the medieval warm period the little ice age and simulated climatic variability the csiro mark 2 coupled global climatic model has been used to generate a 10 000 year simulation for present climatic conditions the model output has been analysed to identify sustained climatic fluctuations such as those attributed to the medieval warm period mwp and the little ice age lia since no external forcing was permitted during the model run all such fluctuations are attributed to naturally occurring climatic variability associated with the nonlinear processes inherent in the climatic system comparison of simulated climatic time series for different geographical locations highlighted the lack of synchronicity between these series the model was found to be able to simulate climatic extremes for selected observations for century timescales as well as identifying the associated spatial characteristics other examples of time series simulated by the model for the usa and eastern russia had similar characteristics to those attributed to the mwp and the lia but smaller amplitudes and clearly defined spatial patterns a search for the frequency of occurrence of specified surface temperature anomalies defined via duration and mean value revealed that these were primarily confined to polar regions and northern latitudes of europe asia and north america over the majority of the oceans and southern hemisphere such climatic fluctuations could not be sustained for reasons explained in the paper similarly sustained sea ice anomalies were mainly confined to the northern hemisphere an examination of mechanisms associated with the sustained climatic fluctuations failed to identify a role for the north atlantic oscillation the el nino southern oscillation or the pacific decadal oscillation it was therefore concluded that these fluctuations were generated by stochastic processes intrinsic to the nonlinear climatic system while a number of characteristics of the mwp and the lia could have been partially caused by natural processes within the climatic system the inability of the model to reproduce the observed hemispheric mean temperature anomalies associated with these events indicates that external forcing must have been involved essentially the unforced climatic system is unable to sustain the generation of long term climatic anomalies

an expanded calibration model for inferring lakewater and air temperatures from fossil chironomid assemblages in northern fennoscandia chironomid temperature inference models based on an expanded data set of surface sediment and limnological data from 53 subarctic lakes in northern fennoscandia have been developed using eight different numerical techniques each based on slightly different underlying statistical models or ecological assumptions the study sites are mostly small shallow bathymetrically simple oligotrophic lakes with a ph range from 5 0 to 7 8 a total organic carbon range from 2 5 to 12 6 mg l 1 a mean july lakewater temperature ranging from 6 1 to 15 4 c and a mean july air temperature ranging from 8 5 to 14 9 c a series of redundancy analyses rda identified sediment organic content maximum lake depth and lakewater temperature as being the most important explanatory variables variance partitioning by partial rdas further suggested that each of these variables accounted for a significant fraction of variance independent from each other different cali bration models were assessed on the basis of their statisti

northern europe climate variations during late holocene evidence from marine skagerrak abstract granulometric and stable oxygen isotope analyses of four sediment cores from two high accumulation areas in the skagerrak ne north sea were carried out in order to reconstruct climate fluctuations and to evaluate climate impact during the upper holocene extremely high sedimentation rates especially in the eastern skagerrak are explained by increased current activity which is responsible for the transport and deposition of high quantities of suspension load during periods of stormy zonal atmospheric circulation patterns these were most frequent during colder periods while warmer phases are characterized by calmer meridional to zonal atmospheric circulation patterns while the subatlantic climate deterioration and the subboreal climate optimum left only indistinct traces in the sediments the roman climate optimum and a colder period between ca 400 and 700 ad are well documented the following medieval warm period is characterized by a clear temperature increase of the waterbody in connection with less frequent advances of atlantic water masses into the skagerak deep and a decrease in bottom current strength a mode of sedimentation prevails similar to that of recent summer conditions suggesting short and mild winters during that period the onset of the little ice age around 1350 ad however shows an intensified bottom current circulation most probably due to amplifying westerly winds and a decrease in water temperatures in connection with more frequent advances of higher saline atlantic waters the little ice age can be divided into 3 phases a stormy zonal onset a calm meridional maximum and a stormy zonal end the stormy phases are characterized by a sedimentation mode similar to that of recent winter conditions while the little ice age maximum shows conditions comparable to exceptional cold modern winters from 1900 ad at the onset of the modern climate optimum the winter type sedimentation decreases and conditions change again to a level comparable to the medieval warm period

reconstruction of late glacial summer temperatures from chironomid assemblages in lac lautrey jura france a chironomid july air temperature inference model based on chironomid assemblages in the surface sediments of 81 swiss lakes was used to reconstruct late glacial july air temperatures at lac lautrey jura eastern france the transfer function was based on weighted averaging partial least squares wa pls regression and featured a leave one out cross validated coefficient of determination r2 of 0 80 a root mean square error of prediction rmsep of 1 53 c and was applied to a chironomid record consisting of 154 samples covering the late glacial period back to the oldest dryas the model reconstructed july air temperatures of 11 12 c during the oldest dryas increasing temperatures between 14 and 16 5 c during the bolling temperatures around 16 5 17 0 c for most of the allerod temperatures of 14 15 c during the younger dryas and temperatures of ca 16 5 c during the preboreal the lac lautrey record features a two step july air temperature increase after the oldest dryas with an abrupt temperature increase of ca 3 3 5 c at the oldest dryas bolling transition followed by a more gradual warming between ca 14 200 and 13 700 bp the transfer function reconstructs a less rapid cooling at the allerod younger dryas transition than other published records possibly an artefact caused by the poor analogue situation during the earliest younger dryas and an abrupt warming at the younger dryas holocene transition during the allerod two centennial scale 1 5 2 0 c coolings are apparent in the record although chronologically not well constrained the first of these cold events may be synchronous with the beginning of the gerzensee oscillation the second is inferred just before deposition of the laachersee tephra at lac lautrey and is therefore coeval with the end of the gerzensee oscillation in contrast to the greenland oxygen isotope records the lac lautrey palaeotemperature reconstruction lacks a clearly defined greenland interstadial gi event 1d and the decreasing temperature trend during the bolling allerod interstadial copyright 2005 john wiley sons ltd

palaeolimnological approaches to climate change with special regard to the biological record abstract lakes systems respond physically chemically and biologically to changes in climate and these responses are registered in many various ways in lake sediment records this paper focuses principally on the biological record and describes recent research that aims to reconstruct i past variability in effective moisture and ii past variability in temperature changes in effective moisture are manifested especially by changes in lake water level in closed lake basins water level change can cause significant changes in water salinity that is registered in sediments by changes in the composition of fossil assemblages especially diatoms in open freshwater lake basins changes in water level are best reconstructed from the aquatic macrofossil record and potentially from the ratio of open water to littoral species of cladocera ostracods and diatoms the most promising biological method for reconstructing past temperature is chironomid analysis and a range of new chironomid temperature transfer functions are being developed however biological responses to changing temperature are usually indirect as a result of temperature effects on water column stratification nutrient cycling and alkalinity generation and in most cases a correct interpretation of the climatic significance of changes in the fossil record requires an understanding of the processes that are operating in the water column a multi proxy whole lake approach is advocated as the best way forward not only as a means of reconstructing past climate but also as a means of assessing the impact of climate change on lake systems

solar and proxy sensitivity imprints on paleohydrological records for the last millennium in west central europe this paper presents a lake level record established for the last millennium at lake saint point in the french jura mountains a comparison of this lake level record with a solar irradiance record supports the hypothesis of a solar forcing of variations in the hydrological cycle linked to climatic oscillations over the last millennium in west central europe with higher lake levels during the solar minimums of oort around ad 1060 wolf around ad 1320 sporer around ad 1450 maunder around ad 1690 and dalton around ad 1820 further comparisons of the saint point record with the fluctuations of the great aletsch glacier swiss alps and a record of rhone river floods from lake bourget french alps give evidence of possible imprints of proxy sensitivity on reconstructed paleohydrological records in particular the great aletsch record shows an increasing glacier mass from ad 1350 to 1850 suggesting a cumulative effect of the little ice age cooling and or a possible reflection of a millennial scale general cooling until the mid 19th century in the northern hemisphere in contrast the saint point and bourget records show a general trend toward a decrease in lake levels and in flood magnitude anti correlated with generally increasing solar irradiance

a two millennium dinoflagellate cyst record from gullmar fjord a swedish skagerrak sill fjord abstract gullmar fjord a sill fjord on the skagerrak coast of western sweden contains a valuable sedimentary archive for the last 2500 years this archive encompasses a temporal record from the roman warm period the dark ages the medieval warm period the little ice age and into the modern warm period a high resolution dinoflagellate cyst analysis has been completed on this archive using material from two cores taken from the deepest part of the fjord alsback deep the recovered dinoflagellate cysts have provided a quantitative temporal record that has been used to construct a dinoflagellate cyst spectrum and has been subjected to both q mode cluster analysis and cabfac factor analysis with varimax rotation in addition the heterotrophic ratio and both the thermophilic and cryophilic ratios have been calculated to assist with the interpretation of the results well preserved and diverse dinoflagellate cyst assemblages have been recovered throughout the sedimentary sequence and have been used to explore surface water conditions within the fjord over this time interval although a clear link is observed between the cyst assemblages and the climate phases of the subatlantic established from previous stable isotope work there was little change in the cyst populations and indeed they reflect the known modern cyst floras however a major change was seen in the incoming of gymnodinium nolleri during the dark age and its reduction to a relict species towards the end of the little ice age comparisons to other published work confirm the regional nature of this dinoflagellate cyst event but its ecological preferences remain enigmatic a second major change was also recognised around the late 1960s early 1970s and was associated with differences in nutrient availability from either a diminution in upwelling as the nao changed from a negative phase to a positive or from marine pollution or a combination of both otherwise the dinoflagellate cyst assemblages can be grouped using the factor analysis into f1 protoperidinium spp indet round brown cysts f2 g nolleri and f3 lingulodinium polyedrum and protoceratium reticulatum the cluster analysis shows a similar subdivision into units closely associated with the recognised climate phases of the subatlantic possible climate environments have been explored but because of the relatively minor variations in the assemblages and the lack of autecological information only relatively small scale changes were recognised except for the clear but complex nature of the recent warm period

holocene fire regime changes from multiple site sedimentary charcoal analyses in the lourdes basin pyrenees france one lake and three peat bogs from the lourdes glacial basin france were used for macrocharcoal analyses and fire frequency reconstruction over the entire holocene 11700 years the chronology was based upon thirty three 14c ams dates comparison of the distribution of both charcoal accumulation rate char and fire return intervals showed that charcoal accumulation significantly differs between the lake and the peat bogs but that frequency calculation overcomes the disparity between these site types a composite frequency was built from the four individual records to assess regional versus local variability and fire regime controls by comparisons with regional fire activity holocene climatic oscillations and vegetation history the millennial variability can be depicted as follows relatively high frequency between 8000 and 5000 cal a bp up to 5 fires 500 yrs relatively low frequency between 5000 and 3000 cal a bp down to 0 fires 500 yrs and an increase between 3000 and 500 cal a bp up to 4 fires 500 yrs from 8000 to 5000 cal a bp fire frequency displays strong synchrony between sites and appears to be mostly driven by increased summer temperature characterizing the holocene thermal maximum htm on the contrary during the last 3000 years fire frequency was heterogeneous between sites and most probably human driven however higher frequency at the millennial scale during the mid holocene strongly suggests that the perception of human driven fire regime depends on the strength of natural controls

compression directions north of the san fernando valley determined from borehole breakouts borehole breakouts in 4 nearly vertical oil wells and several other deviated holes in the san fernando valley and santa susana mountains suggest a maximum horizontal compressive stress direction s h of n49 w these wells provide information about the stress field from 1974 to 1983 in the uppermost crust 3 km depth near the aftershock zones of the january 1994 northridge earthquake and the february 1971 sylmar earthquake this direction of s h is anomalous with respect to the n to nne directions of s h seen in other regional data but is consistent with the structural complexity of this zone including local changes in strike of major thrust fault zones and the presence of lateral ramps in both the santa susana and san fernando faults

large scale convection patterns observed by dmsp the authors present a comprehensive compilation of the average distribution of the electrostatic potential across the high latitude ionosphere the averages are compiled from potentials along the satellite path calculated from thermal ion drift data from instrumentation on the defense meterological satellite program dmsp flights 8 and 9 satellites data were collected from the dmsp f8 satellite during the period september 1987 to december 1990 and from the dmsp f9 satellite during the period march 1988 to december 1990 the potential distributions are separated by geomagnetic position season and orientation of the interplanetary magnetic field imf and then averages of the distributions are calculated the average potential distributions clearly show the displacement of polar cap convection contours to the dusk or dawk flanks under the influence of the imf b sub y component the cross cap potential decreases as imf b sub z changes from southward to northward the average distributions indicate that the development of more than two convection cells for northward imf is either uncommon or nonexistent for imf b sub z 0 and b sub z vert bar b sub y vert bar a distorted pattern is observed in the average potential distribution not a four cell pattern as some previous studies suggest it should be for allmore orientations of the imf the convection reversal boundary at the poleward edge of the auroral zone is observed in the average distributions to be a rotational boundary it is not a shear boundary as suggested by some previous investigations on average the harang discontinuity convection reversal in the auroral zone near midnight is observed to exist weakly or not at all when examining individual passes a strong eastward flow is present sometimes in the region of the harang discontinuity especially on the poleward boundary but not at all times as implied by the heppner maynard model 39 refs 9 figs 2 tabs less

chironomid inferred air temperatures from lateglacial and holocene sites in north west europe progress and problems abstract non biting midges insecta diptera chironomidae are now widely recognised as powerful biological proxies for inferring past climatic change in this paper the response of chironomid assemblages to lateglacial and holocene climatic change from sites in scotland and norway is discussed analyses have shown that midge assemblages have responded to major and minor climatic fluctuations during the last 15 000 yr such as the aegelsee oscillation gerzensee oscillation and younger dryas in the lateglacial and the thermal optimum little ice age and cooling events at 8 2 and 2 0 cal ka bp in the holocene in an attempt to quantify these and other climatic fluctuations a chironomid mean july air temperature inference model based on a modern calibration set of 109 lakes in norway and svalbard has been developed the 3 component weighted averaging partial least squares inference model performs well with a root mean squared error of prediction of 0 90 c and a maximum bias of 0 59 c both based on leave one out cross validation which is lower than chironomid temperature inference models developed in canada switzerland and finland however while temperature inference models perform well in the lateglacial the more subtle climatic changes of the holocene are more difficult to reconstruct because the likely temperature changes are close to the limits of the prediction errors of the existing models to address this problem future work is required to refine and develop the calibration set by further improving taxonomic resolution by adding more lakes to the calibration set and by investigating the influence of other environmental variables on chironomid distributions and abundances

flood and earthquake disturbance of 210pb geochronology lake anterne nw alps dating recent lake sediment records yielding disturbed 210pb profiles has been a problem of wide interest in palaeoclimatic and palaeoseismic studies over the last few centuries when applied to an alpine lake sedimentary record a high resolution sedimentological study reveals that the 210pb profile is disturbed by the occurrence of single event deposits triggered by two different mechanisms flood events deposits and gravity reworking removing disturbed layers from the 210pb profile yields a logarithmic depth activity relationship using a simple 210pb decay model cfcs provides an assessment of mean accumulation rate of continuous sedimentation as opposed to event linked sedimentation the correlation of the thickest four gravity reworked deposits with historically known earthquakes permits both validation and refinement of the age depth relationship this refinement highlights variations in accumulation rate consistent with post little ice age climatic variations

lateglacial summer temperatures in the northwest european lowlands a chironomid record from hijkermeer the netherlands lateglacial environments at hijkermeer northwest netherlands were reconstructed by means of chironomid diatom and pollen analyses diatom assemblages indicate that hijkermeer was a shallow oligo to mesotrophic lake during this period pollen assemblages reflect the typical northwest european lateglacial vegetation development and provide an age assessment for the record from the beginning of the older dryas ca 14 000 calibrated 14c yr bp into the early holocene to ca 10 700 calibrated 14c yr bp the chironomid record is characterized by several abrupt shifts between assemblages typically found in mid latitude subalpine to alpine lakes and assemblages typical for lowland environments based on the chironomid record july air temperatures were reconstructed using a chironomid temperature transfer function from central europe mean july air temperatures of ca 14 0 16 0 c are inferred before the older dryas of ca 16 0 16 5 c during most of the allerod of ca 13 5 14 0 c during the younger dryas and of ca 15 5 16 0 c during the early holocene two centennial scale decreases in july air temperature were reconstructed during the lateglacial interstadial which are correlated with greenland interstadial events gi 1d and 1b the results suggest that vegetation changes in the netherlands may have been promoted by the cooler climate during gi 1d immediately preceding the older dryas biozone and gi 1b the hijkermeer chironomid inferred temperature record shows a similar temperature development as the greenland ice core oxygen isotope records for most of the lateglacial and a good agreement with other temperature reconstructions available from the netherlands this suggests that chironomid based temperature reconstruction can be successfully implemented in the northwest european lowlands and that chironomids may provide a useful alternative to oxygen isotopes for correlating european lake sediment records during the lateglacial 2007 elsevier ltd all rights reserved

testing the reliability of detrital cave sediments as recorders of paleomagnetic secular variations seso cave system central pyrenees spain abstract a paleomagnetic study has been carried out on a waterlaid detrital sedimentary sequence of 240 cm thick within the seso cave system west central pyrenees in these sediments seven charcoal samples were dated using 14c ams ranging from 2080 to 650 cal yr bp 130 bc 1300 ad two levels of human occupation of the cave have been recognized by ceramics associated to the iberian period and to the roman period respectively the detrital sedimentary sequence is made of autochthonous piping detached material from the eocene marls host rock inside of the cavity and allochthonous stream transported sediments from the outside sediments the autochthonous material first 100 cm made of fine grain laminated sediments lutites and marls corresponds to pond facies the allochthonous material 190 240 cm is made of lutites and sands and corresponds to stream facies and both facies are mixed from 100 to 190 cm the increase in sedimentation rate towards the end of the sequence stream facies points to an intensification of the alluvial activity as a possible consequence of a more arid climate during the medieval climate anomaly for the paleomagnetic study 44 discrete cylindrical samples were taken along the detrital sequence the values of the natural remanent magnetization and magnetic susceptibility are significantly lower in the pond sediments than in the stream sediments the declination and inclination of the paleomagnetic characteristic component sister samples analyzed by both alternating field and temperature demagnetizing procedure of each depth point is compared to the spanish archeomagnetic catalog and available geomagnetic models arch3k 1 cals3k 4 cals10k 1b and scha dif 3k in order to determine the accuracy of these sediments recording the earth s magnetic field results suggest that these sediments poorly record the earth s magnetic field however paleomagnetic inclination shows similar results between both demagnetizing methods and the inclination is well recorded especially in the younger stream facies the lack of archeological remains with absolute dates from 925 to 1545 cal yr bp in the iberian paleomagnetic secular variation reference curve has prevented up to now the study of that time period therefore the inclination data from the seso cave deposit is the first record of the iberian paleomagnetic secular variation during most part of the medieval time and they are closer to the inclination values of one geomagnetic model cals10k 1b

chironomids as a tool for inferring holocene climate an assessment based on six sites in southern scandinavia abstract chironomid subfossil assemblages from six low alpine and sub alpine holocene stratigraphies are presented and compared they are from five lakes in mid southern and western norway and one in central sweden when comparing the chironomid inferred july air temperatures there are many time segments with a poor among lake fit in inferred temperatures possible environmental variables influencing the fossil chironomid assemblages are discussed using a modern norwegian calibration data set to indicate taxon environment relationships these analyses indicate that local changes in ph water chemistry and productivity at times may have overridden the regional temperature signal in addition other causes of poor among site temperature fit are discussed in particular those related to chronological uncertainties holocene temperature inferences from single cores based on chironomids may not always be able to provide a reliable regional temperature signal but can act as a guide from which hypotheses about past environmental conditions can be tested with the aid of chironomid inferred temperatures from several sites and from other environmental proxies we have obtained a regional picture of holocene summer temperature change by developing a consensus reconstruction based on the overall temperature signal from all six sites this consensus is developed by fitting a smoother through all 330 site specific temperature deviations from the holocene mean the consensus temperature deviations vary from 0 8 c at 8800 cal years bp to 0 8 c at 6500 cal years bp

10 be exposure dating of the timing of neoglacial glacier advances in the ecrins pelvoux massif southern french alps alpine glacier variations are known to be reliable proxies of holocene climate here we present a terrestrial cosmogenic nuclide tcn based glacier chronology relying on 24 new be 10 exposure ages which constrain maximum neoglacial positions of four small to mid sized glaciers rateau lautaret bonnepierre and etages in the ecrins pelvoux massif southern french alps glacier advances marked by mainly lateral moraine ridges that are located slightly outboard of the little ice age lia c 1250 1860 ad maximum positions were dated to 4 25 0 44 ka 3 66 0 09 ka 2 09 0 10 ka c 1 31 0 17 ka and to 0 92 0 02 ka the 4 2 ka advance albeit constrained by rather scattered dates is to our knowledge exposure dated here for the first time in the alps it is considered as one of the first major neoglacial advance in the western alps in agreement with other regional paleoclimatological proxies we further review alpine and northern hemisphere mid to high latitude evidence for climate change and glacier activity concomitant with the 4 2 ka event the 2 1 ka advance was not extensively dated in the alps and is thought to represent a prominent advance in early roman times other neoglacial advances dated here match the timing of previously described alpine neoglacial events our results also suggest that a neoglacial maximum occurred at etages glacier 0 9 ka ago i e during the medieval climate anomaly mca c 850 1250 ad at rateau glacier discordant results are thought to reflect exhumation and snow cover of the shortest moraine boulders overall this study highlights the need to combine several sites to develop robust neoglacial glacier chronologies in order to take into account the variability in moraine deposition pattern and landform obliteration and conservation

calendar dated glacier variations in the western european alps during the neoglacial the mer de glace record mont blanc massif holocene glacier records from the western european alps are still sparse although a number of sites are well suited to constraining pre and early little ice age lia glacier advances the present study provides the first dendrochronologically based and calendar dated neoglacial glacier chronology for the mont blanc massif french alps it is based on the analysis of over 240 glacially buried pinus cembra subfossil logs and wood remains found either embedded in till or as detrital material in the mer de glace right lateral moraine only a few of the samples were found to be formally in situ but we show that some logs were virtually in situ not rooted but showing little or no evidence of reworking and could be used to accurately reconstruct past glacier margin behavior in space and time uncertainties regarding the other samples may relate to original growth location and or to outer wood decay the resulting dates followed by a were therefore considered maximum limiting ages for glacier advances the main burial events interpreted as glacier advances occurred between ca 1655 and 1544 bc between ca 1230 and 1105 bc between ca 1013 and 962 937 bc at ca 802 777 bc after 608 bc between 312 and 337 ad between ca 485 ad and 606 ad between 1120 and 1178 ad between ca 1248 and 1278 1296 ad and after 1352 ad these advances predate the late lia maxima known from historical sources the magnitude of the advances gradually increased to culminate in three near neoglacial maxima during the 7th 12th and 13th centuries ad followed by a first lia neoglacial maximum in the second half of the 14th century ad the pattern of neoglacial events described here is coherent with central and eastern alpine glacier chronologies this indicates marked synchronicity of late holocene glacier variability and forcing at a regional scale although occasional differences could be detected between western and eastern records the mer de glace record also confirms the link between the timing of sediment erosion in a high elevation glaciated alpine catchment and subsequent deposition in the sub alpine lake bourget

a multi proxy paleolimnological reconstruction of holocene climate conditions in the great basin united states article i nfo article history received 11 february 2009 available online 14 august 2009 a sediment core spanning 7000 cal yr bp recovered from stella lake a small sub alpine lake located in great basin national park nevada was analyzed for subfossil chironomids non biting midges diatoms and organic content estimated by loss on ignition loi subfossil chironomid analysis indicates that stella lake was characterized by a warm middle holocene followed by a cool neoglacial period with the last two millennia characterized by a return to warmer conditions throughout the majority of the core the stella lake diatom community composition is dominated by small periphytic taxa which are suggestive of shallow cool alkaline oligotrophic waters with extensive seasonal ice cover a reconstruction of mean july air temperature mjat was developed by applying a midge based inference model for mjat two component wa pls consisting of 79 lakes and 54 midge taxa rjack 2 0 55 rmsep 0 9 c comparison of the chironomid inferred temperature record to existing regional paleoclimate reconstructions suggests that the midge inferred temperatures correspond well to regional patterns this multi proxy record provides valuable insight into regional holocene climate and environmental conditions by providing a quantitative reconstruction of peak holocene warmth and aquatic ecosystem response to these changes in the great basin a region projected to experience increased aridity and higher temperatures

midges as quantitative temperature indicator species lessons for palaeoecology calibration data sets give a unique opportunity to establish patterns of biological existence and their statistical associations with environmental variables by use of calibration data sets environmental variables can be inferred quantitatively the resulting long time series may assist in distinguishing natural environmental variability from human induced variability both in terms of climate change and biotic turnover however the validity of the palaeoenvironmental reconstructions depends on their accuracy precision and sensibility before performing palaeoenvironmental inferences key mechanisms controlling contemporary species distribution abundances and dynamics should be identified and understood an inference model is developed to produce reconstructions a major challenge lies in validating and interpreting the reconstructions calibration data sets involving midges diptera chironomidae suggest that climate has a broad scale regional control over midge existence and abundance often ove

thermosphere density response to the 20 21 november 2003 solar and geomagnetic storm from champ and grace accelerometer data 1 densities in the 400 500 km height region inferred from accelerometer measurements on the champ and grace satellites are utilized to study the response to the isolated and severe geomagnetic storm of 20 21 november 2003 the champ and grace satellites provide data at approximate local times of 1110 2310 and 1430 0230 hours respectively in a global sense density increases of order 300 800 occur during this storm with relatively little time delay at high latitudes and with about 4 hour delay at the equator significant latitudinal asymmetries in the response are discussed in the context of neutral wind patterns and enhanced summer versus winter joule heating rates at high latitudes comparisons with the nrlmsise 00 empirical model densities during this period show marked differences in amplitude of the response as well as latitudinal and temporal structures evidence for a tight coupling between solar wind and neutral density variability is found for the high latitude summer hemisphere near noon in that densities near 410 km are very responsive to increases in solar wind dynamic pressure even during periods when both bz and by are near zero or positive filtering of the data reveals regional scale 1000 2000 km density anomalies that are common between the champ and grace measurements during the geomagnetic disturbance alternating regions of density enhancements 50 and depressions 50 exist between the pole and low to middle latitudes that have the appearance of a standing wave pattern during magnetically quiet intervals before and after the storm daytime density depressions 4 8 are seen that track the magnetic equator while density enhancements 10 track the latitudes of the ionospheric appleton anomaly peaks large scale 1000 km wave like structures are also prevalent during both day and night during the magnetic disturbance and extend throughout both hemispheres consistent with the concept that these are associated with the so called direct gravity waves forced in the auroral regions and propagating far from the source substantial variability is also present at medium scales 300 500 km but these structures are confined mainly to middle to high latitudes in accord with theoretical expectations grace a and grace b data are used in a feasibility study of the detection of small scale wave activity by taking advantage of the 30 s separation of the satellites in the same orbital plane despite the large amount of maneuvers which are not always recorded this first analysis is promising amplitude variations of order 10 20 and wave speeds of 1000 1500 m s 1 are observed

glacier and lake level variations in west central europe over the last 3500 years on the basis of glacier and lake level records this paper attempts for the first time a comparison between high resolution palaeohydrological and palaeoglaciological data in west central europe over the past 3500 years a data set of tree ring width radiocarbon and archaeological data in addition to historical sources were used to reconstruct fluctuations of the great aletsch the gorner and the lower grindelwald glaciers in the swiss alps the three ice streams experienced nearly synchronous advances at c 1000 600 bc and ad 500 600 800 900 1100 1200 and 1300 1860 these glacier fluctuations show strong correspondence with lake level variations reconstructed in eastern france jura mountains and pre alps and on the swiss plateau this supports the hypothesis of climatically driven fluctuations historical data available for the period since ad 1550 reveal in detail various meteorological conditions behind the successive glacier advances however in agreement with the general trend shown by th

late holocene summer temperature reconstruction from chironomid assemblages of lake anterne northern french alps we present a chironomid based reconstruction of late holocene temperature from lake anterne 2060 m a s l in the northern french alps chironomid assemblages were studied in 49 samples along an 8 m long sediment core covering the last 1800 years july air temperatures were inferred using an inference model based on the distribution of chironomid assemblages in 100 swiss lakes the transfer function has a leave one out cross validated coefficient of determination r of 0 88 a root mean square error of prediction rmsep of 1 40 c despite possible biases induced by methodological aspects and the ecological complexity of the chironomid response to both climate and environmental changes the concordance of the lake anterne temperature reconstruction with other alpine records suggests that the transfer function has successfully reconstructed past summer temperature during the last two millennia the twentieth century is the only section of the record which shows a poor agreement with other climate recons

the record of climatic change in the geological archives of shallow marine coastal and adjacent lowland areas of northern germany abstract the record of climatic change in shallow marine coastal and adjacent lowland areas has been investigated by three different approaches a mass balance study focused on the interaction between sea level rise and holocene sediment accumulation in the coastal lowland area between the ems and weser rivers on the german north sea coast this region which comprises various sedimentary environments such as barrier islands sheltered and open tidal flats bay flats and estuaries is highly suitable for such quantitative studies which can be used to create a model for general mass transport and accumulation processes connected with transgressions over coastal lowlands an integrated geochemical and microfacies study was made to assess the response of shallow marine intertidal and limnic semiterrestrial environments to the climate controlled holocene sea level rise the factors controlling the development of various palaeoenvironments were estimated from the distribution of biomarkers major and trace elements diatoms foraminifera and sedimentary structures observed at high resolution in core sections these data complement those of conventional geological lithostratigraphical archaeological and geobotanical investigations the extensive raised bogs which occur in the pleistocene hinterland adjacent to the coastal zone provided an excellent opportunity to examine peat formation in response to climatic changes in the past on the basis of a large number of 14 c age determinations special attention was paid to the onset and regional expansion of raised bogs in this region and to the question of whether or not the formation of raised bog peat started synchronously in one or in a series of different phases

hemispheric asymmetry of subauroral ion drifts statistical results a large database of more than 18 000 subauroral ion drift said events from dmsp observations from 1987 to 2012 is used to systematically investigate the features of said said occurs mostly at 62 60 magnetic latitude mlat and 22 15 22 45 magnetic local time mlt for geomagnetically quiet conditions and at 58 56 mlat and 22 15 22 45 mlt for geomagnetically disturbed conditions in the north hemisphere nh south hemisphere sh respectively significant north south asymmetries in said occurrence shape and geomagnetic activity variations are found in this statistical study the latitudinal width of a said is larger in the nh than in the sh an interesting finding of this work is that the said occurrence probability peaks have an 180 difference in longitude between the two hemispheres in the geographic coordinates for both geomagnetically quiet and disturbed conditions the said width peaks in almost the same geomagnetic meridian zone with a geomagnetic longitude of 80 120 in both hemispheres significant hemispheric asymmetries and spike signatures with sharp dips are found in all the latitudinal profiles of the horizontal velocities of saids the said is highly correlated to geomagnetic activity indicating that the location and evolution of the said might be influenced by global geomagnetic activity auroral dynamics and the dynamics of ring currents

high latitude plasma outflow as measured by the dmsp spacecraft 1 we have examined the vertical ion flux in the topside high latitude ionosphere from measurements of the vertical ion drift and ion number density made by the dmsp f13 satellite we found that the average vertical flux over the entire high latitude region near 800 km altitude is quite small this suggests that most of the vertical ion flux is associated with a large scale breathing of the upper ionosphere in the polar cap the vertical ion flux is uniformly downward at all locations however in the auroral zone the ion flux is highly structured and a net upward flux is produced only by spatially and temporally confined events containing upward fluxes in excess of 1010 cm 2 s 1 that have no downward counterparts

frequency and intensity of high altitude floods over the last 3 5 ka in northwestern french alps lake anterne in central western europe several studies have shown that colder holocene periods such as the little ice age also correspond to wet periods however in mountain areas which are highly sensitive to erosion processes and where precipitation events can be localized past evolution of hydrological activity might be more complicated to assess these past hydrological changes a paleolimnological approach was applied on a 13 4 m long sediment core taken in alpine lake anterne 2063 m asl and representing the last 3 5 ka lake sedimentation is mainly composed of ood deposits triggered by precipitation events sedimentological and geochemical analyses show that oods were more frequent during cold periods while high intensity ood events occurred preferentially during warmer periods in mild temperature conditions both ood patterns are present this underlines the complex relationship between ood hazards and climatic change in mountain areas during the warmer and or dryer times of the end of iron age and the roman period both the frequency and intensity of oods increased this is interpreted as an effect of human induced clearing for grazing activities and reveals that anthropogenic interferences must be taken into account when reconstructing climatic signals from natural archives

modeling of the global distribution of ionospheric electric fields based on realistic maps of field aligned currents 1 a new approach for modeling the global distribution of ionospheric electric potentials utilizing high precision maps of facs derived from measurements by the orsted and champ satellites as input to a comprehensive numerical scheme is presented the boundary conditions provide a correct treatment of the asymmetry of conductivity and sources of electric potential between the northern and southern hemispheres on the basis of numerical simulation the basic convection patterns developed simultaneously in both hemispheres for equinox and summer winter solstices are obtained a rather complicated dependence of the convection patterns on season linked with the sign of imf by is found in particular the combinations of by 0 summer and by 0 winter the model predicts that the summer cross polar potentials are smaller than the winter potentials the value of the ratio depends on the combination of season imf by sign the ratio is found to be greater for the combination of by 0 southern summer and by 0 northern summer under northward imf conditions at middle latitudes the main features of the mlt profile of the westward and equatorward electric field components are reproduced the model predicts that during solstice the equatorward component of the midlatitude electric field is negative at all local times for by 0 citation lukianova r and f christiansen 2006 modeling of the global distribution of ionospheric electric fields based on realistic maps of field aligned currents j geophys res 111 a03213 doi 10 1029 2005ja011465

palaeoflood activity and climate change over the last 1400 years recorded by lake sediments in the north west european alps a high resolution sedimentological and geochemical study of a high altitude proglacial lake lake blanc aiguilles rouges 2352m a s l revealed 195 turbidites 190 of which are related to flood events over the last 1400 years we used the coarsest sediment fraction of each turbidite as a proxy for the intensity of each flood event because most flood events at this locality are triggered by localized summer convective precipitation events the reconstructed sedimentary record reveals changes in the frequency and intensity of such events over the last millennium comparisons with other temperature palaeohydrological and glacier reconstructions in the region suggest that the most intense events occurred during the warmest periods i e during the medieval climate anomaly ad 800 1300 and the current period of global warming on a multi decadal time scale almost all the flood frequency peaks seem to correspond to warmer periods whereas multi centennial variations in flood frequency appear to follow the regional precipitation pattern consequently this new alpine flood record provides further evidence of a link between climate warming and an increase in the frequency and intensity of flooding on a multidecadal time scale whereas the centennial variability in flood frequencies is related to regional precipitation patterns

holocene temperature variations at a high altitude site in the eastern alps a chironomid record from schwarzsee ob solden austria few well dated quantitative holocene temperature reconstructions exist from high altitude sites in the central eastern alps here we present a chironomid based quantitative reconstruction of mean july air temperatures tjuly throughout the holocene for a remote high mountain lake schwarzsee ob solden situated above the treeline at 2796 m a s l in the austrian alps applying a chironomid temperature inference model developed from lakes of the alpine region to a high resolution chironomid record from the lake provides evidence for early holocene ca 10000 8600 cal yr bp tjuly of up to 8 5 c i e 4 c above the modern 1977 2006 mean july temperature the reconstruction reveals the so called 8 2 ka cold event centered at ca 8250 8000 cal yr bp with temperatures ca 3 c below the early holocene thermal maximum rather warm ca 6 c and productive conditions prevailed during ca 7900 4500 cal yr bp the chironomid record suggests a climate transition between ca 5200 and 4500 cal yr bp to cooler tjuly a distinct cooling trend is evident from ca 4500 until ca 2500 cal yr bp thereafter the study site experienced its coldest conditions around 4 c or less throughout the rest of the holocene with the exception of the warming trend during the late 20th century beside other factors the northern hemisphere summer insolation seems to be the major driving force for the long term trends in tjuly at high altitudes in the eastern alps due to the extreme location of the lake and the limited temperature range represented by the applied calibration data set the chironomid based temperature reconstruction fails to track phases of the late holocene climatic history with tjuly cooler than 4 c further chironomid based palaeoclimate model and down core studies are required to address this problem provide more realistic tjuly estimates from undisturbed high altitude lakes in the alps and extract a reliable regional temperature signal

dependencies of high latitude plasma convection consideration of interplanetary magnetic field seasonal and universal time factors in statistical patterns 1 the database of the nine radars of the super dual auroral radar network superdarn in the northern hemisphere has been analyzed for information on factors that influence the convection of plasma in the high latitude ionosphere the velocity measurements were collected over the period 1998 2002 the data were first used to derive a new statistical model of convection that improves upon the earlier one radar model of ruohoniemi and greenwald 1996 in its specification of the dependence of the convection pattern on the magnitude and direction of the imf in the gsm y z plane we then derived average patterns for secondary sortings by season year and radar such dependencies as emerged were most clearly seen by contrasting the results for by and by the seasonal effect in the convection pattern is found to have similarities to that of the sign of by in particular the combination of by summer by winter reinforces the tendency of the by sign factor to sculpt the dusk and dawn cells into more round crescent crescent round shapes and to shift the crescent cell across the midnight mlt meridian however these combinations are associated with lower estimates of the total cross polar cap potential drop pc while the nonreinforcing combinations produce elevated pc especially by summer there is an overall tendency for pc to increase from winter to summer although the pure seasonal effect on the potential drop is weaker than that of the by sign season factor we did not find pronounced differences among the patterns derived for the 5 individual years which spanned the most recent interval of solar cycle maximum sorting by radar we found few differences among the patterns for by but for by variations emerged that are consistent with a possible dependence on universal time ut the impacts of season and ut on convection in the high latitude ionosphere thus depends on the imf especially the sign of by we speculate that variability in the ionospheric conductivity has a greater effect on magnetosphere ionosphere coupling under by conditions

high resolution chironomid inferred temperature history since ad 1580 from varved lake silvaplana switzerland comparison with local and regional reconstructions chironomids were used to reconstruct mean july air temperatures between c ad 1580 and 2001 at lake silvaplana a varved lake located in the engadine eastern swiss alps the goal of this study was to reconstruct temperature changes at near annual resolution and validate the reconstruction by comparison with records based on early instrumental data documentary proxy evidence dendrochronology geochemical biogenic silica bsi and mineralogical data quartz mica ratios at local and regional scales warmer than the climate normal ad 1961 1990 mean july air temperatures were inferred between c ad 1610 and 1662 ad 1710 and 1740 ad 1790 and 1866 ad 1940 and 1960 and ad 1990 and 2001 colder than the climate normal july air temperatures were reconstructed between c ad 1662 and 1710 ad 1740 and 1790 ad 1866 and 1919 and ad 1970 and 1990 the 420 year chironomid inferred mean july air temperature record was significantly p 0 01 related to june september jjas temperatures reconstructed from e

a chironomid based holocene summer air temperature reconstruction from the swiss alps we developed a quantitative chironomid july air temperature inference model based on surface sediments from 81 swiss lakes and applied it to the holocene subfossil chironomid record of hinterburgsee a small subalpine lake in the northern swiss alps present day mean july air temperature of 11 3 c after smoothing to reduce the high between sample variability of inferred temperatures the reconstruction indicates july air temperatures of 10 4 10 9 c at the end of the younger dryas of 11 9 12 8 c during the early and mid holocene 11500 4000 cal bp and slightly lower temperatures of 11 5 12 0 c during the late holocene 3500 1000 cal bp a warming trend inferred for the past millennium is most likely an artifact of human impact on hinterburgsee s chironomid fauna rather than a genuine temperature signal the most prominent climatological events during the holocene were two periods of lower temperatures at c 10700 10500 cal bp and 8200 7700 cal bp and an abrupt shift to a cooler late holocene cl

7200 years of rhone river flooding activity in lake le bourget france a high resolution sediment record of nw alps hydrology magnetic susceptibility ms was measured with high resolution 5 mm on a 9 m long 14c dated core from lake le bourget savoie france spanning the last 7200 years the strong correlation r 0 85 of the ms with the silicate borne suite of elements si al fe mg k and anti correlation with the carbonate content r 0 87 allows it to be used as a proxy for the fluctuations of the abundance of riverborne clastic fraction versus authigenic carbonates in sediment as the rhone is the only river bringing a significant amount of silicate minerals to the coring site the ms downstream is interpreted as a proxy of the rhone suspended load discharge in lake le bourget this is confirmed over the last 3000 years by the good match with the evolution of hydrological activity of the rhone as it is known through geomorphological studies of well dated archaeological sites over the last 7200 years the record is consistent with the regional record of lake water level fluctuations while the intensity of the ms

reconstruction of temperature in the central alps during the past 2000 yr from a δ18o stalagmite record the precisely dated isotopic composition of a stalagmite from spannagel cave in the central alps is translated into a highly resolved record of temperature at high elevation during the past 2000 yr temperature maxima during the medieval warm period between 800 and 1300 ad are in average about 1 7 8c higher than the minima in the little ice age and similar to present day values the high correlation of this record to d 14 c suggests that solar variability was a major driver of climate in central europe during the past 2 millennia d 2005 elsevier b v all rights reserved

temperature patterns over the past eight centuries in northern fennoscandia inferred from sedimentary diatoms establishing natural climate variability becomes particularly important in remote polar regions especially when considering questions regarding higher than average warming we present a high resolution record of temperature variability for the past 800 yr based on sedimentary diatoms from a treeline lake in finnish lapland the bsizer multiscale smoothing technique is applied to the data to identify significant features in the record at different temporal levels the overall reconstruction shows relatively large multi centennial temperature variability with a total range of about 0 6 0 8 c at millennial scales the temperatures exhibit a statistically significant long term cooling trend prior to industrialization t 0 03 c century at the centennial timescale three warm time intervals were identified around ad 1200 1300 terminal phase of the medieval warm period mwp 1380 1550 and from 1920 until the present pronounced coolness occurred between ad 1600 and 1920 indicative of the little ice age lia at the decadal level certain shorter term climate excursions were revealed the warmest 10 30 yr nonoverlapping periods occurred in ad 1220 1250 1470 1500 and 1970 2000 respectively the classic events of mwp and lia are evident in our record as is also the 20th century warming

quantitative estimates of temperature and precipitation changes over the last millennium from pollen and lake level data at lake joux swiss jura mountains abstract this paper presents quantitative climate estimates for the last millennium using a multi proxy approach with pollen and lake level data from lake joux swiss jura mountains the climate reconstruction based on the modern analogue technique indicates warmer and drier conditions during the medieval warm period mwp mwp was preceded by a short lived cold humid event around ad 1060 and followed by a rapid return around ad 1400 to cooler and wetter conditions which generally characterize the little ice age lia around ad 1450 solar sporer minimum the lia attained a temperature minimum and a summer precipitation maximum the solar maunder minimum around ad 1690 corresponded at joux to rather mild temperatures but maximal annual precipitation these results generally agree with other records from neighbouring alpine regions however there are differences in the timing of the lia temperature minimum depending on the proxy and or the method used for the reconstruction as a working hypothesis the hydrological signal associated with the mwp and lia oscillations at lake joux may have been mainly driven by a shift around ad 1400 from positive to negative nao modes in response to variations in solar irradiance possibly coupled with changes in the atlantic meridional overturning circulation

stacking of discontinuous regional palaeoclimate records chironomid based summer temperatures from the alpine region since multi site reconstructions are less affected by site specific climatic effects and artefacts regional palaeotemperature reconstructions based on a number of sites can provide more robust estimates of centennial to millennial scale temperature trends than individual site specific records furthermore reconstructions based on multiple records are necessary for developing continuous climate records over time scales longer than covered by individual sequences here we present a procedure for developing such reconstructions based on relatively short centuries to millennia discontinuously sampled records as are typically developed when using biotic proxies in lake sediments for temperature reconstruction the approach includes an altitudinal correction of temperatures an interpolation of individual records to equal time intervals a stacking procedure for sections of the interval of interest that have the same records available as well as a splicing procedure to link the individual stacked records into a continuous reconstruction variations in the final stacked and spliced reconstruction are driven by variations in the individual records whereas the absolute temperature values are determined by the stacked segment based on the largest number of records with numerical simulations based on the ngrip 18o record we demonstrate that the interpolation and stacking procedure provides an approximation of a smoothed palaeoclimate record if based on a sufficient number of discontinuously sampled records finally we provide an example of a stacked and spliced palaeotemperature reconstruction 15000 90 calibrated 14c yr bp based on six chironomid records from the northern and central swiss alps and eastern france to discuss the potential and limitations of this approach

role of poleward moving auroral forms in the dawn dusk auroral precipitation asymmetries induced by imf by 1 in a case study we document the detailed spatial temporal structure of the aurora in the 0900 1500 magnetic local time mlt sector during an interval of steady southeast imf orientation emphasis is placed on ground based observations of structure that is often averaged out in large statistical studies a central feature is the phenomenon of poleward moving auroral forms pmafs an ionospheric manifestation of pulsed magnetopause reconnection in the form of flux transfer events ftes whose evolution in both prenoon and postnoon mlts can be monitored under similar interplanetary conditions differences in auroral precipitation associated with pmafs about the noon meridian related to imf by are documented while the prenoon pmafs develop in three stages spanning a latitude range of 500 km the highest latitude stage is absent in postnoon pmafs for by 0 which after the initial intensification progressively fade we suggest that this auroral precipitation asymmetry is closely related to the different field aligned current configuration in pmafs prenoon and pmafs postnoon and the underlying plasma convection pattern we detail the association between the high latitude component of pmafs in the prenoon sector by 0 and a channel of plasma convection located in the dawnside convection cell the latter convection channel located in the regime of old open flux represents an aspect of the svalgaard mansurov effect which is not included in the traditional description the auroral and plasma convection data are placed in the context of recent work on solar wind magnetosphere interconnection topology for a southward pointing imf with a strong by component

near simultaneous polar and dmsp measurements of topside ionospheric field aligned flows at high latitudes near simultaneous observations of topside 0 parallel flows are presented for four periods of measurement by polar and dmsp satellites during april 1996 the polar measurements are from southern perigee measurements near 5000 km altitude while the dmsp measurements were from 840 km altitude these observations provide a view of wide spread upward downward ionospheric o flows over the broad polar region along extended and multiple distinct satellite tracks in general the velocities are upward toward expected cleft and auroral latitudes typically about a 2 10 km s at 5000 km altitude and 0 2 km s at 840 km altitudes at the highest polar cap latitudes downward velocities are more frequent at both altitudes but especially at the lower 840 km altitude the downward velocities were typically a few hundred d s at 840 altitude and 0 1 km s at 5000 km altitude in some instances apparently downward velocities were observed at 840 km altitudes while upward 0 flows were observed at 5000 km altitude on the same flux tube the o density were characteristically 1 10 o cu cm at 5000 km altitude and 10 exp 3 10 exp 40 o cu cm at 840 km altitude while the o flux were characteristically 1 10 exp 5 10 exp 7 o sq cm sec at 5000 km altitudes and characteristically 10 exp 7 10 exp 9 o sq cm sec at 840 km altitude we have also examined the dual altitude parameter measurements for a polar cap field line the polar and dmsp measurements approximately 30 minutes apart and compared them with results from a transport simulation in which a flux tube was subjected to a brief pulse of soft electron precipitation and topside transverse ion heating the simulated density and velocity altitude profiles for 5 minutes later generally matched the observations except that the observed downward velocities 500 600 m s at 840 km altitude were much larger than those simulated

the little ice age signature in a 700 year high resolution chironomid record of summer temperatures in the central eastern alps despite the fact that the little ice age lia is well documented for the european alps substantial uncertainties concerning the regional spatio temporal patterns of temperature changes associated with the lia still exist especially for their eastern sector here we present a high resolution 4 10 years 700 year long mean july air temperature reconstruction based on subfossil chironomid assemblages from a remote lake in the austrian eastern alps to gain further insights into the lia climatic deterioration in the region the record provides evidence for a prolonged period of predominantly cooler conditions during ad 1530 1920 broadly equivalent to the climatically defined lia in europe the main lia phase appears to have consisted of two cold time intervals divided by slightly warmer episodes in the second half of the 1600s the most severe cooling occurred during the eighteenth century the lia temperature minimum about 1 5 c below the long term mean recorded in the mid 1780 s coincides with the strongest volcanic signal found in the greenland ice cores over the past 700 years and may be at least in part a manifestation of cooling that followed the long lasting ad 1783 1784 laki eruption a continuous warming trend is evident since ca ad 1890 1 1 c in 120 years the chironomid inferred temperatures show a clear correlation with the instrumental data and reveal a close agreement with paleotemperature evidence from regional high elevation tree ring chronologies a considerable amount of the variability in the temperature record may be linked to changes in the north atlantic oscillation

thousand years of climate change reconstructed from chironomid subfossils preserved in varved lake silvaplana engadine switzerland abstract fossil chironomids non biting midges from varved lake silvaplana switzerland were used to reconstruct climate mean july air temperatures during the last millennium at the beginning of the record corresponding to the last part of the medieval climate anomaly mca here the period between ca 1032 and 1262 ad the chironomid inferred mean july air temperatures were 1 c warmer p

the north atlantic oscillation forcing through the last 2000 years spatial variability as revealed by high resolution marine diatom records from n and sw europe abstract the tagus pro delta portuguese margin and the skagerrak ne of the north sea are two marine systems controlled by atmospheric changes which at present are mainly determined by fluctuations of the north atlantic oscillation nao on the basis of diatom records from marine sediment cores environmental changes primary productivity and salinity are reconstructed for the last 2000 years for both regions these sites are investigated focusing on the regional response to changing nao forcing both studied sites are characterized by sedimentation rates in the order of 0 12 cm year and 0 47 cm year for the most recent deposits off the tagus pro delta allowing high resolution paleoceanographic reconstructions 8 3 and 2 1 years represented per sample the last 2000 years are a period covering in europe the historical climatic periods known as the dark ages da the medieval warm period mwp and the little ice age lia in the skagerrak the cold periods of the da and lia are marked by diatom dissolution stages whereas at the tagus pro delta the da were associated with increased diatom production and possible upwelling and the onset of the lia corresponded to enhanced flow of the tagus river during the mwp better diatom preservation in the skagerrak related to stronger advection of salty atlantic waters is paralleled by dominant upwelling conditions at the tagus pro delta the two most intense upwelling periods at the tagus pro delta at ad 600 and ad 900 correspond to a dissolution stage and a slight change in salinity in the skagerrak respectively although the comparison of the two study sites suggests a common forcing such as the nao the different inferred behaviors for each main climatic period in each region demonstrate that the nao by its own is not sufficient to explain the climatic variability at a regional scale

summer temperature variations in the european alps a d 755 2004 abstract annually resolved summer temperatures for the european alps are described the reconstruction covers the a d 755 2004 period and is based on 180 recent and historic larch larix decidua mill density series the regional curve standardization method was applied to preserve interannual to multicentennial variations in this high elevation proxy dataset instrumental measurements from high low elevation grid boxes back to 1818 1760 reveal strongest growth response to current year june september mean temperatures the reconstruction correlates at 0 7 with high elevation temperatures back to 1818 with a greater signal in the higher frequency domain r 0 8 low elevation instrumental data back to 1760 agree with the reconstruction s interannual variation although a decoupling between warmer instrumental and cooler proxy data before 1840 is noted this offset is larger than during any period of overlap with more recent high elevation instrumental data even though the proxy time series

superposed epoch analysis of the ionospheric convection evolution during substorms imf by dependence we present superposed epoch analyses of the average ionospheric convection response in the northern and southern hemispheres to magnetospheric substorms occurring under different orientations of the interplanetary magnetic field imf observations of the ionospheric convection were provided by the super dual auroral radar network superdarn and substorms were identified using the far ultraviolet fuv instrument on board the imager for magnetopause to aurora global exploration image spacecraft we find that during the substorm growth phase the expected imf by dependent dawn dusk asymmetry is observed over the entire convection pattern but that during the expansion phase this asymmetry is retained only in the polar cap and dayside auroral zone in the nightside auroral zone the convection is reordered according to the local substorm electrodynamics with any remaining dusk dawn asymmetry being more closely related to the magnetic local time of substorm onset itself only weakly governed by imf by owing to the preponderance of substorms occurring just prior to magnetic midnight the substorm asymmetry tends to be an azimuthal extension of the dusk convection cell across the midnight sector a manifestation of the so called harang discontinuity this results in the northern southern hemisphere nightside auroral convection during substorms generally resembling the expected pattern for negative positive imf by when the preexisting convection pattern in the northern southern hemisphere is driven by positive negative imf by the nightside auroral convection changes markedly over the course of the substorm to establish this same harang configuration

late holocene ecological shifts and chironomid inferred summer temperature changes reconstructed from lake uddelermeer the netherlands abstract this paper presents a late holocene chironomid inferred record of july air temperature from a core obtained from lake uddelermeer in the netherlands the core interval which dates from 2500 to 400 cal yr bp was analysed at multi decadal resolution for organic content pollen spores and npps non pollen palynomorphs and chironomid head capsules these proxies indicate that from 2500 to 1140 cal yr bp the lake was mesotrophic and sustained a littorellion community while the chironomid assemblage was dominated by littoral species associated with macrophytes at 1140 cal yr bp a shift in the lake ecology occurred from low nutrient to high nutrient conditions dominated by algae this shift might be linked to a concurrent increase in human impact and is reflected in the chironomid assemblage by increases in eurytopic taxa which are resistant to disturbances shifts in the chironomid record between 2500 and 1140 cal yr bp do not coincide with changes in lake ecology and are presumably driven by climate change using a norwegian swiss calibration dataset as a modern analogue we produced a chironomid inferred temperature c it reconstruction this reconstruction compares well to other regional temperature reconstructions in timing and duration showing a roman warm period between 2240 and 1760 cal yr bp a dark age cold period starting at 1760 cal yr bp and the medieval climate anomaly beginning at 1280 cal yr bp the c it record indicates a temperature drop of 1 5 c from the roman warm period to the dark age cold period findings improve knowledge of the first millennium ad in nw europe which was characterised by changes in landscape vegetation society and climate

interhemispheric asymmetry of the high latitude ionospheric convection on 11 12 may 1999 1 ionospheric convection over the southern polar cap on 11 12 may 1999 has been studied by using the syowa east and south hf radar data and the dmsp ion driftmeter data when the solar wind density was very low and geomagnetic activity was low the overall convection pattern is consistent with the previous results by ohtani et al 2000 however the syowa radars and the dmsp satellites observed very high 1500 m s westward plasma flows at dusk directed from the nightside toward the dayside only in the southern dark hemisphere the high speed flow was observed continuously across the fields of view of both radars from 1530 ut on 11 may to 0200 ut on 12 may when the solar wind density was close to minimum comparison with the dmsp particle and auroral image data shows that the westward flow regions were located in the middle of the auroral precipitation area the strong asymmetry of the convection between the two hemispheres indicates the importance of the presence absence of solar illumination for the absence presence of the strong and localized ionospheric flows

orbital ice sheet and possible solar forcing of holocene lake level fluctuations in west central europe a comment on bleicher bleicher 2013 discussed interpretations proposed by magny 2004 that holocene lake level fluctuations in west central europe suggest possible solar forcing of climate he pointed out that the me