wave run up on slender piles in design conditions model tests and design rules for offshore wind wave run up on foundations is a very important factor in the design of entrance platforms for offshore wind turbines when the horns reef 1 wind turbine park in denmark was designed the vertical wave run up phenomenon was not well known in the industry hence not sufficiently considered in the design of horns reef 1 as a consequence damage was observed on the platforms this has been the situation for several sites and design tools for platform loads are lacking as a consequence a physical model test study was initiated at aalborg university to clarify wave run up on cylindrical piles for different values of diameter to water depth ratios d h and different wave heights to water depth ratios h h for both regular and irregular waves a calculation model is calibrated based on stream function theory for crest kinematics and velocity head stagnation theory due to increased velocities close to the pile an empirical factor is included on the velocity head the evaluation of the calculation model shows that an accurate design rule can be established even in breaking wave conditions however calibration of a load model showed that it was necessary to increase the run up factor on the velocity head by 40 to take into account the underestimation of run up for breaking or nearly breaking waves given that they produce thin run up wedges and air entrainment two factors not coped with by the measurement system

analysis and modeling of atmospheric gravity waves observed in radarsat sar images four case studies of radarsat synthetic aperture radar sar observations of atmospheric gravity waves are presented to demonstrate sar s capability to measure associated near surface wind field variations a brief review of the main characteristics and scales of atmospheric gravity waves agws first establishes their importance in atmospheric dynamics the shape and scale of the wave patterns observed in successive sar images are compared with those calculated from agw models there is agreement between the small scale wind variations across wave patterns in sar images and the larger scale wind field that plays a role in the generation of the observed waves

intensified monsoon and spatiotemporal changes in precipitation patterns in the nw himalaya during the early mid holocene we have undertaken a high resolution palaeoclimate reconstruction on radiocarbon dated palaeolake sediments from the spiti valley nw himalaya this site lies in the climatically sensitive winter westerlies and indian summer monsoon ism transitional regime and provides an opportunity to reconstruct the precipitation seasonality and extreme precipitation events that are characterised by intensified erosion the lake sediments reveal distinct lithofacies that provide evidence of changes in depositional environment and climate during early to mid holocene 8 7 6 1 cal ka bp we have identified three stages during the period of lake s existence the stage i 8 7 7 6 cal ka bp is marked by lake establishment stage ii 7 6 6 8 cal ka bp by sustained cooler periods and weakened summer monsoon and stage iii 6 8 6 1 cal ka bp by a shift from colder to warmer climate with stronger ism we have identified several short term cooler periods at ca 8 7 8 5 8 3 and 7 2 6 9 cal ka bp based on an overview of regional climate records we show that there is an abrupt switch in precipitation seasonality ca 6 8 cal ka bp that is followed by the onset of the intensified monsoon in the nw himalaya

late quaternary climate variability and vegetation response in ziro lake basin eastern himalaya a multiproxy approach abstract pollen phytolith and stable carbon isotopic records provide new insights into the palaeoenvironmental and palaeoclimatic changes in ziro lake basin sub himalayan arunachal pradesh india since pre lgm time phytoliths record a minor change in grass woodland cover and appear to be more sensitive than pollen grains to climate fluctuations both pollen and non pollen palynomorph data suggest prevalence of a dense c3 species dominated moist semi evergreen forest in the area until the lgm which shows conformity with 13c data the phytolith assemblage indicates an alteration in forest cover with expansion of c4 grasses during the lgm the study further indicates a climatic amelioration with intensification of south west monsoon during 10 2 3 8 ka and an expansion of forest cover after 3 8 ka there was a rising trend of dryness shrinkage in forest cover and a slight increase in c4 species while c3 plants dominated ecosystem variability also points towards a hydrological transformation in the area since pre lgm time application of coexistence approach on pollen data reveals that prior to the lgm the mean annual temperature and mean annual precipitation were approximately 19 3 0 001 c and 1925 15 mm respectively between 10 2 and 3 8 ka mat was about 19 4 0 5 c while map was 1901 41 3 mm between 3 8 and 1 2 ka and onwards a slight increase in mat 0 3c was observed with further decrease in map to 1861 33 4 mm during pre and post lgm times mat was more or less similar in the ziro lake basin which increased gradually after 3 8 ka and was 1 2 c higher than today prior to the lgm map was higher than the present day by 94 mm between 10 2 and 3 8 ka by 70 mm and since 3 8 ka onwards by 30 mm showing a tendency of gradual decline suggesting a consequent increase in dryness

holocene vegetation and climatic variations in central india a study based on multiproxy evidences palynology texture mineralogy geochemistry and magnetic susceptibility analysis of a 2 m deep sediment core from padauna swamp southeastern madhya pradesh infers that between 8600 and 7500 cal yr bp a warm and relatively less humid climate prevailed with open tree savannahs dominated by grasses followed by sedges artemisia and members of chenopodiaceae amaranthaceae with scanty trees viz schrebera aegle marmelos and sterculia urens this is well supported by lower organic to carbonate carbon ratio coarser texture having relatively low cia and magnetic susceptibility values and presence of some primary minerals between 7500 and 6250 cal yr bp the tree savannahs were succeeded by open mixed deciduous forests with the invasion of a few more trees viz madhuca indica holoptelea emblica officinalis mitragyna parvifolia and members of anacardiaceae in response to onset of a warm and humid climate a considerable rise in organic carbon generated from the degradation of plentiful biomass along with increase in clay content with signs of kaolinite and increase in immobile over mobile elements with slightly higher cia and magnetic susceptibility values also suggest climatic amelioration the presence of ruderal plants such as artemisia cannabis sativa and cheno am further infers initiation of human activities in the region between 6250 and 2800 cal yr bp the mixed deciduous forests became more diverse and dense subduing grasses and other herbaceous elements sporadic incursion of shorea robusta sal in forest floristic was recorded around 5000 cal yr bp the overall change in the vegetation mosaic reflects that a warm and more humid climate prevailed in the region probably on account of invigoration of southwest monsoon this observation is further corroborated by other proxy data showing a spurt in organic inorganic carbon ratio increase in clay content with matured mineralogy significantly higher cia and magnetic susceptibility values since 2800 cal yr bp onwards the modern sal dominated deciduous forests were established indicating continuation of warm and more humid climate including timely arrival of sw monsoon coinciding with the shedding of sal seeds as they are viable for a very short period

topography relief and trmm derived rainfall variations along the himalaya 1 along the southern himalayan topographic front the indian summer monsoon modulates erosive processes and rates to investigate the influence of topography and relief on rainfall generation and resultant erosion we processed satellite rainfall amounts for the last 8 years 1998 2005 from the tropical rainfall measurement mission trmm based upon a spatial resolution of 5 5 km for the himalaya we identify 1 the spatial distribution of rainfall and 2 the large scale relationships between topography relief and rainfall locations our results show two distinct rainfall maxima along strike in the himalaya the first outer rainfall peak occurs along the southern margin of the lesser himalaya within a narrow band of mean elevation 0 9 0 4 km and mean relief 1 2 0 2 km the second discontinuous inner band typically occurs along the southern flank of the greater himalaya elevation and relief both 2 1 0 3 km

holocene climatic fluctuations in the gujarat alluvial plains based on a multiproxy study of the pariyaj lake archive western india abstract a sediment core from pariyaj lake from the vatrak river basin located at the desert margin in the gujarat alluvial plains of western india was investigated in a multidisciplinary aspect the goal was to reconstruct the palaeoclimate palaeoenvironment and tectonic history and to understand the role these factors played in the geomorphological evolution of the area during the holocene palaeoclimatic interpretations also shed light on the factors responsible for the rise and fall of the harappan civilisation the results obtained based on multiproxy studies show five climatic phases during the last 11 000 yr bp phase 1 11 000 cal yr bp represents a very humid climate and high precipitation discharge leading to high lake stand as attested by the high pollen concentration of semi evergreen tree taxa phytoliths belonging to cool and moist grasses and large proportion of algae marking the onset of holocene in phase 2 8000 to 9000 cal yr bp a significantly reduced yield of pollen phytoliths and aquatic algae indicates shrinkage of the lake phase 3 7630 cal yr bp shows moderate yield of pollen and phytolith pointing towards fluctuating precipitation conditions phase 4 5864 to 4680 cal yr bp shows very low pollen and phytolith counts indicating a very dry spell finally phase 5 4680 to 3500 cal yr bp shows a good density and diversity of flora the wet climate and high lake stand 11 000 cal yr bp 7630 cal yr bp and after 4680 cal yr bp are synchronous with the lacustrine marine and aeolian records of western india the contribution of winter precipitation at 7630 cal yr bp and after 4680 cal yr bp can be correlated with similar records from rajasthan lake decrease in the precipitation activity the low lake stand and the onset of dry climatic condition between 8000 and 9000 cal yr bp corresponds to a near global anomaly of this period another dry event between 5864 and 4680 cal yr bp documented in pariyaj lake record is synchronous with various proxy records of the mid late holocene afro asiatic monsoonal belt

monsoon variability and chemical weathering during the late pleistocene in the goriganga basin higher central himalaya india stable isotope analysis along with radiocarbon and luminescence dating of late pleistocene lacustrine deposits at burfu in the higher central himalaya are used to interpret hydrologic changes in the lake basin from 15 5 ka to 14 5 ka the burfu lake was largely fed by melting glaciers a warming event at 14 5 ka suggests an enhanced monsoon and increased carbonate weathering from 13 5 ka to 12 5 ka the isotopic data suggest large amplitude climate variability following this the isotope data suggest a short lived abrupt cooling event comprising a 300 yr intense cool period followed by a 500 yr interval of moderate climate a shift in isotope values at 11 3 ka may signify a strengthening monsoon in this region the inferred climatic excursions appear to be correlative at least qualitatively with global climatic events and perhaps the burfu lake sequence provides regional evidence of globally recorded excursions this study also suggests a potential use of radiocarbon ages in specific environments as a paleoenvironmental proxy

carbonate isotopes from high altitude tso moriri lake nw himalayas provide clues to late glacial and holocene moisture source and atmospheric circulation changes abstract high resolution isotopic 18 o and 13 c investigations on endogenic carbonates calcite aragonite from tso moriri lake nw himalaya show dramatic fluctuations during the late glacial and the early holocene and a persistent enrichment trend during the late holocene changes in this lake are largely governed by the input meltwater monsoon precipitation evaporation i e ratio also reflected in changes in the carbonate mineralogy with aragonite being formed during periods of lowest i e using new isotopic data on endogenic carbonates in combination with the available data on geochemistry mineralogy and reconstructed mean annual precipitation we demonstrate that the late glacial and early holocene carbonate 18 o variability resulted from fluctuating indian summer monsoon ism precipitation in nw himalaya this region experienced increasing ism precipitation between ca 13 1 and 11 7 cal ka and highest ism precipitation during the early holocene 11 2 8 5 cal ka however during the late holocene evaporation was the dominant control on the carbonate 18 o regional comparison of reconstructed hydrological changes from tso moriri lake with other archives from the asian summer monsoon and westerlies domain shows that the intensified westerly influence that resulted in higher lake levels after 8 cal ka in central asia was not strongly felt in nw himalaya

rapid changes in the oceanic fronts in the norwegian sea during the last deglaciation implications for the younger dryas cooling event abstract two high resolution cores enam93 21 north of the faeroe islands and troll 89 03 off southwest norway from the se norwegian sea have been investigated for downcore variations in planktic foraminifera ird content and oxygen isotopes in a period from 15 to 9 ka the results exhibit frequent and large amplitude changes in sea surface temperature during the last deglaciation a sudden and profound increase in sst at 12 8 ka is followed by three abrupt and short lived cooling events terminated by the younger dryas cooling the presence of strong temperature gradients in the norwegian sea region during the bolling younger dryas period have implications for the heat flux towards the north a possible time lag may exist between enam93 21 and troll 89 03 at the beginning of the younger dryas cooling these findings indicate that polar waters migrated eastwards at the beginning of the younger dryas period

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

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

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

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

strong coherence between solar variability and the monsoon in oman between 9 and 6 kyr ago variations in the amount of solar radiation reaching the earth are thought to influence climate but the extent of this influence on timescales of millennia to decades is unclear a number of climate records show correlations between solar cycles and climate1 but the absolute changes in solar intensity over the range of decades to millennia are small2 and the influence of solar flux on climate is not well established the formation of stalagmites in northern oman has recorded past northward shifts of the intertropical convergence zone3 whose northward migration stops near the southern shoreline of arabia in the present climate4 here we present a high resolution record of oxygen isotope variations for the period from 9 6 to 6 1 kyr before present in a th u dated stalagmite from oman the 18o record from the stalagmite which serves as a proxy for variations in the tropical circulation and monsoon rainfall allows us to make a direct comparison of the 18o record with the 14c record from tree rings5 which largely reflects changes in solar activity6 7 the excellent correlation between the two records suggests that one of the primary controls on centennial to decadal scale changes in tropical rainfall and monsoon intensity during this time are variations in solar radiation

late quaternary environmental and sea level changes from kolleru lake se india inferences from mineral magnetic geochemical and textural analyses abstract the present study employs mineral magnetic geochemical and textural parameters to elucidate the climate and sea level change signatures from kolleru lake sediments representing the inter deltaic part of the krishna godavari sedimentary basin kg basin for this purpose four cores were obtained which included significant peat the conventional radiocarbon dating suggested that the peat formation took place during 9 ka 6 ka with an average sedimentation rate of 0 31 cm y thermomagnetic analysis identifies titanomagnetite magnetite and hematite as the dominant magnetic mineralogy of the kg basin sediments the variation in magnetic mineralogy is related to paleoclimatic and paleoenvironmental processes the transitions between titano magnetite and hematite coincide with peat layers of the cores as indicated by sirm saturation isothermal remanent magnetization magnetic susceptibility and s ratio defined by irm 0 3t sirm values the various mineral magnetic parameters and s ratio along with major elemental concentrations of ti al fe and zr show signatures of an arid event before 10 ka between 9 ka 8 ka periods and during the last 5 5 ka the overall climate of warm and humid type was inferred from 10 ka to 9 ka which correlates with early holocene optima and 6 ka to 5 5 ka of middle holocene the presence of evaporite crystals in the lowermost part of the cores corroborated by mineral magnetic and geochemical proxies indicates sub aerially weathered facies of the arid late pleistocene similarly the peat layers rich in mangrove pollen indicate sea level changes between 10 ka and 6 ka the sub surface position of the pleistocene weathered layer and the holocene peat layer suggests tectonic subsidence of the area which is situated over the basement graben known as gudiwada sub basin

late holocene drought responsible for the collapse of old world civilizations is recorded in an italian cave flowstone a severe drought in parts of low latitude northeastern africa and southwestern asia 4200 yr ago caused major disruption to ancient civilizations stable isotope trace element and organic fluorescence data from a calcite flowstone collected from the well watered alpi apuane karst of central western italy indicate that the climatic event responsible for this drought was also recorded in mid latitude europe although the timing of this event coincides with an episode of increased ice rafted debris to the subpolar north atlantic the regional ocean atmosphere response seems atypical of similar holocene ice rafting events furthermore comparison of the flowstone data with other regional proxies suggests that the most extreme part of the dry spell occurred toward the end of a longer term climate anomaly

late pleistocene holocene vegetation and indian summer monsoon record from the lahaul northwest himalaya india abstract the high resolution holocene paleomonsoon records from northwest nw himalaya are limited the carbon isotope 13 c total organic carbon toc and pollen analysis were therefore carried out from a peat lake sediment sequence developed in alpine meadows of the chandra valley lahaul nw himalaya in order to reconstruct centennial to millennial scale vegetational changes and indian summer monsoon ism variability during the holocene the chronology of peat lake sediments is constrained with 9 ams 14 c dates the recovered non arboreal pollen nap suggested that during holocene alpine desert steppe meadows and shrubs growing along the stream had developed in the lahaul valley whereas arboreal pollens ap e g pinus quercus cedrus and ulmus presently growing in the southern hill slopes of pir panjal range indicated moisture carrying monsoonal air flow from the south the increased 13 c and low toc values between 12 880 and 11 640 calibrated years before present cal yr bp suggested weakening of ism and low organic carbon production corresponding to the younger dryas yd cold event the gradual depletion in carbon isotope ratio from 11 640 to 8810 cal yr bp indicated enhanced precipitation in the chandra valley in response of increased ism strength in early holocene the short spell of cold and dry climate with gradual decrease in ism intensity between ca 10 398 and 9778 cal yr bp is closely linked with bond event 7 the other prominent cold dry events recorded in present study are i 8810 to 8117 cal yr bp roughly corresponding to global 8 2 ka cold event ii 4808 to 4327 cal yr bp closely preceding the global 4 2 ka cold arid period and iii 1303 to 1609 cal ad corresponding to little ice age lia event the expansion of thermophillous broad leaved taxa viz betula utilis alnus nepalensis quercus semicarpifolia and juglans regia and effective growth of meadow vegetation such as grasses caryophyllaceae and artemisia along with marshy elements i e polygonum and liliaceae between 6732 and 3337 cal yr bp marked warm and wet holocene climate optimum hco period the warm and moist climate from 1158 647 cal yr bp corresponded with global medieval warm period mwp

palaeoclimate interpretation of stable isotope data from lake sediment archives the isotope composition of authigenic and biogenic carbonates and diatom silica are commonly used as palaeoclimate proxies from lake sediments this article reviews the controls on the isotope composition of lacustrine skeletal and non skeletal deposits and illustrates how stable isotope studies contribute to an understanding of changes in temperature precipitation patterns evaporation and the carbon cycle it highlights the differences in the palaeoclimate potential of a wide range of lakes ranging from open to closed lake basins a large number of the case histories but not all are drawn from studies of temperate lakes from europe large closed lake systems in the tropics and elsewhere lose water predominantly through evaporation and contain sediments with variable and generally high 18o values fluctuations in the isotope composition of authigenic or biogenic minerals are mainly a function of long term changes in the precipitation evaporation ratio in contrast small open lakes which have a degree of through flow typically contain sediments with 18o values that vary by no more than a few these variations are generally ascribed to variations in temperature or the isotope composition of precipitation p from which either an annual or seasonally specific signal can be gained these types of lakes are common in northern europe and at high altitudes the interpretation of isotope data from a lacustrine succession requires a knowledge of the local processes that might control and modify the signal their effects need to be quantified and a robust calibration using the modern lake system is necessary to establish the relationship between the measured signal the isotopic composition of the host waters and climate

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

large scale model test investigation on wave run up in irregular waves at slender piles an experimental large scale study on wave run up generated loads on entrance platforms for offshore wind turbines was performed the experiments were performed at grosser wellenkanal gwk forschungszentrum kuste fzk in hannover germany the present paper deals with the run up heights determined from high speed video recordings based on the measured run up heights different types of prediction formulae for run up in irregular waves were evaluated in conclusion scale effects on run up levels seem small except for differences in spray however run up of individual waves is difficult to predict due to high importance of wave form

a δ 13 c record of late quaternary climate change from tropical peats in southern india stable isotope ratios of carbon in soils or lake sediments1 3 and of oxygen and hydrogen in peats4 5 have been found to reflect past moisture variations and hence to provide valuable palaeoclimate records previous applications of the technique to peat have been restricted to temperate regions largely because tropical climate variations are less pronounced making them harder to resolve here we present a 13c record spanning the past 20 kyr from peats in the nilgiri hills southern india because the site is at high altitude 2 000 m above sea level it is possible to resolve a clear climate signal we observe the key climate shifts that are already known to have occurred during the last glacial maximum 18 kyr ago and the subsequent deglaciation in addition we observe an arid phase from 6 to 3 5 kyr ago and a short wet phase about 600 years ago the latter appears to correspond to the mediaeval warm period which previously was believed to be confined to europe and north america6 7 our results therefore suggest that this event may have extended over the entire northern hemisphere

holocene vegetation and climate change in central ganga plain a study based on multiproxy records from chaudhary ka tal raebareli district uttar pradesh india abstract pollen sediment texture and organic inorganic carbon analyses of a 2 1 m thick sediment profile from chaudhary ka tal lake of raebareli district reveals that around 8470 to 6422 cal bp grasslands comprising grasses asteraceae cheno am with interspersed forest groves of madhuca indica holoptelea integrifolia shorea robusta and acacia thrived in the region under a warmer and moderately humid climate than today this is also substantiated by the finer clay sediment with increasing concentrations of moisture and organic carbon the appearance of cerealia pollen 7500 cal bp suggests incipient agrarian practice the record of aquatic elements lemna and typha reflects the existence of lake between 6422 and 3150 cal bp the forest groves became diversified with the invasion of more trees capparis butea monosperma and symplocos reflecting a warm and more humid climate compared to the previous phase attributed to the strengthening of the sw monsoon the higher concentration of organic carbon further confirms good vegetation cover and an increase in aquatic flora depict the expansion of lake a similar vegetation scenario existed 3150 to 1110 cal bp however the forest groves became less varied due to prevailing moderately humid climate owing to weakening of the sw monsoon this is also validated by more carbonate in the sediments from 1110 cal bp a further diminishing trend of trees implies that the region supported open grasslands owing to reduced rainfall under a warm and less humid climate which is corroborated by a further increase in carbonate content

early holocene monsoonal fluctuations in the garhwal higher himalaya as inferred from multi proxy data from the malari paleolake abstract a 4 9 m thick lake sequence formed due to the landslide damming of a stream in the semiarid garhwal himalaya was studied to understand past monsoonal variations in the region the optically stimulated luminescence osl chronology indicates that the lake existed between 12 and 7 ka ago chronologically constrained trends of sand percent organic phosphorus op apatite inorganic phosphorus aip and parameters of environmental magnetism were measured in the paleolake profile measured proxies indicate that the indian summer monsoon ameliorated in the early holocene after 12 ka cooling and it appears that all the proxies from the lake have captured this globally recognized early holocene warming four phases of wet conditions intensified monsoon are recognized at 11 5 ka 11 10 5 ka 10 9 ka and 8 7 ka with maximum uncertainties of 1000 years the wet phases are characterized by high magnetic susceptibility increased op and reduced aip in an attempt to understand the primary forcing of the sharp fluctuations in monsoonal activity in the region we show that changes in magnetic susceptibility match variations of residual atmospheric 14c suggesting a role for solar variability as an explanation of climatic variability

mid late holocene monsoonal variations from mainland gujarat india a multi proxy study for evaluating climate culture relationship a multi proxy study involving palynology phytoliths sedimentology clay mineralogy carbon isotopes and magnetic mineralogy was carried out on wadhwana lake sediments from sub humid zone of mainland gujarat to determine the mid holocene climatic fluctuations and its possible impact on the harappan culture the 1 03 m sediment profile of wadhwana lake shows five paleoclimatic phases the study reveals high lake stand during phase i 7500 5560 cal yr bp a considerable cool and moist climatic condition during phase i is inferred due to the presence of pollen belonging to wet evergreen taxa and high phytolith climatic index ic later part of phase i show gradual replacement of evergreen to deciduous pollen taxa decrease in ic value and dominance of smectite over kaolinite indicating a reduction in wet climatic condition due to decline in the precipitation and prevalence of seasonally dry climate however a large variety of madhuca meliaceae asteraceae pollen taxa abundant fresh water algae chrozophora and ceralia pollen in this period provides evidence of intensified arboriculture and agricultural activity low lake level and dry climate have been documented during phase ii 5560 to 4255 cal yr bp and are synchronous with the lake records of western indian region high values of phytolith aridity index iph high primary minerals increase in the i 13c values provide evidence for excessive dry climatic conditions at 4255 cal yr bp phase iii shows a gradual strengthening of sw monsoon after 3500 cal yr bp phase iv shows a short pulse of dry climatic conditions 3238 to 2709 cal yr bp followed by somewhat similar to present day climate for phase v the study concludes that onset of dry climate after 5500 cal yr bp is a regionally spread synchronous event that has been documented in several lake records of western india it is surmised that the urbanization in harappan civilization in north west india was coincident with the initial phase of declining rainfall of mid holocene the emergence of cultural complexity of harappan civilization should be seen as an initial adaptation to earliest phase of environmental deterioration and its subsequent decline is probably linked with the changing seasonality pattern and excessive dry climate of later phase 4200 4255 cal yr bp of mid holocene

late quaternary sediments minerals and inferred geochemical history of didwana lake thar desert india abstract variations in clastic sediment texture mineralogy of both evaporites formed at the surface and precipitates formed below the lake floor and the relative chemical activities of the major dissolved components of the chemical precipitates have allowed reconstruction of the history of salinity and water level changes in didwana lake thar desert india hypersaline conditions prevailed at about the last glacial maximum with little evidence of clastic sediments entering the lake between ca 13 000 and 6000 b p the lake level fluctuated widely the lake alternately hypersaline and fresh and clastic sediments were delivered to the lake at a low rate deep water conditions occurred ca 6000 b p and clastic influx increased abruptly the water level dropped towards 4000 b p when the lake dried briefly since 4000 b p the lake has been ephemeral with a lowered rate of sedimentation and mildly saline conditions rather like those of today this sequence of changes documented in the lake parallels changes in vegetation recorded in published pollen diagrams from both the thar and the arabian sea correlation of the various lines of evidence suggests that the climate of the last glacial maximum at didwana was dry and windy with a weak monsson circulation the monsson was re established between ca 13 000 and a little before 6000 b p and when winter rainfall increased ca 6000 b p the lake filled to its maximum depth

late quaternary evolution of ashtamudi sasthamkotta lake systems of kerala south west india abstract sedimentological and palynological analysis of two borehole samples collected from the confluence of kallada river with the ashtamudi lake in the south west coast of india have been addressed while ascertaining the late quaternary evolution of the two borehole samples the one collected from pangod 9 03 n 76 42 e reveals a fining upward sequence with medium to coarse sand 3 05 m at base organic carbon rich silt and fine sand dominated sediments 2 m at the middle and yellowish brown muddy sediments 3 2 m at the top the middle layer embeds a suite of partly carbonized sub fossil logs of wet evergreen to semi evergreen vegetation the palynoflora of this layer reveals that the depositional site is within the tidal limit and deposition occurred under high precipitation and atmospheric humidity the similarity in 14 c dates of a wood at 5 m bgl 7490 90 yrs bp and the embedding sediments 7480 80 yrs bp indicate quick burial of the riparian vegetation the west kallada borehole 9 30 n 76 37 e reveals middle to late holocene sequence of clayey silt 6250 110 yrs bp 3880 80 yrs bp and sand resting unconformably over greyish white clayey sand with pebbles and granules derived from laterite provenance palynological analysis shows that the holocene sedimentation took place under marine nearly marine environment and later changed to brackish water and finally to freshwater environment marine transgression 6000 yrs bp coupled with heavy rainfall in the hinterlands was responsible for faster sedimentation in the region the heavy mineral contents especially opaques garnet and sillimanite in the sediment samples of the study area as well as the bathymetric configuration of the ashtamudi sasthamkotta and chelupola lakes reiterate the fact that these lakes have been evolved from an embayment consequent to incomplete partial silting up during early to middle holocene higher sea levels and also under high rainfall of the holocene climatic optimum of around 10 000 7000 yrs bp

hydrological evolution during the last 15 kyr in the tso kar lake basin ladakh india derived from geomorphological sedimentological and palynological records abstract the tso kar lake basin in ladakh northwestern himalayas 33 18 n 78 e 4527 m a s l is located close to the modern boundary of effective moisture transport from the indian summer monsoon in order to reconstruct the possible monsoonal impact on the hydrology of the lake basin during the last 15 kyr we studied the geomorphology of the basin and combined the results with multi proxy records from tso kar lake sediments major analyses comprise geochemical data high resolution x ray fluorescence xrf mineral composition xrd aquatic pollen and non pollen palynomorphs npp although the chronological framework based on 41 14c ams dates remains speculative for the lateglacial and late holocene periods our results indicate major hydrological phases linked to regional climate variations and tectonic activity the maximum glacier advance falls within the period between the global lgm and ca 15 kyr bp while the basin remained open and may have drained along the paleo tso kar river tectonic pulses may have triggered terrace development and the closure of the lake the estimated mean vertical displacement rate accounts for 7 9 mm yr considerable summer monsoon moisture supply occurred for the periods around 12 5 kyr bp and between ca 11 5 and 8 6 kyr bp indicated by deposition of more profundal lake facies and the development of aquatic fauna and flora the lake level rise about 11 8 kyr bp was due to intensified glacier melt and summer monsoon effective moisture supply the lake reached its maximum level and extent between 8 5 and 7 kyr bp under warm moist climate conditions permafrost was absent from the basin summer monsoon influence weakened after 8 kyr bp with a short reverse trend at ca 5 6 kyr bp the lake shrank gradually after 7 kyr bp towards its lowest stand at about 4 2 kyr bp with return of permafrost activity subsequent terrace formation was probably amplified by tectonic movement the lake remained at a low level with minor fluctuations the results indicate that the orbitally driven regional climate variability is well reflected in the tso kar basin by hydrological variations considerable summer monsoon moisture seems to have influenced the area only during the early holocene the late quaternary evolution of the tso kar was controlled by the interplay of climate forces local morphodynamics and tectonic impact

hydrography and climate of the last 4400 years in a sw greenland fjord implications for labrador sea palaeoceanography a multiproxy record including benthic foraminifera diatoms and xrf data of a marine sedi ment core from a sw greenland fjord provides a detailed reconstruction of the oceanographic and cli matic variations of the region during the last 4400 cal years the lower part of our record represents the final termination of the holocene thermal maximum after the onset of the neoglaciation at approxi mately 3 2 ka cal bp the fjord system was subject to a number of marked hydrographical changes that were closely linked to the general climatic and oceanographic development of the labrador sea and the north atlantic region our data show that increased advection of atlantic water irminger sea water from the west greenland current into the labrador sea was a typical feature of northeast atlantic cool ing episodes such as the little ice age and the european dark ages while the advection of irminger sea water decreased significantly during warm episodes such as the mediaeval warm period and the roman warm period whereas the mediaeval warm period was characterized by relatively cool climate as suggested by low meltwater production the preceding dark ages display higher meltwater runoff and consequently warmer climate when compared with european climate these regional climate anomalies indicate persisting patterns of advection of colder respectively warmer air masses in the study region dur ing these periods and thus a long term seesaw climate pattern between west greenland and europe

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

holocene climate records from lake sediments in india assessment of coherence across climate zones abstract holocene lake records constitute an important archive for the reconstruction of paleoclimate despite the overall climatic stability of the holocene the monsoons in india both summer and winter show various episodes of weakening and strengthening during this time interval as the holocene lake records are distributed across the various geomorphic and climatic zones of india they offer the possibility of understanding regional scale variations in terms of both qualitative and quantitative assessment of the available proxy data the present day precipitation in india varies from

a holocene pollen record from the northwestern himalayan lake tso moriri implications for palaeoclimatic and archaeological research this paper presents a new fossil pollen record from tso moriri 32 54 n 78 19 e 4512 m a s l and seeks to reconstruct changes in mean annual precipitation map during the last 12 000 years this high alpine lake occupies an area of 140 km2 in a glacial tectonic valley in the northwestern himalaya the region has a cold climate with a map 300 mm and open vegetation the hydrology is controlled by the indian summer monsoon ism but winter westerly associated precipitation also affects the regional water balance results indicate that precipitation levels varied significantly during the holocene after a rapid increase in map a phase of maximum humidity was reached between ca 11 and 9 6 cal ka bp followed by a gradual decline in map this trend parallels the reduction in the northern hemisphere summer insolation comparison of different palaeoclimate proxy records reveal evidence for a stronger holocene decrease in precipitation in the northern versus the southern parts of the ism domain the long term trend of ism weakening is overlaid with several short periods of greater dryness which are broadly synchronous with the north atlantic cold spells suggesting reduced amounts of westerly associated winter precipitation compared to the mid and late holocene it appears that westerlies had a greater influence on the western parts of the ism domain during the early holocene during this period the westerly associated summer precipitation belt was positioned at mediterranean latitudes and amplified the ism derived precipitation the tso moriri pollen record and moisture reconstructions also suggest that changes in climatic conditions affected the ancient harappan civilisation which flourished in the greater indus valley from approximately 5 2 to 3 cal ka bp the prolonged holocene trend towards aridity punctuated by an interval of increased dryness between ca 4 5 and 4 3 cal ka bp may have pushed the mature harappan urban settlements between ca 4 5 and 3 9 cal ka bp to develop more efficient agricultural practices to deal with the increasingly acute water shortages the amplified aridity associated with north atlantic cooling between ca 4 and 3 6 and around 3 2 cal ka bp further hindered local agriculture possibly causing the deurbanisation that occurred from ca 3 9 cal ka bp and eventual collapse of the harappan civilisation between ca 3 5 and 3 cal ka bp

reconstruction of last glacial to early holocene monsoon variability from relict lake sediments of the higher central himalaya uttrakhand india abstract proglacial lake sediments at goting in the higher central himalaya were analyzed to reconstruct the summer monsoon variability during the last glacial to early holocene sedimentary structures high resolution mineral magnetic and geochemical data suggest that the lacustrine environment experienced fluctuating monsoonal conditions optically stimulated luminescence osl dating indicates that the lake sedimentation occurred before 25 ka and continued after 13 ka during this period goting basin witnessed moderate to strengthened monsoon conditions around 25 ka 23 5 ka 22 5 ka 22 ka 18 ka 17 ka 16 5 ka and after14 5 13 ka the last glacial phase ended with the deposition of outwash gravel dated at 11 ka indicating glacial retreat and the onset of holocene condition additionally centennial scale fluctuations between 16 5 ka and 12 7 ka in the magnetic and geochemical data are seen a close correspondence at the millennial scale between our data and that of continental and marine records from the indian sub continent suggests that goting basin responded to periods of strengthened monsoon during the last glacial to early holocene we attribute the millennial scale monsoon variability to climatic instability in higher northern latitudes however centennial scale abrupt changes are attributed to the result of albedo changes on the himalaya and tibetan plateau

microparticle concentration variations linked with climatic change evidence from polar ice cores the microparticle concentrations in three deep ice cores reveal a substantial increase in the concentration of insoluble particles in the global atmosphere during the latter part of the last major glaciation the ratio of the average particle concentration in the late glacial strata to that in the holocene strata is 6 1 for the core from dome c antarctica 3 1 for the core from byrd station antarctica and 12 1 for the core from camp century greenland whether this temporal correlation between increased atmospheric particle load and the lower surface temperatures is directly causal is unknown however the variations in these two parameters must be satisfactorily resolved in any successful hypothesis that addresses the causes of climatic change

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 high resolution palaeoclimatic record for the last 27 500 years in tropical west africa from the carbon and nitrogen isotopic composition of lacustrine organic matter variations in the carbon and nitrogen isotopic composition of bulk organic matter in the sediments of lake bosumtwi ghana reflect climatically induced changes to the lake and the catchment flora cores spanning the last 27 5 kyr of sedimentation in the lake show large oscillations in 13corg pdb and 15norg air the late pleistocene record is particularly detailed showing changes of ca 20 in carbon and ca 10 in nitrogen isotopic compositions these variations are of complex origin although different in magnitude major isotopic excursions in the two records are generally in phase and reveal the occurrence of two major dry intervals at and immediately following the last glacial maximum the allerod younger dryas period also seems to have been marked by generally dry conditions in this part of tropical west africa nitrogen isotopic evidence suggests that during the period 9 2 3 2 kyr the lake had an extremely stable water column probably due to the absence of a windy or cool dry season or both regular circulation of the water column recommenced during the late holocene and has persisted until the present day

wave height distributions on shallow foreshores wave height distributions on shallow foreshores deviate from those in deep water due to the effects of the restricted depth to height ratio and of wave breaking laboratory data of wave heights on shallow foreshores of different slopes have been analysed to determine these effects and to derive generalised empirical parameterisations a model distribution is proposed consisting of a rayleigh distribution or a weibull distribution with exponent equal to 2 for the lower heights and a weibull with a higher exponent for the higher wave heights the parameters of this distribution have been estimated from the data and expressed in terms of local wave energy depth and bottom slope yielding a predictive model that is found to be significantly more accurate than existing expressions

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

wave run up on cylindrical and cone shaped foundations for offshore wind turbines abstract during the last decade several offshore wind farms were built and offshore wind energy promises to be a suitable alternative to provide green energy however there are still some engineering challenges in placing the foundations of offshore wind turbines for example wave run up and wave impacts cause unexpected damage to boat landing facilities and platforms to assess the forces due to wave run up the distribution of run up around the pile and the maximum run up height need to be known this article describes a physical model study of the run up heights and run up distribution on two shapes of foundations for offshore wind turbines including both regular and irregular waves the influence of wave steepness wave height and water depth on run up is investigated the measured run up values are compared with applicable theories and previous experimental studies predicting run up on a circular pile the results show that the shape of the foundation substantially affects the maximum run up level increasing the expected run up value a new relationship between the wave climate regular and irregular waves and the run up is suggested for this the velocity stagnation head theory is adjusted and second order stokes equations are used to calculate the wave kinematics in the crest the variation of the run up around the pile is measured and it is found that the position with the lowest run up level is located under 135 while the run up at that position amounts to approximately 40 to 50 of the maximum run up

tropical rainforest vegetation climate and sea level during the pleistocene in kerala india abstract the southwestern ghats region of the indian peninsula is unique for its extant endemic rainforest flora supported by high rainfall throughout the year the record of tropical rainforest corresponding to the dynamic series of pleistocene interglacial glacial cycles is poorly known from peninsular india this communication discusses the palynological study of organic matter om deposits 40 ka bp in two well sections chaganachery kerala from the indian peninsula west coast a rich archive of tropical rainforest pollen spores and marine dinoflagellate cysts indicates anoxic fluvio marine estuarine depositional environments during warmer climates with an intensified asian monsoon the geochemical fingerprinting of glass shards indicates the presence of youngest toba ash of 74 ka from northern sumatra and therefore establishes a time controlled stratigraphy thus the depositional time period of the om is related to the sea level highstand of marine isotopic stage 5 1 80 ka which was the host to the ytt shards the late quaternary pollen spores diversity suggests that the modern climatic conditions in the southwestern ghats have facilitated the conservation of moist evergreen rainforest and dry moist deciduous forest the pollen grains show its lineage with the extant flora and some of the fossil pollen recorded during the mesic tertiary period from the indian peninsula thus it appears that the tropical rainforest survived here as plant refugia in xeric glacial quaternary periods perhaps as riparian vegetation and was rejuvenated during the holocene as modern extant flora

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

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

climate change at the 4 2 ka bp termination of the indus valley civilization and holocene south asian monsoon variability 1 planktonic oxygen isotope ratios off the indus delta reveal climate changes with a multi centennial pacing during the last 6 ka with the most prominent change recorded at 4 2 ka bp opposing isotopic trends across the northern arabian sea surface at that time indicate a reduction in indus river discharge and suggest that later cycles also reflect variations in total annual rainfall over south asia the 4 2 ka event is coherent with the termination of urban harappan civilization in the indus valley thus drought may have initiated southeastward habitat tracking within the harappan cultural domain the late holocene drought cycles following the 4 2 ka bp event vary between 200 and 800 years and are coherent with the evolution of cosmogenic 14c production rates this suggests that solar variability is one fundamental cause behind holocene rainfall changes over south asia

reconstructed late quaternary hydrological changes from lake tso moriri nw himalaya abstract we present the results of our investigations on the radiocarbon dated core sediments from the lake tso moriri nw himalaya aimed at reconstructing palaeohydrological changes in this climatically sensitive region based on the detailed geochemical mineralogical and sedimentological analysis we recognise several short term fluctuations superimposed upon seven major palaeohydrological stages identified in this lake since 26 cal ka stage i 20 2 cal ka shallow lake characterised by input of coarse grained detrital sediments stage ii 20 2 16 4 cal ka lake deepening and intensification of this trend ca 18 cal ka stage iii 16 4 11 2 cal ka rising lake levels with a short term wet phase 13 1 11 7 cal ka stage iv 11 2 8 5 cal ka early holocene hydrological maxima and highest lake levels inferred to have resulted from early holocene indian monsoon intensification as records from central asia indicate weaker westerlies during this interval stage v 8 5 5 5 cal ka mid holocene climate deterioration stage vi 5 5 2 7 cal ka progressive lowering of lake level stage vii 2 7 0 cal ka onset of modern conditions the reconstructed hydrological variability in lake tso moriri is governed by temperature changes meltwater inflow and monsoon precipitation increased runoff a regional comparison shows considerable differences with other palaeorecords from peninsular india during late holocene

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

multiproxy record of monsoon variability from the ganga plain during 400 1200 a d abstract understanding on the indian summer monsoon ism variability is chiefly based upon the marine proxies and a few continental records the ganga plain one of the most densely populated regions of the world marked by intensive cultivation of monsoon dependent crops and a rich cultural history is not yet well understood in the context of monsoon variability we present here a 400 1200 a d ams radiocarbon dated record of ropan chhapra tal in the central ganga plain using sedimentology environmental magnetism and stable isotope of oxygen for ism variability the environmental magnetic parameters lf arm sirm lf s ratio b 0 cr and hirm inferred antiferromagnetic mineralogy hematite and or goethite independent of grain size variation during 400 900 a d depicting climate variability within warm humid to warm arid conditions favouring stronger ism seasonality prevalence of ferrimagnetic mineralogy under less oxygenated conditions intermittently demonstrates an altered catchment regime or possibly in response to stronger winter monsoon the higher 18 o values around 500 580 and 740 a d indicate warm and arid conditions under weak ism the lower 18 o values around 480 540 and 700 a d and from 900 to 1200 a d occur during warm and humid conditions indicating maximum intensity of the ism increased silt content from 800 a d onwards is due to increased surface runoff in response to enhanced precipitation and the higher clay percentage around 500 580 and 740 indicates low energy ponding conditions under weak ism the well sorted nature of sediment indicates consistency of the lacustrine environments under fairly uniform energy and constant bottom water conditions under varied monsoonal intensity combinations of sediment textures and stable isotope indicate intense ism at 480 and 540 a d with flooding around 700 a d and a weak monsoon at 580 and 740 a d with drought at 500 a d during 900 1200 a d the multiproxy record suggests strong summer monsoon synchronous with medieval warm period mwp whereas after 1200 a d the weak monsoon phase coincides with the onset of the little ice age lia

record of vegetation and climate during late pleistocene holocene in central ganga plain based on multiproxy data from jalesar lake uttar pradesh india pollen organic inorganic carbon ratio clay mineral texture analyses and radiocarbon dating of a 2 8 m sediment profile from jalesar lake demonstrate that from prior to 42 490 until 13 560 cal bp the central ganga plain supported grassland with scanty trees under a cool and dry climate the sediments deposited during 13 560 5260 cal bp are palynologically barren and coarser in nature with increased inorganic organic carbon ratio depicting the upwarping phase of the ganga plain between 5260 and 4760 cal bp the immigration of more trees including holoptelea acacia and bombax accompanied by higher clay and organic carbon indicate establishment of forest groves under an ameliorating climate the debut of cerealia pollen denotes the initiation of agricultural practices around 4760 3260 cal bp forest groves became diversified substantiated by higher clay with increasing kaolinite and organic carbon indicating warm and humid climate owing to an active sw monsoon the consistent presence of aquatics and rising trend of cerealia pollen suggest lake expansion and acceleration in agricultural practices respectively between 3200 and 1200 cal bp the forest groves became sparse allowing coarser sediments with less organic carbon which implies that climate became less humid since 1200 cal bp diminution of arboreals signifies a weak sw monsoon

stable isotopes in bulk carbonates and organic matter in recent sediments of lake qinghai and their climatic implications abstract multi proxy indices on annual decadal scales during the past 600 years were developed from the surface sediments of lake qinghai based on 210pb and 137cs geochronology the 13ccarb 18ocarb and total carbonate content are consistent with one another in trends and their variations have been mainly ascribed to regional temperature it is suggested that the strong evaporation contributes in modifying 18o of lake water and 13c of the dissolved inorganic carbon of the surface water and appears to be responsible for the covariance between 13ccarb and 18ocarb photosynthesis of the aquatic plants appears to have played a significant role in determining 15n of organic matter the discrimination of 14n and 15n during photosynthesis may have triggered a positive linkage between temperatures and 15norg after removal of the stratigraphic trend variations of total organic carbon toc c n ratio and 13corg have been ascribed to local precipitation toc after removal of the stratigraphic trend is positively correlated with the c n ratio r 0 45