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

a record of holocene climate change from lake geochemical analyses in southeastern arabia lacustrine sediments from southeastern arabia reveal variations in lake level corresponding to changes in the strength and duration of indian ocean monsoon iom summer rainfall and winter cyclonic rainfall the late glacial holocene transition of the region was characterised by the development of mega linear dunes these dunes became stabilised and vegetated during the early holocene and interdunal lakes formed in response to the incursion of the iom at approximately 8500 cal yr bp with the development of c3 dominated savanna grasslands the iom weakened ca 6000 cal yr bp with the onset of regional aridity aeolian sedimentation and dune reactivation and accretion despite this reduction in precipitation the lake was maintained by winter dominated rainfall there was a shift to drier adapted c4 grasslands across the dune field lake sediment geochemical analyses record precipitation minima at 8200 5000 and 4200 cal yr bp that coincide with bond events in the north atlantic a number of these events correspond with changes in cultural periods suggesting that climate was a key mechanism affecting human occupation and exploitation of this region

low concentration of heavy metals in the yangtze estuarine sediments china a diluting setting abstract an examination of the spatial and temporal distribution of 17 major heavy metals i e fe zn ni mg co mn etc was made in the yangtze estuarine sediments revealed by a number of vibrocores taken from the different sediment zones including delta front prodelta and delta shelf transition the results obtained from the numerous core samples which were also measured for pb 210 and cs 137 show that 1 the silty clay comprising the prodelta facies serves as a depositional sink attracting high concentrations of heavy metals delivered from the river mouth 2 after being normalized to aluminum as a proxy for grain size most heavy metals presented in the prodelta facies have lower concentrations than in the other adjacent sediment zones 3 also after normalization concentrations of most heavy metals in the vibrocore sediments tend to increase up core and 4 sedimentation rates in the study area range from 2 0 to 6 0 cm a hence the vibrocores contain a sedimentary record of metal deposition covering more than 50 years it has previously been assumed that sediments off the river mouth were heavily polluted due to industrialization of the shanghai metropolitan area which peaked about 50 years ago however the low concentrations of heavy metals in the study area before and after normalization do not support this assumption the yangtze estuary is characterized largely by the tremendous runoff and unpolluted sediments derived from the upper drainage basin to constitute a unique diluted setting in which the dispersal behavior of heavy metals from the adjacent industrialized coast is influenced substantially as a result the heavy metals in the study area are obviously lower than those previously determined along the coast

polycyclic aromatic hydrocarbons pahs and pb isotopic ratios in a sediment core from shilianghe reservoir eastern china implying pollution sources the history records of polycyclic aromatic hydrocarbons pahs lead and its stable isotope ratios were determined in a sediment core to receive anthropogenic impacts on the shilianghe reservoir in eastern china the historical changes of pahs concentrations pahs fluxes pb al and pb isotope ratios showed a synchronous trend throughout the core suggesting changes in energy usage and correlating closely with the experience of a rapid economic and industrial development of the catchment linyi city in eastern china pahs isomer ratios results reveal pahs in sediments are dominantly anthropogenic pyrogenic source dominated by the combustion of coal and biomass furthermore the pb isotopic composition also clearly indicates that coal combustion dust mainly contributed to the pb burden in the reservoir sediments based on mix end member model of pb isotope ratios coal combustion dust dominated anthropogenic pb sources over fifty years contributing from 31 to 62 of total pb in sediment and the contribution of leaded gasoline was low than average 25 in addition a stable increase of coal combustion source was found in sediment core while the contribution of leaded gasoline had declined in recent decades with the phase out of leaded gasoline in china c 2015 elsevier ltd all rights reserved

very recent and wide spread basaltic volcanism on mars new spacecraft data provide increasing evidence for a dynamic environment on presenta day mars exogenic processes such as impact cratering mass wasting processes and active dune migration have all been observed to modify the surface no traces of current endogenic activity have been found yet but some studies point to very localized volcanism in the last few millions of years however no systematic study of young volcanic surfaces had been performed so far we present absolute model age determinations of plains volcanism on mars as derived from impact crater sizefrequency distributions extended areas in tharsis the largest volcanoa tectonic region on mars have been resurfaced by lava flows in the last few tens of millions of years we also present results on the rheologic properties of these lava flows inferred from morphometric measurements yield strengths are in the range of 100a 300 pa and viscosities reach values of 10 2 to 10 3 pa s indicating basaltic compositions the results imply that mars retained until recently and probably still retains enough internal heat to produce widea spread plaina style volcanism producing lowa viscosity lava flows throughout large parts of tharsis

a re examination of evidence for the north atlantic 1500 year cycle at site 609 ice rafting evidence for a 1500 year cycle sparked considerable debate on millennial scale climate change and the role of solar variability here we reinterpret the last 70 000 years of the subpolar north atlantic record focusing on classic dsdp site 609 in the context of newly available raw data the latest radiocarbon calibration marine09 and ice core chronology gicc05 and a wider range of statistical methodologies a w1500 year oscillation is primarily limited to the short glacial stage 4 the age of which is derived solely from an ice flow model ss09sea subject to uncertainty and offset most from the original chronology results from the most well dated younger interval suggest that the original 1500 500 year cycle may actually be an admixture of the w1000 and w2000 cycles that are observed within the holocene at multiple locations in holocene sections these variations are coherent with 14 c and 10 be estimates of solar variability our new results suggest that the 1500 year cycle may be a transient phenomenon whose origin could be due for example to ice sheet boundary conditions for the interval in which it is observed we therefore question whether it is necessary to invoke such exotic explanations as heterodyne frequencies or combination tones to explain a phenomenon of such fleeting occurrence that is potentially an artifact of arithmetic averaging

holocene palaeoenvironmental records from the high altitude wular lake western himalayas we present a comprehensive record of holocene 11 590 628 cal yr bp climate and hydrographic changes around the wular lake located in kashmir valley india based on the multi proxy investigation

holocene climate variability and change a data based review the holocene thermal maximum with peak temperatures prior to 7 ka bp is mostly accentuated in the northern hemisphere still visible in the southern hemisphere and possibly did not exist in the tropics between this period and the modern warming a remarkable negative temperature trend occurred in the northern hemisphere which was probably the effect of a decreasing orbital induced insolation during the boreal summer on average the northern hemisphere humidity precipitation records do not show any significant trend a mechanistic explanation for the multi decadal to century scale holocene cold relapses which mainly occurred in the atlantic european regions exists for only the early holocene cooling events which are probably the result of a collapse of the meridional overturning circulation owing to freshwater outbursts from the laurentide ice sheet possibly the late holocene cold events after c 4 ka bp are influenced by the covarying influence of major tropical volcanic eruptions and grand solar minima

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

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

sulphur organic carbon and iron relationships in estuarine and freshwater sediments effects of sedimentation rate abstract concentrations of s organic c and fe were investigated in profiles of sediments from two estuarine systems in the sw of western australia in marine affected sediments inorganic s dominates total s and concentrations of total s correlate with fe and not with organic c in freshwater sediments organic s dominates total s and concentrations of total s correlate with organic c and not with fe molar fe s ratios in the estuarine sediments decrease with increasing salinity and approach unity for marine conditions net accumulation rates of s in sediments were estimated with a numerical computer model calibrated with published data on profiles of marine sediments for diffusion of so2 4 sedimentation rates and distributions of s measured depth integrated reduction rates of so2 4 in the marine affected estuarine sediments approach those obtained for fe limited marine conditions at similar rates of sedimentation measured concentrations of inorganic s in anoxic freshwater sediments fit a numerically calculated relationship between inorganic s and sedimentation rate

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

subpolar north atlantic sea surface temperature since 6 ka bp indications of anomalous ocean atmosphere interactions at 4 2 ka bp abstract atmospheric circulation may change with future climate change in response to modification of meridional temperature gradients but the potential influence on ocean circulation is as yet unclear over the mid late holocene atmospheric circulation in the north atlantic region has fluctuated on millennial timescales therefore the ocean response to these changes can be investigated using the paleoceanographic records that have been developed in the north eastern subpolar north atlantic here we present a diatom based sea surface temperature reconstruction from the iceland basin south of iceland the reconstruction shows the warmest temperatures of the record at 6 1 4 ka bp cooler temperatures at 4 2 ka bp and warmer temperatures thereafter inter record comparisons indicate that the cold period at c 4 2 ka bp may have resulted from a strengthened east greenland current and or melting of the greenland ice sheet in response to a negative north atlantic oscillation the findings highlight that atmospheric circulation changes are likely to cause pronounced variations in the latitudinal exchange of heat which may have consequences for deep water formation and global ocean circulation

sensitive moisture response to holocene millennial scale climate variations in the mid atlantic region usa millennial scale climate variability has been increasingly recognized as one of the most prominent features of the holocene however regional responses especially in terms of moisture conditions are poorly documented and understood here we present lithologic and magnetic evidence from white lake in northern new jersey usa to show that low lake levels occurred at about 1 3 3 0 4 4 and 6 1 ka 1 ka 1000 cal yr bp the low lake levels are indicated by heterogeneous coarse calcareous sediment layers showing strong magnetic intensities these detrital layers were likely formed during low stands when shallow water marls were exposed oxidized transported and redeposited this model is supported by laboratory experiments showing that oxidation of marls can enhance magnetic intensities the dry periods inferred from the low lake levels of white lake appear to occur concurrently with the cold periods recorded in the north atlantic sediments the correlation between millennial scale dry wet cycles inferred from lake level fluctuations of white lake and cold warm cycles in north atlantic sediments suggests sensitive moisture responses to holocene millennial scale climate variability the dry cold or wet warm association is supported by instrumental records of the last century showing that the mid atlantic region was dominated by wet conditions while most parts of the conterminous usa experienced droughts when the north atlantic ocean was warm the consistent moisture responses of the mid atlantic region to temperature changes of the north atlantic ocean may have persisted for the past 6000 years

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

holocene weak monsoon intervals indicated by low lake levels at hulun lake in the monsoonal margin region of northeastern inner mongolia china a 170 cm long sediment core spanning the last 10 000 years was recovered from hulun lake in the northeastern margin of the east asian summer monsoon the sediment core was analyzed at 1 cm intervals for grain size distribution and sedimentary component partition these data provide a proxy record of the monsoon variability on millennial to centennial scales during the holocene we used a lognormal distribution function fitting method to partition three to six components from fine to coarse modes within the individual polymodal distributions into overlapping lognormal distributions three coarse components representing nearshore suspension saltation and traction together with the sand fraction percentage and the median grain size of bulk samples indicate the lake levels that fluctuated in response to the intensity of the monsoonal precipitation higher percentages of the nearshore components accompanied by more sand fraction proportions and coarser median grain sizes reflect lower lake stands resulting

the gisp2 δ18o climate record of the past 16 500 years and the role of the sun ocean and volcanoes measured 18o 16o ratios from the greenland ice sheet project 2 gisp2 ice core extending back to 16 500 cal yr b p provide a continuous record of climate change since the last glaciation high resolution annual 18o 16o results were obtained for most of the current millennium a d 818 1985 and record the medieval warm period the little ice age and a distinct 11 yr 18o 16o cycle volcanic aerosols depress central greenland annual temperature 1 5 c maximally and annual 18o 16o for about 4 yr after each major eruptive event on a bidecadal to millennial time scale the contribution of solar variability to holocene greenlandic temperature change is 0 4 c the role of thermohaline circulation change on climate problematic during the holocene is more distinct for the 16 500 10 000 cal yr b p interval analogous to 14c age calibration terminology we express time in calibrated cal yr b p a d 1950 0 cal yr b p the oldest dryas bolling older dryas allerod younger dryas sequence appears in great detail bidecadal variance in 18o 16o but not necessarily in temperature is enhanced during the last phase of lateglacial time and the younger dryas interval suggesting switches of air mass transport between jet stream branches the branched system is nearly instantaneously replaced at the beginning of the bolling and holocene at 14 670 and 11 650 cal yr b p respectively by an atmospheric circulation system in which 18o 16o and annual accumulation initially track each other closely thermodynamic considerations of the accumulation rate temperature relationship can be used to evaluate the 18 o 16o temperature relationship the gisp2 ice layer count years of major gisp2 climate transitions also support the use of coral 14c ages for age calibration

proglacial lake sediment records of holocene climate change in the western cordillera of peru abstract sediment records from proglacial lakes between 9 and 10 s in the western cordillera of the peruvian andes document the waxing and waning of alpine glaciers since the end of the lateglacial stage these records from the southern tropical andes provide supporting evidence that the early holocene between 12 and 8 ka was relatively warm and dry and the middle holocene between 8 and 4 ka was marked by a shift to cooler and possibly wetter conditions in certain regions leading to glacial advances although there were multiple periods of brief ice advances that interrupted the overall trend glaciers in multiple valleys generally retreated from 4 0 ka through the medieval climate anomaly 1 0 0 7 ka this late holocene pattern of ice retreat occurred during a period when lake level studies and both lacustrine and speleothem stable isotopic records indicate wetter conditions relative to the middle holocene suggesting that higher temperatures contributed to the pattern of ice retreat following this period of glacial retreat multiple proxy records suggest that the start of the little ice age 0 6 0 1 ka was a colder and wetter time throughout much of the tropical andes there appear to be two primary synoptic scale climatic controls on temperature and precipitation linked to insolation dynamics that drive changes in ice cover in the southern tropical andes during the holocene 1 the strength of the south america summer monsoon which is linked to northern hemisphere temperatures and the mean position of the intertropical convergence zone over the atlantic and 2 sea surface temperature distributions in the tropical pacific ocean and its influence on atmospheric temperature precipitation and circulation patterns

the variation of summer monsoon precipitation in central china since the last deglaciation abstract two stalagmites c996 1 and c996 2 collected from the jiuxian cave in the shaanxi province in central china have been studied with u series dating and stable isotope analysis thirty eight 230 th dating results showed that the stalagmite c996 1 was continuously deposited through the last 8 5 ka bp thousand years before present present 1950 ad and c996 2 was deposited through the last 19 ka bp excluding two growth hiatuses between 8 3 and 5 7 ka bp and 15 4 and 11 9 ka bp with a relatively stable boundary condition we interpret the 18 o of speleothem calcite as most indicative of the amount of summer monsoon precipitation although temperature and other factors might have some minor impact the 18 o records show notable changes within the last glacial maximum lgm resembling other east asian monsoon records such as those from the hulu and sanbao caves suggesting that significant monsoonal climate changes occurred in eastern asia as far north as the qinling mountains during the lgm interval a comparison of our records to precisely dated contemporaneous speleothem records from other caves shows that the increasing trend of 18 o during the holocene commenced as early as 7 5 ka bp in the low latitude monsoonal area i e the hoti cave while at higher latitudes this shift occurred later such as 7 0 ka bp in the dongge cave 5 3 ka bp in the heshang cave 4 7 ka bp in the sanbao cave and 4 5 ka bp in the jiuxian cave these results imply an asynchronous change of the summer monsoon precipitation occurred in east asia during the holocene the asynchrony may be related to the responses of a coupled tropical and subtropical monsoon system to changes of the insolation and the differences in thermal forcing which result from the complex geographical configuration the variation of sea surface temperature sst in the western tropical pacific may also have important impacts on the summer monsoon precipitation changes in central and northern china because it affects the northwestern pacific subtropical high a monsoon front regulator more robust tests are needed to confirm this phenomenon and to evaluate the contribution of different factors in detail

speleothem based 1000 year high resolution record of indian monsoon variability during the last deglaciation abstract a high resolution record of the indian summer monsoon ism is generated using a 18 o time series from a stalagmite collected from the valmiki cave in southern india this record covers a time span of 1000 years from 15 700 to 14 700 yr bp before 1950 ad with an average sampling resolution of 5 years high amplitude 18 o variation in this record reflects abrupt changes in ism activity during the last deglaciation and suggest an age for the onset of termination 1a t1a at 14 800 yr bp in the indian sub continent this record shows evidence for strong changes in tropical climate during the last deglaciation coincident variability in vspm4 18 o with speleothems from southern china during termination 1a suggests that these caves reflect fluctuations in ism activity the variance in 18 o amplitude reveals significant multidecadal variability in ism activity our record reveals intervals of strong monsoon activity during the later phase of heinrich event 1 h1 and shows synchronous multidecadal variability between ism and east asian monsoon eam spectral analysis of 18 o time series in vspm4 reveals solar forcing and strong ocean atmospheric circulation control on ism dynamics during the studied time interval

monsoon source shifts during the drying mid holocene biomarker isotope based evidence from the core monsoon zone cmz of india abstract a better understanding of past variations of the indian summer monsoon ism that plays a vital role for the still largely agro based economy in india can lead to a better assessment of its potential impact under global climate change scenarios however our knowledge of spatiotemporal patterns of ism strength is limited due to the lack of high resolution continental paleohydrological records here we reconstruct centennial scale hydrological variability during the holocene associated to changes in the intensity of the ism based on a record of lipid biomarker abundances and compound specific stable isotopic composition of a 10 m long sediment core from saline alkaline lonar lake situated in the core monsoon zone of central india we identified three main periods of distinct hydrology during the holocene in central india the period between 10 1 and 6 cal ka bp was likely the wettest during the holocene lower average chain length acl index values 29 4 28 6 and negative 13 c wax values 34 8 to 27 8 of leaf wax n alkanes indicate the dominance of woody c 3 vegetation in the catchment and negative d wax values concentration weighted average 171 to 147 suggest a wet period due to an intensified monsoon after 6 cal ka bp a gradual shift to less negative 13 c wax values particularly for the grass derived n c 31 and appearance of the triterpene lipid tetrahymanol generally considered as a marker for salinity and water column stratification mark the onset of drier conditions at 5 1 cal ka bp an increasing flux of leaf wax n alkanes along with the highest flux of tetrahymanol indicate a major lowering of the lake level between 4 8 and 4 cal ka bp we find evidence for a transition to arid conditions indicated by high and strongly variable tetrahymanol flux in addition a pronounced shift to less negative 13 c wax values in particular for n c 31 25 2 to 22 8 during this period indicates a change of dominant vegetation to c 4 grasses in agreement with other proxy data such as deposition of evaporite minerals we interpret this period to reflect the driest conditions in the region during the last 10 1 ka this transition led to protracted late holocene arid conditions after 4 ka with the presence of a permanent saline lake supported by the sustained presence of tetrahymanol and more positive average d wax values 122 to 141 a late holocene peak of cyanobacterial biomarker input at 1 3 cal ka bp might represent an event of lake eutrophication possibly due to human impact and the onset of cattle livestock farming in the catchment a unique feature of our record is the presence of a distinct transitional period between 4 8 and 4 cal ka bp which was characterized by some of the most negative d wax values during the holocene up to 180 when all other proxy data indicate the driest conditions during the holocene these negative d wax values can as such most reasonably be explained by a shift in moisture source area and or pathways or rainfall seasonality during this transitional period we hypothesize that orbital induced weakening of the summer solar insolation and associated reorganization of the general atmospheric circulation as a possible southward displacement of the tropical rainbelt led to an unstable hydroclimate in central india between 4 8 and 4 ka our findings shed light onto the sequence of changes during mean state changes of the monsoonal system once an insolation driven threshold has been passed and show that small changes in solar insolation can be associated with major hydroclimate changes on the continents a scenario that may be relevant with respect to future changes in the ism system

a genetic model of thrust bounded intermontane basin using scaled sandbox analogue models an example from the karewa basin kashmir himalayas india the himalayan mountain system has many depressions of regional dimensions which are found oriented mostly e w to ne sw mainly to the north of the main boundary fault mbf the karewa basin in the kashmir himalaya has sediments belonging to late neogene to quaternary formations which represent an almost 1 300 m thick succession of sand mud and gravels exposed in the river valleys and the plateau margins of the entire kashmir valley sandbox analogue experiments show a great variety of wedge shapes showing significant changes in the taper angles due to the change in basal friction between two pop ups or depressions pop down of significant dimensions develop along the strike of the growing wedge in order to maintain the critical angle these depressions initially receive material from the hinterland and later on from the foreland end of the wedge the depressions have developed due to the change in the surface slope of the wedge and receive the eroded material only from the adjacent upheaved portions of the wedge on continuation of the experiments in cases where the wedge is highly unstable these depressions are coupled with the wedge along with their sand fills the depositional history of the karewa sediments indicates a sequential evolutionary pattern of the basin and thus represents a natural analogue of the sandbox experiments

the 8k event cause and consequences of a major holocene abrupt climate change abstract a prominent abrupt climate event about 8200 years ago brought generally cold and dry conditions to broad northern hemisphere regions especially in wintertime in response to a very large outburst flood that freshened the north atlantic changes were much larger than typical climate variability before and after the event with anomalies up to many degrees contributing to major displacement of vegetative patterns this 8k event provides a clear case of cause and effect in the paleoclimatic realm and so offers an excellent opportunity for model testing the response to north atlantic freshening has the same general anomaly pattern as observed for older events associated with abrupt climate changes following north atlantic freshening and so greatly strengthens the case that those older events also reflect north atlantic changes the north atlantic involvement in the 8k event helps in estimating limits on climate anomalies that might result in the future if warming caused ice melt and hydrologic cycle intensification at high latitudes lead to major changes in north atlantic circulation few model experiments have directly addressed the 8k event and most studies of proxy records across this event lack the time resolution to fully characterize the anomalies so much work remains to be done

evidence for recent volcanism on mars from crater counts impact craters help characterize the age of a planetary surface because they accumulate with time they also provide useful constraints on the importance of surface erosion as such processes will preferentially remove the smaller craters earlier studies of martian crater populations revealed that erosion and dust deposition are important processes on mars they disagreed however on the age of the youngest volcanism these earlier studies were limited by image resolution to craters larger than a few hundred metres in diameter here we report an analysis using new images obtained by the mars global surveyor spacecraft of crater populations that extend the size distribution down to about 16 m our results indicate a wide range of surface ages with one region lava flows within the arsia mons caldera that we estimate to be no older than 40 100 million years we suggest that volcanism is a continuing process on mars

a tibetan lake sediment record of holocene indian summer monsoon variability article history sedimentological data and hydrogen isotopic measurements of leaf wax long chain n alkanes dwax from an alpine lake sediment archive on the southeastern tibetan plateau paru co provide a holocene perspective of indian summer monsoon ism activity the sedimentological data reflect variations in lake level and erosion related to local ism rainfall over the paru co catchment whereas dwax reflects integrated synoptic scale ism dynamics our results indicate that maximum ism rainfall occurred between 10 1 and 5 2 ka during which time there were five century scale high and low lake stands after 5 2 ka the ism trended toward drier conditions to the present with the exception of a pluvial event centered at 0 9 ka the paru co results share similarities with paleoclimate records from across the tibetan plateau suggesting millennial scale ism dynamics were expressed coherently these millennial variations largely track gradual decreases in orbital insolation the southward migration of the intertropical convergence zone itcz decreasing zonal pacific sea surface temperature sst gradients and cooling surface air temperatures on the tibetan plateau centennial ism and lake level variability at paru co closely track reconstructed surface air temperatures on the tibetan plateau but may also reflect indian ocean dipole events particularly during the early holocene when enso variability was attenuated variations in the latitude of the itcz during the early and late holocene also appear to have exerted an influence on centennial ism rainfall 2014 elsevier b v all rights reserved

past monsoon rainfall variations in peninsular india recorded in a 331 year old speleothem an actively growing stalagmite collected from a cave located in the hills of the western ghats in the uttar kannada district of karnataka india has been studied for stable isotope ratios of oxygen and carbon width of growth layers and grey level changes distinct carbonate layers alternate coarse and compact are seen in cross section each couplet of compact and coarse layer is found to represent a single year a total of 331 such couplets has been counted indicating that the stalagmite started growing in ad 1666 and continued until it was sampled stable isotope ratios of oxygen i 18o and carbon i 13c show variations ranging from 13 6 to 7 9 and from 2 7 to 1 6 respectively we have reconstructed past rainfall changes of the cave site using the amount effect in i 18o of rain speleothem i 18o and instrumental rainfall data from the associated climate subdivision show a significant correlation r 0 62 decadal average several sharp spikes of enrichment and depletion in 18o are indicative of the past deficiency and excess in rainfall most of the severe drought years recorded independently by meteorological observations are found registered in the stalagmite layers during the 331 year period rainfall was highest at ad 1666 and lowest around ad 1900 the stalagmite generated past rainfall record can serve as a reasonable proxy for testing monsoon models

sources and chronology of combustion derived pollution to shilianghe reservoir eastern china evidences from pahs profiles as hg pb and pb isotopes abstract the sedimentary records of polycyclic aromatic hydrocarbons pahs mercury hg arsenic as lead pb and stable pb isotopic ratios were studied in a sediment core collected from shilianghe reservoir in eastern china accumulations and distributions of these pollutants were measured in terms of pahs concentrations pahs fluxes and enrichment factor ef of hg as pb and pb isotopic ratios the accumulations showed a synchronous trend throughout the core due to close correlation with rapid economic and industrial development of the catchment linyi city in eastern china the results from pah isomer ratios reveal that pahs in sediments are dominantly from anthropogenic pyrogenic sources mainly from the combustion of coal and biomass furthermore the pb isotopic composition clearly indicates that coal combustion dust mainly contributed to the pb burden in the reservoir sediments based on mixing end member model of pb isotopic ratios contributions of coal combustion dust are ranged from 31 to 62 mainly from anthropogenic pb sources the contribution of leaded gasoline was lower than average at 25 in addition a steady increase in the contribution from coal combustion sources was found in the sediment core while the contribution of leaded gasoline showed a decline in recent decades due to the phase out of leaded gasoline in china capsule abstract pahs hg as and pb burden in a reservoir of china were chronicled increasing coal combustion dust is responsible for contamination of lake by end member model of pb isotopic ratios

paleoenvironmental shifts spanning the last 6000 years and recent anthropogenic controls inferred from a high altitude temperate lake anchar lake nw himalaya integrating multiproxy results geochemistry mineral magnetism grain size and c n ratio variability supported by 14c ams dating obtained from a 1 4 m sediment core retrieved from high altitude

regional dust deposits on mars physical properties age and history major dust storms on mars play an important role in the deposition and removal of fine dust material thermal radar and visual remote sensing observations provide important constraints on the martian regolith which have been used to determine the location and physical properties of regional dust deposits these deposits are located in three northern equatorial regions tharsis 20 s to 50 n 60 to 190 w arabia 5 s to 30 n 300 to 360 w and elysium 10 to 30 n 210 to 225 w they are covered by fine 2 40 m bright albedo 0 27 particles with fewer exposed rocks and coarse deposits than found elsewhere dust is currently deposited uniformly throughout the equatorial region at a rate of 40 m global storm over geologic time the rate of accumulation may vary from 0 to 250 m yr due to changes in atmospheric conditions produced by orbital variations dust deposited during global storms is subsequently removed only from dark regions resulting in a net accumulation in the low inertia bright regions the thickness of these current dust deposits is 0 1 2 m the thermal inertia places a lower limit of 0 1 m on the thickness of these deposits while the sparse but ubiquitous presence of exposed rocks and the degree of visible mantling indicate that the thickness is less than 5 m dual polarization radar observations of a very rough texture in tharsis are consistent with this model with a 2 m thick dust layer burying most of the surface rocks but permitting radar sampling of the rough subsurface based on their thickness and rate of accumulation the age of these deposits is 105 106 years suggesting a cyclic process of deposition and removal one possible cause may be cyclic variations in the magnitude and location of maximum wind velocities related to variations in mars orbit at present perihelion and maximum wind velocities occur in the south whereas regional dust deposits occur in the north suggesting net transport from south to north orbital parameters oscillate with periods ranging from 5 104 to 106 years the agreement between these periods and the dust deposit age suggests a possible link at different stages in orbit evolution maximum wind velocities will occur in the north with subsequent erosion and redistribution of the accumulated fines based on this model much of the uppermost martian surface is very young and is being continually reworked

accumulation of phosphorus and heavy metals in the swan canning estuary western australia abstract accumulation rates of p and of zn cd pb and cu were measured in sediment cores from the swan canning estuary in western australia the main sources of p in sediments are catchments of the major tributaries ellen brook and avon river since 1940 anthropogenic p has increased about five times in sediments of ellen brook and has almost trebled in sediments of the estuary records show that since 1940 dissolved inorganic p in the estuary has increased between two and three times though dissolved inorganic p appears to be conservatively mixed in the estuary sediment inventories suggest that a significant part of the input of p is retained in the estuary a combination of high concentrations of dissolved p in ellen brook and large fluxes of particulate matter from the avon river could explain this concentrations of zn cd pb and cu in sediments have risen significantly since colonial settlement and unlike p concentrations have been dominated by inputs from sources near the estuary vertical distributions of metals in sediment cores from the estuary suggest that historically concentrations of zn and cd started increasing first followed by cu and then p and pb acid extractable pb unlike zn cd and cu in surface sediments is greater than expected from equilibration with the water column this is attributed to the presence of particulate pb oxides from road runoff

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

tropical climate instability the last glacial cycle from a qinghai tibetan ice core an ice core record from the guliya ice cap on the qinghai tibetan plateau provides evidence of regional climatic conditions over the last glacial cycle 36 cl data suggest that the deepest 20 meters of the core may be more than 500 000 years old the 18 o change across termination i is 5 4 per mil similar to that in the huascaran peru and polar ice cores three guliya interstadials stages 3 5a and 5c are marked by increases in 18 o values similar to that of the holocene and eemian 124 000 years ago the similarity of this pattern to that of ch 4 records from polar ice cores indicates that global ch 4 levels and the tropical hydrological cycle are linked the late glacial stage record contains numerous 200 year oscillations in 18 o values and in dust nh 4 and no 3 levels

rapid early holocene deglaciation of the laurentide ice sheet the demise of the laurentide ice sheet during the early holocene epoch is the most recent and best constrained disappearance of a large ice sheet in the northern hemisphere and thus allows an assessment of rates of ice sheet decay as well as attendant contributions to sea level rise here we use terrestrial and marine records of the deglaciation to identify two periods of rapid melting during the final demise of the laurentide ice sheet when melting ice contributed about 1 3 and 0 7cm of sea level rise per year respectively our simulations with a fully coupled ocean atmosphere model suggest that increased ablation due to enhanced early holocene boreal summer insolation was the predominant cause of laurentide ice sheet retreat although the surface radiative forcing in boreal summer during the early holocene is twice as large as the greenhouse gas forcing expected by the year 2100 the associated increase in summer surface air temperatures is very similar we conclude that our geologic evidence for a rapid retreat of the laurentide ice sheet may therefore describe a prehistoric precedent for mass balance changes of the greenland ice sheet over the coming century

biogeochemistry and paleoclimate variability during the holocene a record from mansar lake lesser himalaya investigation of biogeochemistry and amino acids on a 30 m long core from mansar lake has thrown light on palaeoclimate variability during the holocene period the c n ratio between 6 and 10 with some deviations and 13c mostly between 20 and 22 in the shallow core as well as a c n ratio greater than 13 reaching from 19 to 20 and correspondingly lower 13c of 28 in the deeper core suggest an aquatic source of carbon in the former and a cellulose rich land plant source in the latter this is supported by the abrupt increase in organic carbon content in the deeper core compared to the shallow core which indicates a hot and wet climatic regime during the early holocene and dry and cold during the late holocene period the amino acid data aa c c and aa n n are higher in shallow sediments compared to deeper sediments indicating an aquatic plant source in the shallow core and greater supply of land plant sources in the deeper core the lower percentage of the non protein amino acids alanine ala and amino butyric acid in the shallow core compared to the deeper core indicates different sources of organic matter in the lake basin the higher amino acid ratio asp ala 16 99 av and glu aba 18 18 av in the shallow core and lower ratios 10 32 and 12 41 av in the deeper core and asp glu 1 52 av and ala aba 1 61 av ratios in the former which are potential indicators of the nature of the organic matter are higher in the shallow core relative to the deeper core 1 33 and 1 23 av indicating relative biodegradation of organic matter in deeper sediments it has been observed that the organic matter associated with the dry season is relatively less biodegraded as evidenced from their higher ratios and is more biodegraded in the wet season as their ratios are lower in the river sediments in the absence of a bacterial contribution of organic matter from the soil source in this lake since mansar lake is a non drainage type it is envisaged that the climatic variation may be responsible for biodegradation in the deeper core sediments therefore the c n ratio and 13c values supported by amino acid data the latter being significant in revealing primary productivity and a terrestrial source of organic matter suggest a hot and wet climatic regime during the early holocene ca 7580 bp and a dry and cold in the late holocene period ca 4050 bp

tectono geomorphic indices of the erin basin ne kashmir valley india abstract the present study aims to assess the tectonic activity in the erin basin ne kashmir on the basis of several relevant geomorphic indices and field observations we use digital elevation model srtm and survey of india soi topographic maps in gis environment to compute the geomorphic indices the indices i e convex hypsometric curve high hypsometric integral value h i 0 5 low basin elongation ratio eb 0 17 low mountain front sinuosity values s mf 1 08 average low valley floor width ratios vf 4 suggest that the area is tectonically active moreover prominent irregularities knickpoints knickzones along longitudinal profile of the erin river even in homogenous resistant lithology panjal trap and anomalous stream gradient index sl values reflect that the erin basin is dissected by two faults ef 1 and ef 2 with nnw sse and ssw nne trends respectively the results of this preliminary study further substantiate the recent gps studies which argue that the maximum strain is accumulating in the ne part of the kashmir himalaya

holocene monsoon climate documented by oxygen and carbon isotopes from lake sediments and peat bogs in china a review and synthesis there has been much recent debate about holocene climate variation in the monsoon region of china especially the temporal pattern of variations in precipitation the time transgressive nature of the holocene precipitation maximum and the extent to which variations in regions influenced by the indian summer monsoon ism and the east asian summer monsoon easm have been synchronous we summarize and compare carbonate oxygen isotope records delta o 18 carb from ten lakes within the present day ism region we discuss their paleoclimate significance considering the present day moisture source isotopic composition of precipitation and the hydrological setting the delta o 18 carb records are controlled mainly by the isotopic composition of lake water which in turn is a function of regional precipitation evaporation p e balance and the proportion of precipitation that is monsoon derived we normalized the delta o 18 carb data and used these records to generate an integrated moisture index this index along with oxygen isotope records from speleothems and carbon isotope records delta c 13 org from peats within the monsoon region suggests that holocene climate was broadly synchronous across the monsoon region and within the limits of accuracy of the existing age models provides no strong evidence for previously proposed anti phasing of the ism and the easm stable isotope records from lake sediments and peat bogs have excellent potential for providing high quality paleoclimate data for monsoon asia and complement high resolution speleothem sequences which are only found in certain localities c 2011 elsevier ltd all rights reserved

structure and origin of holocene cold events abstract the present interglacial the holocene spans the period of the last 11 700 years it has sustained the growth and development of modern society the millennial scale decreasing solar insolation in the northern hemisphere summer lead to northern hemisphere cooling a southern shift of the intertropical convergence zone itcz and a weakening of the northern hemisphere summer monsoon systems on the multidecadal to multicentury scale periods of more stable and warmer climate were interrupted by several cold relapses at least in the northern hemisphere extra tropical area based on carefully selected 10 000 year long time series of temperature and humidity precipitation as well as reconstructions of glacier advances the spatiotemporal pattern of six cold relapses during the last 10 000 years was analysed and presented in form of a holocene climate atlas hoclat see http www oeschger unibe ch research projects holocene atlas a clear cyclicity was not found and the spatiotemporal variability of temperature and humidity precipitation during the six specific cold events 8200 6300 4700 2700 1550 and 550 years bp was very high different dynamical processes such as meltwater flux into the north atlantic low solar activity explosive volcanic eruptions and fluctuations of the thermohaline circulation likely played a major role in addition internal dynamics in the north atlantic and pacific area including their complex interaction were likely involved

the climate variability in northern levant over the past 20 000 years the levant constitutes an important region for assessing linkages between climate and societal changes throughout the course of human history however large uncertainties remain in our understanding of the region s hydroclimate variability under varying boundary conditions here we present a new high resolution precisely dated speleothem oxygen carbon isotope and sr ca records spanning the last 20 ka from jeita cave northern levant our record reveals a higher lower precipitation evaporation p e balance during the last glacial maximum and bolling interstadial heinrich stadial 1 the early middle holocene is characterized by a trend toward higher p e state culminating between similar to 7 and 6 ka the middle late holocene is characterized by two millennial length drier periods during 5 3 4 2 and 2 8 1 4 ka on submillennial time scale the northern levant climate variability is dominated by 500 year periodicity comparisons with the regional proxy records suggest persistent out of phase climate variability between the northern and southern levant on a wide range of timescales

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

centennial scale climate cooling with a sudden cold event around 8 200 years ago the extent of climate variability during the current interglacial period the holocene is still debated temperature records derived from central greenland ice cores show one significant temperature anomaly between 8 200 and 8 100 years ago which is often attributed to a meltwater outflow into the north atlantic ocean and a slowdown of north atlantic deep water formation this anomaly provides an opportunity to study such processes with relevance to present day freshening of the north atlantic anomalies in climate proxy records from locations around the globe are often correlated with this sharp event in greenland but the anomalies in many of these records span 400 to 600 years start from about 8 600 years ago and form part of a repeating pattern within the holocene more sudden climate changes around 8 200 years ago appear superimposed on this longer term cooling the compounded nature of the signals implies that far field climate anomalies around 8 200 years ago cannot be used in a straightforward manner to assess the impact of a slowdown of north atlantic deep water formation and the geographical extent of the rapid cooling event 8 200 years ago remains to be determined

late glacial and holocene vegetation indian monsoon and westerly circulation in the trans himalaya recorded in the lacustrine pollen sequence from tso kar ladakh nw india abstract palynological investigation of a 410 cm long core section from tso kar 33 10 n 78 00 e 4527 m a s l an alpine lake situated in the arid ladakh area of nw india at the limit of the present day indian summer monsoon was performed in order to reconstruct post glacial regional vegetation and climate dynamics the area was covered with alpine desert vegetation from ca 15 2 to 14 kyr bp 1 kyr 1000 cal years reflecting dry and cold conditions high influx values of long distance transported pinus sylvestris type pollen suggest prevailing air flow from the west and northwest the spread of alpine meadow communities and local aquatic vegetation is a weak sign of climate amelioration after ca 14 kyr bp pollen data e g influx values of pinus roxburghii type and quercus suggest that this was due to a strengthening of the summer monsoon and the reduced activity of westerly winds the further spread of artemisia and species rich meadows occurred in response to improved moisture conditions between ca 12 9 and 12 5 kyr bp the subsequent change towards drier desert steppe vegetation likely indicates more frequent westerly disturbances and associated snowfalls which favoured the persistence of alpine meadows on edaphically moist sites the spread of chenopodiaceae dominated vegetation associated with an extremely weak monsoon occurred at ca 12 2 11 8 kyr bp during the younger dryas interstadial a major increase in humidity is inferred from the development of artemisia dominated steppe and wet alpine meadows with gentianaceae after the late glacial early holocene transition in response to the strengthening of the summer monsoon monsoonal influence reached maximum activity in the tso kar region between ca 10 9 and 9 2 kyr bp the subsequent development of the alpine meadow steppe and desert steppe vegetation points to a moderate reduction in the moisture supply which can be linked to the weaker summer monsoon and the accompanying enhancement of the winter westerly flow from ca 9 2 to 4 8 kyr bp the highest water levels of tso kar around 8 kyr bp probably reflect combined effect of both monsoonal and westerly influence in the region an abrupt shift towards aridity in the tso kar region occurred after ca 4 8 kyr bp as evidenced by an expansion of chenopodiaceae dominated desert steppe low pollen influx values registered ca 2 8 1 3 kyr bp suggest scarce vegetation cover and unfavourable growing conditions likely associated with a further weakening of the indian monsoon

glacial geomorphology and recent glacial recession of the harmukh range nw himalaya abstract a comprehensive description of the glaciation and glacial geomorphology of the harmukh range northwest himalaya is reported first time in this study the geomorphic system of the range is dominated by glaciation and provides an excellent opportunity to assess the glacial fluctuations from the late quaternary to the present using a time series of the satellite data from 1992 to 2018 the glacier area snout and equilibrium line altitude ela changes of the existing glaciers in the harmukh range were estimated the glacier cover has receded from 7 47 0 58 km2 in 1992 to 6 24 0 62 km2 in 2018 a deglaciation of 16 46 0 24 the glaciers showed an upward shift in ela from 47 m to 80 m during the last two and a half decade the observations revealed that other than the climatic factors the ela change and glacier recessions are influenced by the glacier size mean altitude and the aspect of the glaciers further the high resolution google earth images supplemented by field observations were used for mapping various glacial geomorphic landforms the nature of glacial grooves overdeepenings the height of the lateral moraine deposits and trimlines indicated appreciable thickness of the former glaciers the pattern of the glaciated valleys revealed that the area has predominantly experienced alpine type of glaciation with most of the glaciers centred on the harmukh peak based on the shape and the number of lateral moraine ridges present it is suggested that the area has witnessed three major glacial advances by tracing the outer limits of the glacial valleys moraine boulders and ice scoured terrain it was estimated that the glaciers in the range covered 629 km2 during the glacial maxima the presence of numerous rock glaciers and debris free cirque glaciers on the north eastern slopes of the range indicated a strong climatic and topographical control on the pattern situation and extent of glaciers however there is a need for detailed field based mapping of the glacial geomorphology and geochronological study in order to better understand the nature and extent of paleo glaciation the observed glacier recession and the past climatic variations in this hitherto understudied glaciated region of the kashmir himalaya

oxygen 18 16 variability in greenland snow and ice with 10 3 to 105 year time resolution the 3 km long greenland ice sheet project 2 gisp2 ice core presents a 100 000 year detailed oxygen isotope profile covering almost a full glacial interglacial cycle measuranents of isotopic fluctuations in snow frost and atmospheric water vapor samples collected during summer field seasons up to 20 0 are compatible with the large and abrupt 80 160 changes observed in accumulated tim snow pit 15 80 profiles from the gisp2 summit area however show rapid smoothing of the 180 160 signal near the surface beyond about 2 m depth the smoothedi5180 signal is fairly well preserved and can be interpreted in terms of average local weather conditions and climate the longer climate fluctuations also have regional and often global significance in the older part of the record corresponding to marine isotope stages mis 5a to 5d the effect of orbital climate forcing via the 19 and 23 kyr precession cycles and the 41 kyr obliquity cycle is obvious from the end ofmis 5a at about 75 000 years b p till the end of the glacial at the younger dryas preboreal transition at 11 650 years b p the o180 160 record shows frequent rapid switches between intermediate interstadial and low stadial values fourier spectra of the oscillations that are superimposed on the orbitally induced changes contain a strong periodicity at 1 5 kyr a broad peak at 4 0 kyr and additional shorter periods detailed comparison of the gisp2 180 160 record with the vostok antarctica 15d record pacific ocean foraminiferal 180 160 grande pile france tree pollen and insolation indicates that a counterpart to many of the rapid 180 160 fluctuations of gisp2 can be found in the other records and that the gisp2 isotopic changes clearly are the local expression of climate changes of worldwide extent correlation of events on the independent gisp2 and specmap time scales for the interval 10 000 50 000 years b p shows excellent chronometric agreement except possibly for the event labeled 3 1 the glacial to interglacial transition evidently started simultaneously in the arctic and the antarctic but its development and its expression in greenland isotopes was later suppressed by the influence of meltwater especially from the barents sea ice sheet on deep water formation and ocean circulation meltwaters from different ice sheets bordering the north atlantic also influenced ocean circulation during the bolling allerod interstadial complex and the younger dryas and led to a distinct development of european climate and greenland 180 160 values the holocene interval with long term stable mean isotopic values contains several fluauations with periods from years to millennia dominant is a 6 3 year oscillation with amplitude up to 3 to 4 0 periodicities of 11 and 210 years also found in the solar modulated records of the cosmogenic isotopes 1obe and 14c suggest solar processes as the cause of these cycles depression of180 160 values cooling by volcanic eruptions is observed in stacked gisp215 80 records but the effect is small and not likely to trigger major climate changes

mid to late holocene paleoenvironmental changes and glacier fluctuations reconstructed from the sediments of proglacial lake buruo co northern tibetan plateau abstract glaciers on the tibetan plateau are an important freshwater resource for large populations in south and southeast asia therefore it is important to understand past variations in glacier activity in the region to assess their possible response to ongoing climatic warming here we present the results of analyses of grain size total organic carbon pollen ratio artemisia to chenopodiaceae and the element content of a 435 cm long sediment core from proglacial lake buruo co on the northern tibetan plateau our results indicate that the buruo co catchment experienced relatively warm and humid conditions during 5 2 4 0 cal kyr bp during which retreating glaciers released large amounts of freshwater precipitation was also abundant during this interval as a result of the relatively strong indian summer monsoon and weaker westerlies and thus the lake level was high during 4 0 1 3 cal kyr bp the westerlies were gradually enhanced and the climate became colder and drier in response the glaciers advanced and the lake level decreased during 1 3 0 cal kyr bp under relatively cold conditions a large volume of glacial ice was maintained nevertheless under the westerlies influence the lake level rose four episodes of glacial advance are detected at 3 6 3 4 3 2 2 3 1 9 1 7 and 0 4 0 1 cal kyr bp these episodes correspond well with bond events in the north atlantic implying that climate change and glacial activity at buruo co were largely driven by variations in northern hemisphere insolation and by climatic oscillations in the north atlantic region via the influence of the westerlies

climate induced denudational changes during the little ice age inferred from 10be meteoric 9be ratio a case study from the core monsoon zone of india abstract denudation rates are often estimated with high uncertainty using the average mass of material discharged through a drainage basin or considering the rate of surface processes estimating long term denudation rates through these conventional methods requires the assumption that the surficial processes have remained constant throughout time since the earth s surface has been obliterated throughout the geological time by climate tectonics or the recent anthropogenic activities the present rate of change may not represent past processes this study presents changes in denudation rate using the 10be meteoric 9be ratio for the past 600 years from anshupa lake sediment record in the core monsoon zone of india paleodenudation rate estimated using 10be meteoric 9be varies from 392 42 to 95 6 t km2 yr intense indian summer monsoon ism during the periods of solar maxima which caused decadal scale floods in the indian sub continent favored a higher rate of denudation than the periods of solar minima that experienced droughts in the indian sub continent due to weakening of ism

phosphorus distribution in the estuarine sediments of the daliao river china abstract the objective of this study was to investigate the phosphorus distribution in the estuarine sediments of the daliao river intensively affected by municipal effluent and agricultural activity for about 50 years surface sediment samples were taken at 35 sites in the estuarine area and phosphorus species and contents of total p al fe and ca in the sediments were measured results showed that the content of total p in the sediments ranged from 230 to 841 mg kg 1 with an average of 549 mg kg 1 ca bound p residual p al bound p reductant soluble p fe bound p and soluble and loosely bound p were averagely 44 5 21 6 13 6 11 7 8 9 and 0 2 of total p respectively with the gradual increase of total p content al bound p reductant soluble p and fe bound p generally increased while the rest species of p did not this might indicate that anthropogenic p is bound to al and fe oxides regression analysis showed that al bound p and sum of fe bound p and reductant soluble p were correlated to the contents of total al and fe respectively on the other hand ca bound p was not correlated to the content of total ca in the sediment probably suggesting that ca p was mainly from authigenic marine origin whereas the content of total p in the estuarine sediments of the daliao river was within the range of total p content for chinese and worldwide river estuaries as well as coastal sediments non calcium apatite phosphorus content in the estuarine sediments of the daliao river was relatively higher indicating higher release risk and bioavailability of p in the sediment on the other hand the molar ratio of total fe to total p was 16 34 in the estuarine sediments of the daliao river suggesting that iron oxides hydroxides in the sediments might be able to sequester more phosphorus therefore the accumulation or release of p in from the estuarine sediments might be dependent on the external loading of p and the estuarine eutrophication may be sustained by the internal bioavailable p pools following the decrease of the external p loading

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

a self replication model for long channelized lava flows on the mars plains 1 a model is presented for channelized lava flows emplaced by a self replicating levee building process over long distances on the plains of mars such flows may exhibit morphologic evidence of stagnation overspills and upstream breakouts however these processes do not inhibit the formation and persistence of a prominent central channel that can often be traced for more than 100 km the two central assumptions of the self replication model are 1 the flow advances at the average upstream velocity of the molten core and 2 the fraction of the lava that travels faster than the average upstream velocity forms stationary margins in the advancing distal zone to preserve the self replication process for an exemplary 300 km long flow north of pavonis mons the model indicates that 8 m of crust must have formed during emplacement as determined from the channel and levee dimensions when combined with independent thermal dynamic estimates for the crustal growth rate relatively narrow constraints are obtained for the flow rate 2250 m3 s 1 emplacement duration 600 d and the lava viscosity of the molten interior 106 pa s minor transient overspills and breakouts increase the emplacement time by only a factor of 2 the primary difference between the prodigious channelized martian flows and their smaller terrestrial counterparts is that high volumetric flow rates must have persisted for many hundreds of days on mars in contrast to a few hours or days on earth

the temperature of europe during the holocene reconstructed from pollen data we present the first area average time series reconstructions of warmest month coldest month and mean annual surface air temperatures across europe during the last 12 000 years these series are based on quantitative pollen climate reconstructions from over 500 pollen sites assimilated using an innovative four dimensional gridding procedure this approach combines three dimensional spatial gridding with a fourth dimension represented by time allowing data from irregular time series to be focussed onto a regular time step we provide six regional reconstructed temperature time series as well as summary time series for the whole of europe the results suggest major spatial and seasonal differences in holocene temperature trends within a remarkably balanced regional and annual energy budget the traditional mid holocene thermal maximum is observed only over northern europe and principally during the summer this warming was balanced by a mid holocene cooling over southern europe whilst central europe occupied an intermediary position changes in annual mean temperatures for europe as a whole suggest an almost linear increase in thermal budget up to 7800 bp followed by stable conditions for the remainder of the holocene this early holocene warming and later equilibrium has been mainly modulated by increasing winter temperatures in the west which have continued to rise at a progressively decreasing rate up to the present day

simulation of holocene cooling events in a coupled climate model three potential mechanisms behind centennial scale holocene cooling events are studied in simulations performed with the coupled climate model ecbilt clio 1 internal variability 2 solar forcing and 3 freshwater forcing in experiments with constant preindustrial forcings three centennial scale cooling events occur spontaneously in 15 000 years these rare events represent an unstable internal mode of variability that is characterised by a weaker thermohaline circulation a more southward location of the main site of deep water formation expanded sea ice cover and cooling of 101c over the nordic seas this mode is visited more frequently when the climate is cooled by abruptly reducing the solar constant by 5 or 3 wm 2 prescribing a solar forcing of the same magnitude but following a sinusoidal function with a period of 100 or 1000 years does not result in any centennial scale cooling events the latter forcing does however result in more frequent individual cold years in the north atlantic region that are related to local weakening of the deep convection and sea ice expansion adding realistic freshwater pulses to the labrador sea is also able to trigger centennial scale cooling events with temperature anomalies resembling proxy evidence for the cooling event at 8 2 kyr bp suggesting that freshwater forcing is a valid explanation for early holocene cooling events r 2007 elsevier ltd all rights reserved

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

phosphorus content and fractionation of phosphate in the surface sediments of the daliao river system in china the daliao river system in china has been seriously affected by long term intensive industrial urban and agricultural activities the objectives of this study were to determine the total phosphorus tp content and forms of phosphate in the sediments and investigate geochemical relationships between p forms and sediment mineral phases twenty seven samples of surface sediments were collected and analyzed for p and major elements chemical forms of phosphate in the sediments were measured by sequential selective extraction method results indicate that tp in the sediments of the daliao river system averaged 703 mg kg 1 in the range from 206 to 1 342 mg kg 1 the sediments in the tributaries and near cities contained high tp due to discharge of municipal and industrial effluents the distribution of phosphate in the various mineral phases followed the order ca p res p rs p fe p al p s l p for the hun river and taizi river and ca p fe p res p rs p al p s l p for the daliao river fe and ca contents in the sediments were positively correlated to fe associated p fe p and rs p and ca p respectively in addition sediment organic matter fe and ca contents were positively correlated to tp in the sediments however al content was not correlated to al p or tp in the sediments generally the sediments contaminated by effluents and in tidal zone contained more bioavailable p possible release of p from these sediments to overlying water might pose potential risk on estuarine eutrophication

climate change and the collapse of the akkadian empire evidence from the deep sea the akkadian empire ruled mesopotamia from the headwaters of the tigris euphrates rivers to the persian gulf during the late third millennium b c archeological evidence has shown that this highly developed civilization collapsed abruptly near 4170 150 calendar yr b p perhaps related to a shift to more arid conditions detailed paleoclimate records to test this assertion from mesopotamia are rare but changes in regional aridity are preserved in adjacent ocean basins we document holocene changes in regional aridity using mineralogic and geochemical analyses of a marine sediment core from the gulf of oman which is directly downwind of mesopotamian dust source areas and archeological sites our results document a very abrupt increase in eolian dust and mesopotamian aridity accelerator mass spectrometer radiocarbon dated to 4025 125 calendar yr b p which persisted for 300 yr radiogenic nd and sr isotope analyses confirm that the observed increase in mineral dust was derived from mesopotamian source areas geochemical correlation of volcanic ash shards between the archeological site and marine sediment record establishes a direct temporal link between mesopotamian aridification and social collapse implicating a sudden shift to more arid conditions as a key factor contributing to the collapse of the akkadian empire

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

high resolution millennial and centennial scale holocene monsoon variability in the higher central himalayas abstract relict lake sediments situated within the transition of the lesser and higher central himalayas show a persistent millennial to centennial scale monsoon variability during the holocene based on high resolution geochemical data supported by radiocarbon dating six phases of enhanced indian summer monsoon ism with varying magnitude have been identified these are dated between 10 000 9600 9500 9200 8600 5800 5000 4200 3500 2400 and 1800 1000 cal yr bp the millennial and multi centennial scale phases of enhanced ism are broadly comparable with the existing continental and marine records from the monsoon dominated region of se asia suggesting sensitivity of the regions to short term climatic perturbations further the study observed that the phases of weakened ism largely correlate with the drift ice record of the northern atlantic implying a coupling between short term solar irradiance induced glacial boundary condition in the northern atlantic and the millennial and multi centennial scale monsoon variability in the central himalaya

late holocene aridification recorded in the stable carbon and nitrogen isotope composition of soils from nainital lesser himalaya abstract this study incorporates micromorphology geochemistry and stable carbon and nitrogen isotope compositions of soil organic matter 13c and 15n in a radiocarbon dated holocene alfisol section from nainital northwest himalaya india to understand pedogenic and vegetation response to changing indian summer monsoon ism soil micromorphology suggests this soil to be an alfisol that formed in semiarid to humid conditions extensive illuviation with thick clay pedofeatures found in the bt horizon suggests wet conditions and intense monsoon during early to middle holocene 9 0 4 6 ka the 13c varies from 14 2 to 22 6 and reflects abrupt changes in the proportions of c3 and c4 plants in the ecosystem during late holocene an average 13c of 21 6 1 0 during early to middle holocene 9 0 4 6 ka indicates that the vegetation was dominated by c3 plants growth under hot humid and strong monsoonal conditions on the other hand 13c 16 7 2 1 during late holocene 4 1 ka suggests distinct vegetation shift towards increasing c4 plants abundance related to aridification weak ism at 4 ka the pattern of 15n variability in the soil is similar to that observed for the 13c variability in the profile the 15n varies from 4 4 to 8 3 with significantly more positive values during late holocene weaker monsoon compared to early to middle holocene stronger monsoon consistent with the relationship between 15n and mean annual precipitation observed on a global scale our study demonstrates a strong and rapid adjustment of vegetation in response to ism variability during holocene