the medieval climate anomaly in the iberian peninsula reconstructed from marine and lake records abstract selected multi proxy and accurately dated marine and terrestrial records covering the past 2000 years in the iberian peninsula ip facilitated a comprehensive regional paleoclimate reconstruction for the medieval climate anomaly mca 900 1300 ad the sequences enabled an integrated approach to land sea comparisons and despite local differences and some minor chronological inconsistencies presented clear evidence that the mca was a dry period in the mediterranean ip it was a period characterized by decreased lake levels more xerophytic and heliophytic vegetation a low frequency of floods major saharan eolian fluxes and less fluvial input to marine basins in contrast reconstruction based on sequences from the atlantic ocean side of the peninsula indicated increased humidity the data highlight the unique characteristics of the mca relative to earlier the dark ages da ca 500 900 years ad and subsequent the little ice age lia 1300 1850 years ad colder periods the reconstruction supports the hypothesis of trouet et al 2009 that a persistent positive mode of the north atlantic oscillation nao dominated the mca

stratigraphy of the 1902 and 1929 nuee ardente deposits mt pelee martinique mild nuee ardentes in 1902 1903 and 1929 1930 at mt pelee formed high aspect ratio h a r deposits i e deposits with a high thickness extent ratio in the riviere blanche channel several violent nuees ardentes from may to august 1902 yielded low aspect ratio l a r deposits unevenly blanketing an area of 58 km2 on the southwestern flank of the volcano three closely spaced nuees ardentes on august 30 additionally affected 56 km2 on the southeastern flank the l a r deposits are divided into eight stratigraphic units u1 u8 either compound or consisting of a single flow unit the deposits of the largest nuees ardentes on may 8 20 and august 30 1902 are identified as u1 u3 and u8 respectively and can be traced over most of the area individual l a r flow units are lenticular and show large erratic lateral variations of thickness and grain size most flow units consist of three distinct beds bed 1 is a few centimeters thick lenticular fines depleted layer bed 2 is the thickest layer and contains more silt sized ash than bed 1 it is normally graded as a whole though reverse grading may occur in the lower part bed 2 generally consists of two parts bed 2a nonbedded and bed 2b finer grained and laminated with cross bedding and duned structures bed 3 is a thin silty capping layer which contains accretionary lapilli the distribution of the l a r flow units especially of the coarse grained facies suggests that they were formed from overpressured blast flows expanding radially from the vent at a high rate in the same manner as the laterally directed blast of mount st helens on may 18 1980 the transport system of the major 1902 nuees ardentes was an inflated relatively low concentration turbulent cloud as suggested by several lines of evidence 1 the transported material was able to cross ridges up to 300 m high 2 many scour and fill and other erosional features can be observed in the deposits at any distance from the vent 3 survivors within the devastated area on may 8 did not experience a dense low profile cloud but instead a choking hot ash laden cloud 4 many human corpses in st pierre remained where they fell instead of having floated away if the current flow surge terminology were to be used the 1902 blast flows would be better considered as pyroclastic surges the normally graded multi layered structure of the flow units is also consistent with deposits primarily formed from relatively low concentration flows

microphysical consequences of the spatial distribution of ice nucleation in mixed phase stratiform clouds mixed phase stratiform clouds can persist even with steady ice precipitation fluxes and the origin and microphysical properties of the ice crystals are of interest vapor deposition growth and sedimentation of ice particles along with a uniform volume source of ice nucleation lead to a power law relation between ice water content wi and ice number concentration ni with exponent 2 5 the result is independent of assumptions about the vertical velocity structure of the cloud and is therefore more general than the related expression of yang et al 2013 the sensitivity of the wi ni relationship to the spatial distribution of ice nucleation is confirmed by lagrangian tracking and ice growth with cloud volume cloud top and cloud base sources of ice particles through a time dependent cloud field based on observed wi and ni from indirect and semi direct aerosol campaign a lower bound of 0 006 m 3 s 1 is obtained for the ice crystal formation rate

alpine lacustrine varved record reveals summer temperature as main control of glacier fluctuations over the past 2250 years glacier fluctuations are a key indicator of changing climate their reconstruction beyond historical times unravels glacier variability and its forcing factors on long time scales which can considerably improve our understanding of the climate glacier relationship here we present a 2250 year long reconstruction of particle mass accumulation rates recorded in the lacustrine sediments of lake truebsee central swiss alps that are directly related to glacier extent thus reflecting a continuous record of fluctuations of the upstream located titlis glacier mass accumulation rate values show strong centennial to multi centennial fluctuations and reveal 12 well pronounced periods of enhanced values corresponding to times of maximum extent of the neighboring lower grindelwald glacier this result supports previous studies of proglacial lake sediments that documented high mass accumulation rate values during glacier advances the strong variability in the lake truebsee mass accumulation rate record thus represents a highly sensitive paleoclimatic archive which mirrors rapid and pronounced feedbacks of titlis glacier to climatic changes over the past 2250 years the comparison of our data with independent paleo temperature reconstructions from tree rings suggests that variations in mean summer temperature were the primary driving factor of fluctuations of titlis glacier also advances of titlis glacier occurred during the grand solar minima dalton maunder sporer wolf of the last millennium this relation of glacier extent with summer temperature reveals strong evidence that the mass balance of this alpine glacier is primarily controlled by the intensity of glacier melting during summer

sedimentological and palaeohydrological characterization of late pleistocene and holocene tufa mound palaeolakes using trenching methods in the spanish pyrenees

arid and humid phases in southern spain during the last 4000 years the zonar lake record cordoba a multiproxy study of sediment cores from zonar lake 37 29 00 n 4 41 22 w 300 m a s l supported by 11 14c ams dates provides the first high resolution centennial scale reconstruction of past h

catastrophic early holocene sea level rise human migration and the neolithic transition in europe abstract the collapse of the laurentide ice sheet and release of freshwater 8740 8160 years ago abruptly raised global sea levels by up to 1 4 m the effect on human populations is largely unknown here we constrain the time of the main sea level rise and investigate its effect on the onset of the neolithic across europe an analysis of radiocarbon ages and palaeoshoreline reconstruction supports the hypothesis that flooding of coastal areas led to the sudden loss of land favoured by early farmers and initiated an abrupt expansion of activity across europe driven by migrating neolithic peoples

2000 year environmental history of a karstic lake in the mediterranean pre pyrenees the estanya lakes spain abstract the sediment record of the estanya lakes pre pyrenees spain indicates that this region was intensely affected by land use during the middle and modern ages which contrasts with the present day poor socioeconomic development of the region the correlation between sediment and biotic data and well known historical events suggests a reliable history of environmental changes in this area during the last 2000 years changes in lake level were mainly controlled by climatic factors whereas properties such as lithology organic carbon ostracods and pollen content are mainly associated with lake management and land use major sedimentological changes resulted from the use of the lake for hemp retting at the start of the xivth century subsequent depopulation of the area in the xxth century led to the progressive recovery of the lacustrine ecosystem

timing of deglaciation and postglacial environmental dynamics in nw iberia the sanabria lake record abstract the multiproxy study sedimentology geochemistry and diatoms of sediment cores from sanabria lake 42 07 30 n 06 43 00 w 1000 m a s l together with a robust 14c chronology provides the first high resolution and continuous sedimentary record in the region extending back the last 26 ka the development of a proglacial lake before 26 cal ka bp demonstrates the onset of deglaciation before the global last glacial maximum similarly to other alpine glaciers in southern european mountains rapid deglaciation occurred at the beginning of the greenland interstadial gi 1e bolling 14 6 cal ka bp following a short lived episode of glacier re advance 14 4 14 2 cal ka bp gi 1d a climatic improvement at 13 9 cal ka bp suggests the glaciers retreated from the lake basin during the gi 1c another glacier reactivation phase occurred between ca 13 0 12 4 ka starting earlier than the onset of gs 1 younger dryas rapid deglaciation during the early holocene 11 7 10 1 cal ka bp was followed by a period of higher river discharge 10 1 8 2 cal ka bp after 8 2 ka the holocene is characterized by a general decreasing trend in humidity punctuated by the driest phase during the mid holocene ca 6 8 4 8 a wetter interval between 4 8 and 3 3 cal ka bp and a relatively decline of rainfall since then till present with a minor increase in humidity during some phases ca 1670 1760 of the little ice age discrete silt layers intercalated in the organic rich holocene deposits reflect large flooding events of the tera river ca 10 1 8 4 7 5 6 2 5 7 5 6 4 6 4 2 3 7 3 3 3 1 2 7 2 5 and 2 0 cal ka bp their synchronicity with a number of cold and humid events described in the atlantic demonstrates a strong control of nw iberian climate by north atlantic dynamics at centennial millennial scale comparison with western mediterranean records points to similar regional dynamics during the holocene although modulated in the nw iberian peninsula by the stronger atlantic influence

hierarchy of facies of pyroclastic flow deposits generated by laacher see type eruptions the upper quaternary pyroclastic flow deposits of laacher see volcano show compositional and structural facies variations on four different scales 1 eruptive units of pyroclastic flows composed of many flow units 2 depositional cycles of as many as five flow units flow units containing 3 regional intraflow unit facies and 4 local intraflow unit subfacies these facies can be explained by successively overlapping processes beginning in the magma column and ending with final deposition the pyroclastic flow deposits thus reflect major aspects of the eruptive history of laacher see volcano a drastic changes in eruptive mechanism due to increasing access of water to the magma chamber and b change in chemical composition and crystal and gas content as evacuation of a compositionally zoned magma column progressed the four scales of facies result from four successive sets of processes 1 differentiation in the magma column and external factors governing the mechanism of eruption 2 temporal variations of factors inducing eruption column collapse 3 physical conditions in the eruption column and the way in which its collapse proceeds and 4 interplay of flow inherent and morphology induced transport mechanics

origin and emplacement of a pyroclastic flow and surge unit at laacher see germany abstract within the pyroclastic ejecta sequence of laacher see volcano west germany are many repeated phreatomagmatic depositional cycles a complete cycle begins with a thin low aspect ratio fines depleted breccia layer followed by a sequence with several coarse to fine grained cross bedded units in turn overlain by a massive pyroclastic flow layer each sequence is interpreted in terms of water magma interaction and effects upon the eruption column the breccia represents the triggering eruption with a high eruption column where fines were winnowed out and fallback from high altitudes produced a low aspect ratio layer the cross bedded sequence containing more fine grained ash resulting from an increase in amount of water represents a fluctuating eruption column of sufficient height to produce large antidunes within 700 meters of the rim the massive pyroclastic flow layer which contains more fine grained ash than the underlying layers represents the culmination of the eruption where an increase in amount of water interacting with the magma resulted in a dense and very low eruption column producing a dense laminar moving pyroclastic flow

late holocene record from a loire river incised paleovalley french inner continental shelf insights into regional and global forcing factors abstract sediment core kv14bis was retrieved from the fosse du croisic a loire river incised paleovalley located in the inner shelf of the bay of biscay this core 5 4 m length covers the past 2 6 cal kyr bp with high sedimentation rate a multiproxy approach x ray imagery xrf data grain size analyses and benthic foraminiferal assemblages was applied in order to reconstruct the hydrological regime of the loire river during the late holocene this hydrological regime was further linked to climate forcing e g solar activity north atlantic oscillation nao and human activity our data describe a succession of several dry humid periods the humid periods are centered on 2 2 1 3 and 0 5 cal kyr bp and are characterized by high terrigenous flux fine silty sedimentation relatively high organic carbon content and high proportions of the epiphytic foraminiferal species planorbulina mediterranensis this species was probably brought to the study site by the loire river plume attached on floating algae the dry periods are centered on 2 5 1 5 1 2 cal kyr bp and 1900 ce and are characterized by low terrigenous input and high carbonate content due to abundant shell debris during periods of low river runoff deposition of a sand particle population grain size 200 m could indicate increased storminess this latter may have remobilized sediments from shallower depths during these generally dry periods on the continent the overall coherence of our results with several european continental records supports a pluri centennial scale regional climate control of humidity and storminess resembling that of the nao spectral analyses emphasized a possible additional control of solar activity through deforestation and soil erosion early human impact was also probably superimposed on this climatic forcing

lateral variations in the taupo ignimbrite abstract the young non welded taupo ignimbrite shows remarkable lateral variations which are documented by granulometric and component analyses and studies of maximum clast size and density the grain size spans practically the entire known ignimbrite field the coarser proximal ignimbrite having a median diameter 100 times greater than the finest distal ignimbrite the content and maximum size of lithic fragments decrease also by a factor of 100 between proximal and distal parts the content of free crystals first rises to reach a peak but thereafter decreases to attain a very low value in far distal exposures the pumice maximum size decreases by a factor of about 10 and the most conspicuously coarse pumice rocks occur in a girdle nearly halfway out from vent to distal limit the pumice in each grain size class decreases in density to half of its near source value in distal ignimbrite the overall outward trend is towards an ignimbrite which consists wholly of fine vitric ash some distal exposures closely approach this condition these variations are accounted for by a combination of processes operating in the moving ash flow one is a continuous fragmentation of pumice leading to a rounding of the clasts a progressive decrease in maximum size the generation of much vitric dust and the liberation of crystals another is a continuous sedimentation of heavy constituents lithics and crystals and an antipathetic rise of lighter coarse pumice towards the top of the flow these processes operated in a moving flow whose upper layers travelled progressively farther from source it is the topmost layers strongly depleted in heavy constituents and enriched in light pumice which have travelled the farthest and constitute the far distal parts of the ignimbrite a number of ignimbrite facies are characterized the ignimbrite proper with its proximal distal and pumice concentration zone facies the deposits which form in the head and are then over ridden by the body of the flow including the fines depleted ignimbrite variant and the heavies enriched ground layer and the ignimbrite veneer deposits which are left behind by the flow which differ little from the ignimbrite except in their landscape mantling form and the occurrence in them of lee side coarse pumice lenses

abrasion in pyroclastic flows the relative size of glass rims coating crystals in the matrix ash provides a semi quantitative measure of abrasion of ash grains in pyroclastic flows median abrasion indices areacrystal areaglass rim are 8 4 to 18 5 in laacher see pyroclastic flow units but only 4 to 6 3 in assocciated fallout showing stronger abrasion of ash particles in the pyroclastic flows all pyroclasts undergo strong attrition in the vent but clasts in pyroclastic flows undergo a second major phase of abrasion during high energy near vent flow abrasion of ash particles is weaker during lower energy higher strength motion further downstream suggesting that high contents of fine ash in distal deposits are due to diminishing elutriation rather than high rate of attrition

post collapse volcanic history of calderas on a composite volcano an example from roccamonfina southern italy roccamonfina part of the roman potassic volcanic province is an example of a composite volcano with a complex history of caldera development the main caldera truncates a cone constructed predominantly of this caldera may have been associated with one of the ignimbritic eruptions of the brown leucitic tuff blt around 385 000 yr bp the campagnola tuff the youngest ignimbrite of the blt however drapes the caldera margin and must postdate at least the initial stages of collapse during the subsequent history of the caldera there were several major explosive eruptions the largest of these was that of the galluccio tuff at about 300 000 yr bp it is likely that there was further collapse within the main caldera associated with these eruptions it is of note that despite these subsequent major explosive eruptions later collapse occurred within the confines of the main caldera between eruptions caldera lakes developed producing numerous lacustrine beds within the caldera fill extensive phases of phreatomagmatic activity generated thick sequences of pyroclastic surge and fall deposits activity within the main caldera ended with the growth of a large complex of basaltic trachyandestite lava domes around 150 000 yr bp early in the history of roccamonfina sector collapse on the northern flank of the volcano formed the northern caldera one of the youngest major events on roccamonfina occurred at the head of this northern caldera with explosive activity producing the conca ignimbrite and associated caldera there is no evidence that there was any linkage in the plumbing systems that fed eruptions in the main and northern calderas

autumnal mixed phase cloudy boundary layers in the arctic abstract two mixed phase cloudy boundary layer events observed over the arctic ice pack in autumn are extensively analyzed the local dynamic and thermodynamic structure of the boundary layers is determined from aircraft measurements including analysis of turbulence longwave radiative transfer and cloud microphysics the large scale forcing is determined from the national centers for environmental prediction reanalysis fields while mesoscale forcing is estimated from 40 km aircraft box patterns the two cases differed somewhat in their local static stability surface characteristics and large scale forcing one case was characterized by a stably stratified cloudy boundary layer over a heterogeneous surface containing numerous open leads the other case occurred over a fairly homogenous surface of multiyear ice and consisted of a surface based stable layer surmounted by a low level jet and a cloud topped mixed layer an important large scale factor in the development of low clouds appears to have been w

climate variability in se europe since 1450 ad based on a varved sediment record from etoliko lagoon western greece to achieve deeper understanding of climate variability during the last millennium in se europe we report new sedimentological and paleoecological data from etoliko lagoon western greece the record represents the southernmost annually laminated i e varved archive from the balkan peninsula spanning the little ice age allowing insights into critical time intervals of climate instability such as during the maunder and dalton solar minima after developing a continuous ca 500 year long varve chronology high resolution xrf counts stable isotope data measured on ostracod shells palynological including pollen and dinoflagellate cysts and diatom data are used to decipher the season specific climate and ecosystem evolution at etoliko lagoon since 1450 ad our results show that the etoliko varve record became more sensitive to climate change from 1740 ad onwards we attribute this shift to the enhancement of primary productivity within the lagoon which is documented by an up to threefold increase in varve thickness this marked change in the lagoon s ecosystem was caused by i increased terrestrial input of nutrients ii a closer connection to the sea and human eutrophication particularly from 1850 ad onwards and iii increasing summer temperatures integration of our data with those of previously published paleolake sediment records tree ring based precipitation reconstructions simulations of atmospheric circulation and instrumental precipitation data suggests that wet conditions in winter prevailed during 1740 1790 ad whereas dry winters marked the periods 1790 1830 ad dalton minimum and 1830 1930 ad the latter being sporadically interrupted by wet winters this variability in precipitation can be explained by shifts in the large scale atmospheric circulation patterns over the european continent that affected the balkan peninsula e g north atlantic oscillation the transition between dry and wet phases at etoliko points to longitudinal shifts of the precipitation pattern in the balkan peninsula during the little ice age

lithic enriched segregation bodies in pyroclastic flow deposits of laacher see volcano east eifel germany small volume ca 0 6 km3 pyroclastic flow deposits at laacher see contain lithic breccias and two types of ground layers that differ significantly in their structure and composition from the main body of flow units lithic breccia bodies up to 3 5 m thick containing up to 85 weight lithic blocks occur locally at various distances from the vent the deposition of these breccias was apparently governed by the strong influence of paleomorphology on the dynamics of the pyroclastic flows the breccias were deposited at three main changes in bottom gradient along the path of the pyroclastic flows the accumulation of large lithics is explained a by compression of flows on the rising bottom close to the vent b by thinning of flows accelerating over a steep incline c by deceleration of the pre concentrated lower part of flows in hydraulic jumps and d possibly by a stationary vortex at the inner bend of a valley curvature poorly sorted lithic rich ground layers laterally highly variable in internal structure and composition are restricted to marginal regions of the pyroclastic flow deposits within deep and narrow valleys they are interpreted as having formed due to the extreme roughness of the valley walls enforcing irregular turbulent flow and intense fluidization of the flow head in which density dominated segregation of lithics occurred wellsorted lapilli rich ground layers of constant lateral thickness were probably generated by a more regularly moving less intensely fluidized head of pyroclastic flows in which size dominated segregation was effective but density segregation was minor a model of the temporal and longitudinal evolution of a flow head is proposed close to the vent the head is exclusively erosive with increasing distance erosive power declines and erosion is paralleled by ground layer formation under strong fluidization further from the vent the head ceases to erode while fluidization is still sufficient for ground layer formation when fluidization declines to a level ineffective for segregation ground layers terminate while the head advances and only terminates when plug flow dominates

the 1 5 ka varved record of lake montcortes southern pyrenees ne spain abstract the karstic lake montcortes sedimentary sequence spanning the last 1548 yr constitutes the first continuous high resolution multi proxy varved record in northern spain sediments consist of biogenic varves composed of calcite organic matter and detrital laminae and turbidite layers calcite layer thickness and internal sub layering indicate changes in water temperature and seasonality whereas the frequency of detrital layers reflects rainfall variability higher temperatures occurred in lake montcortes in ad 555 738 825 875 1010 1322 and 1874 present lower temperatures and prolonged winter conditions were recorded in ad 1446 1598 1663 1711 and 1759 1819 extreme and multiple precipitation events dominated in ad 571 593 848 922 987 1086 1168 1196 1217 1249 1444 1457 1728 1741 and 1840 1875 indicating complex hydrological variability in ne spain since ad 463 the sedimentary record of lake montcortes reveals a short term relation between rainfall variability and the detrital influx pronounced during extended periods of reduced anthropogenic influences in pre industrial times during warm climate episodes population and land use increased in the area after the onset of the industrialization the relationship between climate and human activities decoupled and population dynamics and landscape modifications were therefore mostly determined by socio economic factors

changes in mid and far field human landscape use following the laacher see eruption c 13 000 bp abstract around 13 000 years ago the laacher see volcano east eifel volcanic field rhenish shield erupted cataclysmically the thick tephra blanket in the eruption s near field covered and thereby preserved a large number of archaeological sites ranging from very small to some of the largest and richest sites known from the late glacial in this proximal region there is a striking contrast in the number of sites prior to the eruption and the almost complete lack of sites dating to the period after the event i e to greenland interstadial 1a the preservative function of the tephra cover itself may explain this near field pattern but it is shown here that similar stratigraphic observations can also be made in the laacher see eruption s mid field towards the west and in particular to the north east the aim of this paper is to review the stratigraphic relations of known archaeological sites outside the near field of the laacher see event with a particular focus on the german federal state of hesse and adjacent areas of lower saxony and the thuringian basin here a number of archaeological sites are known where strata of laacher see tephra cap human occupation most often these sites are not reoccupied until much later in prehistory suggesting that the eruption may have led either to a complete or a near complete abandonment of the affected regions or at the very least to a major reorganisation of landscape use

between the north atlantic oscillation and the siberian high a 4000 year snow accumulation history inferred from varved lake sediments in finland clastic organic varved sediments from the boreal lake kalliojarvi central finland record changes in snow accumulation for more than 4000 years the varve record was reconstructed using digital image analysis from 4132 varve yr bp to present with 2 2 counting error and is supported by paleomagnetic data two laminae are identified in a typical varve structure 1 the minerogenic lamina which accumulates during spring as a result of catchment erosion triggered by spring floods and 2 the organic lamina which is composed of allochthonous and autochthonous organic matter that accumulates during summer autumn and winter the minerogenic influx is related to variations in snow accumulation and follows the different phases of the north atlantic oscillation nao decreased snow accumulation is related to a weakened nao phase thus the minerogenic influx record provides additional information about nao variation the fe mn ratio is related to changes in redox conditions at the lake floor the oxygen ava

eruption of a major holocene pyroclastic flow at citlaltepetl volcano pico de orizaba mexico 8 5 9 0 ka abstract multiple volcanic eruptions occurred between 8500 and 9000 yr b p from the central crater of citlaltepetl volcano generating a series of pyroclastic flows that formed a deposit with a total volume of about 0 26 km3 d r e the flows descended in all directions around the crater but they were mostly controlled by topography and deposited in valleys or local topographic depressions up to about 30 km from vent although the flows were apparently emplaced without much violence some features of the deposits reveal local turbulent conditions and an expanded fluidization that can be related to moderate flow velocities the deposit has two members the lower one consists of multiple flow units and the upper one includes a single flow unit and a thin basal pumice fall both members are lithologically similar and dominated by dense andesitic scoriae with minor amounts of different pumice types andesitic dacitic and banded and lithics in a silty matrix the eruption probably had a low pressure boiling over mechanism and was possibly triggered by mixing of dacitic and andesitic magmas juvenile material in the pyroclastic flow deposit is compositionally similar to that of holocene lava flows at citlaltepetl which have apparently resulted from magma homogenization of mafic and silicic end members because the system is continuously injected with new basaltic andesitic magma a recurrence of explosive activity is possible in future eruptions

a hot miocene subaqueous scoria flow deposit in the shimane peninsula sw japan abstract a subaqueous scoria flow deposit occurs in the miocene takashibiyama formation in sw japan faunal assemblages in associated sediments suggest an outer shelf to upper bathyal environment with water depth likely between 200 and 1500 m the deposit 5 7 m thick is similar to subaerial scoria flow deposits containing mainly non to moderately vesiculated hyalopilitic basaltic andesite lapilli and coarse ash the essential basaltic andesite clasts are variably vesiculated even within single clasts and are commonly cracked with curviplanar surfaces whereas the inner parts are cracked in a pattern similar to perlitic cracks the clasts are blocky with curviplanar surfaces if non to poorly vesiculated and are fibrous with irregular shapes and flattened by compaction if more vesiculated at one proximal location fines depleted rootless pipes 5 90 cm wide and 1 3 m long occur and spherical to amoebic vesicles 0 01 0 3 mm in diameter and filled with stilbite quartz or greenish brown clay are common in the fine ash matrix and in siltstone clasts contained in the deposit the vesicles represent open spaces once supported by gas and the rootless pipes are interpreted as gas escape pipes magnetization vectors of essential clasts are dispersed not at random but around a single direction suggesting that the clasts gained thermoremanent magnetism mainly during cooling in the flow or during post emplacement cooling and then rotated to some extent by differential movement of the flow or by gas escape in the deposit the vesicularity shape and texture of essential clasts suggest a phreatomagmatic eruption involving magmatic vesiculation and dynamic interaction of magma and ambient water the perlitic cracks in the inside of the essential clasts and the paleomagnetic vectors of the essential clasts indicate that the flow was initially hot and that the deposit cooled slowly internal depositional features change rapidly over only 500 m rootless pipes and vesicles in the fine ash matrix and siltstone clasts are therefore absent at distal locations indicating that an initially cohesionless debris flow quickly became sufficiently turbulent to mix with ambient seawater

a multi proxy μ xrf inferred lake sediment record of environmental change spanning the last ca 2230 years from lake kanono northland new zealand abstract reliable interpretation of annual resolution climate proxies for wind precipitation and detrital influx are required for identifying the onset and periodicities of climatic events in particular this is essential for the evaluation of inter annual decadal and centennial trends driven by shifting positions of the southern westerly winds sww and subsequent storm belts associated with the southern annular mode sam and el nino southern oscillation enso here we present a quasi annual data set of xrf time series spanning ca 2230 years from lake sediment cores from lake kanono northland new zealand the xrf time series were interpreted using a combination of principal component analysis pca and cluster analysis then verified with comparison to regionally averaged empirical rainfall and wind climate station data our results show that the wavelet patterns align with the pca results allowing the xrf time series to be classified into group i detrital and group ii biological productivity and normalized climate proxies the normalized group ii xrf time series wavelet analyses displayed periodicities in the 2 16 year frequency likely associated with enso from ca 237 bce 1330 ce the data show clear evidence of both polynesian and european settlement phases in this part of northern new zealand and that polynesian settlement impact was coeval with changes in enso intensity and a phase shift in sam ca 1350 ce the medieval climate anomaly mca and the little ice age lia appear in the xrf time series data as separate clusters this data suggests that the mca is associated with windy dry conditions with intermittent storminess during the lia the 2 16 year periodicity associated with enso decreased and centennial to multi decadal length periodicities increase which may be an indication of an underlying sam signal within the data european settlement also had a direct impact on the lake basin via increased detrital influx likely from farming activities and intensification of local forestry operations

annually resolved lake record of extreme hydro meteorological events since ad 1347 in ne iberian peninsula abstract we present an annual reconstruction of extreme rainfall events interpreted from detrital layers and turbidites interbedded within a varved sediment record since the 14 th century in montcortes lake ne spain 1027 m a s l clastic microfacies intercalated within the biochemical calcite varves were characterized and their depositional dynamics interpreted using high resolution geochemical and sedimentological analyses annual number of detrital layers was compared against instrumental records of extreme daily rainfalls providing minimum rainfall thresholds and return periods associated to the identified types of clastic microfacies non continuous detrital layers were deposited during rainfall events higher than 80 mm 2 year return period while graded detrital layers and turbidites were associated with higher magnitude rainfall events 90 mm and 4 year return period the frequency distribution of extreme hydro meteorological events is not stationary and its pattern coincides with historical floods from the nearby segre river high frequency of heavy rainfalls occurred during the periods ad 1347 1400 and ad 1844 1894 a lower frequency of heavy rainfall was found during the periods ad 1441 1508 1547 1592 1656 1712 1765 1822 and 1917 2012 the 20 th century stands out as the longest interval within the studied period of very low number of extreme rainfall events variability in extreme rainfall events prior to the 20 th century is in phase with solar activity suggesting a mechanistic link in mid latitude atmospheric circulation patterns that ceased during the 20 th century

evidence of liquid dependent ice nucleation in high latitude stratiform clouds from surface remote sensors 1 ground based lidar radar and microwave radiometer observations at eureka canada barrow alaska and over the western arctic ocean measure physical characteristics and morphology of stratiform clouds despite transition of a cold atmosphere 15 c through ice supersaturated conditions ice is not observed until soon after a liquid layer several cases illustrating this phenomenon are presented in addition to long term observations from three measurement sites characterizing cloud phase frequency this analysis demonstrates that clouds composed entirely of ice occur less frequently than liquid topped mixed phase clouds at temperatures warmer than 25 to 30 c these results indicate ice formation generally occurs in conjunction with liquid at these temperatures and suggest the importance of liquid dependent ice nucleation mechanisms

climate palaeohydrology and land use change in the central iberian range over the last 1 6 kyr the la parra lake record a multiproxy study of a 7 m long sedimentary sequence from lake la parra 39 50 948 1 52 1014 m a s l supported by 11 14c ams and 210pb 137cs dates provides a robust high resolution hydrological and environmental variability record for the last 1600 years of the las torcas sinkhole complex in the central iberian range the succession of depositional environments in lake la parra sinkhole is controlled by both changes in the regional water table and by the balance between sedimentary input through ephemeral creeks and in lake production of carbonates and organic matter although synergetic links with climate are likely phases of increased sediment delivery to the lake at c ad 500 700 c ad 1000 ad 1450 1500 ad 1550 650 and since 1700 till recent times are driven primarily by human impact in the watershed prior to c ad 300 the sinkhole was dry then became a lake at the end of the roman period ad 350 when the doline was flooded and it has not dried out during the last 1600 years moderate

seasonal effects of water temperature and dissolved oxygen on the isogdgt proxy tex86 in a mediterranean oligotrophic lake abstract to appraise the application of isoprenoid glycerol dialkyl glycerol tetraethers isogdgts as paleoclimate proxies in small lakes we investigated the effect of seasonal variability in temperature and dissolved oxygen concentration do on the gdgt contents and its proxy in the water column of an oligotrophic karst lake in the catalan pre pyrenees lake montcortes from october 2013 to november 2014 we collected suspended particulate matter spm monthly at three depths and retrieved the sediment from a trap located at 20 m below the lake surface the gdgt contents in the spm and sediment trap presented a marked seasonal variation showing the highest values in summer and autumn in addition the isogdgt proxy tex86 in spm and sediment trap showed a marked seasonal variability which matched the temperatures of the upper water column and fit the published global trend between tex86 and mean annual lake surface temperature lst however in the hypolimnion where oxygen was depleted for most of the study period we found that tex86 co varied with do this further confirms previous claims with seasonal field data that the sedimentary tex86 lst signal may be confounded by do conditions consequently the application of tex86 to estimate lst should be carefully appraised in environments with depleted do conditions

maar diatreme phreatomagmatism at hopi buttes navajo nation arizona usa remnants of an extensive maar diatreme volcanic field are magnificently exposed at various depths of erosion in the hopi buttes volcanic field of northeastern arizona field and petrographic studies of both the maar and diatreme elements of a selection of volcanoes within the field show that 1 lower sections of the maar rim sequences are typically rich in sandy mudrock derived from the pre eruptive mio pliocene bidahochi formation and the muddy bidahochi sediment was soft and wet at the time of maar eruptions 2 beds higher within the rims contain generally increased proportions of sandstone clasts from the triassic wingate formation in the diatremes late emplaced breccia has deeper seated lithics than more marginal breccia emplaced earlier and 3 many vents are topped by megacryst enriched scoria and spatter and deep seated xenoliths are known only from upper diatreme and craterfilling tephra these observations show that 1 eruptions at hopi buttes involved interaction of magma with unconsolidated mudrock at shallow levels and the phreatomagmatic processes that provided the bulk of the energy involved in the violent eruptions were driven by the interaction of magma and wet sediment 2 the locus of explosive activity migrated downward as eruptions progressed and 3 the closing stage of many eruptions was characterized by rapid magma rise and relative depletion of water

modern sedimentary analogues and integrated monitoring to understand varve formation in the mediterranean lake montcortes central pyrenees spain abstract varved sediments provide unique opportunities to carry out high resolution paleoclimatic and paleoenvironmental reconstructions with accurate time control to better interpret the sediment record it is necessary to understand the physical chemical and biological factors that influence varve formation and preservation we explored the link between the annual limnological cycle and current varve deposition in the oligotrophic hard water lake montcortes central pyrenees the varves of this lake consist of couplets of dark organic and light calcareous laminae a two year limnological monitoring 10 2013 10 2015 combined with a sediment trap study were conducted at monthly resolution limnological and sedimentological measurements were compared with meteorological data although the lake was considered meromictic in the first limnological studies we documented total mixing of the water column both winters in spite of this long periods of stratification and hypolimnetic anoxia create suitable conditions for varve formation and preservation sediment deposition followed a clear seasonal pattern related to biological processes in the euphotic zone during summer and fall calcite precipitation was favored by high calcite saturation indices and enhanced primary production that promoted relatively high ph values as a result of co2 uptaking there was considerable variability in the amount of calcite deposition between years which was linked to seasonal temperature differences in addition calcite crystal sizes and diatom fluxes showed seasonal patterns related to calcite saturation index and changes in water stratification which in turn were also related to temperature variability seasonal sedimentation patterns were strongly linked to primary producers and especially sensitive to temperature shifts it results in a clear seasonal signal and varve formation we compared our results with previous sedimentological interpretations of the varved record of this lake this study improves the interpretation of lake montcortes sediment record extending back several millennia

vertical motions in arctic mixed phase stratiform clouds abstract the characteristics of arctic mixed phase stratiform clouds and their relation to vertical air motions are examined using ground based observations during the mixed phase arctic cloud experiment mpace in barrow alaska during fall 2004 the cloud macrophysical microphysical and dynamical properties are derived from a suite of active and passive remote sensors low level single layer mixed phase stratiform clouds are typically topped by a 400 700 m deep liquid water layer from which ice crystals precipitate these clouds are strongly dominated 85 by mass by liquid water on average an in cloud updraft of 0 4 m s 1 sustains the clouds although cloud scale circulations lead to a variability of up to 2 m s 1 from the average dominant scales of variability in both vertical air motions and cloud microphysical properties retrieved by this analysis occur at 0 5 10 km wavelengths in updrafts both cloud liquid and ice mass grow although the net liquid mass growth is usually largest betwee

the eruptive center of the late quaternary laacher see tephra about 5 km3 of phonolite magma were erupted 11 000 years ago in the laacher see area in plinian and vulcanian eruptions the eruptive vents for all tephra in dispute for over 200 years must have been located entirely within the laacher see basin because 1 all deposits are thickest in the tuffring surrounding the basin with one exception pyroclastic flow deposits are thickest 2 to 6 km away from the rim of the basin having ponded in radial valleys three plinian fallout layers show minor secondary thickness maxima 12 to 16 km east of laacher see 2 axes of all depositional fans and single tephra sheets converge in the laacher see basin 3 diameters of both lithic and pumice clasts reach their maxima in outcrops close to laacher see volcano 4 directions of asymmetric ballistic impact sags indicate the laacher see basin as source area 5 the dimension of laacher see crater roughly corresponds to the erupted volume of phonolitic tephra 5 3 km3 magma dre and lithic clasts 0 7 km3 6 xenolith types are consistent with an eruptive center within the laacher see basin 7 the systematic chemical and mineralogical zonation of the tephra deposits from highly differentiated aphyric phonolite at the base to highly phyric mafic phonolite at the top strongly suggests eruption from a single compositionally zoned magma column 8 several lines of evidence indicate migration of the main eruptive focus from the south to the north during the later part of the eruption both vents however being confined within the laacher see basin

holocene and little ice age glacial activity in the marbore cirque monte perdido massif central spanish pyrenees the marbore cirque which is located in the southern central pyrenees on the north face of the monte perdido peak 42 40 0 n 0 5 0 w 3355 m contains a wide variety of holocene glacial and perig

human climate interactions in the central mediterranean region during the last millennia the laminated record of lake butrint albania lake butrint 39 47 n 20 1 e is a ca 21 m deep coastal lagoon located in sw albania where finely laminated sediments have been continuously deposited during the last millennia the multi proxy analysis sedimentology high resolution elemental geochemistry and pollen of a 12 m long sediment core supported by seven ams radiocarbon dates and 137cs dating enable a precise reconstruction of the environmental change that occurred in the central mediterranean region during the last 4 5 cal kyrs bp sediments consist of triplets of authigenic carbonates organic matter and clayey laminae fluctuations in the thickness and or presence of these different types of seasonal laminae indicate variations in water salinity organic productivity and runoff in the lake s catchment as a result of the complex interplay of tectonics anthropogenic forcing and climate variability the progradation of the pavllo river delta favoured by variable human activity from the nearby ancient city of butrint led to the progressive isolation of this hydrological system from the ionian sea the system evolved from an open bay to a restricted lagoon which is consistent with archaeological data an abrupt increase in mass wasting activity between 1515 and 1450 bc likely caused by nearby seismic activity led to the accumulation of 24 homogenites up to 17 cm thick they have been deposited during the onset of finely laminated sedimentation which indicates restricted anoxic bottom water conditions and higher salinity periods of maximum water salinity biological productivity and carbonate precipitation coincide with warmer intervals such as the early roman warm period rwp 500 bc 0 ad the medieval climate anomaly mca 800 1400 ad and recent times after 1800 ad conversely lower salinity and more oxic conditions with higher clastic input were recorded during 1400 500 bc the late roman and the early medieval periods 0 800 ad and during the little ice age 1400 1800 ad hydrological fluctuations recorded in butrint are in phase with most central and western mediterranean records and correlate with nao variability in contrast opposite hydrological patterns have been recorded in the eastern balkans and the levant during the last millennium emphasizing a complex spatial variability in the region phases of maximum settlement intensity in butrint roman late antique coincide with warmer and or stable climate periods 0 800 ad and mca respectively indicating a long term influence of climatic conditions on human activities the late holocene sedimentary record of lake butrint demonstrates the complex interplay of climate variability tectonics and human impact in the recent evolution of coastal mediterranean regions

pyroclastic flow deposits from a kimberlite eruption the orapa south crater botswana abstract the orapa diamond mine republic of botswana exposes a bi lobate kimberlite pipe that erupted during the late cretaceous epoch 93 ma through archaean basement and volcano sedimentary rocks of the karoo supergroup geological mapping of the crater zone of the south pipe has revealed a 15 25 m thick in situ kimberlite pyroclastic flow deposit the pyroclastic deposit fills in the crater and completely drapes lower units indicating that the parent flow originated from an adjacent kimberlite pipe the unit comprises a basal coarse lithic concentration layer exhibiting imbricated clasts which grades upwards into massive poorly sorted lapilli tuff the tuff contains abundant sub vertical degassing structures defined by lithic enrichment and depletion in fine grained material degassing structures commonly emanate from blocks in the basal layer the presence of degassing structures and a coarse basal layer distinguishes this deposit from pipe filling massive volcaniclastic kimberlite which is typically homogeneous in terms of texture and clast size over distances on the order of 100s of metres studies of the thermal remanent magnetism in basalt clasts from the deposit together with serpentine diopside assemblages indicate that it was emplaced at elevated temperatures on the order of 200 440 c consistent with deposition from a pyroclastic flow the lithofacies characteristics can be explained by the interaction of the pyroclastic flow with the complex topography of a pre existing crater

quantifying human induced eutrophication in swiss mountain lakes since ad 1800 using diatoms sedimentary diatom assemblages from three lakes in the southeastern swiss alps were analysed at high temporal resolution since ad 1800 altered land use patterns increasing population and exploitation through tourism are clearly reflected in annually laminated sediments of lej da san murezzan lake st moritz and lej da silvaplauna lake silvaplana diatom assemblages originally dominated by cyclotella taxa are replaced by taxa indicating higher total phosphorus tp concentrations such as asterionella formosa fragilaria crotonensis and stephanodiscus parvus in lej da la tscheppa located well above the treeline in a catchment that was hardly exposed to human impact cyclotella comensis prevails throughout the entire sediment sequence quantitative estimates of past tp concentrations were inferred using a newly developed regional diatom tp inference model based on 119 modern samples in lej da la tscheppa diatoms imply stable low tp concentrations 10 g l which can be considered as natural background concentration elevated tp levels are inferred for lej da san murezzan max 60 g l since ad 1910 and for lej da silvaplauna max 40 g l since ad 1950 corroborated by changes in sedimentary biogenic silica concentration and organic carbon content since ad 1970 improved waste water management led to a considerable reduction in tp loading in lej da silvaplauna and lej da san murezzan

lacustrine carbonates of iberian karst lakes sources processes and depositional environments abstract carbonates are the main components of iberian quaternary lake sediments in this review we summarize the main processes controlling carbonate deposition in extant iberian lakes located in mesozoic and tertiary carbonate dominated regions and formed through karstic activity during the late quaternary the lakes relatively small 1 ha to 118 ha and relatively shallow zmax 11 to 40 m provide examples of the large variability of sedimentary facies depositional environments and carbonate sources hydrology is dominated by groundwater inflow except those directly connected to the fluvial drainage nine lakes have been selected for this review and the main facies in palustrine littoral and profundal environments described and interpreted clastic carbonates occur in all iberian lakes due to the carbonate composition of the bedrocks surface formations and soils of the watersheds low temperatures and dilute meteoric waters seem responsible for the low carbonate content of sediments in high elevation lakes in the glaciated terrains in the pyrenees and the cantabrian mountains clastic carbonates are dominant in small karst lakes with functional inlets where sediment infill is dominated by fining upward sequences deposited during flood events re working of littoral carbonates is common in shallow environments and during low lake level stages in most lakes endogenic carbonate production occurs in two settings i littoral platforms dominated by chara and charophyte meadows and ii epilimnetic zone as biologically mediated calcite precipitates continuous preservation of varves since the mid holocene only occurs in one of the deeper lakes montcortes lake up to 30 m where calcite laminae textures massive fining upward and coarsening upward reflect seasonal changes in limnological conditions however varves have been formed and preserved in most of the lakes during short periods associated with increased water depth and more frequent meromictic conditions most iberian lakes are in a mature stage and karstic processes are not very active an outstanding example of a lake with intense karstic activity is banyoles lake where increased spring discharge after long rainy periods causes large remobilization and re suspension of the sediments accumulated in the deepest areas leading to the deposition of thick homogeneous layers homogeinites the iberian karst lake sequences underline the large variability of facies carbonate sources and depositional environments in small lake systems they illustrate how lake types evolve through the existence of a lake basin at centennial or even smaller time scales hydrology is the paramount control on facies and depositional environment patterns distribution and lake evolution and consequently a lake classification is proposed based on hydrology and sediment input a correct interpretation of carbonate sources and depositional history is a key for using lake sequences as archives of past global changes

a 2500 year multi proxy reconstruction of climate change and human activities in northern spain the lake arreo record abstract lake arreo sequence western ebro basin spain illustrates the century scale climatic variability and human interactions in the landscape during the last 2 5 kyr in the low lands of northern spain two sediment cores from shallow water and deep water environments were analyzed using sedimentological geochemical mineralogical biological diatoms pollen and charcoal content and radiometric techniques for absolute dating the shallow water sequence indicates a rapid evolution from an alluvial influenced wetland prior to 7th century bc to a wetland during the ibero roman humid period bc 630 ad 465 and a deeper carbonate producing lake during the dark ages cold period ad 465 890 the deep water core shows the transition from a more saline lake during the arid medieval climate anomaly mca ad 890 1300 to less saline meromictic conditions particularly since the onset of the little ice age lia ad 1300 1870 during the last 2 5 kyr arid conditions occurred prior to 1st century ad during the mca and late 19th mid 20th century while colder temperatures and relatively more humid conditions were more frequent during the dark ages particularly the 7th century ad and the lia the evolution of the lake also reflects changes in grazing and agricultural practices since the roman period associated to the exploitation of nearby salt mining periods of intense human pressure on the lake watershed occurred during the high middle ages ad 890 1180 and the modern period ad 1600 1830

patterns of human occupation during the early holocene in the central ebro basin ne spain in response to the 8 2 ka climatic event abstract the central ebro river basin ne spain is the most northern area of truly semi arid mediterranean climate in europe and prehistoric human occupation there has been strongly influenced by this extreme environmental condition modern climate conditions single out this region due to the harsh environment characterised by the highest absolute summer temperatures of the ebro river basin the bajo aragon region se ebro river basin was intensively populated during the early holocene 9400 8200 cal yr bp but the settlements were abandoned abruptly at around 8200 cal yr bp we propose that this archaeological silence was caused by the regional impact of the global abrupt 8 2 ka cold event available regional paleoclimate archives demonstrate the existence of an aridity crisis then that interrupted the humid early holocene that environmental crisis would have forced hunter gatherer groups from the bajo aragon to migrate to regions with more favourable conditions i e more humid mountainous areas and only return in the neolithic coherently archaeological sites persist during this crisis in the nearby iberian range maestrazgo and the north ebro river area pre pyrenean mountains and along the northwestern ebro basin

revealing climatic variability of the last three millennia in northwestern iberia using pollen influx data climatic variability of the last 3 millennia in nw iberia has been documented using high resolution pollen analysis of vir 18 core retrieved from the ria de vigo 42degrees14 07 n 8degrees47 37 w the depth age model is based on two accelerator mass spectrometry c 14 dates and three historically dated botanical events in galicia the expansion of juglans and pinus as well as the introduction of eucalyptus during the last 3000 years the relative pollen record demonstrates the occurrence of an open deciduous oak forest indicating a humid and temperate climate in northwestern iberia two step forest reduction since 975 cal bc suggests climate as the main cause rather than major socio economic changes documented in historical archives absolute pollen influx has been compared with instrumental summer and winter temperatures and tentatively used as a proxy of short decadal scale and low amplitude similar to 1degreesc temperature variations this new approach allows us to detect for the first time in nw iberia the millennial scale climatic cyclicity suggested by north atlantic records challenging the apparent climatic stability reflected by the relative pollen record the little ice age is recorded as low pollen influx values between 1400 and 1860 cal ad with a cold maximum at 1700 cal ad maunder minimum the roman and medieval warm periods are detected through high pollen influx values at 250 cal bc 450 cal ad and 950 1400 cal ad respectively c 2003 elsevier science b v all rights reserved

laacher see tephra a widespread isochronous late quaternary tephra layer in central and northern europe a late quaternary tephra layer widespread in central and northern europe resulted from explosive plinian and phreatomagmatic eruptions of the laacher see volcano 11 000 yr b p the tephra is distinguished from other late quaternary andesitic rhyolitic airfall tuff layers in northern europe and from basaltic or trachytic tuff deposits in southern europe by its phonolitic composition and abundance of sanidine plagioclase clinopyroxene amphibole and sphene the proximal tephia sequence at laacher see is divided into three main deposits the predominantly plinian deposits of lower and middle laacher see tephra llst and mlst and phreatomagmatic deposits of the upper laacher see tephra ulst the mlst member is further subdivided into beds a b and c1 c2 and c3 the chemical composition of the magma is highly differentiated phonolite in the llst to mlst b sections but mafic phonolite in the mlst c1 to ulst sections all deposits are considered to be isochronous the frequency maximum of 16 radiocarbon datings indicating an eruption about 11 000 50 yr b p distal ash was deposited in three main fans directed to the northeast lst traced up to 1 100 km distance south lst traced up to 600 km and southwest lst traced up to 100 km tephrostratigraphic correlation of the distal ash deposits is based on a the major element composition of glass shards b lithology and c heavy mineral analyses the northeastern fan consists of deposits from llst mlst b and mlst c1 eruptive phases the southern fan comprises mlst a mlst c2 and ulst deposits and the southwestern fan consists exclusively of ash from the ulst eruptive phase northeastern transport of ash during eruptive phases with high plinian eruption columns but southern and southwestern transport of ash along phases of relatively low eruption columns are interpreted in terms of prevailing southwesterly paleowinds at high altitudes tropopause level but northerly winds dominating in the lower atmosphere the laacher see eruption columns were emplaced into an atmosphere vertically zoned with respect to paleowind directions which also explains the near vent shifting of llst mlst b and mlst c1 iso pach axes from east southeast to northeast within the first 20 km of transport

palaeoclimatic implications from micro facies data of a 5900 varve time series from the pianico interglacial sediment record southern alps abstract varve micro facies analyses have been carried out on a 405 cm thick annually laminated sediment sequence from the pianico palaeolake in the southern alps considered to correlate with the mis 11 interglacial this varve counted interval represents the uppermost 5900 yr of a ca 400 kyr old interglacial lacustrine deposit with a minimum length of 16 000 varve years intercalated in the varve succession are i detrital layers ii debris flows slump deposits and iii micritic calcite layers the annual couplets are composed of a dominant light summer layer of biochemically precipitated calcite and a thin dark winter layer consisting of organic and minerogenic detritus microscopic correlation of individual couplets in two outcrops 130 m apart demonstrated basin wide continuity of varve deposition summer layers have been found to be composed of up to four sub layers differing in grain size most likely reflecting discrete pulses of calcite precipitation two long periods of pronounced decreases in varve thickness occur within the interglacial 1100 varve years and during the decline of full interglacial conditions 480 varve years suggesting colder climatic conditions the decreases in varve thickness are further accompanied by changes in the pattern of summer sub layering the first cold interval reflects an exceptionally long intra interglacial climatic fluctuation indicating a mode of climatic variability different from the present interglacial wavelet analyses of seasonal layer thickness data revealed that periodic variations of solar activity 88 yr and 208 yr cycles and probably of thermohaline circulation 512 yr cycle impact on varve formation at certain intervals of the studied time window

fragility of western mediterranean landscapes during holocene rapid climate changes abstract in this paper we explore the evidence for holocene rapid climate changes rccs in western mediterranean records examining similarities and differences in the timing and nature of impacts on different components of the natural environment vegetation fluvial and coastal sedimentation fire activity soil formation marine lacustrine and fluvial archives of the western mediterranean iberian peninsula and northwest africa provide evidence for both pervasive millennial scale climatic variability and abrupt decadal to centennial scale transitions we focus in particular on three rccs characterised by high latitude cooling glacier advances and north atlantic ice rafting events the mid holocene rcc interval 6 5 cal ka bp the late holocene rcc interval 3 5 2 5 cal ka bp and the historical rcc interval known as the little ice age lia 1300 1950 ad evidence from multiple records indicates wide ranging impacts of rccs in the western mediterranean region the three rcc intervals were characterised however by contrasting hydrological situations in the western mediterranean with prevailing dry conditions including marked aridification events during the rcc intervals 6 5 and 3 5 2 5 cal ka bp and prevailing or recurrent wet conditions during the lia we examine issues of proxy sensitivity in palaeoecological and geomorphological records and evaluate examples of contrasting geomorphological responses to regional climatic triggers between humid and semi arid sectors of the western mediterranean finally we consider the long term sensitivity of the region to rapid climate change the role of threshold changes and the extent to which this region represents a fragile landscape

modeling immersion freezing with aerosol dependent prognostic ice nuclei in arctic mixed phase clouds while recent laboratory experiments have thoroughly quantified the ice nucleation efficiency of different aerosol species the resulting ice nucleation parameterizations have not yet been extensively evaluated in models on different scales here the implementation of an immersion freezing parameterization based on laboratory measurements of the ice nucleation active surface site density of mineral dust and ice nucleation active bacteria accounting for nucleation scavenging of ice nuclei into a cloud resolving model with two moment cloud microphysics is presented we simulated an arctic mixed phase stratocumulus cloud observed during flight 31 of the indirect and semi direct aerosol campaign near barrow alaska through different feedback cycles the persistence of the cloud strongly depends on the ice number concentration it is attempted to bring the observed cloud properties assumptions on aerosol concentration and composition and ice formation parameterized as a function of these aerosol properties into agreement depending on the aerosol concentration and on the ice crystal properties the simulated clouds are classified as growing dissipating and quasi stable in comparison to the default ice nucleation scheme the new scheme requires higher aerosol concentrations to maintain a quasi stable cloud the simulations suggest that in the temperature range of this specific case mineral dust can only contribute to a minor part of the ice formation the importance of ice nucleation active bacteria and possibly other ice formation modes than immersion freezing remains poorly constrained in the considered case since knowledge on local variations in the emissions of ice nucleation active organic aerosols in the arctic is scarce

environmental change and archaeology lake evolution and human occupation in the eastern sahara during the holocene abstract the west nubian palaeolake is the most large scale hydrographic evidence in the eastern sahara of the early to mid holocene wet phase that affected northern africa it is the result of a significant increase in local rainfall due to the northward shift of the tropical rainfall belt a series of fieldwork based differential gps dgps measurements along several profiles across the west nubian palaeolake basin provides the first precise topographic data from this up to a 5330 km2 large palaeolake feature in combination with sedimentological geochemical and archaeological results an almost complete picture of significant palaeoclimatic changes and human occupation during the early to mid holocene for this region is presented different stages of palaeolake evolution ranging from non existence of the lake through stable freshwater conditions to its extinction were identified in the period from 9400 to 3800 14c yr bp these lake stages coincide with phases of intensive human inhabitation between ca 6300 and 3500 14c yr bp and include at least four settlement phases distinguishable by style of pottery these are known from adjacent areas of the palaeolake region emphasizing strong prehistoric cultural connections in the eastern sahara during the highstands of the palaeolake in the early to mid holocene the dotted wavy line pottery relates to the early khartoum type culture with its supra regional distribution from the nile valley to the chad and possibly with slightly different forms even to the atlantic coast later in the holocene western nubia with its large palaeolakes and migration paths along palaeowadis such as wadi howar acted as an important natural and cultural link between the nile valley and the chad basin until the region was deserted during the fourth millennium bp

geochemical investigation of the south wellesley island wetlands insight into wetland development during the holocene in tropical northern australia the south wellesley islands in the gulf of carpentaria northern australia were the recent focus of a palynological investigation which found vegetation change during the holocene was driven by coastal progradation and regional climate here we present new elemental data from x ray fluorescence core scanning which provides non destructive continuous and high resolution analysis from three wetlands across bentinck island the largest of the south wellesley islands elemental data and grain size analyses are combined with lead 210 210pb and accelerator mass spectrometry ams carbon 14 14c dates an open coastal environment was present 1250 cal a bp on the south east coast of bentinck island with sediment supply incorporating fluvial deposition and detrital input of titanium and iron from eroding lateritic bedrock prograding shorelines dune development and river diversion formed a series of swales parallel to the coast by 800 cal a bp forming the marralda wetlands wetlands developed at sites

effects of ice number concentration on dynamics of a shallow mixed phase stratiform cloud 1 previous modeling studies have shown high sensitivity of mixed phase clouds to ice number concentration ni with simulated clouds often transitioning from mixed phase to ice only regime within a narrow range of ni to better understand the mechanisms behind this transition we analyze several simulations of a mixed phase stratiform arctic cloud observed on 26 april 2008 during the indirect and semi direct aerosol campaign isdac in the base run ni is constrained to match the measured value and a persistent mixed phase cloud is formed with properties similar to those observed when ni is quadrupled hi ice the liquid water path is reduced by half within two hours the changes in liquid water are accompanied by diminishing radiative cooling and slowing vertical mixing exposing complex interactions among microphysics radiation and dynamics deviations of base and hi ice from a simulation without ice are used to explore the linearity of the model response to variation in ni it is shown that early changes in cloud condensate amount and radiative cooling rate are proportional to ni while changes in the vertical buoyancy flux and dynamics are qualitatively different in hi ice compared to base the nonlinear with respect to ni reduction in buoyancy flux drives the initial response of the mixed layer dynamics to the appearance of ice and subsequently determines the sustainability of liquid water in the cloud in this case two additional sensitivity experiments link the decreased buoyancy production to the latent heat release from the depositional ice growth while confirming the importance of the cloud radiation feedback

physical processes in volcanic eruptions mechanisms are modeled in terms of dynamic physico chemical processes in this respect volcanology shares with much of earth science in general the benefits that accrue from the application of the methods and concepts of other disciplines to its problems basic concepts from the fields of thermo dynamics fluid mechanics and rheology have been particularly impor tant in fostering new insights recent developments have been so numerous as to make it necessary to limit the scope of this review and thus we concentrate here on the basic physical processes involved in the rise of magma to the surface and the distribution of cruption products on thc ground or in the atmosphere the perspective of planetary volcanism wilson hcad 1983 underlines the fact that volcanoes can be regarded as probes of the composition and structure of a planetary interior as a function of position depth and time

a new late quaternary palaeohydrological record from the humid tropics of northeastern australia abstract high resolution x ray fluorescence xrf is presented as a robust palaeoclimatic proxy suitable for use on late pleistocene to holocene sediments located in a volcanic crater on the atherton tableland in northeastern queensland australia the proxy allows identification of wet and dry shifts in a complex sedimentary sequence comprised of peat gyttja laminated organic rich muds and fine clastic silt rich sediments significant correlation is found between the xrf record and other proxies including magnetic susceptibility humification grain size macrocharcoal 13c and c n and pollen sixteen wetter periods are identified in the 37 ka sedimentary record for bromfield swamp three wetter periods commence in late marine isotope stage 3 nine in the early glacial one in the late de glacial and four in holocene nineteen drier periods are identified four in late mis 3 seven in the early glacial one during the lgm one in the late de glacial period and six in the holocene the xrf record for bromfield swamp is specifically used to identify periods of abrupt climate change marked changes in effective precipitation are detected at 32 690 30 080 24 660 21 870 11 880 10 020 9170 and 5120 cal yr bp the detection of these abrupt climate events may allow correlation with records from terrestrial sites across the southern hemisphere and potentially the northern hemisphere

long lifetime ice particles in mixed phase stratiform clouds quasi steady and recycled growth ice particles play an important role in precipitation and radiation transfer in stratiform mixed phase clouds lagrangian ice particle tracking in mixed phase clouds is applied in both a 3 d time dependent velocity field produced by a large eddy simulation cloud model and a 2 d idealized field it is found that more than 10 of ice particles have lifetimes longer than 1 5 h much longer than the large eddy turnover time or the time for a crystal to fall through the depth of a nonturbulent cloud an analysis of trajectories in a 2 d idealized field shows that there are two types of long lifetime ice particles quasi steady and recycled growth for quasi steady growth ice particles are suspended in the updraft velocity region for a long time for recycled growth ice particles are trapped in the large eddy structures and whether ice particles grow or sublimate depends on the ice relative humidity profile within the boundary layer some ice particles can grow after each cycle in the trapping region until they are too large to be trapped and thus have long lifetimes the relative contribution of the recycled ice particles to the cloud mean ice water content depends on both the dynamic and thermodynamic properties of the mixing layer in particular the total ice water content of a mixed phase cloud in a decoupled boundary layer can be much larger than that in a fully coupled boundary layer