organic flux to the benthic ecosystem reaches a maximum during the cold younger dryas period it is possible that cold conditions at the time of the younger dryas have allowed an enhanced vertical mixing and deep water cascading in the gulf of lion this may have resulted in an increase of primary and export production this putative intensification of deep water cascading would have occurred after the sustained rise of the global sea level from 16 to 12 5 cal kyr bp the deglacial sea level rise may also have played an important role in favouring the downslope movement of dense shelf water enriched in organic matter originating from the early rhone delta complex the conditions during the holocene were characterized by a low surface productivity and oligotrophic environment similar to the modern situation

late quaternary climatic change in france estimated from multivariate pollen time series abstract in regions like southern france where usual analytical techniques are unsatisfactory due to the heavy influence of human activity and the existence of a complex climate the quantitative reconstruction of climate from pollen is particularly difficult that is why an original method has been performed the first step of the method based on best analogs estimation and multiple regression is to calculate a relationship between climate monthly temperature and precipitation and modern pollen spectra for data from 182 sites the result is called the analog climate the second step of the method an original combination of canonical correlation and principal components analyses extracts the common information from several fossil pollen sequences to produce a so called paleobioclimate this step removes the effects of local differences in the vegetation among nearby sites and also reduces the effects of human disturbance in the third step the signals obtained from the first two steps are merged by kalman filter into a final reconstruction where the noise is reduced by around 37 the results presented with a 95 confidence level suggest that the pleni wurm was 7 to 13 c colder than present and had 20 to 60 less precipitation than today this large confidence takes into account the climatic diversity of the region at 13 000 yr b p the climate reached the modern level of precipitation but the temperature was just less than present the subsequent decrease of precipitation is less important than that of temperature this fact may explain the advance of alpine glaciers during the younger dryas preboreal warming was abrupt 3 to 4 c per 500 yr and precipitation increased more slowly

geochemistry of core sediments from the middle tagus alluvial plain portugal since the last glacial using background determination methods to outline environmental changes this work deals with the geochemistry of the sediments from the santarem entre valas sev borehole in the middle tagus alluvial plain in portugal methods for background determination were used notably the concentration length and cumulative frequency methods both methods were in excellent agreement for the elements of interest namely au as fe u cu pb zn co and cr with these results five segments in the sev borehole were identified to have higher than background values for at least two or more of these elements the most important segment spans at least 1 500 years during the early holocene warm period with almost all elements with anomalous values this has been interpreted as the result of enhanced weathering of the host rocks upstream as a consequence of deglaciation since the last glacial maximum and general wetter conditions known to have occurred in this region no other segment of the core has shown a similar variety of elements with higher than background values but the upper segments correlate with the particular mineralogy on the sediments due to the development of an estuarine environment at circa 3 000 4 000 cal years bp the presence of charcoal and charred organic matter during the beginning of the bronze age characterises the segment with the first high values of cu but apart from deforestation and land use that affected this region at the time this anomaly is likely due to the chemical affinity of cu to organic matter and not to anthropogenic activities finally the upper meter of the core sediments spanning 812 years have a clear anthropogenic signal for cu also seen in other two boreholes and systematic high values for au and pb although cu is surely an indication of secular agricultural practices vineyard sulphatation au and pb might be the natural accumulation from weathering of ancient mine wastes scattered in the hercynian massif upstream

retreat velocity of the north atlantic polar front during the last deglaciation determined by 14 c accelerator mass spectrometry the glacial oscillations which dominate the quaternary global climate are closely related to changes in incoming solar radiation but the details of palaeoclimatic spectra suggest that other parameters usually referred to as feedback have significantly increased the climatic response to extraterrestrial forcing1 the last deglaciation appears to be one of the more characteristic examples of nonlinearity because its abruptness strongly contrasts with the smooth shape of the associated solar radiation maximum dated at 11 000 yr bp in addition the presence of the younger dryas cold event concomitant with the solar radiation maximum could be interpreted as a transitory phenomenon caused by the rapid meltwater influx linked to the first phase of the ice sheet s disintegration2 3 here using accelerator mass spectrometry we date precisely the movements of the polar front during the whole period of glacial retreat 15 000 8 000 yr bp our results show that the polar front has moved between 35 n and 55 n in 1 000 yr for the earliest retreat 12 500 12 000 bp and moved almost instantaneously that is 400 yr during the two abrupt climatic changes associated with the younger dry as cold event

late quaternary fluvial dynamics of the jarama river in central spain the jarama river and its catchment provide a valuable natural archive to study and reconstruct past environmental conditions in central spain this region is highly prone to changes in the hydrological cycle under predicted climate warming in particular with respect to aridity periods rainfall variability and the occurrence of extreme flood events this paper presents 15 exposures covering a time span of the last 44 ka which were documented in the field and of which seven exposures were soil chemical analyzed regarding soil texture organic matter as well as carbonate and iron content ages are based on radiocarbon dating on 32 samples latest holocene sediments were found within the channel belt where permanent remobilization of sediments takes place due to the migration of the meandering river course in more distal floodplain positions sediment sequences show a complex fluvial architecture referring to periods of varying character and intensity of alluviation as well as periods of geomorphic stability indicated by soil formation furthermore sedimentation patterns vary along different river sections aggradations of coarse gravels took place between 40 and 18 ka cal bp over the entire valley floor alluviation of fine material was documented between 17 and 16 at 7 5 between 5 1 and 3 3 at 2 8 between 2 1 and 1 5 at 1 0 and around 0 4 ka cal bp until recent times astonishingly in late holocene times between 4 2 and 3 1 ka cal bp aggradations of coarse gravels even in distal floodplain areas overlap with sedimentation of fine material in adjacent river sections pointing to a complex constellation of parameters involved periods of soil formation were detected around 43 at 31 between 16 and 12 6 after 7 5 until 5 1 between 2 8 and 2 1 and at times after 1 5 ka cal bp phases of geomorphic stagnation were found at 38 ka cal bp and for a duration of 200 years at 3 0 ka cal bp and refer to absent geomorphic or pedogenic processes all these patterns are an expression of the interaction between climatic variations tectonic impulses and human influences a comparison with other terrestrial archives enabled us to reconstruct late pleistocene and holocene palaeoenvironmental conditions on a regional scale and furthermore to link specific stages of floodplain development to prevalent influencing variables thus with emphasis on the fluvial system response a model of a cause and effect relationship is presented that concentrates on rapid climate changes long lasting climatic deteriorations and the role of human interventions