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

carbon and nitrogen loss rates during aging of lake sediment changes over 27 years studied in varved lake sediment we used a collection of ten freeze cores of annually laminated varved lake sediment from nylandssjon in northern sweden collected from 1979 to 2007 to follow the long term loss of carbon c and

indian monsoon variability in the last 2000 years as inferred from benthic foraminifera abstract the effect of ambient conditions on living rose bengal stained benthic foraminifera has been studied from the shelf and slope of the central western bay of bengal to assess the applicability of temporal changes in benthic foraminiferal morpho groups angular asymmetrical and rounded symmetrical to reconstruct past monsoon changes we report that the riverine influx and associated processes control the relative abundance of angular asymmetrical aabf and rounded symmetrical rsbf benthic foraminiferal morpho groups in the central western bay of bengal subsequently temporal variations in relative abundance of aabf in a gravity core collected from outfall region of the pennar river are used to reconstruct decadal scale past monsoon variability during the last 1887 years an increased monsoon discharge is observed during the medieval warm period mwp and lower during the little ice age lia the periodic changes with a frequency of 123 and 238 years are also identified indicating a close relationship between monsoon and solar activity

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 indian monsoon and its variability for over 300 years the monsoon has been viewed as a gigantic land sea breeze it is shown in this paper that satellite and conventional observations support an alternative hypothesis which considers the monsoon as a manifestation of seasonal migration of the intertropical convergence zone itcz with the focus on the indian monsoon the mean seasonal pattern is described and why it is difficult to simulate it is discussed some facets of the intraseasonal variation such as active weak cycles break monsoon and a special feature of intraseasonal variation over the region namely poleward propagations of the itcz at intervals of 2 6 weeks are considered vertical moist stability is shown to be a key parameter in the variation of monthly convection over ocean and land as well as poleward propagations special features of the bay of bengal and the monsoon brought out by observations during a national observational experiment in 1999 are briefly described

glacial to holocene swings of the australian indonesian monsoon the australian indonesian monsoon is an important component of the climate system in the tropical indo pacific region 1 however its past variability relation with northern and southern high latitude climate and connection to the other asian monsoon systems are poorly understood here we present high resolution records of monsoon controlled austral winter upwelling during the past 22 000 years based on planktic foraminiferal oxygen isotopes and faunal composition in a sedimentary archive collected offshore southern java we show that glacial interglacial variations in the australian indonesian winter monsoon were in phase with the indian summer monsoon system consistent with their modern linkage through cross equatorial surface winds likewise millennial scale variability of upwelling shares similar sign and timing with upwelling variability in the arabian sea on the basis of element composition and grain size distribution as precipitation sensitive proxies in the same archive we infer that austral summer monsoon rainfall was highest during the bolling allerod period and the past 2 500 years our results indicate drier conditions during heinrich stadial 1 due to a southward shift of summer rainfall and a relatively weak hadley cell south of the equator we suggest that the australian indonesian summer and winter monsoon variability were closely linked to summer insolation and abrupt climate changes in the northern hemisphere the seasonality of the global monsoon is of central importance to the global hydrologic cycle and its environmental influence on human societies palaeoclimate reconstructions generally agree that the strengths of the east asian monsoon and the indian monsoon are tightly coupled to the northern hemisphere climate through zonal migrations of the monsoon convection centres also interpreted as intertropical convergence zone itcz migration 26 the mechanism of the australianindone

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

a mid to late holocene record of palaeoclimatic changes from nal sarovar a palaeodesert margin lake in western india with a view to obtain palaeoclimatic data from a climatically sensitive region we have studied core samples from nal sarovar a large shallow lake lying within the palaeodesert margin of thar in western india a combination of c n ratios and 13c on a radiocarbon dated core section have been used as climatic proxies a high resolution record extending back to ca 6 6 ka bp has been reconstructed the data indicate that in the past climate has varied from drier to wetter than present on time scales of few hundreds to few thousands of years there are however significant differences on the timing of these wet and dry periods when compared with the available data from lakes farther north in rajasthan further it looks unlikely that during the 6 6 ka the catchment areas of nal sarovar experienced such a significant increase in rainfall as has been suggested for the rajasthan lakes interestingly drier periods in nal sarovar data appear to correlate well with periods of glacier expansion in eurasia indicating that the palaeoclimatic variations recorded in nal sarovar are a regional feature 1997 john wiley sons ltd

northeast monsoon variations during the holocene inferred from palaeochannels and active channels of the palar river basin southern peninsular india the present day palar river and its palaeochannel located in the southern peninsular india were investigated with a multidisciplinary approach the main aim of the study was to reconstruct the palaeoenvironment history of the palar river basin and to delineate the role of holocene fluctuations that played a major role in the geomorphological evolution of the region since the holocene period the results obtained based on sedimentary facies analysis supported by elemental concentrations and optically stimulated luminescence osl dates reveal distinct seven climatic phases since the past 10 ka phase 1 signifies a very high precipitation as attested by the low cwi with high rb sr ratio subsequent to phase 1 a decreasing trend in the northeast monsoon rainfall nemr is observed phase 2 phase 3 4 83 3 59 ka reflects a decrease in nemr further supported by low mn al mg al and chemical index of alteration cia values phase 4 3 59 ka is marked by high sand flux higher k al ti al rb sr and ba

variations of indian monsoon precipitation during the last 32 kyr reflected in the surface hydrography of the western bay of bengal hydrography of the bay of bengal is highly influenced by the river runoff and rainfall during the southwest monsoon we have reconstructed 18 osw sea surface salinity and sea surface temperature sst changes in the bay of bengal by using paired measurements of 18 o and mg ca in a planktonic foraminifera species globigerinoides ruber from core sk218 1 in the western bay of bengal in order to understand the rainfall variability associated with southwest monsoon over the past 32 kyr our sst reconstructions reveal that bay of bengal was 3 2 c cooler during the lgm as compared to present day temperature and a 3 5 c rise in sst is documented from 17 to 10 ka both sst and 18 osw exhibit greater amplitude fluctuations during mis 2 which is attributable to the variability of ne monsoon rainfall and associated river discharge into the bay of bengal in association with strong seasonal temperature contrast on set of strengthening phase of sw monsoon was started during bolling allerod as evidenced by the low 18 osw values 14 7 ka 18 osw show consistently lower values during holocene with an exception around 5 ka which suggests that the freshening of bay of bengal due to heavy precipitation and river discharge caused by strong sw monsoon results of this study signify that the maximum fluctuations of the ne monsoon rainfall during mis 2 appear to be controlled by the

elastic uplift in southeast greenland due to rapid ice mass loss this is the publisher s version also available electronically from http onlinelibrary wiley com

seasonal temperature variability of the neoglacial 3300 2500 bp and roman warm period 2500 1600 bp reconstructed from oxygen isotope ratios of limpet shells patella vulgata northwest scotland abstract seasonal sea surface temperature variability for the neoglacial 3300 2500 bp and roman warm period rwp 2500 1600 bp which correspond to the bronze and iron ages respectively was estimated using oxygen isotope ratios obtained from high resolution samples micromilled from radiocarbon dated archaeological limpet patella vulgata shells the coldest winter months recorded in neoglacial shells averaged 6 6 0 3 c and the warmest summer months averaged 14 7 0 4 c one neoglacial shell captured a year without a summer which may have resulted from a dust veil from a volcanic eruption in the katla volcanic system in iceland rwp shells record average winter and summer monthly temperatures of 6 3 0 1 c and 13 3 0 3 c respectively these results capture a cooling transition from the neoglacial to rwp which is further supported by earlier studies of pine history in scotland pollen type analyses in northeast scotland and european glacial events the cooling transition observed at the boundary between the neoglacial and rwp in our study also agrees with the abrupt climate deterioration at 2800 2700 bp also referred to as the subboreal subatlantic transition and therefore may have been driven by decreased solar radiation and weakened north atlantic oscillation conditions

a conceptual model for soils containing large gas bubbles offshore site investigations have indicated the presence of undissolved gas bubbles in the soils forming the sea bed at various locations throughout the world the gas bubbles are typically much larger than the normal void spaces so they cannot be considered as occluded bubbles within the pore water which simply change the compressibility of the pore fluid the effect of these large bubbles on the engineering properties of the soil must be understood if offshore construction is to take place in areas of gas bearing sediments this paper describes a conceptual model for soils containing large gas bubbles the model consists of a matrix of saturated soil surrounding isolated gas filled cavities the cavities forming the bubble sites are fixed within the soil so that gas drainage occurs only by the movement of dissolved gas the behaviour of the model is complicated by the processes of localized consolidation and bubble flooding des recherches conduites en mer ont indique qu il y a partout dans le monde d

high latitude holocene paleosecular variation and magneto stratigraphic correlation between two lakes on spitsbergen 78 n abstract paleomagnetic signals in cores from two nearby lakes linnevatn and skardtjonn on spitsbergen 78 n record high latitude geomagnetic field variations for the last 10000 years although the paleomagnetic signal in the lake linnevatn core has probably been modified by subsampling effects application of a latitude invariant transformation procedure yields logs with directional amplitudes similar to the transformed holocene paleosecular variation master curve from the uk stratigraphic correlations based on pattern recognition suggest maximum ages of the lacustrine sediments in agreement with 14c age determinations age depth curves based on more than six magnetic datum horizons from each core reveal an abrupt increase in sedimentation rate in linnevatn from about 0 4 mm year 1 to about 0 8 mm year 1 around 2500 b p vertical inclinations in both cores between about 3500 and 6000 b p are interpreted to reflect a stationary magnetic pole in the region of the sampling sites this adds further arguments for the proposed sudden dipole shift recognized around 3500 b p in paleomagnetic records from high latitude 63 n lacustrine sediments in alaska

effects of dissociation on the shear strength and deformation behavior of methane hydrate bearing sediments abstract a series of tests were conducted in order to investigate the shear strength and deformation behavior of methane hydrate bearing sediments during dissociation using the thermal recovery method or depressurization method an innovative temperature controlled high pressure triaxial apparatus which can reproduce the in situ conditions of hydrate reservoirs was used the results indicate that 1 the failure strength of isotropically consolidated methane hydrate bearing sediments which dissociated completely using the thermal recovery method is less than that of pure toyoura sand however the initial stiffness and volumetric strain are higher than that of pure toyoura sand 2 the thermal recovery method will cause the failure of methane hydrate bearing sediments when the axial load is higher than the strength of methane hydrate bearing sediments after dissociation 3 the depressurization method will not cause collapse of methane hydrate bearing sediments during depressurization however water pressure recovery will lead to failure when the axial load is larger than the strength of the methane hydrate bearing sediments after dissociation 4 the depressurization rate shows little effect on the ultimate deformation of methane hydrate bearing sediments while the initial deformation rate increases with increasing depressurization rate 5 the larger the reduction of pore pressure the larger axial strain and volumetric strain

palaeoclimatic interpretation of high resolution oxygen isotope profiles derived from annually laminated speleothems from southern oman high resolution stable isotope profiles of three contemporaneously deposited stalagmites from a shallow cave in southern oman provide an annually resolved record of indian ocean monsoon rainfall variability for the past 780 years uranium series age dating and counts of annual growth bands enable an excellent age calibration although modern speleothems do not grow in perfect isotopic equilibrium oxygen isotope ratios 18o are a proxy for the amount of monsoon rainfall this is supported by the statistically significant correlation between 18o and the thickness of annual bands whereas 18o is inversely correlated with annual band thickness additionally overlapping 18o profiles are very similar in pattern and range indicating that sample specific noise did not blur the climatic signal the longest oxygen isotope profile derived from stalagmite s3 clearly shows the transition at 1320 ad from a generally wetter medieval warm period to a drier little ice age that lasted from approximately ad 1320 1660 in southern oman the decrease in monsoon rainfall since the 1960s is also obvious in meteorological records from northern africa and india indicating that our speleothem based rainfall records do not only reflect local monsoon rainfall variability

the late pleistocene and holocene stratigraphy and paleolimnology of lakes kivu and tanganyika abstract evidence from diatoms chemistry and sedimentology shows that lakes kivu and tanganyika experienced late pleistocene low stands 86 to 300 m for kivu and 250 to 350 m for tanganyika both lakes had higher 2 10 fold sedimentation rates prior to 11 500 yr b p about 9900 yr b p upwelling became important in southern lake tanganyika which had been deepening for at least several millenia by 9400 yr b p kivu had become deep and dilute with overflow via the ruzizi river to lake tanganyika southern lake tanganyika became more stably stratified about 5200 yr b p volcanism and hydrothermal activity in kivu began about 5000 yr b p and the salinity reached 3 ppt and the lake became strongly stratified the ruzizi river outflow was interrupted from 3500 yr b p until recently the sedimentary record implies that sudden hydrothermal activity and sublacustrine volcanism in kivu has probably been the cause of its impoverished fauna these results show that high lake levels in the eastern rift of africa from 10 000 to 7000 yr b p were paralleled in the western rift given the great volumes of these lakes climate has not caused great variations in salinity the diatom floras however have been remarkably sensitive to changes in stratification and nutrient supply volcanism has been a major force in the limnological and biological evolution of lake kivu while both kivu and tanganyika have responded to changes in precipitation and wind stress

sediment undulations induced by free gas in muddy marine sediments a modeling approach 1 sediment undulations observed on the continental shelf in muddy prodeltas are often marked by the presence of gas in the upslope location the growth and migration of bubbles within fine grained muddy sediments are associated with sediment fracturing that damages the sediment and changes its effective mechanical properties the presented theoretical investigation demonstrates by modeling that undulations may be induced by creep deformations downslope from the region with gas presence comparison of the dimensions of the modeled undulations with the observed ones suggests that the undulations may be enhanced over time by different processes e g by the different types of the sediment deposition

corrigendum to introduction holocene climate and cultural evolution in late prehistoric early historic west asia quaternary research 66 2006 372 387

holocene climate and cultural evolution in late prehistoric early historic west asia abstract the precipitation climatology and the underlying climate mechanisms of the eastern mediterranean west asia and the indian subcontinent are reviewed with emphasis on upper and middle tropospheric flow in the subtropics and its steering of precipitation holocene climate change of the region is summarized from proxy records the indian monsoon weakened during the holocene over its northernmost region the ganges and indus catchments and the western arabian sea southern regions the indian peninsula do not show a reduction but an increase of summer monsoon rain across the holocene the long term trend towards drier conditions in the eastern mediterranean can be linked to a regionally complex monsoon evolution abrupt climate change events such as the widespread droughts around 8200 5200 and 4200 cal yr bp are suggested to be the result of altered subtropical upper level flow over the eastern mediterranean and asia the abrupt climate change events of the holocene radically altered precipitation fundamental for cereal agriculture across the expanse of late prehistoric early historic cultures known from the archaeological record in these regions social adaptations to reduced agro production in both dry farming and irrigation agriculture regions are visible in the archaeological record during each abrupt climate change event in west asia chronological refinement in both the paleoclimate and archaeological records and transfer functions for both precipitation and agro production are needed to understand precisely the evident causal linkages

a holocene late pleistocene geomagnetic inclination record from grandfather lake sw alaska summary our study of lake sediments from grandfather lake in sw alaska n59 8181 w158 5597 yields the first geomagnetic inclination record for alaska that spans the entire holocene the record is based on three overlapping sets of piston cores and is well dated by seven ams radiocarbon dates its magnetic component consists of psd 5 15 m magnetite that occurs in concentrations ranging from 10 to 1000 ppm some samples may also contain titanomagnetite tm30 as a minor component variations in the concentration of magnetic minerals are caused by changes in sediment source and organic productivity the magnetic inclination record shows several features between present and 15 ka bp which shed light on the short term behaviour of the geomagnetic field at high latitudes and can be used for site correlations a distinct drop in inclination near 12 ka bp is a record of a possible local magnetic excursion

holocene east asian monsoonal precipitation pattern revealed by grain size distribution of core sediments of daihai lake in inner mongolia of north central china abstract two sediment cores recovered in the central part of daihai lake in north central china were analysed at 2 to 4 cm intervals for grain size distribution grain size distributions of the lake sediments are inferred to be a proxy for past changes in east asian monsoon precipitation such that greater silt size percentage and higher median grain size reflect increased monsoonal precipitation rates the grain size record of daihai lake sediments spanning the last ca 10 000 yr indicates that the monsoonal precipitation in the lake region can be divided into three stages the early middle and late holocene during the early holocene before ca 7900 cal yr bp the median grain size md and the silt fraction content were relatively low and constant suggesting relatively low precipitation over the lake region the middle holocene between ca 7900 and 3100 cal yr bp was marked by intensified and highly variable monsoonal precipitation as indicated by high and variable md values and silt contents of the lake sediments during this period average precipitation rate gradually increased from ca 7900 to 6900 cal yr bp displayed intense oscillations between ca 6900 and 4400 cal yr bp and exhibited a decreasing trend while fluctuating from ca 4400 to 3100 cal yr bp although generally high during the middle holocene both the md and the silt content assumed distinctly low values at the short intervals of ca 6500 6400 6000 5900 5700 5600 4400 4200 cal yr bp implying that monsoonal precipitation might have been significantly reduced during these intervals during the late holocene since ca 3100 cal yr bp grain size values suggest that precipitation decreased however during the late holocene relatively higher md values and silt contents occurring between ca 1700 to 1000 cal yr bp may denote an intensification of hydrological cycles in the lake area changes in the east asian monsoonal precipitation were not only directly linked with the changing seasonality of solar insolation resulting from progressive changes in the earth s orbital parameters but also may have been closely related to variations in the temperature and size of the western pacific warm pool in the intensity of the el nino southern oscillation and in the path and strength of the north equatorial current in the western pacific

indian monsoon variations during three contrasting climatic periods the holocene heinrich stadial 2 and the last interglacial glacial transition in contrast to the east asian and african monsoons the indian monsoon is still poorly documented throughout the last climatic cycle last 135 000 years pollen analysis from two marine sediment cores nghp 01 16a and nghp 01 19b collected from the offshore godavari and mahanadi basins both located in the core monsoon zone cmz reveals changes in indian summer monsoon variability and intensity during three contrasting climatic periods the holocene the heinrich stadial hs 2 and the marine isotopic stage mis 5 4 during the ice sheet growth transition during the first part of the holocene between 11 300 and 4200 cal years bp characterized by high insolation minimum precession maximum obliquity the maximum extension of the coastal forest and mangrove reflects high monsoon rainfall this climatic regime contrasts with that of the second phase of the holocene from 4200 cal years bp to the present marked by the development of drier vegetation in a context of low insolation maximum precession minimum obliquity the historical period in india is characterized by an alternation of strong and weak monsoon centennial phases that may reflect the medieval climate anomaly and the little ice age respectively during the hs 2 a period of low insolation and extensive iceberg discharge in the north atlantic ocean vegetation was dominated by grassland and dry flora indicating pronounced aridity as the result of a weak indian summer monsoon the mis 5 4 glaciation also associated with low insolation but moderate freshwater fluxes was characterized by a weaker reduction of the indian summer monsoon and a decrease of seasonal contrast as recorded by the expansion of dry vegetation and the development of artemisia respectively our results support model predictions suggesting that insolation changes control the long term trend of the indian monsoon precipitation but its millennial scale variability and intensity are instead modulated by atmospheric teleconnections to remote phenomena in the north atlantic eurasia or the indian ocean

dinoflagellate cyst distribution in sediments of western bay of bengal role of sea surface conditions bay of bengal is a shallow marine basin exposed to seasonal fluctuation in precipitation and run off thus salinity temperature nutrient and productivity vary along the latitudinal and onshore offshore gradient in the bay of bengal these parameters directly affect primary productivity including that of dinoflagellate cysts the spatial distribution of organic walled dinoflagellates cyst is studied in the 50 surface samples of eight transects from the western bay of bengal to infer variation in the environmental conditions in the region the cyst diversity consists of 40 taxa with an overall high dominance of protoperidinioid cysts over gonyalaucoides based on the study distinct onshore and offshore dinocyst assemblages are identified the high productive coastal upwelling region is characterised by the dominance of gonyalaucoid dinocyst species bitectatodinium spongium zonneveld 1997 zonneveld and jurkschat 1999 indicating its adaptability to the fluctuating salinity and high nutrient conditions the outer shelf to middle slope regions of western bay of bengal is dominated by the protoperidinioid species this is in contrast to the gonyalaucoid dinocyst assemblages of the outer shelf to middle slope regions in other oceans since protoperidinioids prefer high nutrient and reducing environmental conditions for growth and preservation their presence suggest high nutrient availability due to the river discharge and low oxygen condition in the slope region in bay of bengal statistical analyses of the sea surface parameters and dinoflagellate cyst abundance data indicate that salinity and silicates as a major source of nutrient played a major role in the distribution of dinoflagellate cyst in the bay of bengal

molecular proxies for paleoclimatology we summarize the applications of molecular proxies in paleoclimatology marine molecular records especially are proving to be of value but certain environmentally persistent compounds can also be measured in lake sediments loess deposits and ice cores the fundamentals of this approach are the molecular parameters the compound abundances and carbon hydrogen nitrogen and oxygen isotopic contents which can be derived by the analysis of sediment extracts these afford proxy measures which can be interpreted in terms of the conditions which control climate and also reflect its operation we discuss two types of proxy those of terrigenous and those of aquatic origin and exemplify their application in the study of marine sediments through the medium of ten case studies based in the atlantic mediterranean and pacific oceans and in antarctica the studies are mainly for periods in the present the holocene and particularly the last glacial interglacial but they also include one study from the cretaceous the terrigenous proxies which are measures of continental vegetation are based on higher plant leaf wax compounds i e long chain circa c30 hydrocarbons alcohols and acids they register the relative contributions of c3 vs c4 type plants to the vegetation in the source areas the two marine proxies are measures of sea surface temperatures sst the longer established one u37k is based on the relative abundances of c37 alkenones photosynthesized by unicellular algae members of the haptophyta the newest proxy tex86 is based on c86 glycerol tetraethers gdgts synthesized in the water column by some of the archaeal microbiota the crenarchaeota

geochemical cycling of redox sensitive metals in sediments from lake malawi a diagnostic paleotracer for episodic changes in mixing depth changes in heat balance wind stress and lake level can affect the efficiency of mixing and depth of oxygen penetration in deep tropical lakes this study examines how transient changes in these parameters as reflected by the redox state of bottom waters are recorded in the sedimentary record of lake malawi we measured concentration profiles of redox sensitive metals across a layer of oxidized sediment deposited within a sequence composed of reduced sediments in a core taken at 298 m water depth 100 m below the present day chemocline by examining a range of metals that exhibit different geochemical behaviors mobilization under reducing fe mn versus oxidizing u conditions formation of insoluble sulfides cd mo pb zn susceptibility to scavenging onto fe or mn oxyhydroxide precipitates co mo pb v zn we are able to outline a sequence of events consistent with the formation of this feature 1 at some time before 11 ky bp there was an episode of penetration of oxygenated waters to depths close to or greater than that of this core i e substantially deeper in the lake basin than at present at this time diagenetically remobilized fe and mn were oxidized and precipitated in a near surface sediment horizon 2 fe and mn oxyhydroxides that precipitated from the water column as metal rich anoxic waters were mixed upward into oxygenated waters were deposited in an immediately overlying layer of the sediment such material continued to accumulate in surface sediments for a few hundred years until oxic conditions no longer prevailed in overlying waters 3 as the depth of the chemocline rose relative to the present day lake surface this authigenic material was in turn overlain by reducing sediments 4 subsequent diagenetic remobilization at the top and bottom of this redox sandwich resulted in formation of horizons enriched in u mo and sulfide forming metals notably cd along the redox gradients both above and to a lesser extent below the layer of oxidized sediment these enrichments immobilized under reducing conditions will remain as permanent markers of the episode of deepening of the chemocline even after reduction and remobilization of the oxidized fe and mn solids in addition such markers may be useful in determining whether observed episodic interruptions in deposition of varved sediments in the deep anoxic basins of lake malawi are due to bioturbation brought on by episodes of deeper oxygen penetration in the water column

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

a review of lacustrine paleomagnetic records from western north america 0 40000 years bp abstract a review of 16 lake sediment paleomagnetic records from western north america spanning time intervals over the last 40 000 yr bp provides evidence that many of these lacustrine records have recorded geomagnetic secular variation with wavelengths on the order of a few hundred years the younger studies 0 13 300 yr bp show general morphologic agreement among inclination records but most of the declination records are difficult to correlate among the older records there are major disagreements over the existence of the mono lake excursion specifically five studies contain evidence for the excursion but six studies do not show any record of it because errors in radiocarbon dating will distort down core time scales the younger records were rescaled with time scales that were constructed from extremal correlations of long wavelength 1000 2000 yr high amplitude 10 20 inclination features with these new time scales the excellent temporal and morphologic agreement between the fish lake oregon and blue lake idaho declination records confirms the existence of errors in the radiocarbon time scales the lack of agreement among the other rescaled declination records indicates that the records have been distorted or altered by sedimentary and geologic processes and or by sampling measuring and data analysis procedures in terms of the regional geomagnetic record fish lake and blue lake present a 3300 yr master curve of secular variation for northeastern oregon and southwestern idaho the lack of correlation among the other records however prevents us from drawing definite conclusions about the areal variation of the geomagnetic field in western north america over the past 40000 yr bp

millennial scale vegetation and climatic changes from an early to mid holocene lacustrine archive in central ganga plains using multiple biotic proxies abstract the indo gangetic floodplains have many abandoned meander cut offs and oxbow lakes that can serve as potential archives for high resolution paleoclimatic reconstruction previously a few of these lakes have been investigated for understanding the regional holocene climatic history but these studies are generally limited by a lack of high chrono stratigraphic resolution to develop an understanding of the role of local and or regional climate forcings an oxbow lake baraila tal in the central ganga plains has been studied using multiple biotic proxies such as pollen phytoliths diatoms and sponge spicules millennial scale climatic fluctuations and vegetation history for the early to mid holocene period have been reconstructed using 17 ams radiocarbon dates from two trenches 3 4 m deep five major biotic zones have been delineated between 13 2 and 4 8 kyr bp zone i 13 12 kyr bp shows small patches of dry tropical woody flora along with tall c4 grass indicating a moderately dry climate the presence of low temperature herbs indicates an active ne monsoon but the paucity of arboreals indicates a weakened indian summer monsoon ism the high percentages of phacotus lenticularis cysts in zone ii 12 9 kyr bp indicate the presence of stagnant lime rich inland waters under relatively colder climatic conditions the appearance of evergreen forest groves around 11 5 kyr bp indicates an increase in humidity and lake deepening was inferred between 10 9 and 10 3 kyr bp sediment accumulation rate shows a sudden drop at 10 3 kyr bp indicating a complete cut off of the oxbow lake from the fluvial channel zone iii 9 8 kyr bp records millennial scale drying with a complete absence of aquatic pollen between 8 9 and 7 7 kyr bp the expansion of short c4 grass in zone iv 8 7 kyr bp further indicates drier conditions zone v 7 5 kyr bp shows very high percentages of sponge spicules that flourish in clear waters and represents a strengthened ism and a subsequent lake expansion

indian summer monsoon during the last two millennia abstract the monsoon is a large scale feature of the tropical atmospheric circulation affectingpeople and economies in the world s most densely populated regions future trends due to naturalvariabilityandhuman inducedclimatechangesareuncertain palaeoclimaterecordscanimprove ourunderstanding of monsoon dynamics and thereby reduce this uncertainty palaeoclimate records haverevealed a dramatic decrease in the asian summer monsoon since the early holocene maximum9kabp herewefocusonthelast2ka wheresomerecordsindicateanincreasingtrendinthesummermonsoon analysing globigerina bulloides upwelling records from the arabian sea we nd theweakest monsoon occurred 1500 a bp with an increasing trend towards the present copyright 2010 john wiley sons ltd keywords monsoon holocene tropics india arabian sea introduction earth s climate is changing as a result of both natural andanthropogenic causes one region of the world that isparticularly susceptible to shifts in climate and extremeweather events is the indian subcontinent in this denselypopulated region both droughts and oods as well as trends inthe seasonal receipt of rainfall have the potential to bedevastating from economic agricultural and public healthperspectives the southwest indian monsoon is the maincontributor to india s yearly rainfall budget therefore unravelling past trends of the monsoon rains is critical tounderstanding future monsoon trends india ishome tooneofthelongesttimeseriesofinstrumentalclimate observations the all india monsoon rainfall index spanning 1844 to the present sontaake et al 1993 parthasarathy et al 1994 this record is remarkable bothfor showing an absence of a long term trend and for showing alarge variation in rainfall from one year to the next records ofthe atmospheric circulation such as the indian monsoon index imi based on the arabian sea winds are much shorter andspan only the past 50 a wang et al 2001 these records alsoindicate large variations from one year to the next and do notreveal a trend blending appropriate instrumental records withpalaeo observations from ocean sediments cave deposits orotherproxies canprovidealongerperspectiveonthemonsoonand its natural variability than otherwise would be available the monsoon is the result of both the seasonally changingthermal contrast between the land and ocean and the seasonalmigration of the intertropical convergence zone itcz whichreaches its northernmost location in summer exacerbating thethermally driven pressure gradient gadgil 2003 duringwinter the air over the land is cooler and denser than the airover the water this creates a surface pressure contrast that isenhanced by the position of the itcz over the ocean south ofthe continent of india resulting in a dry northeasterly wind thatblows across the continent in spring the continent warmsquickly compared to the surrounding water the winds thenreverse and a southwesterly wind blows across the arabiansea bringing moisture laden air towards india the south westerly winds that bring the monsoon rains also causeupwelling and sea surface cooling in the arabian sea producing a distinctive fossil record that can be tied to themonsoon winds via well known physical mechanisms a variety of indian and asian summer monsoon indices havebeen developed from instrumental records in general throughout india and asia in summer stronger winds overthe ocean and increased rainfall over land are correlated withthe large scale atmospheric circulation fig 1 the webster yang index wyi is a broad scale index of the monsooncirculation covers a large continuous area 40 1108 e 0 208n and measures the difference in strength between low level 850hpa and upper level 200hpa winds webster and yang 1992 in contrast the imi measures the arabian sea windsby subtracting the low level 850hpa zonal wind over land 20 308 n 60 908 e from the low level 850hpa winds in

mid to late holocene indian winter monsoon variability from a terrestrial record in eastern and southeastern coastal environments of sri lanka the southeastern coastal plain of sri lanka contains holocene sediment archives representing the winter monsoon variability because this region is protected from both summer monsoon and cyclonic rainfall chemical biological mineralogical and physical climate proxies were studied in sediment cores extracted from three different coastal estuaries and lagoons situated on the southeastern coast to derive winter monsoon variability these cores displayed minimum influence of sea level related changes in sediments clay normalized proxy records suggest intervals of aridity from 7300 to 6750 semi aridity from 6250 to 4600 yr bp and aridity from 4000 to 3000 and 1100 to 500 cal yr bp with a short wet interval from 6500 to 6250 cal yr bp and a wet interval from 3000 to 1500 yr bp our results match the timing of previously published climate events for holocene variations in the indian summer monsoon wavelet analysis of the detrended climate proxy records identify significant periodicities at 2

diatom inferred wind activity at lac du sommet southern quebec canada a multiproxy paleoclimate reconstruction based on diatoms chironomids and pollen for the past 9500 years paleo surface wind for southern quebec was inferred quantitatively for the past 9500 years from diatom assemblages archived in the sediment of the shallow mountain lac du sommet using biweekly sediment trap samples along an elevation gradient in the study area the wind reconstruction was compared with diatom inferred dissolved organic carbon concentration chironomid inferred mean august air temperature pollen grain size and loss on ignition increased lake circulation interpreted as indicating stronger surface winds was inferred from diatoms around 8700 4500 3000 to 2000 cal yr bp and during the past 250 years increased lake stratification was diatom inferred from 7500 to 5000 cal yr bp and between 1500 and 500 cal yr bp diatom inferred paleowinds were congruent with the regional fire history in general diatom production was significantly correlated with diatom inferred lake circulation diatom inferred lake circulation and diatom production were not correlated with the pollen assemblage ch

palaeoecology and the harappan civilisation of south asia a reconsideration abstract climatic change has often been cited as a determining factor in cultural changes in the context of the harappan civilisation of northwestern south asia 2500 1900 bc while these claims have been critiqued by archaeologists they continue to be accepted by non archaeologists including quaternary scientists the purpose of this paper is to assess the available evidence and published arguments and to provide a constructive working synthesis of evidence for the palaeoenvironmental setting of northwestern south asia for the mid to late holocene especially ca 4000 1000 cal bc and its possible connection to important cultural changes we conclude that harappan urbanism emerged on the face of a prolonged trend towards declining rainfall no climatic event can be blamed for a precipitous end of this civilisation although strategic local shifts in agriculture that may have begun in response to prolonged droughts at ca 2200 bc may have contributed to the de urbanisation process and the restructuring of human communities over the following 200 300 yr

biomarker records of late neogene changes in northeast african vegetation open savannah grasslands dominated by c4 plants became a significant component of northeast african vegetation during the late neogene we present molecule specific carbon isotopic mea surements of terrestrial plant biomarkers preserved in marine sed iments off northeast africa that allow reconstruction of orbital scale vegetation changes in short time windows over the past 9 4 m y the biomarker data show large amplitude vegetation vari ability as early as 3 8 ma with the greatest c4 expansion occurring after 3 4 ma we sampled orbital scale oscillations of up to 5 almost as large as the observed late neogene range of 7 sug gesting that large and repeated oscillations between more open and more closed landscapes were an important aspect of northeast af rican vegetation change during the past 4 m y

coupled sea surface temperature seawater δ18o reconstructions in the arabian sea at the millennial scale for the last 35 ka two sediment cores from the western 905 10 46 9 n 51 56 4 e water depth 1586 m and eastern sk17 15 15 n 72 58 e water depth 840 m arabian sea were used to study past sea surface temperatures sst and seawater 18o 18ow variations for the past 35 ka we used coupled mg ca 18o calcite variability in two planktonic foraminiferal species globigerinoides ruber which thrives throughout the year and globigerina bulloides which occurs mainly when surface waters contain high nutrients during upwelling or convective mixing ssts in both areas based on mg ca in g ruber were 3 to 4 c lower during the last glacial maximum lgm 21 ka than today and the holocene period the sst records based on g bulloides also indicate general cooling down to 18 c in both areas ssts in the western arabian sea based on g bulloides were always lower than those based on g ruber indicating the presence of strong seasonal temperature contrast during the holocene and lgm we interpret the consistent presence of this seasonal temperature contrast to reflect a combination of seasonal summer upwelling sw monsoon and winter convective mixing ne monsoon in the western arabian sea in the eastern arabian sea g bulloides based ssts were slightly lower about 1 c than g ruber based ssts during the holocene indicating the almost absence of a seasonal temperature gradient similar to today however a large seasonal temperature contrast occurred during the lgm which favors the assumption that strong ne monsoon winds forced winter upwelling or convective mixing offshore goa sst and 18ow reconstructions reveal evidence of millennial scale cycles particularly in the eastern arabian sea here the stadial periods northern hemisphere cold periods such as younger dryas and heinrich events are marked by increasing ssts and salty sea surface conditions relative to those during the interstadial periods indeed the 18ow record shows evidence of low saline surface waters during interstadial periods indicating increased freshwater runoff from the western ghats as a consequence of enhanced sw monsoon intensity

abrupt changes in the asian southwest monsoon during the holocene and their links to the north atlantic ocean during the last ice age the indian ocean southwest monsoon exhibited abrupt changes that were closely correlated with millennial scale climate events in the north atlantic region1 2 3 suggesting a mechanistic link in the holocene epoch which had a more stable climate the amplitude of abrupt changes in north atlantic climate was much smaller and it has been unclear whether these changes are related to monsoon variability here we present a continuous record of centennial scale monsoon variability throughout the holocene from rapidly accumulating and minimally bioturbated sediments in the anoxic arabian sea our monsoon proxy record reveals several intervals of weak summer monsoon that coincide with cold periods documented in the north atlantic region4 including the most recent climate changes from the medieval warm period to the little ice age and then to the present we therefore suggest that the link between north atlantic climate and the asian monsoon is a persistent aspect of global climate

geochemical signatures of late holocene paleo hydrological changes from phulera and pokharan saline playas near the eastern and western margins of the thar desert india abstract stratigraphical mineralogical geochemical and optical dating methods were used to reconstruct paleo hydrological changes in two playas phulera 500 mm a and pokharan 200 mm a in near extremum climatic regions of the thar desert sediment successions in shallow profiles from phulera and pokharan contain three and four stratigraphic units respectively each with characteristic geochemical properties these units reflect changes in chemical weathering detrital input salinity and provide a measure of the changes in precipitation i e monsoon through time sediments from pokharan suggest short rainfall events during ca 6 6 4 ka relatively stable fresh water higher and persistent rainfall regime during 4 2 3 ka and a hyper saline low rainfall condition during 2 3 1 1 ka sediments at phulera record hyper saline low rainfall lacustrine conditions during 1 4 ka higher abundance of gypsum in pokharan 2 3 1 1 ka and proto dolomite in phulera 2 3 1 4 ka are nearly synchronous and reflect enhancement of salinity selenite crystals in pokharan and large desiccation cracks in buried horizons at phulera reflect desiccation of playas at ca 2 ka both playas progressively became less saline after 1 4 ka given the regional nature of this record these changes are attributed to fluctuation of the monsoon over the indian sub continent

a multi proxy reconstruction of monsoon variability in the late holocene south india abstract pookode lake kerala south india a fresh water lake situated at an altitude of 770 m a s l receives predominantly rains from the south west monsoon a sediment core 125 cm long was investigated for sediment texture dating and geochemical composition radiocarbon dates obtained on the organic carbon rich sediments of the pookode lake range in age from the mid holocene to more recent 6240 565 14 c bp bc 4786 to ad 1434 cal geochemical data of the sediment cores were corroborated with phytolith and pollen studies although phytoliths occur in the entire sediment core pollen assemblages start occurring only since 1500 14 c bp ad 650 cal the sediments older than 1500 14 c bp were not suitable for the preservation of the pollen assemblages there is a major change in the lake hydrology indicating lacustrine conditions subsequent to 1500 bp occurrence of diatoms in the upper sediment layers of the sediment core indicates shallowing of the lake both the medieval warm period mwp and the little ice age lia are represented in the pookode lake sediment core sediment texture chemical weathering intensity cwi values supported by phytolith and pollen assemblages indicate that overall warm and dry conditions prevailed during 6200 420 14 c bp bc 4786 ad 1434 cal but this was interrupted by short intense wet phases between 3900 and 1900 bc 4000 ad 300 cal 1400 760 ad 800 ad 1200 cal and 420 140 14 c bp ad 1570 ad 1860 cal the wet events resulted from the strengthening of south west monsoon swm causing rising water levels and brief expansion of the pookode lake margin

late quaternary climate history of the horton plains central sri lanka abstract a 6 m long core was retrieved from a mire at ca 2200 m a s l in the horton plains national park central sri lanka the material collected consists of a mixture of organic matter and clastic particles which have been subject to bio litho and chronostratigraphic analyses the pollen spectra suggest semi arid conditions and a relatively species poor plant community from 24 000 until 18 500 cal yr bp associated with a weaker south west monsoon swm during the late pleistocene the climate was fluctuating between relatively dry and humid conditions as the result of changes in the monsoonal regime the onset of the moonson caused a semi humid climate resulting in an expansion of the upper montane rain forest umrf the strengthening of the swm was interrupted by two relatively dry climatic events each lasting ca 2000 years the early holocene was characterised by a per humid event followed by a hyper humid event both influenced by a further strengthening of the swm due to the orbitally induced maximum increment of summer insolation the middle holocene was marked by a trend towards semi arid climatic conditions during the late holocene the swm rains strengthened again

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

mid holocene extreme hydrological events in the eastern great rann of kachchh western india abstract the present study is an attempt to reconstruct the paleohydrological conditions during the mid holocene in the hyper arid terrain of the northern great rann of kachchh remote sensing detailed field geomorphology sedimentology geochemistry and optical chronology suggests that the fluvial sediments fringing the khadir island were transported locally and deposited during the extreme hydrological events corresponding to the mid to late holocene indian summer monsoon ism variability overall five extreme hydrological events are deciphered during the last 5 ka which broadly correlates with periods of strengthened ism our data indicate that the emergence and decline of the harappan civilization was unrelated to any major fluvial system in the region

decadal centennial scale monsoon variations in the arabian sea during the early holocene 1 an essential prerequisite for the prediction of future climate change due to anthropogenic input is an understanding of the natural processes that control earth s climate on timescales comparable to human lifespan the early holocene period was chosen to study the natural climate variability in a warm interval when solar insolation was at its maximum the monsoonal system of the tropics is highly sensitive to seasonal variations in solar insolation and consequently marine sediments from the region are a potential monitor of past climate change here we show that during the early holocene period rapid 18o changes of the summer upwelling dwelling foraminifer g bulloides of up to 0 6 in core 905 from the arabian sea occurred on decadal centennial timescales this 18o change predominantly translates into summer temperature variations of roughly 2 3 c within the resolution of the ams14c dating the isotope changes occur in phase with precipitation induced 18o variations recorded in a stalagmite in the hoti cave in oman neff et al 2001 from this relationship we conclude that solar insolation affecting the monsoonal system not only induced the precipitation changes as recorded in oman in the sense of neff et al 2001 but also controlled temperature variations in the upwelled waters found off somalia the present study demonstrates that decadal scale climate records can be obtained from nonlaminated ocean sediment records and that coherent rapid high amplitude climate change is recorded in the arabian sea on a regional scale of 2000 km

sediment undulations on the llobregat prodelta signs of early slope instability or sedimentary bedforms a field of sediment undulations has been mapped by means of high resolution multibeam bathymetry and seismic reflection profiles in the llobregat river prodelta off the city of barcelona catalonia spain similar features had previously been recognized in other prodelta environments and interpreted either as downslope sediment deformation or sedimentary structures induced by bottom currents or hyperpycnal flows since the study area is undergoing significant offshore development proper interpretation of such sediment undulations is needed for a correct risk assessment the occurrence of the sedi ment undulations is restricted to the prodelta front on slope gradients between 3 and 0 2o the undulations have developed at the edge and atop an area of gas bearing sediments within the late holocene high stand mud wedge an evaluation is made of the character istics of the sediment undulations in order to determine the most likely process for the origin of these structures amongst these characteristics are the continuity of the reflec tions and lack of diffractions in between different undulations their size distribution large to small both from shallow to deep and with depth in section the asymmetry de creasing from proximal to distal the crest to trough vertical distance on the landward side of the undulations up to 0 5 m and the lack of features that could indicate a pro gressive movement such as growth structures and drag folds these characteristics indi cate that the sediment undulations on the llobregat river prodelta do not result from sediment deformation but rather from the interaction of bottom currents generated by hyperpycnal flows from the llobregat river with regional sea water circulation their identification as sediment waves implies that such features do not pose a major hazard for further offshore development

sedimentary response to milankovitch type climatic oscillations and formation of sediment undulations evidence from a shallow shelf setting at gela basin on the sicilian continental margin abstract a multi proxy chronological framework along with sequence stratigraphic interpretations unveils composite milankovitch cyclicity in the sedimentary records of the last glacial interglacial cycle at ne gela basin on the sicilian continental margin chronostratigraphic data including foraminifera based eco biostratigraphy and 18 o records tephrochronological markers and 14 c ams radiometric datings was derived from the shallow shelf drill sites geob14403 54 6 m recovery and geob14414 27 5 m collected with both gravity and drilled mebo cores in 193 m and 146 m water depth respectively the recovered intervals record marine isotope stages and substages mis from mis 5 to mis 1 thus comprising major stratigraphic parts of the progradational deposits that form the last 100 ka depositional sequence calibration of shelf sedimentary units with borehole stratigraphies indicates the impact of higher frequency 20 ka sea level cycles punctuating this 100 ka cycle this becomes most evident in the alternation of thick interstadial highstand hst wedges and thinner glacial forced regression fsst units mirroring seaward shifts in coastal progradation albeit their relatively short lived depositional phase these subordinate hst units form the bulk of the 100 ka depositional sequence two mechanisms are proposed that likely account for enhanced sediment accumulation ratios sar of up to 200 cm ka during these intervals 1 intensified activity of deep and intermediate levantine intermediate water liw associated to the drowning of mediterranean shelves and 2 amplified sediment flux along the flooded shelf in response to hyperpycnal plumes that generate through extreme precipitation events during overall arid conditions equally the latter mechanism is thought to be at the origin of undulated features resolved in the acoustic records of mis 5 interstadials which bear a striking resemblance to modern equivalents forming on late holocene prodeltas of other mediterranean shallow shelf settings

sedimentary geochemical record of human induced environmental changes in the lake brunnsviken watershed sweden environmental changes in lake brunnsviken its watershed and the greater stockholm region since the middle of the nineteenth century have left interpretable geochemical imprints in the bottom sediments these humaninduced perturbations within the lake s watershed included agriculture urbanization sewage and industrial disposal and water column aeration smaller d 15 ntotal values high organic carbon mass accumulation rates low c n ratios and larger d 13 corg values identify periods of increased nutrient delivery and elevated primary productivity in the lake c s ratios that change from high to low trace the transition from an oxic hypolimnion to an anoxic one during the periods of high productivity accumulations of redox sensitive trace elements increase during the anoxic period and are further magnified during a time of industrial waste discharge into the lake a recent decrease in black carbon concentrations in sediments reflects the conversion from wood and coal to cleaner forms of energy

holocene aridification of india 1 spanning a latitudinal range typical for deserts the indian peninsula is fertile instead and sustains over a billion people through monsoonal rains despite the strong link between climate and society our knowledge of the long term monsoon variability is incomplete over the indian subcontinent here we reconstruct the holocene paleoclimate in the core monsoon zone cmz of the indian peninsula using a sediment core recovered offshore from the mouth of godavari river carbon isotopes of sedimentary leaf waxes provide an integrated and regionally extensive record of the flora in the cmz and document a gradual increase in aridity adapted vegetation from 4 000 until 1 700 years ago followed by the persistence of aridity adapted plants after that the oxygen isotopic composition of planktonic foraminiferglobigerinoides ruberdetects unprecedented high salinity events in the bay of bengal over the last 3 000 years and especially after 1 700 years ago which suggest that the cmz aridification intensified in the late holocene through a series of sub millennial dry episodes cultural changes occurred across the indian subcontinent as the climate became more arid after 4 000 years sedentary agriculture took hold in the drying central and south india while the urban harappan civilization collapsed in the already arid indus basin the establishment of a more variable hydroclimate over the last ca 1 700 years may have led to the rapid proliferation of water conservation technology in south india

monsoon influenced variations in plankton community structure and upper water column stratification in the western bay of bengal during the past 80 ky abstract to enhance our understanding of the forcing factors of marine biological community structure in the bay of bengal we studied proxies for biogenic carbonate and silicate production in the western bay of bengal and compared them with proxies for upper ocean stratification and strength of the indian summer monsoon ism specifically we investigated the record in a sediment core from the western bay of bengal that extended to approximately 80 ky before the present bp the records of globigerinoides ruber sensu stricto 18o minus neogloboquadrina dutertrei 18o 18or d were used to investigate changes in upper ocean stratification we reconstructed variations in mass accumulation rates mars of caco3 and biogenic silica bsi to discuss plankton community structure greater difference between globigerinoides ruber sensu stricto 18o and neogloboquadrina dutertrei 18o during the marine isotope stage mis 1 and 5a indicate intervals with less saline and more stratified conditions in contrast the relatively small difference between both planktic foraminiferal 18o during mis 2 and 4 indicates diminished stratification during these periods elevated carbonate production during mis 2 and 4 demonstrated by the increase in caco3 mar could have been driven by lower freshwater influx to the western bay of bengal resulting from lower ism precipitation and thus the increased mixing and upwelling of deep nitrate into the photic zone the relative increase in bsi mar during periods of high ism precipitation and decreased salinity of surface waters suggests a limited recovery in biological siliceous production under interglacial conditions possibly due to enhanced fluvial sio4 delivery to the ocean fluctuations of 18or d during mis 3 indicate that freshwater stratification was moderate and insufficient to restrict upwelling this might have induced moderate biogenic silica and carbonate productions during this period

middle to late holocene environmental changes in the depositional system of the tropical brackish bolgoda lake coastal southwest sri lanka abstract the tropical bolgoda lake is one of the largest lagoonal estuaries in sri lanka organic constituents in this lake were investigated using 28 surface sediments three cores from the lake and four short cores from mangrove mud elemental and molecular compositions of sediments and living organic matter om were determined using cns elemental analysis and gas chromatography mass spectrometry respectively chronology of events was determined using accelerated mass spectrometry ams 14 c data for bulk oms woods and mollusk shells the history of bolgoda lake can be divided into two major chrono stratigraphic divisions namely a lower sedimentary succession from ca 7 0 cal ky b p to 2 5 cal ky b p and an upper sedimentary succession from ca 2 5 cal ky b p to the recent according to the sapropelic depositional system concentrations of the mangrove biomarker taraxone increased significantly at ca 7 0 cal ky b p the lower part of the sediment sequence had moderate productivity and was mainly deposited under marine terrestrial influence in oxygen poor anoxic conditions during mid holocene sea level highstands a drastic increase in total organic carbon toc content reaching 29 was found in one of the bolgoda cores this increase occurred because of sea level regression at about 2 5 cal ky b p this change was probably caused by development of a beach rock sandbar and the estuary system changed to a semi closed lake due to the sea level regression as a result aquatic vascular plants predominate in this depositional system after ca 2 5 cal ky b p toc content decreased slightly but relatively high toc contents were maintained in the muddy sediments in moderately sized and shallow 1 2 m tropical estuaries lagoons such as bolgoda lake drastic changes in toc contents may be the most sensitive indicator of sea level variations increase in higher plant om with higher n c 29 n c all and n c 37 n c all alkane ratios also suggest a climatic transition from wetter to somewhat drier after the middle holocene accumulations of pyrogenic polycyclic aromatic hydrocarbons pahs in the modern sediments record anthropogenic activity after european settlement in the 15th century

molecular and isotopic records of c4 grassland expansion in the late miocene abstract siwalik paleosol and bengal fan sediment samples were analyzed for the abundance and isotopic composition ofn alkanes in order to test for molecular evidence of the expansion of c4 grasslands on the indian subcontinent the carbon isotopic compositions of high molecular weight alkanes in both the ancient soils and sediments record a shift from low 13c values ca 30 to higher values ca 22 prior to 6 ma this shift is similar in magnitude to that recorded by paleosol carbonate and fossil teeth and is consistent with a relatively rapid transition from dominantly c3 vegetation to an ecosystem dominated by c4 plants typical of semi arid grasslands the n alkane values from our paleosol samples indicate that the isotopic change began as early as 9 ma reflecting either a growing contribution of c4 plants to a dominantly c3 biomass or a decrease in water availability to c3 plants molecular and isotopic analyses of other compounds including n alcohols and low molecular weightn alkanes indicate paleosol organic matter contains contributions from a mixture of sources including vascular plants algae and or cyanobacteria and microorganisms a range of inputs is likewise reflected in the isotopic composition of the total organic carbon from these samples in addition then alkanes from two samples show little evidence for pedegenic inputs and we suggest the compounds were derived instead from the paleosol s parent materials we suggest the record of vegetation in ancient terrestrial ecosystems is better reconstructed using isotopic signatures of molecular markers rather than bulk organic carbon this approach provides a means of expanding the spatial and temporal records of c4 plant biomass which will help to resolve possible tectonic climatic or biological controls on the rise of this important component of the terrestrial biosphere

strong influence of water vapor source dynamics on stable isotopes in precipitation observed in southern meghalaya ne india to calibrate 18o time series from speleothems in the eastern indian summer monsoon ism region of india and to understand the moisture regime over the northern bay of bengal bob we analyze the 18o and d of rainwater collected in 2007 and 2008 near cherrapunji india d values range from 18 5 to 144 4 while 18o varies between 0 8 and 18 8 the local meteoric water line lmwl is found to be indistinguishable from the global meteoric water line gmwl late ism september october rainfall exhibits lowest 18o and d values with little relationship to the local precipitation amount there is a trend to lighter isotope values over the course of the ism but it does not correlate with the patterns of temperature and rainfall amount 18o and d time series have to be interpreted with caution in terms of the amount effect in this subtropical region we find that the temporal trend in 18o reflects increasing transport distance during the ism isotopic changes in the northern bob surface waters during late ism and vapor re equilibration with rain droplets using an isotope box model for surface ocean waters we quantify the potential influence of river runoff on the isotopic composition of the seasonal freshwater plume in the northern bob temporal variations in this source can contribute up to 25 of the observed changes in stable isotopes of precipitation in ne india to delineate other moisture sources we use backward trajectory computations and find a strong correlation between source region and isotopic composition palaeoclimatic stable isotope time series from northeast indian speleothems likely reflect changes in moisture source and transport pathway as well as the isotopic composition of the bob surface water all of which in turn reflect ism strength stalagmite records from the region can therefore be interpreted as integrated measures of the ism strength

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

palaeoenvironmental implications of evaporative gaylussite crystals from lonar lake central india we have undertaken petrographic mineralogical geochemical and isotopic investigations on carbonate minerals found within a 10 m long core from lonar lake central india with the aim of evaluating their potential as palaeoenvironmental proxies the core encompasses the entire holocene and is the first well dated high resolution record from central india while calcite and or aragonite were found throughout the core the mineral gaylussite was found only in two specific intervals 4630 3890 and 2040 560 cal a bp hydrochemical and isotope data from inflowing streams and lake waters indicate that evaporitic processes play a dominant role in the precipitation of carbonates within this lake isotopic d 18 o and d 13 c studies on the evaporative gaylussite crystals and residual bulk carbonates calcite from the long core show that evaporation is the major control on d 18 o enrichment in both the minerals however in case of d 13 c additional mechanisms for example methanogenesis gaylussite and phytoplankton productivity calcium carbonate play an additional important role in some intervals we also discuss the relevance of our investigation for palaeoclimate reconstruction and late holocene monsoon variability copyright 2013 john wiley sons ltd

a multi proxy reconstruction of the late holocene climate evolution in lake bolgoda sri lanka abstract palaeoclimate investigations in sri lanka have been rarely attempted despite being located directly in the path of the inter tropical convergence zone in this study a 4 1 m undisturbed sediment core was retrieved from the bolgoda lake situated in the western coast of sri lanka and influenced by the strong southwest monsoons mollusc shells in the core were dated and the age depth model indicated a depositional history extending from 2941 cal yr bp to the present grain size major and trace elements total organic c and n content and stable c and n isotopes were analysed in freeze dried sediments to reconstruct the palaeoclimate changes the multi proxy records in the core revealed four distinct zones that show distinct variations in physical and chemical conditions in the lake associated with climate change zone 1 2941 to 2390 cal yr bp 385 252 cm indicated the climate to be warm and humid with intense precipitation the resulting high lake level helped in organic matter preservation in bottom sediments zone 2 2390 to 1782 cal yr bp 252 140 cm indicated an unstable dry period associated with weak precipitation consequently low lake level and intense degradation of organic matter occurred in this zone zone 3 1782 to 1299 cal yr bp 140 60 cm indicated a resurgence of intense monsoon along with warm and humid conditions zone 4 1299 cal yr bp to present 60 0 cm indicated dry conditions with less intense monsoon low lake level and extensive degradation of organic matter vascular plants were the predominant organic matter source into the lake during the late holocene in contrast algal input was significant between 2390 cal yr bp and 2153 cal yr bp the palaeoclimate evidences in this study showed an overall weakening trend of sw monsoon during the late holocene and this was consistent with changes happening in other locations as in southern and western india

long period geomagnetic secular variations since 12 000 yr bp a comparison of secular variation records of the geomagnetic field inclination obtained from palaeomagnetic studies of european and north american post glacial and late glacial sediments suggests that geomagnetic westward drift has persisted through the past 12 000 yr between 12 000 and 2 500 yr bp the overall average drift rate was between 0 14 and 0 16 deg yr 1 at 2 500 yr bp it is tentatively suggested that the drift rate increased and rose to a maximum of nearly 0 5 deg yr 1 before decreasing to historically observed values of 0 25 deg yr 1

archaeo and paleosecular variation and long term asymmetries of the geomagnetic field this report summarizes progress made during the last four years in i obtaining records of the geomagnetic secular variation using paleomagnetic techniques ii analysis and modelling of the secular variation and iii the study of asymmetries in the time averaged field seen both as departures from the geocentric axial dipole model and as statistical differences between polarity states

mechanical behaviour of unsaturated marine sediments experimental and theoretical approaches abstract the costa target areas exhibit different slope failure events which reflect different triggering mechanisms including gas hydrates dissociation gas hydrates stability law depends on temperature pore pressure gas chemistry and pore water salinity any change in the equilibrium parameters may convert the hydrate to gas plus water causing significant weakening of the sediment and generating a rise of pore pressure a significant consequence of the hydrate melting is the gas production which alters significantly the behaviour and mechanical properties of the marine sediments and could be very hazardous when the sediment is unloaded in undrained conditions the behaviour of the unsaturated marine sediment has to be accurately identified in order to quantify the geological risks associated to the hydrate dissociation see for instance sultan n cochonat p foucher j p mienert j this volume effect of gas hydrates melting on seafloor slope instability thus in this work five tests were carried out on synthetic marine sediments in order to identify the gas effect on the hydro mechanical behaviour of unsaturated marine sediments based on the experimental results obtained from this study on previous constitutive models alonso e e gens a josa a 1990 a constitutive model for partially saturated soils geotechnique 40 3 405 430 gens a alonso e e 1992 a framework for the behaviour of unsaturated expansive clays can geotech j 29 1013 1032 and on the relationship of van genuchten van genuchten m th 1980 a closed form equation for predicting the hydraulic conductivity of unsaturated soils soil sci soc am j 44 892 898 a new mathematical formulation was proposed to simulate the behaviour of the unsaturated soil qualitative comparison between experimental results and model predictions shows the capacity of the proposed model to reasonably reproduce the essential features of the hydro mechanical behaviour of marine unsaturated sediment experimental and simulation results show that unloading tidal cycles erosion natural slope instabilities excavation a submarine unsaturated sediment slope in shallow water is much more hazardous than unloading the same submarine slope in deep water

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

elastic wave velocity in marine sediments with gas hydrates effective medium modeling we offer a first principle based effective medium model for elastic wave velocity in unconsolidated high porosity ocean bottom sediments containing gas hydrate the dry sediment frame elastic constants depend on porosity elastic moduli of the solid phase and effective pressure elastic moduli of saturated sediment are calculated from those of the dry frame using gassmann s equation to model the effect of gas hydrate on sediment elastic moduli we use two separate assumptions a hydrate modifies the pore fluid elastic properties without affecting the frame b hydrate becomes a component of the solid phase modifying the elasticity of the frame the goal of the modeling is to predict the amount of hydrate in sediments from sonic or seismic velocity data we apply the model to sonic and vsp data from odp hole 995 and obtain hydrate concentration estimates from assumption b consistent with estimates obtained from resistivity chlorinity and evolved gas data

holocene forcing of the indian monsoon recorded in a stalagmite from southern oman a high resolution oxygen isotope record from a thorium uranium dated stalagmite from southern oman reflects variations in the amount of monsoon precipitation for the periods from 10 3 to 2 7 and 1 4 to 0 4 thousand years before the present ky b p between 10 3 and 8 ky b p decadal to centennial variations in monsoon precipitation are in phase with temperature fluctuations recorded in greenland ice cores indicating that early holocene monsoon intensity is largely controlled by glacial boundary conditions after approximately 8 ky b p monsoon precipitation decreases gradually in response to changing northern hemisphere summer solar insolation with decadal to multidecadal variations in monsoon precipitation being linked to solar activity

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

a paleomagnetic record from tangle lakes alaska large amplitude secular variation at high latitudes a paleomagnetic study of a core from the tangle lakes area of alaska has provided information about the nature of secular variation between 2 700 and 4 600 years b p the data indicate that the amplitudes of fluctuations in inclination and declination were substantially larger than those which would be expected from the present configuration of the geomagnetic field from this single site it is not possible to determine whether the observed secular variation arises mainly from the dipole or the non dipole component of the field if the dipole component is responsible then the data indicate that about 3 350 years b p the geomagnetic pole shifted by about 20 in a period of less than 150 years this shift is comparable to one proposed to have occurred about 500 years ago

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

a mid to late holocene record of vegetation decline and erosion triggered by monsoon weakening and human adaptations in the south east indian peninsula the mid to late holocene monsoon decline led to aridification of the indian peninsula impacting the early agricultural practices in the region our analysis of organic carbon mineral magnetic properties and ams 14c dating of a 54 2 m long sediment core cy from the godavari delta india showed changes in the organic carbon source and sediment provenance which are linked to the changes in vegetation and soil rock erosion caused by widespread aridification and associated human adaptation in central india our results show a decline in the concentration of ferrimagnetic minerals indicating reduced input from the basalts of the deccan plateau after 6 0 cal ka bp in response to the weaker indian monsoon 13c values show a distinct increase from 4 9 cal ka bp indicating an increase in c4 plant sources under the continued weak monsoon phase whereas a higher ferrimagnetic mineral concentration in the sediment suggested an increased deccan basalt source abrupt increase in 13c values and decrease in

late holocene paleoenvironmental changes inferred from manasbal lake sediments kashmir valley india abstract paleoclimate investigations and reconstruction using the lake sediment cores of kashmir valley have been rarely attempted the basin is influenced by indian summer monsoon westerlies and the local katabatic winds in the present study an 80 cm undisturbed sediment core was retrieved from the manasbal lake situated in north western himalaya sediments were dated using 14c method and the age depth model indicated a depositional history extending from 3345 yrs bp to the present grain size major and trace elements toc om contents c n ratio and diatom assemblages were applied to reconstruct the paleoenvironmental changes around the area the a cn k diagram displays that the weathering intensity of the manasbal lake sediments are moderate to highly weathered and the sediments have been derived from nearby and mixed source origin several wet and cold phases were identified during 3300 yrs bp to 2500 yrs bp and 1800 yrs bp to 1300 yrs bp due to intense precipitation reflect high lake level these wet phases are marked by higher sand and silt content c n ratio and high allochthonous input with less abundance of diatom species clay om toc contents and high cia values consequently low lake level and dry and cold period from 3345 yrs bp to 3300 yrs bp and 2500 yrs bp to 1800 yrs bp is observed these inferences are corroborated with the trace elemental ratios cia and cwi data our data indicate that the westerlies and localised katabtic winds rather than the indian summer monsoons played a major role in controlling the past climate around the manasbal lake kashmir valley

variability of el nino southern oscillation activity at millennial timescales during the holocene epoch the variability of el nino southern oscillation enso during the holocene epoch in particular on millennial timescales is poorly understood palaeoclimate studies have documented enso variability for selected intervals in the holocene but most records are either too short or insufficiently resolved to investigate variability on millennial scales1 2 3 here we present a record of sedimentation in laguna pallcacocha southern ecuador which is strongly influenced by enso variability and covers the past 12 000 years continuously we find that changes on a timescale of 2 8 years which we attribute to warm enso events become more frequent over the holocene until about 1 200 years ago and then decline towards the present periods of relatively high and low enso activity alternating at a timescale of about 2 000 years are superimposed on this long term trend we attribute the long term trend to orbitally induced changes in insolation and suggest internal enso dynamics as a possible cause of the millennial variability however the millennial oscillation will need to be confirmed in other enso proxy records

holocene paleoclimates of india we present a comprehensive summary of the available palaeoclimate records from india and compare the results from different proxies the results indicate i fluctuating lake levels during the early holocene the period of relatively higher lake levels from increased precipitation efficiency was reached only 7 2 6 0 cal kyr bp possibly due to increased contribution from winter rainfall ii the onset of aridity in nw india could have begun as early as 5 3 cal kyr bp subsequently there were multiple wet events but of shorter duration and smaller magnitude than during the mid holocene iii there is evidence of several short term climate events in the proxy record however in the absence of a rigorous chronological framework a detailed regional correlation is not possible at this stage finally a comparison between marine and terrestrial records indicates that episodes of strongest and weakest monsoon winds were not always associated with wettest and driest episodes respectively in the nw indian lakes

palaeosecular variation of the earth s magnetic field during the last 10000 years based on the annually laminated sediment of lake nautajarvi central finland a palaeomagnetic study of the lake nautajarvi sediment sequence in central finland demonstrates that varved lake sediments can provideregionally applicable secular variations curves for holocene stratigraphic correlation and age control based on x ray radiography and digital image analysis techniques we constructed an inherent and continuous varve chronology for the lake nautajarvi varve sequence which covers nearly 10000 years with an estimated counting error of less than 1 and a mean sedimentation rate of 0 66 mm yr 1 we reconstructed a record of the palaeomagnetic secular variation psv of the earth s magnetic field in this nearly 7 m long section of clastic organic varves mineral magnetic measurements indicated that pseudosingle domain magnetite is the major carrier of the remanence psv shows many of the familiar features of declination and inclination that have previously been recorded in northern europe in addition the lake nautajarvi record contains a continuous record of relative palaeoi

a north to south transect of holocene southeast atlantic continental margin sediments relationship between aerosol transport and compound specific δ13c land plant biomarker and pollen records 1 we examined near surface late holocene deep sea sediments at nine sites on a north south transect from the congo fan 4 s to the cape basin 30 s along the southwest african continental margin contents distribution patterns and molecular stable carbon isotope signatures of long chain n alkanes c27 c33 and n alkanols c22 c32 are indicators of land plant vegetation of different biosynthetic types which can be correlated with concentrations and distributions of pollen taxa in the same sediments calculated clusters of wind trajectories and satellite aerosol index imagery afford information on the source areas for the lipids and pollen on land and their transport pathways to the ocean sites this multidisciplinary approach on an almost continental scale provides clear evidence of latitudinal differences in lipid and pollen composition paralleling the major phytogeographic zonations on the adjacent continent dust and smoke aerosols are mainly derived from the western and central south african hinterland dominated by deserts semi deserts and savannah regions rich in c4 and cam plants the northern sites congo fan area and northern angola basin which get most of their terrestrial material from the congo basin and the angolan highlands may also receive some material from the chad region very little aerosol from the african continent is transported to the most southerly sites in the cape basin as can be expected from the present position of the phytogeographic zones the carbon isotopic signatures of the n alkanes and n alkanols both become isotopically more enriched in 13c from north to south the results of the study suggest that this combination of pollen data and compound specific isotope geochemical proxies can be effectively applied in the reconstruction of past continental phytogeographic developments

late holocene geochemical history inferred from sambhar and didwana playa sediments thar desert india comparison and synthesis abstract the sambhar and didwana playas from the eastern margin of the thar desert annual precipitation of 300 450 mm have been investigated for mineralogy major and trace element geochemistry of near surface sediments geochemical data and evaporite mineralogy of sediments from the playa surface and shallow depths provide insight to the present day geochemical processes and the different vertical phases of pore water activity detrital minerals from both the playas reflect igneous and metamorphic source rocks in their catchments the zeolite type mineral analcime naalsi 2 o 6 h 2 o is assumed to be authigenic in origin a product of chemical reaction between the hypersaline brine and detrital feldspars the evaporite mineralogy is dominated by halite calcite and dolomite major differences between the evaporite mineralogy of the surface sediments of two playas are the occurrence of trace amounts of the h 2 o bearing carbonate trona na 3 h co 3 2 2h 2 o in the didwana and k and mg bearing sulphate and chloride minerals e g polyhalite k 2 mgca 2 so 4 4 2h 2 o carnallite kmgcl 3 6h 2 o and sylvite kcl in the sambhar based on the distribution of major and trace elements the surface sediments from both playas are divided into three geochemical zones fed by river and rainwaters the playa surfaces show enrichment of insoluble cations and hydrolysates in the outermost zone and soluble oxides and cations in the innermost zone further the shallow depth profiles are also divided into distinct geochemical zones based on the elemental ratios the sub recent zone i reflects low chemical weathering and higher aeolian input the middle zone ii indicates relatively higher weathering index and zone iii enriched in evaporites also shows low chemical weathering despite the fact that the sambhar and didwana are separated only by 50 km they show significant differences in terms of evaporite mineralogy and inorganic composition of surface sediments we interpret this to be a manifestation of local variations in precipitation inflow and aeolian influx

the seismic stratigraphic record of lake level fluctuations in lake challa hydrological stability and change in equatorial east africa over the last 140 kyr abstract seismic reflection data from crater lake challa mt kilimanjaro equatorial east africa reveal a 210 m thick sedimentary infill containing distinct seismic stratigraphic signatures of late quaternary lake level fluctuations extrapolation of a well constrained age model on the cored upper part of the sequence suggests that these lake level fluctuations represent a detailed and continuous record of moisture balance variation in equatorial east africa over the last 140 kyr this record indicates that the most severe aridity occurred during peak penultimate glaciation immediately before 128 kyr bp coeval with heinrich event 11 and during a last interglacial megadrought period between 114 and 97 kyr bp in comparison last glacial maximum lgm aridity was modest it was preceded by 75 000 years of relatively stable and moist climate conditions interrupted by eleven short lived dry spells five of which match the timing of heinrich events 2 to 6 climate history near the east african equator reflects variation in the precessional forcing of monsoon rainfall modulated by orbital eccentricity but precession driven moisture fluctuations were less extreme than those observed in northern and southern tropical africa the near continuous moist climate from 97 to 20 5 kyr bp recorded in the lake challa record contrasts with the trend towards greater aridity after 70 kyr bp documented in equatorial west africa this long period of moist glacial climate and a short relatively modest lgm drought can be attributed to greater independence of western indian ocean monsoon dynamics from northern high latitude glaciation than those in the tropical atlantic ocean this rather persistent moist glacial climate regime may have helped maintain high biodiversity in the tropical forest ecosystems of the eastern arc mountains in tanzania

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

a 35 myr north american leaf wax compound specific carbon and hydrogen isotope record implications for c4 grasslands and hydrologic cycle dynamics article i nfo hydrology source region and timing of precipitation are important controls on the climate of the great plains of north america and the composition of terrestrial ecosystems moisture delivered to the great plains varies seasonally and predominately derives from the gulf of mexico atlantic ocean with minor contributions from the pacific ocean and arctic region for this work we evaluate long term relationships for the past 35 million years between north american hydrology climate and floral change using isotopic records and average carbon chain lengths of higher plant n alkanes from gulf of mexico sediments dsdp site 94 we find that carbon isotope values 13 c of n alkanes corrected for variations in the 13 c value of atmospheric co2 provide minor evidence for contributions of c4 plants prior to the middle miocene a sharp spike in c4 input is identified during the middle miocene climatic optimum and the influence of c4 plants steadily increased during the late miocene into the pleistocene consistent with other north american records chain length distributions of n alkanes indicative of the composition of higher plant communities remained remarkably constant from 33 to 4 ma however a trend toward longer chain lengths occurred during the past 4 million years concurrent with an increase in 13 c values indicating increased c4 plant influence and potentially aridity the hydrogen isotope values d of n alkanes are relatively invariant between 33 and 9 ma and then become substantially more negative 75 from 9 to 2 ma changes in the plant community and temperature of precipitation can solely account for the observed variations in d from 33 to 5 ma but cannot account for plio pleistocene d variations and imply substantial changes in the source region of precipitation and seasonality of moisture delivery we posit that hydrological changes were linked to tectonic and oceanographic processes including the shoaling and closure of the panamanian seaway amplification of north atlantic deep water production and an associated increase of meridional winds the southerly movement of the intertropical convergence zone near 4 ma allowed for the development of a near modern pressure storm track system driving increased aridity and changes in seasonality within the north american interior

reconstruction of the variability of the southwest monsoon during the past 3 ka from the continental margin of the southeastern arabian sea from temporal variation in 18o in globigerinoidesruber and g sacculifer and geochemical indices of weathering erosion chemical index of alteration al and ti we infer rapid southwest monsoon swm deterioration with dwindling fluvial and detrital fluxes at ca 450 650 1000 and 1800 2200 cal a bp during the late holocene we have evaluated the role of solar influx reconstructed and high latitude climate variability archived in grip and gisp 2 cores on swm precipitation broadly our 18o climate reconstruction is concordant with grip and gisp 2 and supports a teleconnection through atmospheric connection between the swm and the north atlantic climate albeit temporal extents of the little ice age and medieval warm period from high latitude are not entirely coeval moreover there is a humid climate and enhanced precipitation during the terminal stages of the little ice age the medieval warming ca ad 800 1300 is not synchronous either and is punctuated by an arid event centred at 1000 a bp although the delineation of the specific influence of solar influx on swm precipitation is elusive we surmise that swm precipitation is a complex phenomenon and local orography along southwestern india may have a role on the entrapment of moisture from the southwest trade winds when these hit land copyright 2009 john wiley sons ltd

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

a framework for the behaviour of unsaturated expansive clays the paper presents a framework for describing the mechanical behaviour of unsaturated expansive clays it is an extension of an existing formulation developed for unsaturated soils of low activity the extended framework is based on the distinction within the material of a microstructural level where the basic swelling of the active minerals takes place and a macrostructural level responsible for major structural rearrangements by adopting simple assumptions concerning the coupling between the two levels it is possible to reproduce major features of the behaviour of unsaturated expansive clays some selected qualitative comparisons between model predictions and experimental results reported in the literature are presented despite the simplified hypotheses made a very encouraging agreement is obtained key words capillarity clay model unsaturation suction expansive soils

slope failure dynamics and impacts from seafloor and shallow sub seafloor geophysical data case studies from the costa project holocene and slightly pre holocene submarine landslide are found both in high latitude glacial dominated margins and in lower latitude river dominated margins this paper constitutes a major assessment on some of the best studied submarine instabilities in the world we review and update from original data and literature reports the current state of knowledge of storegga traenadjupet and finneidfjord slides from the mid norwegian margin afen slide from the faeroe shetland channel big 95 slide and central adriatic deformation belt cadeb from continental slope and inner continental shelf settings off the ebro and po rivers in the mediterranean sea canary slide west of the westernmost youngest canary islands and gebra slide off the northern tip of the antarctic peninsula in the southern hemisphere i e those studied in the continental slope stability costa project the investigated slides range in size from the gigantic 90 000 km2 and almost 3000 km3 storegga slide to the tiny 1 km2 and 0 001 km3 finneidfjord slide not only do individual submarine landslides rarely involve processes precisely fitting with pre established categories mostly based on subaerial research but also they display complex mechanical behaviors within the elastic and plastic fields individual events can involve simultaneous or successive vertical to translational movements including block detachment block gliding debris flow mud flow and turbidity currents the need for an in depth revision of the classification criteria and eventually for a new classification system based on the new imaging capabilities provided by modern techniques is more than obvious we suggest a new system which for the moment is restricted to debris flows and debris avalanches volume calculation methods are critically reviewed and the relations between some key geomorphic parameters are established for the selected slides the assumed volume missing from scar areas does not necessarily match the actual volume of sediment remobilised by an individual event since in situ sediment can be remoulded and eventually incorporated during the slide downslope journey cadeb a shore parallel prodelta detached from its source is the exception to the good correlation found between across slope width and alongslope length with slide area height drop measured from the headwall upper rim to its foot correlates with the debris deposit maximum thickness unless the slide moves into restricted areas which prevent farther forward expansion of the deposit such as gebra and big 95 in such cases over thickened deposits are found a particularly loose and fluid behavior can be deduced for slides showing an over thinned character such as the canary slide that traveled 600 km scar areas and slip planes have been investigated with particular emphasis although slide headwalls might present locally steep gradients up to 23 for storegga slide the slope gradients of both the failed segment margins and the main slip planes are very low max 2 and usually around 1 and less an exception is the finneidfjord slide 20 5 that occurred in 1996 because of a combination of climatic and anthropogenic factors leading to excess pore pressure and failure mechanically distinct low permeable clayey weak layers often correspond to slip planes beyond the slide headwall since not only formation of these weak layers but also sedimentation rates are climatically controlled we can state that slide pre conditioning is climatically driven too run out distances reflect the degree of disintegration of the failed mass of sediment the total volume of initially failed material and transport mechanisms including hydroplanning commonly specific run outs could be attributed to distinct elements such as cohesive blocks and looser matrix as nicely illustrated by the big 95 slide total run outs usually correspond to matrix run outs since the coarser elements tend to rest at shorter distances outrunner blocks are finally a very common feature proving the ability of those elements to glide over long distances with independence of the rest of the failed mass in addition to pre conditioning factors related to geological setting and sedimentation conditions a final trigger is required for submarine landslides to take place which is most often assumed to be an earthquake in high latitude margins earthquake magnitude intensification because of post glacial isostatic rebound has likely played a major role in triggering landslides although it cannot be totally ruled out there is little proof at least amongst the costa slides that gas hydrate destabilisation or other processes linked to the presence of shallow gas have acted as final triggers

sharp decrease in summer monsoon strength 4000 3500 cal yr b p in the central higher himalaya of india based on pollen evidence from alpine peat age constrained pollen data and magnetic susceptibility of an alpine peat profile from the garhwal higher himalaya display a continuous record of climate and monsoon trends for the past 7800 yr about 7800 cal yr b p dominance of evergreen oak quercus semecarpifolia alder alnus and grasses in the pollen record reflect a cold wet climate with moderate monsoon precipitation from 7800 to 5000 cal yr b p vegetation was progressively dominated by conifers indicating ameliorated climate with a stronger monsoon a warm humid climate with highest monsoon intensity from 6000 4500 cal yr b p represents the mid holocene climatic optimum between 4000 and 3500 cal yr b p the abundance of conifers sharply decreased with the greatest increase in evergreen oak this trend suggests progressive cooling with a decrease in the monsoon to its minimum about 3500 cal yr b p two relatively minor cold dry events at ca 3000 and 2000 cal yr b p marked step wise strengthening of the monsoon until ca 1000 cal yr b p after a cold dry episode that culminated ca 800 cal yr b p the monsoon again strengthened and continued until today a sharp decrease in temperature and rainfall at 4000 3500 cal yr b p represents the weakest monsoon event of the holocene record this cold dry event correlates with proxy data from other localities of the indian subcontinent arabian sea and western tibet

early holocene to present palaeoenvironmental shifts and short climate events from the tropical wetland and lake sediments kukkal lake southern india geochemistry and palynology the kukkal basin tamil nadu india receives most of its rain from the southwest monsoon swm a sediment core from kukkal lake preserves a continuous sediment record from the early holocene to p