vegetation dynamics around lake baikal since the middle holocene reconstructed from the pollen and botanical composition analyses of peat sediments implications for paleoclimatic and archeological research the present paper summarizes the current evidence of natural changes in the forest and forest steppe areas of the lake baikal region lbr since ca 7 cal ka bp covering the period from the late neolithic to the present time to reconstruct local to small regional scale vegetation changes and their probable causes during this period pollen content and peat botanical composition were analyzed from three radiocarbon dated peat sections located near lake baikal for better understanding of the local and regional environmental history and climate variability during the middle and late holocene the results are compared with published environmental records from lacustrine and mire sediments from the lbr and from elsewhere the comparison confirms the earlier interpretations that the middle and late holocene vegetation dynamics in the lbr was primarily driven by natural forcing and likely was associated with large scale circulation processes controlling the regional water balance rather than with human activities some synchronous changes in environmental and archeological data likely point to a possible causal link between past climate changes and the cultural history of the region the kuchelga 53

peat accumulation in northern wetlands abstract mean long term rates of peat accumulation are higher in boreal and temperate peat deposits than in subarctic regions of canada although peatlands are extensive in the subarctic climatic change probably accounts for the development of southern peatlands during the middle to late holocene and for the late holocene decline in growth of many subarctic peat deposits in northwestern peat deposits peat of wet sphagnum lawns and treed wetlands tended to accumulate more rapidly than peat of sphagnum hummocks and sedge fens long term net rates of carbon accumulation in canadian peatlands typically range from 10 to 35 g c m2 yr

the influence of climate hydrology and permafrost on holocene peat accumulation at 3500 m on the eastern qinghai tibetan plateau peatland of the eastern qinghai tibetan plateau lies at the convergence of the east asian and indian monsoon systems in eastern asia to understand the evolution of this peatland and its potential to provide new insights into the holocene evolution of the east asian monsoon a 6 m peat core was collected from the undisturbed central part of a peat deposit near hongyuan the age depth profile was determined using 16 14c ams age dates the peat analysed for a range of environmental variables including carbon nitrogen and hydrogen concentration bulk density 13c and the associated spring water analysed for hydrogen and oxygen isotopes the age depth profile of the recovered peat sequence covers the period from 9 6 to 0 3 kyr bp and is linear indicating that the conditions governing productivity and decay varied little over the holocene using changes in carbon density organic carbon content and its 13c cold dry periods of permafrost characterised by low density and impeded surface drainage were identified the low 18o and d values of the spring water emanating around the peat deposit down to 13 8 and 102 vsmow respectively with an inverse relationship between electrical conductivity and isotopic composition indicate precipitation under colder and drier conditions relative to the present day in view of the current annual mean air temperature of 1 c this suggests conditions in the past have been conducive to permafrost inferred periods of permafrost correspond to independently recognised cold periods in other holocene records from across china at 8 6 8 2 7 8 5 6 4 2 3 1 and 1 8 1 5 kyr bp the transition to a cold dry climate appears to be more rapid than the subsequent recovery and cold dry periods at hongyuan are of longer duration than equivalent cold dry periods over central and eastern china light dark banding peat on a scale of 15 30 years from 9 6 to 5 5 kyr bp may indicate a strong influence of decadal oscillations possibly the pacific decadal oscillation and a potential link between near simultaneous climatic changes in the northwest pacific enso movement of the intertropical convergence zone and the east asian monsoon

quantification of holocene asian monsoon rainfall from spatially separated cave records abstract a reconstruction of holocene rainfall is presented for southwest china an area prone to drought and flooding due to variability in the east asian monsoon the reconstruction is derived by comparing a new high resolution stalagmite 18 o record with an existing record from the same moisture transport pathway the new record is from heshang cave 30 27 n 110 25 e 294 m and shows no sign of kinetic or evaporative effects so can be reliably interpreted as a record of local rainfall composition and temperature heshang lies 600 km downwind from dongge cave which has a published high resolution 18 o record wang y j cheng h edwards r l he y q kong x g an z s wu j y kelly m j dykoski c a li x d 2005 the holocene asian monsoon links to solar changes and north atlantic climate science 308 854 857 by differencing co eval 18 o values for the two caves secondary controls on 18 o e g moisture source moisture transport non local rainfall temperature are circumvented and the resulting 18 o signal is controlled directly by the amount of rain falling between the two sites this is confirmed by comparison with rainfall data from the instrumental record which also allows a calibration of the 18 o proxy the calibrated 18 o record provides a quantitative history of rainfall in southwest china which demonstrates that rainfall was 8 higher than today during the holocene climatic optimum 6 ka but only 3 higher during the early holocene significant multi centennial variability also occurred with notable dry periods at 8 2 ka 4 8 4 1 ka 3 7 3 1 ka 1 4 1 0 ka and during the little ice age this holocene rainfall record provides a good target with which to test climate models the approach used here of combining stalagmite records from more than one location will also allow quantification of rainfall patterns for past times in other regions

impact of aeolian processes on peat accumulation late glacial holocene history of the hamernia peat bog roztocze region south eastern poland abstract the hamernia peat bog in the roztocze region started to develop in the allerod within the deflation basin divided into two sub basins by a parabolic dune formed in the older or the oldest dryas lithological and palynological analyses as well as radiocarbon dating of samples from three logs cored in different parts of the peat bog indicate that up to the subatlantic when the top of the dune bar was inundated the evolution of both sub basins was different in hydrological and sedimentological aspects aeolian processes were active in the younger dryas generating delivery of mineral material to both sub basins however the intensiveness of this process was much lower than in earlier cold phases as indicated by the limited spatial and temporal delivery of this material restricted mainly to the wind ward sub basin the nature of the next short episode of mineral material delivery to one sub basin recorded during the climate cooling at the turn of the boreal and the atlantic phases is not clear local aeolian or slope processes water erosion accompanied by mass movements are suspected to be responsible for this episode the youngest stage of slight but continuous mineral material delivery caused by aeolian processes started in the climate cooling at the beginning of the subatlantic and was contemporary with the intensification of human activity in this area the geological history in the late vistulian and the holocene suggests that the last dune forming stage in this area occurred during the older dryas

development and refinement of proxy climate indicators from peats peat especially from acidic mires bogs is a natural archive of past environmental change reconstructions of past climate from bogs commenced in the 19th century through examination of visible peat stratigraphy and later formed the basis for a postglacial climatic scheme widely used in northwest europe nevertheless misconceptions as to how bogs grow led to a 50 year lacuna in peat climate study before the concept of cyclic regeneration in bogs was refuted in recent decades research using proxy climate indicators from bogs has burgeoned a range of proxies for past hydrological change has been developed as well as use of pollen bog oaks and pines and other data to reconstruct past temperatures most of this proxy climate research has been carried out in northern europe but peat based research in parts of asia and north america has increased particularly during the last decade while research has also been conducted in australia new zealand and south america this paper reviews developments in proxy climate reconstructions from peatlands chronicles use of a range of palaeo proxies such as visible peat stratigraphy plant macrofossils peat humification testate amoebae and non pollen palynomorphs and explains the use of wiggle match radiocarbon dating and relationship to climate shifts it details other techniques being used increasingly such as biomarkers stable isotopes inorganic geochemistry and estimation of dust flux and points to new proxies under development although explicit protocols have been developed recently for research on ombrotrophic mires it must be recognised that not all proxies and techniques have universal applicability owing to differences in species assemblages mire formation topographic controls and geochemical characteristics

radiocarbon dating peatland development key steps in reconstructing past climate in the central appalachian mountains abstract canaan valley in west virginia contains a greater area of peatlands than any other locality in the mid atlantic highlands extensive fieldwork focused on peat stratigraphy combined with high resolution radiocarbon dating was used to evaluate five peatlands within canaan valley national wildlife refuge cvnwr one hundred soil cores were profiled and described 30 with laboratory analysis including 52 radiocarbon dates calibrated basal peat dates from the five peatlands indicate the onset of peat genesis ranged from 18 600 to 15 200 cal yr bp basal peat dates on the two oldest cores are 1800 to 2200 years older than published dates on peat initiation in any other appalachian mountain peatlands peat accumulation rates varied from 0 02 mm yr to 1 34 mm yr with a mean of 0 14 mm yr results of age depth profiles for six well dated cores consistently exhibit rapid accumulation during the late pleistocene heinrich stadial 1 bolling allerod interstadial and younger dryas cold stadial lower accumulation rates in the early holocene greenlandian age even lower accumulation rates during the mid holocene northgrippian age and the most rapid peat accumulation at the onset of the late holocene early meghalayan age a paucity of shallow peat dating younger than 2000 bp may reflect a reduction in peat accumulation or mixing of surface vegetation into near surface soil horizons soil cores from cvnwr suggest a somewhat different peat development history than the process of terrestrialization previously proposed for other peatland ecosystems in the region

mid late holocene climate variations in southeast china inferred by the intermountain peat records from fujian china abstract the climate of southeastern china is strongly influenced by the easm and tcs which produce most of the precipitation in this area and sustain large scale industrial and agriculture activities however proxy climate records from this area are sparse because of the dense population and intensive human activities in this study a total of ten well dated peat cores collected from the intermountain basins in fujian province were evaluated to explore the initiation histories of the peat bogs and 13 c c of cellulose extracted from four cores were further analyzed to investigate the precipitation history over the last thousand years lithological characteristics of the peat sections show that coarse gravel and sands occur at the bottom of each core which implies that erosion may be the constraint for the initiation of these peat bogs the formation of intermountain peatlands indicates rapidly weakening erosion which in turn suggests a decline in intensive rainfall and or total rainfall based on ams ages three cores show consistent basal ages of approximately 4 2 ka bp whereas five cores exhibit consistent basal ages centered at approximately 1 2 ka bp this staged increasing trend of peat bogs distribution since the mid holocene coincides with the gradual decline in the intensity of the easm intensity suggested by the chinese stalagmite 18 o records which indicates that intensive rainfall in the fujian area has decreased as the easm has weakened during the late holocene this long term change on insolation scale may be connected to insolation and sst of the western north pacific ocean the 13 c c exhibits large variability in amplitude from 27 5 to 11 3 and the periods of heavier 13 c c and lighter 13 c c corresponded to the layers of gray muddy silt and black peat respectively we interpret the large amplitude variability in 13 c c as a reflection of changes in the proportions of submerged plant matter which is rich in 13 c heavier 13 c c indicates a higher proportion of submerged plants with more detritus input and suggests wetter hydrological conditions with higher precipitation the changes in 13 c c over time show that there was a rapid decreasing trend of 13 c c around 800 yr bp which indicated that precipitation decreased since 800 yr bp this decrease in precipitation was consistent with the decrease in temperature from the mwp to the lia which implies that there was a wetter climate during the mwp and a less wet during the lia in southeastern china

holocene peatland initiation lateral expansion and carbon dynamics in the zoige basin of the eastern tibetan plateau the zoige basin on the eastern tibetan plateau has the largest area of highland peatlands in china however the development history of these peatlands is still poorly understood understanding how these carbon rich ecosystems responded to change in the asian summer monsoons during the holocene will provide insight into the peatland carbon accumulation processes under different climate boundary conditions here we document the timing of initiation and expansion histories of these peatlands using 59 new basal peat ages across the zoige basin with 29 ages for initiation analysis and 30 additional ages for lateral expansion analysis also we synthesized basal ages from 26 sites and carbon accumulation records at four sites from previous studies in this region the results show that the peatland initiation is widespread at 11 5 10 and 7 6 kyr 1 kyr 1000 cal yr bp and the minimum initiation periods occurred after 5 kyr our multiple basal ages along eight transects show that slopes are a dominant control on peatland lateral expansion rates with very slow and less variable rates at slopes 0 4 degrees furthermore we found a significant relationship between peatland basal ages and peat depths from 85 sites suggesting relatively uniform peat properties carbon accumulation rates from detailed downcore analysis at four sites and on the basis of peat depth basal age relationship show similar patterns with a peak carbon accumulation at 10 8 kyr on the basis of estimated mean values of bulk density and carbon content from the region the holocene average c accumulation for the zoige basin is 31 1 g c m 2 yr the widespread peatland initiation and rapid accumulation in the early holocene were likely in response to higher temperature and stronger summer monsoon intensity while the slowdown of peatland development during the late holocene might have been caused by climate cooling and drying

palaeoclimate reconstruction based on pollen records from the tangke and riganqiao peat sections in the zoige plateau china abstract palynological analysis was performed to characterize the holocene paleoflora of china s zoige plateau and the implications for the plateau s palaeoclimate using the tangke and riganqiao peat sections atomic mass spectrometry 14 c dates and modern surface soil pollen materials were used to reconstruct the palaeoclimate parameters from 7940 to 6420 cal bp the climate under which the tangke section formed was slightly warm and humid from 6420 to 6030 cal bp the climate was warm and humid from 6030 to 3790 cal bp the climate was slightly cold and dry from 3790 to 1580 cal bp the climate was cold and dry and from 1580 cal bp to the present the climate was very warm and humid from 7320 to 6955 cal bp the climate under which the riganqiao section formed was warm and humid from 6955 to 5467 cal bp the climate was very cold and dry from 3641 to 5467 cal bp the climate was slightly cold and dry from 2337 to 3641 cal bp the climate was warm and slightly humid and from 2337 to 615 cal bp the climate was warm and slightly humid several cold and dry events have therefore occurred since 8000 cal bp in both sections there is a close relationship between peat mire development and paleoenvironmental change during the five periods recorded in the two sections

role of seasonal transitions and westerly jets in east asian paleoclimate abstract the summer rainfall climate of east asia underwent large and abrupt changes during past climates in response to precessional forcing glacial interglacial cycles as well as abrupt changes to the north atlantic during the last glacial however current interpretations of said changes are typically formulated in terms of modulation of summer monsoon intensity and do not account for the known complexity in the seasonal evolution of east asian rainfall which exhibits sharp transition from the spring regime to the meiyu and then again from the meiyu to the summer regime we explore the interpretation that east asian rainfall climate undergoes a modulation of its seasonality during said paleoclimate changes following previous suggestions we focus on role of the westerly jet over asia namely that its latitude relative to tibet is critical in determining the stepwise transitions in east asian rainfall seasons in support of this linkage we show from observational data that the interannual co variation of june july august rainfall and upper tropospheric zonal winds show properties consistent with an altered timing of the transition to the meiyu summer and with more northward shifted westerlies for earlier transitions we similarly suggest that east asian paleoclimate changes resulted from an altered timing in the northward evolution of the jet and hence the seasonal transitions in particular the transition of the jet from south of the plateau to the north that determines the seasonal transition from spring rains to the meiyu in an extreme scenario which we speculate the climate system tended towards during stadial cold phases of d o stadials and periods of low northern hemisphere summer insolation the jet does not jump north of the plateau essentially keeping east asia in prolonged spring conditions we argue that this hypothesis provides a viable explanation for a key paleoproxy signature of d o stadials over east asia namely the heavier mean 18o of precipitation as recorded in speleothem records the southward jet position prevents the low level monsoonal flow which is isotopically light from penetrating into the interior of east asia as such precipitation there will be heavier consistent with speleothem records this hypothesis can also explain other key evidences of east asian paleoclimate changes in particular the occurrence of dusty conditions during north atlantic stadials and the southward migration of the holocene optimal rainfall

temperature responses to quasi 100 yr solar variability during the past 6000 years based on δ18o of peat cellulose in hongyuan eastern qinghai tibet plateau china abstract during the past 6000 years the temperature variation trend inferred from 18o of peat cellulose in a peat core from hongyuan eastern qinghai tibet plateau southwestern china is similar to the atmospheric 14c concentration trend and the modeled solar output trend the general trend of hongyuan 18o during the past millennium also coincides well with the atmospheric 14c concentration trend the 10be concentration trend in an ice core from the south pole the reconstructed total solar irradiance trend as well as the modeled solar output trend in addition temperature events also correspond well to solar perturbations during the past 6000 years therefore the driving force of holocene temperature variations should be properly ascribed to solar activity the spectrum analysis further illustrates that quasi 100 yr fluctuation of solar activity was probably responsible for temperature variations in northeast qinghai tibet plateau during the past 6000 years

timing of mylonitization in the funatsu shear zone within hida belt of southwest japan implications for correlation with the shear zones around the ogcheon belt in the korean peninsula abstract the funatsu shear zone is an early mesozoic dextral ductile shear zone located in the hida belt of southwest japan consisting mainly of granite mylonites the jurassic funatsu granites intrude the hida metamorphic rocks and the granite mylonites the shrimp u pb zircon ages of granite mylonites in the funatsu shear zone around the tateyama area are 250 2 2 ma and 240 2 ma shrimp u pb zircon age of the okumayama granodiorite which is a member of the funatsu granites and which intrudes the granite mylonite is 191 3 ma we interpret that the timing of mylonitization in the funatsu shear zone to be after 240 ma and prior to 191 ma triassic to early jurassic and possibly around 215 211 ma late triassic corresponding to the k ar ages of hornblende in basic inclusions of the granite mylonite in the korean peninsula dextral ductile shear movement occurred in the cheongsan shear zone of south central ogcheon belt during middle to late triassic time accompanied by the intrusion of jurassic daebo granites which are correlated to the funatsu granites the similarities in geology deformation characteristics timing of mylonitization and paleogeographic location suggest that the funatsu shear zone can be correlated to the cheongsan shear zone

paleoclimate influence on early diagenesis of plant triterpenes in the dajiuhu peatland central china abstract aromatic derivatives of vascular plant triterpenoids are common in recent and ancient sediments coal and petroleum understanding their early diagenetic alterations and their relation with environmental conditions can facilitate their applications in paleoenvironmental reconstructions here we present a high resolution record of aromatic triterpenes in a holocene peat core collected in the dajiuhu peatland central china these aromatic triterpenes are derivatives of plant triterpenoids with oleanane ursane and lupane carbon skeletons and exist in three different structural groups aromatic des a triterpenes aromatic pentacyclic triterpenes and c ring cleaved aromatic triterpenes such a high diversity of aromatic triterpenes in a young peat deposit is compelling evidence for rapid microbial mediation of these important degradation pathways during very early diagenesis of particular importance is the occurrence of c ring cleaved aromatic triterpene and aromatic des a triterpenes in the dajiuhu peat samples which until now have not been identified in recent sediments the downcore profile shows that the microbial aromatization process of oleanoids positively correlates with paleoclimate change during dry or warm intervals highly aromatized products such as tetraaromatic triterpenes become predominant over their triaromatic homologs in contrast triaromatic triterpenes become dominant during wet or cold intervals in addition this study provides further evidence to support that the climate pattern in the middle reaches of the yangtze river is different from that in north china during 13 9 4 ka these findings suggest that aromatic triterpenes can be valuable tools for holocene paleoenvironmental reconstructions

the first continuous late glacial holocene peat bog multi proxy record from the dolomites ne italian alps abstract paleoclimate and paleoenvironmental studies in the north eastern italian alps have been hampered by the rarity of well preserved high altitude deposits and the lack of high resolution multi proxy records with adequate chronological control this paper presents the first complete late glacial to holocene peat succession from the dolomites danta di cadore belluno italian alps a 7 m core was used to evaluate the potential of the ombrotrophic val di ciampo peat deposit 1400 m a s l as an archive of environmental and climate change the depth age scale is based upon independent 14 c and 210 pb dates and combined with peat stratigraphy demonstrates that the peat core covers more than 13 200 cal bp extending to the end of the last part of the late glacial bulk density inorganic matter content pore water ph conductivity ca mg ratios and ca sr and ti trends were used to identify changes in trophic conditions through the bog the boundary between ombrotrophic and minerotrophic conditions occurs at approximately 400 cm below the surface and demonstrates that this core is the longest eastern alpine ombrotrophic record yet obtained corresponding to 7000 cal bp the high resolution chemical data of this peat archive improves our understanding of european alpine holocene climate variability and the relationship between natural climate fluctuations and anthropogenic climate change during the present interglacial in the dolomites

a 5500 year proxy climate and vegetation record from blanket mire at talla moss borders scotland a monolith of peat taken from an upland blanket mire at talla moss southern scotland was sub jected to peat humification and pollen analyses to produce both a proxy climate record and a vegetational history covering the last 5500 years while the peat showed little visible stratigraphy with no intimation of major peat humification changes colorimetric data indicate a markedly oscillatory climate record which is apparently largely independent of or out of phase with major vegetational changes the raw data imply particular wet shifts in climate at c 3455 bp c 2600 bp c 1930 bp c 1095 bp with a markedly wet or cool and wet episode commencing at c 540 bp these are central age estimates and should not be regarded as precise dates for the inferred climate shifts other wet shifts apparently date from c 3070 bp c 2265 bp and c 1700 bp although the first of these corresponds with pollen evidence for significant prehistoric human activity in the locality spectral analysis of the peat h

holocene climate change in central eastern brazil reconstructed using pollen and geochemical records of pau de fruta mire serra do espinhaco meridional minas gerais abstract studies dealing with the reconstruction of holocene climate change of tropical areas are scarce of these multi proxy investigations using peatlands are still absent in this paper we present the holocene record of environmental changes in central eastern brazil reconstructed from a core sampled in pau de fruta mire serra do espinhaco meridional brazil we combined palynological and geochemical analyses supported by core stratigraphy 14 c dating and multivariate statistics the location of the mire is ideal because it is in an area which is directly associated with the south atlantic convergence zone sacz six main phases of change suggested by vegetation and local and regional landscape dynamics were described in phase i 10 000 7360 cal yr bp the climate was very wet and cold and was accompanied by soil instability in the mire catchment severe local erosion and the 8 2 ka event was easily recognizable by a large increase in the deposition of regional dust phase ii 7360 4200 cal yr bp was characterized by wet and warm conditions catchment soil stability and enhanced deposition of regional dust in phase iii 4200 2200 cal yr bp climate was dry and warm and soil erosion in the catchment increased again in phase iv 2200 1160 cal yr bp dry and punctuated cooling was reconstructed together with enhanced deposition of regional dust phase v 1160 400 cal yr bp reflects sub humid climatic conditions like the current climate the lowest inputs of local and regional dust and the largest accumulation of peat in the mire while in phase vi

neoholocene palaeoenvironmental changes in the southern roztocze region se poland the kobyle jezioro raised bog case study abstract the pollen diagram from the kobyle jezioro raised bog situated in the source area of the tanew river in the roztocze region covers the whole neoholocene the deposit thickness about 3 5 m has permitted high resolution pollen peat including macrofossils and lithology analyses vegetational and palaeoenvironmental changes in this part of the roztocze were recorded in pollen spectra and organic deposits palynological evidence shows the typical neoholocene succession which corresponds with the phenomena described from central europe from mixed deciduous forests at the decline of the climatic optimum through hornbeam and beech dominated forests to pine forests peat accumulation in the kobyle jezioro peat bog started during increased climatic humidity at the beginning of the subboreal and originally a fen peat was formed raised bog peat layers make up the uppermost 80 cm of the deposit within the fen deposits can be found layers of transitional peat indicating short term episodes of water deficiency in the early subboreal phase short term climatic dryness and towards its end drainage of the bog resulting from the lowering of the groundwater table in the source area of the tanew river the growth of the raised bog started at the beginning of the climate deterioration in the little ice age and the unstable climatic conditions are reflected in the numerous periodical mineral aeolian material supplies in the developing ombrogenic bog the accumulation of the younger section of transitional and raised peats during the little ice age reflects the local hydrological changes in the source area of the tanew river

peatland development and climate changes in the dajiuhu basin central china over the last 14 100 years abstract peatlands are one of the optimal archives for paleoclimate research and their records contain a detailed history of climatic and environmental variations during their formation here we collected a peat profile from the dajiuhu basin in central china and analyzed several geochemical proxies such as total organic carbon toc total nitrogen tn titanium ti and aluminum al to investigate the history of peat development the results show that the peat growth was initiated after around 12 8 cal ka bp at the sampling site and the toc and tn contents kept stable during the holocene except during the periods of 10 5 9 0 cal ka bp and recent 1 5 cal ka bp however compared with other toc records in the dajiuhu basin the history of peat development varied greatly in different sampling sites indicating that the peat development in the dajiuhu basin probably responds to both climate changes and local geological and hydrological conditions investigations of the interactions between climate change and peat development record in this study suggest that peat development presented significant responses to the large and rapid decreases in east asian summer monsoon intensity such as the 9 2 ka monsoon weakening event however the obvious long term decreasing trend of monsoon precipitation during the mid late holocene did not lead to the degradation of the dajiuhu peat probably resulting from relatively stable temperature in addition the sharp decrease of toc and tn values in the surface 15 cm of dajiuhu peat was probably attributed to increased human activity

mid holocene vegetation reconstruction from vanevan peat south eastern shore of lake sevan armenia a sediment core has been retrieved from vanevan peat south eastern shore of lake sevan armenia which is today disconnected from lake sevan thanks to an artificial shallowing of the lake based on 5 radiocarbon dates vanevan record covers the mid holocene from ca 7800 to ca 5100 cal bp the late holocene is today absent in the peat stratigraphy due to modern peat exploitation by surface mining this study focuses on a multi proxy approach including pollen charcoals and pollen inferred climate reconstruction an open land steppic vegetation is recorded up to ca 7700 cal bp followed by a more forested landscape during the mid holocene up to ca 5700 cal bp and ending again with an open land vegetation to the end of record 5100 cal bp this vegetation dynamics responds to general climate changes documented in the near east whether human activities are documented since ca 7500 cal bp late neolithic in vanevan they remain marginal and probably did not affect the area early holocene dry climate which caused the steppic environment to be widespread through the near east is strongly related to low late spring precipitation pmay jun 180 mm mid holocene forested landscape and increasing lake level seem related to late spring precipitation 28 which is the main change in estimated climate parameters this has to be linked with reinforcement of the westerlies and less active siberian high which are inversely involved in the following dry phase starting at ca 5700 cal bp

paleotemperature variability in central china during the last 13 ka recorded by a novel microbial lipid proxy in the dajiuhu peat deposit the asian summer monsoon is a very important climatic component affecting the land ecosystem on the eastern asian continent here we assess microbe derived lipid biomarker evidence from a well date

influence of the intertropical convergence zone on the east asian monsoon a palaeoclimate record spanning the past 16 000 years with nearly annual time resolution has been obtained from lake huguang maar in china the magnetic properties and titanium content of the lake sediments are thought to reflect changes in the east asian winter monsoon strength thus providing a complement to palaeoclimate archives that record the strength of the rain bearing summer monsoon the records point to an anti correlation between winter and summer monsoon strength best explained by migration of the intertropical convergence zone itcz a belt of low pressure air at the equator interestingly the decline of china s tang dynasty and the mayan civilization broadly coincide with drought periods recorded in lake huguang maar and cariaco basin sediments respectively did major shifts in the position of the itcz catalyse simultaneous events in civilizations on opposite sides of the pacific ocean the asian australian monsoon is an important component of the earth s climate system that influences the societal and economic activity of roughly half the world s population the past strength of the rain bearing east asian summer monsoon can be reconstructed with archives such as cave deposits1 2 3 but the winter monsoon has no such signature in the hydrological cycle and has thus proved difficult to reconstruct here we present high resolution records of the magnetic properties and the titanium content of the sediments of lake huguang maar in coastal southeast china over the past 16 000 years which we use as proxies for the strength of the winter monsoon winds we find evidence for stronger winter monsoon winds before the bolling allerod warming during the younger dryas episode and during the middle and late holocene when cave stalagmites suggest weaker summer monsoons1 2 3 we conclude that this anticorrelation is best explained by migrations in the intertropical convergence zone similar migrations of the intertropical convergence zone have been observed in central america for the period ad 700 to 900 refs 4 6 suggesting global climatic changes at that time from the coincidence in timing we suggest that these migrations in the tropical rain belt could have contributed to the declines of both the tang dynasty in china and the classic maya in central america

paleoecological evidence for abrupt cold reversals during peak holocene warmth on baffin island arctic canada a continuous record of insect chironomidae remains preserved in lake sediments is used to infer temperature changes at a small lake in arctic canada through the holocene early holocene summers at the study site were characterized by more thermophilous assemblages and warmer inferred temperatures than today presumably in response to the positive anomaly in northern hemisphere summer insolation peak early holocene warmth was interrupted by two cold reversals between 9 5 and 8 cal ka bp during which multiple cold stenothermous chironomid taxa appeared in the lake the earlier reversal appears to correlate with widespread climate anomalies around 9 2 cal ka bp the age of the younger reversal is equivocal but it may correlate with the 8 2 cal ka bp cold event documented elsewhere widespread abrupt climate shifts in the early holocene illustrate the susceptibility of the climate system to perturbations even during periods of enhanced warmth in the northern hemisphere

reconstructing late holocene vegetation and fire histories in monsoonal region of southeastern china abstract eastern subtropical china is a key region for understanding the variability of the east asian summer monsoon easm multidisciplinary studies in southeastern china have shown that the summer monsoon intensity declined in the mid late holocene we present a high resolution pollen record of the last 4000 cal yr bp in jinggang mts of jiangxi province southeastern china the identified pollen taxa from the core can be statistically divided into three groups corresponding to evergreen deciduous and wetland communities the transitions between evergreen and deciduous coniferous pollen associations is likely caused by temperature fluctuations indicating that climate was relatively cool at 3800 3200 cal yr bp and 2200 1300 cal yr bp and warmer at 3200 2800 cal yr bp and 1300 800 cal yr bp the vegetation study suggests that an alnus dominant association represents a secondary forest that usually takes place and expand after repeated forest fires the charcoal concentration from the core depicts at least six major forest fire events since 4000 cal yr bp most of which were followed by the development of an alnus forest community this result suggests that the easm weakened toward the late holocene and that its related decrease in moisture led to large forest wildfires furthermore the rapid formation of a swamp and the subsequent development of the alnus wetland community at 550 cal yr bp suggest a gradual drying up of the lake which was likely related to the little ice age as a result of a substantial burning related to an intensification of the human cultivation practices alnus reached its highest values in the last 200 years along with abundant wetland herbs pioneer ferns mainly dicranopteris and high charcoal concentrations the present evidence of several sharp floristic and climate changes coincides with either the collapse or the beginning of some chinese dynasties which will need further research on the relationship between natural and human cultural changes

a new greenland ice core chronology for the last glacial termination 1 we present a new common stratigraphic timescale for the north greenland ice core project ngrip and grip ice cores the timescale covers the period 7 9 14 8 kyr before present and includes the bolling allerod younger dryas and early holocene periods we use a combination of new and previously published data the most prominent being new high resolution continuous flow analysis cfa impurity records from the ngrip ice core several investigators have identified and counted annual layers using a multiparameter approach and the maximum counting error is estimated to be up to 2 in the holocene part and about 3 for the older parts these counting error estimates reflect the number of annual layers that were hard to interpret but not a possible bias in the set of rules used for annual layer identification as the grip and ngrip ice cores are not optimal for annual layer counting in the middle and late holocene the timescale is tied to a prominent volcanic event inside the 8 2 kyr cold event recently dated in the dye 3 ice core to 8236 years before a d 2000 b2k with a maximum counting error of 47 years the new timescale dates the younger dryas preboreal transition to 11 703 b2k which is 100 150 years older than according to the present grip and ngrip timescales the age of the transition matches the gisp2 timescale within a few years but viewed over the entire 7 9 14 8 kyr section there are significant differences between the new timescale and the gisp2 timescale the transition from the glacial into the bolling interstadial is dated to 14 692 b2k the presented timescale is a part of a new greenland ice core chronology common to the dye 3 grip and ngrip ice cores named the greenland ice core chronology 2005 gicc05 the annual layer thicknesses are observed to be log normally distributed with good approximation and compared to the early holocene the mean accumulation rates in the younger dryas and bolling periods are found to be 47 2 and 88 2 respectively

response of humification degree to monsoon climate during the holocene from the hongyuan peat bog eastern tibetan plateau abstract the humification degree of peat has been used to indicate climate variations in europe with a dominant maritime climate however little research has been done so far in asia with a monsoon climate here for the first time the absorbance value time series of the alkali extraction of hongyuan peat from the eastern tibetan plateau is determined this is used as the proxy indicator for the humification degree of peat and we compare it with the 13 c time series of the carex mulieensis cellulose in the peat which has been used as a proxy indicator for the indian ocean summer monsoon during the holocene our data show that the humification degree of peat can sensitively reflect the strength variation of the indian ocean summer monsoon both on orbital and millennial timescales higher humification degree corresponds with stronger monsoon activity and lower humification degree corresponds with weaker monsoon activity the proxy climate significance of the humification degree of the peat in the eastern tibetan plateau region seems to differ from that in the european continent this difference could be attributed to the influences of local biogeochemical processes caused by the monsoon climate including the varying combination of moisture and temperature the alternating drying rewetting variation and the freeze thaw effect

cryptic abundance of long chain iso and anteiso alkanes in the dajiuhu peat deposit central china abstract long chain 2 methyl and 3 methyl alkanes occur widely in modern plants and in recent and ancient sediments but their presence in peat deposits has not been reported here we document an early holocene enrichment of long chain 2 methyl alkanes in the dajiuhu peat deposit accompanied by traces of 3 methyl alkanes the 2 methyl alkanes showed a strong odd even predominance and were dominated by c 27 and c 29 homologs their 13 c values were 5 7 less negative than those of the n alkanes with the same carbon numbers our previous paleoenvironmental reconstruction for this peat sequence indicated that the interval enriched in long chain 2 methyl alkanes corresponded to a period with a very wet climate although not resolved possible sources of the long chain 2 methyl alkanes with relatively enriched 13 c composition include submerged aquatic plants utilizing bicarbonate or heterotrophic microbes in the peatland and its catchment

hydrology mediated differential response of carbon accumulation to late holocene climate change at two peatlands in southcentral alaska abstract peatlands are among the largest reservoirs of terrestrial carbon in the northern hemisphere understanding how this reservoir will respond to climate changes is critical to assessing potential climate feedbacks peatland carbon accumulation rates pcar are controlled by the difference between production and decomposition which is affected by local and climatic factors including hydrology and temperature to better understand how local controls can influence the response of pcar to climate change we investigated modern hydrology paleohydrology and pcar at two nearby sphagnum dominated peatlands with different surficial geology lowland and moraine settings in southcentral alaska modern hydrological data indicated a higher rate of subsurface drainage at the lowland site suggesting greater hydrologic sensitivity to prolonged dry periods of the past we investigated past responses of these peatlands to well documented climatic changes like the medieval climate anomaly mca at 1000 600 cal yr bp and little ice age lia at 600 200 cal yr bp using water table depth wtd inferred from testate amoebae and pcar calculated from loss on ignition and 14 c dating analyses our results indicate that wtd and pcar remained relatively stable at the moraine site throughout the last 1100 years including the mca and lia however the lowland site experienced relatively stable wtd and higher pcar during the mca but highly variable wtd and lower pcar during the lia these differences suggest that hydrology and likely decomposition were the primary control on pcar at these peatlands our results highlight the importance of local scale controls like surficial geology in mediating the response of peatland hydrology and carbon accumulation to climate change

lacustrine record from the eastern tibetan plateau associated with asian summer monsoon changes over the past 6 ka and its links with solar and enso activity a multi parameter absolute dated lacustrine record from the eastern tibetan plateau provides a continuous history of the asian summer monsoon asm over the past 6000 years the record broadly follows the trend in northern hemisphere summer insolation however it diverges during a period of increased moisture and thermal conditions during the past 1300 years broadly corresponding to the asm 2 kyr shift this shift as referred by cheng et al nature 534 640 646 10 1038 nature18591 2016 may be related to atlantic meridional overturning circulation variations and potentially to increased forcing by greenhouse gases coincident with reduced enso activity the record is punctuated by several weak monsoon intervals cross correlation of the sub millennial scale monsoon record with solar activity and enso records shows that most of the monsoon variability potentially results from changes in solar irradiation and has a strong teleconnection with enso activity

regional climate change from peat stratigraphy for the mid to late holocene in central ireland at the millennial scale bog surface wetness bsw records show a clear holocene climate event stratigraphy with major phases comparable with other regional climate proxies such as chironomid inferred temperature records moving towards the centennial scale however and towards the limits of chronological certainty within the records regional differences are apparent which likely reflect the more heterogeneous precipitation patterns which occur on shorter timescales the bsw data presented in this paper are reconstructed from testate amoebae assemblages from central ireland and are compared with other regional records the results suggest that this region is in phase with the north of ireland in terms of timings and durations of climate change but the comparisons are less clear with a stacked and tuned record from northern britain that shows an apparent offset compared to the irish records this may reflect variations in past regional precipitation or be a function of the tuning and stacking process the broad phases of comparison between the irish records and the extension of the central irish record back to 6000 cal bp allow comparisons with low frequency temperature reconstructions from chironomids which also show a broad level of correlation with cooler temperatures relating to wetter bsw at centennial to millennial timescales

vegetation responses to the last glacial and early holocene environmental changes in the northern leizhou peninsula south china abstract a well dated palynological record spanning the interval 40 500 7060 cal yr bp retrieved from a peatland on the leizhou peninsula in south china clearly shows regional vegetation and climate changes during the last glacial period pollen data showed that the study region was mainly covered by subtropical evergreen trees during marine isotope stage 3 mis 3 indicating a subtropical climate with relatively high temperature and precipitation during mis 2 subtropical evergreen deciduous forest with large areas of grassland occurred implying cooler and drier conditions some tropical forest elements increased during the early holocene indicating a warm and wet trend several millennial scale oscillations of the pollen records appeared to correlate with the cold anomalies in the north atlantic region our records agree well with many records from other regions but they are a bit different than that inferred from the neighboring huguang maar lake furthermore our results suggest that the vegetation surrounding xialu peatland was strongly influenced by the migration of the intertropical convergence zone itcz and variability in the east asian summer monsoon easm changes of atmospheric co2 concentration pco2 levels may have also affected the long term vegetation changes in the study region

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

water rich sublithospheric melt channel in the equatorial atlantic ocean the lithosphere asthenosphere boundary is the most extensive boundary on earth separating the mobile plate above from the convecting mantle below but its nature remains a matter of debate using an ultra deep seismic reflection technique here we show a systematic seismic image of two deep reflectors that we interpret as the upper and lower limits of the lithosphere asthenosphere boundary beneath a 40 70 million year old oceanic lithosphere in the atlantic ocean these two reflections correspond to 1 260 c and 1 355 c isotherms and bound a low velocity channel suggesting that the lithosphere asthenosphere boundary is thermally controlled we observe a clear age dependency of this sublithospheric channel its depth increases with age from 72 km where it is 40 myr old to 88 km where it is 70 myr old whereas its thickness decreases with age from 18 km to 12 km we suggest that partial melting facilitated by water is the main mechanism responsible for the low velocity channel the required water concentration for melting increases with age nevertheless its corresponding total mass remains relatively constant suggesting that most of the volatiles in the oceanic sublithospheric channel originate from a horizontal flux near the ridge axis

holocene peatland development along the eastern margin of the tibetan plateau knowledge of peatland initiation accumulation and decline or cessation is critical in understanding peatland development and the related carbon source sink effect in this study we investigated the development of three peat profiles along the eastern margin of the tibetan plateau etp and compared the results with those of our previous work along this transect our work showed that the initiation over the northern etp is later and the slowdown cessation earlier than in the middle to southern etp the timing of optimum peatland formation over the northern etp lags the holocene climatic optimum these spatio temporal differences are likely to be related to the intensity of asian summer monsoon our work suggests that some peatlands along the etp transect have returned or are now returning their previously captured carbon to the atmosphere and thus act as carbon sources some peatlands still have net accumulation at present but the rates have been reduced concomitant with the decreasing summer monsoon intensity we speculate that more of the previously stored carbon in the etp peatlands will be re emitted to the atmosphere if the aridity continues as might occur under a continuous global warming scenario

concordant monsoon driven postglacial hydrological changes in peat and stalagmite records and their impacts on prehistoric cultures in central china asian monsoon records are widely documented but specific proxies of monsoonal rainfall are limited we present here two new independent proxy records from peatland and stalagmite archives that indicate a high degree of concordance between monsoon driven hydrological changes occurring since the last deglaciation in a broad region of central china the wet periods elevated the water table in the dajiuhu peatland as recorded by reduced mass accumulation rates of hopanoids biomarkers for aerobic microbes confirmed by molecular phylogenic analyses the hopanoid based reconstruction is supported by the first report of the environmental magnetism parameter arm sirm anhysteretic remanent magnetization saturation isothermal remanent magnetization ratio of fine magnetic particles to total ferrimagnetic particles in a stalagmite from heshang cave in central china heavy rainfall resulted in the enhanced transport of coarse particles to the cave and thus low arm sirm values in the stalagmite the hydrological conditions inferred from the two records reveal three relatively long wet periods in central china 13 11 5 k y ago 9 5 7 0 k y ago and 3 0 1 5 k y ago archaeological evidence for the hydrological impacts on regional populations comes from the observation that temporal shifts among six distinctive cultures of the neolithic period to the iron age in central china occurred during wet periods or flood episodes spatiotemporal distributions of 1600 prehistoric settlement sites correlate with the proxy inferred fluctuating hydrological conditions with enhanced flooding risk forcing major relocations of human settlements away from riparian zones

a high resolution absolute dated holocene and deglacial asian monsoon record from dongge cave china abstract we present a continuous record of the asian monsoon over the last 16 ka from 18o measurements of stalagmite calcite over 900 oxygen isotopic measurements providing information on shifts in monsoon precipitation are combined with a chronology from 45 precise 230th dates 18o and therefore asian monsoon intensity generally follows changes in insolation although changes in 18o are generally accommodated in abrupt shifts in contrast to smoothly varying insolation indicating that threshold effects may be important 18o decreased dramatically 3 at the start of the holocene 11 5 ka and remained low for 6 ka four positive 18o events centered at 11225 97 yr bp 1 05 10880 117 yr bp 1 15 9165 75 yr bp 1 4 and a double event centered at 8260 64 yr bp 1 1 and 8080 74 yr bp 1 0 punctuated this period of high monsoon intensity all four events correlate within error with climate changes in greenland ice cores thus the relationship between the asian monsoon and the north atlantic observed during the glacial period appears to continue into the early holocene in addition three of the four events correlate within error with outburst events from lake agassiz the decline of monsoon intensity in the mid late holocene is characterized by an abrupt positive shift in 18o which occurs at 3550 59 yr bp 1 1 in 100 yr in addition the holocene is punctuated by numerous centennial and multi decadal scale events amplitudes 0 5 to 1 up to half the amplitude of the glacial interstadial events seen in the last glacial period thus holocene centennial and multi decadal scale monsoon variability is significant although not as large as glacial millennial scale variability the monsoon shows a strong connection with northern south american hydrological changes related by changes in itcz position spectral analysis of the 18o record shows significant peaks at solar periodicities of 208 yr and 86 yr suggesting variation is influenced by solar forcing however there are numerous other significant peaks including peaks at el nino frequencies observed for high resolution portions of the record between 8110 and 8250 yr which suggest that changes in oceanic and atmospheric circulation patterns in addition to those forced by solar changes are important in controlling holocene monsoon climate in addition for this high resolution portion we observe a distinctive biennial oscillation of the asian monsoon which has been associated with the tropospheric biennial oscillation tbo

holocene variability of the east asian summer monsoon from chinese cave records a re assessment oxygen isotope records from stalagmites in caves in southern china interpreted as proxy rainfall records reflecting the intensity of the east asian summer monsoon indicate gradual monsoon weakening for the last 9000 years as also documented for the indian monsoon coupled with high precision dating the speleothem proxy records have been used to test monsoon links with orbital forcing solar changes iceberg discharges in the north atlantic ocean currents and atmospheric methane however these benchmark cave records do not match other published dated e asian proxy rainfall record specifically here independently calibrated rainfall records from loess palaeosol magnetic properties and cave oxygen isotope intercomparisons which show variable e asian monsoon intensity through the entire holocene the strong correlation of the cave records with the extraregional indian monsoon record yet their mismatch with these other dated chinese rainfall records might be reconciled if the speleothem isotope variations reflect not changes in holocene rainfall amount but in rainfall source declining holocene influence of isotopically lighter indian monsoon sourced moisture over china would have resulted in increasing proportions of isotopically heavier rainfall sourced from the more oceanic e asian monsoon individual speleothems may thus regionally record holocene changes in indian monsoon intensity and isotopic influence conversely the other chinese proxy records described here reflect changes in rainfall amount and thus in e asian summer monsoon intensity for the holocene the e asian and the indian monsoon responses to orbital forcing are likely to have differed specifically due to e asian internal feedbacks and the seasonal contrasts between the two monsoon systems

holocene vegetation and climate histories in the eastern tibetan plateau controls by insolation driven temperature or monsoon derived precipitation changes abstract the climates on the eastern tibetan plateau are strongly influenced by direct insolation heating as well as monsoon derived precipitation change however the moisture and temperature influences on regional vegetation and climate have not been well documented in paleoclimate studies here we present a well dated and high resolution loss on ignition peat property and fossil pollen record over the last 10 000 years from a sedge dominated fen peatland in the central zoige basin on the eastern tibetan plateau and discuss its ecological and climatic interpretations lithology results indicate that organic matter content is high at 60 80 between 10 and 3 ka 1 ka 1000 cal yr bp and shows large magnitude fluctuations in the last 3000 years ash free bulk density as a proxy of peat decomposition and peatland surface moisture conditions oscillates around a mean value of 0 1 g cm 3 with low values at 6 5 4 7 ka reflecting a wet interval and an increasing trend from 4 7 to 2 ka suggesting a drying trend the time averaged mean carbon accumulation rates are 30 6 gc m 2 yr for the last 10 000 years higher than that from many northern peatlands tree pollen mainly from picea mostly reflecting temperature change in this alpine meadow forest ecotonal region has variable values from 3 to 34 during the early holocene reaches the peak value during the mid holocene at 6 5 ka and then decreases until 2 ka the combined peat property and pollen data indicate that a warm and wet climate prevailed in the mid holocene 6 5 4 7 ka representing a monsoon maximum or optimum climate for the region the timing is consistent with recent paleo monsoon records from southern china and with the idea that the interplays of summer insolation and other extratropical large scale boundary conditions including sea surface temperature and sea level change control regional climate the cooling and drying trend since the mid holocene likely reflects the decrease in insolation heating and weakening of summer monsoons regional synthesis of five pollen records along a south north transect indicates that this climate pattern can be recognized all across the eastern tibetan plateau the peatland and vegetation changes in the late holocene suggest complex and dramatic responses of these lowland and upland ecosystems to changes in temperature and moisture conditions and human activities

peatland evolution and associated environmental changes in central china over the past 40 000 years central china has experienced stronger summer monsoon during warm periods such as marine isotope stages mis 1 and 3 and weaker summer monsoon during cool periods such as mis 2 the evolution history of dajiuhu subalpine peatland in central china can help investigate how the expansion and shrinkage of peatland were associated with monsoonal strength over the last glacial interglacial cycle here we apply bulk organic carbon and molecular biomarkers hopane and n alkane to reconstruct the evolution history for the dajiuhu peatland over the past 40 000 yr the results indicate fluctuations between lacustrine and peat like deposition during mis 3 steady lacustrine deposition during mis 2 and peatland initiation and expansion during mis 1 in the dajiuhu peatland therefore at the glacial interglacial scale warmer summer and cooler winter conditions in interglacial periods are crucial to trigger peat deposition whereas reduced evaporation in glacial period instead of decreased monsoonal driven precipitation would have played a predominant role in the regional effective moisture balance however within the holocene mis 1 monsoonal precipitation changes appear to be the main controller on millennial scale variations of water table level of the dajiuhu peatland

asian monsoon hydrometeorology from tes and sciamachy water vapor isotope measurements and lmdz simulations implications for speleothem climate record interpretation observations show that heavy oxygen isotope composition in precipitation 18 o p increases from coastal southeastern se china to interior northwestern nw china during the wet season contradicting expectations from simple rayleigh distillation theory here we employ stable isotopes of precipitation and vapor from satellite measurements and climate model simulations to characterize the moisture processes that control asian monsoon precipitation and relate these processes to speleothem paleoclimate records we find that 18 o p is low over se china as a result of local and upstream condensation and that 18 o p is high over nw china because of evaporative enrichment of 18 o as raindrops fall through dry air we show that 18 o p at cave sites over southern china is weakly correlated with upstream precipitation in the core of the indian monsoon region rather than local precipitation but it is well correlated with the 18 o p over large areas of southern and central china consistent with coherent speleothem 18 o p variations over different parts of china previous studies have documented high correlations between speleothem 18 o p and millennial timescale climate forcings and we suggest that the high correlation between insolation and speleothem 18 o p in southern china reflects the variations of hydrologic processes over the indian monsoon region on millennial and orbital timescales the 18 o p in the drier part north of 30 n of china on the other hand has consistently negative correlations with local precipitation and may capture local hydrologic processes related to changes in the extent of the hadley circulation

lateglacial and holocene climate disturbance and permafrost peatland dynamics on the seward peninsula western alaska abstract northern peatlands have accumulated large carbon c stocks acting as a long term atmospheric c sink since the last deglaciation how these c rich ecosystems will respond to future climate change however is still poorly understood furthermore many northern peatlands exist in regions underlain by permafrost adding to the challenge of projecting c balance under changing climate and permafrost dynamics in this study we used a paleoecological approach to examine the effect of past climates and local disturbances on vegetation and c accumulation at a peatland complex on the southern seward peninsula alaska over the past 15 ka 1 ka 1000 cal yr bp we analyzed two cores about 30 m apart nl10 1 from a permafrost peat plateau and nl10 2 from an adjacent thermokarst collapse scar bog for peat organic matter om c accumulation rates macrofossil pollen and grain size analysis a wet rich fen occurred during the initial stages of peatland development at the thermokarst site nl10 2 the presence of tree pollen from picea spp and larix laricinia at 13 5 12 1 ka indicates a warm regional climate corresponding with the well documented bolling allerod warm period a cold and dry climate interval at 12 1 11 1 ka is indicated by the disappearance of tree pollen and increase in poaceae pollen and an increase in woody material likely representing a local expression of the younger dryas yd event following the yd the warm holocene thermal maximum htm is characterized by the presence of populus pollen while the presence of sphagnum spp and increased c accumulation rates suggest high peatland productivity under a warm climate toward the end of the htm and throughout the mid holocene a wet climate induced several major flooding disturbance events at 10 ka 8 1 ka 6 ka 5 4 ka and 4 7 ka as evidenced by decreases in om and increases in coarse sand abundance and aquatic fossils algae chara and water fleas daphnia the initial peatland at permafrost site nl10 1 is characterized by rapid c accumulation 66 g c m 2 yr 1 high om content and a peak in sphagnum spp at 5 8 4 6 ka suggesting the lack of permafrost a transition to extremely low c accumulation rates of 6 3 g c m 2 yr 1 after 4 5 ka at this site suggests the onset of permafrost aggradation likely in response to neoglacial climate cooling as documented across the circum arctic region a similar decrease in c accumulation rates also occurred at non permafrost site nl10 2 time weighted c accumulation rates are 21 8 g c m 2 yr 1 for core nl10 1 during the last 6 5 ka and 14 8 g c m 2 yr 1 for core nl10 2 during the last 15 ka evidence from peat core analysis and historical aerial photographs shows an abrupt increase in sphagnum spp and decrease in area of thermokarst lakes over the last century suggesting major changes in hydrology and ecosystem structure likely due to recent climate warming our results show that the thermokarst permafrost complex was much more dynamic with high c accumulation rates under warmer climates in the past while permafrost was stabilized and c accumulation slowed down following the neoglacial cooling in the late holocene furthermore permafrost presence at local scales is controlled by both regional climate and site specific factors highlighting the challenge in projecting responses of permafrost peatlands and their c dynamics to future climate change

a geochemical record of the link between chemical weathering and the east asian summer monsoon during the late holocene preserved in lacustrine sediments from poyang lake central china abstract this paper presents relatively high resolution geochemical records spanning the past 4000 cal yr bp obtained from the lacustrine sediments of poyang lake in central china the variations in the intensity of the east asian summer monsoon easm are traced using the k na ti na al k kaolinite illite and clay feldspar ratios together with the chemical index of alteration cia as indicators of chemical weathering during the last 4000 years the proxy records of chemical weathering from poyang lake exhibit an overall enhanced trend consistent with regional hydrological changes in previous independent records further comparisons and analyses demonstrate that regional moisture variations in central china is inversely correlated with the easm intensity with weak easm generating high precipitation in central china our data reveal three intervals of dramatically dry climatic conditions i e ca 4000 3200 cal yr bp ca 2800 2400 cal yr bp and ca 500 200 cal yr bp a period of weak chemical weathering related to cold and dry climatic conditions occurred during the little ice age lia whereas more intense chemical weathering reflecting warm and humid climatic conditions was recorded during the medieval warm period mwp besides an intensification of chemical weathering in poyang lake during the late holocene agrees well with strong enso activity suggesting that moisture variations in central china may be predominantly driven by enso variability

chinese stalagmite δ 18 o controlled by changes in the indian monsoon during a simulated heinrich event carbonate cave deposits in india and china are assumed to record the intensity of monsoon precipitation because the 18 o of the carbonate tracks the isotopic signature of precipitation these records show spatially coherent variability throughout the last ice age and suggest that monsoon strength was altered during the millennial scale climate variations known as dansgaard oeschger events and during the heinrich cooling events here we use a numerical climate model with an embedded oxygen isotope model to assess what caused the shifts in the oxygen isotope signature of precipitation during a climate perturbation designed to mimic a heinrich event our simulations show that a sudden increase in north atlantic sea ice extent during the last glacial period leads to cooling in the northern hemisphere reduced precipitation over the indian basin and weakening of the indian monsoon the precipitation is isotopically heavier over india and the water vapour exported to china is isotopically enriched our model broadly reproduces the enrichment of 18 o over northern india and east asia evident in speleothem records during heinrich events we therefore conclude that changes in the 18 o of cave carbonates associated with heinrich events reflect changes in the intensity of indian rather than east asian monsoon precipitation