the evolution of mun river in southeast asia and its relationship with the environmental changes in the late middle pleistocene based on sedimentologic and palynological evidences abstract the mun river is located in the khorat plateau of mainland southeast asia the watershed covers more than one third of this area however how the ancient river developed is still not so clear in this study a sandpit along the ancient river terrace at bam som tha chang subdistrict chaloem phra kiat district nakhon ratchasima province thailand is investigated with respect to the stratigraphy and sedimentology the physical features of the sediment particle size sphericity and sorted level at different depths are analyzed and described the layers composing the stratigraphic profile are classified based on the sedimentary profiles twenty two sampling layers classified into 3 members are recognized over 14 m depth three distinct river development cycles along the vertical section are identified along the vertical section the stratigraphic stages correspond to the sedimentary members are suggested with the substances fining upwards generally the stage at the bottom is shallow lake or flood plain deposit the middle section represents a stage which is channel river deposit and the upper section represents a stage which is dry land to aeolian deposit pollen records match well with fluvial development the ancient river dynamics reconstruction is an approach to analysis the palaeoenvironment and will provide more information

development of vegetation and continental aridity in northwestern africa during the late pliocene the pollen record of odp site 658 abstract a 200 m long marine pollen record from odp site 658 21 n 19 w reveals cyclic fluctuations in vegetation and continental climate in northwestern africa from 3 7 to 1 7 ma these cycles parallel oxygen isotope stages prior to 3 5 ma the distribution of tropical forests and mangrove swamps reached cape blanc 5 n of the present distribution between 3 5 and 2 6 ma forests occurred at this latitude during irregular intervals and nearly disappeared afterwards likewise a saharan paleoriver flowed continuously until isotope stage 134 3 35 ma when river discharge ceased wind transport of pollen grains prevailed over fluvial transport pollen indicators of trade winds gradually increased between 3 3 and 2 5 ma a strong aridification of the climate of northwestern africa occurred during isotope stage 130 3 26 ma afterwards humid conditions reestablished followed by another aridification around 2 7 ma repetitive latitudinal shifts of vegetation zones ranging from wooded savanna to desert flora dominated for the first time between between 2 6 and 2 4 ma as a response to the glacial stages 104 100 and 98 although climatic conditions recorded in the pliocene were not as dry as those of the middle and late pleistocene latitudinal vegetation shifts near the end of the pliocene resembled those of the interglacial glacial cycles of the brunhes chron

human adaptation to mid to late holocene climate change in northeast thailand this article integrates palaeoenvironmental and archaeological sequences covering the mid to late holocene in northeast thailand the former reveal the fluctuating intensity of the asian summer mo

a limited area model of the gulf stream design initial experiments and model data intercomparison abstract a primitive equation n layer eddy resolving creation model has been applied to the gulf stream system from cape hatteras to cast of the grand banks 78 45 w 30 48 n within the limitations of the model realistic coastlines bottom topography and forcing functions have been used a two layer version of the model was driven by observed mean climatological wind forcing and mass transport prescribed at inflow outflow was determined by a radiation boundary condition and an integral constraint on the mass field in each layer specification of a deep western boundary current dwbc was included in some model runs six numerical experiments from a series of over fifty integrated to statistical equilibrium were selected for detailed description and intercomparison with observations the basic case consisted of a flat bottom regime driven by wind forcing only realistic inflow transport in the upper layer was then prescribed and two different outflow specifications at the eastern boundary were s

applications of organic geochemistry to paleolimnological reconstructions a summary of examples from the laurentian great lakes the organic matter content of lake sediments contains information that helps to reconstruct past environmental conditions evaluate histories of climate change and assess impacts of humans on local ecosystems the elemental isotopic and molecular compositions of organic matter buried in sediment provide evidence of the biota that have lived in a lake and its catchment area and they serve as proxies of organic matter delivery and accumulation sedimentary records from the north american great lakes provide examples of applications of organic geochemistry to paleolimnological reconstructions the records of these lakes date from retreat of the laurentide ice sheet around 12 ka include the mid holocene hypsithermal and show consequences of recent human changes low corg ntotal ratios indicate that most of the sediment organic matter in the great lakes is from algal production yet changes in biomarker molecule compositions also show that varying amounts of land plant organic matter have been delivered to the lakes elevated algal productivity that accompanies nutrient enrichments of lake waters is recorded as excursions to less negative 13c values in the organic matter of sediments that were deposited in the 1960s and 1970s increased organic carbon mass accumulation rates mirror the isotopic excursions in most parts of the great lakes accumulations of petroleum residues and pyrogenic polycyclic aromatic hydrocarbons in sediments identify fluvial and eolian delivery of organic matter components to different parts of the great lakes emerging applications of multiple and novel organic geochemical proxies to paleolimnological reconstructions are promising yet some potentially important measurements remain underutilized

late miocene to pliocene palaeogeography of the paratethys and its relation to the mediterranean abstract the palaeogeographic evolution of the paratethyan and mediterranean realms are reconstructed with three maps ranging from the late miocene to the middle late pliocene the maps are based on the facial analysis of selected deposits clastic input slope slide process analyses as well as biogeographic data of the planktic benthic and terrestrial biota characteristic fossil assemblages are used for palaeobathymetric and palaeohydrologic interpretations restoration of palaeogeographic connections the palaeogeographic reconstructions are palinspastically restored after dercourt j ricou l e vrielynck b eds 1993 atlas tethys palaeoenvironmental maps gauthier villars paris pp 1 307 14 maps the paleogeographic atlas of northern eurasia 1997 inst tectonics lithospheric plates moscow 26 maps with modifications maps have been prepared for the terminal tortonian early messinian late pannonian early maeotian late messinian pontian salinity crisis time and piacenzian gelasian akchagilian they illustrate the neogene palaeogeographic evolution during and after the attic orogenesis though the emerging mountain system of the alpine foldbelt increasingly separated the paratethys from the mediterranean tethys paratethys connections remained extant and sufficiently effective for limited communication between both basins they governed many features of the cyclic depositional history and biogeographic evolution of the eastern paratethys

coordinated hydrological regimes in the indo pacific region during the past two millennia instrumental data suggest that major shifts in tropical pacific atmospheric dynamics and hydrology have occurred within the past century potentially in response to anthropogenic warming to better understand these trends we use the hydrogen isotopic ratios of terrestrial higher plant leaf waxes delta d wax in marine sediments from southwest sulawesi indonesia to compile a detailed reconstruction of central indo pacific warm pool ipwp hydrologic variability spanning most of the last two millennia our paleodata are highly correlated with a monsoon reconstruction from southeast asia indicating that intervals of strong east asian summer monsoon easm activity are associated with a weaker indonesian monsoon im furthermore the centennial scale oscillations in our data follow known changes in northern hemisphere climate e g the little ice age and medieval warm period implying a dynamic link between northern hemisphere temperatures and ipwp hydrology the inverse relationship between the easm and im suggests that migrations of the intertropical convergence zone and associated changes in monsoon strength caused synoptic hydrologic shifts in the ipwp throughout most of the past two millennia

apparent changes in the climatic state of the deep north atlantic ocean determination of any long term changes in the large scale characteristics of the deep ocean circulation would be an important clue in understanding the climatic interactions of the ocean and atmosphere in the summer of 1981 the rv atlantis ii reoccupied two transatlantic sections at nominal latitudes of 24 30 n and 36 16 n with a conductivity temperature depth instrument ctd one purpose of the work was to make a comparison with previous surveys conducted during the international geophysical year igy 1 when sections were obtained in october 1957 and april may 1959 we report here that significant warming occurred in an ocean wide band from 700 m to 3 000 m with a maximum temperature difference of 0 2 c these changes are sufficient to expand the water column by several centimetres the historical temperature salinity curve was apparently unchanged interannual changes in local water mass characteristics have been proposed previously2 3 perhaps it would be most surprising if no changes were seen to occur what remains obscure is the significance of these changes and the extent to which they represent long term climate trends or merely the minor and random fluctuations to be expected in any complex fluid system

late quaternary palynology in marine sediments a synthesis of the understanding of pollen distribution patterns in the nw african setting abstract after a review of the first steps in marine palynology we show that the understanding of the northwest african setting is crucial to evaluate the potential of marine palynological studies elsewhere we studied distribution patterns of pollen grains in recent marine sediments off nw africa and were able to clearly relate patterns to modern pollen source areas vegetation belts and operating transport systems wind belts and ocean currents in particular patterns of quercus artemisia chenopodiaceae amaranthaceae ephedra gramineae and wet forest trees are very indicative of the position of the vegetation belts on the adjacent continent aeolian pollen transport is carried out by the northeast trade winds and the african easterly jet aej in the rain forest belt transport of pollen and fern spores also occurs by rivers a detailed comparison between recent pollen rain samples from terrestrial and marine sites between 21 and 12 n showed that the latitudinal range of vegetation belts is clearly reflected in the pollen samples of both environments a migration of the southern border of the sahara is reflected by the changing ratio between chenopodiaceae amaranthaceae pollen from the desert and gramineae pollen from the savannah belt distribution patterns of pollen for 9000 and 18 000 14 c yr bp last glacial maximum time slices based on pollen records from eleven marine cores between portugal and the gulf of guinea show significant latitudinal migrations of vegetation belts but a stable position of the main wind trajectories the aej had a stable position around 21 n the belt with trade winds had a stable position from morocco southwards changing vigour of the trade winds is clearly reflected by the patterns of isopollen contours and by changes in pollen influx records

origin of dolomites in the cretaceous maha sarakham evaporites of the khorat plateau northeast thailand abstract the khorat plateau of northeast thailand and laos was an area of widespread deposition of evaporites and siliciclastics maha sarakham formation during the cretaceous and three types of dolomites are associated with this formation 1 limpid dolomite 2 coarse subhedral and euhedral dolomite and 3 saddle dolomite limpid dolomite is present as isolated crystals in recrystallized clear halite beds while the other two types are only present as authigenic clusters and individual large crystals within the widespread basal anhydrite unit bau 1 1 m which defines the lowest member of the formation the 18 o pdb isotopic values and the 87 sr 86 sr ratios of the limpid dolomite are within the range of cretaceous seawater petrography and carbon and oxygen isotopes suggest that limpid dolomite was formed under shallow burial during times of freshening in a mostly marine fed aggrading halite salina dolomite formation was possibly influenced by bacterial metabolism the coarse crystalline and saddle dolomite types float within a matrix of coarse recrystallized anhydrite in the basal anhydrite the 18 o isotopic values of the coarse subhedral and euhedral dolomite types are more negative than the limpid dolomite and the 87 sr 86 sr ratios are more radiogenic than typical marine dolomite of the cretaceous saddle dolomite has even more negative 18 o isotopic values than the coarse euhedral dolomite the 87 sr 86 sr ratios of the saddle dolomite are also radiogenic the isotopic and petrographic data indicate that the dolomites in the basal anhydrite unit are late and authigenic but do not appear to replace a precursor carbonate rather they appear to have precipitated within the deep burial environment along a 1 2 m thick subsurface mixing interface between warm upwelling basinal brines and dense highly saline brines created by dissolving the underside of the overlying impervious halite bed the upwelling basinal waters presumably rose through the underlying siliciclastics of the khorat group and then moved laterally along the base of the maha sarakham salt the result of this inferred hydrologic process apparently is an accumulation of burial dolomite and recrystallized residual anhydrite in a petrographically complex unit that ultimately appear to be a solution residue the basal anhydrite unit

interlaboratory fission track dating of volcanic ash levels from eastern paratethys a mediterranean paratethys correlation abstract the age of glass shard levels interlayered in sarmatian deposits from the southwestern russia are measured with the fission track method the results obtained from different laboratories moscow pisa campinas using their specific techniques are in good agreement so proving a good interlaboratory agreement the results suggest a new correlation between paratethys and the mediterranean area in better agreement with the global climatic trend of this period according to the proposed scheme the chersonian maeotian boundary 9 9 5 ma is correlatable with the vallesian turolian boundary continental mediterranean stratigraphy and with the middle tortonian marine mediterranean stratigraphy the bessarabian time span between 12 5 and 11 ma is correlatable with the lower vallesian and with the upper serravallian the beginning of the volhynian that is the beginning of the sarmatian 14 13 5 ma is correlatable with the upper astaracian and with the lower boundary of the serravallian due to the large experimental errors of the ages and possible systematic errors the proposed stratigraphic sequence may be regarded as a working hypothesis to be confirmed by further data

dynamic impact of oscillating sources on the north atlantic deep circulation a process study in this process study the dynamic effects of fluctuating deep water sources on the deep circulation of the north atlantic are examined by means of a 1 layer model the model is used with a realistic topography of the atlantic ocean between 65 n and 25 s and has an open southern boundary according to observations the northern inflow of deep water is subject to variability on timescales between days and decades the same holds for the deep western boundary current dwbc which acts as a link between the deep water inflow and the interior circulation the timescales of the observed variability motivate the forcing functions used in the model they determine the nature of the models response the flow response relative to the local mean flow can be considerably larger than the original perturbation at the source normalizing the perturbed flow with the local steady state flow leads to the identification of sensitive areas their location and shape are determined by the difference between the characteristic travel paths of the perturbation and the streamlines of the steady state circulation in the eastern equatorial atlantic a forcing with periods between 1 and 3 months gives rise to larger flow perturbations than a forcing with periods between half a year and 1 year forcing with the latter periods leads to a stronger response in the western equatorial atlantic and in the interior ocean changes in the direction of the deep equatorial flow are driven by low frequency oscillations of the dwbc in the model this is consistent with observations in the area perturbations radiate into the interior away from the eastern boundary as long rossby waves as this propagation is along geostrophic contours consequently large parts of the abyssal interior are inaccessible the results support the notion that the area where the dwbc encounters the equator is not only a key region for the slow interhemispheric exchange of heat and tracers but also for the transport of information by fast internal waves along the equator

quaternary fauna and flora of the southern urals region bashkortostan republic from the 1960s a considerable amount of data on mammals molluscs and vegetation from quaternary deposits of the southern urals region has been produced the age of key stratigraphic localities was established by using different geological and palaeontological evidence palaeomagnetic and absolute dating the flora and fauna history is summarized for the southern part of the urals the result is that the history of fossil organic forms and plant associations could be traced characteristic complexes could be recognized and a curve with changes in the vegetation could be constructed results of biostratigraphical investigations are given in the review

eastward flow through the mid atlantic ridge at 11 n and its influence on the abyss of the eastern basin abstract the dilute antarctic bottom water of the north atlantic eastern trough is supplied from the western trough through fractures in the mid atlantic ridge in particular the influence on eastern trough property distributions of flow through the romanche and vema fracture zones near the equator and 11 n respectively has been noted previously here new observations are reported that document the abyssal circulation of the northeastern atlantic basins gambia abyssal plain south canary basin and north canary basin in particular the dominance of vema influence the absence of romanche influence and the existence of a system of deep western boundary currents and estimated transport deep isopycnals slope steeply across the vema s eastern end near 39 w corresponding to a geostrophic transport through the vema of 2 1 to 2 3 106 m3s 1 colder than 2 0 c this is half or more of the estimated bottom water that flows north across the equator into the subtropical western north atlantic this transp

effects of a concave bottom geometry on the upwelling driven circulation in an abyssal ocean basin abstract bottom water circulation in a bowl shaped or concave abyssal basin driven by upwelling is investigated using a simple numerical model in a basin wholly contained in one hemisphere the concave bottom geometry introduces a strong topographic beta effect around the rim of the basin also the character of the circulation is fundamentally altered from the circulation pattern in a flat bottom basin where a sluggish northeastward interior flow is compensated by a strong western boundary current to a basinwide cyclonic recirculation of a substantially greater strength without western intensification in contrast circulation in a similar basin that straddles the equator fails to show a significant difference from the circulation in a flat bottom basin this dichotomy between equatorial and midlatitude basins can be understood in terms of the geometry of the underlying geostrophic contours

hydroclimatic shifts in northeast thailand during the last two millennia the record of lake pa kho the southeast asian mainland is located in the central path of the asian summer monsoon a region where paleoclimatic data are still sparse here we present a multi proxy toc c n delta c 13 bio

lake kumphawapi revisited the complex climatic and environmental record of a tropical wetland in ne thailand kumphawapi which is thailand s largest natural freshwater lake contains a 10 000 year long climatic and environmental archive new data sets stratigraphy chronology hydrogen isotopes plant macrofossil and charcoal records for two sedimentary sequences are here combined with earlier multi proxy studies to provide a comprehensive reconstruction of past climatic and environmental changes for northeast thailand gradually higher moisture availability due to a strengthening of the summer monsoon led to the formation of a large shallow lake in the kumphawapi basin between 10 700 and c 7000 cal bp the marked increase in moisture availability and lower evaporation between c 7000 and 6400 cal bp favoured the growth and expansion of vegetation in and around the shallow lake the increase in biomass led to gradual overgrowing and infilling to an apparent lake level lowering and to the development of a wetland multiple hiatuses are apparent in all investigated sequences between c 6500 and 1400 cal b

interpentadal variability of temperature and salinity in the deep north atlantic 1970 1974 versus 1955 1959 historical hydrographic observations have been composited and objectively analyzed for the north atlantic ocean for two pentads 1955 59 and 1970 74 for the purpose of studying the temporal variability of the thermohaline structure of the deep north atlantic ocean statistically significant differences between the two pentads are found in the deep ocean at 1750 m depth most of the north atlantic increased in temperature approximately 0 1 c and salinity 0 025 from the earlier to the later period an exception to this was a region in the eastern atlantic between 33 n and 50 n where a cooling 0 1 c and freshening 0 025 occurred changes at other depths as evidenced by difference fields of temperature along 24 5 n and 36 5 n are in agreement with differences found by roemmich and wunsch 1984 who described changes at these latitudes between sections taken in the late 1950 s and sections taken in 1981

cold outflow from the faroe bank channel abstract the exchange of water between the norwegian sea and the north atlantic around the faroe islands was investigated in 1987 and 1988 combining ctd data with shipborne acoustic doppler current profiler adcp measurements tests were devised to assess the accuracy of the adcp measurements and the results are described it is found that estimating a reference velocity for geostrophic measurements is limited by the presence of tides of order 10 cm s 1 in the outflow of cold water from the faroe bank channel which reaches speeds of nearly 1 m s 1 the error is acceptably small but strong time dependent components are revealed the discharge of cold water is traced 75 km beyond the sill of this channel and changes in potential temperature salinity and potential vorticity on an isopycnal surface are attributed to intense mixing an effective diffusivity near 100 cm2 s 1 is derived and k h instability demonstrated as a plausible source of the turbulent energy six current meter moorings were deployed from

the huguang maar lake a high resolution record of palaeoenvironmental and palaeoclimatic changes over the last 78 000 years from south china abstract a series of seven piston cores from the huguang maar lake situated near the south china sea coastline provides insight into regional palaeoenvironmental and palaeoclimatic changes in southern china over the last 78 000 years the data set comprises a high resolution record of magnetic susceptibility dry density and water content total organic carbon and inorganic carbon total nitrogen biogenic silica bsio2 and palynological results the time scale was developed by ams 14c dating of 17 terrestrial plant macro fossils during the last glacial the huguang record is characterised by an alternation of more temperate and humid periods from 78 to 58 and 48 to 40 5 ka bp and periods with predominance of grassland vegetation and possibly lowered lake level from 58 to 48 and ca 40 5 to 15 ka bp the huguang data have been compared to regional marine and terrestrial records in order to discuss variability of the south east asian monsoon system for most of the last glacial period the huguang proxies do not exhibit marked millennial scale variability as known from some long se asian and many north atlantic records this picture changes at about 15 cal ka bp when the huguang and greenland records appear to correlate well a short climatic reversal which is assumed to reflect a younger dryas type event is well recorded in the huguang record during the holocene the huguang multi proxy data show a much higher variability than during the last glacial stage probably reflecting at least for the early mid holocene fluctuations in monsoon activity however the last 4000 years of the sediment record are clearly influenced by enhanced human activity and thus difficult to interpret in terms of palaeoclimate change

biomarker hydrogen isotope composition δd as proxy for holocene hydroclimatic change and seismic activity in sw peloponnese greece we present a 6000 year long record tracing hydroclimate changes in sw greece based on hydrogen isotope composition of aquatic plant derived n c 23 alkanes d c23 in a sediment core from the messe

vegetation succession and climate change across the plio pleistocene transition in eastern azerbaijan central eurasia 2 77 2 45 ma abstract the plio pleistocene transition marked a key moment in global climate history characterised by the onset of major glaciations in the northern hemisphere the palaeoenvironmental history of the plio pleistocene transition is not well known for the caspian sea region despite its importance for global climate dynamics here we present an independently 40ar 39ar dated high resolution terrestrial palynological record spanning the plio pleistocene boundary based on a lacustrine marine sedimentary sequence from eastern azerbaijan despite complex pollen transport pathways and the proximity of closely stacked mountain vegetation belts in the greater and lesser caucasus the record shows that regional vegetation responded to milankovitch forced glacial interglacial cycles tentatively correlated with global climatic records spanning mis g8 to 98 2 77 2 45 ma the persistence of mesophilous forests during glacial times indicates that some settings in the south caspian basin acted as glacial refugia and that vegetation response to glaciations was muted by increased moisture availability linked to caspian transgression the palynological record shows a relationship with global 18o stacks and specifically to the obliquity record we anticipate that precise correlation with the global climatostratigraphic timescale will allow better understanding of the nature and timing of important transgressive events in the caspian sea and their relevance on a global scale

final closure of panama and the onset of northern hemisphere glaciation abstract the greenland ice sheet is accepted as a key factor controlling the quaternary glacial scenario however the origin and mechanisms of major arctic glaciation starting at 3 15 ma and culminating at 2 74 ma are still controversial for this phase of intense cooling ravelo et al 1 a c ravelo d h andreasen m lyle a o lyle m w wara regional climate shifts caused by gradual global cooling in the pliocene epoch nature 429 2004 263 267 proposed a complex gradual forcing mechanism in contrast our new submillennial scale paleoceanographic records from the pliocene north atlantic suggest a far more precise timing and forcing for the initiation of northern hemisphere glaciation nhg since it was linked to a 2 3 c surface water warming during warm stages from 2 95 to 2 82 ma these records support previous models g h haug r tiedemann effect of the formation of the isthmus of panama on atlantic ocean thermohaline circulation nature 393 1998 673 676 2 claiming that the final closure of the panama isthmus 3 0 2 5 ma j groeneveld s steph r tiedemann d nurnberg d garbe schonberg the final closure of the central american seaway geology in prep 3 induced an increased poleward salt and heat transport associated strengthening of north atlantic thermohaline circulation and in turn an intensified moisture supply to northern high latitudes resulted in the build up of nhg finally culminating in the great irreversible climate crash at marine isotope stage g6 2 74 ma in summary there was a two step threshold mechanism that marked the onset of nhg with glacial to interglacial cycles quasi persistent until today

distribution and circulation of labrador sea water abstract labrador sea water is the final product of the cyclonic circulation of subpolar mode water in the open northern north atlantic mccartney and talley 1982 the temperature and salinity of the convectively formed subpolar mode water decrease from 14 7 c 36 08 to 3 4 c 34 88 on account of the cumulative effects of excess precipitation and cooling the coldest mode water is labrador sea water which spreads at mid depths and is found throughout the north atlantic ocean north of 40 n and along its western boundary to 18 n a vertical minimum in potential vorticity is used as the primary tracer for labrador sea water labrador sea water is advected in three main directions out of the labrador sea 1 northeastward into the irminger sea 2 southeastward across the atlantic beneath the north atlantic current and 3 southward past newfoundland with the labrador current and thence westward into the slope water region crossing under the gulf stream off cape hatteras the labrador sea water core is

environmental control of pollen grain distribution patterns in the gulf of guinea and offshore nw africa the areas of marine pollen deposition are related to the pollen source areas by aeolian and fluvial transport regimes whereas wind transport is much more important than river transport pollen distribution patterns ofpinus artemisia chenopodiaceae amaranthaceae and asteraceae tubuliflorae trace atmospheric transport by the northeast trades pollen transport by the african easterly jet is reflected in the pollen distribution patterns of chenopodiaceae amaranthaceae asteraceae tubuliflorae andmitracarpus grass pollen distribution registers the latitudinal extension of sahel savannas and dry open forests marine pollen distribution patterns of combretaceae melastomataceae alchornea andelaeis reflect the extension of wooded grasslands and transitional forests pollen from the guinean congolian zambezian forest and from the sudanian guinean vegetation zones mark the northernmost extension of the tropical rain forest rhizophora pollen in marine sediments traces the distribution of mangrove swamps only near the continent pollen ofrhizophora mitracarpus chenopodiaceae amaranthaceae and pollen from the sudanian and guinean vegetation zones are transported by the upwelling under current and the equatorial under current where those currents act as bottom currents the distribution of pollen in marine sediments reflecting the position of major climatic zones desert dry tropics humid tropics can be used in tracing climatic changes in the past

summer monsoon precipitation variations in central china over the past 750 years derived from a high resolution absolute dated stalagmite abstract a 2 3 year resolution record of stalagmite oxygen isotope variations from the south flank of the qinling mountains central china has revealed the asian summer monsoon asm precipitation variations in the investigated area over the past 750 years the summer monsoon precipitation gradually increased since 1249 ad reaching its highest values in the period 1535 1685 ad and then decreased with substantial decadal to centennial scale fluctuations the monsoon precipitation increased again between 1920 and 1970 ad three intervals of high monsoon precipitation were identified 1535 1685 ad 1755 1835 ad and 1920 1970 ad three intervals of low precipitation were inferred in 1249 1325 ad 1390 1420 ad and 1890 1915 ad the 18 o composition and lithological features of the stalagmite coincidently indicate a wetter climate during the little ice age lia which is also confirmed by climate records from chinese historical documents within this area a comparison with other high resolution speleothem records indicates regional differences in monsoon precipitation variability from the south to the north of central china in the last 750 years on decadal to centennial scale power spectrum analysis of the 18 o record shows significant 117 8 34 6 14 10 3 and 6 year periodicities these periodicities are widely observed in the climate records from asm controlled areas of china and are consistent with the gleissburg periodicity br ckner periodicity sunspot periodicity of solar activity and el nino southern oscillation enso periodicity these correlations suggest that both solar activity and enso periodicity may have had important influences on asm precipitation in china over the past 750 years

evidence for barotropic wave radiation from the gulf stream abstract highly energetic velocity fluctuations associated with topographic rossby waves are frequently observed over the continental slope and rise off the united states and canadian east coast it has been suggested that the energy source for these waves could be eastward propagating gulf stream meanders which can couple to the westward propagating rossby waves if the meander shape is time dependent in this study a historical archive of all available current meter data from the western north atlantic has been examined for evidence of energy radiation from the gulf stream via barotropic topographic rossby waves maps of abyssal eddy kinetic energy eke and reynolds stress were constructed for four frequency bands including motions with periods between 256 and 7 8 days to examine distributions of these quantities over the largest possible geographical area maximum eddy kinetic energy is observed along the mean axis of the gulf stream at low frequencies 50 250 days but this maximum shifts north a

the holocene history and development of the tonle sap cambodia abstract the tonle sap the great lake of central cambodia is the central component of wetland ecosystems in the lower mekong river basin and is of enormous conservation value the lake s unusual hydraulic relationship with the mekong river and its consequent sensitivity to monsoon variability makes the tonle sap sensitive to climate change exploring the dynamics and development of this system under different climate regimes of the past offers a perspective on possible future impacts which is critical for sound management biostratigraphic and sedimentological data derived from cores of lake sediment indicate that during the period 7000 to ca 5500 14 c years before present the lake was less variable than present in terms of depth during the annual cycle of flood and may have been strongly influenced by saline tidal waters associated with higher than present seas levels as regional environments became drier and more seasonal in the late holocene more sediment was re suspended during the increasingly marked dry season lake level minimum lowering the effective sediment accumulation rate contrary to current interpretations of the history of the lake and associated wetland ecosystems the data presented here imply that regional hydraulic connections between the lake and the mekong river existed from at least the early holocene

sea level induced variations in clay mineral composition in the southwestern south china sea over the past 17 000 yr variations in clay mineral composition of sediment cores from the margin and continental slope of the sunda shelf southern south china sea se asia covering the past 17 000 yr reflect changing influences of sediment sources together with clay mineral partitioning processes in shallow waters we identify the deglacial sea level rise as the principal factor driving these changes during the late glacial high values of kaolinite are interpreted to reflect a higher contribution of clays from soils that have formed on the exposed sunda shelf and in the southern archipelagos of indonesia at this time core sites were located in close proximity to the mouths of the sunda shelf palaeo drainage systems on the emerged shelf sundaland the progressive landward displacement of the coastline and breakdown of these vast drainage systems during deglaciation led to a decrease in influence of the kaolinite rich southern sources when the coastline had retreated closely to its present day position in mid holocene times the former dominance of southern sources was replaced by a stronger influence of illite rich sources e g borneo the overriding control of sea level changes on the clay mineral distribution patterns precludes a definite climatic interpretation of clay mineral data in terms of climatic monsoonal changes in such highly dynamic sedimentary environment

contrasting pliocene fluvial depositional systems within the rapidly subsiding south caspian basin a case study of the palaeo volga and palaeo kura river systems in the surakhany suite upper productive series onshore azerbaijan abstract the south caspian basin contains major hydrocarbon reservoirs within the largely early pliocene productive series this paper describes and contrasts outcrops of the uppermost 500 m of the series the surakhany suite deposited by two of the main fluvial systems that supplied the azeri margin of the basin sedimentary facies and for the first time from the productive series palynological analyses document fluvial channel belt complexes sheetflood overbank and flood plain to flood plain lake environments the productive series on the apsheron peninsula azerbaijan was supplied predominantly from the north by the palaeo volga river system it displays an overall fining upward trend such that the surakhany suite at lokbatan is dominated by mudstone siltstone and coarser grained sediments make up 28 of the section channel bodies are on average 1 5 m thick and form 13 of the succession in the sub surface of the apsheron peninsula ratty wireline log responses also indicate that siltstone and sandstone bodies are predominantly thin bedded with sp derived net to gross sand ratios of 0 35 0 40 the succession in the kura basin was sourced predominantly from the west by the palaeo kura river system it displays a coarsening upward trend such that in the middle and upper surakhany suite at babazanan siltstone and coarser sediments make up 52 of the section it is characterised by numerous stacked and laterally continuous channel sandstone bodies that are on average 5 8 m thick and comprise 42 of the outcrop in the sub surface of the kura basin wireline log responses of the surakhany suite have a blocky character and indicate sp derived net to gross sand ratios of 0 26 0 38 these values are similar to calculated sandstone volumes at outcrop 44 the palynological data including multivariate analyses show that the main controls on palynomorph distribution are the degree of fluvial or lacustrine influence subaerial exposure and salinity despite their more lithic nature surakhany suite sandstones derived from the palaeo kura river system along the kurovdag babazanan neftchala trend have similar or better petrophysical properties than those derived from the palaeo volga river on the apsheron peninsula and its offshore continuation this is probably due to their coarser grain size this combined with their greater sandstone body thickness would suggest that the axis of the kura basin forms the most promising part of the azeri sector of the south caspian basin for exploration within the uppermost part of the productive series

environmental conditions framing the first evidence of modern humans at tam pa ling laos a stable isotope record from terrestrial gastropod carbonates abstract mainland southeast asia is a key region to interpret modern human migrations however due to a scarcity of terrestrial proxies environmental conditions are not well understood this study focuses on the tam pa ling cave site in northeast laos which contains the oldest evidence for modern humans in indochina dating back to mis 4 70 8 ka snail remains of camaena massiei found throughout the stratigraphic sequence contain a valuable oxygen and carbon isotope record of past local vegetation and humidity changes our data indicate that before the last glacial maximum lgm northeast laos was characterized by a humid climate and forested environments with the onset of the lgm a major climatic shift occurred inducing a sharp decrease in precipitation and a significant decline in woodland habitats in favor of the expansion to more open landscapes only during the holocene did forests return in northeast laos resembling present conditions the first homo sapiens arriving in indochina therefore encountered landscapes dominated by woodlands with a minor proportion of open habitats

persistent multidecadal power of the indian summer monsoon article i nfo the instrumental record of indian summer monsoon ism precipitation displays two complete manifesta tions of an inferred multidecadal cycle hitherto no precipitation sensitive proxy record from the indian subcontinent has had the necessary resolution and length to adequately assess whether this observed feature is an inherent aspect of the ism system on longer timescales here we present compelling evidence for persistence of this cycle using a millennial length ad 600 1550 and sub annually resolved speleothem oxygen isotope record 18 o from dandak cave in east central india the record displays a high degree of correlation with a speleothem based asian monsoon reconstruction from wanxiang cave in north central china on annual to decadal timescales showing theregional significanceof these findings theobserved period inourmonsoonreconstructionissimilartothatassociatedwiththegleissbergsolarcycleandmultidecadalsea surface temperature variability in the north atlantic amo both of which are often cited as the prominent pacemakers of ism variability on multidecadal timescales we document transient coherence between ism precipitation amount and solar variability that persists exclusively in the century prior to and during the medieval climate anomaly nominally ad 950 1300 the non stationary nature of the sfv monsoon relationship presented here may be evidence of the time varying influence of tropical ocean atmosphere dynamics on the solar monsoon link however it is not possible to show with significance that this period of coherenceisanythingmorethananartifactoftwotimeserieswithsimilarspectra wetherefore areinclinedto interpret our record as evidence of a minimal role of solar variability in driving persistent multidecadal variability of the ism multidecadal sst variability in the north atlantic remains as the likely alternative driver for persistence of this cycle regardless of the causative mechanism s the amplitude and regional signature of the observed cycle in ism precipitation highlight its societal importance with respect to forecasting ism precipitation on multidecadal timescales

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

tham lod rockshelter pang mapha district north western thailand evolution of the lithic assemblages during the late pleistocene abstract tham lod pang mapha district mae hong son province is one of the rockshelters in the limestone karst of north western thailand the site was excavated from 2002 to 2006 under the direction of one of us r s in the context of the highland archeological project the stratigraphical sequence of the site provided dates ranging from late pleistocene 35 ka tl to late holocene 3000 bp thousands of lithic and faunal remains occur throughout the sequence ceramics and metal items appear in the upper layer holocene noteworthy are the few human burials in the late pleistocene layers this paper presents the lithic material from area 2 sectors s20w10 and s21w10 unearthed from the stratigraphic layers 3 to 10 late pleistocene artefacts are mostly made in locally available grey sandstone which is overwhelming in all the layers the lithic assemblage includes a large proportion 2 3 of rock fragments brought to the site and artificially or thermally broken these are mostly small fragments as some of the artefacts are definitely considered as hoabinhian the detailed technological study of the lithic industry will help in understanding this techno cultural facies and in tracing how the stone artefacts were manufactured used maintained and finally discarded by the hunters gatherers analysis of the whole sequence in tham lod aims at reconstructing the technical evolution in the context of the late pleistocene climatic changes in this part of eurasia

oceanic wave dynamics and interdecadal variability in a climate system model western boundary disturbances detected in the first multicentury integration of the national center for atmospheric research climate system model are analyzed and the role they play in the model interdecadal variability is investigated the boundary signals propagate southwestward along the coast of north america at depth they reach the equator and propagate along the equator but with decreasing amplitude away from the western boundary their southwestward propagation is associated with the evolution of the western boundary current system the gulf stream system in the upper part of the water column and the deep western boundary current at depth from weaker than average to stronger than average conditions thus the boundary disturbances seem to play an important role in the model thermohaline circulation variability at interdecadal timescales they show similarities with the boundary waves found in ocean only models exhibiting interdecadal variability and their role in the model s response to changes in the rate of sinking appears to be in agreement with the theory of the spin up of the deep ocean circulation the main result of this study is that the similarities with ocean only results and theories support the idea that interdecadal timescales of variability originate from the ocean dynamics

palynology and micropalaeontology of the pliocene pleistocene transition in outcrop from the western caspian sea azerbaijan potential links with the mediterranean black sea and the arctic ocean abstract new palynological ostracod and foraminiferal data are presented from a long outcrop section in the jeirankechmez river valley azerbaijan near the western coast of the caspian sea the interval studied includes the upper part of the pliocene productive series and overlying plio pleistocene akchagylian akchagyl and apsheronian apsheron regional stages productive series sediments were deposited in a closed fluvio lacustrine basin isolated from any marine influence the onset of akchagyl deposition is marked by a lithological change associated with a significant flooding event that at its maximum extent reached the sea of azov and into present day iran kazakhstan turkmenistan and russia at the jeirankechmez locality the lowermost beds of the akchagyl contain predominantly freshwater assemblages with very minimal marine or brackish content showing that the onset of akchagyl deposition was not a marine induced event reworked mesozoic palynomorphs occur frequently in this lowermost interval including the reworked pollen taxa aquilapollenites triprojectus that were eroded from the north or north east significant marine influence is evident ca 30 m above the base of the akchagyl in the studied outcrop marked by the cassidulina beds which contain a distinct but low diversity assemblage of foraminifera that occurs widely and can be correlated in many parts of the greater caspian region dinoflagellate cysts dinocysts in the marine interval include frequent specimens very similar to algidasphaeridium capillatum matsuoka and bujak a species only previously recorded from the northern bering sea the combined evidence from these dinocysts and foraminifera suggests that a marine i e seaway connection existed briefly between the arctic ocean and the caspian sea at the very end of the pliocene re examination of core material from the adriatic sea shows that cassidulina reniforme norvang was present in the mediterranean during and shortly after the last glacial maximum the possibility that the end pliocene marine incursion came from the mediterranean via the black sea region to the caspian sea cannot be entirely ruled out but is considered unlikely biometric analyses are applied to obtain a better understanding of the palaeoenvironmental significance of the assemblages dominated by cassidulinids an interval 300 m thick is assigned to the apsheron regional stage on the basis of predominantly brackish ostracod and dinocyst associations the dinocysts are of peri paratethyan affinity and closely resemble species first described from miocene and pliocene sediments in the pannonian and dacic basins of eastern europe many similarities exist in the microplankton records dinocysts and acritarchs between the caspian sea the black sea and central paratethys

on the role of interior mixing and air sea fluxes in determining the stratification and circulation of the oceans abstract the problem of determining the eastern boundary basic stratification and the buoyancy driven circulation of the oceans is addressed a global integral constraint relating the interior stratification and the air sea heat fluxes is derived based on the condition that the total mass of water of given density is constant in a steady state ocean this constraint is then applied to two simple analytic models the first is a continuous nonlinear diffusive model of the lower mid depth and bottom circulation below the influence of the wind driven circulation it shows the tendency of the vertical density profile to look like an exponential profile in the presence of mixing the integral constraint is used to relate the stratification and circulation of the bottom and mid depth waters to the air sea heat fluxes at the surface where the deep densities outcrop the second model is a layered one of the wind driven circulation mid depth and bottom water the eastern boundary stratification of the model i

episode of strengthened summer monsoon climate of younger dryas age on the loess plateau of central china abstract the baxie loess section just east of the tibetan plateau contains evidence showing that the asian monsoon climate experienced an abrupt reversal near the end of the last glacial age rapid deposition of dust under cool dry full glacial conditions gave way to an interval of soil development and reduced dust influx attributed to a strengthening of the warm moist summer monsoon a subsequent abrupt increase in dust deposition a response to a weakening of the summer monsoon was later followed by renewed soil formation as summer monsoon circulation again intensified during the early holocene by one interpretation the thin upper loess is a manifestation of the european younger dryas oscillation however in this case the available 14c ages require either that 1 onset of loess deposition lagged the beginning of the younger dryas event in europe by as much as 2000 calibrated 14c years or 2 all the 14c ages are too young possibly due to contamination alternatively the late glacial paleosol the top of which is synchronous with the abrupt end of the late glacial 18o anomaly in the dye 3 greenland ice core records the younger dryas event such an interpretation is consistent with general circulation model simulations of younger dryas climate that show strong seasonality and a strengthened summer monsoon and with marine cores from the western pacific ocean that contain evidence of pronounced cooling of surface waters during younger dryas time

a simple model of abyssal circulation including effects of wind buoyancy and topography abstract we examine problems of steady abyssal circulation using an inviscid planetary geostrophic layered model the model includes an active wind driven upper layer and arbitrary topography forcing is in the form of specified interlayer mass fluxes from which we model global upwelling and geothermal heating the results considered in this study are appropriate to the shadow zone of a pacific sized moderately wind forced oceanic basin it is found that topographic effects global upwelling and geothermal heating may all control the abyssal circulation at least locally within realistic values of their parameter ranges suggesting that a better understanding of the geothermal and interior buoyancy flux fields is necessary for an understanding of abyssal circulation in the ocean the model reduces to a nonlinear extension of the one layer abyssal circulation model of stommel and arons generalized to include mass flux structure and topography and this limit is shown to be valid in an oceanic shadow zon

holocene sea levels and palaeoenvironments malay thai peninsula southeast asia sedimentological and palynological investigations of great songkhla lakes east coast of the malay thai peninsula southeast asia reveal sedimentary sequences rich in palynomorph assemblages dominated by pollen of mangroves and freshwater swamps compared with other regions in southeast asia the assemblages are of relatively low diversity geochronological data indicate that the great songkhla lakes record one of the earliest mangrove environments in southeast asia 8420 8190 cal yr bp which are subsequently replaced by a freshwater swamp at 7880 7680 cal yr bp owing to the decline of marine influence sea level observations from great songkhla lakes and other areas of the malay thai peninsula reveal an upward trend of holocene relative sea level from a minimum of 22 m at 9700 9250 cal yr bp to a mid holocene high stand of 4850 4450 cal yr bp which equates to a rise of c 5 5 mm yr the sea level fall from the high stand is steady at c 1 1 mm yr geophysical modelling shows that hydroisostasy

the geoarchaeology of the prehistoric ditched sites of the upper mae nam mun valley ne thailand iii late holocene vegetation history abstract the upper mae nam river mun valley of northeast thailand has been occupied at least since the bronze age but is notable for the rapid expansion of intense town based iron age settlement the area presently forms the seasonally arid core of mainland southeast asia and is presently dominated by increasingly saline soils low productivity rice cultivation and regrowth semi arid scrub however the archaeological evidence for this region indicates a highly productive natural environment within the last two millennia pollen sequences from the infill of iron age features provide the first palynological evidence for this part of northeast thailand detailing late holocene vegetational change the area around the sites was initially dominated by forest which then underwent two phases of the replacement by mosaics of grassland probable rice cultivation arboriculture and scrub prior to a subsequent phase of forest and woodland regeneration spatial patterning of the study area s palaeovegetation appears to have been complex while a general progress of landscape change is evident local compositional differences are also clear although the region s archaeological and especially geomorphological evidence suggests significant climatic change during this period the pollen record as in studies further north in the region for the same period appears to have been dominated by human influences of note are the effects of intensified human settlement and thus increased land and natural resource use at present this late holocene pollen sequence yields no evidence for a direct relationship with climatic change

bottom water circulation in the western north atlantic abstract antarctic bottom water flows into the western north atlantic across the equator shifting from the western side to the eastern side of the trough between the american continents and the mid atlantic ridge as it continues north this is puzzling because such large scale motion is thought to be controlled by dynamics that disallows an eastern boundary current previous explanations for the transposition involve a necessarily small scale density current that changes sides because of the change in sign of rotation across the equator or a topographic effect that changes the sign of the effective mean vorticity gradient and thus requires an eastern boundary current here an alternative explanation for the overall structure of bottom flow is given a source of mass to a thin bottom layer is assumed to upwell uniformly across its interface into a less dense layer at rest a simple formula for the magnitude of the upwelling and thickness of the layer is derived that depends on the source strength to th

late holocene sedimentary and environmental development of the northern mekong river delta vietnam abstract a sedimentological and palynological study of three sediment cores from the northern mekong river delta shows the regional sedimentary and environmental development since the mid holocene sea level highstand a sub to intertidal flat deposit of mid holocene age is recorded in the northernmost core shoreline deposits in all three cores show descending ages from n to s documenting 1 the early stages of the late holocene regression and 2 the subsequent delta progradation the delta plain successions vary from floodplain deposits with swamp like elements to natural levee sediments the uppermost sediments in all cores show human disturbance to varying degrees the most intense alteration is recorded in the northernmost core where the palynological signal together with a charcoal peak indicates the profound change of the environment during the modern land reclamation the sediments from at least one of the three presented cores do not show a true delta facies succession but rather estuary like features as also observed in records from southern cambodia this absence is probably due to lack of accommodation space during the initial phase of rapid delta progradation which impeded the development of true delta successions as shown in cores from the southern mekong river delta

evolution and variability of the asian monsoon system state of the art and outstanding issues the asian monsoon is comprised of the indian and east asian subsystems these two components are linked to one another in varying degrees by regions of strong sensible heating indo asian landmass and strong latent heat export the western pacific warm pool and the southern subtropical indian ocean variability within the indian and east asian subsystems interactions among them and the extent to which they interact with other climate phenomena e g enso are current topics of modern and paleoclimate research this work provides an overview of past and current paleomonsoon research on tectonic to interannual time scales with a primary focus on marine sediment records while past and current work has contributed greatly to our understanding of paleomonsoon variability at all time scales additional efforts are required to make further progress in two critical areas 1 additional efforts are needed in terms of proxy development and evaluation requiring concerted efforts at long term sediment trap deployments in key monsoon influenced regions as well as development of adequate and widely available core top databases these are necessary to assess the impact of modern oceanographic and seafloor processes on potential monsoon proxies 2 additional effort is also needed in acquiring a sufficient geographic distribution of downcore records to assess linkages among the subsystems and their role in the context of extratropical climate change these records should have high sedimentation rates including varved sections this requires substantial survey support to identify the most appropriate coring and drilling targets c 2004 elsevier ltd all rights reserved

spinup of source driven circulation in an abyssal basin in the presence of bottom topography abstract spinup of the circulation driven by an inflow into an abyssal basin containing a simple large scale topographic feature is studied using an inverted one and a half layer shallow water model two types of topography one a plateau and the other a depression are considered in both cases the topography gives rise to a region of closed geostrophic contours the character of the adjustment and the resultant flow differ markedly between the closed geostrophic contour region and the region outside long wave processes set up a modified stommel arons flow outside the closed contour region while inside the closed contour region frictional spinup leads to a vigorous recirculation it is shown that the ratio of the velocity of the recirculation to that of the stommet arons flow is equal to half the ratio of the radius of the closed contour region to the stommel boundary layer thickness moreover it is shown that the recirculation inside the closed contour region is always cyclonic whether the topog

pollen evidence for late pliocene early pleistocene vegetation and climate change in the north caucasus north western caspian region abstract pollen and spores have been analysed in deposits of the akchagylian apsheronian in the north western caspian sea region providing a picture of past vegetation and climate change for the late pliocene to early pleistocene on the basis of pollen assemblages in sediment cores and outcrops from the north caucasus the caucasus mineral nyye vody region the tersko sunzhensky area and the foothills of dagestan climatic fluctuations and related changes in vegetation can be recognized for the time from 3 6 to 0 8 ma the lower akchagylian is characterized at first by an open landscape dominated by steppe vegetation in the middle of the lower akchagylian the transgression of the palaeo caspian spread and the treeless landscapes of the earliest akchagylian were replaced by forests with thermophilic relicts during the middle upper akchagylian and apsheronian periods the vegetation cover of the north caucasus gradually changed forests were replaced with steppe and semi desert vegetation in response to episodes of aridification and changes were evident in the structure of the dendroflora the vegetation of the north caucasus shows changes consistent with climatic warming at around 3 2 ma which coincides with a period of warming in the mediterranean and probable represents the mid pliocene warm period

fluvial processes in a forested anastomosing river flood partitioning and changing flow patterns in an effort to further our understanding of multiple channel systems this paper presents data on the flood response of channels in one of the last wooded semi natural anastomosing systems in europe the gearagh ireland is characterized by hundreds of small islands separated by interconnected channels of low slope these include channels that cross islands at right angles to the main flow and blind anabranching channels islands are relatively stable and wooded with evidence of division by channel erosion and growth by in channel sedimentation four active zone cross profiles were surveyed each containing between seven and 13 channels velocities were measured in several channels before and during two separate floods from these observations channels have been categorised into three types fast shallow and trapezoidal slow deep and more irregular and flood channels during the floods interchannel flows were caused by variations in water surface elevations due to backing up behind debris dams and it is suggested that this is the origin of the anomalous cross island channels and one cause of island division another potential cause of island division blind anabranching channels is the result of concentrated bank scour between root masses biotic components such as debris dams tree root masses and tree throw pits play a key role in the partitioning of flow and cause variations in channel velocities and the overbank velocity distribution the implications of these observations for channel pattern maintenance are briefly discussed

a 40 000 year palynological record from north east thailand implications for biogeography and palaeo environmental reconstruction abstract there are few palaeoenvironmental data from the indo chinese peninsula that document environmental and climatic conditions prior to the holocene this study of pollen and spores from a small peat swamp in north east thailand provides a record of vegetation change covering ca 40 000 years b p before present these data indicate that the region supported a fagaceous coniferous forest similar to contemporary vegetation described from south west china climatic conditions were cooler and probably drier than present day climates in thailand levels of biomass burning are relatively high throughout this period tropical broad leaf deciduous forest becomes dominant at the pleistocene holocene boundary with the fragmentation of fagaceous coniferous forest in response to increased temperatures

late pleistocene monsoon variability in northwest thailand an oxygen isotope sequence from the bivalve margaritanopsis laosensis excavated in mae hong son province abstract long continuous records of late quaternary environmental change are rare in southeast asia yet they are crucial for understanding the nature of early human dispersal and occupation in the australasian region we present a new record of palaeomonsoon activity extending back to 35 000 bp years before the present based on the analysis of oxygen isotope ratios 18 o in the freshwater bivalve margaritanopsis laosensis excavated from the tham lod and ban rai rockshelters in mae hong son province northwest thailand long term changes in the m laosensis 18 o record reflect changes in the 18 o of the river water in which these organisms grew and correlate well with changes in speleothem 18 o records of east asian monsoon rainfall from hulu cave and dongge cave in china the new northwest thailand 18 o sequence indicates wetter and relatively unstable climatic conditions from 35 000 to 20 000 bp followed by drier conditions from 20 000 to 11 500 bp a period of peak aridity occurred around 15 600 bp during heinrich event 1 suggesting that the intertropical convergence zone shifted southward when the north atlantic region cooled however there is little evidence for the younger dryas event at 12 800 11 500 bp after 9 800 bp precipitation increased substantially and climatic variability declined our findings provide an improved baseline against which to gauge interactions between early humans and climate change in southeast asia for example there was no significant change in the prehistoric flake stone technology used at tham lod and ban rai despite the bivalve 18 o evidence for substantial climate change in the region also the climatic impact of the younger dryas event appears to have been less intense in northwest thailand compared to the cooling and drying observed in china and may explain why agriculture made a relatively late appearance in thailand possibly involving migrants from china

local scale proxy evidence for the presence of closed canopy forest in north western borneo in the late pleistocene bones of strategy i bats from the archaeological record of the great cave of niah sarawak abstract the limits of the distribution of closed canopy forest in southeast asia during the glacial cycles of the pleistocene are the subject of continuing debate in this context this paper reports the results of an analysis of a novel line of evidence as a local scale case study 22 dated assemblages of bat bones that were recovered from the archaeological sequences of the great cave of niah in sarawak malaysian borneo were examined by examination of the morphological characteristics of the distal articulation of the humerus seven families and nine genera were identified five species level attributions could be made these assemblages formed a time series of 14 chronological intervals 48 0 35 ky bp ky bp 103 calibrated years before present 1950 incorporating samples from the high glacial interval 26 18 ky bp and last glacial maximum 23 19 ky bp bones of bat taxa that are adapted to forage in the cluttered environments in the interior of closed canopy forest strategy i bats were employed as proxy evidence for the presence of closed canopy forested habitats in the vicinity bones of strategy i bats principally small hipposideros spp were identified in all examined assemblages and intervals in the time series statistical testing indicated no evidence of differences in the absolute frequency of distal humeri from strategy i bats in the pleistocene samples 48 11 8 ky bp or in the entire time series 48 0 35 ky bp and no significant linear trend was found in the time series to suggest an increase of the bones strategy i bat taxa with the onset of the holocene these findings suggest that closed canopy forest habitats have been a persistent component in the landscape around the great cave of niah since 48 ky bp a taphonomic hypothesis is proposed to explain the dichotomy between the findings of this study and the pollen record of the site

prolonged monsoon droughts and links to indo pacific warm pool a holocene record from lonar lake central india abstract concerns about the regional impact of global climate change in a warming scenario have highlighted the gaps in our understanding of the indian summer monsoon ism also referred to as the indian ocean summer monsoon and the absence of long term palaeoclimate data from the central indian core monsoon zone cmz here we present the first high resolution well dated multiproxy reconstruction of holocene palaeoclimate from a 10 m long sediment core raised from the lonar lake in central india we show that while the early holocene onset of intensified monsoon in the cmz is similar to that reported from other ism records the lonar data shows two prolonged droughts pd multidecadal to centennial periods of weaker monsoon between 4 6 3 9 and 2 0 6 cal ka a comparison of our record with available data from other ism influenced sites shows that the impact of these pd was observed in varying degrees throughout the ism realm and coincides with intervals of higher solar irradiance we demonstrate that i the regional warming in the indo pacific warm pool ipwp plays an important role in causing ism pd through changes in meridional overturning circulation and position of the anomalous walker cell ii the long term influence of conditions like el nino southern oscillation enso on the ism began only ca 2 cal ka bp and is coincident with the warming of the southern ipwp iii the first settlements in central india coincided with the onset of the first pd and agricultural populations flourished between the two pd highlighting the significance of natural climate variability and pd as major environmental factors affecting human settlements

testing the savannah corridor hypothesis during mis2 the boh dambang hyena site in southern cambodia abstract the boh dambang karstic site in southern cambodia kampot province is a mammal bone rich deposit in a hyena site very few hyena sites have been recovered in the pleistocene of southeast asia thus little information is known about the foraging abilities of hyenas during that period and their decline in the region while the other hypercarnivores tiger leopard and dhole persisted until present day to constrain the site we applied luminescence red tl and single grain osl esr and u th dating methods to the sediments and faunal teeth respectively the resulting age estimates suggest that the site represents an accumulation of a young deposit with faunal teeth in the range of 25 18 ka that was last exposed to sunlight between 8 and 7 ka and an older deposit containing older teeth 100 80 ka that have been eroded from the upper caves in the system and incorporated into the younger deposit thus the faunal age of 25 18 ka mis2 provides the best estimate for the age of the hyena site during lgm 26 5 19 ka we analysed the assemblage of isolated teeth in terms of taxonomic diversity and abundance the role of bone accumulators either carnivores or rodents has been precised through a taphonomic analysis diet was reconstructed through measurement of 13 c values of tooth enamel the taphonomic analysis reveals that the hyenas were the main bone accumulators at boh dambang porcupines were aslo a factor in the accumulation of remains the results show that the spotted hyenas hunted large sized herbivores 600 kg in a mixed environment dominated by grassland these data along with evidence from other pleistocene faunas from southeast asian mainland in terms of prey preference of hyenas rhinoceroses versus large bovines also reveal marked differences in relation to habitat type possible causes of the decline of the spotted hyena in the indochinese sub region hypercarnivory high trophic level comparable foraging strategies with hunters gatherers and climatic changes are tentatively proposed at this point

quaternary time scales for the pontocaspian domain interbasinal connectivity and faunal evolution the pontocaspian black sea caspian sea region has a very dynamic history of basin development and biotic evolution the region is the remnant of a once vast paratethys sea it contains some of the best eurasian geological records of tectonic climatic and paleoenvironmental change the pliocene quaternary co evolution of the black sea caspian sea is dominated by major changes in water lake and sea levels resulting in a pulsating system of connected and isolated basins understanding the history of the region including the drivers of lake level and faunal evolution is hampered by indistinct stratigraphic nomenclature and contradicting time constraints for regional sedimentary successions in this paper we review and update the late pliocene to quaternary stratigraphic framework of the pontocaspian domain focusing on the black sea basin caspian basin marmara sea and the terrestrial environments surrounding these large mostly endorheic lake sea systems

estimates of the mean circulation in the deep 2 000m layer of the eastern north atlantic a total of 131 current meter records of between 6 and 24 month duration are analysed to describe the deep flow field of the eastern north atlantic from 19 to 54 n and from the continental slope to the mid atlantic ridge mean flows are weak and may be statistically indeterminate in some records and locations but appear to indicate cyclonic circulations around the iberia and porcupine abyssal plains with a generally southward flow along the mid atlantic ridge and a deep northward slope current where measurements exist along the eastern boundary the deepest inflow to the north eastern basin that has been identified to date takes place through the discovery gap of 4 700 m sill depth at 37 25 n 15 45 w in the azores portugal ridge south of that ridge observations are sparse and no systematic circulation is yet evident these observations are discussed in relation to recent geostrophic estimates of the deep circulation

a 900 year 600 to 1500 a d record of the indian summer monsoon precipitation from the core monsoon zone of india 1 we present a near annually resolved record of the indian summer monsoon ism rainfall variations for the core monsoon region of india that spans from 600 to 1500 a d from a 230th dated stalagmite oxygen isotope record from dandak cave our rainfall reconstruction which spans the medieval warm period mwp and the earliest portion of the little ice age lia indicates that the short instrumental record of ism underestimates the magnitude of monsoon rainfall variability periods of severe drought lasting decades occurred during the 14th and mid 15th centuries and coincided with several of india s most devastating famines

pliocene environmental change in west africa and the onset of strong ne trade winds odp sites 659 and 658 abstract pliocene vegetation dynamics and climate variability in west africa have been investigated through pollen and xrf scanning records obtained from sediment cores of odp site 659 18 n 21 w the comparison between total pollen accumulation rates and ti ca ratios which is strongly correlated with the dust input at the site showed elevated aeolian transport of pollen during dusty periods comparison of the pollen records of odp site 659 and the nearby site 658 resulted in a robust reconstruction of west african vegetation change since the late pliocene between 3 6 and 3 0 ma the savannah in west africa differed in composition from its modern counterpart and was richer in asteraceae in particular of the tribus cichorieae between 3 24 and 3 20 ma a stable wet period is inferred from the fe k ratios which could stand for a narrower and better specified mid pliocene mid piacenzian warm time slice the northward extension of woodland and savannah albeit fluctuating was generally greater in the pliocene ne trade wind vigour increased intermittently around 2 7 and 2 6 ma and more or less permanently since 2 5 ma as inferred from increased pollen concentrations of trade wind indicators ephedra artemisia pinus our findings link the ne trade wind development with the intensification of the northern hemisphere glaciations inhg prior to the inhg little or no systematic relation could be found between sea surface temperatures of the north atlantic with aridity and dust in west africa

recirculating components to the deep boundary current of the northern north atlantic abstract the meridional overturning system of the north atlantic is conventionally thought of as transporting warm water 4 c to high latitudes and covd water to low latitudes the northern cold water sources for this system are dense overflow from the nordic seas and less dense water from the labrador sea lsw the overflow components are carried westward by a deep northern boundary current dnbc that is shown here actually to begin southeast of the overflow regions the dnbc lies along the southern side of a system of islands and submarine ridges that divides the nordic seas from the subpolar basins the overflows act to increase the transport of the dnbc and this transport is further increased through the entrainment of warm waters once inside the labrador sea the dnbc is joined by lsw before continuing south to low latitudes as a cold deep western boundary current dwbc however published transport estimates are larger than can be explained by warm water entrainment alone thus indicating entrainment also of recirculating cold components the subject of this paper their sources are shown to be the lsw and cold abyssal waters originating from the southern hemisphere the lsw is entrained downward into the denser part of the dnbc and laterally into the upper part of the dwbc whereas the cold abyssal waters are supplied by an eastern intensified northward flow in the eastern atlantic that serves as the initial source of the dnbc and by a similar northward flow in the western atlantic the meridional overturning system described includes recirculations and poleward transport of cold water in addition tothe components described by the conventional system the cold abyssal waters in both the eastern and western basins have relatively low levels of oxygen and high concentrations of silicate reflecting their southern origin but their influence in the northwestern atlantic is somewhat obscurred by strong recirculating cyclonic gyres in the newfoundland and labrador basins this influence is detected by a deep silicate maximum extending poleward from the mid latitude western atlantic through the two gyres with eastern concentration and recirculating back diluted toward the south in the dwbc within the respective basins such a maximum also extends northward through the irminger basin into the dnbc but there is an ambiguity as to whether this is a direct extension of the signal from the south in the western basin or if it comes from the mid latitude eastern basin by way of westward flow through the charlie gibbs fracture zone it is perhaps consequence of both estimates of the volume transports of the various recirculating cold components indicate that they supply about as much water to the deep boundary currents as do the combined cold water sources in the north

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

spin up and breakdown of source driven deep north atlantic flow over realistic bottom topography in this study we examine the time dependent behaviour of the deep north atlantic dynamics we use a 1 layer nonlinear shallow water model with realistic topography and high spatial resolution it is driven by an inflow of deep water from a northern source and by parameterized density exchange processes at the interface the evolving circulation pattern is complex the mid atlantic ridge with the charlie gibbs fracture zone has a fundamental influence on the large scale flow field a reduction of the inflow causes a temporary reversal of the interior currents the perturbation travels along the geostrophic contours the response times of the currents for the spin up and breakdown experiments are of the order of years they differ for different areas of the north atlantic ocean the area which is affected last by the perturbation is the northwesternmost interior corner which is close to the position of the source

global teleconnections of meridional overturning circulation anomalies there is a wide range of evidence from both models and palaeoclimatic data that indicates the possibility of abrupt changes in the oceanic meridional overturning circulation moc however much of our dynamical understanding of the moc comes from steady state models that rely upon the assumption of thermodynamic equilibrium and are therefore only valid on millennial time scales here a dynamical model for the global teleconnections of moc anomalies on annual to multidecadal time scales is developed it is based on a linear theory for the propagation of zonally integrated meridional transport anomalies in a reduced gravity ocean and allows for multiple ocean basins connected by a circumpolar channel to the south the theory demonstrates that the equator acts as a low pass filter to moc anomalies as a consequence moc anomalies on decadal and shorter time scales are confined to the hemispheric basin in which they are generated and have little impact on the remainder of the global ocean the linear theory is compared with the results of a global nonlinear numerical integration which it reproduces to a good approximation

a high resolution absolute dated late pleistocene monsoon record from hulu cave china oxygen isotope records of five stalagmites from hulu cave near nanjing bear a remarkable resemblance to oxygen isotope records from greenland ice cores suggesting that east asian monsoon intensity changed in concert with greenland temperature between 11 000 and 75 000 years before the present yr b p between 11 000 and 30 000 yr b p the timing of changes in the monsoon as established with 230th dates generally agrees with the timing of temperature changes from the greenland ice sheet project two gisp2 core which supports gisp2 s chronology in this interval our record links north atlantic climate with the meridional transport of heat and moisture from the warmest part of the ocean where the summer east asian monsoon originates

on the significance of sea level variations and shelf paleo morphology in governing sedimentation in the southern south china sea during the last deglaciation abstract deglacial sedimentation on the outer sunda shelf the shelf margin and slope shows a close correlation with the stages of flooding of the emerged shelf it is mainly controlled by the relationship between shelf paleo physiography and changes in sea level and sediment supply based on the sedimentological and geochemical variability at five sites along a transect across the outer shelf and the continental slope covering the last 20 000 years four intervals of significant depositional changes are identified the first reorganization in the sedimentation regime which was established during sea level lowstand is associated with the drowning of the lower course of the north sunda river between 16 5 and 14 5 ka during and following the rapid rise in sea level at 14 5 14 ka sedimentation on the slope is characterized by an accelerated decrease in the supply of terrigenous material associated with the flooding of the middle part of the paleo valley this abrupt change in sedimentation is followed by a period of gradual decrease of terrigenous supply to the slope when the surrounding plains of the river valley were flooded 14 8 5 ka the final change occurred between ca 8 5 and 6 ka when the coastline reached its modern position and modern sedimentary patterns are established this change probably marks the end of reworking by transgression given the synchroneity of sedimentological changes along the transect across the sunda shelf and into the deep sea with the environmental shifts on the central shelf sedimentation on the margin and slope appears to be mainly controlled by the interrelationship of sea level shelf paleo physiography and sediment supply moreover the records display lateral changes through time associated with stages of the deglacial transgression which mask any potential sedimentological variability due to changes in precipitation vegetation or atmospheric circulation this fact cautions the interpretation of near shore sedimentary records as unequivocal recorders of local climate change e g se asian monsoon and highlights the need to include variations in shelf physiography and sea level in future paleoceanographic studies

palaeoclimate dynamics in continental southeast asia over the last 30 000calyrs bp abstract although the asian monsoon is the dominant source of precipitation across continental southeast asia projections of future climate trends in this region remain unclear this is partly because historic climate records are relatively short precluding our ability to understand long term climate dynamics and potential drivers of change in this synthesis 17 palaeorecords from sites located in continental southeast asia provide a synopsis of regional palaeoclimate dynamics over the last 30 000 cal yrs bp the results indicate that over millennial timescales the dominant control on asian monsoon intensity is solar insolation linked to orbital changes from ca 30 to 11 9 cal kyr bp climatic conditions are interpreted to have been cold and arid most probably dominated by a strong asian winter monsoon marked changes occurred during the pleistocene holocene transition including a shift to warmer wetter climatic conditions at ca 11 5 cal kyr bp which was apparently synchronous across the region during the early to mid holocene warmer wetter climatic conditions were established consistent with a strong asian summer monsoon inferred from the dongge cave 18o speleothem record intriguingly contrasting sub regional palaeoclimatic trends are captured in the synthesis most notably during the holocene possibly due to differing sub regional climatic and environmental influences including differences in the role of the asian monsoon the westerlies and or topographical effects however because of uncertainties relating to the age control of many of the palaeorecords it is not possible to make this interpretation with confidence further work involving comprehensive radiocarbon dating of sequences and the development of high resolution palaeoclimatic reconstructions are urgently required if we are to identify decadal to centennial scale changes across continental southeast asia and test hypotheses of synchroneity in the region

climate and hydrographic variability in the indo pacific warm pool during the last millennium planktonic foraminiferal mg ca and delta o 18 derived sea surface temperature and salinity records from the makassar strait indonesia show a long term cooling and freshening trend as well as considerable centennial scale variability during the last millennium the warmest temperatures and highest salinities occurred during the medieval warm period mwp while the coolest temperatures and lowest salinities occurred during the little ice age lia these changes in the western pacific along with observations from other high resolution records indicate a regionally coherent southern displacement of the inter tropical convergence zone during the lia with more arid conditions in the northern tropics and wetter conditions in the southern tropics

modeling the large scale influence of geothermal sources on abyssal flow an approximate temperature perturbation equation for a continuously stratified deep ocean layer on an equatorial plane is presented a vertically integrated flow is allowed which in the present study is forced by uniform upwelling solutions with truncated vertical structure are presented which are forced by a representation of localized geothermal heat sources solutions exhibit a range of behavior from passive advection to plume depending on the ratio of barotropic flow speed to long rossby wave phase speed owing to the different phase speeds of the vertical modes the forced vertical structure is dispersed which can result in positive and negative temperature anomalies both upstream and downstream of the source furthermore it is clear that the ability of localized sources to influence upstream conditions is enhanced in equatorial regions compared with higher latitudes where the background flow is better able to advect the temperature perturbations downstream depending on the strength of the imposed temperature anomaly at the source there may or may not be a large scale reversal of the total flow field thus the correlations between temperature geostrophic shear and a passive tracer such as 3he can be positive negative or zero away from the geothermal source

orbital and suborbital climate variability in the sulu sea western tropical pacific 1 a detailed record of planktic 18o from a sediment core in the sulu sea located between the south china sea and the western pacific warm pool reveals that for the past 400 kyr 1 kyr 1000 years 18o variability on orbital timescales is similar to that caused by changes in ice volume alone this result indicates that in the sulu sea temperature driven changes in planktic 18o on orbital times scales were generally compensated for by the effects of sea level and changes in seasonal monsoon intensity on the local freshwater budget as well as by other changes in the tropical hydrologic cycle and their attendant effects on surface water 18o increased freshening of the western tropical pacific warm pool is reminiscent of la nina conditions however we argue that the mean tropical climate state was not more la nina like than today on broader spatial scales suborbital variability occurred in the sulu sea throughout the past 400 kyr suggesting little sensitivity to ice volume or to glacial interglacial changes in tropical hydrology variations on 4 10 kyr timescales appear to be linked to those in the north atlantic region suggesting a common forcing of that variability we suggest that sulu sea salinity variations were a response to suborbital climate variability in the north atlantic region transmitted via changes in the intensity of the east asian summer monsoon we suggest that a north atlantic origin of that tropical suborbital variability can be reconciled with weak glacial amplification in the tropics if the tropical response is nonlinear

late pleistocene and holocene development of the interior peat accumulating basin of tropical tasek bera peninsular malaysia the stratigraphy of holocene peat deposits from an interior lowland basin of tropical peninsular malaysia provides insight into the hydrological ecological and climatic controls on tropical peatland development interpretations about vegetation and climate dynamics including storm intensity over the past 5000 years are integrated with regional and global climatic and eustatic changes to serve as a proxy for past ecology and climate tasek bera basin tbb is a lowland dendritic basin in tropical peninsular malaysia accumulation of organic matter occurred in local lakes during the last glacial maximum lgm but widespread peat deposition did not start until 5300 bp when climatic changes led to the evolution of a wetland system peat accumulation progressively expanded with terrestrialisation of channels and subbasins to paludification of the riparian part of the lowland forest zone lithofacies can be distinguished despite the highly diverse peat and organic rich sediment composition as a result of the climatic and hydrologic changes over the past 5300 years peat accumulation rates ranging from 0 7 to 2 5 mm year are highest in pandanaceae environments and lowest in high ash swamp forests and environments dominated by cyperaceae transects of peat cores across the mire system show the stratigraphic complexities of the peat is the result of hydrological variations and thus plant successional changes ash yield shows that periods of high mineral matter input into the drainage system occurred since the mid holocene indicating rapid and cyclic changes in frequency and magnitude of runoff events and by inference storms stratigraphic analysis of peat and ash yield are tools that provide a proxy for development of holocene hydrologic events in topogenous peat deposits

high resolution x ray fluorescence core scanning analysis of les echets france sedimentary sequence new insights from chemical proxies the les echets sediment sequence has recently been the subject of a high resolution multi proxy study which revealed shifts in lake productivity linked to greenland stadials and interstadials over the last 40 ka wohlfarth et al 2008 rapid ecosystem response to abrupt climate changes during the last glacial period in western europe 40 16 ka geology 36 407 410 here we present new elemental data for this sequence as acquired using an x ray fluorescence core scanning system which provides in situ high resolution continuous multi element analyses it was found that the strength of associations between the studied elements ti rb k zr si ca sr mn and fe varied over time with changes in lake status which are ultimately driven by changes in climate increases in fine grained detrital input as indicated by ti rb k and zr rb overlap with independently established periods of lower lake productivity and are interpreted to represent more arid conditions several of these arid periods are coincident with low diatom concentrations and the timing of heinrich events h4 h3 and h2 the duration of the environmental impacts linked to the h events varied by proxy with elemental data ti and zr rb estimating shorter events than the diatom data periods of lower detrital input and coarser grain sizes agreed in time with periods of higher lake productivity the elemental data provide new insights into hydrological changes and related sediment processes within the catchment and highlight the need for multi element and multi proxy approaches when reconstructing climate change using lacustrine sediment sequences copyright 2011 john wiley sons ltd

holocene environmental change at inle lake shan state myanmar and its implications for the regional development of agriculture abstract we report pollen charcoal and diatom records from the upper 4 m of a core from inle lake myanmar spanning the entire holocene to investigate the changing palaeoenvironments in which early agriculture developed from 12 000 to 10 500 cal yr bp a grass swamp existed until it was flooded by rising lake levels indicated by the onset of marl deposition at the site the onset of higher lake levels coincided with a transition from conifer rich forest to mixed deciduous evergreen forest and a reduction in local biomass burning lake levels remained high until 6400 cal yr bp thereafter fluctuating with possible dry phases at 4050 2400 and 1100 cal yr bp increased burning is apparent from 2200 cal yr bp inferred to represent the onset of human forest clearance to its very reduced state today the inle lake record compares with holocene sequences in china thailand and india and marine cores south of myanmar which similarly show a regional pattern of drier conditions in the early greenlandian stage followed by maximum lake levels in the early northgrippian stage fluctuating lake levels are evident in the later northgrippian and meghalayan stages after 6000 cal yr bp this pattern coincides with precessional reduction in summer insolation in the region which weakens the asian monsoon the present day bare catchments of inle lake probably mostly resulted from forest destruction over the last 2000 years although hints of human presence can be inferred throughout the older record

adaptations to sea level change and transitions to agriculture at khao toh chong rockshelter peninsular thailand this study reports on an analysis of human adaptations to sea level changes in the tropical monsoonal environment of peninsula thailand we excavated khao toh chong rockshelter in krabi and recorded archaeological deposits spanning the last 13 000 years a suite of geoarchaeological methods suggest largely uninterrupted deposition against a backdrop of geological data that show major changes in sea levels although there is a small assemblage of mostly undiagnostic ceramics and stone artefacts there are some distinct changes in stone artefact technology and ceramic fabric there is a substantial faunal assemblage with changes in both the mammalian and shellfish taxa during the pleistocene holocene transition that correlate with local sea level fluctuation this assemblage provides an opportunity to explore subsistence behaviours leading up to the transition to the neolithic we explore the implications for current debates on the prehistoric origins of agricultural subsistence in mainland southeast asia the data highlight the importance of local contingencies in understanding the mechanisms of change from foragers to agriculturalists

lake kumphawapi an archive of holocene palaeoenvironmental and palaeoclimatic changes in northeast thailand the long term climatic and environmental history of southeast asia and of thailand in particular is still fragmentary here we present a new c 14 dated multi proxy sediment record toc c n cns

the leading mode of indian summer monsoon precipitation variability during the last millennium 1 the internally generated intraseasonal variability of the indian summer monsoon is characterized by intermittent periods of enhanced active and deficient break precipitation which produce a quasi east west precipitation dipole over the indian subcontinent here we present multicentennial length and near annually resolved reconstructions of monsoon precipitation inferred from absolute dated and instrumentally calibrated speleothem oxygen isotope records from regions central and northeast india that have diametric responses to active break monsoon circulation patterns on centennial timescales ad 1400 2008 precipitation variability from these two regions exhibit opposing behavior oscillating between periods with a persistently active dominated ad 1700 to 2007 and a break dominated ad 1400 to 1700 regime the switch between these regimes occurs abruptly within decades at a time ad 1650 1700 when a proxy record of upwelling intensity from the arabian sea suggest an abrupt increase in the monsoon winds on the basis of these observations we hypothesize that the frequency distribution of active break periods varies on centennial timescales implying a leading role of internal dynamics in governing the ism response to slowly evolving changes in the external boundary conditions

the inference of north atlantic circulation patterns from climatological hydrographic data we present a review of spiral techniques which have recently been developed for the determination of absolute velocity profiles from hydrographic observations a specific technique is then designed and applied to the north atlantic part of levitus 1982 climatological hydrographic atlas with the aim of estimating reference velocities and diffusivities for heat salt and potential vorticity these quantities are determined on a 1 grid from the local gradients of temperature and salinity under the constraints of the thermal wind relations and the conservation of the respective tracers including diapycnic and isopycnic mixing terms the estimation procedure includes the statistical framework of inverse modeling in the weighting of the constraints by the data noise variances and the determination of the covariances of the model parameters the resulting circulation pattern bears strong resemblance to the classical view of the north atlantic circulation as put foreward by wust 1935 and defant 1941 the upper layers are dominated by the gulf stream north atlantic current system with a broad subtropical gyre recirculation in the lower layer a western boundary current is fed from norwegian sea overflow penetrating the gibbs fracture zone and partly circulating around the labrador sea as a consequence of the climatological averaging the currents appear in broad shape with much reduced velocities in particular in the upper layer the vertical structure reveals an almost horizontal level of no motion pattern much along the concepts of defant 1941 diffusion coefficients were determined for an upper layer depth of mixed layer to 800 m depth and a lower layer 800 m to 2000 m the spatial pattern of these coefficients correlates with maps of eddy activity showing higher values in the strong current regimes and low values within the subtropical and subpolar gyre average values in the lower layer of the quiet regions are 10 5 m s and 10 m s for the diapycnal and isopycnal diffusivity respectively and 10 1 m s for the vertical diffusivity of vorticity which yields 10 m s for the lateral diffusivity of potential vorticity toward the regions of strong currents and in the upper layer these values roughly increase by an order of magnitude