climate forcings on vegetation of the southeastern yucatan peninsula mexico during the middle to late holocene abstract climate and vegetation history from the yucatan peninsula southeastern mexico are inferred from a mangrove sediment core deposited between the middle and late holocene 5600 1700 cal yr b p in the rio hondo delta fossil pollen and concentrations of ca and fe and ca fe ratio in sediments are used to record changes in vegetation and climate palaeoecological and palaeoclimatic interpretations obtained from pollen abundances and associations and fe ca ratio coincide with dynamics of major global forcings of climate change like itcz enso and global cooling mesic conditions enabled tropical forest expansion during the middle holocene 5600 3650 cal yr b p although there were periodic dry episodes at 5200 cal yr b p and at 4300 cal yr b p that caused disturbance and enabled herbaceous vegetation to expand changes in sedimentation and a gradual change from semi evergreen to dry tropical forest occurred at 3650 cal yr b p with increasing enso activity and southward migration of the itcz during transition of the middle to late holocene the driest period and lowest forest cover occurred between 2600 and 2000 cal yr b p data show that over the last two millennia influence of the enso on southeastern mexico is stronger compared to other proxy records of climate variability from the caribbean region

holocene reef growth dynamics on kodakara island 29 n 129 e in the northwest pacific abstract the spatial distribution of modern coral reefs in the northwest pacific nwp is restricted to approximately 30 n understanding the high latitude reef growth process and its correlation to climate change may provide important insights into future reef growth at even higher latitudes in response to global warming we conducted field surveys and obtained seven cores from the raised reefs of kodakara island 29 n 129 e in the nwp to determine the changes in and response of reef growth dynamics to millennial scale climate change through the holocene to reconstruct the timing of the reef growth 37 coral ages were determined using accelerator mass spectrometry ams radiocarbon dating the island is characterized by three holocene reef terraces terraces i to iii which were uplifted ca 2 4 ka 1 0 0 4 ka and in the modern era three growth hiatuses occurred circa 5 9 5 8 ka 4 4 4 0 ka and 3 3 3 2 ka which correlate with millennial scale climate changes hamanaka et al 2012 the reef growth began at least 8 ka relatively rapid vertical growth of 3 6 3 3 m kyr 1 occurred between 8 and 6 ka the reef started growing near land and then gradually extended seaward the reef growth around the reef slope decelerated after 6 ka and most likely coincided with the first and second hiatuses detected landward in contrast with the reef flat which resumed its growth after the third hiatus event the reef mound accretion on the slope ceased definitively terrace i was uplifted ca 2 4 ka the reef growth reactivated ca 1 3 ka and the reef grew at a rate of 9 1 m kyr 1 between 1 3 and 1 0 ka this rate is the fastest growth recorded in this study this time interval corresponds to the medieval climatic anomaly mca the cause of the delayed reef growth between 2 4 and 1 4 ka remains unclear but it may imply the existence of a late holocene hiatus due to a weaker kuroshio current kc ca 1 7 ka and to strong el nino southern oscillation enso activity between 2 and 1 5 ka in the east pacific the timing of the hiatuses agrees with the weakening of the kc and the more frequent el nino events during the positive phase of the pacific decadal oscillation pdo whereas the rapid growth coincides with la nina conditions such as the mca during the negative phase of the pdo our results indicate that the climate event at approximately 4 ka caused the largest change in the reef growth and it may have affected reefs throughout the pacific region specifically the enso and pdo phases may have impacted the reef growth and kc behavior

hornblende bearing leucosome development during syn orogenic crustal extension in the tormes gneiss dome nw iberian massif spain abstract the high grade lower unit of the tormes gneissic dome tgd nw sector of the iberian massif contains tonalitic orthogneissic bodies that were migmatized during a heterogeneous ductile shearing related to a major episode of syn orogenic extensional deformation d2 both peak and retrograde p t conditions were deduced from the analysis of reaction textures related to superimposed s2 fabrics developed during exhumation analysis of mineral zoning and thermobarometric calculations in cakfmash and kfmash systems syn thermal peak partial melting of the tonalitic orthogneisses via a biotite dehydration melting reaction yielding hornblende k feldspar and melt produced stromatic migmatites with leucosomes parallel to the s2 foliation of the mesosome as well as discordant patchy pegmatitic migmatites the deduced post thermal peak p t path comprises an initial phase of decompression combined with cooling from 5 5 6 kbar at 750 c to ca 4 4 5 kbar at 675 c consistent with the sequence of initial retrograde mineral assemblages present in high t mylonitic s2 fabrics the later part of the syn d2 p t path indicates a significant cooling and is recorded by lower amphibolite to greenschist assemblages related to the later mylonitic s2 fabrics the proposed melt reaction generating hornblende bearing leucosomes may be important for crustal differentiation processes at mid crustal levels during syn orogenic extension as well as for the production of certain types of high level granites the necessary conditions are large volumes of source material of intermediate composition and the production of a sufficient melt fraction

multi proxy evidence for millennial scale changes in north pacific holocene hydroclimate from the kenai peninsula lowlands south central alaska abstract the holocene hydroclimate of south central alaska has been studied extensively but conflicting interpretations between oxygen isotope paleoclimate datasets are seemingly as common as converging reconstructions in part due to the challenges of interpreting oxygen isotope ratios in terms of climate here we present a new holocene record of biogenic silica abundance bsi diatom flora and diatom oxygen isotopes 18obsi analyzed in sediments from sunken island lake sil in the kenai peninsula lowlands which we interpret in the context of previously published paleoclimate records and use to understand regional changes in hydroclimate changes in lake level documented by aerial photography coupled with a survey of regional lake water isotopes indicate sil is sensitive to changes in the balance of precipitation and evaporation p e however an analysis of sil 18obsi over the instrumental period indicates that 18obsi is sensitive to both p e and the isotope composition of precipitation 18oprecip which is driven by changes in the aleutian low atmospheric pressure cell al we attribute a 2 increase in 18obsi from 5 5 to 4 5 ka cal bp to a stronger al which resulted in the delivery of isotopically heavier precipitation to the kenai lowlands and wetter conditions during the late holocene these interpretations are supported by late holocene increases in the relative abundance of planktonic diatoms and bsi inferred storminess and by evidence for higher than present lake levels on the paleo shorelines above sil at 1 5 0 5 ka cal bp our dataset demonstrates that this region was characterized by relatively low lake levels and dry climate in the early holocene a strengthening of the al in the late holocene and wetter climate during the late holocene until recent decades

mount logan ice core record of tropical and solar influences on aleutian low variability 500 1998 a d continuous high resolution paleoclimate records from the north pacific region spanning the past 1500 years are rare and the behavior of the aleutian low alow pressure center the dominant climatological feature in the gulf of alaska remains poorly constrained here we present a continuous 1500 year long calibrated proxy record for the strength of the wintertime december march alow from the mount logan summit pr col 5200 m asl ice core soluble sodium time series we show that ice core sodium concentrations are statistically correlated with north pacific sea level pressure and zonal wind speed our alow proxy record reveals a weak alow from circa 900 1300 a d and 1575 1675 a d and a comparatively stronger alow from circa 500 900 a d 1300 1575 a d and 1675 a d to present the mount logan alow proxy record shows strong similarities with tropical paleoclimate proxy records sensitive to the el nino southern oscillation and is consistent with the hypothesis that the medieval climate anomaly was characterized by more persistent la nina like conditions while the little ice age was characterized by at least two intervals of more persistent el nino like conditions the mount logan alow proxy record is significantly p 0 05 correlated and coherent with solar irradiance proxy records over various time scales with stronger solar irradiance generally associated with a weaker alow and la nina like tropical conditions however a step like increase in alow strength during the dalton solar minimum circa 1820 is associated with enhanced walker circulation furthermore rising co2 forcing or internal variability may be masking the twentieth century rise in solar irradiance

ice core paleovolcanic records from the st elias mountains yukon canada 1 we previously reported a record of regionally significant volcanic eruptions in the north pacific using an ice core from eclipse icefield st elias mountains yukon canada the acquisition of two new ice cores from eclipse icefield along with the previously available eclipse icefield and mount logan northwest col ice cores allows us to extend our record of north pacific volcanism to 550 years before present using a suite of four ice cores spanning an elevation range of 3 5 km comparison of volcanic sulfate flux records demonstrates that the results are highly reproducible especially for the largest eruptions such as katmai a d 1912 correlation of volcanic sulfate signals with historically documented eruptions indicates that at least one third of the eruptions recorded in st elias ice cores are from alaskan and kamchatkan volcanoes although there are several moderately large volcanic explosivity index vei 4 eruptions recorded in only one core from eclipse icefield the use of multiple cores provides signals in at least one core from all known vei 4 eruptions in alaska and kamchatka since a d 1829 tephrochronological evidence from the eclipse ice cores documents eruptions in alaska westdahl redoubt trident and katmai kamchatka avachinsky kliuchevoskoi and ksudach and iceland hekla several unidentified tephra bearing horizons with available geochemical evidence suggesting alaskan and kamchatkan sources were also found we present a reconstruction of annual volcanic sulfate loading for the north pacific troposphere based on our ice core data and we provide a detailed assessment of the atmospheric and climatic effects of the katmai eruption

recent volume and area changes of kaskawulsh glacier yukon canada recent surface elevation changes of kaskawulsh glacier yukon canada are quantified by comparing an air photo derived dem from 1977 and airborne lidar measurements from 1995 2000 and 2007 surface area changes are assessed using historical aerial photography from 1956 and satellite imagery from 1977 to 2007 combined these measurements provide some of the first detailed records of volume change of a large yukon glacier between 1977 and 2007 kaskawulsh glacier underwent a decrease in area of 1 53 and a decrease in volume of 3 27 5 94 km 3 w e the terminus also retreated by 655 m over the period 1956 2007 there was relatively minor volume change over the period 1977 95 0 01 km 3 w e a 1 while over the periods 1995 2000 and 2000 07 volume losses occurred at a relatively constant rate of 0 51 and 0 50 km 3 a 1 w e respectively since 1995 thinning has been prominent throughout the ablation zone while relative stability and even slight thickening has occurred in the accumulation zone these findings are similar to those recently observed at other nearby alaskan glaciers

a speleothem record of holocene paleoclimate from the northern wasatch mountains southeast idaho usa abstract a speleothem stable isotope record from minnetonka cave located in the northern wasatch mountains is shown to be a winter season biased record of holocene paleoclimate the season specific sensitivity of the record provides an opportunity to more robustly evaluate long term variability in large scale pacific teleconnection patterns such as enso and pdo as precipitation anomalies associated with these teleconnection patterns occur primarily in winter seasonal climate composite maps of high and low snowpack years at the study site demonstrate that winter precipitation is strongly linked to the relative strength of the aleutian low and the associated changes from to more meridional or more zonal steering level wind patterns minnetonka cave data suggest wetter cooler than modern early holocene winters and a dry middle holocene with a consistent warming trend from 7400 to 3800 bp after 4000 bp data suggest a return to wetter and or colder than modern winters for much of the late holocene prolonged winter dry intervals are identified from 7400 to 6000 bp and 4200 bp

holocene atmospheric circulation in the central north pacific a new terrestrial diatom and δ18o dataset from the aleutian islands the north pacific is a zone of cyclogenesis that modulates synoptic scale atmospheric circulation yet there is a paucity of instrumental and paleoclimate data to fully constrain its long term state and variability we present the first holocene oxygen isotope record 18odiatom from the aleutian islands using siliceous diatoms preserved in heart lake on adak island 51 85 n 176 69 w this study builds on previous work demonstrating that heart lake sedimentary 18odiatom values record the 18o signal of precipitation and correlate significantly with atmospheric circulation indices over the past century we apply this empirical relationship to interpret a new 9 6 ka 18odiatom record from the same lake supported by diatom assemblage analysis our results demonstrate distinct shifts in the prevailing trajectory of storm systems that drove spatially heterogeneous patterns of moisture delivery and climate across the region during the early mid holocene a warmer wetter climate prevailed due to a predominantly westerly aleutian low that enhanced advection of warm 18o enriched pacific moisture to adak and culminated in a 18odiatom maxima 33 3 at 7 6 ka during the holocene thermal maximum after 4 5 ka relatively lower 18odiatom indicates cooler drier conditions associated with enhanced northerly circulation that persisted into the 21st century our analysis is consistent with surface climate conditions inferred from a suite of terrestrial and marine climate proxy records this new holocene dataset bridges the gap in an expanding regional network of paleoisotope studies and provides a fresh assessment of the complex spatial patterns of holocene climate across beringia and the atmospheric forces driving them

abrupt weakening of the summer monsoon in northwest india 4100 yr ago climate change has been suggested as a possible cause for the decline of urban centers of the indus civilization 4000 yr ago but extant paleoclimatic evidence has been derived from locations well outside the distribution of indus settlements here we report an oxygen iso tope record of gastropod aragonite 18 o a from holocene sediments of paleolake kotla dahar haryana india which is adjacent to indus settlements and documents indian summer mon soon ism variability for the past 6 5 k y a 4 increase in 18 o a occurred at ca 4 1 ka mark ing a peak in the evaporation precipitation ratio in the lake catchment related to weakening of the ism although dating uncertainty exists in both climate and archaeological records the drought event 4 1 ka on the northwestern indian plains is within the radiocarbon age range for the beginning of indus de urbanization suggesting that climate may have played a role in the indus cultural transformation

thermodynamic calculation of emplacement pressures for batholithic rocks california implications for the aluminum in hornblende barometer the aluminum in hornblende ah barometer has been widely used to estimate the emplacement pressure p of granitic rocks application of the barometer has remained controversial because the controls on the aluminum content of hornblende imposed by temperature t magma composition and fluid composition remain incompletely understood in this paper the p t conditions of equilibration for 19 rocks from the mesozoic batholiths of california are estimated by simultaneous evaluation of 1 the p sensitive reaction tremolite phlogopite 2 anorthite 2 albite 2 pargasite 6 quartz k feldspar and 2 previously published amphibole plagioclase thermometer equilibria p estimates for the batholiths range from 1 2 to 7 4 kbar and are consistent with independent geologic evidence the highest p samples 5 1 7 4 kbar are located near the san andreas fault furthermore it appears that regional p gradients determined by previous ah barometry studies are valid but that the absolute values of the p estimates will need to be revised somewhat 1 5 kbar i suggest that the method of this study provides a viable thermodynamics based alternative to conventional ah barometry that requires no a priori assumptions about t or bulk composition

is there evidence for solar forcing of climate in the gisp2 oxygen isotope record abstract changes in solar constant over an 11 yr cycle suggest a certain but limited degree of solar forcing of climate the high resolution climate oxygen isotope record of the greenland gisp2 greenland ice sheet project 2 ice core has been analyzed for solar and volcanic influences the atmospheric14c record is used as a proxy of solar change and compared to the oxygen isotope profile in the gisp2 ice core an annual oxygen isotope profile is derived from centimeter scale isotope measurements available for the post a d 818 interval associated extreme summer and winter isotope ratios were found to yield similar climate information over the last millennium the detailed record of volcanic aerosols converted to optical depth and volcanic explosivity change was also compared to the isotope record and the oxygen isotope response calibrated to short term volcanic influences on climate this calibration shows that century scale volcanic modulation of the gisp2 oxygen isotope record can be neglected in our analysis of solar forcing the timing estimated order of temperature change and phase lag of several maxima in14c and minima in18o are suggestive of a solar component to the forcing of greenland climate over the current millennium the fractional climate response of the cold interval associated with the maunder sunspot minimum and14c maximum as well as the medieval warm period and little ice age temperature trend of the past millennium are compatible with solar climate forcing with an order of magnitude of solar constant change of 0 3 even though solar forcing of climate for the current millennium is a reasonable hypothesis for the rest of the holocene the century scale events are more frequent in the oxygen isotope record than in the14c record and a significant correlation is absent for this interval oceanic atmospheric circulation forcing of climate may dominate solar forcing during the surprisingly strong 1470 yr climate cycle of the 11 000 75 000 yr b p interval is rather hypothetical

late holocene drought responsible for the collapse of old world civilizations is recorded in an italian cave flowstone a severe drought in parts of low latitude northeastern africa and southwestern asia 4200 yr ago caused major disruption to ancient civilizations stable isotope trace element and organic fluorescence data from a calcite flowstone collected from the well watered alpi apuane karst of central western italy indicate that the climatic event responsible for this drought was also recorded in mid latitude europe although the timing of this event coincides with an episode of increased ice rafted debris to the subpolar north atlantic the regional ocean atmosphere response seems atypical of similar holocene ice rafting events furthermore comparison of the flowstone data with other regional proxies suggests that the most extreme part of the dry spell occurred toward the end of a longer term climate anomaly

holocene storminess inferred from sediments of two lakes on adak island alaska abstract the abundance of sedimentary organic material from two lakes was used to infer past holocene storminess on adak island where frequent storms generate abundant rainfall and extensive cloud cover andrew and heart lakes are located 10 km apart their contrasting physical characteristics cause the sedimentary organic matter to respond differently to storms their records were synchronized using correlated tephra beds sedimentation rates increased between 4 0 and 3 5 ka in both lakes over the instrumental period andrew lake biogenic silica content bsi is most strongly correlated with winter sunlight availability which influences photosynthetic production and river input which influences the dilution of bsi by mineral matter heart lake bsi is likely affected by wind driven remobilization of sediment as suggested by correlations among bsi the north pacific index and winter storminess the results indicate relatively stormy conditions from 9 6 to 4 0 ka followed by drying between 4 0 and 2 7 ka with the driest conditions from 2 7 to 1 5 ka the stormiest period was between ad 500 and 1200 then drying from 1150 to 1500 and more variable until 1850 this record of holocene storminess fills a major gap at the center of action for north pacific wintertime climate

thermobarometry of garnet clinopyroxene hornblende granulites from the kapuskasing structural zone amphibole mixing properties and standard state properties for the end members tremolite tschermakite pargasite ferrotremolite ferrotschermakite and ferropargasite have been refined through analysis of relevant phase equilibrium experiments coexisting cummingtonite hornblende pairs and natural mineral parageneses when merged with the mineral properties given by r g berman these amphibole properties allow the calculation of numerous equilibria suitable for thermobarometry in a wide range of bulk compositions at amphibolite to granulite metamorphic grades the method was applied to texturally equilibrated garnet pyroxene hornblende gneisses and compared both to results based on anhydrous assemblages and to those for garnet biotite gneisses from the kapuskasing structural zone thermometer resetting is apparent only in garnet biotite gneisses whereas touching garnet pyroxene pairs in mafic gneiss show little evidence of retrograde fe mg exchange computed metamorphic temperatures garnet clinopyrox

reduction in himalayan snow accumulation and weakening of the trade winds over the pacific since the 1840s 1 in 1884 blanford suggested that summer rainfall over northwest india was anti correlated with snow cover during the preceding winter and spring in the western himalaya walker elaborated on this suggestion in his seminal work on predictors of the indian summer monsoon a body of work that forms the basis of our understanding of how eurasia influences this monsoonal circulation recently a number of studies have questioned the existence of this relationship or have proposed a more complex coupling between eurasian snow cover including the himalaya and the indian summer monsoon here we present a 196 year record of snow accumulation from a himalayan ice core that contains a decreasing trend in accumulation that began in the 1840s indian summer monsoon rainfall shows no evidence of such a trend and we argue that this reduction in snow accumulation is associated with a long term weakening of the trade winds over the pacific ocean citation zhao h and g w k moore 2006 reduction in himalayan snow accumulation and weakening of the trade winds over the pacific since the 1840s geophys res lett 33 l17709

structural relationship between the sea of marmara basin and the north anatolian fault zone the north anatolian fault naf zone is 1500 km long extending almost up to the greek mainland in the west it is a seismically active right lateral strike slip fault that accommodates the relative motion between the turkish block and black sea plate the sea of marmara lies along the western part of the naf and shows evidence of subsidence in this area pure strike slip motion of the fault zone changes into extensional strike slip movement that is responsible for the creation of the sea of marmara and the north aegean basins the northern half of the sea of marmara is interpreted as a large pull apart basin this basin is subdivided into three smaller basins separated by strike slip fault segments of uplifted blocks ne sw basinal areas are covered by horizontally layered sedimentary sequences uplifted blocks have undergone compressional stress all the blocks are subsiding and are undergoing vertical motions and rotations relative to one another the uplifted blocks exhibit positive bouguer gravity anomalies according to gravity interpretation there is relative crustal thinning under the sea of marmara the northern side of the sea of marmara is marked by a distinctive deep rooted magnetic anomaly which is dissected and shifted southward by strike slip faulting the southern shelf areas of the sea of marmara are dominated by short wavelength magnetic anomalies of shallow origin

temporal and spatial aspects of peatland initiation following deglaciation in north america abstract a set of simple ecological models accounts well for the cumulative initiation of peatlands throughout north america in relation to glacial retreat the most parsimonious form incorporates first a delay term to account for the lag during which newly deglaciated land became suitable for peatland initiation and second an intrinsic rate of initiation related to the probability of migration and establishment of plant propagules from elsewhere the goodness of fit of the models based on 1680 basal peat dates throughout the continent allows projection of past trends into the future factors contributing to the lag of about 4000 years between deglaciation and peatland initiation are suggested and data on colonization of deglaciated land by beavers known to initiate peatlands are presented the rate of peatland initiation peaked between 7000 and 8000 years ago but remains appreciable today a marked depression of peatland initiation 8360 8040 bp interrupted the peak rate the time of the interruption matches the 8200 bp cold dry event recorded in greenland ice cores and suggests that this event caused a substantial continent wide depression of an important ecosystem function i e carbon sequestration from the atmosphere by peat deposition spontaneous initiation of new peatlands is projected to continue for millennia to come

crustal thickening and deformation sequence in the footwall to the suture of the variscan belt of northwest spain abstract the sequence of formation and propagation of structures as well as the evolution of crustal thickening in the variscan belt of northwest spain are proposed in this paper the foreland of this mountain belt shows thin skinned tectonics a polyphase deformation with associated regional metamorphism is recognized in the hinterland zones two important culminations the narcea and lugo antiforms are present in an e w cross section through the footwall to the suture of this orogen such culminations are derived from the stacking of several thrust systems generated during two successive periods the sequence of thrust emplacement helps to clarify the formation of different types of structures at the same time in different places in the orogen

postglacial climates inferred from a lake at treeline southwest yukon territory canada abstract pollen chironomid and ostracode records from a lake located at alpine treeline provide regional paleoclimate reconstructions from the southwest yukon territory canada the pollen spectra indicate herbaceous tundra existed on the landscape from 13 6 11 ka followed by birch shrub tundra until 10 ka although picea pollen dominated the assemblages after 10 ka low pollen accumulation rates and picea percentages indicate minimal treeline movement through the holocene chironomid accumulation rates provide evidence of millennial scale climate variability and the chironomid community responded to rapid climate changes ostracodes were found in the late glacial and early holocene but disappeared due to chemical changes of the lake associated with changes in vegetation on the landscape inferred mean july air temperature total annual precipitation and water depth indicate a long term cooling with increasing moisture from the late glacial through the holocene during the younger dryas 12 9 11 2 ka cold and dry conditions prevailed the early and mid holocene were warm and dry with cool wet conditions after 4 ka and warm dry conditions since the end of the little ice age

solar forcing of centennial scale east asian winter monsoon variability in the mid to late holocene abstract centennial scale variability of the east asian winter monsoon during the holocene is poorly understood because suitable archives and proxies are lacking here we present a high resolution 30 yr spacing planktonic foraminiferal o 18 record of neogloboquadrina incompta dextral form which reflects sea surface temperature during the winter season for the last 6000 yrs from marine sediments in the western north pacific stronger winter monsoons indicated by cooler winter ssts correspond to weaker summer monsoons indicated by the cave oxygen isotopes in centennial scale variability the variability also shows good correlation with o 18 records in lake sediments and ice cores from the yukon territory canada spanning the last 4500 yrs suggesting east west climate coupling across the north pacific furthermore the climate changes across the north pacific co vary over widespread regions such as the eastern tropical pacific and the northern red sea and the reconstructed solar activity the cross spectral and wavelet analyses show that the east asian winter monsoon shares some cyclicity with the solar variability our results suggest that the solar activity is a fundamental forcing producing the centennial scale eawm variability mediated by the large scale climate linkages

holocene sea ice conditions and circulation at the chukchi alaskan margin arctic ocean inferred from biomarker proxies two sediment cores from the chukchi sea margin were investigated for the arctic sea ice biomarker ip25 along with marine and terrestrial sterols and glycerol dialkyl glycerol tetraethers gdgts this is the first paleoclimatic application of ip25 in the chukchi alaskan region of the arctic which is key for understanding arctic pacific interactions and is experiencing rapid sea ice retreat under present warming sea ice and related circulation conditions were characterized in this study with a multicentury resolution for the long term holocene record to multidecadal for the last several centuries sea ice was found to be present during the entire record but with considerable spatial and temporal variability after very low deglacial ip25 values possibly related to permanent sea ice and or an iceberg dominated environment cores from the upper slope and shelf show ip25 maxima interpreted as representing a relative proximity to the sea ice margin in the early ca 8 9 ka and middle ca 5 6 ka holoce

coherent late holocene climate driven shifts in the structure of three rocky mountain lakes large scale atmospheric pressure centers such as the aleutian and icelandic low have a demonstrated relationship with physical lake characteristics in contemporary monitoring studies but the responses to these phenomena are rarely observed in lake records we observe coherent changes in the stratification patterns of three deep 30 m lakes inferred from fossil diatom assemblages as a response to shifts in the location and intensity of the aleutian low and compare these changes with similar long term changes observed in the 18o record from the yukon specifically these records indicate that between 3 2 and 1 4 ka the aleutian low shifted westward resulting in an increased frequency of storm tracks across the pacific northwest during winter and spring this change in atmospheric circulation ultimately produced deeper mixing in the upper waters of these three lake systems enhanced stratification between 4 5 and 3 3 ka and from 1 3 ka to present suggests a strengthened aleutian low and more meridion

coupled impacts of sea ice variability and north pacific atmospheric circulation on holocene hydroclimate in arctic alaska arctic alaska lies at a climatological crossroads between the arctic and north pacific oceans the modern hydroclimate of the region is responding to rapidly diminishing sea ice driven in part by changes in heat flux from the north pacific paleoclimate reconstructions have improved our knowledge of alaska s hydroclimate but no studies have examined holocene sea ice moisture and ocean atmosphere circulation in arctic alaska limiting our understanding of the relationship between these phenomena in the past here we present a sedimentary diatom assemblage and diatom isotope dataset from schrader pond located 80 km from the arctic ocean which we interpret alongside synthesized regional records of holocene hydroclimate and sea ice reduction scenarios modeled by the hadley centre coupled model version 3 hadcm3 the paleodata synthesis and model simulations suggest the early and middle holocene in arctic alaska were characterized by less sea ice a greater contribution of isotopically heavy arctic derived moisture and wetter climate in the late holocene sea ice expanded and regional climate became drier this climatic transition is coincident with a documented shift in north pacific circulation involving the aleutian low at 4 ka suggesting a holocene teleconnection between the north pacific and arctic the hadcm3 simulations reveal that reduced sea ice leads to a strengthened aleutian low shifted west potentially increasing transport of warm north pacific water to the arctic through the bering strait our findings demonstrate the interconnectedness of the arctic and north pacific on multimillennial timescales and are consistent with future projections of less sea ice and more precipitation in arctic alaska

a 100 year record of north pacific volcanism in an ice core from eclipse icefield yukon territory canada iceland and the 1989 redoubt alaska eruptions non sea salt so4 2 residuals above a robust spline and empirical orthogonal function eof analysis were used to identify volcanic so4 2 signatures volcanic sulfate values are more conservatively identified by the eof analysis as sulfate deposition from other sources is more robustly accounted for some eruptions are also recorded as peaks in non sea salt chloride the volcanic signals in the eclipse ice core are mostly attributable to alaskan aleutian or kamchatkan eruptions conversely the eclipse ice core provides a poor record of globally significant tropical eruptions these results are promising for the development of longer ice core based records of paleovolcanism in the north pacific rim index terms 0305 atmospheric composition and structure aerosols and particles 0345 4801 0370 atmospheric composition and structure volcanic effects 8409 8409 volcanology atmospheric effects 0370 keywords yukon territory ice cores volcanism atmospheric effects kamchatka alaska

five millennia of paleotemperature from tree rings in the great basin usa the instrumental temperature record is of insufficient length to fully express the natural variability of past temperature high elevation tree ring widths from great basin bristlecone pine pinus longaeva are a par ticularly useful proxy to infer temperatures prior to the instrumental record in that the tree rings are annually dated and extend for millennia from ring width measurements integrated with past treeline elevation data we infer dec adal to millennial scale temperature variability over the past 4 500 years for the great basin usa we find that twentieth century treeline advances are greater than in at least 4 000 years there is also evidence for substantial volcanic forcing of climate in the preindustrial record and considerable covariation between high elevation tree ring widths and temperature estimates from an atmosphere ocean general circulation model over much of the last millennium a long term temperature decline of 1 1 c since the mid holocene underlies substantial volcanic forcing of climate in the preindustrial record

holocene climate changes in eastern beringia nw north america a systematic review of multi proxy evidence abstract reconstructing climates of the past relies on a variety of evidence from a large number of sites to capture the varied features of climate and the spatial heterogeneity of climate change this review summarizes available information from diverse holocene paleoenvironmental records across eastern beringia alaska westernmost canada and adjacent seas and it quantifies the primary trends of temperature and moisture sensitive records based in part on midges pollen and biogeochemical indicators compiled in the recently published arctic holocene database and updated here to v2 1 the composite time series from these proxy records are compared with new summaries of mountain glacier and lake level fluctuations terrestrial water isotope records sea ice and sea surface temperature analyses and peatland and thaw lake initiation frequencies to clarify multi centennial to millennial scale trends in holocene climate change to focus the synthesis the paleo data are used to frame specific questions that can be addressed with simulations by earth system models to investigate the causes and dynamics of past and future climate change this systematic review shows that during the early holocene 11 7 8 2 ka 1 ka 1000 cal yr bp rather than a prominent thermal maximum as suggested previously temperatures were highly variable at times both higher and lower than present approximate mid 20th century average with no clear spatial pattern composited pollen midge and other proxy records average out the variability and show the overall lowest summer and mean annual temperatures across the study region during the earliest holocene followed by warming over the early holocene the sparse data available on early holocene glaciation show that glaciers in southern alaska were as extensive then as they were during the late holocene early holocene lake levels were low in interior alaska but moisture indicators show pronounced differences across the region the highest frequency of both peatland and thaw lake initiation ages also occurred during the early holocene during the middle holocene 8 2 4 2 ka glaciers retreated as the regional average temperature increased to a maximum between 7 and 5 ka as reflected in most proxy types following the middle holocene thermal maximum temperatures decreased starting between 4 and 3 ka signaling the onset of neoglacial cooling glaciers in the brooks and alaska ranges advanced to their maximum holocene extent as lakes generally rose to modern levels temperature differences for averaged 500 year time steps typically ranged by 1 2 c for individual records in the arctic holocene database with a transition to a cooler late holocene that was neither abrupt nor spatially coherent the longest and highest resolution terrestrial water isotope records previously interpreted to represent changes in the aleutian low pressure system around this time are here shown to be largely contradictory furthermore there are too few records with sufficient resolution to identify sub centennial scale climate anomalies such as the 8 2 ka event the review concludes by suggesting some priorities for future paleoclimate research in the region

the 1200 year composite ice core record of aleutian low intensification future changes in north pacific wintertime climate will be largely determined by the response of the aleutian low alow pressure system to anthropogenic forcing although the alow has intensified over the twentieth century global climate model projections of future alow variability are equivocal in order to evaluate decadal to centennial alow forcing mechanisms and provide context for the modern intensification here we combine a new denali ice core alaska sea salt sodium record with the mount logan ice core yukon sodium record to develop a composite 1200 year record of alow variability the composite record indicates that the recent secular alow intensification began circa 1741 and is unprecedented in magnitude and duration over the past millennium north pacific ice core snow accumulation and stable isotope records are consistent with this interpretation the alow intensification is associated with warming tropical pacific sea surface temperatures consistent with dynamic theory and instrumental correlations

connecting the atlantic sector and the north pacific mt logan ice core stable isotope records during the holocene the role of el nino the 18o holocene of the mt logan ice core is very different from those of eastern arctic canada and greenland the large changes seen in logan dwarf even the largest change the cooling event 8200 years ago in the atlantic sector cores large changes in logan s 18o and d are related to the state of el nino as reflected by the quelccaya 18o series it is found that the lagged auto difference series of the ice core records from the agassiz ice cap greenland and the 23 site stack of paleotemperature records of kaufman et al kaufman ds schneider dp mckay np ammann cm bradley rs briffa kr et al 2009 recent warming reverses long term arctic cooling science 325 1236 produce highly significant matches to the mt logan 18o series these correspondences suggest a lag of 1200 years this lag time is what some models of the diffusive great ocean conveyor d goc predict for the average travel time from the north atlantic to the tropical eastern pacific monte carlo testing of the correlation

water saturated and undersaturated melting of metaluminous and peraluminous crustal compositions at 10 kb evidence for the origin of silicic magmas in the taupo volcanic zone new zealand and other occurrences

early and late holocene glacial fluctuations and tephrostratigraphy cabin lake alaska marked changes in sediment types deposited in cabin lake near cordova alaska represent environmental shifts during the early and late holocene including fluctuations in the terminal position of sheridan glacier cabin lake is situated to receive meltwater during periods when the outwash plain of the advancing sheridan glacier had aggraded a brief early holocene advance from 11 2 to 11 0 cal ka is represented by glacial rock flour near the base of the sediment core non glacial lake conditions were restored for about 1000 years before the water level in cabin lake lowered and the core site became a fen the fen indicates drier than present conditions leading up to the holocene thermal maximum an unconformity spanning 5400 years during the mid holocene is overlain by peat until 1110 ce when meltwater from sheridan glacier returned to the basin three intervals of an advanced sheridan glacier are recorded in the cabin lake sediments during the late holocene 1110 1180 1260 1540 and 1610 1780 ce the sedimentary sequence also contains the first five reported tephra deposits from the copper river delta region and their geochemical signatures suggest that the sources are the cook inlet volcanoes redoubt augustine and crater peak and possibly mt churchill in the wrangell volcanic field copyright 2013 john wiley sons ltd

paleoceanography of the gulf of alaska during the past 15 000 years results from diatoms silicoflagellates and geochemistry article i nfo abruptly during the bolling allerod bo al warm interval 14 7 12 9 cal ka declined during the younger dryas yd cold interval 12 9 to 11 7 cal kyr bp and rose again during the earliest holocene at this site the record after 11 cal kyr bp is dominated by oceanic diatoms and silicoflagellates with geochemical proxies displaying more subtle variation cores ew0408 66jc in the yakobi sea valley near cross sound and ew0408 11jc in the gulf of esquibel contain an expanded composite record along the southeast alaskan margin core 66jc contains a detailed record of the bo al and yd diatoms and silicoflagellates indicate that coastal upwelling and biosiliceous productivity were strong during the bo al but declined during the yd sea ice related diatoms increased in abundance during the yd indicating cooler but less productive waters

a synthesis of abrupt changes in the asian summer monsoon since the last deglaciation we have compiled 36 previously published palaeoclimate records to determine the timing and spatial pattern of century scale abrupt changes in asian monsoon precipitation since the last deglaciation we identify abrupt events from 1 the interpretations of the authors of these records and 2 the more objective moving t test calculation our results indicate that abrupt climatic changes occurred at 11 5 cal ka 4 5 5 0 cal ka and ad 1300 at the start of the holocene 11 5 cal ka asian monsoon precipitation increased dramatically this climatic change is synchronous with an abrupt warming in the north atlantic during the middle holocene there was a time of preferred and widespread weakening in monsoon strength 4 5 5 0 cal ka this result contradicts previous notions of either a gradual trend towards drier conditions or a series of abrupt events that occurred in an unorganized fashion across space and time the middle holocene abrupt event could have been synchronous with an abrupt cooling event in the north atlantic as well as a warming and intensie cation of internannual variability in the tropical pacie c in contrast to previous periods precipitation changes at ad 1300 have a heterogeneous spatial pattern we e nd no conclusive evidence for a change in the asian monsoon at 8 2 cal ka as suggested by several previous studies more high resolution data may be needed to observe this short lived event overall our results attest to the potential for rapid and major shifts in asian monsoon precipitation that may be triggered by variations in other components of the climatic system

regional atmospheric circulation change in the north pacific during the holocene inferred from lacustrine carbonate oxygen isotopes yukon territory canada analyses of sediment cores from jellybean lake a small evaporation insensitive groundwater fed lake provide a record of changes in north pacific atmospheric circulation for the last 7500 yr at 5 to 30 yr resolution isotope hydrology data from the southern yukon indicate that the oxygen isotope composition of water from jellybean lake reflects the composition of mean annual precipitation 18op recent changes in the 18o of jellybean sedimentary calcite 18oca correspond to changes in the north pacific index npi a measure of the intensity and position of the aleutian low al pressure system this suggests that 18op variability was related to the degree of fractionation during moisture transport from the gulf of alaska across the st elias mountains and that holocene shifts were controlled by the intensity and position of the al following this model between 7500 and 4500 cal yr b p long term trends suggest a predominantly weaker and or westward al between 4500 and 3000 cal yr b p the al shifted eastward or intensified before shifting westward or weakening between 3000 and 2000 cal yr b p rapid shifts eastward and or intensification occurred 1200 and 300 cal yr b p holocene changes in north pacific atmospheric circulation inferred from jellybean lake oxygen isotopes correspond with late holocene glacial advances in the st elias mountains changes in north pacific salmon abundance and shifts in atmospheric circulation over the beaufort sea

holocene climate records from lake sediments in india assessment of coherence across climate zones abstract holocene lake records constitute an important archive for the reconstruction of paleoclimate despite the overall climatic stability of the holocene the monsoons in india both summer and winter show various episodes of weakening and strengthening during this time interval as the holocene lake records are distributed across the various geomorphic and climatic zones of india they offer the possibility of understanding regional scale variations in terms of both qualitative and quantitative assessment of the available proxy data the present day precipitation in india varies from

petrology of garnet cordierite sillimanite gneisses from the el tormes thermal dome iberian hercynian foldbelt w spain the core of the el tormes thermal dome situated in the central part of one of the main metamorphic belts of the iberian peninsula is formed by garnet cordierite biotite sillimanite pelitic gneisses these rocks that very often are cut by minor intrusions of al rich s type granites are metatexitic gneisses in which there exists garnet showing different stages of resorption and transformation into an aggregate of cordierite plagioclase biotite the garnet mantled and corroded mainly by cordierite has never been found to occur in contact with the prismatic sillimanite of the matrix thus indicating that the continuous reaction gr sill q cd has taken place the presence of corroded biotite inside the garnet rimming cordierite of the aggregates as well as inside the cordierite of the matrix which usually includes remmants of sillimanite indicates that the continuous reaction bi sill q cd fk h2o has occurred too therefore a realistic net reaction for these aggretates should be represented by the univariant at a given x text h text 2 text o equilibrium biotite sillimanite garnet quartz cordierite k feldspar h2o 1

the δ18o record along the greenland ice core project deep ice core and the problem of possible eemian climatic instability over 70 000 samples from the 3029 m long greenland ice core project grip ice core drilled on the top of the greenland ice sheet summit have been analyzed for 8o a highly detailed and continuous 8o profile has thus been obtained and is discussed in terms of past temperatures in greenland we also discuss a three core stacked annual 8o profile for the past 917 years the short term 50 years variability of the annual 8o signal is found to be 1 in the holocene and estimates for the coldest parts of the last glacial are 3 or higher these data also provide insights into possible disturbances of the stratigraphic layering in the core which seems to be sound down to the onset of the eemian spectral analysis of highly detailed sequences of the profile helps determine the smoothing of the 8o signal which for the holocene ice is found to be considerably stronger than expected we suggest this is due to a process involving diffusion of water molecules along crystal boundaries in the recrystallizing ice matrix deconvolution techniques were employed for restoring with great confidence the highly attenuated annual 8o signal in the holocene we confirm earlier findings of dramatic temperature changes in greenland during the last glacial cycle abrupt and strong climatic shifts are also found within the eem sangamon interglaciation which is normally recorded as a period of warm and stable climate in lower latitudes the stratigraphic continuity of the eemian layers is consequently discussed in section 3 of this paper in terms of all pertinent data which we are not able to reconcile

dinoflagellate cyst based reconstructions of mid to late holocene winter sea surface temperature and productivity from an anoxic fjord in the ne pacific ocean abstract published contemporary dinoflagellate distributional data from the ne pacific margin and estuarine environments n 136 were re analyzed using canonical correspondence analysis cca and partial canonical correspondence analysis pcca these analyses illustrated the dominant controls of winter temperature and productivity on the distribution of dinoflagellate cysts in this region dinoflagellate cyst based predictive models for winter temperature and productivity were developed from the contemporary distributional data using the modern analogue technique and applied to subfossil data from two mid to late holocene 5500 calendar years before present present cores tul99b03 and tul99b11 collected from effingham inlet a 15 km long anoxic fjord located on the southwest coast of vancouver island that directly opens to the pacific ocean through barkley sound sedimentation within these basins largely comprises annually deposited laminated couplets each made up of a winter deposited terrigenous layer and spring to fall deposited diatomaceous layer the effingham inlet dinoflagellate cyst record provides evidence of a mid holocene gradual decline in winter sst ending with the initiation of neoglacial advances in the region by 3500 cal bp a reconstructed late holocene increase in winter sst was initiated by a weakening of the california current which would have resulted in a warmer central gyre and more el nino like conditions

space and time variation of δ18o and δd in antarctic precipitation revisited 1 to better understand the variations over time of precipitation water isotopes measured in polar ice cores we have developed an intermediate complexity model icm of atmospheric water vapor transport and associated isotopic distillation the model builds directly from earlier work by d fisher and m hendricks and is calibrated against the measured modern spatial distribution of d and deuterium excess d model improvements include a correction to the equation governing advective transport which solves a major puzzle arising from the earlier work the new model shows isotopic data to be consistent with dominance of eddy diffusive transport at high latitudes model experiments are used to show that a wide variety of climate changes in subtropical source regions can affect antarctic d and that such d changes are consistently anticorrelated with changes of d magnitudes of d d are 1 to 5 and are much higher at the ice sheet margin than in the interior of the continent changes in the relative dominance of diffusive and advective transport are also shown to cause anticorrelated changes of similar magnitude isotopic sensitivities to temperature change d t are shown to also vary spatially with low values in marginal zones and higher values inland effects of ocean surface relative humidity on antarctic d are shown to be nearly uniform across the continent in contrast to earlier results given by petit et al 1991 but quantitatively small the method used by vimeux et al 2001 for folding humidity effects into source temperature effects is supported we draw attention to a pervasive misapplication of marine composition corrections to antarctic d records arguments are made in support of simple interpretations of calibrated ice core isotopic time series in terms of temperature changes despite the potential complexities in the system

formal subdivision of the holocene series epoch a discussion paper by a working group of intimate integration of ice core marine and terrestrial records and the subcommission on quaternary stratigraphy international commission on stratigraphy this discussion paper by a working group of intimate integration of ice core marine and terrestrial records and the subcommision on quaternary stratigraphy sqs of the international commission on stratigraphy ics considers the prospects for a formal subdivision of the holocene series epoch although previous attempts to subdivide the holocene have proved inconclusive recent developments in quaternary stratigraphy notably the definition of the pleistocene holocene boundary and the emergence of formal subdivisions of the pleistocene series epoch mean that it may be timely to revisit this matter the quaternary literature reveals a widespread but variable informal usage of a tripartite division of the holocene early middle or mid and late and we argue that this de facto subdivision should now be formalized to ensure consistency in stratigraphic terminology we propose an early middle holocene boundary at 8200 a bp and a middle late holocene boundary at 4200 a bp each of which is linked to a global stratotype section and point gssp should the proposal find a broad measure of support from the quaternary community a submission will be made to the international union of geological sciences iugs via the sqs and the ics for formal ratification of this subdivision of the holocene series epoch copyright 2012 john wiley sons ltd

volcanic aerosol records and tephrochronology of the summit greenland ice cores the recently collected greenland ice sheet project 2 gisp2 and greenland ice core project ice cores from summit greenland provide lengthy and highly resolved records of the deposition of both the aerosol h2so4 and silicate tephra components of past volcanism both types of data are very beneficial in developing the hemispheric to global chronology of explosive volcanism and evaluating the entire volcanism climate system the continuous time series of volcanic so42 for the last 110 000 years show a strong relationship between periods of increased volcanism and periods of climatic change the greatest number of volcanic so42 signals many of very high magnitude occur during and after the final stages of deglaciation 6000 17 000 years ago possibly reflecting the increased crustal stresses that occur with changing volumes of continental ice sheets and with the subsequent changes in the volume of water in ocean basins sea level change the increase in the number of volcanic so42 signals at 27 000 36 000 and 79 000 85 000 years ago may be related to initial ice sheet growth prior to the glacial maximum and prior to the beginning of the last period of glaciation respectively a comparison of the electrical conductivity of the gisp2 core with that of the volcanic so42 record for the holocene indicates that only about half of the larger volcanic signals are coincident in the two records other volcanic acids besides h2so4 and other so42 sources can complicate the comparisons although the threshold level picked to make such comparisons is especially critical tephra has been found in both cores with a composition similar to that originating from the vatnaoldur eruption that produced the settlement layer in iceland mid a d 870s from the icelandic eruption that produced the saksunarvatn ash 10 300 years ago and from the icelandic eruption s that produced the z2 ash zone in north atlantic marine cores 52 700 years ago the presence of these layers provides absolute time lines for correlation between the two cores and for correlation with proxy records from marine sediment cores and terrestrial deposits containing these same tephras the presence of both rhyolitic and basaltic shards in the z2 ash in thegisp2 core and the composition of the basaltic grains lend support to multiple icelandic sources torfajokull area and katla for the z2 layer deposition of the z2 layer occurs at the beginning of a stadial event further reflecting the possibility of a volcanic triggering by the effects of changing climatic conditions

progressive refolding in ductile shear zones abstract the foliation formed in a ductile shear zone can become folded by continuing shear in the zone without the foliation having to enter the shortening sector of the flow field if the foliation lies parallel to the shear plane infinitesimal variations in the rate of shear strain cause compensating rotations that may amplify into folds small increases in the rate cause backward rotations counter to the sense of shear these do not amplify small decreases cause forward rotations that do amplify

water isotope diffusion rates from the northgrip ice core for the last 16 000 years glaciological and paleoclimatic implications abstract a high resolution 0 05 m water isotopic record o 18 is available from the northgrip ice core in this study we look into the water isotope diffusion history as estimated by the spectral characteristics of the o 18 time series covering the last 16 000 years the diffusion of water vapor in the porous medium of the firn pack attenuates the initial isotopic signal predominantly having an impact on the high frequency components of the power spectrum higher temperatures induce higher rates of smoothing and thus the signal can be used as a firn paleothermometer we use a water isotope diffusion model coupled to a steady state densification model in order to infer the temperature signal from the site assuming the accumulation and strain rate history as estimated using the gicc05 layer counted chronology and a dansgaard johnsen ice flow model the temperature reconstruction accurately captures the timing and magnitude of the bolling allerod and younger dryas transitions a holocene climatic optimum is seen between 7 and 9 ky b2k with an apparent cooling trend thereafter our temperature estimate for the holocene climatic optimum points to a necessary adjustment of the ice thinning function indicating that the ice flow model overestimates past accumulation rates by about 10 at 8 ky b2k this result is supported by recent gas isotopic fractionation studies proposing a similar reduction for glacial conditions finally the record presents a climatic variability over the holocene spanning millennial and centennial scales with a profound cooling occurring at approximately 4000 years b2k the new reconstruction technique is able to provide past temperature estimates by overcoming the issues apparent in the use of the classical o 18 slope method it can at the same time resolve temperature signals at low and high frequencies

lake carbonate δ18o records from the yukon territory canada little ice age moisture variability and patterns abstract a 1000 yr history of climate change in the central yukon territory canada is inferred from sediment composition and isotope geochemistry from small groundwater fed seven mile lake recent observations of lake water 18 o lake level river discharge and climate variations suggest that changes in regional effective moisture precipitation minus evaporation are reflected by the lake s hydrologic balance the observations indicate that the lake is currently 18 o enriched by summer evaporation and that during years of increased precipitation when groundwater inflow rates to the lake increase lake water 18 o values decrease past lake water 18 o values are inferred from oxygen isotope ratios of fine grained sedimentary endogenic carbonate variations in carbonate 18 o supplemented by those in carbonate and organic 13 c c n ratios and organic carbon carbonate and biogenic silica accumulation rates document changes in effective moisture at decadal time scales during the early little ice age period to present results indicate that between ad 1000 and 1600 effective moisture was higher than today a shift to more arid climate conditions occurred after ad 1650 the 19th and 20th centuries have been the driest of the past millennium temporal variations correspond with inferred shifts in summer evaporation from marcella lake 18 o a similarly small stratified alkaline lake located 250 km to the southwest suggesting that the combined reconstructions accurately document the regional paleoclimate of the east central interior comparison with regional glacial activity suggests differing regional moisture patterns during early and late little ice age advances

the deglacial transition on the southeastern alaska margin meltwater input sea level rise marine productivity and sedimentary anoxia 1 oxygen isotope data from planktonic and benthic foraminifera on a high resolution age model 44 14c dates spanning 17 400 years document deglacial environmental change on the southeast alaska margin 59 33 32 n 144 9 21 w 682 m water depth surface freshening i e 18o reduction of 0 8 began at 16 650 170 cal years b p during an interval of ice proximal sedimentation likely due to freshwater input from melting glaciers a sharp transition to laminated hemipelagic sediments constrains retreat of regional outlet glaciers onto land circa 14 790 380 cal years b p abrupt warming and or freshening of the surface ocean i e additional 18o reduction of 0 9 coincides with the bolling interstade of northern europe and greenland cooling and or higher salinities returned during the allerod interval coincident with the antarctic cold reversal and continue until 11 740 200 cal years b p when onset of warming coincides with the end of the younger dryas an abrupt 1 reduction in benthic 18o at 14 250 290 cal years b p likely reflects a decrease in bottom water salinity driven by deep mixing of glacial meltwater a regional megaflood event or brine formation associated with sea ice two laminated opal rich intervals record discrete episodes of high productivity during the last deglaciation these events precisely dated here at 14 790 380 to 12 990 190 cal years b p and 11 160 130 to 10 750 220 cal years b p likely correlate to similar features observed elsewhere on the margins of the north pacific and are coeval with episodes of rapid sea level rise remobilization of iron from newly inundated continental shelves may have helped to fuel these episodes of elevated primary productivity and sedimentary anoxia

a lagrangian approach to modelling stable isotopes in precipitation over mountainous terrain a lagrangian rayleigh distillation model is used to track the evolution of stable isotopes in precipitation over mountainous terrain from the pacific coast of canada to two alpine field sites in the canadian rocky mountains precipitation 18o at vancouver constrains the model and air mass back trajectories provide the water vapour pathway for 10 winter storm events isotopic values along storm pathways are modelled with a classical rayleigh model that prescribes a linear decrease in temperature and pressure from initial to final conditions and two models that account directly for orographic precipitation processes by i applying an orographic rainfall model and ii using north american regional reanalysis data to calculate the change in vapour content along storm pathways all models are significant predictors of snowpack 18o but the orographic model provides the best fit to precipitation weighted 18o for each storm the improvement in modelled 18o by accounting for terrain along storm trajectories illustrates the need to account for orographically driven moisture loss when modelling vapour transport to ice core sites with mountainous upwind terrain this finding is also applicable to isotopic studies of paleoaltimetry and source areas of groundwater recharge copyright 2011 john wiley sons ltd

the southwest indian monsoon over the last 18 000 years previously published results suggest that the strength of the sw indian monsoon can vary significantly on century to millenium time scales an observation that has important implications for assessments of future climate and hydrologic change over densely populated portions of asia we present new well dated multi proxy records of past monsoon variation from three separate arabian sea sediment cores that span the last glacial maximum to late holocene to a large extent these records confirm earlier published suggestions that the monsoon strengthened in a series of abrupt events over the last deglaciation however our data provide a somewhat refined picture of when these events took place and suggest the primacy of two abrupt increases in monsoon intensity one between 13 and 12 5 ka and the other between 10 and 9 5 ka this conclusion is supported by the comparisons between our new marine data and published paleoclimatic records throughout the african asian monsoon region the comparison of data sets further supports the assertion that maximum monsoon intensity lagged peak insolation forcing by about 3000 years and extended from about 9 5 to 5 5 ka the episodes of rapid monsoon intensification coincided with major shifts in north atlantic european surface temperatures and ice sheet extent this coincidence coupled with new climate model experiments suggests that the large land sea thermal gradient needed to drive strong monsoons developed only after glacial conditions upstream of and on the tibetan plateau receded cold north atlantic sea surface temperatures european ice sheets and extensive asian snow cover it is likely that abrupt changes in seasonal soil hydrology were as important to past monsoon forcing as were abrupt snow related changes in regional albedo our analysis suggests that the monsoon responded more linearly to insolation forcing after the disappearance of glacial boundary conditions decreasing gradually after about 6 ka our data also support the possibility that significant century scale decreases in monsoon intensity took place during the early to mid holocene period of enhanced monsoon strength further highlighting the need to understand paleomonsoon dynamics before accurate assessments of future monsoon strength can be made

holocene variations in the asian monsoon inferred from the geochemistry of lake sediments in central tibet we present a record of monsoon variations for the early and middle holocene that is inferred from the geochemistry of sediment cores from ahung co a lake in central tibet the resolution of this record is better than 50 yr and the age model is derived from radiocarbon ages of terrestrial charcoal which eliminates errors associated with the lake hard water effect we made down core geochemical measurements of carbonate organic carbon c n and 13c of bulk organic matter 13c and 18o of carbonate and dolomite proxy calibration and modern water balance reconstruction show that these are proxies for lake depth and the amount of monsoon precipitation we find that lake level and monsoon precipitation have been decreasing at ahung co since the early holocene 7500 cal yr b p superimposed on this trend are rapid declines in monsoon rainfall at 7000 7500 and 4700 cal yr b p and seven century scale wet dry oscillations the cores do not contain sediment from the last 4000 yr surface sediments from the lake accumulated during the 20th century however from this we argue that lake levels have risen again recently following a late holocene dry period

variscan exhumation of a subducted paleozoic continental margin the basal units of the ordenes complex galicia nw spain a structural and metamorphic study was carried out in the basal units of the ordenes complex in spain thought to represent a subducted part of the paleozoic margin of gondwana according to their metamorphic evolution this part of the margin was subducted at the onset of the variscan orogeny becoming part of an accretionary complex developed below a colliding element built previously variations in the pt conditions of the first high pressure metamorphic event along the units indicate a polarity of the subduction to the west subsequent underthrusting of more continental material blocked the subduction and triggered the ascent and exhumation of the basal units whereas the convergence continued recumbent folds and thrusts developed along with successive normal detachments compressional and extensional structures were synchronous or alternated in time and together induced the thinning and tapering of the orogenic wedge and its lateral spreading the unroofing took place locally under an inverted temperature gradient caused by a detachment which carried a part of the hot mantle wedge above the subduction zone over the subducted units

century scale solar variability and alaskan temperature change over the past millennium 1 correlation of geologic histories from 130 alaskan glaciers with a record of solar variation suggests that multi decadal to century scale temperature variations in the north pacific and arctic sectors have been influenced by solar forcing over the past thousand years mountain glacier fluctuations are primarily a record of summer cooling and the composite glacial history from three climatic regions across alaska shows ice expansions approximately every 200 years compatible with a solar mode of variability the modulating effects of the cold phases of the pacific decadal oscillation and the arctic oscillation may when in phase with decreased solar activity serve to amplify cooling forcing glacier advance

holocene environmental history of the aishihik region yukon canada a 2 7 m sediment core from wa01 a small pond in southwest yukon canada unofficial name 61 14 41 n 136 55 35 w 1000 m above sea level documents the postglacial vegetation and climate history of the aishihik basin open birch shrub tundra established at the site ca 10 900 cal years bp immediately after deglaciation picea glauca established ca 10 200 cal years bp and an open spruce forest ecosystem has since remained dominant on the landscape a gradual increase in alnus crispa starting ca 6600 cal years bp has also been noted in other studies from central yukon suggesting a significant climate transition in yukon at this time an alternating pattern in sediment loss on ignition also beginning ca 6600 cal years bp may be broadly related to trends in 18o values from the mount logan and jellybean lake oxygen isotope records and is most likely reflective of periodic changes in available moisture in the region resulting from alterations in the strength and position of the aleutian low press

formal subdivision of the quaternary system period present status and future directions abstract the quaternary system period and pleistocene series epoch were defined in 2009 by the global boundary stratotype section and point gssp for the gelasian stage age 2 58 ma which aligns with marine isotope stage mis 103 and approximates the gauss matuyama chron boundary contrary to earlier reports the vrica gssp 1 80 ma was repurposed in 2011 to define the calabrian stage effectively completing the lower pleistocene subseries subepoch the candidate for the middle pleistocene subseries and proposed chibanian stage gssp 774 ka is the chiba section japan it aligns with mis 19 and approximates the matuyama brunhes chron boundary 773 ka the upper pleistocene subseries with a base traditionally marked by the onset of the last interglacial is not yet defined by gssp the holocene series epoch was formally defined in 2008 by a gssp in the ngrip2 greenland ice core with an age of 11 700 yr b2k before 2000 ce and in 2018 was subdivided using climatic events at 8 2 and 4 2 ka into the greenlandian northgrippian and meghalayan stages ages and their corresponding lower early middle upper late subseries subepochs the northgrippian gssp 8236 yr b2k is defined in the ngrip1 greenland ice core and the meghalayan gssp 4250 yr b2k in a speleothem from meghalaya india this subdivision formally introduces the rank of subseries subepoch and incorporates by far the briefest of all stages into the geological time scale using ice cores and a speleothem for gssps is unique to the holocene the presently undefined term anthropocene is already used extensively and like holocene subdivisional terms its functionality will be enhanced by formal definition the anthropocene should not be confused with anthropogenic it reflects a tipping point in the earth system response to the marked intensification of human impacts not simply the fact of human impact the geological anthropocene as currently envisioned would start in the mid twentieth century holding the rank of series and terminating the holocene but not interfering with its subdivision other than to terminate the meghalayan stage

the mt logan holocene late wisconsinan isotope record tropical pacific yukon connections the ice core recovered from prospector russell col on mt logan 5 4 km a s l in the yukon spans over 20 000 years this unique record offers a pacific view of the stable isotope and chemical record from the lateglacial to the present the timescale is based on seasonal counted years the largest known volcanic acid signatures and the major shift in stable isotopes and chemistry at the end of the younger dryas there are large and sustained changes in the stable isotopic record that are anti correlated with marine and continental chemistry series the oxygen 18 in this area is not a proxy for palaeotemperature but rather for source region the last major isotope shift in ad 1840 in 18 o and chemistry is compared with the quinn s enso record during periods of more frequent la nina stronger tropical easterlies there is more zonal flow of water vapour transport to the pacific northwest 18 o values are larger and the deuterium excess d smaller these periods coincide with periods of lower accumulation precipitation in southern yukon the holocene 18 o record indicates many large shifts between the meridional strong el nino and zonal la nina comparison of the logan isotopic record and the moisture temperature sensitive time series of peat bog inception dates for the northwest shows a strong correlation 0 36 that points to high accumulation rates coincident with low 18 o and enhanced meridional flow major changes in the core at 4200 bp and 7000 8000 bp point to enhanced meridional flow which coincide with big changes in the pacific palaeorecords of the balance between el nino and la nina 4200 bp seems to have inaugurated the modern enso world

a synchronized dating of three greenland ice cores throughout the holocene as part of the effort to create the new greenland ice core chronology 2005 gicc05 a synchronized stratigraphical timescale for the holocene parts of the dye 3 grip and ngrip ice cores is made by using volcanic reference horizons in electri cal conductivity measurements to match the cores the main annual layer counting is carried out on the most suited records only exploit ing that the three ice cores have been drilled at locations with different climatic con ditions and differences in ice flow however supplemental counting on data from all cores has been performed between each set of reference horizons in order to verify the valid ity of the match after the verification the main dating is transferred to all records us ing the volcanic reference horizons as tie points an assessment of the mean annual layer thickness in each core section confirms that the new synchronized dating is consistent for all three cores the data used for the main annual layer counting of the past 7900 years are the dye 3 grip and ngrip stable isotope records as the high accumulation rate at the dye 3 drill site makes the seasonal cycle in the dye 3 stable isotopes very resistant to firn diffusion an effort has been made to extend the dye 3 holocene record the new syn chronized dating relies heavily on this record of 75 000 stable isotope samples the dat ing of the early holocene consists of an already established part of gicc05 for grip and ngrip which has now been transferred to the dye 3 core gicc05 dates the younger dryas termination as defined from deuterium excess to 11 703 b2k 130 years earlier than the previous grip dating

enhanced late holocene enso pdo expression along the margins of the eastern north pacific abstract pacific climate is known to have varied during the holocene but spatial patterns remain poorly defined this paper compiles terrestrial and marine proxy data from sites along the northeastern pacific margins and proposes that they indicate 1 suppressed enso conditions during the middle holocene between 8000 and 4000 cal bp with a north pacific that generally resembled a la nina like or more negative pdo phase and 2 a climate transition between 4200 and 3000 cal bp that appears to be the teleconnected expression to a more modern like enso pacific compared to modern day conditions the compiled data suggest that during the middle holocene the aleutian low was generally weaker during the winter and or located more to the west while the north pacific high was stronger during the summer and located more to the north coastal upwelling off california was more enhanced during the summer and fall but suppressed during the spring oregon and california sea surface temperatures ssts were cooler the santa barbara basin had an anomalous record suggesting warmer ssts late holocene records indicate a more variable el nino like and more positive pdo pacific the aleutian low became more intensified during the winter and or located more to the east the north pacific high became weaker and or displaced more to the south coastal upwelling off california intensified during the spring but decreased during the fall oregon and california ssts became warmer recording the shoreward migration of sub tropical gyre waters during the fall while spring upwelling cooler sst increased in the santa barbara basin the high resolution proxy records indicate enhanced enso and pdo variability after 4000 cal bp off southern california 3400 cal bp off northern california and by 2000 cal bp in southwestern yukon a progressively northward migration of the enso teleconnection during the late holocene is proposed

subdividing the holocene series epoch formalization of stages ages and subseries subepochs and designation of gssps and auxiliary stratotypes the holocene which currently spans 11 700 years is the shortest series epoch within the geological time scale gts yet it contains a rich archive of evidence in stratigraphical contexts that are frequently continuous and often preserved at high levels of resolution on 14 june 2018 the executive committee of the international union of geological sciences formally ratified a proposal to subdivide the holocene into three stages ages along with their equivalent subseries subepochs each anchored by a global boundary stratotype section and point gssp the new stages are the greenlandian lower early holocene subseries subepoch with its gssp in the greenland ngrip2 ice core and dated at 11 700 a b2k before 2000 ce the northgrippian middle holocene subseries subepoch with its gssp in the greenland ngrip1 ice core and dated at 8236 a b2k and the meghalayan upper late holocene subseries subepoch with its gssp in a speleothem from mawmluh cave north eastern india with a date of 4250 a b2k we explain the nomenclature of the new divisions describe the procedures involved in the ratification process designate auxiliary stratotypes to support the gssps and consider the implications of the subdivision for defining the anthropocene as a new unit within the gts less

ice core net snow accumulation and seasonal snow chemistry at a temperate glacier site mount waddington southwest british columbia canada a 141m ice core was recovered from combatant col 51 385 n 125 258 w 3000ma s l mount waddington coast mountains british columbia canada records of black carbon dust lead and water stable isotopes demonstrate that unambiguous seasonality is preserved throughout the core despite summer surface snowmelt and temperate ice high accumulation rates at the site 4 m ice eq a 1 limit modification of annual stratigraphy by percolation of surface meltwater the ice core record spans the period 1973 2010 an annually averaged time series of lead concentrations from the core correlates well with historical records of lead emission from north america and with ice core records of lead from the greenland ice sheet the depth age scale for the ice core provides sufficient constraint on the vertical strain to allow estimation of the age of the ice at bedrock total ice thickness at combatant col is 250 m an ice core to bedrock would likely contain ice in excess of 200 years in age accumulation at combatant col is significantly correlated with both regional precipitation and large scale geopotential height anomalies

interpreting h2o isotope variations in high altitude ice cores using a cyclone model 1 vertical profiles of isotope 18o or d values versus altitude z from sea level to high altitude provide a link to cyclones which impact most ice core sites cyclonic structure variations cause anomalous variations in ice core time series which may obscure the basic temperature signal only one site mount logan yukon provides a complete versus z profile generated solely from data at other sites such a profile has to be constructed by supplementing field data this requires using the so called isotopic or thermometer which relates to a reference temperature t the construction of gapped sections of versus z curves requires assuming a typical atmospheric lapse rate dt dz where t is air temperature and using the slope d dt of a site derived thermometer to calculate d dz using a three layer model of a cyclone examples are given to show geometrically how changes in the thickness of the middle mixed layer leads to the appearance of anomalous values in time series producing decalibration of the thermometer there the results indicate that restrictions apply to the use of the thermometer in ice core paleothermometry according to site altitude regional meteorology and climate state

oxygen isotope records of holocene climate variability in the pacific northwest abstract oxygen isotope 18o measurements of authigenic carbonate from cleland lake southeastern british columbia paradise lake central british columbia and lime lake eastern washington provide a 9000 year holocene record of precipitation evaporation balance variations in the pacific northwest both cleland lake and paradise lake are small surficially closed basin systems with no active inflows or outflows lime lake is surficially open with a seasonally active overflow water isotope values from cleland and paradise plot along the local evaporation line indicating that precipitation evaporation balance is a strong influence on lake hydrology in contrast lime lake water isotope values plot on the local meteoric water line signifying minimal influence by evaporation to infer past hydrologic balance variations at a high temporal resolution we sampled the cleland paradise and lime lake sediment cores at 1 60 mm intervals 3 33 years per sample on average and measured the isotopic composition of fine grained

lake sediment records of holocene hydroclimate and impacts of the mount mazama eruption north central washington usa abstract multi proxy sediment records from castor lake and scanlon lake north central washington provide a late quaternary perspective on lake catchment hydrologic and ecosystem responses to climate change and the mazama volcanic ashfall event analyses of authigenic carbonate mineral oxygen and carbon isotope values organic carbon and nitrogen content and sedimentological facies were conducted on sediment from castor lake in order to reconstruct lake catchment hydrologic balance the source and abundance of organic matter and variations in lake level sedimentary facies characterization was conducted on the scanlon lake sediment in order to provide supporting evidence for the lake level shifts inferred from the castor lake data marked changes in castor lake proxy values occur from 12 860 to 11 440 calendar years before present yr bp suggesting lake catchment responses to the younger dryas cold reversal including higher lake levels substantial variability in productivity and increased catchment erosion high 18o values at 9630 yr bp indicate that lake levels were lower than at present and that the early holocene was dry sedimentological analyses and 18o data demonstrate that subsequent to the mazama climactic eruption 7600 yr bp a transition to the lowest lake levels of the holocene occurred over several centuries with maximum 18o values at 7290 90 uncertainty range 7020 7500 yr bp and low lake levels persisting until 6190 5960 6410 yr bp lithological changes in the scanlon lake record support these inferences the lowest 18o values of the holocene occur in sediment from 5000 yr bp indicating high lake levels at this time after which a secular trend toward higher 18o values and lower lake levels occurred the prolonged lowstand in the centuries following the mazama eruption suggests that catchment hydrologic characteristics were strongly impacted by the ashfall through effects on soil water retention capacity that similar responses may have occurred in comparable settings within the mazama ashfall zone and that such volcanic events have the potential confound the climate signal in lake sediment records were a similar event to happen in the future catchment hydrology stream river discharge and lake catchment ecosystem dynamics could be affected for centuries

solid electrical conductivity ecm from four agassiz ice cores ellesmere island nwt canada high resolution signal and noise over the last millennium and low resolution over the holocene the solid dc electrical conductivity ecm electrical conductivity method of polar ice cores has become an important tool in identifying and quantifying volcanic acid layers and this paper addresses the question of how much signal and noise there is in single ecm series a number of high resolution 10 samples year ice core ecm records from the agassiz ice cap are correlated over the last 900 years corre lations decrease with distance apart due to local drift and melt layer noise but correlations are probably reduced also by differences in methodology and core storage it is found that only peak sizes in the uppermost two percentiles retain their ranking and recognizability from core to core with continuous sampling however the smaller peaks can be cross identified between cores even though they lose their size rank averaging or stacking several ecm records reduces the noise five year averages of ecm for the holocene are presented for the agassiz cores and their correlations interpreted as functions of distance apart and differences in method the large scale melting in the early holocene 8ka to 10ka almost completely de acidifies the ice in all the agas siz cores

data review on the small mammals from the late early pleistocene of vallparadis estacio layer evt7 valles penedes basin ne iberian peninsula biochronological and palaeoenvironmental implications abstract the chronology of layer evt7 of the vallparadis estacio section has been a hotly debated topic during recent years with some authors supporting an age close to the early middle pleistocene boundary 0 83 ma others favouring an age older than the jaramillo magnetostratigraphic subchron ca 1 2 ma and others proposing a chronology between 0 98 and 0 95 ma for layer evt7 here we review the biochronological data from evt7 and review the biochronology based on the study of mimomys savini using all the available remains of this species which is the most abundant rodent species from this layer based on the morphologic and biometric comparison with remains of the same species from other similarly aged iberian localities gran dolina td4 6 from atapuerca and barranco leon d and fuente nueva 3 from the guadix baza basin we propose an estimated age for evt7 in the chronologic range from 0 99 to 0 94 ma we further perform a paleoenvironmental study based on the whole small mammal assemblage from evt7 which allows us to infer an open and humid environment in the vicinity of a lacustrine area or fluvial course recently published work also studied the rodent assemblage from evt7 however in this study only a part of the small mammals recovered from evt7 was studied and therefore its results can be partially biased

improved age estimates for the white river and bridge river tephras western canada new 14c ages date the eruptions that produced the white river and bridge river tephras two important holocene marker beds in western canada the 14c ages were obtained on trees in growth position buried in coarse tephra and a pyroclastic flow near the source vents the mean calendric age of the white river eruption based on four 14c ages is 1147 cal years bp calibrated years approximately equivalent to calendric years or ad 803 the 2 age range obtained from the two most precise 14c ages is 1014 1256 cal years bp or ad 694 936 the mean age of the bridge river eruption determined both from i the single most precise outer ring 14c age and ii the weighted mean of six outer ring 14c ages is 2360 cal years bp or 411 bc 2 age range 2349 2704 cal years bp or 755 400 bc

late holocene aridification recorded in the stable carbon and nitrogen isotope composition of soils from nainital lesser himalaya abstract this study incorporates micromorphology geochemistry and stable carbon and nitrogen isotope compositions of soil organic matter 13c and 15n in a radiocarbon dated holocene alfisol section from nainital northwest himalaya india to understand pedogenic and vegetation response to changing indian summer monsoon ism soil micromorphology suggests this soil to be an alfisol that formed in semiarid to humid conditions extensive illuviation with thick clay pedofeatures found in the bt horizon suggests wet conditions and intense monsoon during early to middle holocene 9 0 4 6 ka the 13c varies from 14 2 to 22 6 and reflects abrupt changes in the proportions of c3 and c4 plants in the ecosystem during late holocene an average 13c of 21 6 1 0 during early to middle holocene 9 0 4 6 ka indicates that the vegetation was dominated by c3 plants growth under hot humid and strong monsoonal conditions on the other hand 13c 16 7 2 1 during late holocene 4 1 ka suggests distinct vegetation shift towards increasing c4 plants abundance related to aridification weak ism at 4 ka the pattern of 15n variability in the soil is similar to that observed for the 13c variability in the profile the 15n varies from 4 4 to 8 3 with significantly more positive values during late holocene weaker monsoon compared to early to middle holocene stronger monsoon consistent with the relationship between 15n and mean annual precipitation observed on a global scale our study demonstrates a strong and rapid adjustment of vegetation in response to ism variability during holocene