the last 7500 cal yr b p of westerly rainfall in central chile inferred from a high resolution pollen record from laguna aculeo 34 s abstract we report multiproxy analyses of a sediment core obtained from laguna aculeo that spans the past 7500 years laguna aculeo 33 50 s 70 55 w is one of the few natural inland lakes located in the mediterranean zone of central chile near the northern margin of the influence of the southern westerlies the record shows elevated pollen counts of halophytes and seasonally drying of the lake basin prior to 5700 cal yr b p indicating severe aridity and warmer than present conditions this was followed by the establishment of a fresh water lake along with an increase in arboreal and herbaceous plant diversity between 5700 and 3200 cal yr b p an intensification of this trend started at 3200 cal yr b p along with the abrupt decrease of halophytes until 100 cal yr b p within this humid period pollen accumulation rates show large amplitude fluctuations coeval with numerous turbidite layers suggesting a highly variable and torrential rainfall pattern this intense and variable precipitation regime is probably associated with the el nino southern oscillation enso phenomenon we suggest that the modern mediterranean climate of central chile was established at 3200 cal yr b p paleovegetation and paleolimnological changes starting at 100 cal yr b p correlate with documented human activity surrounding the lake

major storm periods and climate forcing in the western mediterranean during the late holocene abstract big storm events represent a major risk for populations and infrastructures settled on coastal lowlands in the western mediterranean where human societies colonized and occupied the coastal areas since the ancient times the variability of storm activity for the past three millennia was investigated with a multi proxy sedimentological and geochemical study from a lagoonal sequence mappings of the geochemistry and magnetic susceptibility of detrital sources in the watershed of the lagoon and from the coastal barriers were undertaken in order to track the terrestrial or coastal marine origin of sediments deposited into the lagoon the multi proxy analysis shows that coarser material low magnetic susceptibility and high strontium content characterize the sedimentological signature of the paleostorm levels identified in the lagoonal sequence a comparison with north atlantic and western mediterranean paleoclimate proxies shows that the phases of high storm activity occurred during cold periods suggesting a climatically controlled mechanism for the occurrence of these storm periods besides an in phase storm activity pattern is found between the western mediterranean and northern europe spectral analyses performed on the sr content revealed a new 270 year solar driven pattern of storm cyclicity for the last 3000 years this 270 year cycle defines a succession of ten major storm periods sp with a mean duration of 96 54 yr periods of higher storm activity are recorded from 680 to 560 cal yr bc sp10 end of the iron age cold period from 140 to 820 cal yr ad sp7 to sp5 with a climax of storminess between 400 and 800 cal yr ad dark ages cold period and from 1230 to 1800 cal yr ad sp3 to sp1 little ice age periods of low storm activity occurred from 560 cal yr bc to 140 cal yr ad sp9 and sp8 roman warm period and from 820 to 1230 cal yr ad sp4 medieval warm period

hydroclimate in africa during the medieval climate anomaly the medieval climate anomaly mca is a recognized period of distinct pre industrial climate change with a core period of 1000 1200 ce the field of palaeoclimatology has made major progress over the past 15 years during which a great number of high and medium resolution case studies were published reconstructing climate change of the past millennia in many parts of the world regional data coverage has now reached a point which allows compiling palaeoclimate maps for well defined time intervals here we present hydroclimatic trend maps for the mca in africa based on 99 published study locations key hydroclimatic proxy curves are visualized and compared in a series of 16 correlation panels proxy types are described and possible issues discussed based on the combined mca dataset temporal and spatial trends are interpreted and mapped out three areas have been identified in africa in which rainfall seems to have increased during the mca namely tunisia western sahel and the majority of southern africa at the same time a reduction in precipitation occurred in the rest of africa comprising of nw and ne africa west africa eastern africa and the winter rainfall zone of south africa mca hydroclimate change in africa appears to have been associated with characteristic phases of ocean cycles as also supported by modern climate observations aridity in morocco typically coincides with the positive phase of the north atlantic oscillation nao whilst increased rainfall in the western sahel is often coupled to the positive phase of the atlantic multidecadal oscillation amo reduction in rainfall in the region gulf of aden southern red sea to eastern africa could be linked to a negative indian ocean dipole iod or a derived long term equivalent indian ocean cycle parameter the intertropical convergence zone itcz appears to have been shifted pole wards during the mca for both the january and july positions mca hydroclimate mapping revealed major data gaps in the sahara south sudan somalia central african republic democratic republic of congo angola northern mozambique zambia and zimbabwe special efforts are needed to fill these gaps e g through a dedicated structured research program in which new multiproxy datasets are created based on the learnings from previous african mca studies

aeolian sediment reconstructions from the scottish outer hebrides late holocene storminess and the role of the north atlantic oscillation northern europe can be strongly influenced by winter storms driven by the north atlantic oscillation nao with a positive nao index associated with greater storminess in northern europe however palaeoclimate reconstructions have suggested that the nao storminess relationship observed during the instrumental period is not consistent with the relationship over the last millennium especially during the little ice age lia when it has been suggested that enhanced storminess occurred during a phase of persistent negative nao to assess this relationship over a longer time period a storminess reconstruction from an nao sensitive area the outer hebrides is compared with late holocene nao reconstructions the patterns of storminess are inferred from aeolian sand deposits within two ombrotrophic peat bogs with multiple cores and two locations used to distinguish the storminess signal from intra site variability and local factors the results suggest storminess increased after 1000 cal yrs bp with higher storminess during the medieval climate anomaly mca than the lia supporting the hypothesis that the nao storminess relationship was consistent with the instrumental period however the shift from a predominantly negative to positive nao at c 2000 cal yrs bp preceded the increased storminess by 1000 years we suggest that the long term trends in storminess were caused by insolation changes while oceanic forcing may have influenced millennial variability

evidence for holocene sea level and climate change from almenara marsh western mediterranean in the almenara marsh western mediterranean four cores were analyzed to establish the relationship between the marsh record of the almenara marshlands and the environmental factors responsible for its evolution during the holocene one hundred and eighty six samples were collected for sedimentologic and paleontological study 63 for biomarker analysis 5 for amino acid racemization aar dating and 5 for 14 c dating litho and biofacies analyses identified distinct paleoenvironments with the presence of a marsh environment alternating with inputs of alluvial material and marine sediments biomarkers indicated the constant presence of terrestrial herbaceous plants together with a variable development of aquatic macrophytes during the holocene transgression the almenara marsh was occupied by oligohaline marsh facies with an oscillating water level and peat formation which was established at the bottom of the record at 7570 cal yr bp and persisted until 3100 780 yr aar maximum surface flooding occurred at 5480 cal yr bp registered 450m from the current coastline at least three peat beds dated with 14 c dating and aar correlated with bond episode 5900 cal yr bp and wanner episodes 4800 4500 and 3300 3500 cal yr bp cycles and thus correspond to a regional model that affected the northern hemisphere

climatic signals in multiple highly resolved stable isotope records from greenland abstract twenty ice cores drilled in medium to high accumulation areas of the greenland ice sheet have been used to extract seasonally resolved stable isotope records relationships between the seasonal stable isotope data and greenland and icelandic temperatures as well as atmospheric flow are investigated for the past 150 200 years the winter season stable isotope data are found to be influenced by the north atlantic oscillation nao and very closely related to sw greenland temperatures the linear correlation between the first principal component of the winter season stable isotope data and greenland winter temperatures is 0 71 for seasonally resolved data and 0 83 for decadally filtered data the summer season stable isotope data display higher correlations with stykkisholmur summer temperatures and north atlantic sst conditions than with sw greenland temperatures the linear correlation between stykkisholmur summer temperatures and the first principal component of the summer season stable isotope data is 0 56 increasing to 0 66 for decadally filtered data winter season stable isotope data from ice core records that reach more than 1400 years back in time suggest that the warm period that began in the 1920s raised southern greenland temperatures to the same level as those that prevailed during the warmest intervals of the medieval warm period some 900 1300 years ago this observation is supported by a southern greenland ice core borehole temperature inversion as greenland borehole temperature inversions are found to correspond better with winter stable isotope data than with summer or annual average stable isotope data it is suggested that a strong local greenland temperature signal can be extracted from the winter stable isotope data even on centennial to millennial time scales

holocene paleoclimate inferred from salinity histories of adjacent lakes in southwestern sicily italy marked uncertainties persist regarding the climatic evolution of the mediterranean region during the holocene for instance whether moisture availability gradually decreased remained relatively constant or increased during the last 7000 years remains a matter of debate to assess holocene limnology hydrology and moisture dynamics the coastal lakes lago preola and gorgo basso located in southwestern sicily were investigated through several stratigraphic analyses of ostracodes including multivariate analyses of assemblages transfer functions of salinity and biochemical analyses of valves sr ca 18o and 13c during the early holocene the gorgo basso and lago preola ostracode records are similar after an initial period of moderate salinity 1690 6100 mg l from ca 10 000 8190 cal yr bp syndepositional or diagenetic dissolution of ostracode valves suggests that salinity declined to 250 mg l from ca 8190 to 7000 cal yr bp at both sites after ca 6250 cal yr bp the ostracode records are strikingly different lago preola became much more saline with paleosalinity values that ranged from 2270 to about 24 420 mg l we suggest that lago preola s change from a freshwater to mesosaline lake at about 6250 cal yr bp was related to sea level rise and resulting intrusion of seawater influenced groundwater in contrast gorgo basso remained a freshwater lake the salinity of gorgo basso declined somewhat after 6250 cal yr bp in comparison to the early holocene ranging from about 550 to 1680 mg l cypria ophtalmica a species capable of rapid swimming and flourishing in waters with low dissolved oxygen levels became dominant at approximately the time when greek civilization took root in sicily 2600 cal yr bp and it completely dominates the record during roman occupation roughly 2100 to 1700 cal yr bp these freshwater conditions at gorgo basso suggest high effective moisture when evergreen olive oak forests collapsed in response to increased greco roman land use and fire ostracode valve geochemistry sr ca 18o suggests significant changes in early vs late holocene hydrochemistry either as changes in salinity or in the seasonality of precipitation harmonizing the autecological and geochemical data from gorgo basso suggests the latter was more likely with relatively more late holocene precipitation falling during the spring summer and fall than winter compared to the early holocene our ostracode inferred paleosalinity data indicate that moisture availability did not decline during the late holocene in the central mediterranean region instead moisture availability was lowest during the early holocene and most abundant during the late holocene

climate changes reconstructed from a glacial lake in high central asia over the past two millennia abstract climatic changes in arid central asia aca over the past two millennia have been widely concerned however less attention has been paid to those in the high central asia hca where the asian water tower nurtures the numerous oases by glacier and or snow melt here we present a new reconstruction of the temperature and precipitation change over the past two millennia based on grain size of a well dated glacial lake sediment core in the central of southern tianshan mountains the results show that the glacial lake catchment has experienced cold wet climate conditions during the dark age cold period 300 600 ad dacp and the little ice age 1300 1870 ad lia whereas warm dry conditions during the medieval warm period 700 1270 ad mwp integration of our results with those of previously published lake sediment records stalagmite 18o records ice core net accumulation rates tree ring based temperature reconstructions and mountain glacier activities suggest that there has a broadly similar hydroclimatic pattern over the hca areas on centennial time scale during the past two millennia comparison between hydroclimatic pattern of the hca and that of the aca areas suggests a prevailing warm dry and cold wet hydroclimatic pattern over the whole westerlies dominated central asia areas during the past two millennia we argue that the position and intensity of the westerlies which are closely related to the phase of the north atlantic oscillation nao and the strength of the siberian high pressure sh could have jointly modulated the late holocene central asia hydroclimatic changes

nao signal recorded in the stable isotopes of greenland ice cores 1 the winter 18o signal is extracted from 7 greenland ice cores covering the past 700 years to filter out noise and local variations in the 7 isotope records a principal component analysis is carried out on the ice core data a comparison between the time series of the first principal component pc1 with 67 years of winter december to march temperature measurements from 3 southern greenland synoptic stations shows highly significant correlations southern greenland winter temperatures are known to be greatly influenced by the north atlantic oscillation nao a good proxy for southern greenland temperatures is therefore expected to reveal at least parts of the nao signal it is shown that the pc1 time series indeed is significantly correlated to the nao during the winter months the inclusion of ice core winter season 18o time series in future multiproxy nao reconstructions is therefore recommended

δ 18 o values of cave drip water a promising proxy for the reconstruction of the north atlantic oscillation we present cave monitoring data and two drip water 18o models for the herbstlabyrinth adventhohle hl cave system germany winter climate of the cave region is influenced by the north atlantic oscillation nao as documented by the positive correlations between winter temperature winter rainfall 18o values and the winter nao index cave monitoring data show that recharge of the aquifer at the hl cave system mainly occurs during winter months confirming our drip water model which calculates recharge as the difference between precipitation and potential evapo transpiration cave drip water from the hl cave system should thus be a sensitive proxy for reconstruction of the nao the infiltration models accounting for mixing effects occurring in the karst aquifer show a very good agreement with the monitoring data comparison of the modelled and the monitored drip water 18o values suggests a mean residence time of the water in the aquifer of 12 months and a transmission time of 10 months using these parameters a long term dataset from the nearby meteorological station frankfurt am main and the rainfall 18o data from our monitoring program we model the 18o values of the cave drip water for the last 144 years despite of the favourable conditions of the hl cave system for nao reconstruction the modelled drip water 18o time series only shows a moderate correlation with the winter nao index r 0 33 the major reason for the relatively low correlation is the substantial contribution of precipitation from the remaining seasons to the drip water for instance due to heavy precipitation events occurring during summer these rainfall events bias the seasonality of infiltration and weaken the winter nao signal recorded in the drip water 18o values reconstruction of the nao from speleothems is thus challenging in particular considering further complications arising from chronological uncertainties and calcite precipitation under conditions deviating from isotopic equilibrium these problems may at least in part be avoided by multi proxy studies of annually laminated stalagmites

norwegian fjord sediments reveal nao related winter temperature and precipitation changes of the past 2800 years abstract the north atlantic oscillation nao is the leading mode of atmospheric circulation variability in the north atlantic region associated shifts of storm tracks precipitation and temperature patterns affect energy supply and demand fisheries and agricultural as well as marine and terrestrial ecological dynamics long term nao records are crucial to better understand its response to climate forcing factors and assess predictability and shifts associated with ongoing climate change a recent study of instrumental time series revealed nao as main factor for a strong relation between winter temperature precipitation and river discharge in central norway over the past 50 years here we compare geochemical measurements with instrumental data and show that primary productivity recorded in central norwegian fjord sediments is sensitive to nao variability this observation is used to calibrate paleoproductivity changes to a 500 year reconstruction of winter nao luterbacher et al 2001 conditioned on a stationary relation between our climate proxy and the nao we establish a first high resolution nao proxy record nao tfj from marine sediments covering the past 2800 years the nao tfj shows distinct co variability with climate changes over greenland solar activity and northern hemisphere glacier dynamics as well as climatically associated paleo demographic trends the here presented climate record shows that fjord sediments provide crucial information for an improved understanding of the linkages between atmospheric circulation solar and oceanic forcing factors

reconstructed centennial variability of late holocene storminess from cors fochno wales uk future anthropogenic climate forcing is forecast to increase storm intensity and frequency over northern europe due to a northward shift of the storm tracks and a positive north atlantic oscillation however understanding the significance of such a change is difficult because the natural variability of storminess beyond the range of instrumental data is poorly known here we present a decadal resolution record of storminess covering the late holocene based on a 4 m long core taken from the peat bog of cors fochno in mid wales uk storminess is indicated by variations in the minerogenic content as well as bromine deposited from sea spray twelve episodes of enhanced storm activity are identified during the last 4 5 cal ka bp although the age model gives some uncertainty in the timings it appears that storminess increased at the onset and close of north atlantic cold events associated with oceanic changes with reduced storm activity at their peak cors fochno is strongly influenced by westerly moving storms so it is suggested that the patterns were due to variations in the intensity of westerly airflow and atmospheric circulation during times when the latitudinal temperature gradient was steepened

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

investigating the maximum resolution of µxrf core scanners a 1800 year storminess reconstruction from the outer hebrides scotland uk micro x ray fluorescence xrf core scanning is capable of measuring the elemental composition of lake sediment at sub millimetre resolution but bioturbation and physical mixing may degrade envir

upper water mass variability in the anegada jungfern passage ne caribbean during the last 11 100 cal yr using qualitative and quantitative analyses of planktonic foraminifera assemblages 18o measurements mg ca temperature relationship globigerinoides ruber pink sensu stricto data and sea surface temperatures ssts derived from artificial neural network ann transfer functions a reconstruction was made of upper water mass variability in the anegada jungfern passage ajp northeastern caribbean sea over the last c 11 100 years our record is based on the study of two marine sediment cores and reveals three main circulation stages during the holocene in the early holocene 11 100 6300 cal yr bp ann based sst estimations indicate moderately cooler than present winter condition in the ne caribbean with ssts of 25 5 c these conditions presumably reflect advection of well mixed upper water masses from the guyana upwelling area associated with a strong atlantic meridional overturning circulation amoc and enhanced trade wind activity linked to a more northerly location of the inter tropical convergence zone itcz between 6300 and 3700 cal yr bp a relative warming of winter ssts 26 5 c was probably related to a weaker circulation and upper water mass mixing because of less intense trade wind activity as the itcz moved southwards from 3700 cal yr bp to the present the region was characterised by small seasonal sst variations and generally stable winter and summer ssts the data suggest a minor shift in the sub surface inflow pattern during the last 2000 years possibly related to changes in northern hemisphere large scale atmospheric circulation also observed at higher latitude the ann based temperature pattern is supported by fluctuations in the mg ca derived temperature record although temperature maxima derived from the mg ca ratio appear anomalously high on a holocene timescale we conclude that the northeastern caribbean sst and circulation regime have been mainly dependent on the position of the itcz which in turn is controlled by changes in hemispheric solar insolation

detrital events and hydroclimate variability in the romanian carpathians during the mid to late holocene the romanian carpathians are located at the confluence of three major atmospheric pressure fields the north atlantic the mediterranean and the siberian despite its importance for understanding past human impact and climate change high resolution palaeoenvironmental reconstructions of holocene hydroclimate variability and in particular records of extreme precipitation events in the area are rare here we present a 7500 year long high resolution record of past climatic change and human impact recorded in a peatbog from the southern carpathians integrating palynological geochemical and sedimentological proxies natural climate fluctuations appear to be dominant until 4500 years before present yr bp followed by increasing importance of human impact sedimentological and geochemical analyses document regular minerogenic deposition within the bog linked to periods of high precipitation such minerogenic depositional events began 4000 yr bp with increased depositional rates during the medieval warm period mwp the little ice age lia and during periods of societal upheaval e g the roman conquest of dacia the timing of minerogenic events appears to indicate a teleconnection between major shifts in north atlantic oscillation nao and hydroclimate variability in southeastern europe with increased minerogenic deposition correlating to low nao index values by linking the minerogenic deposition to precipitation variability we state that this link persists throughout the mid to late holocene

millennial scale cycles of aridity as a driver of human occupancy in central spain human settlements around the fluvial wetland of las tablas de daimiel central spain have been related to the water availability in this area for nearly 5500 years however the relationship of the hydrology of the wetland to climate change remains uncertain whilst archaeological and pollen data provide contradictory arguments statistical empirical mode decomposition of geochemical data from core s 1 reveals arid periods ca 1 8 cal ka bp ca 3 3 cal ka bp and ca 5 5 cal ka bp between which periods both bronze age and iberian roman settlements developed these periods can be identified in other records of the iberian peninsula and around the western mediterranean comparison of these records points to a complex spatial pattern that evolved in time and despite a number of forcings volcanism solar activity atmosphere ocean interactions being invoked to explain such periods there is no clear mechanism to explain their spatial pattern and the changes that have taken place since 2 5 ka bp

surface textures and dynamics of the 2005 lava dome at shiveluch volcano kamchatka shiveluch is one of the largest and most active andesitic volcanoes of the kuril kamchatka arc it commonly alternates between vulcanian explosive eruptions and periods of dome growth and subsequent dome collapse driven block and ash flows the volcano was in an extended period of heightened activity for most of the period 2004 2010 we examined this activity in detail using thermal infrared tir remote sensing as part of the urgent request protocol urp program of the advanced spaceborne thermal emission and reflection radiometer aster instrument and confirmed the results with ground based photography and airborne tir camera data high spatial resolution tir images were collected during both daytime and nighttime satellite overpasses prior to and following the large explosive event eruption of 27 february 2005 and the dome growth that followed during a field campaign in august 2005 a helicopter overflight designed to acquire visible and tir data of the active dome was performed this was a nadir looking low altitude overflight and the first ever of shiveluch volcano involving non russian scientists the image data revealed an active crease structure in the center of the dome with a distinctly different crescent shaped high temperature 380 c zone roughly perpendicular to the crease in order to provide a time context and estimate extrusion rates the airborne data were compared to the spaceborne aster data and long distance ground based photography of the dome acquired by our russian colleagues the presence of a crease structure and the complex thermal pattern on the surface were both unexpected discoveries that reveal the way in which exogenous dome growth was occurring at the time this highly active period at shiveluch provides a unique example to better understand silicic lava dome growth using tir data the results also demonstrate a straightforward approach for fusing ground air and spaceborne image data which could be applied to other active domes around the world

abrupt holocene climate change as an important factor for human migration in west greenland west greenland has had multiple episodes of human colonization and cultural transitions over the past 4 500 y however the explanations for these large scale human migrations are varied including climatic factors resistance to adaptation economic marginalization mercantile exploration and hostile neighborhood interactions evaluating the potential role of climate change is complicated by the lack of quantitative paleoclimate reconstructions near settlement areas and by the relative stability of holocene temperature derived from ice cores atop the greenland ice sheet here we present high resolution records of temperature over the past 5 600 y based on alkenone unsaturation in sediments of two lakes in west greenland we find that major temperature changes in the past 4 500 y occurred abruptly within decades and were coeval in timing with the archaeological records of settlement and abandonment of the saqqaq dorset and norse cultures which suggests that abrupt temperature changes profoundly impacted human civilization in the region temperature variations in west greenland display an antiphased relationship to temperature changes in ireland over centennial to millennial timescales resembling the interannual to multidecadal temperature seesaw associated with the north atlantic oscillation

persistent positive north atlantic oscillation mode dominated the medieval climate anomaly the medieval climate anomaly mca was the most recent pre industrial era warm interval of european climate yet its driving mechanisms remain uncertain we present here a 947 year long multidecadal north atlantic oscillation nao reconstruction and find a persistent positive nao during the mca supplementary reconstructions based on climate model results and proxy data indicate a clear shift to weaker nao conditions into the little ice age lia globally distributed proxy data suggest that this nao shift is one aspect of a global mca lia climate transition that probably was coupled to prevailing la nina like conditions amplified by an intensified atlantic meridional overturning circulation during the mca

holocene vegetation history and quantitative climate reconstructions in a high elevation oceanic district of the italian alps evidence for a middle to late holocene precipitation increase abstract we reconstructed the vegetation and climate history during the last 10 ka in a high elevation sedimentary record armentarga peat bog 2345 m asl on the southern flank of the european alps through the study of paleoecological and sedimentary proxies we included a specific elevational transect of modern pollen accumulation rates for timberline forming trees and shrubs alnus viridis pinus sylvestris mugo pinus cembra quantitative reconstructions of july temperature and annual precipitation were obtained by applying numerical transfer functions built on an extensive pollen climate calibration set from the european alps changes in elevational vegetation arrangement were primarily driven by phases of precipitation increase and to a lesser extent by millennial scale temperature changes already known from glacier timberline chironomids and speleothem records at alpine scale changes in pollen inferred annual precipitation occurred in three main steps an early holocene moderately humid phase is mirrored by the early spread of alnus viridis dwarf forests precipitation started to increase at 6 2 ka cal bp a further prominent step forward at the middle to late holocene transition led to the high values of snowfall and runoff characterizing today s oceanic elevational climates of the outer italian alps this change led to timberline depression and grassland expansion locally human impact was weak at the late neolithic bronze age transition this event correlates with lake level oscillations in the northern mediterranean borderlands suggesting intensification of southern air masses conveyed by tyrrhenian cyclones towards windward districts

holocene climate change in arctic canada and greenland abstract this synthesis paper summarizes published proxy climate evidence showing the spatial and temporal pattern of climate change through the holocene in arctic canada and greenland our synthesis includes 47 records from a recently published database of highly resolved holocene paleoclimate time series from the arctic sundqvist et al 2014 we analyze the temperature histories represented by the database and compare them with paleoclimate and environmental information from 54 additional published records mostly from datasets that did not fit the selection criteria for the arctic holocene database combined we review evidence from a variety of proxy archives including glaciers ice cores and glacial geomorphology lake sediments peat sequences and coastal and deep marine sediments the temperature sensitive records indicate more consistent and earlier holocene warmth in the north and east and a more diffuse and later holocene thermal maximum in the south and west principal components analysis reveals two dominant holocene trends one with early holocene warmth followed by cooling in the middle holocene the other with a broader period of warmth in the middle holocene followed by cooling in the late holocene the temperature decrease from the warmest to the coolest portions of the holocene is 3 0 1 0 c on average n 11 sites the greenland ice sheet retracted to its minimum extent between 5 and 3 ka consistent with many sites from around greenland depicting a switch from warm to cool conditions around that time the spatial pattern of temperature change through the holocene was likely driven by the decrease in northern latitude summer insolation through the holocene the varied influence of waning ice sheets in the early holocene and the variable influx of atlantic water into the study region

aridity events during the last 4000 years in western mediterranean marshes almenara and benicasim marshes e spain abstract facies and geochemical analysis applied to marsh deposits are useful proxies for the reconstruction of aridity for the last millennia the comparison of facies and geochemical records among cores from the almenara and benicasim marshes allows to identify changes in water level si al al ca and salinity of the feeding waters mg al na al s al these changes in turn represent fluctuations in the position of the saline fresh groundwater boundary which can be related to variations in sea level and rainfall for the last 4000 years three events recording higher salinity conditions ca 3 4 ka bp ca 3 ka bp and ca 1 8 ka bp are noticeable in the record comparison to other studies around the western mediterranean basin allows us to correlate these events to arid episodes and to identify their forcing mechanisms these aridity events are correlative to small falls in solar activity and surface sea temperature sst during positive north atlantic oscillation nao periods despite the small magnitude of these changes the sensitivity of the system amplified the result providing a conspicuous signal

magnetic and geochemical signatures of flood layers in a lake system river floods holds the capasity to erode and transport sediments that are deposited whenever the discharge is redused in catchments that are subjected to repeated flooding downstream lakes can therefore contain a record of past events across multiple timescales high resolution core scanning analyses such as x ray fluorescence xrf scanning and magnetic susceptibility ms provide data that are frequently used to detect flood layers in soft sediment archives such as lakes fjords and ocean basins deposits of past floods also can potentially reveal information about the evolution of flood events as well as source area here we explore ways in which subtle variability in high resolution data can be utilized and subsequently vetted by high precision measurements in order to delineate the copious information that can be extracted from soft sediment records by combining magnetic hysteresis measurements and first order reversal curves forcs with inductively coupled plasma optical emission spectrometer icp oes measurements of chemical elements on 36 samples questions about flood dynamics and variability are raised and also sources of noise in high resolution scanning techniques are discussed specifically we show that a lake flood record from southern norway containing 92 floods distributed over 10 000 years can be sub divided into two groups of floods that were generated either by spring snow melting intense summer rainstorms or a combination of both the temporal evolution of this pattern shows a marked shift towards spring floods around 2000 years ago compared to the earlier part of the record this article is protected by copyright all rights reserved

the impact of late holocene land use change climate variability and sea level rise on carbon storage in tidal freshwater wetlands on the southeastern united states coastal plain this study examines holocene impacts of changes in climate land use and sea level rise slr on sediment accretion carbon accumulation rates car and vegetation along a transect of tidal freshwater forested wetlands tffw to oligohaline marsh along the waccamaw river south carolina 4 sites and along the savannah river georgia 4 sites we use pollen plant macrofossils accretion and car from cores spanning the last 1500 6000 years to test the hypothesis that tffw have remained stable throughout the late holocene and that marshes transitioned from tffw during elevated slr during the medieval climate anomaly with further transformation resulting from colonial land use change results show low and stable accretion and car through much of the holocene despite moderate changes associated with holocene paleoclimate in all records the largest observed change occurred within the last 400 years driven by colonial land clearance shifting terrigenous sediment into riparian wetlands resulting in order of magnitude increases in accretion and c accumulation the oligohaline marshes transitioned from tffw 300 500 years ago coincident with colonial land clearance post colonial decreases in car and accretion occur because of watershed reforestation over the last century all sites show evidence of recent decades to century swamp forest decline due to increasing salinity and tidal inundation from slr this study suggests that allochthonous sediment input during colonialization helped maintain tffw but that current slr rates are too high for tffw to persist although higher accretion rates in oligohaline marshes increases the resilience of tidal wetlands as they transition from tffw to marsh

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

holocene glacier and climate fluctuations of the maritime ice cap hogtuvbreen northern norway holocene fluctuations of a small outlet glacier from the ice cap hogtuvbreen at 65 n in coastal northern norway are reconstructed based on distal glacier fed lake sediments complemented by a moraine sequence dated by lichenometry glaciers respond to changes in accumulation season precipitation ablation season temperature and redistribution of snow by wind hence reconstructions of glacier fluctuations based on distal glacier fed lakes may give detailed information about past climate at a potentially high temporal resolution yet the importance of any of these climate components is often difficult to solve here we apply the liestol relationship which expresses the relationship between ablation season temperature and annual accumulation of snow at the equilibrium line altitude ela to the reconstructed local temperature precipitation wind ela tpw ela to infer the relative importance of winter balance and ablation season temperature as causes of reconstructed glacier variation the reconstruct

solar forcing as an important trigger for west greenland sea ice variability over the last millennium abstract arctic sea ice represents an important component of the climate system and the present reduction of sea ice in the arctic is of major concern despite its importance little is known about past changes in sea ice cover and the underlying forcing mechanisms here we use diatom assemblages from a marine sediment core collected from the west greenland shelf to reconstruct changes in sea ice cover over the last millennium the proxy based reconstruction demonstrates a generally strong link between changes in sea ice cover and solar variability during the last millennium weaker or stronger solar forcing may result in the increase or decrease in sea ice cover west of greenland in addition model simulations show that variations in solar activity not only affect local sea ice formation but also control the sea ice transport from the arctic ocean through a sea ice ocean atmosphere feedback mechanism the role of solar forcing however appears to have been more ambiguous during an interval around ad 1500 after the transition from the medieval climate anomaly to the little ice age likely to be driven by a range of factors

impact of extended nao buoyancy forcing on the subpolar north atlantic and climate variability over the last millenium 1 we examine the impact of forcing a regional eddy permitting ocean model of the subpolar north atlantic with anomalous buoyancy fluxes corresponding to extended extreme states of the north atlantic oscillation nao we find a weakened enhanced meridional overturning circulation moc in our low high nao simulations such results may be consistent with ideas that suggest the medieval warm period mwp and the little ice age are associated with periods when the nao is predominantly in one phase our results also show multidecadal moc variability with a period of 70 years in our high nao simulation in comparison to an equilibrium like circulation under low nao related forcing a less stable climatic state is therefore suggested to occur under high nao forcing which may be consistent with ideas that suggest the warming associated with the mwp did not occur synchronously over the north atlantic the variability appears to be brought about by internal oceanic processes

modes of climate variability synthesis and review of proxy based reconstructions through the holocene abstract modes of climate variability affect global and regional climates on different spatio temporal scales and they have important impacts on human activities and ecosystems as these modes are a useful tool for simplifying the understanding of the climate system it is crucial that we gain improved knowledge of their long term past evolution and interactions over time to contextualise their present and future behaviour we review the literature focused on proxy based reconstructions of modes of climate variability during the holocene i e the last 11 7 thousand years with a special emphasis on i proxy based reconstruction methods ii available proxy based reconstructions of the main modes of variability i e el nino southern oscillation pacific decadal variability atlantic multidecadal variability the north atlantic oscillation the southern annular mode and the indian ocean dipole iii major interactions between these modes and iv external forcing mechanisms related to the evolution of these modes this review shows that modes of variability can be reconstructed using proxy based records from a wide range of natural archives but these reconstructions are scarce beyond the last millennium partly due to the lack of robust chronologies with reduced dating uncertainties technical issues related to proxy calibration and difficulty elucidating their stationary impact or not on regional climates over time while for each mode the available reconstructions tend to agree at mutidecadal timescales they show notable disagreement on shorter timescales beyond the instrumental period the reviewed evidence suggests that the intrinsic variability of modes can be modulated by external forcing such as orbital solar volcanic and anthropogenic forcing the review also highlights some modes experience higher variability over the instrumental period which is partly ascribed to anthropogenic forcing these features stress the paramount importance of further studying their past variations using long climate proxy records for the progress of climate science

8000 years of north atlantic storminess reconstructed from a scottish peat record implications for holocene atmospheric circulation patterns in western europe north atlantic storminess can affect human settlements infrastructure and transport links all of which strongly impact local national and global economies an increase in storm frequency and intensity is predicted over the northeast atlantic in the 21st century because of a northward shift in storm tracks and a persistently positive north atlantic oscillation nao driven by recent atmospheric warming although documentary records of north atlantic storminess exist these are generally limited to the last c 1000 2000 years this paper presents a continuous high resolution proxy record of storminess spanning the last 8000 years from a 6 m long core taken from a peat bog in northern scotland bromine concentrations in the peat derived from sea spray are used to reconstruct storm frequency and storm intensity and mire surface wetness is used as an indicator of longer term climate shifts the results suggest a relationship between positive phases of the nao and increased north atlantic storminess however subtle differences between bromine concentrations and mire surface wetness suggest that high intensity but perhaps less frequent periods of storminess are not necessarily associated with a wetter climate

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

winter precipitation changes during the medieval climate anomaly and the little ice age in arid central asia abstract the strength of the north atlantic oscillation nao is considered to be the main driver of climate changes over the european and western asian continents throughout the last millennium for example the predominantly warm medieval climate anomaly mca and the following cold period of the little ice age lia over europe have been associated with long lasting phases with a positive and negative nao index its climatic imprint is especially pronounced in european winter seasons however little is known about the influence of nao with respect to its eastern extent over the eurasian continent here we present speleothem records 13c 18o and sr ca from the southern rim of fergana basin central asia revealing annually resolved past climate variations during the last millennium the age control of the stalagmite relies on radiocarbon dating as large amounts of detrital material inhibit accurate 230th dating present day calcification of the stalagmite is most effective during spring when the cave atmosphere and elevated water supply by snow melting and high amount of spring precipitation provide optimal conditions seasonal precipitation variations cause changes of the stable isotope and sr ca compositions the simultaneous changes in these geochemical proxies however give also evidence for fractionation processes in the cave by disentangling both processes we demonstrate that the amount of winter precipitation during the mca was generally higher than during the lia which is in line with climatic changes linked to the nao index but opposite to the higher mountain records of central asia several events of strongly reduced winter precipitation are observed during the lia in central asia these dry winter events can be related to phases of a strong negative nao index and all results reveal that winter precipitation over the central eurasian continent is tightly linked to atmospheric nao modes by the westerly wind systems

variability of the north atlantic oscillation over the past 5 200 years the north atlantic oscillation influences climate in the arctic region and northern europe reconstructions of circulation patterns associated with the north atlantic oscillation from a 5 200 year long lake sediment record suggest that the atmospheric circulation responded to significant transitions in northern hemisphere climate

coherency of late holocene european speleothem δ18o records linked to north atlantic ocean circulation speleothem 18o records provide valuable information about past continental environmental and climatic conditions although their interpretation is often not straightforward here we evaluate a compilation of late holocene speleothem 18o records using a monte carlo based principal component analysis mc pca method that accounts for uncertainties in individual speleothem age models and for the variable temporal resolution of each 18o record the mc pca approach permits not only the identification of temporally coherent changes in speleothem 18o it also facilitates their graphical depiction and evaluation of their spatial coherency the mc pca method was applied to 11 holocene speleothem 18o records that span most of the european continent apart from the circum mediterranean region we observe a common shared mode of speleothem 18o variability that suggests millennial scale coherency and cyclicity during the last 4 5 ka these changes are likely caused by variability in atmospheric circulation akin to that associated with the north atlantic oscillation reflecting meridionally shifted westerlies we argue that these common large scale variations in european speleothem 18o records are in phase with changes in the north atlantic ocean circulation indicated by the vigour of the iceland scotland overflow water isow the strength of the subpolar gyre spg and an ocean stacked north atlantic ice rafted debris ird index based on a recent modelling study we conclude that these changes in the north atlantic circulation history may be caused by wind stress on the ocean surface driven by shifted westerlies however the mechanisms that ultimately force the westerlies remain unclear

high resolution holocene climate and hydrological variability from two major mediterranean deltas nile and rhone high resolution records of sea surface temperatures ssts and terrestrial n alkanes terr alkanes combined with pollen from the same sedimentary sequences were generated to assess variations in the nile river discharge over the holocene these independent proxy records indicate a period of wetter conditions in the nile watershed during the early holocene consistent with insolation driven enhanced monsoon precipitation known as the african humid period ahp the detection of a dry episode around 9200 yr bp in the terr alkane and pollen time series suggests a temporary weakening of the monsoon intensity most probably triggered by extratropical cooling in the north atlantic an interval of c4 grass expansion between 8800 and 8400 yr bp was also evidenced from the terr alkane distribution and confirmed by palynological data ssts of the coastal waters off the nile delta reveal strong fluctuations in the early holocene followed by a slight warming and two pronounced cold intervals around 3500 yr bp and 150

reconstruction of mid to late holocene winter temperatures in the skagerrak region using benthic foraminiferal mg ca and δ18o reconstruction of skagerrak deep water renewal is used to assess regional changes in winter thermal conditions over the past 6800 years changes in winter climate conditions from the skagerrak region are in turn linked to shifts in holocene large scale atmospheric circulation patterns prevailing over northern europe we use melonis barleeanus mg ca from two sediment cores in the central skagerrak to reconstruct temperature of skagerrak intermediate water representing the warm season temperature variability and deep water for monitoring skagerrak deep water renewal reflecting the winter temperature variability in addition m barleeanus 18o is used from the deeper core to reconstruct salinity also monitoring the deep water renewal our results show that the skagerrak deep water experienced phases of particularly enhanced renewal during the mid holocene reflecting severe winter conditions followed by a general shift to reduced renewal as a consequence of milder winter conditions over the north sea a

paleoceanographical development off sisimiut west greenland during the mid and late holocene a multiproxy study abstract a multiproxy study of paleoceanographic and climatic changes in holsteinsborg dyb on the west greenland shelf shows that the area is sensitive to variations in the mixing between the two components of the west greenland current i e the atlantic water of the irminger current and the polar water from the east greenland current a seismic profile illustrates the general development in the area since the deglaciation and analyses of benthic foraminifera stable isotopes 18 o and 13 c and x ray fluorescence elemental counts in two cores covering ca 6650 and 1100 years respectively provide details on the oceanographic changes during the mid and late holocene the chronology is based on 210 pb and ams 14 c age determinations during the time interval of 6650 1600 cal yr bp the bottom waters are characterized by the presence of modified atlantic water with some influence of meltwater either local or regional depleted 18 o values and relatively high si fe ratio suggest warmer conditions from 6650 to 3800 cal yr bp corresponding in time to part of the holocene thermal maximum followed by a general slight cooling with some fluctuation after 3800 cal yr bp at 1600 cal yr bp there is an abrupt change in almost all investigated proxies the foraminiferal assemblage and the 18 o values suggest cold low salinity bottom water conditions and there is indication of seasonal sea ice cover between 1400 and 1200 cal yr bp corresponding in time to the dark ages cold period and to a minimum in solar irradiance from ca 1150 to 580 cal yr bp a time interval equivalent to the historical medieval warm period mwp the foraminiferal fauna remains indicative of cold low salinity bottom waters but without any indication of sea ice cover the influence of polar water meltwater at the sea floor during the mwp is thought to be a result of enhanced mixing of the two components of the west greenland current caused by an increase in wind activity during generally positive north atlantic oscillation conditions maybe combined with a displacement of the irminger current pathway to the outer shelf during the little ice age lia there is a strong influence of modified atlantic water at the sea floor related to sea ice formation and stratification of the water column after ad 1900 the benthic foraminiferal assemblage suggests a slight increase in polar water influence and thereby mixing even though the environment is not much different from that during the lia

observed feedback between winter sea ice and the north atlantic oscillation abstract feedback between the north atlantic oscillation nao and winter sea ice variability is detected and quantified using approximately 30 years of observations a vector autoregressive model var and testable definitions of granger causality and feedback sea ice variability is quantified based on the leading empirical orthogonal function of sea ice concentration over the north atlantic the greenland sea ice dipole gsd which in its positive polarity has anomalously high sea ice concentrations in the labrador sea region to the southwest of greenland and low sea ice concentrations in the barents sea region to the northeast of greenland in weekly data for december through april the var indicates that nao index n anomalies cause like signed anomalies of the standardized gsd index g and that g anomalies in turn cause oppositely signed anomalies of n this negative feedback process operates explicitly on lags of up to four weeks in the var but can generate more persistent effects because o

a well verified multiproxy reconstruction of the winter north atlantic oscillation index since a d 1400 abstract a new well verified multiproxy reconstruction of the winter north atlantic oscillation nao index is described that can be used to examine the variability of the nao prior to twentieth century greenhouse forcing it covers the period a d 1400 1979 and successfully verifies against independent estimates of the winter nao index from european instrumental and noninstrumental data as far back as 1500 the best validation occurs at interannual timescales and the weakest at multidecadal periods this result is a significant improvement over previous proxy based estimates which often failed to verify prior to 1850 and is related to the use of an extended reconstruction model calibration period that reduced an apparent bias in selected proxies associated with the impact of anomalous twentieth century winter nao variability on climate teleconnections over north atlantic sector land areas although twentieth century nao variability is somewhat unusual comparable periods of persistent positive phase

the north atlantic oscillation and its imprint on precipitation and ice accumulation in greenland interannual to decadal fluctuations in net precipitation and ice accumulation are examined over greenland it is shown that in western greenland these fluctuations are correlated with the north atlantic oscillation the analysis is based on two complementary data sources a highly resolved net precipitation and accumulation history over 15 years derived form the reanalysis data of the european centre for medium range weather forecasts and a composite ice accumulation record representative for the western part of central greenland it is suggested that western greenland snow accumulation is a good proxy for the nao index with the potential for the reconstruction of a long time series

appraising timing response of paleoenvironmental proxies to the bond cycle in the western mediterranean over the last 20 kyr the timing of climate responses to the bond cycle is investigated in the western mediterranean periodicities had been previously reported in a marine sediment record from this region spanning the last 20 kyr and registered by diverse paleoenvironmental proxies in particular those associated with terrigenous input redox conditions productivity sea surface temperature sst and salinity further cross spectral analyses on these time series reveal leads lags in the 1400 year climate cycle considering as reference a terrigenous input proxy the k al ratio all the paleoenvironmental proxies displayed time shifts varying from ca 700 year to ca 350 year sst and salinity variations show a first leaded response with the inflow of cold and less salty atlantic waters followed by a time lead of 525 year progresively arid conditions with an increase of eolian dust transport to the area given by the zr al signal are observed the intensification of dust transport could have triggered a latest biological response lead by 350 year with an increase of productivity as suggested by the ba al ratio lastly changes in the mediterranean thermohaline circulation indicated by a selected redox proxy the u th ratio are observed these results support that the oceanic response triggered the atmospheric response to the bond cycle in the western mediterranean changes in the north atlantic oscillation mode and in the inter tropical convergence zone migrations with variations in the monsoon activity or saharan winds system are considered as main forcing mechanisms with a complex relationship of the involved phenomena

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

climatic and hydrological variations during the past 8000 years in northern xinjiang of china and the associated mechanisms abstract this paper reviews the published literature regarding the climatic and hydrological variations of the past 8000 years in the northern xinjiang of china in hope that some of the controversies surrounding the holocene climate history can be reconciled based on the well tested premise that the overall relationship between the a c ratios and the bioclimates in arid and semi arid areas of china still holds we compared the a c ratio based smi standardized moisture index of five selected lacustrine sequences our comparison shows that the regional average smi had a general rising trend and the rising trend was reasonably corroborated by other pollen proxies the rising trend can be explained by invoking its climatic linkage with the north atlantic ocean and a possible linkage with enso is an additional or an alternative mechanism for explaining the rising trend the nearly parallel rising trends of seven 18o indicated ssi curves standardized salinity index mean that the lake water salinity has been rising since 8 0 cal ka bp the rising trend can be explained by invoking the holocene variations in the areal extent of ice covers in the tianshan mountains and the altay mountains that is the persistent shrinking of the ice extent in the mountains generated less and less melting water supplies to the lakes and thus resulted in saltier and saltier waters in the lakes the contradiction between the increasing trend of the basin wide moisture and the increasing trend of the lake water salinity can be reconciled as follows the increasing trend of the precipitation accompanied by the lowering tend of the temperature might have increasingly enhanced the effective soil moisture in northern xinjiang but the increase in the basin wide moisture was not enough to compensate for the decrease in the lake inflowing water resulted from the shrinkage of ice covered areas in the mountains

sub sea surface temperatures in the polar north atlantic during the holocene planktic foraminiferal mg ca temperature reconstructions holocene sea surface temperatures in the eastern fram strait are reconstructed based on mg ca ratios measured on the planktic foraminifer neogloboquadrina pachyderma sin the reconstructed sub sea surface temperatures ssstmg ca fluctuate markedly during the earliest holocene at 11 7 and 10 5 kyr bp this is probably in response to the varying presence of sea ice and deglacial meltwater between 10 5 7 9 kyr bp the ssstmg ca values are relatively high 4 c and more stable reflecting high insolation and intensified poleward advection of atlantic water after 7 9 kyr bp the ssstmg ca values decline to an average of 3 c throughout the mid holocene these changes can be attributed to a combined effect of reduced poleward oceanic heat advection and a decline in insolation as well as a gradually increased influence of eastward migrating arctic water the ssstmg ca values increase and vary between 2 1 c and 5 8 c from 2 7 kyr bp to the present this warming is in contrast to declining late holocene in

multi decadal periods of enhanced aeolian activity on the north eastern tibet plateau during the last 2ka abstract the north eastern tibetan plateau is regarded as key area for the understanding of the holocene paleoclimate in central asia during the last decade a special emphasis has been placed on multi decadal to millennial scale climate fluctuations especially in the context of the recent climate change however most reconstructions are based on lake sediments tree rings and speleothems whereas only little information from terrestrial archives is included this study presents multi decadal scale climate fluctuations based on optical stimulated luminescence osl ages from aeolian sediments from three catchment areas six phases of enhanced aeolian accumulation during the last 2000 years each lasting around 80 200 years were identified the first three phases 1630 1725 ce 1450 1530 ce and 1250 1350 ce occurred during the little ice age the other three 750 950 ce 390 540 ce 50 225 ce during the so called dark ages cooling aeolian processes were strongly reduced during the medieval climate anomaly a comparison with other proxy records indicates that the formation of aeolian archives on the north eastern tibetan plateau during the late holocene is facilitated by cool and dry climate conditions during times of weaker asian summer monsoon and probably enhanced westerlies the results show that short term climate fluctuations can be reconstructed from non continuous and heterogeneous terrestrial archives in a semi arid environment provided a sufficient number of osl ages from aeolian sediments is available

centennial scale vegetation and north atlantic oscillation changes during the late holocene in the southern iberia high reso ce to lution pollen analysis charcoal non pollen palynomorphs and magnetic susceptibility have been analyzed in the sediment record of a peat bog in sierra nevada in southern iberia the study of these proxies provided the reconstruction of vegetation climate fire and human activity of the last 4500 cal yr bp a progressive trend towards aridification during the late holocene is observed in this record this trend is interrupted by millennial and centennial scale variability of relatively more humid and arid periods arid conditions are recorded between 4000 and 3100 cal yr bp being characterized by a decline in arboreal pollen and with a spike in magnetic susceptibility this is followed by a relatively humid period from 3100 to 1600 cal yr bp coinciding partially with the iberian roman humid period and is indicated by the increase of pinus and the decrease in xerophytic taxa the last 1500 cal yr bp are characterized by several centennial scale climatic oscillations generally arid conditions from 450 to 1300 ce depicted by a decrease in pinus and an increase in artemisia comprise the dark ages and the medieval climate anomaly since 1300 to 1850 ce pronounced oscillations occur between relatively humid and arid conditions four periods depicted by relatively higher pinus coinciding with the beginning and end of the little ice age are interrupted by three arid events characterized by an increase in artemisia these alternating arid and humid shifts could be explained by centennial scale changes in the north atlantic oscillation and solar activity

biomarkers in coastal marshlands environmental characteristics of the mazarron basin during the middle pleistocene mis 7 and holocene mis 1 abstract we reconstructed the paleoenvironmental conditions of the mazarron basin during mis 7 and mis 1 based on their alkane and fatty acid contents their mineralogy and the fossil content of an amino acid dated sediment sequence the n alkane and fatty acid indices proved to be excellent paleoenvironmental proxies for studying the paleo hydrogeological and paleoclimatological evolution of this marshland three geochemical units gus were identified from the abundance of the c25 n alkane and the acl tarhc and paq values confirming the importance of phases with terrestrial plant input or aquatic macrophyte predominance these gus were used to define three paleoenvironmental episodes pes during mis 7 in pe7 1 the contribution of algal and aquatic macrophytes predominated in a temporarily flooded saline muddy plain in pe7 2 the major contribution was from aquatic macrophytes flooded marsh although it was marked by episodes of emersion with greater terrestrial contribution at the top of the mis 7 record pe7 3 there was a significant reduction in the water depth with the main input deriving from terrestrial plants in a muddy alluvial plain six pes were established during mis 1 holocene of which three predominately received organic matter derived from aquatic macrophytes while the major contribution in the other three came from terrestrial plants the two sets of pes were linked to episodes of increased and decreased water level respectively this interpretation is consistent with the characteristics of the sediment facies with pe1 1 1 3 and 1 5 corresponding to a marsh with deeper water and a greater input of detrital materials and pe1 2 1 4 and 1 6 to a shallow environment with carbonates and gypsum deposits direct marine influence was limited so the oscillations in the water level in the marsh were likely to be more related to climatic changes drier wetter phases and recent tectonics than to large changes in sea level emersion led to degradation of the organic matter and enrichment in short chain and branched saturated fatty acids

labrador current variability over the last 2000 years the ice loaded labrador current lc is an important component of the western north atlantic circulation that influences the position and strength of the northern limb of the north atlantic current nac this flow of cold and fresh polar waters originating from the arctic has a marked impact on the north atlantic climate yet little is known about its variability beyond the instrumental period in this study we present the first sub decadal alkenone based 2000 year long sea surface temperature sst records from the western labrador sea a climatically crucial region at the boundary between the lc and the nac our results show a clear link between the lc strength and the northern annular mode nam with a stronger nam and a more vigorous lc during the medieval climate anomaly mca this suggests enhanced lc activity upon future global warming with implications for the atlantic meridional overturning circulation amoc

evolution of subpolar north atlantic surface circulation since the early holocene inferred from planktic foraminifera faunal and stable isotope records abstract past changes in the surface flow regime of two main eastern north atlantic warm water pathways toward the nordic seas were reconstructed based on faunal analyses in combination with carbon and oxygen stable isotope measurements in planktic foraminifera the investigated sites in the surroundings of the faroe islands are located in the transitional area where surface waters of subpolar and subtropical origin mix before entering the arctic mediterranean in these areas large amplitude millennial variability in the characteristics of the upper water column appears modulated by changes in the intensity of the subpolar gyre circulation from 7 8 to 6 ka bp faunal records indicate a deep mixed layer which in conjunction with lighter 18 o values suggest that the inflowing atlantic waters were dominated by a relatively cooler and fresher water mass reflecting a strengthening of the subpolar gyre under conditions of enhanced positive nao like forcing and reduced meltwater input a shift in the hydrographic conditions occurred during the mid holocene centered at 5 ka bp at this time increasing upper water column stratification and the incipient differentiation of the stable isotopic signal of the iceland faroe and faroe shetland surface water masses suggest increasing influx of warmer more saline surface waters from the subtropical gyre as subpolar gyre circulation weakened the mid holocene decline in subpolar gyre strength is presumably related to a shift toward a low state of the nao like forcing associated with decreased solar irradiance later in the holocene from 4 ka bp to present the increased frequency and reduced amplitude of the surface hydrographic changes reflect corresponding fluctuations in subpolar gyre circulation these high frequency oscillations in subpolar gyre strength suggest increased surface circulation sensitivity to moderate freshwater fluxes to the labrador irminger sea basin highlighting the importance of the salinity balance in modulating subpolar gyre dynamics particularly under conditions of low nao atmospheric forcing

palaeoclimate the enigmatic 1 500 year cycle solar forcing has been invoked to explain persistent millennial scale climate variations during the holocene two climate reconstructions one based on sea ice drift and one on north atlantic storminess call this link into question

high resolution holocene record in the southeastern bay of biscay global versus regional climate signals abstract core ks10b north east atlantic 43 50 n 2 03 w water depth 550 m was recovered at a location of high sediment deposition and hence includes a high resolution palaeoclimatic record for the southeastern bay of biscay over the last 9000 cal yr bp the effect of global and regional climatic forcing factors e g orbital forcing north atlantic oscillation nao and their subsequent control on water temperature sea level hydrology and continental influence were investigated by studying planktic and benthic foraminiferal faunas 150 m sedimentology and stable isotopes results indicate probable episodic long term incursions of the warm and salty iberian poleward current ipc into the bay of biscay during the holocene by the intermittent presence of subtropical globigerinoides ruber in the otherwise temperate fauna these incursions seem to be triggered by negative nao like conditions our data show five main climatic periods which are in general agreement with the literature data on the climatic variability in the north atlantic and the iberian peninsula the early holocene 9000 7400 cal yr bp is characterized by low sea level significant downslope transport eutrophic benthic settings and high surface water productivity these environmental characteristics are probably due to the general wet and warm climate under a prevailing negative nao increasing precipitation and river runoff and favouring the incursion of the ipc into the bay of biscay the climatic optimum appears between 7400 and 6000 cal yr bp under a generally positive nao index in the following 6000 3500 cal yr bp surface water cooling is matching a steep decline of the northern hemisphere summer insolation meanwhile benthic settings are changing progressively towards present day trophic conditions the time interval from 3500 to 1800 cal yr bp encompasses the iberian roman humid period characterized by warm and humid conditions and increasing primary production under a prevailing negative nao index the last 1800 years were characterized by stable cool conditions reflecting a change towards a positive nao state

holocene flood frequency across the central alps solar forcing and evidence for variations in north atlantic atmospheric circulation the frequency of large scale heavy precipitation events in the european alps is expected to undergo substantial changes with current climate change hence knowledge about the past natural variability of floods caused by heavy precipitation constitutes important input for climate projections we present a comprehensive holocene 10 000 years reconstruction of the flood frequency in the central european alps combining 15 lacustrine sediment records these records provide an extensive catalog of flood deposits which were generated by flood induced underflows delivering terrestrial material to the lake floors the multi archive approach allows suppressing local weather patterns such as thunderstorms from the obtained climate signal we reconstructed mainly late spring to fall events since ice cover and precipitation in form of snow in winter at high altitude study sites do inhibit the generation of flood layers we found that flood frequency was higher during cool periods coinciding with lows in solar activity in addition flood occurrence shows periodicities that are also observed in reconstructions of solar activity from 14 c and 10 be records 2500 3000 900 1200 as well as of about 710 500 350 208 suess cycle 150 104 and 87 gleissberg cycle years as atmospheric mechanism we propose an expansion shrinking of the hadley cell with increasing decreasing air temperature causing dry wet conditions in central europe during phases of high low solar activity furthermore differences between the flood patterns from the northern alps and the southern alps indicate changes in north atlantic circulation enhanced flood occurrence in the south compared to the north suggests a pronounced southward position of the westerlies and or blocking over the northern north atlantic hence resembling a negative nao state most distinct from 4 2 to 2 4 kyr bp and during the little ice age south alpine flood activity therefore provides a qualitative record of variations in a paleo nao pattern during the holocene additionally increased south alpine flood activity contrasts to low precipitation in tropical central america cariaco basin on the holocene and centennial time scale this observation is consistent with a holocene southward migration of the atlantic circulation system and hence of the itcz driven by decreasing summer insolation in the northern hemisphere as well as with shorter term fluctuations probably driven by solar activity

palaeoclimate and palaeoceanographic conditions in the westernmost mediterranean over the last millennium an integrated organic and inorganic approach previous studies have revealed the excellence of the westernmost mediterranean records for reconstructing climate conditions over the last two millennia in particular inorganic and organic proxies have revealed a coherent signal of climate and oceanographic responses during this time here we compare and integrate both proxy records for reconstructing climate and oceanographic conditions with focus on the last millennium the higher temperatures indicated by lipid based proxies during the medieval climate anomaly mca are coincident with drier conditions indicated by inorganic proxies in contrast lower temperatures and humid conditions are indicated during the little ice age lia the industrial period was characterized by increasing humidity in comparison with the previous lia however a progressive aridification occurred since the second half of the twentieth century coexisting with a warming trend and higher contribution of c3 grasses proxy records are also interpreted to show atlantic water inflow at ad 1450 and 1950 and an intensification of the upwelling conditions coinciding with a prolonged positive north atlantic oscillation nao phase in the intervals ad 1000 1450 and 1960 1990 large scale oceanic atmospheric circulation patterns the nao and the atlantic meridional circulation and solar irradiance variations seem to have played the major key role during the last millennium together with anthropogenic contributions in the more recent record

vegetation changes and associated climatic changes in the southern altai mountains within china during the holocene the location of the altai mountains at the limits of both the pacific and atlantic influences implies that this mountain range is an important climatic boundary based on pollen data of 188 samples