effects of sample mass and macrofossil type on radiocarbon dating of arctic and boreal lake sediments dating lake sediments by accelerator mass spectrometry ams 14 c analysis of terrestrial plant macrofossils overcomes one of the main problems associated with dating bulk sediment samples i e the presence of old organic matter even so many ams dates from arctic and boreal sites appear to misrepresent the age of the sediment to understand the nature of these apparent dating anomalies better we conducted a series of 14 c dating experiments using samples from alaskan and siberian lake sediment cores first to test whether our analytical procedures introduced a sample mass bias we obtained 14 c dates for different sized pieces of single woody macrofossils in these sample mass experiments statistically equivalent ages were found for samples as small as 0 05 mg c secondly to assess whether macrofossil type influenced dating results we conducted sample type experiments in which 14 c dates were obtained for different macrofossil types sieved from the same depth in the sediment we dated materials from multiple levels in sediment cores from upper capsule lake north slope northern alaska and grizzly lake copper river basin southern alaska and from single depths in other records from northern alaska in several of the experiments there were significant discrepancies between dates for different plant tissues and in most cases wood and charcoal were older than other macrofossil types usually by several hundred years this pattern suggests that 14 c dates for woody macrofossils may misrepresent the age of the sediment by centuries perhaps because of their longer terrestrial residence time and the potential in built age of long lived plants this study identifies why some 14 c dates appear to be inconsistent with the overall age depth trend of a lake sediment record and it may guide the selection of 14 c samples in future studies

a 2100 year trace element and stable isotope record at decadal resolution from rice lake in the northern great plains usa a 2100 year multiple proxy record at decadal resolution from a topographically closed but hydrolog ically open lake basin was used to reconstruct changes in lake salinity and evaporative intensity and to evaluate the reliability of different proxies for inferring climatic change in the glaciated northern great plains ngp at rice lake north dakota the ostracode mg ca ratios show good correlation with other ostracode diatom and aeolian proxy records from other sites in the ngp all of these records show significant century scale periodicities which have been related to solar variability as inferred from atmospheric radiocarbon records this coherent and consistent pattern suggests that these sites record climatic variability at regional scales the interval of the mediaeval climatic anomaly from 900 to 550 cal yr bp contains two pronounced dry periods during the following little ice age a single period of frequent drought that peaked at 300 cal yr bp was bracketed by wet periods before and af

moisture and temperature changes associated with the mid holocene tsuga decline in the northeastern united states abstract a decline of hemlock tsuga populations at ca 5 5 ka thousands of calibrated radiocarbon years before 1950 ad stands out as the most abrupt vegetation change of the holocene in north america but remains poorly understood after decades of study recent analyses of fossil pollen have revealed a concurrent abrupt oak quercus decline and increases in the abundance of beech fagus and pine pinus on cape cod in eastern massachusetts but the replacement of drought tolerant oaks by moisture sensitive beeches appears inconsistent with low lake levels in the region at the same time the oak and beech changes are also limited to coastal areas and the coastal inland differences require an explanation here we develop a new lake level reconstruction from deep pond cape cod by using a transect of sediment cores and ground penetrating radar gpr profiles to constrain the past elevations of the sandy littoral zone of the pond the reconstruction shows that a series of multi century episodes of low water coincide with the abrupt hemlock and oak declines and interrupt subsequent phases of hemlock recovery the lake level variations equal precipitation deficits of 100 mm superimposed on a holocene long moisture increase of 400 mm however because moisture deficits do not easily explain the oak and beech changes we also evaluate how the climate preferences of the regional vegetation changed over time by matching the fossil pollen assemblages from deep pond with their modern equivalents reconstructions of the precipitation requirements of the vegetation correlate well even in detail with the lake level record r 0 88 at deep pond and indicate close tracking of effective moisture precipitation minus evapotranspiration by the vegetation despite the abrupt species declines which could have decoupled climate and vegetation trends reconstructions of the temperature preferences of the vegetation indicate that coastal sites may have cooled by 0 5 2 5 c after ca 5 5 ka while inland sites warmed by 0 5 1 c the change in coastal temperature preferences agrees with sea surface cooling in the western atlantic ocean of 1 c consequently the persistence of low hemlock abundance after 5 5 ka in the northeast u s may have resulted from oceanic changes that produced multi century droughts and thus delayed the post decline recovery of hemlock populations

ice sheet sources of sea level rise and freshwater discharge during the last deglaciation we review and synthesize the geologic record that constrains the sources of sea level rise and freshwater discharge to the global oceans associated with retreat of ice sheets during the last deglaciation the last glacial maximum 26 19 ka was terminated by a rapid 5 10 m sea level rise at 19 0 19 5 ka sourced largely from northern hemisphere ice sheet retreat in response to high northern latitude insolation forcing sea level rise of 8 20 m from 19 to 14 5 ka can be attributed to continued retreat of the laurentide and eurasian ice sheets with an additional freshwater forcing of uncertain amount delivered by heinrich event 1 the source of the abrupt acceleration in sea level rise at 14 6 ka meltwater pulse 1a 14 15 m includes contributions of 6 5 10 m from northern hemisphere ice sheets of which 2 7 m represents an excess contribution above that derived from ongoing ice sheet retreat widespread retreat of antarctic ice sheets began at 14 0 15 0 ka which together with geophysical modeling of far field sea level records suggests an antarctic contribution to this meltwater pulse as well the cause of the subsequent younger dryas cold event can be attributed to eastward freshwater runoff from the lake agassiz basin to the st lawrence estuary that agrees with existing lake agassiz outlet radiocarbon dates much of the early holocene sea level rise can be explained by laurentide and scandinavian ice sheet retreat with collapse of laurentide ice over hudson bay and drainage of lake agassiz basin runoff at 8 4 8 2 ka to the labrador sea causing the 8 2 ka event

influences of forested and grassland vegetation on late quaternary ecosystem development as recorded in lacustrine sediments geosphere biosphere interactions are ubiquitous features of the earth surface yet the development of interactions between newly exposed lithologic surfaces and colonizing plants during primary succession after glaciation are lacking temporal detail to assess the nature rate and magnitude of vegetation influence on parent material and sediment delivery we analyzed ecosystem and geochemical proxies from lacustrine sediment cores at a grassland site and a forested site in the northern united states over time terrigenous inputs declined at both sites with increasing amounts of organic inputs toward present the similarities between sites were striking given that the grassland sequence began in the early holocene and the forested sequence began after the last glacial maximum multiple mechanisms of chemical weathering hydrologic transport and changes in source material potentially contribute to this pattern although there were strong links between vegetation composition and nitrogen cycling at each site it appears that changes in forest type or from oak woodland to grassland did not exert a large influence on elemental k ti si ca fe mn and s abundance in the sedimentary sequences rather other factors in the catchment lake system determined the temporal sequence of elemental abundance

holocene marine transgression in the black sea new evidence from the northwestern black sea shelf abstract for two decades the timing and rate of holocene marine transgression and the level of the black sea prior to the transgression has been the focus of many geological palaeoecological and archaeological studies the potential importance of confirming or rejecting the catastrophic flood hypothesis by refining the chronology of the marine transgression and determining the water level of the early holocene black sea neoeuxinian lake is the aim of many ongoing black sea palaeoecological studies in this report we review previous studies and present new data on the early holocene marine transgression obtained from multidisciplinary studies of several cores from different parts of the black sea core 342 from the edge of the dniester paleovalley on nw shelf is particularly important because it provides wood and leaf material from several peat and muddy peat beds each up to 10 cm thick inter layered in a coastal succession with mud clay and shell coquina ams ages for wood fragments and sedge leaves in the peat layers provide critical new data for calibrating and re tuning of previously published shell and bulk detrital peat ages our multi disciplinary study of geological material recovered from different shelf areas of the black sea refines the chronology of the marine transgression and clarifies conflicting interpretations of the water level and salinity of the neoeuxinian lake prior to the initial mediterranean inflow imi and transgression of mediterranean water in the holocene we find that 1 the level of the late neoeuxinan lake prior to the early holocene mediterranean transgression stood around 40 m bsl but not 100 m or more as suggested by advocates of catastrophic rapid prominent flooding of the black sea by mediterranean water 2 at all times the neoeuxinan lake was brackish with salinity not less that 7 psu 3 by 8 9 ka bp the black sea shelf was already submerged by the mediterranean transgression an increase in salinity took place over 3600 years with rate of the marine water incursion being estimated in the order of 0 05 cm 1 7 cm a 1 4 the combined data set of sedimentological characteristics and microfossil data establish that the holocene marine transgression was of a gradual progressive nature in the early holocene

rapid thinning of the laurentide ice sheet in coastal maine usa during late heinrich stadial 1 abstract few data are available to infer the thinning rate of the laurentide ice sheet lis through the last deglaciation despite its importance for constraining past ice sheet response to climate warming we measured 31 cosmogenic 10 be exposure ages in samples collected on coastal mountainsides in acadia national park and from the slightly inland pineo ridge moraine complex a 100 km long glaciomarine delta to constrain the timing and rate of lis thinning and subsequent retreat in coastal maine samples collected along vertical transects in acadia national park have indistinguishable exposure ages over a 300 m range of elevation suggesting that rapid century scale thinning occurred at 15 2 0 7 ka similar to the timing of abrupt thinning inferred from cosmogenic exposure ages at mt katahdin in central maine davis et al 2015 this rapid ice sheet surface lowering which likely occurred during the latter part of the cold heinrich stadial 1 event 19 14 6 ka may have been due to enhanced ice shelf melt and calving in the gulf of maine perhaps related to regional oceanic warming associated with a weakened atlantic meridional overturning circulation at this time the ice margin subsequently stabilized at the pineo ridge moraine complex until 14 5 0 7 ka near the onset of bolling interstadial warming our 10 be ages are substantially younger than marine radiocarbon constraints on lis retreat in the coastal lowlands suggesting that the deglacial marine reservoir effect in this area was 1 200 14 c years perhaps also related to the sluggish atlantic meridional overturning circulation during heinrich stadial 1

synchronization of late glacial vegetation changes at crystal lake illinois usa with the north atlantic event stratigraphy abstract late glacial 17 11 cal ka bp pollen records from midwestern north america show similar vegetation trends however poor dating resolution wide interval pollen counts and variable sedimentation rates have prevented the direct correlation with the north atlantic event stratigraphy as represented in the greenland ice core records thus preventing the understanding of the teleconnections and mechanisms of late quaternary events in the northern hemisphere the widespread occurrence of late glacial vegetation and climates with no modern analogs also hinders late glacial climate reconstructions a high resolution pollen record with a well controlled age model from crystal lake in northeastern illinois reveals vegetation and climate conditions during the late glacial and early holocene intervals late glacial crystal lake pollen assemblages dominated by picea mariana and fraxinus nigra with lesser amounts of abies and larix suggest relatively wet climate despite fluctuations between colder and warmer temperatures vegetation changes at crystal lake are coeval with millennial scale trends in the ngrip ice core record but major shifts in vegetation at crystal lake lag the ngrip record by 300 400 yr this lag may be due to the proximity of the laurentide ice sheet the ice sheet s inherent slowness in response to rapid climate changes and its effect on frontal boundary conditions and lake effect temperatures

a model of the western laurentide ice sheet using observations of glacial isostatic adjustment we present the results of a new numerical model of the late glacial western laurentide ice sheet constrained by observations of glacial isostatic adjustment gia including relative sea level ind

mid holocene palaeolimnological record of a southern hemisphere subtropical lake spanning the last 6000 years lake jennings fraser island australia the study of climate mechanisms in the southern hemisphere during the holocene remains an area of active research that lacks the spatial and temporal connectivity characteristic of northern hemisphere research the subtropical temperate climate transition zone of eastern australia provides a unique location to investigate long term environmental changes during the holocene lake jennings on fraser island was used to investigate climate change in this transition zone using palaeolimnological techniques the beginning of the lake jennings record 6000 to 3500 cal ybp is characterised by fluctuations in geochemical signals an abundance of sponge spicules and a lack of diatom species results suggest gradually increasing precipitation and water depth which affect nutrient cycling however the biological functioning of the lake is difficult to interpret due to the absence of diatoms possibly a result of turbidity dissolution and or predation by freshwater sponges during the late holocene 3500 cal

a high resolution record of climate variability and landscape response from kettle lake northern great plains north america abstract a decadal scale multiproxy record of minerals pollen and charcoal from kettle lake north dakota provides a high resolution record of climate and vegetation change spanning the entire holocene from the northern great plains ngp in north america the chronology is established by over 50 ams radiocarbon dates this record exhibits millennial scale trends evident in other lower resolution studies but with much more detail on short term climate variability and on the rapidity and timing of major climatic shifts as a proxy for precipitation we utilize the rate of endogenic carbonate sedimentation which depends on groundwater inflow which in turn depends on precipitation independent cluster analyses of mineral and pollen data reveal major holocene mode shifts at 10 73 ka ka cal yr bp 9 25 ka and 4 44 ka the early holocene 11 7 9 25 ka was generally wet with perhaps a trend to higher evaporation associated with warming temperatures a switch from calcite to aragonite deposition associated with a severe but brief drought occurred at 10 73 ka from 10 73 ka to 9 25 ka climate was generally humid but punctuated at 100 300 yr intervals by brief droughts including the most severe drought of the entire holocene at 9 25 ka this event was coeval with the 9 3 9 2 ka event in the greenland ice cores and observed at a number of sites worldwide in contrast the prominent 8 2 ka event in greenland is not remarkable at kettle lake the prominence of the 9 25 event locally in the ngp may be due to a major drawdown and northward retreat of lake agassiz at this time reducing its mesoclimatic effect on the ngp and thrusting the region into an insolation controlled regime the mid holocene 9 25 4 44 ka was characterized by great variability in moisture on a multi decadal scale with severe droughts alternating with more humid periods the high abundance of the weedy but drought intolerant ambrosia generally during the mid holocene and specifically during the multi decadal drought periods is seemingly paradoxical but can be explained by high interannual variability of moisture overlaid on the multi decadal variability the late holocene 4 44 ka present was also characterized by multi decadal variability in moisture but was generally wetter than the mid holocene and the magnitude of variability was less the trends in wet dry mineral pollen and charcoal proxies were similar to the mid holocene but late holocene mineral pollen assemblages are distinct from mid holocene the shift to wetter climate in the late holocene was more gradual than the abrupt shift to arid conditions 9 25 ka which may explain the asymmetric retreat and readvance of forest along the eastern margin of the ngp precipitation variations in the ngp have been linked with pacific and atlantic sea surface temperatures and mid holocene drought in the ngp has been linked with sustained la nina like conditions in the pacific these linkages may explain the decadal and millennial scale variations seen in the ngp but cause of the prominent century scale variations remains elusive

a new method to constrain soil development time using both osl and radiocarbon dating abstract the time over which a soil has developed since the parent materials were deposited and subaerially exposed referred to here as soil development time is of considerable interest to pedologists geomorphologists geologists archeologist and paleoclimatologists soil development time has been estimated both indirectly based on the degree of soil development and directly by radiocarbon dating of soil organic matter optically stimulated luminescence osl dating of parent material deposition and through exposure dating using cosmogenic nuclides here we propose a new model for estimating the soil development time by subtracting the low molecular weight lmw or pyrolysis volatile 14c age of the uppermost a horizon of a soil from the osl age of the c horizon of the parent material soil time osl age parent c horizon 14c age lmw fraction of uppermost a horizon the lmw organic compound fraction represents the most mobile carbon compounds in the soil organic carbon pool and is least resistant to physical chemical and biodegradation in the soil environment potentially yielding the youngest 14c age osl dating of the c horizon provides an estimate of the time since deposition of unconsolidated parent material thus the difference in the two ages can be used to estimate the time that has elapsed for pedogenic alteration from deposition of the parent material to the most recent additions of soil organic carbon we applied this new approach in four scenarios 1 in a modern soil that developed downward in loess 2 in a buried soil developed in aggrading loess a cumulative soil which grows upward 3 in a buried soil formed in dune sand and 4 in a counterexample showing that simple subtraction is not always appropriate because of changes in soil s parent materials from loess to sand these case studies reveal that this approach constrains soil development time more reasonably than can be commonly done with either osl or radiocarbon dating alone the difference in 14c ages between the uppermost and lowermost sola of a soil profile almost certainly underestimates the time of soil development and the difference in osl ages taken from sediment units overlying and underlying a buried soil most likely overestimates it a combination of osl and radiocarbon dating better constrains soil development time broadening the applications of these two dating methods beyond their use for cross checking the accuracy of the other dating method

high resolution 14c dating of a 25 000 year lake sediment record from equatorial east africa abstract we dated a continuous 22 m long sediment sequence from lake challa mt kilimanjaro area kenya tanzania to produce a solid chronological framework for multi proxy reconstructions of climate and environmental change in equatorial east africa over the past 25 000 years the age model is based on a total of 168 ams 14 c dates on bulk organic matter combined with a 210 pb chronology for recent sediments and corrected for a variable old carbon age offset this offset was estimated by i pairing bulk organic 14 c dates with either 210 pb derived time markers or 14 c dates on grass charcoal and ii wiggle matching high density series of bulk organic 14 c dates variation in the old carbon age offset through time is relatively modest ranging from 450 yr during glacial and late glacial time to 200 yr during the early and mid holocene and increasing again to 250 yr today the screened and corrected 14 c dates were calibrated sequentially statistically constrained by their stratigraphical order as a result their constrained calendar age distributions are much narrower and the calibrated dates more precise than if each 14 c date had been calibrated on its own the smooth spline age depth model has 95 age uncertainty ranges of 50 230 yr during the holocene and 250 550 yr in the glacial section of the record the 13 c values of paired bulk organic and grass charcoal samples and additional 14 c dating on selected turbidite horizons indicates that the old carbon age offset in lake challa is caused by a variable contribution of old terrestrial organic matter eroded from soils and controlled mainly by changes in vegetation cover within the crater basin

rapid and widespread vegetation responses to past climate change in the north atlantic region ongoing anthropogenic perturbations to the atmosphere and biosphere increase the risk of future abrupt changes in the climate system and generate concern about the ability of natural ecosystems to respond to rapid climate change study of past climatic events and biotic responses can inform us about potential future change qualitatively fast local responses of plant taxa to abrupt late glacial climate oscillations have been reported from individual records and attributed to short migration distances in areas of high topographic relief by using quantitative time series analyses we show that vegetation responses to late glacial climate change around the north atlantic were rapid and widespread and occurred in areas of differing relief cross correlation analysis of 11 high resolution lacustrine records in eastern north america and europe indicates vegetation response times consistently of 200 yr and often 100 yr despite regional differences in physiography and species composition vegetation lags of 200 yr confirm theoretical predictions and the apparently tight coupling between vegetation and atmosphere suggests that recent climatic trends may already have begun to affect plant population abundances and distributions

the magnitude of error in conventional bulk sediment radiocarbon dates from central north america abstract although the carbon reservoir problem with bulk sediment radiocarbon dates from lakes has long been recognized many synoptic studies continue to use chronologies derived from such dates for four sites in central north america we evaluate chronologies based on conventional radiocarbon dates from bulk sediment versus chronologies based on accelerator mass spectrometry ams radiocarbon dates from terrestrial plant macrofossils the carbon reservoir error varies among sites and temporally at individual sites from 0 to 8000 yr an error of 500 2000 yr is common this error has important implications for the resolution of precise event chronologies

four thousand years of environmental change and human activity in the cochabamba basin bolivia the cochabamba basin bolivia is on the ancient road network connecting andean and lowland areas little is known about the longevity of this trade route or how people responded to past environmental changes the eastern end of the cochabamba valley system constricts at the vacas lake district constraining the road network and providing an ideal location in which to examine past human environmental interactions multi proxy analysis of sediment from lake challacaba has allowed a c 4000 year environmental history to be reconstructed fluctuations in drought tolerant pollen taxa and calcium carbonate indicate two periods of reduced moisture availability c 4000 3370 and c 2190 1020 cal yr bp compared to adjacent wetter episodes c 3370 2190 and c 1020 cal yr bp present the moisture fluctuations broadly correlate to el nino southern oscillation variations reported elsewhere high charcoal abundance from c 4000 to 2000 yr ago indicates continuous use of the ancient road network a decline in charcoal and an increase in dung fungus sporormiella c 1340 1210 cal yr bp suggests that cultural changes were a major factor in shaping the modern landscape despite undisputable impacts of human populations on the polylepis woodlands today we see no evidence of woodland clearance in the challacaba record

temperature variations in the southern great lakes during the last deglaciation comparison between pollen and gdgt proxies abstract our understanding of deglacial climate history in the southern great lakes region of the united states is primarily based upon fossil pollen data with few independent and multi proxy climate reconstructions here we introduce a new well dated fossil pollen record from stotzel leis oh and a new deglacial temperature record based on branched glycerol dialkyl glycerol tetraethers brgdgts at silver lake oh we compare these new data to previously published records and to a regional stack of pollen based temperature reconstructions from stotzel leis silver lake and three other well dated sites the new and previously published pollen records at stotzel leis are similar but our new age model brings vegetation events into closer alignment with known climatic events such as the younger dryas yd brgdgt inferred temperatures correlate strongly with pollen based regional temperature reconstructions with the strongest correlation obtained for a global soil based brgdgt calibration r2 0 88 lending confidence to the deglacial reconstructions and the use of brgdgt and regional pollen stacks as paleotemperature proxies in eastern north america however individual pollen records show large differences in timing rates and amplitudes of inferred temperature change indicating caution with paleoclimatic inferences based on single site pollen records from 16 0 to 10 0ka both proxies indicate that regional temperatures rose by 10 c roughly double the 5 c estimates for the northern hemisphere reported in prior syntheses change point analysis of the pollen stack shows accelerated warming at 14 0 1 2ka cooling at 12 6 0 4ka and warming from 11 6 0 5ka into the holocene the timing of bolling allerod b a warming and yd onset in our records lag by 300 500 years those reported in syntheses of temperature records from the northern mid latitudes this discrepancy is too large to be attributed to uncertainties in radiocarbon dating and correlation between pollen and brgdgt temperature reconstructions rules out vegetation lags as a cause however the yd termination appears synchronous among the brgdgt record regional pollen stack and northern hemisphere stack the cause of the larger and lagged temperature changes in the southern great lakes relative to northern hemisphere averages remains unclear but may be due to the effects of continentality and ice sheet extent on regional climate evolution

expanded response surfaces a new method to reconstruct paleoclimates from fossil pollen assemblages that lack modern analogues pollen based paleoclimatic interpretations of late glacial to early holocene climates 17 9 ka in midwestern north america are hampered by samples that lack modern analogues unresolved questions include the magnitude and direction of temperature seasonality i e were these climates more or less seasonal than present and the temporal changes in precipitation central to the no analogue problem is the truncation of modern pollen climate relationships for abundant late glacial taxa such as fraxinus here we present a new method called the expanded response surface ers method developed to reconstruct climates from no analogue pollen assemblages and applied to a high resolution late glacial pollen record from crystal lake illinois to test hypotheses about late glacial climates the key assumptions central to the ers method are 1 plant species and pollen abundances follow symmetrical unimodal distributions along climatic gradients 2 taxa with truncated distributions in modern climate space occupy a subset of their fundamental niche and 3 expansion of truncated distributions by mirroring around the distributional mode recovers the portion of the fundamental niche not realized in the modern climate space with the ers method we expanded modern pollen climate relationships by mirroring pollen abundances for each taxon around a mode defined with respect to four climate axes mean winter temperature mean summer temperature mean winter precipitation and mean summer precipitation the ers method reconstructed past temperatures and precipitation during the height of no analogue conditions 14 160 12 370 cal yr bp for 37 of the crystal lake samples where techniques that employed only modern observational data found matches for only 13 of the fossil samples the total climate space of the expanded taxa set allowed analogue matches under more seasonal than present climates with higher than present precipitation the ers climate reconstructions for the height of no analogue conditions indicated cooler than present summer and winter temperatures similar to present seasonal range in temperatures higher than present winter precipitation and similar to present summer precipitation these results thus suggest that high moisture availability helped drive the formation of the midwestern no analogue communities with high fraxinus nigra abundances but do not show higher than present temperature seasonality notwithstanding the higher than present insolation seasonality at this time during the no analogue late glacial interval picea mariana f nigra and larix stands probably grew on low lying poorly drained soils in the crystal lake region whereas abies picea glauca quercus and ostrya carpinus grew on upland positions with better soil drainage

numeric control on the late glacial chronology of the southern laurentide ice sheet derived from ice proximal lacustrine deposits abstract we used a combination of radiocarbon and osl dating in ice proximal lacustrine silt and clay and outwash sand to estimate when ice of the green bay lobe of the laurentide ice sheet began retreating from its maximum position in south central wisconsin the radiocarbon ages indicate that lakes had formed in the two tributary valleys by 17 2 and 20 1 ka respectively the osl ages indicate that the green bay lobe was at its maximum position from about 26 4 5 1 ka to 21 4 3 3 ka these data provide entirely new chronologic control on late wisconsin marine isotope stage 2 glacial event in the upper midwest as well as the opportunity to directly compare radiocarbon and osl ages in this setting

pattern of southern laurentide ice sheet margin position changes during heinrich stadials 2 and 1 abstract with concerns over rising global temperatures ice sheet stability and implications for sea level rise the responses of former ice sheets to past climate change provide useful insights into linkages between the atmosphere cryosphere and oceans one example is the behavior of the laurentide ice sheet lis during heinrich stadials times of cooler sea surface temperature sst in the north atlantic using existing cosmogenic surface exposure ages varve chronologies radiocarbon ages and optically stimulated luminescence ages from the southern lis margin this report tests the hypothesis that the southern side of the lis advanced during times of surface cooling of the north atlantic this test reconstructs the timing of local glacial maxima and the times immediately pro and preceding them from multiple areas and compares them to the timing of heinrich stadial 2 hs2 26 6 23 6 ka and to the timing of heinrich stadial 1 hs1 19 3 15 3 ka during hs2 southern sector lobes new england region huron erie lobe lake michigan lobe green bay lobe and the chippewa lobe advanced towards their maximum position except for the des moines lobe for which there is no applicable data during hs1 these same lobes experienced substantial retreat but the des moines lobe advanced thus the southern laurentide margin behaved differently during the two heinrich stadials this pattern may be attributed to differing east west temperature gradients across north america and associated changes in atmospheric circulation

rock hyrax middens a palaeoenvironmental archive for southern african drylands abstract like many of the world s subtropical regions southern africa is highly sensitive to changes in the earth s climate system but a dearth of reliable palaeoenvironmental records means that relatively little is known about how regional environments have been affected over centennial to multi millennial timescales to a large extent this sensitivity is a function of the position of these regions at the interface between temperate and tropical circulation systems the resulting seasonality and irregularity of rainfall have limited the development of suitable archives such as lakes and wetlands for the preservation of palaeoenvironmental proxies this paper reviews and evaluates the value of rock hyrax middens as novel palaeoenvironmental archives in southern africa considered are 1 the contemporary taxonomy distribution and ecology of hyraxes 2 the mechanisms of hyrax midden development their physical and chemical structure rates of accumulation and age and 3 the palaeoenvironmental proxies preserved within hyrax middens including fossil pollen stable isotopes and biomarkers the interpretive constraints and opportunities offered by these various midden characteristics are assessed with a view to demonstrating the potential of these deposits widespread as they are through arid and semi arid southern africa in providing a more detailed and chronologically resolved view of late quaternary palaeoenvironments across the subcontinent

episodes of low dissolved oxygen indicated by ostracodes and sediment geochemistry at crystal lake illinois usa low dissolved oxygen during the summer and early fall controls profundal continental ostracode distribution in crystal lake mchenry county illinois favoring cypria ophthalmica and physocypria globula at water depths from 6 to 13 m these species also thrived in the lake s profundal zone from 14 165 to 9600 calendar year before present cal yr b p during the late bolling allerod and younger dryas chronozones and early holocene characterized by sand cemented tubules large aquatic gastropod shells and littoral ostracode valves thin 1 6 cm tempestite deposits punctuate thicker deposits of organic gyttja from 16 080 to 11 900 cal yr b p the succeeding 2300 yr 11 900 9600 cal yr b p lack tempestites and reconstructed water depths were at their maximum deposition of marl under relatively well oxygenated conditions occurred during the remainder of the holocene until the arrival of europeans when the lake returned to a pattern of seasonally low dissolved oxygen such conditions are also indicated in the lake sediment by the speciation of phosphorus high concentrations of organic carbon and abundant iron and manganese occluded to mineral grains initial low dissolved oxygen was probably caused by the delivery of dissolved p and fe in shallow groundwater the chemistry of which was influenced by spodosol pedogenesis under a spruce forest the triggering may have been regionally warm and wet conditions associated with retreat of the lake michigan lobe south central laurentide ice sheet

delayed deglaciation or extreme arctic conditions 21 16 cal kyr at southeastern laurentide ice sheet margin 1 the conventionally accepted ages of the last glacial maximum lgm retreat of the southeastern laurentide ice sheet lis are 26 21 cal kyr derived from bulk sediment radiocarbon ages and 28 23 cal kyr varve estimates utilizing accelerator mass spectrometry ams 14c dating of earliest macrofossils in 13 lake bog inorganic clays we find that vegetation first appeared on the landscape at 16 15 cal kyr suggesting ice had not retreated until that time the gap between previous age estimates and ours is significant and has large implications for our understanding of ocean atmosphere linkages older ages imply extreme arctic conditions for 9 5 cal kyr a landscape with no ice yet no deposition in lakes our new ams chronology of lis retreat is consistent with marine evidence of deglaciation from the n atlantic showing significant freshwater input and sea level rise only after 19 cal kyr with a cold meltwater lid perhaps delaying ice melt

correspondence regarding atmospheric changes in north america during the last deglaciation from dune wetland records in the midwestern united states by wang h stumpf a j miao x lowell t v 2012 quaternary science reviews 58 124 134

silver and lead in high altitude lake sediments proxies for climate changes and human activities abstract high altitude lake sediments are often used as archives for environmental changes and their chemical and isotopic compositions provide significant constraints on natural and anthropogenic long term changes that have occurred in their catchment area here trace element concentrations and pb isotopes are presented for two sedimentary cores from lake blanc huez in the french alps to trace the impact of climate changes and human activities over the holocene lead and ag contents are very high and clearly dominated by input from a pb ag vein located a few meters from the lakeshore a vein that also buffers the pb isotopes mining of this vein in medieval times is recorded in the corresponding lake sediments with high ag content coupled with high pb u ratio these chemical characteristics can be used to constrain the major holocene climate changes significant advances of glaciers next to the lake produced sediments with ag and pb concentration peaks and high pb u ratios due to accelerated erosion of the pb ag vein similar to the effects of the medieval mining in contrast reduced glacier activity led to the formation of organic rich sediments with high u and as contents and low pb u ratios more generally the observed combination of chemical changes could be used elsewhere to decipher environmental changes over long periods of time

devising quality assurance procedures for assessment of legacy geochronological data relating to deglaciation of the last british irish ice sheet this contribution documents the process of assessing the quality of data within a compilation of legacy geochronological data relating to the last british irish ice sheet a task undertaken as part of a larger community based project britice chrono that aims to improve understanding of the ice sheet s deglacial evolution as accurate reconstructions depend on the quality of the available data some form of assessment is needed of the reliability and suitability of each given age s in our dataset we outline the background considerations that informed the quality assurance procedures devised given our specific research question we describe criteria that have been used to make an objective assessment of the likelihood that an age is influenced by the technique specific sources of geological uncertainty when these criteria were applied to an existing database of all geochronological data relating to the last british irish ice sheet they resulted in a significant reduction in data considered suitable for synthesis the assessed data set was used to test a bayesian approach to age modelling ice stream retreat and we outline our procedure that allows us to minimise the influence of potentially erroneous data and maximise the accuracy of the resultant age models

a multiproxy micro xrf pollen chironomid and stable isotope lake sediment record for the lateglacial to holocene transition from thomastown bog ireland a multiproxy lateglacial environmental record is presented for a ca 3 5 m lacustrine sequence retrieved from a small basin ca 2 km2 at thomastown bog in county meath ireland sediment chemistry pollen chironomid and stable isotope data provide a detailed picture of catchment and lake system changes from the end of the last glacial gs 2a to the early holocene that correspond closely to existing local and regional models of climate change concomitant adjustments in independent proxy records are matched to the ngrip oxygen isotope curve giving 12 event episodes ranging from major climatic shifts to lower amplitude centennial to sub centennial scale adjustments including a previously unreported regressive period of landscape instability during the north west european rammelbeek phase the study emphasizes the potential of palaeoenvironmental reconstruction from sediment chemistry where the sediment mixing system reflects autochthonous versus allochthonous inputs the investigation also indicates problems of interpreting isotope data derived from bulk marl due to possible lag effects controlling the delivery of soil and groundwater and multiple sources of hco3 aq these research findings have implications for core site selection and for studies attempting to use stable isotopes for correlation purposes

abrupt changes in indian summer monsoon strength during the last deglaciation and early holocene based on stable isotope evidence from lake chenghai southwest china identifying variability and the mechanisms driving variability in the indian summer monsoon ism since the last deglaciation is critical for understanding past hydroclimatic change in this study we present an accelerator mass spectrometry radiocarbon dated record of delta o 18 variations in authigenic carbonates derived from lake chenghai in southwest china a region that receives moisture mainly from the indian ocean the delta o 18 values vary from 11 9 to 0 1 parts per thousand providing a detailed record of variations in ism precipitation delta o 18 values and lake hydrological balance the record shows that the ism generally strengthened in the post glacial between 15 6 and 8 8 cal ka bp but that three centennial to millennial scale drought events were superimposed on the long term trend drought events as indicated by substantial positive shifts in 8 18 0 value occurred from 15 6 0 2 to 14 4 0 2 12 5 0 2 to 11 7 0 2 and 10 1 0 1 to 10 0 0 1 cal ka bp corresponding to the heinrich 1 younger dryas and bond 7 cold events in the north atlantic region respectively the timings of these droughts are suggested to be related to meltwater discharge into the north atlantic the weakened atlantic meridional overturning circulation which leads in turn to the southward migration of the intertropical convergence zone and cooling in the tropical indian ocean

new occurrences of the white river ash east lobe in subarctic canada and utility for estimating freshwater reservoir effect in lake sediment archives abstract the freshwater reservoir effect fre in the canadian subarctic complicates development of high resolution age depth models based on radiocarbon dates from lake sediments volcanic ashfall layers tephras provide chronostratigraphic markers that can be used to estimate age offsets we describe the first recorded occurrence of a visible tephra in a lacustrine sequence in the central northwest territories the tephra observed in pocket lake near yellowknife is geochemically and stratigraphically attributed to the white river ash east lobe wrae 833 850 ce 1117 1100 cal bp which originated from an eruption of mount churchill alaska we also observed the wrae as a cryptotephra in bridge lake 130 km to the ne suggesting that records of this tephra are potentially widespread in cnt lakes the identification of this tephra presents opportunities for use of the wrae as a dating tool in the region and to quantify the magnitude of the fre in order to correct radiocarbon age depth models two well dated sediment cores from pocket lake containing a visible wrae record indicate a fre of 200 years at the time of the ash deposition which matches closely with the estimated fre of 245 years at the lake sediment water interface although additional results from other lakes in the region are required this finding implies that fre estimates for the late holocene in the region may be based either on down core wrae radiocarbon age model offsets or on radiocarbon dates obtained from the sediment water interface

a combined pollen and δ18osphagnum record of mid holocene climate variability from durres maar eifel germany in this study we investigate pollen and oxygen isotopes of moss cellulose from the peat bog durres maar in the eifel low mountain range germany 450 m a s l to quantitatively infer mid holocene climate change for the period between 7000 and 3800 cal bp pollen was analysed on the same samples from which sphagnum leaves were isolated to extract cellulose for the determination of its oxygen isotope composition 18osphagnum to quantitatively estimate january and july temperature and annual precipitation from the pollen data we applied a probabilistic indicator taxa method pdf method the pollen based reconstructions indicate july temperatures 1 c higher around 6000 cal bp than after 5500 cal bp which is consistent with a 1 decrease in 18osphagnum during the same period while the pollen based climate reconstructions indicate little variability in summer temperature after 5500 cal bp winter temperature shows several pronounced cold excursions of 2 4 c in this period which was likel

tearing of stagnant slab subducted slabs of oceanic lithosphere below the western pacific tend to be stagnant in the transition zone with poorly known mechanical properties typical examples are the izu bonin and japan slabs that meet each other to form a cusplike junction beneath southwest japan here we show that these two slabs are torn apart at their junction when they bend to flatten over the 660 kilometer discontinuity as is expected from a simple geometric argument we present three lines of evidence for this ongoing slab tear

middle to late holocene delta plain evolution of the kimotsuki lowland kyushu southern japan abstract the evolution of delta plains and coastal floodplains is commonly believed to be influenced by sea level and climate changes however regional climate change influences on the evolution of delta plains and floodplains are poorly understood compared with responses to rapid sea level rise since the last deglaciation this study investigated the kimotsuki lowland delta plain evolution kyusyu southern japan including allogenic controls based on 28 auger cores and 28 radiocarbon ages large scale crevasse splay deposition occurred at 7000 6000 cal yr bp in response to sea level rise or increased sediment supply following a volcanic eruption afterwards widespread peat was formed in the absence of substantial fluvial sedimentation decreased precipitation from a weakened east asian summer monsoon may have dried the peatlands around 4000 cal yr bp with increasing precipitation and storminess around 2000 cal yr bp peat formation resumed at areas further from the kimotsuki river while increased overbank flows deposited organic rich mud near the river these changes may reflect an increased frequency of la nina events and higher ocean surface temperatures of the kuroshio extension the increased storminess around 2000 cal yr bp may have produced similar influences on delta plain and coastal floodplain evolution across the east asia region the results of this study suggest that regional climate change in the late holocene has a potential to control the evolution of coastal floodplains and delta plains

improving the reliability of bulk sediment radiocarbon dating abstract radiocarbon dated chronologies are the most extensively applied dating technique when investigating the last 45 000 years in lake and marine sediments a single macrofossil or several microfossils are the preferred sample material because they have a 14c age that accurately reflects the time of deposition however absence of macro or microfossils are a recurring challenge often it is necessary to use bulk sediment samples for radiocarbon dating but they frequently yield ages clearly exceeding the depositional timeframe due to occurrence of organic material of older origin until now it has not been possible to assess if the dating result of a bulk sediment sample is reliable or to adequately explain the mechanisms behind age disagreement between bulk and macro and microfossils in this study we investigate the age offset between paired bulk and macrofossil ages in sediment cores from three lakes in se and e greenland furthermore we distinguish three quantifiable main carbon sources in the samples a recent terrestrial organic fragments b recent aquatic organic matter and c reworked land derived old carbon through pyrolysis organic geochemistry organic petrographic microscopy and isotopic fractionization our results show that the offset between bulk humic fraction and macrofossil radiocarbon ages in three similar lakes range from 9 14c yr to 20 1 14c kyr we observe a reduced age offset between bulk and macrofossil ages and thereby a higher reliability of bulk humic fraction ages correlated with increased values of toc c n ratio and high co2 release in pyrolysis s3 value we recommend that future studies presenting bulk sediment chronologies apply pyrolysis organic geochemistry organic petrographic microscopy and isotopic fractionization as demonstrated here to select reliable sediment intervals for bulk dating and retrieve more robust results

middle late holocene caribbean aridity inferred from foraminifera and elemental data in sediment cores from two cuban lagoons abstract coastal lagoons are rarely used as paleoclimate archives because of their complex geomorphic histories which can be affected by both climate and sea level change combined foraminiferal and xrf element analysis of sediment cores from punta de cartas and playa bailen cuba isolated the effects of climate change wet vs dry on the lagoon environments foraminiferal assemblages from both punta de cartas and playa bailen show increasing diversity over the past 4000 yr bp with a prominent increase at 1400 1100 yr bp assemblages were initially dominated by ammonia spp e g ammonia tepida and elphidium spp e g elphidium excavatum indicating brackish conditions but increased miliolid species e g triloculina spp quinqueloculina spp indicate a shift to more marine conditions up core correspondingly terrigenous input to the lagoon fe ti ti ca and k declined over the past 4000 yr bp with a flexion at 1200 1100 yr bp that is likely a consequence of decreasing precipitation fe ti and k have been used as proxies for detrital erosion and transport rates in tropical and sub tropical basins with greater input during wet periods but have rarely been applied to shallow lagoon systems coincident changes in the xrf and foraminiferal data indicate decreased freshwater input to the lagoon and support an inference for the onset of drier climate conditions similar temporal patterns in the foraminifera and xrf records from the two lagoons which are 10 km apart suggest a regional climate influence with increasingly arid conditions developing since the middle holocene 4 kyr bp a pronounced drying over the last 1200 years agrees with other climate records from the caribbean

ancient plutonic processes on mars inferred from the detection of possible anorthositic terrains the formation of the silicate mineral anorthosite is thought to require magmatic processes that are not expected on mars because of its predominately mafic terrains localized spectral detections by the mars reconnaissance orbiter are consistent with anorthosite suggestive of ancient intrusive igneous processes similar to those active on earth

possible solar forcing of century scale drought frequency in the northern great plains a 2100 yr decadal resolution salinity and aridity proxy record of lacustrine ostracode shell mg ca ratios from a closed basin lake in the northern great plains shows statistically significant periodicities of 400 200 130 and 100 yr these periodicities are similar to the three principal solar oscillation periods 420 218 143 yr as inferred from the atmospheric radiocarbon record suggesting strong solar forcing of century scale drought frequency with a fundamental 400 yr period and its 2nd 3rd and 4th harmonics our proxy record correlates visually and statistically cross spectral analysis with the atmospheric 14 c record solar proxy and the gisp2 greenland ice sheet project two 18 o record climate proxy showing that solar minima are in phase with drought periods in the northern great plains and cold periods in greenland this spectral similarity together with phase correlation indicates a possible teleconnection of century scale global climate fluctuations through common solar forcing

stratified interglacial lacustrine sediments from baffin island arctic canada chronology and paleoenvironmental implications abstract thirteen of 18 piston cores recovered from robinson lake in the mid arctic vegetation zone of baffin island arctic canada penetrated stratified lacustrine sediment beneath a thin over consolidated diamict till and postglacial lacustrine sediment the sub till lacustrine units are up to 120 cm thick of which the upper several decimeters frequently contain thick layered mats of aquatic moss pollen and diatoms are common throughout both lacustrine units a series of 23 ams 14c dates defines the chronology of the postglacial sequence which records a succession from a pioneer grass and oxyria dominated tundra between 10 4 and 8 ka bp to a sedge dominated tundra after 8 ka bp limiting 14c dates place the sub till lacustrine sediments more than 40 ka bp 10 luminescence dates centered on 85 ka indicate they were deposited late in oxygen isotope stage ois 5 the dominance of shrub and tree pollen especially shrub birch and alder in sub till lacustrine samples indicates low arctic tundra farther north than at any time during the holocene pollen concentrations are comparable to or higher than in the holocene units cooling late in the interglacial is indicated by declining birch and alder pollen percentages in the upper part of the section diatom floras in both the sub till and postglacial lacustrine sequences indicate similar development of lake water chemistry but input of silica and weathering products was greater in the older lake cycle suggesting more vigorous catchment processes macrofossils in the sub till units are characteristic of lakes ice free in summer based on pollen assemblages indicating local and regional vegetation diagnostic of summer temperatures higher than the holocene we interpret the sub till lacustrine units to be of interglacial character by analogy with holocene plant succession in central and eastern canada all of keewatin and labrador ungava must have been ice free throughout this interval suggesting essentially complete deglaciation of the laurentide ice sheet at the time

the anatomy of a climatic oscillation vegetation change in eastern north america during the younger dryas chronozone century scale climate changes reshaped circulation patterns over the north atlantic and adjacent regions during the last glacialto interglacial transition here we show that vegetation across eastern north america shifted dramatically at the beginning and end of the younger dryas chronozone ydc 12 900 11 600 cal yr b p when changes in ocean circulation rapidly cooled and then warmed the north atlantic sea surface on both the site specific scale and the continental scale vegetation changed only gradually during the millennia before 15 000 13 000 cal yr b p and after 11 000 9000 cal yr b p the ydc but climate changes ca 12 900 and 11 600 cal yr b p altered the vegetation on both spatial scales within centuries plant associations changed and some taxa rapidly migrated hundreds of kilometers 300 km within b100 yr in limited regions near the north atlantic coast abrupt cooling ca 12 900 cal yr b p resulted in a return to earlier vegetation types elsewhere however the vegetation patterns during the ydc were distinct from those of both earlier and later intervals they indicate abrupt non reversing seasonal temperature changes that were probably related to atmospheric circulation changes during the ydc rather than to the direct influence of north atlantic sea surface temperatures atmospheric circulation patterns during the ydc were unique within the last 21 000 yr because of a unique combination of climate controls insolation ice sheet extent and atmospheric composition were significantly different from their full glacial states even when the north atlantic returned to near full glacial conditions the ydc vegetation patterns demonstrate 1 rapid ecological responsiveness to abrupt climate change and 2 spatially varied patterns of ydc climate change r 2002 elsevier science ltd all rights reserved

ecosystem development following deglaciation a new sedimentary record from devils lake wisconsin usa abstract processes and rates of ecosystem development can be reconstructed using lacustrine sedimentary sequences but this approach often requires records that contain the start of primary succession most lakes in the upper midwestern u s were formed by glaciers at the end of the last ice age approximately 11 700 cal yr bp devils lake wisconsin is a rare example of a lake from this region whose sediments extend into the pleistocene and may include the last glacial maximum sediment magnetic geochemical pollen and charcoal records were generated from a 10 m core whose basal sediments may be 28 000 years old together with a previously published pollen record these proxies combine to reveal a history of long term climatic vegetative and geologic change during the late pleistocene to holocene we identify six sedimentary units that indicate a series of consecutive events rather than a predictable trajectory of ecosystem development at the site productivity in the lake was low during the late pleistocene and increased during the holocene as reflected by the sediment lithology which shows a sudden shift from glacial vivianite rich and organic poor clastic dominated sediments to holocene diatomaceous sapropels several important processes initiated around 17 000 cal yr bp including the onset of organic matter accumulation and fire in the terrestrial ecosystem however the post glacial landscape was not devoid of vegetation because pollen assemblages indicate that terrestrial vegetation likely a spruce tundra survived near the site a switch to a hardwood forest period during the holocene also led to a change in the fire regime with increased frequency of burning aquatic ecosystem productivity lagged terrestrial ecosystem productivity throughout the record nutrient cycling as recorded by sedimentary 15n was variable but not directional and appeared to be correlated with climate conditions early in the record and terrestrial ecosystem processes later in the record throughout the holocene magnetic mineral concentration decreased as productivity increased and the source of magnetic material shifted from almost exclusively lithogenic to approximately 50 derived from soil or biogenic sources magnetic grain size ambrosia pollen percentages and charcoal concentration increased and 15n decreased in the most recent part of the record due to anthropogenic influence in the region including agricultural activities

postglacial vegetation and climate in the northwestern great plains of montana abstract two pollen records from the northern great plains of montana portray vegetational and climatic changes during the last 12 200 yr in a region where few other data are available a 6 4 m core from guardipee lake east of the rocky mountains in the area formerly covered by the two medicine glacial lobe contains the glacier peak g and mt st helens jy volcanic ashes pollen percentage data are dominated by pinus poaceae artemisia and chenopodiaceae amaranthaceae high nonarboreal percentages and small amounts of juniperus alnus salix and populus pollen in sediments deposited between ca 12 200 and ca 9300 yr b p suggest a temperate grassland with shrubs growing locally in mesic settings after ca 9300 yr b p an increase in chenopodiaceae amaranthaceae pollen and a concomitant decline in artemisia indicate the development of more xerophytic grassland and the beginning of the altithermal period the lake probably was intermittently dry thoughout the holocene a high sedimentation rate and the presence of cereal taxa characterize the last ca 100 yr of euroamerican settlement lost lake at the northern margin of the highwood mountains yielded a 16 94 m core with no volcanic ashes that spans the last 9400 yr high amounts of chenopodiaceae amaranthaceae artemisia and poaceae pollen from ca 9400 to ca 6000 yr b p suggest the presence of xeric grassland and a climate drier than at present after ca 6000 yr b p chenopodiaceae amaranthaceae values declined and artemisia poaceae pinus picea salix alnus and betula increased the inferred spread of shrubs in wet habitats at this time and the expansion of forest in nearby mountain ranges indicate the end of the altithermal period and the onset of cooler moister conditions

holocene moisture and east asian summer monsoon evolution in the northeastern tibetan plateau recorded by lake qinghai and its environs a review of conflicting proxies abstract climatic and environmental changes in the northeastern tibetan plateau are controlled by the asian summer monsoon asm and the westerlies two key circulation components of the global climate system which directly affect a large human population and associated ecosystems in eastern asia during the past few decades a series of holocene palaeoclimatic records have been obtained from sediment cores from lake qinghai and from various other geological archives in the surrounding area of the northeastern tibetan plateau however because of uncertainties regarding the sediment chronologies and the climatic significance of the proxies used the nature of holocene climatic changes in the region remains unclear and even controversial here we review all major classes of the published data from drilled cores from lake qinghai as well as other evidence from lakes and aeolian deposits from surrounding areas in order to reconstruct changes in moisture patterns and possible summer monsoon evolution in the area during the holocene combining the results of moisture and precipitation proxies such as vegetation history pollen based precipitation reconstruction aeolian activity lake water depth lake level changes salinity and sediment redness we conclude that moisture and precipitation began to increase in the early holocene reached their maximum during the middle holocene and decreased during the late holocene similar to the pattern of the east asian summer monsoon easm in northern china it is clear that the region experienced a relatively dry climate and weak easm during the early holocene as indicated by relatively low tree pollen percentages and fluctuating pollen concentrations generally low lake levels of lake qinghai and the adjacent lake hurleg and lake toson in the qaidam basin and widely distributed aeolian sand deposition in the lake qinghai basin and the nearby gonghe basin to the south and in the eastern qaidam basin to the west we argue that the ostracod 18o record which is widely used as a proxy of effective moisture and summer monsoon intensity in lake sediments at least in lake qinghai and which exhibits light values in the early holocene and heavier values thereafter cannot be used to reflect the strength of the easm or the intensity of monsoon precipitation as is also the case for leaf wax 2h records rather we argue that as is the case of the chinese speleothem 18o record which also is often interpreted as an easm proxy it reflects variation in the 18o of precipitation overall we suggest that the easm significantly affected precipitation in the northeastern tibetan plateau during the holocene and that it increased in strength during the early holocene reached a maximum during the middle holocene and decreased during the late holocene

vegetation history in central kentucky and tennessee usa during the last glacial and deglacial periods abstract knowledge about vegetation dynamics during the last glacial and deglacial periods in southeastern north america is under constrained owing to low site density and problematic chronologies new pollen records from two classic sites anderson pond tn and jackson pond ky supported by ams 14 c age models span 25 2 13 7 ka and 31 0 15 4 ka respectively a transition from pinus dominance to picea dominance is recorded at jackson pond ca 26 2 ka coincident with heinrich event h2 anderson and jackson ponds record a transition from conifer to deciduous tree dominance 15 9 and 15 4 ka respectively marking the development of no analog vegetation characterized by moderate to high abundances of picea quercus carya ulmus fraxinus ostrya carpinus cyperaceae and poaceae and preceding by 2000 yr the advent of similar no analog vegetation in glaciated terrain to the north no analog vegetation developed as a time transgressive south to north pattern mediated by climatic warming sporormiella abundances are consistently low throughout the jackson and anderson pond records suggesting that megafaunal abundances and effects on vegetation varied regionally or possibly that the sporormiella signal was not well expressed at these sites additional records with well constrained chronologies are necessary to assess patterns and mechanisms of vegetation dynamics during the last glacial and deglacial periods

reconciling divergent trends and millennial variations in holocene temperatures cooling during most of the past two millennia has been widely recognized and has been inferred to be the dominant global temperature trend of the past 11 700 years the holocene epoch however long term cooling has been difficult to reconcile with global forcing and climate models consistently simulate long term warming the divergence between simulations and reconstructions emerges primarily for northern mid latitudes for which pronounced cooling has been inferred from marine and coastal records using multiple approaches here we show that temperatures reconstructed from sub fossil pollen from 642 sites across north america and europe closely match simulations and that long term warming not cooling defined the holocene until around 2 000 years ago the reconstructions indicate that evidence of long term cooling was limited to north atlantic records early holocene temperatures on the continents were more than two degrees celsius below those of the past two millennia consistent with the simulated effects of remnant ice sheets in the climate model community climate system model 3 ccsm3 ccsm3 simulates increases in growing degree days a measure of the accumulated warmth above five degrees celsius per year of more than 300 kelvin days over the holocene consistent with inferences from the pollen data it also simulates a decrease in mean summer temperatures of more than two degrees celsius which correlates with reconstructed marine trends and highlights the potential importance of the different subseasonal sensitivities of the records despite the differing trends pollen and marine based reconstructions are correlated at millennial to centennial scales probably in response to ice sheet and meltwater dynamics and to stochastic dynamics similar to the temperature variations produced by ccsm3 although our results depend on a single source of palaeoclimatic data pollen and a single climate model simulation they reinforce the notion that climate models can adequately simulate climates for periods other than the present day they also demonstrate that amplified warming in recent decades increased temperatures above the mean of any century during the past 11 000 years

late quaternary vegetation climate and fire history of the southeast atlantic coastal plain based on a 30 000 yr multi proxy record from white pond south carolina usa the patterns and drivers of late quaternary vegetation dynamics in the southeastern united states are poorly understood due to low site density problematic chronologies and a paucity of independent paleoclimate proxy records we present a well dated 15 accelerator mass spectrometry 14 c dates 30 000 yr record from white pond south carolina that consists of high resolution analyses of fossil pollen macroscopic charcoal and sporormiella spores and an independent paleotemperature reconstruction based on branched glycerol dialkyl tetraethers between 30 000 and 20 000 cal yr bp open pinus picea forest grew under cold and dry conditions elevated quercus before 26 000 cal yr bp however suggest warmer conditions in the southeast before the last glacial maximum possibly corresponding to regionally warmer conditions associated with heinrich event h2 warming between 19 700 and 10 400 cal yr bp was accompanied by a transition from conifer dominated to mesic hardwood forest sporormiella spores were not detected and charcoal was low during the late glacial period suggesting megaherbivore grazers and fire were not locally important agents of vegetation change pinus returned to dominance during the holocene with step like increases in pinus at 10 400 and 6400 cal yr bp while charcoal abundance increased tenfold likely due to increased biomass burning associated with warmer conditions low intensity surface fires increased after 1200 cal yr bp possibly related to the establishment of the mississippian culture in the southeast

an assessment of the minimum timing of ice free conditions of the western laurentide ice sheet abstract this study presents an investigation of the minimum timing of retreat of the western laurentide ice sheet which covered parts of canada and the northern united states during the wisconsin glaciation the retreat of the ice sheet is poorly constrained due to low spatial resolution of chronological data that indicate ice free conditions a limitation of radiocarbon and luminescence dating methods is that it is only possible to determine the time when it is certain that ice is absent from a region which may differ substantially from the true date of ice margin retreat the minimum timing of ice free conditions is determined using a model of ice sheet retreat inferred from landforms that formed during the late stages of glaciation and extrapolating the calibrated probability distribution of chronological data in the opposite direction the analysis excludes radiocarbon samples from materials that have been shown to give artificially old ages such as bulk sediments the results of the analysis identify 55 dates that have the most impact on the model the retreat of the western laurentide ice sheet commenced by at least 15 000 cal yr bp while the minimum timing of ice free conditions between the laurentide ice sheet and the cordillera is after 11 000 cal yr bp a lack of data in the keewatin sector prevents the determination of a precise timing of ice free conditions in the last vestiges of the laurentide ice sheet the model provides a guide to where additional samples could improve chronological control on ice margin location

holocene high resolution quantitative summer temperature reconstruction based on subfossil chironomids from the southeast margin of the qinghai tibetan plateau this paper reports the first quantitative summer mean july temperature reconstruction based on subfossil chironomids from the southeast margin of the qinghai tibetan plateau qtp covering the end of the last deglaciation and the entire holocene spanning 11 800 cal yr bp to the present the record is based on 223 chironomid samples throughout a 927 cm sediment core providing a temporal resolution of 50 years per sample we validate the record by applying several statistical reconstruction diagnostics and comparing with pollen and diatom records from the same sediment core the record suggests the summer temperature varies by 2 5 c across the entire period a generally warmer period occurred between c 8500 and c 6000 cal yr bp and a cooling trend was initiated from c 5500 cal yr bp the overall pattern broadly matches the summer insolation at 30 n and the asian summer monsoon records from the surrounding regions suggesting that summer temperatures from the southeast margin of the qtp respond to insolation forcing and monsoon driven variability on a multi millennial time scale modifications of this overall trend are observed on the finer temporal resolution and we suggest that solar activity could be an important mechanism driving the centennial scale variability it may have a strengthened effect in the late holocene when the monsoon influence weakened further detailed investigation is needed to disentangle these effects on the climate change over the highlands of southwestern china

episodic deposition of illinois valley peoria silt in association with lake michigan lobe fluctuations during the last glacial maximum the chronology and cause of millennial depositional oscillations within last glacial loess of the central lowlands of the united states are uncertain here we present a new age model that indicates the peoria silt along the illinois river valley accumulated episodically from 28 500 to 16 000 cal yr bp as the lake michigan lobe margin fluctuated within northeastern illinois the age model indicates accelerated loess deposition coincident with regional glacial advances during the local last glacial maximum a weakly developed paleosol the jules geosol represents a period of significantly slower deposition from 23 700 to 22 000 cal yr bp a gastropod assemblage based reconstruction of mean july temperature shows temperatures 6 10 c cooler than modern during peoria silt deposition stable oxygen and carbon isotope values 18 o and 13 c of gastropod carbonate do not vary significantly across the pedostratigraphic boundary of the jules geosol suggesting slower loess accumulation was a result of reduced glacial sediment supply rather than direct climatic factors however a decrease in 18 o values occurred between 26 000 and 24 000 cal yr bp synchronous with the lake michigan lobe s southernmost advance this 18 o decrease suggests a coupling of regional summer hydroclimate and ice lobe position during the late glacial period

pronounced variations in fagus grandifolia abundances in the great lakes region during the holocene mesic tree species such as fagus grandifolia and tsuga canadensis experienced multiple abundance declines in eastern north america during the last 8000 years but the causes remain unclear this paper presents a new sub centennial record of holocene vegetation fire and sedimentological changes at spicer lake in to test hypotheses about the role of fire and hydrological variations on shifts in vegetation composition four pollen zones are reported abies picea forests 15 11 8 ka bp pinus dominated mixed forest 11 8 10 6 ka bp transitional mixed forest 10 6 6 8 ka bp and deciduous forest characterized by the expansion and high variability of f grandifolia after 6 8 ka bp macroscopic charcoal indicates five to seven fires between 6 1 and 4 4 ka bp and no fires between 4 4 and 2 ka bp despite several large declines in f grandifolia and more fires after 1 8 ka bp likely linked to declining f grandifolia abundances after 1 1 ka bp six peaks in mineralogenic sediments are suggestive of hydro

century scale paleoclimatic reconstruction from moon lake a closed basin lake in the northern great plains estimates of past lake water salinity from fossil diatom assemblages were used to infer past climatic conditions at moon lake a climatically sensitive site in the northern great plains a good correspondence between diatom inferred salinity and historical records of mean annual precipitation minus evapotranspiration p et strongly suggests that the sedimentary record from moon lake can be used to reconstruct past climatic conditions century scale analysis of the holocene diatom record indicates four major hydrological periods an early holocene transition from an open freshwater system to a closed saline system by 7300 b p which corresponds with a transition from spruce forest to deciduous parkland to prairie and indicates a major shift from wet to dry climate a mid holocene period of high salinity from 7300 to 4700 b p indicating low effective moisture p et a transitional period of high salinity from 4700 to 2200 b p characterized by poor diatom preservation and a late holocene period of variable lower salinity during the past 2 200 yr indicating fluctuations in effective moisture

a multi proxy study of changing environmental conditions in a younger dryas sequence in southwestern manitoba canada and evidence for an extraterrestrial event multi proxy analyses of a sequence spanning the younger dryas yd in the glacial lake hind basin of manitoba provides insight into regional paleohydrology and paleovegetation of meltwater rivers and lakes spanning 4000 yr the sequence is controlled by 25 new accelerator mass spectrometry ages this lake dammed by the laurentide ice sheet overflowed into lake agassiz the pre yd interval records rapid sedimentation from meltwaters that headed in proglacial lakes in the canadian prairies that are known to have been catastrophically released when ice or sediment barriers were breached pollen in this phase is dominated by pre quaternary forms eroded from paleocene bedrock at the onset of the yd at 12 8 cal ka the sudden appearance of concentrations of nanodiamonds high temperature magnetic spherules platinum and iridium provide evidence of an extraterrestrial et event that others have identified at more than 40 sites in north america major changes in oceans and climate and the catastrophic outflow of nearby lake agassiz at the onset of the yd may be related lower water levels and a reduction of souris river inflow to lake hind followed which are reflected by more clayey and organic rich sediments and a decrease in pre quaternary palynomorphs this may have resulted from the deepening of river valleys caused by the release of meltwater triggered by the et event wetlands then began to develop leading to peat deposition from 12 3 to 11 cal ka this was followed by a fluvial episode depositing sand and then by increased holocene aridity that resulted in accumulation of a thick sequence of dune sands a dry woodland environment with a mix of conifers especially picea and larix and deciduous trees especially populus and quercus covered the uplands from 13 to 10 cal ka

three dimensional visualization of a near vertical slab tear beneath the southern mariana arc the use of a three dimensional ray tracing inversion algorithm has greatly enhanced the resolution of gradients and strong variations in wave speeds to create improved p wave tomographic images of the mariana arc region the images obtained from the mariana arc region show relatively low amplitudes of heterogeneity due to the limited number of seismic stations in the area despite these limitations detailed interpretations of the three dimensional geometry and morphology of the pacific plate subducting beneath the philippine sea plate have provided a three dimensional model of the steep dip of the pacific plate and the curvature of the slab beneath the mariana arc in unprecedented detail the new p wave tomography and seismicity depict a previously unidentified e w trending near vertical tear in the subducting plate at the southern end of the mariana arc that divides the arc into two distinct segments a steeply dipping curved slab penetrating the lower mantle and a short 250 km depth slab along the challenger deep segment of the arc the slab tear is likely to be the result of the need to accommodate the reduced volume the slab must occupy as it is subducted beneath the philippine sea plate along a curved arc

patterns of hydroclimatic change in the rocky mountains and surrounding regions since the last glacial maximum abstract the paleohydrologic record of western north america since the last glacial maximum reveals a wide range of hydroclimatic variability in time and space to improve the understanding of abrupt hydroclimatic shifts and millennial scale hydrologic changes in the central rocky mountains we reconstruct the lake level histories of two small lakes in the beartooth and bighorn mountains in northern wyoming over the past 17 ka to do so we use ground penetrating radar gpr and sediment cores to track the elevations of shoreline sediments within the lakes through time we compare the stratigraphies with those from four other lakes in wyoming and colorado and find widespread evidence for a terminal pleistocene drought from 15 to 11 ka an early holocene humid period from 11 to 8 ka and mid holocene aridity from 8 to 5 5 ka the northern wyoming lakes also provide evidence of high levels in the pleistocene possibly before ca 15 ka and rapid hydroclimatic changes that may have correlated with heinrich event 1 ca 16 8 ka we place the changes in a broad context by summarizing and mapping water level changes from 107 additional previously studied lakes important patterns include 1 extensive drying across the western u s after 15 ka 2 sub regional differences during the pleistocene holocene transition 3 a north south contrast from 9 to 6 ka consistent with a northward shift in storm tracks as the influence of the laurentide ice sheet diminished and 4 rapid increases in effective moisture across much of western north america from 6 to 4 ka

historical seismicity of the mont dore volcanic province auvergne france unraveled by a regional lacustrine investigation new insights about lake sensitivity to earthquakes lake sediments are relevant natural seismographs over long time scale however because tectonic events are not systematically recorded in lake sediments one forthcoming challenge for paleoseismology is to better assess lake sensitivity to earthquakes to this end a limnogeological investigation including hydroacoustic mapping techniques core sampling and multi proxy sediment analyses has been conducted within four small volcanic lakes located in the mont dore province auvergne france an area with a moderate seismo tectonic activity results show the existence of several gravity reworking processes in the lakes over the last millennium around ad 1300 the occurrence of synchronous events in lakes pavin chauvet montcineyre and guery 100 km 2 area highlights an undocumented earthquake as a common trigger for slope failures in disconnected basins at regional scale the record of this tectonic event may have been favored by human induced increase in sediment load chauvet and montcineyre and or after an abrupt lake level drop pavin affecting the sediment stability in addition synchronous turbidites and mass wasting deposits mwd recorded in lakes pavin and guery provide evidence for a seismic activity during the xix th century potential triggers are historical earthquakes that occurred either in the mont dore area or in the southern part of the limagne fault at this time despite moderate seismic activity in this intraplate volcanic domain these results highlight the role of tectonics as a major trigger in the sedimentary processes dominating these lacustrine infills within the diversity of studied sites it appears that lake sensitivity to earthquakes was not constant over time this sensitivity can be expressed as a combination of external factors namely earthquake magnitude and lake epicenter distance and internal factors such as lake morphology nature of sediment lake level fluctuations and human induced changes in catchment sedimentary load

hydrologic variation in the northern great plains during the last two millennia abstract reconstructions of lake water salinity at decadal resolution for the last 2000 yr are compared among three lakes in north dakota to infer regional patterns of drought the intersite comparisons are used to distinguish local variation in climate or hydrology from regional patterns of change at one lake diatom inferred salinity and lake water mg ca inferred from ostracode shell chemistry are coherent both in terms of direction and magnitude of change indicating that each is a robust technique for reconstructing lake water chemistry the data show that the last 2000 yr have been characterized by frequent shifts between high and low salinity suggesting shifts between dry and moist periods long intervals of high salinity suggest periods of multiple decades when droughts were intense and frequent thus indicating times when drought was more persistent than in the 20th century both the medieval period and little ice age were hydrologically complex and there is no clear evidence to suggest that either interval was coherent or unusual in effective moisture relative to long term patterns differences among the three sites may be attributed to variation in local hydrology and these differences emphasize the need for multiple sites in deriving regional climate interpretations from paleoecological data

radiocarbon geochemistry of modern and ancient arctic lake systems baffin island canada the accuracy of arctic lake chronologies has been assessed by measuring the14c activities of modern carbon sources and applying these isotopic mass balances to dating fossil lake materials small 1 km2 shallow 25 m arctic lakes with watersheds 12 km2have soil and peat stratigraphic sections with14c activities ranging from 98 to 51 modern the14c activity of particulate organic carbon dissolved organic carbon and dissolved inorganic carbon from lake and stream waters ranges from 121 to 95 modern the sediment water interface of the studied lakes shows consistent14c ages of 100014c yr although the14c activity of living aquatic vegetation is 115 modern radiocarbon measurements of components of the lacustrine carbon pool imply that the 100014c yr age of the sediment water interface results from deposition of14c depleted organic matter derived from the watershed

reply to comments by curry et al 2013 on atmospheric changes in north america during the last deglaciation from dune wetland records in the midwestern united states

vegetation history since the last glacial maximum in the ozark highlands usa a new record from cupola pond missouri abstract the timing and drivers of vegetation dynamics and formation of no analog plant communities during the last deglaciation in the unglaciated southeastern us are poorly understood we present a multi proxy record spanning the past 19 800 years from cupola pond in the ozarks mountains consisting of replicate high resolution pollen records 25 ams radiocarbon dates and macrofossil charcoal and coprophilous spore analyses full glacial pinus and picea forests gave way to no analog vegetation after 17 400 yr bp followed by development of quercus dominated holocene forests with late holocene rises in pinus and nyssa vegetation transitions replicated in different cores are closely linked to hemispheric climate events rising quercus abundances coincide with increasing northern hemisphere temperatures and co 2 at 17 500 yr bp declining pinus and picea at 14 500 yr bp are near the bolling allerod onset and rapid decline of fraxinus and rise of ostrya carpinus occur 12 700 yr bp during the younger dryas the cupola no analog vegetation record is unusual for its early initiation 17 000 yr bp and for its three vegetation zones representing distinct rises of fraxinus and ostrya carpinus sporormiella was absent and sedimentary charcoal abundances were low throughout suggesting that fire and megaherbivores were not locally important agents of disturbance and turnover the cupola record thus highlights the complexity of the late glacial no analog communities and suggests direct climatic regulation of their formation and disassembly

pollen record of the mid to late holocene centennial climate change on the east coast of south korea and its influential factors abstract to understand historical climate change in western pacific coastal areas a sediment core soj 2 from the stable sedimentary environment of the songjiho lagoon on the east coast of south korea was obtained for centennial resolution palynological analysis the ages of the soj 2 core is well controlled by carbon 14 dating with high resolution accelerator mass spectrometry ams and the results indicated a general warm to cold climate trend from the mid holocene to the present which can be divided into two different stages a warmer stage between 6842 and 1297 cal yr bp and a colder stage from 1297 cal yr bp to the present with fluctuations during these stages the climate was wetter from 6842 to 6227 cal yr bp and 4520 to 1297 cal yr bp and was drier from 6227 to 4520 cal yr bp the climate changed to cold and dry during the period from 1297 425 cal yr bp the impact of human activity on the climate began at approximately 1297 cal yr bp and became pronounced starting in 425 cal yr bp the general cooling trend may represent a response to decreasing solar insolation however the relative dryness or wetness of the climate may have been co determined by westerlies and the east asian summer monsoon easm the climate had a teleconnection with the north atlantic region resulting from changes in solar activity nevertheless ei nino southern oscillation enso activity played an important role in impacting the easm changes in western pacific coastal areas

the structure of holocene climate change in mid latitude north america abstract a sequence of long term and rapid changes during the holocene appears in a network of 40 well resolved paleoclimate datasets from mid latitude north america including records of pollen inferred temperatures alkenone derived sea surface temperatures ssts lake level changes dust accumulation and lake isotopes from idaho to maine statistical analyses reveal that changes in insolation and the laurentide ice sheet explain 51 7 of the variance in the records especially multi millennial trends but peak rates of change indicate additional rapid changes at ca 10 8 9 4 8 3 7 0 5 5 5 2 4 7 2 1 and 0 9 ka step changes between 9 4 and 8 3 ka relate to ice sheet dynamics that warmed much of the region and changes at 5 5 ka were the largest since the demise of the ice sheet the shift at 5 5 ka initiated widespread cooling and increases in effective moisture which culminated in the coolest wettest millennia in most areas after 2 1 ka replicated evidence from multiple records also shows a spatially varied set of multi century fluctuations including 1 low temperatures and high effective moisture at 5 5 4 8 ka in the mid continent and 2 repeated phases of low ssts cool summers and drought superimposed upon long cooling moistening trends in eastern north american since 5 5 ka

cosmogenic nuclide age estimate for laurentide ice sheet recession from the terminal moraine new jersey usa and constraints on latest pleistocene ice sheet history

a chronological framework for the holocene vegetational history of central minnesota the steel lake pollen record abstract paleorecords from minnesota and adjacent areas have often been used to evaluate large scale climatic processes in the mid continent of north america however most of these records are compromised by chronological flaws making problematic any comparisons with climatic interpretations based on other records e g gisp2 in greenland we report here a high resolution pollen record with a secure chronology constrained by 26 14 c dates on terrestrial macrofossils from steel lake central minnesota about 11 2 ka cal bp 11 000 calibrated yr before present the late glacial picea forest near steel lake was succeeded abruptly by pinus banksiana and or resinosa the pinus forest began to open 9 4 ka cal bp with the expansion of prairie taxa and a pine parkland or savanna prevailed until about 8 ka cal bp when quercus replaced pinus to become the dominant tree in the prairie areas for 4500 yr the close chronological control permits the correlation of key vegetational changes with those at other reliably dated sites in the eastern dakotas and in minnesota suggesting that the abrupt decline of the spruce forest was time transgressive from southwest to northeast during 2000 yr and that the development of prairie was time transgressive in the same direction over 2600 yr correlation of key pollen horizons at steel lake with those in the high resolution pollen profiles of elk lake ca 50 km northwest of steel lake suggests that the well known elk lake varve chronology for the early holocene is about 1000 yr too young

patterns of holocene environmental change in the midwestern united states abstract four pollen sequences along a transect from north central iowa to southeast wisconsin reveal the distribution of prairie and forest during the holocene and test the use of pollen isopolls in locating the holocene prairie forest border prairie was dominant in central iowa and climate was drier than present from about 8000 to 3000 yr b p during the driest part of this period in central iowa 6500 5500 yr b p mesic forest prevailed in eastern iowa and wisconsin suggesting conditions wetter than at present prairie replaced the mesic forest about 5400 yr b p in eastern iowa but did not extend much farther east mesic forests were replaced in southern wisconsin and northern illinois about 5400 yr b p by xeric oak forests this change from mesic to xeric conditions at 5400 yr b p was widespread and suggests that the intrusion of drier pacific air was blocked by maritime tropical air from the gulf of mexico until the late holocene in this area

the largest prehistoric landslide in northwestern slovakia chronological constraints of the kykula long runout landslide and related dammed lakes abstract this study deals with the chronology of the largest long runout landslide in the northwesterrn part of the western flysch carpathians kysucke beskydy mts slovakia despite the impossibility of using direct radiocarbon dating method time constraints for the evolution of the landslide were determined on the basis of the dating of various sedimentological geomorphological elements situated on and adjacent to the landslide body the results show that the landslide evolved between 10 3 and 9 0 ka 14 c bp i e in the wider transitional phase between the late glacial lg and the holocene the main mass movement activity took place at the turn of the younger dryas preboreal chronozones whereas retrogressive activity continued up to the preboreal boreal transition radiocarbon dating together with pollen analysis and sedimentology of landslide dammed palaeolakes and colluvial peat bogs revealed almost continuous holocene palaeogeographical records between 10 3 and 3 3 ka 14 c bp periods of enhanced sediment supply to the reservoirs in 9 9 9 0 8 4 8 2 6 9 6 5 and 4 5 ka 14 c bp correlate well with palaeogeomorphic and palaeohydrological records from nearby polish carpathians the study confirms that the lg holocene transition represented a favourable period for the evolution of large landslides not only in glaciated high mountain areas but also in medium high mountains of central europe

using multi proxy palaeoecology to test a relict status of refugial populations of calcareous fen species in the western carpathians the distribution pattern of relict and specialised species in calcareous fens was revealed to be non stochastic with ancient fens harbouring more of these species than younger ones this phenomenon could be caused by long lasting in situ survivals over millennia but direct palaeoecological evidence is lacking we addressed the question whether at least some ancient calcareous fens indeed retained open fen patches throughout the holocene using a palaeoecological approach involving proxies with different taphonomies pollen vascular plants bryophytes molluscs we identified three old fens in the western carpathians where several postglacial relict species have recently been found and we reconstructed their histories with respect to sedimentary processes vegetation structure and dynamics of relict species the development at all the sites started with a semi open fen community dominated by sedges and brown mosses the site with the highest recent number of relict species was reconstructed to harbour open patches continually since the late glacial to the present including the middle holocene when open fen patches were restricted by contrast at the site with the lowest recent number of relict species a large sedimentary hiatus suggested peat mineralisation or erosion that prevented the survival of light demanding species at all the sites characteristic snails of european glacial periods occurred during fen initiation but disappeared around the early middle holocene transition the probability of a relict species being present in a modern fen community increases with fen age but it also depends on the continual existence of open fen patches and peat accumulation throughout the middle holocene

sea level change and subsidence in the delaware estuary during the last 2200 years abstract we produced eight new sea level index points that reconstruct a 2 5 m relative sea level rsl rise at sea breeze in the delaware bay from 200 bce to 1800 ce the precision of our reconstruction improved upon existing data by using high resolution surveying methods ams radiocarbon dating of in situ plant macrofossils collected immediately above the basal contact between pre holocene sand and salt marsh sediments foraminifera as sea level indicators and by accounting for tidal range changes through time our new data were combined with a database of 65 sea level index points available for the delaware bay to estimate the rate of rsl rise in the upper 1 26 0 33 mm yr and lower bay 1 30 0 36 mm yr using a spatial temporal model correction for changes in tidal range through time removed the disparity in rate between the upper and lower delaware bay that had previously been postulated after paleotidal correction the rates of rsl rise estimated for the delaware bay 1 25 0 27 mm yr correlate with the 1 3 mm yr rate reported for new jersey maryland and virginia and confirm that the maximal ongoing forebulge collapse along the u s atlantic coast is focused on the mid atlantic

evidence for warm wet heinrich events in florida analyses of pollen and plant macrofossils from a new core spanning the past 60 000 years from lake tulane florida show a strong antiphase relationship in temperature between florida and the north atlantic region during the pleistocene oak scrub and prairie phases were coeval with long intense dansgaard oeschger interstadials warm periods that initiated bond cycles pine phases were coeval with the north atlantic long stadials cold periods that ended bond cycles and were terminated by heinrich events lake levels were higher during pine phases and climate was wetter however climate in florida was also warmer during these phases which were cold periods in the north atlantic perhaps diminution of thermohaline circulation before and during heinrich events reduced northward heat transport and retained warmth in the subtropical atlantic and gulf of mexico

interactions of climate and fire at two sites in the northern great plains usa abstract the relationship of fire and climate in explaining the origin and maintenance of the grasslands of the northern great plains has long been of interest i examined the hypothesis that burning was more frequent during wet years using charcoal to reconstruct fire histories near coldwater lake in southcentral nd and rice lake in northcentral nd and published records of ostracod mg ca ratios as a proxy for climate at these same two sites over the past 10 000 years charcoal influx rates for coldwater 0 04 5 68 mm 2 cm 2 year 1 greatly exceeded influx rates for rice 2 cm 2 year 1 both sites showed strong significant periodicities of 1500 1800 800 900 and 130 140 years but charcoal maxima and minima were only similar at 4200 cal years bp charcoal influx during the past 2000 years also revealed strong periodicities of between 310 400 and 140 years at both sites comparison of smoothed charcoal influxes and ostracod mg ca ratios suggests that both proxies are responding to changes in climate when smoothed with a 320 400 year window increases in charcoal influx typically preceded rises in ostracod mg ca ratio by 50 100 years and further smoothing 140 year window of the residuals suggested a variable relationship between mg ca ratios and charcoal influx these results do not clearly support or reject the fuel limitation hypothesis and this lack of clear support may result from a climate driven shifts in the mix of c 3 and c 4 grasses resulting in maximum productivity at intermediate moisture levels b possibly different responses of charcoal and mg ca ratios to summer vs winter precipitation or c ground water driven lags in the response of mg ca ratios to shifts in climate comparison of the results from this study with other studies suggests that links between fire and fuels at finer time scales 0 100 years may be broadly constrained by longer term 500 2000 years patterns of climate in the northern great plains

bulk sediment 14c dating in an estuarine environment how accurate can it be abstract due to a lack of marine macrofossils in many sediment cores from the estuarine baltic sea researchers are often forced to carry out 14c determinations on bulk sediment samples however ambiguity surrounding the carbon source pathways that contribute to bulk sediment formation introduces a large uncertainty into 14c geochronologies based on such samples and such uncertainty may not have been fully considered in previous baltic sea studies we quantify this uncertainty by analyzing bulk sediment 14c determinations carried out on densely spaced intervals in independently dated late holocene sediment sequences from two central baltic sea cores our results show a difference of 600 14c yr in median bulk sediment reservoir age or r t bulk between the two core locations 1200 14c yr for one core 620 14c yr for the other indicating large spatial variation furthermore we also find large downcore i e temporal r t bulk variation of at least 200 14c yr for both cores we also find a difference of 585 14c yr between two samples taken from the same core depth we propose that studies using bulk sediment 14c dating in large brackish water bodies should take such spatiotemporal variation in r t bulk into account when assessing uncertainties thus leading to a larger but more accurate calibrated age range less

the effects of dental wear on impairing mammoth taxonomy a reappraisal of the newton mammoth bradford county northeastern pennsylvania a mammoth skeleton found at the newton site a kettle lake 15 km southeast of towanda pennsylvania has been referred to mammuthus columbi on the basis of its high narrow skull however the specimen s thin enamel 1 3 1 8 mm and moderately high lamellar frequency 8 8 75 lophs dm resemble some specimens of mammuthus primigenius prehistoric range maps show that a columbian mammoth inhabiting the towanda area would be a significant outlier from this species range however its location would align well with the range of m primigenius to better ascertain the newton mammoth s identification we examine herein the effects of dental wear on the morphology of mammoth molars as mammoth molars wear the enamel lophs become more broadly spaced and the enamel ridges thicken towards the base of the crown thus an older m primigenius with extensively worn molars might display thicker enamel and a lower lamellar frequency and might therefore appear to be a columbian mammoth on the basis of dental morphology alone our results show that the molars of the newton mammoth are well worn and are characterized by an enamel thickness and lamellar frequency that aligns better with m primigenius than with m columbi we conclude that one must take into account the effects of dental wear when classifying mammoth species using solely molars

centennial to millennial hydroclimatic fluctuations in the humid northeast united states during the holocene paleoclimate records indicate that the hydroclimate of the northeast united states changed continuously during the holocene but the signals of multi century variations have been difficult to distinguish from local effects and noise systematic replication of the signals can help diagnose the patterns of change here we use ground penetrating radar gpr and sediment core analyses to extend and compare the regional network of lake level records we reconstruct the histories of two lakes in northeast pennsylvania which show that multi century hydrologic changes observed in coastal new england extended to the susquehanna river watershed correlations with isotopic and marine temperature records r 0 65 indicate that high temperatures coincided with low water at 4 9 3 8 and 2 8 2 0 ka widely recognized holocene events at ca 4 2 and 2 7 ka therefore may have shared similar ocean atmosphere dynamics in this region low water levels in pennsylvania from ca 5 5 4 9 ka however demonstrate that other multi century changes had different patterns at ca 5 5 ka anti phased inland and coastal hydrologic changes followed a sharp temperature decline and produced drought possibly as far inland as the great lakes the long term increase in water levels since then underscores that current pluvial conditions in the region probably lack a holocene precedent

a 50 000 year record of climate oscillations from florida and its temporal correlation with the heinrich events oscillations of pinus pine pollen in a 50 000 year sequence from lake tulane florida indicate that there were major vegetation shifts during the last glacial cycle episodes of abundant pinus populations indicate a climate that was more wet than intervening phases dominated by quercus oak and ambrosia type ragweed and marsh elder the pinus episodes seem to be temporally correlated with the north atlantic heinrich events which were massive periodic advances of ice streams from the eastern margin of the laurentide ice sheet possible links between the tulane pinus and heinrich events include hemispheric cooling the influences of mississippi meltwater on sea surface temperatures in the gulf of mexico and the effects of north atlantic thermohaline circulation on currents in the gulf

oscillations in the indian summer monsoon during the holocene inferred from a stable isotope record from pyrogenic carbon from lake chenghai southwest china abstract a robust well dated record of centennial scale abrupt changes in the asian summer monsoon is crucial for understanding the potential forcing factors and their environmental effects in this study we analyzed the stable carbon isotopes of pyrogenic carbon 13cpc in a 556 cm long sediment core retrieved from lake chenghai in the yunnan plateau china the results provide a continuous 7660 year precipitation record of the indian summer monsoon ism they indicate that from 7600 cal yr bp precipitation in the lake chenghai catchment gradually increased until 5030 cal yr bp and then subsequently decreased in the second half of the holocene in addition at least six centennial scale droughts occurred at about 7300 6300 5500 3400 2500 and 500 cal yr bp our findings suggest that ism intensity is primary controlled by variations in solar irradiance on a centennial time scale this external forcing may be amplified by north atlantic cooling events and el nino southern oscillation activity in the eastern tropical pacific which shift the intertropical convergence zone further southwards

reconstruction of the glacial history after the last glacial maximum in the italian central alps using schmidt s hammer r values and crystallinity ratio indices of soils abstract despite the ongoing development of cosmogenic techniques to reconstruct deglaciation and glacial advances these techniques are not always feasible for logistical and economic reasons in this study we used schmidt hammer r values sh and crystallinity ratio crf indices of soils together with a limited number of absolute 14c dates to outline the glacial evolution of the gavia valley the study area is a sector of the italian central alps with a glacial history that is poorly understood methodologically we found that sh can be successfully applied to late pleistocene surfaces younger than 15ka in this alpine region the sh method generally underestimates the ages with respect to the crf indices and the 14c dates a total of 7 different glacial phases were found in the study area 14 7ka i phase 13 7ka ii phase 12 2 11 8ka iii phase 10 2 9 7ka iv phase 7 5ka v phase 5 5ka vi phase 1 9ka vii phase these phases are generally consistent with the literature however the little ice age was surely less extended respect the other holocene advances v and vi phase this suggests that relatively short climatic variations during the holocene were locally important