weakening and strengthening of the indian monsoon during heinrich events and dansgaard oeschger oscillations the dansgaard oeschger oscillations and heinrich events described in north atlantic sediments and greenland ice are expressed in the climate of the tropics for example as documented in arabian sea sediments given the strength of this teleconnection we seek to reconstruct its range of environmental impacts we present geochemical and sedimentological data from core so130 289kl from the indus submarine slope spanning the last similar to 80 kyr elemental and grain size analyses consistently indicate that interstadials are characterized by an increased contribution of fluvial suspension from the indus river in contrast stadials are characterized by an increased contribution of aeolian dust from the arabian peninsula decadal scale shifts at climate transitions such as onsets of interstadials were coeval with changes in productivity related proxies heinrich events stand out as especially dry and dusty events indicating a dramatically weakened indian summer monsoon potentially increased winter monsoon circulation and increased aridity on the arabian peninsula this finding is consistent with other paleoclimate evidence for continental aridity in the northern tropics during these events our results strengthen the evidence that circum north atlantic temperature variations translate to hydrological shifts in the tropics with major impacts on regional environmental conditions such as rainfall river discharge aeolian dust transport and ocean margin anoxia key points intensity of indian monsoon is traced with geochemical and grain size analyses of sediments fluvial versus aeolian sediment input to arabian sea mimics do oscillations during heinrich events the indian monsoon weakened distinctly

early diagenesis in deep sea turbidites the imprint of paleo oxidation zones sediment cores up to 35 m long have been recovered from turbidite sequences in the madiera abyssal plain and the southern nares abyssal plain detailed geochemical analyses of these sediments si al fe mn ca organic and inorganic carbon and associate pore waters nitrate ammonia silicate fe2 mn2 and alkalinity provide representative profiles of both steady state and nonsteady state diagenetic reactions initiated by oxidation and reduction processes models demonstrate that chemical transport in the pore water system is diffusion dominated over periods of a few thousands of years to several hundreds of thousands of years mn and fe mobilized in the subsurface mildly reducing sediments are precipitated as easily reducible oxyhydroxides in the near surface oxidized sediments nonsteady state profiles show the influence of episodic and rapid turbidite deposition and the imprint of oxidation zones that developed as the result of oxygen diffusion into the upper portions of turbidites during intervals of slow pelagic deposition the time required for development of oxidation zones between turbidites ranges from 2 0 to 15 ka in the madeira abyssal plain and from 0 2 to 2 4 ka in the southern nares abyssal plain paleo oxidation zones can be recognized in old turbidites by distinct changes in color between lower and upper portions of the deposit in the basal unoxidized portion of the turbidite the sediments are characteristically dark green gray or brown in the paleo oxidized zone the sediments are pale green blue or yellowish brown these zones in both the madeira and southern nares abyssal plains contain distinctly less organic c and carbonate in the paleo oxidized zone as compared with the unoxidized sediments depletion of carbonate content in the oxidized zones in the southern nares abyssal plain is particularly significant in that as much as 80 of the initial carbonates have been lost also the relative amounts of weak acid soluble fe and mn are generally less in the paleo oxidized zones due to the initial oxidation of metal carbonate and metal hydroxide forms to easily reducible oxide forms which are then subsequently solubilized under the mildly reducing conditions at depth in the sediment column

evolution of the indian summer monsoon and terrestrial vegetation in the bengal region during the past 18 ka the indian summer monsoon ism is a major global climatic phenomenon long term precipitation proxy records of the ism however are often fragmented and discontinuous impeding an estimation of the magnitude of precipitation variability from the last glacial to the present to improve our understanding of past ism variability we provide a continuous reconstructed record of precipitation and continental vegetation changes from the lower ganges brahmaputra meghna catchment and the indo burman ranges over the last 18 000 years 18 ka the records derive from a marine sediment core from the northern bay of bengal nbob and are complemented by numerical model results of spatial moisture transport and precipitation distribution over the bengal region the isotopic composition of terrestrial plant waxes dd and d13c of n alkanes are compared to results from an isotope enabled general atmospheric circulation model isocam for selected time slices pre industrial mid holocene and heinrich stadial 1 comparison of proxy and model results indicate that past changes in the dd of precipitation and plant waxes were mainly driven by the amount effect and strongly influenced by ism rainfall maximum precipitation is detected for the early holocene climatic optimum ehco 10 5 6 ka bp whereas minimum precipitation occurred during the heinrich stadial 1 hs1 16 9 15 4 ka bp the isocam model results support the hypothesis of a constant moisture source i e the nbob throughout the study period relative to the pre industrial period the model reconstructions show 20 more rain during the mid holocene 6 ka bp and 20 less rain during the heinrich stadial 1 hs1 respectively a shift from c4 plant dominated ecosystems during the glacial to subsequent c3 c4 mixed ones during the interglacial took place vegetation changes were predominantly driven by precipitation variability as evidenced by the significant correlation between the dd and d13c alkane records when compared to other records across the ism domain precipitation and vegetation changes inferred from our records and the numerical model results provide evidence for a coherent regional variability of the ism from the last glacial to the present

latest pleistocene and holocene glacier fluctuations in the himalaya and tibet abstract the timing and extent of latest pleistocene and holocene alpine glacier fluctuations in the himalaya and tibet are poorly defined due to the logistical and political inaccessibility of the region and the general lack of modern studies of the glacial successions nevertheless renewed interest in the region and the aid of newly developing numerical dating techniques have provided new insights into the nature of latest pleistocene and holocene glacier oscillations these studies provide abundant evidence for significant glacial advances throughout the last glacial cycle in most high himalayan and tibetan regions glaciers reached their maximum extent early in the last glacial cycle however true last glacial maximum glacier advances were significantly less extensive notable glacier advances occurred during the lateglacial and the early holocene with minor advances in some regions during the mid holocene there is abundant evidence for multiple glacial advances throughout the latter part of the holocene although these are generally very poorly defined and were less extensive than the early holocene glacier advances the poor chronological control on latest pleistocene and holocene glacial successions makes it difficult to construct correlations across the region and with other glaciated regions in the world which in turn makes it hard to assess the relative importance of the different climatic mechanisms that force glaciation in this region the lateglacial and holocene glacial record however is particularly well preserved in several regions notably in muztag ata and kongur and the khumbu himal these successions have the potential to be examined in detail using newly developing numerical dating methods to derive a high resolution record of glaciation to help in paleoclimatic reconstruction and understanding the dynamics of climate and glaciation in the himalaya and tibet

a 25 ka indian ocean monsoon variability record from the andaman sea recent paleoclimatic work on terrestrial and marine deposits from asia and the indian ocean has indicated abrupt changes in the strength of the asian monsoon during the last deglaciation comparison of marine paleoclimate records that track salinity changes from asian rivers can help evaluate the coherence of the indian ocean monsoon iom with the larger asian monsoon here we present paired mg ca and d 18 o data on the planktic foraminifer globigerinoides ruber white from andaman sea core rc12 344 that provide records of sea surface temperature sst and d 18 o of seawater d 18 osw over the past 25 000 years ka before present bp age control is based on nine accelerator mass spectrometry ams dates on mixed planktic foraminifera mg ca sst data indicate that sst was 31c cooler during the last glacial maximum lgm than the late holocene andaman sea d 18 osw exhibited higher than present values during the lateglacial interval ca 19 15 ka bp and briefly during the younger dryas ca 12 ka bp lower than present d 18 osw values during the bolling allerod ca 14 5 12 6 ka bp and during the early holocene ca 10 8 5 5 ka bp are interpreted to indicate lower salinity reflect some combination of decreased evaporation precipitation e p over the andaman sea and increased irrawaddy river outflow our results are consistent with the suggestion that iom intensity was stronger than present during the bolling allerod and early holocene and weaker during the late glaciation younger dryas and the late holocene these findings support the hypothesis that rapid climate change during the last deglaciation and holocene included substantial hydrologic changes in the iom system that were coherent with the larger asian monsoon r 2007 elsevier ltd all rights reserved

the timing of mediterranean sapropel deposition relative to insolation sea level and african monsoon changes the mediterranean basin is sensitive to global sea level changes and african monsoon variability on orbital timescales both of these processes are thought to be important to the deposition of organic rich sediment layers or sapropels throughout the eastern mediterranean yet their relative influences remain ambiguous a related issue is that an assumed 3 kyr lag between boreal insolation maxima and sapropel mid points remains to be tested here we present new geochemical and ice volume corrected planktonic foraminiferal stable isotope records for sapropels s1 holocene s3 s4 and s5 marine isotope stage 5 in core lc21 from the southern aegean sea the records have a radiometrically constrained chronology that has already been synchronised with the red sea relative sea level record and this allows detailed examination of the timing of sapropel deposition relative to insolation sea level and african monsoon changes we find that sapropel onset was near synchronous with monsoon run off into the eastern mediterranean but that insolation sapropel monsoon phasings were not systematic through the last glacial cycle these latter phasings instead appear to relate to sea level changes we propose that persistent meltwater discharges into the north atlantic e g at glacial terminations modified the timing of sapropel deposition by delaying the timing of peak african monsoon run off these observations may reconcile apparent model data offsets with respect to the orbital pacing of the african monsoon our observations also imply that the previous assumption of a systematic 3 kyr lag between insolation maxima and sapropel midpoints may lead to overestimated insolation sapropel phasings finally we surmise that both sea level rise and monsoon run off contributed to surface water buoyancy changes at times of sapropel deposition and their relative influences differed per sapropel case depending on their magnitudes sea level rise was clearly important for sapropel s1 whereas monsoon forcing was more important for sapropels s3 s4 and s5

variability of southwest indian summer monsoon precipitation during the bolling allerod we have generated a high resolution 20 yr 2 3 0 th dated stalagmite oxygen isotope record from timta cave in the western himalaya in india that documents southwest indian summer monsoon ism precipitation variations during the bolling allerod interstadial from 15 2 to 11 7 ka compared with the glacial and younger dryas ism precipitation was enhanced during the bolling allerod ism precipitation was apparently coupled to variations in the east asian monsoon and north atlantic climate on millennial and multicentennial time scales during the deglaciation analyses of a high growth rate interval 2 5 yr resolution encompassing the late bolling early alterod suggest that multidecadal monsoon variability was an important aspect of ism behavior at that time the frequency spectrum of ism precipitation during this time interval is similar to that of the 1 4 c record and other ism precipitation records during the latest holocene this raises the hypothesis that multidecadal climate dynamics during the late boiling early allerod may have been similar to those that operated during the last several millennia even though the boundary conditions of these two time intervals were very different

sr and nd isotopes in river sediments from the ganga basin sediment provenance and spatial variability in physical erosion 1 sr and nd concentrations and isotope compositions in sediment of the ganga river from gangotri to rajmahal and its tributaries have been measured to determine provenance and the spatial variability in physical erosion among the ganga subbasins sr and nd in silicates range from 37 to 138 and from 10 to 36 g g with 87sr 86sr and nd of 0 7474 0 8428 and 25 5 to 15 5 respectively the results suggest that 65 of ganga mainstream sediments are derived from the higher himalayan crystallines highlighting intense physical erosion in this region the 87sr 86sr values of sediments in the gangetic plain show nearly identical trends during two seasons with a sharp and significant decrease at barauni downstream of gandak confluence this brings out the major impact of the sediment contribution from the gandak to the ganga mainstream model calculation suggests that about half of the ganga sediment at rajmahal is sourced from the gandak the erosion rates in the himalayan subbasins of the ganga range between 0 5 and 6 mm a where a is years with the gandak having the highest erosion rate high relief and intense precipitation over the headwater basins of the gandak appear to drive the rapid and focused erosion of this basin the results of this study and those in literature suggest that the eastern syntaxis brahmaputra the western syntaxis indus and the gandak have much higher physical erosion rates than the other himalayan basins focused erosion in the hot spots of these river basins contributes significantly to the global riverine sediment budget and influence regional tectonics

the ti al molar ratio as a new proxy for tracing sediment transportation processes and its application in aeolian events and sea level change in east asia abstract ti al molar ratios of sediments in various sedimentary environments are used to explain sediment transportation from source regions to sink areas samples were collected from outcrops soils fluvial lake and marine sediment environments initial ti al molar ratios of sediments are controlled by those of parent soils or rocks these ratios tend to decline gradually as a result of heavy mineral gravity fractionation during transportation sedimentary ti al molar ratios in sink areas such as lakes and pelagic environments are lower than those in source regions in this study for the changjiang river huanghe river and kaoping river ti al molar ratios decline considerably from downstream to estuary environments additionally well sorted aeolian sands have extremely low ti al molar ratios in northern china the ti al molar ratios of aerosol particles found in taiwan and the east china sea show reduced ratios as a result of asia dust storm episodes furthermore lower ti al molar ratios in deep ocean sediments were discovered by tracing the distribution of sedimentary ti al molar ratios in the south china sea when sea levels dropped during glacial periods the river estuary was closer to deep marine areas and carried more terrestrial sediments into deep marine environments the closer estuary with relatively higher ti al ratio would lead increase of ti al molar ratios in deep sea sediments in this study ti al molar ratio is promoted as a new proxy to help with understanding changes in sedimentary environments

the bengal depositional system from rift to orogeny abstract the bengal depositional system is defined as the surface depositional environments and the underlying sediment accumulation extending from the alluvial lacustrine and paludal sediments of the lower ganges and brahmaputra rivers across the bengal delta the bangladesh continental shelf and slope to and including the bengal fan together it is one of the greatest sediment accumulations in the modern world and is comparable in volume to the great sediment accumulations of the geological past the history of formation started with the mesozoic breakup of eastern gondwanaland the northward drift of india its collision with the southern margin of asia rotation and bending of the western sunda arc and the penetration of the indian continental mass into southern asia during this history the regional tectonics evolved and sources and provenance of the sediments changed with the ultimate uplift of the tibetan plateau and the himalayas

the role of the indian summer monsoon and the mid latitude westerlies in himalayan glaciation review and speculative discussion new dates for late quaternary glaciations in the himalayas show that during the last glacial cycle glaciations were not synchronous throughout the region rather in some areas glaciers reached their maxima at the global glacial maximum of c 18 20 ka bp whereas in others glaciers were most extensive at c 60 30 ka bp comparison of these data with palaeoclimatic records from adjacent regions suggest that on millennial timescales himalayan glacier fluctuations are controlled by variations in both the south asian monsoon and the mid latitude westerlies

a review on the provenance discrimination of sediments in the yellow sea the yellow sea has been extensively studied for the understanding of dispersal patterns and limits of sediments from neighboring countries including china and korea although sedimentological mineralogical and geochemical approaches have been tried to solve the problems especially including the identification of sediment sources in and around the yellow sea the published results are not enough for understanding them suggestions on sediment origins budgets sediment accumulation rates mineralogical and geochemical compositions are not coincident to each other and sometimes even controversial for example conflicts on the distribution patterns of smectite and calcium carbonate the provenance of the southeastern yellow sea mud and sedimentation rates in there the ratios of v al and mn al in korea and china river sediments the origin of ba and pb in sandy sediments of the northeastern yellow sea and so on various geochemical indicators from the literature for the provenance discrimination in the yellow sea are reviewed here in depth and corresponding discussions are described separately research topics for the future study also are suggested for the proper access to the understanding of the origin and dispersal patterns of the yellow sea sediments especially focusing on the geochemical approaches d 2003 elsevier science b v all rights reserved

provenance discrimination of siliciclastic sediments in the middle okinawa trough since 30 ka constraints from rare earth element compositions the late quaternary paleoceanography and paleoenvironment in the okinawa trough east china sea have been well reconstructed over the last decade while in contrast the provenance of terrigenous sediments that have accumulated there remains enigmatic in this study rare earth elements ree were used to investigate provenance changes in sediments from core dgks9604 taken from the middle okinawa trough discrimination plots based on ree fractionation parameters suggest that the cored sediments have variable provenances over the last 30 ka with the lower part ca 31 8 2 ka ultimately originating mostly from the changjiang yangtze river and the upper part 7 1 0 ka primarily from taiwan during the last glacial maximum and early deglacial period sea level was low and the main stream of the kuroshio current was deflected to the east of the ryukyu islands as a result the changjiang derived sediments might have dominated sedimentation of the middle okinawa trough however since about 7 ka the main stream of the kuroshio current strengthened in the area of the trough as sea level approximated the modern position this caused near bottom transport of fine grained sediments from the continental margin to the trough to become weak and instead taiwan derived terrigenous sediments dominated in the middle trough the changing provenances of terrigenous sediments into the middle okinawa trough are closely related to the evolution of oceanic circulation and sea level in the east china sea two tephra layers in the core have distinct ree compositions and correlate well with two volcanic eruptions at 7 6 and 25 8 ka in southern japan

major ion chemistry of the ganga brahmaputra river system weathering processes and fluxes to the bay of bengal the ganga brahmaputra one of the world s largest river systems is first in terms of sediment transport and fourth in terms of water discharge a detailed and systematic study of the major ion chemistry of these rivers and their tributaries as well as the clay mineral composition of the bed sediments has been conducted the chemistry of the highland rivers upper reaches of the ganga the yamuna the brahmaputra the gandak and the ghaghra are all dominated by carbonate weathering ca mg and hco3 account for about 80 of the cations and anions in the lowland rivers the chambal the betwa and the ken hco3 excess over ca mg and a relatively high contribution of na k to the total cations indicate that silicate weathering and or contributions from alkaline saline soils and groundwaters could be important sources of major ions to these waters the chemistry of the ganga and the yamuna in the lower reaches is by and large dictated by the chemistry of their tributaries and their mixing proportions illite is the dominant clay mineral about 80 in the bedload sediments of the highland rivers kaolinite and chlorite together constitute the remaining 20 of the clays in the chambal betwa and ken smectite accounts for about 80 of the clays this difference in the clay mineral composition of the bed sediments is a reflection of the differences in the geology of their drainage basins the highland rivers weather acidic rocks whereas the others flow initially through basic effusives the ganga brahmaputra river system transports about 130 million tons of dissolved salts to the bay of bengal which is nearly 3 of the global river flux to the oceans the chemical denudation rates for the ganga and the brahmaputra basins are about 72 and 105 tons km yr 1 respectively which are factors of 2 to 3 higher than the global average the high denudation rate particularly in the brahmaputra is attributable to high relief and heavy rainfall

formation and variability of a northerly itcz in a hybrid coupled agcm continental forcing and oceanic atmospheric feedback abstract despite the equatorial symmetry of the annual mean insolation the intertropical convergence zone itcz and the collocated band of high sea surface temperature sst assume perennial northern latitudes over the eastern pacific and atlantic an atmospheric general circulation model is coupled with an intermediate ocean model to study continental forcing and oceanic atmospheric interaction that act to break the equatorial symmetry the model reaches a statistically symmetric mean state under perfectly symmetric conditions with the continental coasts running along meridians when a bulge of landmass is added to the eastern continent north of the equator it initiates a coupled ocean atmosphere wave front that propagates westward across the ocean basin cooling the ocean surface and suppressing deep convection on and south of the equator as a result the itcz shifts into the northern hemisphere in contrast to this basinwide response little latitudinal asymmetry develops in the coupled model when

sedimentary responses to the indian summer monsoon variations recorded in the southeastern andaman sea slope since 26ka abstract paleoenvironment and paleoclimate change in the andaman sea during the last 26 ka were reconstructed from high resolution records of grain size major elements and sr nd isotopes in core adm 9 the values of end 0 and 87sr 86sr were in good agreement with those of irrawaddy river sediments indicating a common source of origin two sensitive grain size intervals 3 4 7 5 and 16 8 21 2 m were identified the former was controlled primarily by sea level change whereas the latter was related to irrawaddy river discharge and south west current transport driven by the indian summer monsoon ism proxies of chemical weathering k al and terrigenous input ti ca coupled with sensitive grain size interval 16 8 21 2 m population revealed that the ism was weak during 15 26 ka bp and then strengthened gradually to a maximum during 7 9 ka bp subsequently the ism exhibited a generally declining trend to 2 ka bp the variation in the ism recorded in this work is consistent with ism variations observed in an open area in the northern indian ocean and adjacent continents implying the evolution of the asia summer monsoon since 26 ka

blue ocean paleoproductivity estimates from pelagic carbonate mass accumulation rates more than 95 of the carbon lost from the blue ocean reservoir to the sedimentary sink appears to be transferred as skeletal caco3 produced in the surface waters this skeletal caco3 carries a productivity signal which is much better preserved in the underlying pelagic carbonate sediments than that of the refractory organic carbon accompanying it here we develop a new method to quantify this signal in terms of organic carbon paleoproductivity using the sedimentary mass accumulation rates of pelagic carbonate these are converted into carbonate transit paleofluxes which are then translated into the corresponding transit fluxes of organic carbon via the carbonate to organic carbon ratios reported from deep moored sediment trap experiments in modern blue ocean environments paleoproductivity can then be estimated quantitatively by using published algorithms describing the relationship between the export production of particulate organic carbon at depth and primary productivity in the euphotic zone although our approach seems rather straightforward it contains several pitfalls the effects of which are highlighted by an example comprising three paleocene oligocene to recent pelagic carbonate sequences drilled during odp leg 121 in the eastern indian ocean although some extreme values are likely due to errors such as poorly constrained datum levels and dissolution peaks the results for the quaternary and neogene correlate well from site to site and are within the productivity range of present day low to medium latitude open oceans our method may provide an opportunity to actually quantify blue ocean primary productivity in sedimentary carbonate environments but requires validation by other more established ones

sedimentary responses to the sea level and indian summer monsoon changes in the central bay of bengal since 40 ka abstract we present a sedimentary multi index comprehensive study on sediment core bob 56 collected from the central bay of bengal bob with an attempt to understand the sedimentary processes and their responses to sea level change and the indian summer monsoon ism since the last glacial period we revealed the temporal evolution of terrigenous input and provided a brief discussion of the implications of our sedimentary indexes for ocean productivity then we proposed a simple depositional model in the central bob since the last glacial period as indicated by the geochemistry mineralogy and physical indexes including linear sedimentary rate lsr ti ca rb sr and quartz calcite ratios the terrigenous input was higher during the last glacial period than during the holocene period and the sea level is suggested to be responsible for this significant distinction through the depositional center transition in the bob at the glacial interglacial scale similar terrigenous input patterns with solar radiation and precipitation before 18 ka indicated that the monsoon controlled these situations at precession related scales synchronous changes with records in the north atlantic ocean during the last deglaciation and early holocene suggested terrigenous input responses to the climate changes that also recorded by high latitude sedimentary system at millennial scales indicated by the element caco3 ba and sr authigenic accumulation rates the paleoproductivity in the central bob was at a roughly equivalent level during the last glacial period and the holocene period different terrestrial nutrient inputs and ism related ocean surface stratifications were suggested to be responsible for the level of paleoproductivity this study provides a brief understanding of the sedimentary response to the climate and emphasizes the different roles of the sea level and ism in the central bob

late quaternary productivity changes in the western equatorial atlantic evidence from 230th normalized carbonate and organic carbon accumulation rates paleoproductivity changes in the western equatorial atlantic have been estimated from carbonate and marine organic carbon accumulation for the last 180 000 yr from a ceara rise sediment core geob 1523 1 accumulation rates were calculated by normalizing to excess 230th activity paleoproductivity from carbonate accumulation was estimated by a correlation between carbonate and organic carbon fluxes derived from sediment traps deployed in oligotrophic waters results indicate minor productivity changes varying around 30 gc m 2 yr 1 for organic carbon derived estimations and around 45 gc m 2 yr 1 for carbonate derived estimations suggesting that the study area remained a low productivity region throughout the time period examined maxima in western atlantic paleoproductivity occurred during the warm substages of glacials and interglacials in contrast to the eastern tropical atlantic where maxima are recorded in the cold substages this contrast might be caused by a deepening of the thermocline and nutricline in the west connected with a synchronous shallowing in the east the carbonate preservation record was examined for the last 380 000 yr based on variations in percent planktonic foraminiferal fragments and percent coarse fraction only minor carbonate dissolution above 3300 m water depth is observed except for three main dissolution events at isotope stages 4 8 4 and 10 considerable carbonate loss during these intervals is attributed to a decreased production of north atlantic deep water which is associated with vertical expansion of southern source deep water

sr nd isotopic evidence of terrigenous flux variations in the bay of bengal implications of monsoons during the last 34 000 years 1 sr and nd isotopic compositions of a sediment core from the bay of bengal are used to constrain the provenance and transport pathways of their terrigenous component during the 3 to 34 14c kyr bp the results clearly demonstrate a distinctly different source for detrital fluxes on the ninetyeast ridge from that of distal and western fan sediments there is a systematic pattern of climate related variability in 87sr 86sr and nd o values at the studied location pulses of low 87sr 86sr higher radiogenic nd and high silt content occurring at 5 7 kyr intervals suggest significant changes in the detrital source increased supply of irrawaddy derived sediments appears to be the dominant source for these pulses our results support the hypothesis that rapid cold events of north atlantic heinrich events are characterized by the intensified northeast monsoon

increasing chemical weathering in the himalayan system since the last glacial maximum continental chemical weathering is central in earth s surface biogeochemical cycles as it redistributes elements across reservoirs such as the crust and the oceans however the evolution of weathering through time and its response to external forcing such as changes in climate remain poorly constrained in this work a composite sediment record from the bay of bengal is used to document the evolution of chemical weathering in the himalayan system himalayan range and indo gangetic floodplain the world largest sediment conveyor to the oceans since the last glacial maximum lgm the degree of weathering of the sediments is documented using mobile to immobile ratios such as k si and h2o si as well as detrital calcite abundance robust weathering proxies are derived by correcting the chemical composition of sediment for sorting effects that occur during transport and deposition the bay of bengal record is also further compared to the chemical composition of modern river sediments from the ganga and brahmaputra basin weathering proxies all indicate that the sediments exported by the ganga and brahmaputra rivers became increasingly weathered over the past 21 kyr whereas sr nd and major elements suggest a constant sediment provenance in the system over the last 21 kyr these changes in the degree of weathering of the sediments show that the weathering flux exported by the system to the indian ocean during the lgm was significantly lower than at present and demonstrate that chemical weathering in continental scale basins such as the ganga and brahmaputra responds to late quaternary climate changes

shelf sedimentation off the ganges brahmaputra river system evidence for sediment bypassing to the bengal fan the nature of shelf sedimentation seaward of the world9s largest sediment dispersal system is examined by using sedimentological and geochronological techniques on a unique suite of sediment cores and grab samples sediments from the ganges brahmaputra river system are currently accumulating on the shelf in water depths of less than about 80 m forming a clinoform like deposit similar to subaqueous deltas found off other major river systems the highest sediment accumulation rates on the shelf occur near the head of the swatch of no ground a major submarine canyon that indents the shelf west of the present river mouths this observation together with textural data suggests that river sediments are transported seaward and westward and that the swatch of no ground is currently a major conduit for the transport of sediments from the bengal shelf

c4 plants decline in the himalayan basin since the last glacial maximum abstract the bengal fan turbiditic system supplied by the ganga brahmaputra river system provides an integrated record of himalayan system erosion thanks to minor inputs of marine organic matter and almost complete preservation of riverine organic carbon organic matter buried in bengal fan sediments is a proxy of himalayan basin paleo vegetation the active channel levee system of the middle fan documents the last 19 ka and allows the reconstruction of vegetation change in the himalayan basin since the last glacial maximum lgm we measured 13 c of organic carbon c org in order to track changes in the proportions of c3 and c4 plants in the himalayan basin from lgm to mid holocene 13 c of bulk c org shifts of 3 4 towards more negative values relative abundance of individual n alkanes reveals that terrestrial higher plant inputs represent a dominant fraction of c org buried in bengal fan sediments 13 c of higher plants biomarkers mimic that of bulk c org showing that the later can be used as continental paleo vegetation proxy 13 c negative shift from lgm to mid holocene mostly indicates the transition from a dominant input of c4 plants to a dominant input of c3 plants and therefore reveals that c4 plants were more abundant in the basin under glacial conditions vegetation repartition in the basin simulated using the caraib dynamic vegetation model is consistent with c org data the model indicates a dominance of c4 plants in the gangetic plain during the lgm while eastern part of the basin remains dominated by c3 plants the comparison between our data and proxies of regional paleo climate suggests that the large decline of c4 plants after the lgm was due to combined increase of atmospheric co 2 and humidity levels integrated record of himalayan basin paleo vegetation suggests more arid conditions during the lgm than during the mid holocene and agrees with reconstructions of the monsoon indicating stronger sw monsoon during interglacial and stronger ne monsoon during glacial periods

a note on the extent of glaciation throughout the himalaya during the global last glacial maximum abstract quantitative chronologies for the impressive glacial successions that occur throughout the himalaya have until recently been almost totally lacking within the last decade two new techniques have promised to remedy this situation these techniques optically stimulated luminescence and cosmogenic nuclide surface exposure dating enable the age of many glacial features to be determined and have allowed us to study the extent and timing of himalayan glaciation in the late quaternary new data show that the local last glacial maximum lgm occurred during the early part of the last glacial cycle in most areas during marine isotope stage 3 mis 3 mis 3 was a time of increased insolation when the south asian summer monsoon strengthened and penetrated further north into the himalaya the concomitant increased precipitation occurring as snow at high altitudes produced positive glacier mass balances thereby allowing glaciers to advance on the other hand during the global lgm 18 24 ka himalayan glaciation was very restricted in extent generally extending

major and trace element geochemistry of bay of bengal sediments implications to provenances and their controlling factors major and trace elements of sediments from a 13 m long piston core sk187 pc33 from the western bay of bengal have been investigated in this study to infer about the changes in provenances and related controlling factors during the last glacial interglacial period factor analysis of these geochemical dataset ascertains dominant role of riverine supply of sediments in regulating the geochemistry of sk187 pc33 sediments the al normalized major k and ti and trace elemental cu and cr ratios of these marine sediments fall within the ranges observed for their major provenances viz ganga brahmaputra and the godavari krishna gk rivers and depth profiles of these ratios showed significant variations with synchronous excursion at around the last glacial maxima lgm implying a change in their provenances with relatively reduced himalayan contribution during this climatic event relatively higher cia and ti ca ratios with lower k al ratios of these sediments during the holocene hint intense chemical weathering in the river basins in response to strengthened monsoon during this period inverse model calculation of al normalized elemental ratios of the sediments estimated an average sediment contribution of 66 13 and 34 13 from the himalayan and the peninsular indian rivers to the core site respectively consistent with the depth profiles of elemental ratios the estimated sediment contributions from the himalayan rivers are observed to decrease by 20 from the himalayan rivers particularly that of the ganga to the studied location during the lgm lowering of sediment supply from the himalaya ganga during the lgm is due to weakening of south west monsoon and reduction in available exposure area for weathering due to extent of glacier cover outcomes of this study underscore the strong linkage between erosion and climate

evaluating optical lightness as a proxy for carbonate content in marine sediment cores abstract optical lightness is increasingly being used as a proxy for the carbonate content of marine sediment we compared three measurements of optical lightness gray scale brightness and l to carbonate content to test the reliability of these measurements as carbonate content proxies in five piston cores from isotope stages 1 though 6 0 130 ka all measures of optical lightness are reasonable proxies of relative but not absolute changes in carbonate content in contrast in the upper sediments of odp hole 997a which are holocene to pliocene in age lightness values in only the top 10 m of the 180 m analyzed exhibit a strong correlation to carbonate content to better understand which factors control the optical lightness of sediments we analyzed samples in which carbonate content remained constant while the composition of three common clay minerals chlorite illite and kaolinite was varied kaolinite even at a concentration of 20 did not significantly change optical lightness however 20 illite reduced optical lightness by 30 and 20 chlorite reduced lightness by 20 we conclude that regional and temporal changes in the composition of the non carbonate sediment fraction may significantly alter the relationship between lightness and carbonate content we recommend that care must be taken when applying these measures to sediment sequences which span long time intervals or to sediment samples taken over a broad geographical areas

seasonality and interannual variability of particle fluxes to the deep bay of bengal influence of riverine input and oceanographic processes abstract results from sediment trap experiments conducted from october 1987 until november 1997 in the deep northern central and southern bay of bengal northern indian ocean revealed significant monsoon induced seasonal and interannual variations in total and component fluxes distinct regional differences occurred related to the variable effect of terrestrial input and the development of relatively small scaled oceanographic processes the enormous fluvial input to the bay during swm is reflected in the high average content of lithogenic matter between 39 at the northernmost and 12 6 at the most distal sampling site in the southern bay of bengal generally the riverine input supports a relative increase in the fluxes of biogenic opal at the stations nearest to the continent nbbt n cbbt terrestrial inputs determine seasonal and interannual variabilities lateral supply of lithogenic matter from the shelf regions lead to distinct increase of fluxes with depth high flux events of 300 mg m 2 d 1 consisting of 50 lithogenics occur in the central bay of bengal during nem and in the northern bay of bengal during swm in response to resuspension of shelf sediments and severe floods when riverine input by ganges brahmaputra and the offshore propagation of the river plume during swm is reduced the advection from an upwelling area along the east coast of india during ne sw intermonsoon becomes the most prominent control mechanism for both biogenic and lithogenic fluxes at nbbt n in the central bay of bengal cbbt fluxes are characterized by a bimodal pattern high carbonate dominated fluxes during swm and nem occur mainly due to wind induced nutrient supply whereas high opal rich fluxes during sw ne intermonsoon are controlled by both upwelling as well as supply of riverine and shelf derived matter wind forcing is the dominant factor controlling particle fluxes at the most distal stations nbbt s sbbt leading to distinct maxima during swm with high abundance of biogenic components here interannual variations of particle fluxes are associated with changes in marine productivity induced by oceanographic processes this is most obvious for sbbt where the advection of upwelled water from the west coast of india in some years results in highest swm fluxes and a distinct shift towards biogenic opal

late pleistocene desiccation of lake victoria and rapid evolution of cichlid fishes lake victoria is the largest lake in africa and harbors more than 300 endemic species of haplochromine cichlid fish seismic reflection profiles and piston cores show that the lake not only was at a low stand but dried up completely during the late pleistocene before 12 400 carbon 14 years before the present these results imply that the rate of speciation of cichlid fish in this tropical lake has been extremely rapid

south asian summer monsoon variability during the last 54 kyrs inferred from surface water salinity and river runoff proxies highlights ba ca and 18osw records of core sk 168 reveal distinct changes in sam intensity sam over the irrawaddy strengthened beginning at 18 ka leading observed changes in the arabian sea by 2 3 kyrs peak monsoon strength during the mid holocene in the andaman sea consistent with model simulations changes in upper ocean stratification indicate limited influence of nh insolation abstract the past variability of the south asian monsoon is mostly known from records of wind strength over the arabian sea while high resolution paleorecords from regions of strong monsoon precipitation are still lacking here we present records of past monsoon variability obtained from sediment core sk 168 gc 1 which was collected at the alcock seamount complex in the andaman sea we utilize the ecological habitats of different planktic foraminiferal species to reconstruct freshwater induced stratification based on paired mg ca and 18o analyses and to estimate seawater 18o 18osw the difference between surface and thermocline temperatures t and 18osw 18osw is used to investigate changes in upper ocean stratification additionally ba ca in g sacculifer tests is used as a direct proxy for riverine runoff and sea surface salinity sss changes related to monsoon precipitation on land our 18osw time series reveals that upper ocean salinity stratification did not change significantly throughout the last glacial suggesting little influence of nh insolation changes the strongest increase in temperature gradients between the mixed layer and the thermocline is recorded for the mid holocene and indicate the presence of a significantly shallower thermocline in line with previous work the 18osw and ba ca records demonstrate that monsoon climate during the lgm was characterized by a significantly weaker southwest monsoon circulation and strongly reduced runoff based on our data the south asian summer monsoon sam over the irrawaddyy strengthened gradually after the lgm beginning at 18 ka this is some 3 kyrs before an increase of the ba ca record from the arabian sea and indicates that south asian monsoon climate dynamics are more complex than the simple n s displacement of the itcz as generally described for other regions minimum 18osw values recorded during the mid holocene are in phase with ba ca marking a stronger monsoon precipitation which is consistent with model simulations

reconstructing chemical weathering physical erosion and monsoon intensity since 25 ma in the northern south china sea a review of competing proxies reconstructing the changing strength of the east asian summer monsoon has been controversial because different proxies many being indirect measures of rainfall tell contrasting stories about how this has varied over long periods of geologic time here we present new sr isotope grain size and clastic flux data and synthesize existing proxies to reconstruct changing chemical erosion in the northern south china sea since the oligocene using the links between weathering rates and monsoon strength established in younger sediments as a way to infer intensity chemical proxies such as k rb l al and the chemical index of alteration cia together with clay proxies like kaolinite illite chlorite show a steady decline in alteration after a sharp fall following a maximum at the mid miocene climatic optimum mmco 15 5 17 2 ma probably as a result of cooling global temperatures in contrast physical erosion proxies including bulk ti ca and clastic mass accumulation rates mar show peaks at 21 23 ma similar to 19 ma and 15 5 17 2 ma implying faster run off in the absence of drainage capture rates increase again likely driven by slightly increased run off after 13 ma but decrease after 8 ma which is identified as a period of summer monsoon weakening sr isotope composition correlates with hematite goethite and the spectral proxy crat to show stronger weathering linked to more monsoonal seasonality these proxies argue for a strengthening of the east asian monsoon after 22 23 ma followed by an extended period of monsoon maximum between 18 and 10 ma then weakening there is some suggestion that the summer monsoon may have strengthened since 3 4 ma after reaching a minimum in the pliocene c 2014 elsevier b v all rights reserved

high resolution greenland ice core data show abrupt climate change happens in few years the last two abrupt warmings at the onset of our present warm interglacial period interrupted by the younger dryas cooling event were investigated at high temporal resolution from the north greenland ice core project ice core the deuterium excess a proxy of greenland precipitation moisture source switched mode within 1 to 3 years over these transitions and initiated a more gradual change over 50 years of the greenland air temperature as recorded by stable water isotopes the onsets of both abrupt greenland warmings were slightly preceded by decreasing greenland dust deposition reflecting the wetting of asian deserts a northern shift of the intertropical convergence zone could be the trigger of these abrupt shifts of northern hemisphere atmospheric circulation resulting in changes of 2 to 4 kelvin in greenland moisture source temperature from one year to the next

high resolution elemental records from the south china sea and their paleoproductivity implications 1 the biogenic related elements ca sr ba p cd scavenged al and ti were analyzed by inductively coupled plasma mass spectrometry icp ms and inductively coupled plasma atomic emission spectrometry icp aes for core ns93 5 from the west slope of the south china sea terrestrial input as estimated from the accumulation of ti was higher during glacials than during interglacials carbonate accumulation rates are inversely related to those of terrestrial input suggesting higher production of calcareous phytoplankton during interglacials the accumulation patterns of authigenic sr ba p and cd match that of carbonate further indicating higher calcareous phytoplankton production during interglacials scavenged al and excess sio2 which is related to biogenic opal exhibit higher accumulation rates during glacials and correspond with changes in terrestrial input this indicates that terrestrial input driven is important to siliceous phytoplankton production but not for calcareous phytoplankton production as calcareous phytoplankton is the dominant component of the biogenic sediments in the south china sea particularly during interglacials previous inference of higher productivity in the south china sea during glacials based on only the biogenic opal proxy needs to be reconsidered

holocene itcz and indian monsoon dynamics recorded in stalagmites from oman and yemen socotra abstract high resolution oxygen isotope 18o profiles of holocene stalagmites from four caves in northern and southern oman and yemen socotra provide detailed information on fluctuations in precipitation along a latitudinal transect from 12 n to 23 n 18o values reflect the amount of precipitation which is primarily controlled by the mean latitudinal position of the itcz and dynamics of the indian summer monsoon ism during the early holocene rapidly decreasing 18o values indicate a rapid northward displacement in the mean latitudinal position of the summer itcz and the associated ism rainfall belt with decadal to centennial scale changes in monsoon precipitation correlating well with high latitude temperature variations recorded in greenland ice cores during the middle to late holocene the summer itcz continuously migrated southward and monsoon precipitation decreased gradually in response to decreasing solar insolation a trend which is also recorded in other monsoon records from the indian and east asian monsoon domains importantly there is no evidence for an abrupt middle holocene weakening in monsoon precipitation although abrupt monsoon events are apparent in all monsoon records they are short lived and clearly superimposed on the long term trend of decreasing monsoon precipitation for the late holocene there is an anti correlation between ism precipitation in oman and inter monsoon spring autumn precipitation on socotra revealing a possible long term change in the duration of the summer monsoon season since at least 4 5 ka bp together with the progressive shortening of the ism season gradual southward retreat of the mean summer itcz and weakening of the ism the total amount of precipitation decreased in those areas located at the northern fringe of the indian and asian monsoon domains but increased in areas closer to the equator

volcanogenic hydrothermal iron rich materials from the southern part of the central indian ocean basin abstract we report the occurrences of magnetite rich spherules ti rich particles and possibly nontronite recovered at 19 s and 76 e from the pelagic clay in the central indian ocean basin ciob it is proposed that the magnetite spherules were formed as a result of volcanic activity in this part of the ciob while the presence of nontronite suggests localized hydrothermal activity the magnetic spherules and the associated materials are compared with similar occurrences 555 km to the north in the vicinity of the 76 30 e fracture zone considering radiolarian age dating of the sediment the age of the volcano hydrothermal episode responsible for the formation of these materials seems to be between 425 and 650 ka it is inferred that there could have been widespread local volcanism in the ciob

monsoon influenced variation in productivity and lithogenic sediment flux since 110 ka in the offshore mahanadi basin northern bay of bengal abstract the indian monsoon drives seasonal changes in precipitation and weathering across india as well as circulation and productivity in the northern indian ocean variation in paleo monsoon intensity and its effect on productivity and lithogenic fluxes is poorly constrained in the bay of bengal in this paper we present analysis of a sediment record from the offshore mahanadi basin recovered during the indian national gas hydrate program expedition 01 site nghp 01 19b we reconstruct variation in biogenic and lithogenic components during the last 110 kyr using measurements of total organic carbon toc total nitrogen tn toc tn caco3 biogenic silica bsi 13toc 15tn bulk mineralogy from x ray diffraction bulk and lithogenic grain size distribution magnetic susceptibility bulk density and ca br and zr rb from x ray fluorescence xrf the mass accumulation rate mar of caco3 a function of marine productivity drastically increased between 70 and 10 ka and is correlated to previously documented elevated asian dust fluxes and increased bay of bengal salinity during a weakened southwest monsoon decreased freshwater input over this period likely diminished stratification allowing for increased mixing and nutrient availability thus enhancing productivity despite weaker southwest monsoon winds the mar of lithogenic material is highest during the holocene suggesting that sediment supply driven by monsoon intensity is a stronger control on margin sedimentation than sea level at the mahanadi basin over the entire record magnetic susceptibility and xrf zr rb are strongly correlated with caco3 suggesting higher primary mineral input under a weakened southwest monsoon toc tn and 13toc also increase under glacial conditions suggesting higher relative input of terrestrial c4 organic matter these results highlight the mahanadi basin as a supply dominated margin where terrigenous sedimentation is strongly influenced by monsoon intensity and that productivity is limited by variation in monsoon driven stratification on glacial interglacial timescales rather than a direct response to monsoon winds

retrospective dry bulk density estimates from southeast indian ocean sediments comparison of water loss and chloride ion methods abstract knowledge of absolute accumulation rates permits quantitative comparison between and within sediment components from cores of differing age and lithologic character dry bulk density is an essential parameter in the calculation of absolute accumulation rates dry bulk density measurements require a wet volume term and are best made when a core is first recovered such measurements were not routinely made on eltanin cores from the southeast indian ocean in an effort to recover this information we have estimated the dry bulk density of sixty samples from five eltanin cores using a water loss method and a chloride ion method which is independent of the state of desiccation of the cores based on the consistency of the results using these two independent methods we feel confident in our estimation of dry bulk density comparison of dry bulk density and caco 3 allowed us to develop the following non linear regression equation for estimating the dry bulk density based on caco 3 a more easily and accurately measured property 3 104x10 3 caco 3 2 2 176x10 3 caco 3 0 430 this equation can be used to estimate dry bulk density to within 0 097 g cm 3 thus providing the information needed to reliably calculate absolute accumulation rates our indian ocean dry bulk density equations are different from those developed by similar techniques for the pacific and atlantic oceans indicating that different lithologies necessitate the development of regional equations

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

distribution of c n and p in the sediments of the ganges brahmaputra meghna river system in the bengal basin the bengal basin is one of the geologically youngest and tectonically active drainage regimes of the world which includes the total lower ganges brahmaputra meghna gbm river system one of the highest sediment dispersal systems in the world the sediment load in this system comprises exclusively fine sand silt and clay river bed sediments and suspended matter from stations situated uniformly all over the basin have been analyzed in order to understand the spatial distribution and biogeochemical processing of the c n and p in the system among the ganges brahmaputra and meghna subbasins variations in total phosphorus tp and nitrogen tn contents in the bulk and 63 m fraction of the bed sediments are statistically insignificant but total carbon tc content varies significantly among the three subbasins there is a gradual increase in the concentration of tc from the meglna towards the ganges subbasin attributable to the nature of the floodplain and bank materials which supply major sediment load to the river channels the tp concentration is 2 to 5 times more in the suspended matter than that in any particle size fraction of the sediments although excellent correlation between corg and tn suggests their coorigin the influence of inorganic nitrogen is evident in very low c n ratios the c n ratio varies from 2 to 11 suggesting complete degradation of the organic matter and or enrichment of inorganic nitrogen in the sediments the plant available phosphorus pap varies from 1 78 to 6 98 of tp and indicates a significant anthropogenic contribution the corg tn and c n ratio in the bed sediments of the lower gbm system are in the range comparable with other river basins of the subcontinent

millennial scale trends in west pacific warm pool hydrology since the last glacial maximum models and palaeoclimate data suggest that the tropical pacific climate system plays a key part in the mechanisms underlying orbital scale and abrupt climate change atmospheric convection over the western tropical pacific is a major source of heat and moisture to extratropical regions and may therefore influence the global climate response to a variety of forcing factors the response of tropical pacific convection to changes in global climate boundary conditions abrupt climate changes and radiative forcing remains uncertain however here we present three absolutely dated oxygen isotope records from stalagmites in northern borneo that reflect changes in west pacific warm pool hydrology over the past 27 000 years our results suggest that convection over the western tropical pacific weakened 18 000 20 000 years ago as tropical pacific and antarctic temperatures began to rise during the early stages of deglaciation convective activity as inferred from oxygen isotopes reached a minimum during heinrich event 1 ref 10 when the atlantic meridional overturning circulation was weak pointing to feedbacks between the strength of the overturning circulation and tropical pacific hydrology there is no evidence of the younger dryas event in the stalagmite records however suggesting that different mechanisms operated during these two abrupt deglacial climate events during the holocene epoch convective activity appears to track changes in spring and autumn insolation highlighting the sensitivity of tropical pacific convection to external radiative forcing together these findings demonstrate that the tropical pacific hydrological cycle is sensitive to high latitude climate processes in both hemispheres as well as to external radiative forcing and that it may have a central role in abrupt climate change events

evolution of weathering patterns in the indo burman ranges over the last 280 kyr effects of sediment provenance on 87sr 86sr ratios tracer a high resolution study of mineralogy and major element geochemistry combined with sr and nd isotopes has been conducted on high sedimentation rate cores collected off the irrawaddy river mouth in the andaman sea and the bay of bengal to reconstruct the erosional and weathering history of the irrawaddy river basin in both cores nd 0 values imply that both glacial and interglacial sediments share a common crustal source the irrawaddy river strong glacial interglacial cycles are recorded by 87sr 86sr interglacial periods yield values between 0 713 and 0 717 whereas glacial periods show higher values between 0 717 and 0 719 variations of the pedogenic clays smectite and kaolinite to primary mineral feldspar quartz illite and chlorite ratios show strong precessional cycles suggesting a control by past changes in the summer monsoon intensity each increase in pedogenic clays content is also associated with a net loss of labile elements na k and ca from the detrital minerals under chemical weathering wet periods of summer monsoon reinforcement correspond to an increase in weathering of the irrawaddy plain soils and a decrease of 87sr 86sr ratio plotting 87sr 86sr versus 87rb 86sr gives a pseudo isochrons interpreted as a mixing line representing the strength of chemical weathering during glacial stages enhanced physical erosion induced by glacier scour and frost action in the highland of the irrawaddy river basins produced high volumes of unaltered rb rich minerals the low sea level of glacial times constricted the river to the main channel in the lower reaches and permitted an efficient transport of unaltered rb rich minerals with high radiogenic sr composition from the high relief of the indo burman ranges and the tibetan plateau to the indian ocean

late holocene vegetation and ocean variability in the gulf of oman fossil pollen and dinocyst records in marine sequences are frequently combined to reveal the response of vegetation and ocean conditions to changes in both regional and global climate in this study we analysed pollen and dinocysts within a clearly laminated sediment core off the iranian coast in the gulf of oman an extremely data poor area to reconstruct climatic change during the late holocene last 1900 years the vegetation record from southern iran indicates a replacement of savannah by desert formations at c 910 ce shortly after the islamic invasion and the subsequent collapse of the sassanid empire from c 910 to 1145 ce during the medieval climate anomaly mca the vegetation was heavily dominated by desert formations such as amaranthaceae caryophyllaceae asteraceae centaurea and calligonum in parallel in the gulf of oman the presence of impagidinium paradoxum indicates a lack of freshwater discharge into the ocean around this time the desert taxa of the mca were subsequently replaced by savannah formations at c 1145 ce comprised mainly of poaceae and cyperaceae corresponding to the little ice age lia indicating generally wetter climatic conditions a sudden increase in spiniferites ramosus 1 63 at c 1440 ce suggests an increase in the strength of the sw summer monsoon with increased freshwater discharge into the ocean at this time our data indicate that over the past two millennia the nw arabian sea region has alternated between contrasting climatic conditions with firstly a humid phase equivalent to the cultural period of the sassanid empire a significantly drier climate during the mca and a relatively wetter climate during the lia the mechanisms resulting in dry conditions during the mca in the middle east associated with the northward shift of the itcz and the intensification of the indian summer monsoon may be similar to those causing the dry conditions which dominated the early holocene in the near east our palaeoenvironmental proxy data support current observations that a globally anthropogenically induced warmer climate is likely to lead to increased drought severity in the middle east putting additional stress on governments already struggling with poverty and social tensions

modulation and amplification of climatic changes in the northern hemisphere by the indian summer monsoon during the past 80 k y high frequency suborbital variations dansgaard oeschger cycles characterize the climatic history of the northern hemisphere as observed in greenland ice cores deep sea sediments of the north atlantic the californian borderland the arabian sea the south china sea and the chinese loess area paleoceanographic data from core kl126 from the bay of bengal in combination with data from the other asian monsoonal areas indicate that the feedback processes involving snow and dust of the tibetan plateau vary the summer monsoon capacity to transport moisture into central south asia and into the atmosphere we postulate that the summer monsoon initiates amplifies and terminates these cycles in the northern hemisphere

sediment characteristics and transportation dynamics of the ganga river abstract understanding of river systems that have experienced various forcing mechanisms such as climate tectonics sea level fluctuations and their linkages is a major concern for fluvial scientists the 2525 km long ganga river derives its fluvial flux from northern part of the indian subcontinent and drops in the ganga brahmaputra delta and the bengal fan regions this paper presents a study of the ganga river sediments for their textural properties grainsize characteristics and transportation dynamics a suite of recently deposited sediments 189 bedload samples and 27 suspended load samples of the river and its tributaries was collected from 63 locations dry and wet sieve methods of grainsize analysis were performed and folk and ward s parameters were calculated transportation dynamics of the sediment load was assessed by means of channel hydrology flow sediment rating curves bedform mechanics grainsize images and cumulative curves textural properties of the bedload sediments of the ganga river tributaries originating from the himalaya orogenic belt the northern indian craton and the ganga alluvial plain regions are characterised by the predominance of fine to very fine sand medium to fine sand and very fine sand to clay respectively downstream textural variations in the bedload and suspended load sediments of the ganga river are therefore complex and are strongly influenced by lateral sediment inputs by the tributaries and channel slope at the base of the himalaya a very sharp gravel sand transition is present in which median grainsize of bedload sediments decreases from over 0 16 to 2 46 within a distance of 35 km downstream decline in mean grainsize of bedload sediments in the upper ganga river within the alluvial plain can be expressed by an exponential formula as mean grainsize in 0 0024 distance in kilometres from the himalayan front 1 29 it is a result of selective transport phenomena rather than of abrasion the condition attributed to channel competence with low gradient of 70 to 25 cm km coarsening of the bedload sediments in the middle segment of the river develops due to the coarse bedload sediments mean grainsize 1 8 2 2 supply from the tributaries of the northern indian craton region and increased unit stream power the ganga river sediments show a wide range of grainsize parameters bedload sediments mean grainsize 1 5 3 8 standard deviation 0 3 0 7 skewness 0 2 0 5 and kurtosis 0 8 2 4 suspended load sediments mean grainsize 2 9 5 0 standard deviation 0 6 1 6 skewness 0 6 0 4 and kurtosis 0 7 4 6 mean grainsize of the bedload sediments is 2 6 which is 1 3 units coarser than the suspended load sediments the cumulative grainsize curves of the bedload sediments show a distinct break in slope representing nearly 80 of the bedload sediment transported as graded suspension during the peak monsoon discharge most of the bedload sediments are transported as the discontinuous fine sandy graded suspension by the unidirectional unsteady shooting flow at a high transport rate about 8 106 tons d a model of sedimentation transportation at river channel is proposed the ganga river mobilises a total of 729 106 tons of sediments annually through a narrow zone within its river valley under the present hydrogeological conditions the river sedimentation is climatically controlled and is predicted to produce a 2000 km long 2 to 40 km wide and 25 to 50 m thick ribbon shaped well sorted symmetrically skewed fine sand body

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

the late oligocene early miocene himalayan belt constraints deduced from isotopic compositions of early miocene turbidites in the bengal fan abstract we present a mineralogical and isotopic study of early miocene turbidites from the bengal fan which are the oldest sediments recovered during odp leg 116 clay fractions are dominated by illite and chlorite and have low 18o 11 16 the clays are dominantly derived from a metamorphic precursor by physical erosion and have undergone only minor low t water rock exchange and chemical weathering sr and nd isotope analysis of silt and clay fractions and coarse muscovite biotite and feldspar fractions are remarkably similar to those of the presently exposed high himalaya crystalline hhc sequence the data show that a close analogue of the hhc was already subaerially exposed to active erosion during early miocene rb sr data on the biotite separates has been used to evaluate the time elapsed between cooling through the closure temperature for sr in biotite in the hhc ca 325 c and final sedimentation in the bengal fan despite the large uncertainties in the initial 87 sr 86 sr values of sedimentary mixtures our estimates of the elapsed time between cooling and deposition are short 4 14 ma assuming a transport time scale 1 ma deduced exhumation rates are in the same range of modern values 1 3 mm yr since ca 30 ma given that a the rocks exposed at the surface b the style of weathering and c rates of exhumation were similar to the present we infer that the factors controlling erosion of the early miocene himalayan belt were also similar to the present the data suggest that the early miocene himalayan belt had significant relief and induced orographic effects on precipitation similar to the modern mountain range it appears that the thrusting along the main central thrust mct or similar structures has uplifted metamorphic basement analogous to the present hhc at sufficiently high rate to maintain steep relief throughout miocene time despite high average erosion rates

sea level changes forced ice breakouts in the last glacial cycle new results from coral terraces abstract sea level cycles recorded by coral terraces at huon peninsula hp in papua new guinea match rapid climate changes that occurred between 30 000 and 65 000 years ago seen in greenland ice cores and marine sediments each cycle of 6000 7000 years ended with a sea level rise of 10 15 m lasting 1000 2000 years following a longer period of falling sea level precise dating shows that each rise corresponds to a heinrich episode of ice rafted detritus in north atlantic signalling massive ice outbreak from north america sea level may be the trigger that forced near synchronous breakouts of ice from north america and eastern greenland the hp sea level changes also correspond to similar cycles in benthic oxygen isotopes reported from the north atlantic which are too large to be explained entirely in terms of ice volumes jointly the sea level and isotope records suggest that the north atlantic deep ocean cooled as sea level fell and warmed as sea level rose in each 6000 year cycle

evaporation precipitation changes in the eastern arabian sea for the last 68 ka implications on monsoon variability 1 variations in sea surface temperature sst 18o of sea water 18ow and salinity were reconstructed for the past 68 ka using a sediment core aas9 21 from the eastern arabian sea eas in order to understand the changes in evaporation and precipitation associated with the monsoon system the mg ca derived sst record varies by 4 c it shows that marine isotope stage mis 4 was warmer than mis 3 that the last glacial maximum was 4 c cooler than the present and that there was a 2 c increase within the holocene mis 4 records higher 18ow and salinity values than mis 2 suggesting variable flow of low salinity bay of bengal flow into the eas during glacial periods the transition from mis 4 to mis 3 was marked with a conspicuous shift from higher to lower 18ow values which reflects a decrease in the evaporation precipitation budget in the eas perhaps due to the strengthening of southwest monsoon monsoon reconstructions based on 18ow reveal that monsoon driven precipitation was higher during mis 3 and mis 1 and was lower during mis 2 and mis 4 this is consistent with earlier monsoon reconstructions based on upwelling indices from the western arabian sea however the amplitude of monsoon fluctuations derived through upwelling indices and 18ow varies significantly which may indicate spatial variability of monsoon rainfall

the significance of large sediment supply active tectonism and eustasy on margin sequence development late quaternary stratigraphy and evolution of the ganges brahmaputra delta abstract borehole data from the ganges brahmaputra delta system unveil an intriguing late quaternary history controlled by immense sediment discharge tectonics and eustasy sea level first intersected a major portion of the lowstand surface 10 000 11 000 cal yr bp marking the onset of sediment trapping and delta growth despite rapid sea level rise 1 cm yr sediment load was sufficient to maintain relative shoreline stability during this time by 7000 cal yr bp accommodation was quickly infilled with slowed sea level rise leading to upstream channel migration and widespread dispersal of sands this forced coastal progradation along the western delta front where the ganges was situated and much of the river s fine grained discharge bypassed the subaerial delta and formed a prograding deltaic clinoform on the shelf concurrently brahmaputra sediments were sequestered to an inland tectonic basin thus starving the adjacent shoreline and leading to transgression along the eastern delta by 5000 cal yr bp the two rivers had migrated or changed course to discharge along the eastern delta shoreline which began to prograde into what is now the modern river mouth estuary present delta configuration appears to have developed by 3000 cal yr bp evolution of the tectonically active ganges brahmaputra g b system reveals important similarities and differences with other deltas overall facies succession follows that of basic models progressing from an alluvial valley to coastal marine delta front to a prograding subaerial delta plain however the timing thickness and controls of these deposits differ immense sediment discharge from the ganges and brahmaputra rivers allowed initial delta growth 2000 3000 yr earlier than the global average despite debouching onto a canyon incised high energy margin subsequently a thick 50 m transgressive systems tract was formed during the early holocene phase of delta aggradation contrasting with extensive shoreline retreat documented along most margins highstand progradation of coastal and shelf sequences ensued by the middle holocene but subsiding inland basins also favored accumulation of a thick to 40 m highstand sequence in the lower floodplains unlike many other delta systems subsidence in the subaerial g b delta is not dominated by compaction but rather by plate driven tectonic processes that generate rates up to 4 mm year overall the huge sediment load tectonic subsidence major seismic events and a nearshore canyon system have led to widespread sediment dispersal and sequence formation across the subaerial delta shelf and deep sea bengal fan throughout the late quaternary

rapid sea level fall and deep ocean temperature change since the last interglacial period we have dated huon peninsula papua new guinea and barbados corals that formed at times since the last interglacial period applying both 230 th and 231 pa dating techniques as a test of age accuracy we show that marine isotope stage mis 5e ended prior to 113 1 8 0 7 kyr when sea level was 319 m during mis 5b sea level was 357 m at 92 6 8 0 5 kyr having dropped about 40 m in approximately 10 kyr during the mis 5c 5b transition sea level then rose more than 40 m during the mis 5b 5a transition also in about 10 kyr mis 5a lasted until at least 76 2 8 0 4 kyr at a level of 324 m at that time combined with earlier data that places mis 4 sea level at 381 m at 70 8 kyr our late mis 5a data indicate that sea level fell almost 60 m in less than 6 kyr 10 6 m kyr during the mis 5 4 transition the magnitude of the drop is half that of the glacial interglacial amplitude and approximatelyequivalent to the volume of the present dayantarctic ice sheet during this interval the minimum average rate of net continental ice accumulation was 18 cm yr likely facilitated by efficient moisture transport from lower latitudes at three specific times 60 6 8 0 3 50 8 8 0 3 and 36 8 0 2 kyr during mis 3 sea level was between 385 and 374 m sea level then dropped to 3107 m at 23 7 8 0 1 kyr early in mis 2 before dropping further to last glacial maximum lgm values and then rising to present values during the last deglaciation times of rapid sea level drop correspond to times of high winter insolation at low northern latitudes and high winter latitudinal gradients in northern hemisphere insolation supporting the idea that these factors mayhave resulted in high water vapor pressure in moisture sources and efficient moisture transport to high latitude glaciers therebycontributing to glacial buildup we combined our sea level results with deep sea n 18 o records as a means of estimating the temperature and ice volume components in the marine n 18 o record this analysis confirms large deep ocean temperature shifts following mis 5e and during termination i deep ocean temperatures changed bymuch smaller amounts between mis 5c and 2 maximum temperature shift in the deep pacific is about 2 whereas the shift at a site in the atlantic is 4 under glacial conditions temperatures at both sites are near the freezing point the shift in the atlantic is likelycaused bya combination of changing proportions of northern and southern source waters as well as changing temperature at the sites where these deep waters form

sedimentary system response to the global sea level change in the east china seas since the last glacial maximum abstract the east china seas ecs is one of the world s largest continental shelf seas based on the combination of global sea level change and sequence stratigraphy we systematically investigated the evolution of sedimentary system in the ecs since the last glacial maximum lgm we have defined the transgressive boundary layer and constructed several sedimentary models of the ecs on the sequence stratigraphy and evolution of tidal sand ridges since the lgm and sediment source to sink during the high sea level the result shows that the ecs represent a typical case for large scale continental shelf response to the global sea level change three sedimentary system tracts had been formed in the ecs since the lgm first is the lowstand system tract corresponding to the late of last glaciation and lgm 23 15 4 cal kyr b p the progressive wedge occurred along the okinawa trough slope and the paleo coastal zone pcz along the continental shelf edge second is the transgressive system tract corresponding to the last deglaciation 15 4 7 cal kyr b p a large scale transgressive boundary layer and tidal sand ridges were formed in this stage third is the highstand system tract corresponding to the high sea level since 7 cal kyr b p the eddy mud coastal current mud present tidal sand ridge delta tidal flat and beach have been accumulating since then the global sea level change after lgm can be divided into seven phases of which four rapidly rising phases rrp i ii iii iv and three slowly rising phases srp i ii iii are distinguished the tidal sand ridges were formed in the srp and transgressive boundary layer in the rrp the tidal sand ridges can be divided into three types including radicalized channel and emanative the modern circulation current system of the ecs had been built in the end of the last deglaciation the effect of sediment source to sink in the ecs is closely correlative to the current system driven by the interaction of the east asian monsoon and kuroshio the major sediment source is from the river discharge of the huanghe and changjiang river and coastal resuspension the muddy sediment in the eddy and coastal current which cover the tidal sand ridges and transgressive boundary layer is a major sediment sink in the modern ecs

dominant northern hemisphere climate control over millennial scale glacial sea level variability abstract based on a radiocarbon and paleomagnetically dated sediment record from the northern red sea and the exceptional sensitivity of the regional changes in the oxygen isotope composition of sea water to the sea level dependent water exchange with the indian ocean we provide a new global sea level reconstruction spanning the last glacial period the sea level record has been extracted from the temperature corrected benthic stable oxygen isotopes using coral based sea level data as constraints for the sea level oxygen isotope relationship although the general features of this millennial scale sea level records have strong similarities to the rather symmetric and gradual southern hemisphere climate patterns we observe in constrast to previous findings pronounced sea level rises of up to 25 m to generally correspond with northern hemisphere warmings as recorded in greenland ice core interstadial intervals whereas sea level lowstands mostly occur during cold phases corroborated by climber 2 model results the close connection of millennial scale sea level changes to northern hemisphere temperature variations indicates a primary climatic control on the mass balance of the major northern hemisphere ice sheets and does not require a considerable antarctic contribution

timing duration and transitions of the last interglacial asian monsoon thorium 230 ages and oxygen isotope ratios of stalagmites from dongge cave china characterize the asian monsoon and low latitude precipitation over the past 160 000 years numerous abrupt changes in 18o 16o values result from changes in tropical and subtropical precipitation driven by insolation and millennial scale circulation shifts the last interglacial monsoon lasted 9 7 1 1 thousand years beginning with an abrupt less than 200 years drop in 18o 16o values 129 3 0 9 thousand years ago and ending with an abrupt less than 300 years rise in 18o 16o values 119 6 0 6 thousand years ago the start coincides with insolation rise and measures of full interglacial conditions indicating that insolation triggered the final rise to full interglacial conditions

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