quantification of holocene asian monsoon rainfall from spatially separated cave records abstract a reconstruction of holocene rainfall is presented for southwest china an area prone to drought and flooding due to variability in the east asian monsoon the reconstruction is derived by comparing a new high resolution stalagmite 18 o record with an existing record from the same moisture transport pathway the new record is from heshang cave 30 27 n 110 25 e 294 m and shows no sign of kinetic or evaporative effects so can be reliably interpreted as a record of local rainfall composition and temperature heshang lies 600 km downwind from dongge cave which has a published high resolution 18 o record wang y j cheng h edwards r l he y q kong x g an z s wu j y kelly m j dykoski c a li x d 2005 the holocene asian monsoon links to solar changes and north atlantic climate science 308 854 857 by differencing co eval 18 o values for the two caves secondary controls on 18 o e g moisture source moisture transport non local rainfall temperature are circumvented and the resulting 18 o signal is controlled directly by the amount of rain falling between the two sites this is confirmed by comparison with rainfall data from the instrumental record which also allows a calibration of the 18 o proxy the calibrated 18 o record provides a quantitative history of rainfall in southwest china which demonstrates that rainfall was 8 higher than today during the holocene climatic optimum 6 ka but only 3 higher during the early holocene significant multi centennial variability also occurred with notable dry periods at 8 2 ka 4 8 4 1 ka 3 7 3 1 ka 1 4 1 0 ka and during the little ice age this holocene rainfall record provides a good target with which to test climate models the approach used here of combining stalagmite records from more than one location will also allow quantification of rainfall patterns for past times in other regions

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

slope and deep sea abundance across scales southern ocean isopods show how complex the deep sea can be how animals are distributed in the world s largest surface environment the deep sea is poorly understood the andeep antarctic benthic deep sea biodiversity colonisation history and recent community patterns iii cruise probed richness and abundance of one group peracarid crustaceans isopods amphipods cumaceans tanaidaceans mysidaceans as a model of deep sea fauna across southern ocean so sites analysis of samples from the andeep cruises reveals so isopods to be highly abundant rich and endemic as many other taxa in the region are known to be samples taken across three spatial scales include sites tens hundreds and thousands of kilometers apart sites stretching from the southern cape basin south atlantic to continental antarctica and including depths from 1030 to 5000 m across these spatial scales we investigated ecological success abundance of peracarids at order family and species levels remarkably no significant relationship was found between abundance and spatial scale at any taxonomic level that is the variability in abundance at major regional scale is no different to that across just tens of kilometres most taxa were represented in only a few samples but we suggest most inhabitants of the deep weddell sea environment to be very patchy rather than rare separate plots of family genus and species abundance by sample number revealed this to be true nearly all genera and species are an order of magnitude more abundant than background levels in just one or two samples our isopod and amphipod samples reveal the atlantic sector of the so one of the most dynamic and important regions influencing the global deep sea environment to be highly complex our study suggests that at least with regard to the study taxa and area the typical comparisons of regions that are made by ecologists miss the scale at which crucial ecological variability happens even without ice scours creating topographical complexity as on the shelf the deep weddell sea is clearly complex at scales smaller than that measured to date

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

response of alpine vegetation to climate changes in the nanling mountains during the second half of the holocene abstract studying the response of vegetation to past climate changes may help better predict the potential impacts of future climate changes on the terrestrial ecosystems here we present a pollen record that covers the second half of the holocene from the nanling mountains southern china our record reveals six cooling events occurring during 5600 4800 4400 4100 3800 3300 3200 2900 1600 1400 and 500 380 cal yr bp in this area these cooling events broadly correspond to the episodic weakening of the asian summer monsoon and the bond events in the north atlantic realm suggesting a common forcing mechanism given that temperature has an important effect on the vertical distribution of alpine vegetation in this area the projected future warming may lead to a large upward shift of the upper forest line and a threat to the life of alpine tree species on the nanling mountains for example under the rcp8 5 scenario mean surface air temperature is projected to increase by 4 9 c by the end of this century this magnitude of warming definitely would result in the disappearance of tsuga chinensis in this area

benthic infaunal communities across the weddell sea basin and south sandwich slope antarctica abstract the present study represents the first quantitative investigation of deep sea benthic infauna in antarctica box cores and multicores were used to collect sediment from 12 stations across the slope and abyssal basin of the weddell sea and the slope off the south sandwich islands including sites in the south sandwich trench 6300 m the multicore was a more efficient sampler than the box core nine phyla of invertebrates were found dominated by annelids 67 crustaceans 20 other phyla 13 a total of 117 taxa were identified to the species level 72 were polychaetes 45 were crustaceans many taxa are new to science highest densities were at the 1000 m depth on the western slope of the weddell sea 260 individuals per 0 1 m 2 and at ca 2200 m on the south sandwich slope 132 individuals per 0 1 m 2 lowest densities were in the central weddell sea basin 39 individuals per 0 1 m 2 species richness and rarefaction analysis suggest that the fauna is undersampled the 117 species identified in this study were represented by only 237 specimens indicating that species were being added at a rate of one species for every two specimens collected rarefaction curves do not begin to reach an asymptote supporting high estimates of diversity some species appear to be limited to distinct zones in upper and middle slope depths other species extend from the slope to the abyssal basin and at least two species appear to be restricted to the abyssal basin in general the densities of infauna on the slopes surrounding the weddell sea basin have lower densities than well studied areas off north america however abyssal populations in antarctica appear to have denser infaunal populations than those from off new england and the north pacific gyre productive surface waters of the weddell sea and subsequent sinking of phytoplankton to the seabed are probable reasons for the higher benthic productivity in antarctic abyssal sediments similarity analyses were not informative because so few species were collected two stations in the weddell abyssal basin were the only ones to exhibit a high level of similarity due to two shared polychaetes data on reproductive status of some polychaetes suggest that species limited to abyssal depths are reproducing there other species with broader depth ranges may be receiving recruits from slope depths the results suggest that the deep water infauna in antarctica is largely endemic but has some components that occur along other continental margins and adjacent abyssal basins

holocene variations in asian monsoon moisture a bidecadal sediment record from the south china sea the east asian monsoon system involves extensive transport of sensible latent heat between land and sea and from low to high latitudes our high resolution bidecadal marine records present a first detailed history of monsoon climate change over the holocene the high amplitude perturbation in monsoon moisture centered at 8 150 years ago and the monsoon maximum in the early holocene show inter hemispheric teleconnections to both a cool episode in greenland and to the indian monsoon monitored in the arabian sea periodicities of 84 102 and especially near 775 years in monsoon variation suggest a climatic forcing both by long term oscillations in thermohaline circulation and possibly solar activity cycles

flow of bottom water in the northwestern weddell sea the weddell sea is known to feed recently formed deep and bottom water into the antarctic circumpolar water belt from whence it spreads into the basins of the world ocean the rates are still a matter of debate to quantify the flow of bottom water in the northwestern weddell sea data obtained during five cruises with r v polarstern between october 1989 and may 1998 were used during the cruises in the weddell sea five hydrographic surveys were carried out to measure water mass properties and moored instruments were deployed over a time period of 8 5 years to obtain quasi continuous time series the average flow in the bottom water plume in the northwestern weddell sea deduced from the combined conductivity temperature depth and moored observations is 1 3 0 4 sv intensive fluctuations of a wide range of timescales including annual and interannual variations are superimposed the variations are partly induced by fluctuations in the formation rates and partly by current velocity fluctuations related to the large scale circulation taking into account entrainment of modified warm deep water and weddell sea deep water during the descent of the plume along the slope between 0 5 sv and 1 3 sv of surface ventilated water is supplied to the deep sea this is significantly less than the widely accepted ventilation rates of the deep sea if there are no other significant sources of newly ventilated water in the weddell sea either the dominant role of weddell sea bottom water in the southern ocean or the global ventilation rates have to be reconsidered

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

solar forcing of centennial scale east asian winter monsoon variability in the mid to late holocene abstract centennial scale variability of the east asian winter monsoon during the holocene is poorly understood because suitable archives and proxies are lacking here we present a high resolution 30 yr spacing planktonic foraminiferal o 18 record of neogloboquadrina incompta dextral form which reflects sea surface temperature during the winter season for the last 6000 yrs from marine sediments in the western north pacific stronger winter monsoons indicated by cooler winter ssts correspond to weaker summer monsoons indicated by the cave oxygen isotopes in centennial scale variability the variability also shows good correlation with o 18 records in lake sediments and ice cores from the yukon territory canada spanning the last 4500 yrs suggesting east west climate coupling across the north pacific furthermore the climate changes across the north pacific co vary over widespread regions such as the eastern tropical pacific and the northern red sea and the reconstructed solar activity the cross spectral and wavelet analyses show that the east asian winter monsoon shares some cyclicity with the solar variability our results suggest that the solar activity is a fundamental forcing producing the centennial scale eawm variability mediated by the large scale climate linkages

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

paleotemperature variability in central china during the last 13 ka recorded by a novel microbial lipid proxy in the dajiuhu peat deposit the asian summer monsoon is a very important climatic component affecting the land ecosystem on the eastern asian continent here we assess microbe derived lipid biomarker evidence from a well date

a new bathymetric compilation highlighting extensive paleo ice sheet drainage on the continental shelf south georgia sub antarctica a grid derived from a new compilation of marine echo sounding data sets has allowed us to visualize and map the geomorphology of the entire continental shelf around south georgia at an unprecedented level of detail the grid is the first continuous bathymetric data set covering south georgia to include multibeam swath bathymetry and represent them at a subkilometer resolution large and previously undescribed glacially eroded troughs linked to south georgia s modern day fjords radiate from the island marking the former pathways of large outlet glaciers and ice streams a tectonic or geological influence is apparent for the major troughs where glaciers have exploited structural weaknesses on the continental block bed forms lining the troughs give some first insights into glacial dynamics within the troughs suggesting arteries of fast flowing ice occupied these topographic depressions in the past and operated over both bedrock and sedimentary substrates on the outer shelf and within the troughs large ridges and banks are also common interpreted as terminal lateral and recessional moraines marking former positions of ice sheets on the shelf and their subsequent reorganization during deglaciation a small trough mouth fan has developed at the mouth of at least one of the cross shelf troughs demonstrating a focused sediment delivery to the margin slides and slide scars are also present on parts of the margin showing that margin stability perhaps also related to glaciation has been an important factor in depositional processes on the continental slope implications of the new observations are that ice sheets have been more extensive on south georgia than any previous studies have reported their age may date back to late miocene times and evolution of the shelf system has probably involved numerous late cenozoic glacial episodes however relatively fresh seafloor geomorphology coupled with evidence from other maritime antarctic islands heard island and kerguelen island indicating extensive glaciation at the last glacial maximum raises the possibility that the extent of sub antarctic glaciation for the last glacial period has until now been underestimated

upper slope processes and seafloor ecosystems on the sabrina continental slope east antarctica abstract this study applies detailed seafloor bathymetry data and seafloor images to understand upper slope features and how these influence the distribution of seafloor biota on the east antarctic margin the east antarctic slope on the sabrina margin has been shaped by diverse processes related to repeated glaciation differences in the morphology of gullies on the upper slope enable an understanding of the likely processes that have been active on this margin gully morphology varies according to changes in slope gradient which may have driven variations in sedimentation areas of lower slope angles may have led to rapid sediment deposition during glacial expansion to the shelf edge and subsequent sediment failure typically gullies in these areas are u shaped initiate well below the shelf break are relatively straight and long and have low incision depths consistent with formation due to mass wastage areas of higher slope angles likely experienced enhanced flow of erosive turbidity currents during glaciations associated with the release of sediment laden basal meltwaters sediment laden subglacial meltwater flows typically create gullies such as those we observe that initiate at or near the shelf break are v shaped in profile and have high sinuosity deep incision depths and a relatively short downslope extent the short downslope extent reflects a reduced sediment load associated with increased seawater entrainment as the slope becomes more concave in profile these differences in gully morphology have important habitat implications associated with differences in the composition and beta diversity of the seafloor communities this upper slope region also supports seafloor communities that are distinct from those on the adjacent shelf highlighting the uniqueness of this environment for biodiversity conservation strategies therefore need to consider slope and shelf communities as distinct and equally important components of the antarctic ecosystem

the antarctic ice sheet during the last glacial maximum and its subsequent retreat history a review abstract an emerging body of evidence from studies of the last glacial interglacial cycle suggests that the east and west antarctic ice sheets have not advanced and retreated in concert the west antarctic ice sheet advanced to the outer shelf in most regions during the last glacial maximum lgm the retreat from the shelf commenced shortly after the lgm and continued into the late holocene the west antarctic ice sheet in ross and amundsen seas slid across a deforming bed at least during the final phases of extended glaciation this implies that at this time the ice sheet had a low profile differences in the number and locations of grounding zone wedges and smaller grounding zone features from trough to trough imply that individual west antarctic ice sheet ice streams retreated episodically details concerning the expansion retreat and behavior of the east antarctic ice sheet eais are more sparse the picture emerging is that the eais did not expand to the continental shelf edge during the lgm rather it achieved a maximum extent of a mid shelf position in some locations while in other areas the ice terminus was situated near its present location the timing of retreat along sectors within the eais appears diachronous and in places occurred prior to the lgm the antarctic peninsula shelf contained considerably more ice during the lgm than previously proposed the results presented in this paper support more recent published ice sheet models that call for greater contributions of melting ice from west antarctica including the antarctic peninsula to the post glacial rise in sea level

a model for the structure of the antarctic slope front the antarctic slope front is an oceanic front that appears to be a semi permanent feature situated above or near long sections of the shelf break of the antarctic continental shelf these sections include the shelf break of the ross and weddell seas it is distinguished by a v shaped structure unique to coastal antarctica in which isopycnals slope downward from near the surface on both the shallow continental shelf and the deep continental slope sides toward the bottom near the upper part of the slope in the regions where it is observed the overflow of dense water from the shelf down the slope is observed or presumed to occur such overflows entrain fluid from the overlying stratified environment into the downflow and this entrainment acts as a distributed sink of the overlying fluid a model of this frontal structure is constructed here consisting of the downslope flow modelled as a plume and the overlying fluid governed by quasi geostrophic dynamics with the effect of the plume on the latter being represented by a suitable distribution of sinks the alongslope currents follow from geostrophy and potential vorticity conservation two distinct flow regimes are found in the first regime a realistic depiction of the two sided v shaped structure is obtained where most of the fluid flowing off the shelf enters the downflow at the top of the slope constituting the shallow side of the v and fluid from offshore enters the deep side of the v alongslope flow in this region is mostly eastward in the second regime where most of the fluid flowing off the shelf passes over the downflow only the shallow side of the v is present and alongslope flow is westward near the shelf break and eastward further offshore

reconstructing late holocene vegetation and fire histories in monsoonal region of southeastern china abstract eastern subtropical china is a key region for understanding the variability of the east asian summer monsoon easm multidisciplinary studies in southeastern china have shown that the summer monsoon intensity declined in the mid late holocene we present a high resolution pollen record of the last 4000 cal yr bp in jinggang mts of jiangxi province southeastern china the identified pollen taxa from the core can be statistically divided into three groups corresponding to evergreen deciduous and wetland communities the transitions between evergreen and deciduous coniferous pollen associations is likely caused by temperature fluctuations indicating that climate was relatively cool at 3800 3200 cal yr bp and 2200 1300 cal yr bp and warmer at 3200 2800 cal yr bp and 1300 800 cal yr bp the vegetation study suggests that an alnus dominant association represents a secondary forest that usually takes place and expand after repeated forest fires the charcoal concentration from the core depicts at least six major forest fire events since 4000 cal yr bp most of which were followed by the development of an alnus forest community this result suggests that the easm weakened toward the late holocene and that its related decrease in moisture led to large forest wildfires furthermore the rapid formation of a swamp and the subsequent development of the alnus wetland community at 550 cal yr bp suggest a gradual drying up of the lake which was likely related to the little ice age as a result of a substantial burning related to an intensification of the human cultivation practices alnus reached its highest values in the last 200 years along with abundant wetland herbs pioneer ferns mainly dicranopteris and high charcoal concentrations the present evidence of several sharp floristic and climate changes coincides with either the collapse or the beginning of some chinese dynasties which will need further research on the relationship between natural and human cultural changes

pollen records from southern taiwan implications for east asian summer monsoon variation during the holocene pollen records from two cores retrieved from a valley basin in southern taiwan show major changes in vegetation and climate occurring during the holocene between 11 400 and 8200 cal yr bp the up

submarine slopes with an exponential curvature abstract the curvature of submarine slopes is a little used source of information on transport processes and sediment composition in a survey of modern submarine slopes selected from all over the world about 15 are characterized by very regular profiles with sharp shelfbreaks and concave upward curvature an exponential function describes this morphology very well these exponential profiles are from three very different depositional settings a continental margin close to a young mountain belt with very high rates of sedimentation high latitude continental margins with evidence of ice cover during quaternary glacial intervals and a carbonate platform margin we propose that the curvature is controlled by the exponential decay of transport capacity with increasing distance from the shelf edge while exponential decrease of transport may be a general property of most slopes the development of a regular exponential profile is commonly disturbed by other factors in particular by the interplay with wave dominated transport at the upper boundary during sea level fluctuations and with turbidite dominated sedimentation at the lower boundary the good exponential fit of the profiles described here results from the fact that vertical shifts of the shelfbreak are very small compared to the horizontal progradation the three depositional settings mentioned above prevent the shelf edge from fluctuations in the vertical high rates of sedimentation and therefore rapid progradation result in minimal movements of the shelfbreak ice covered margins are limited by the grounding level of the ice and margins built by reef organisms are stationary because the hard limestone is relatively resistant to erosion during lowstands of sea level the numerical value of the exponent is distinctly different for sandy and muddy slopes indicating the possibility of using the curvature to deduce sediment composition of submarine slopes

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

deep water sedimentary environments of the northwestern weddell sea and south sandwich islands antarctica abstract two transects have been sampled using short cores multi and box seabed photography video sequences and sediment profile images across the northwestern weddell sea and south sandwich forearc antarctica a total of 12 core stations were examined for sediment structure texture and composition to determine their depositional history four of the core stations from the weddell continental slope abyssal plain and south sandwich forearc and trench were further examined for trace metal analysis ba u mn and pb for sediment source and palaeoproductivity and 210pb for age profiles and depth of mixing by bioturbation the 3055 m station at the base of the weddell continental slope recovered laminated muddy silty contourites with a surface layer of hemipelagites with abundant ice rafted debris possibly originating from the 1995 larsen a and 2002 larsen b ice shelf disintegration this is interpreted as a moderate energy depositional environment influenced by weddell sea bottom water along slope current reworking sediment sediment sources to this station include the direct input of clastic material from ice with variation in sediment sources from in situ current winnowing and along slope transport reflected in the mn li and ba li ratios the 4760 m station on the weddell abyssal plain recovered hemipelagites interpreted as a low energy depositional environment with sediment supplied both from direct ice rafting and pelagic settling during productive seasonally ice free periods the 210pb profiles indicate a sedimentation rate of 0 024 cm year 1 with the 206 207pb isotope ratios suggesting a principle sediment source from ice rafting the 2292 and 6326 m stations from the slope and floor of the south sandwich forearc recovered pelagic and turbiditic sediments this is interpreted as a high energy down slope depositional environment with high surface biogenic productivity and sediment supply leading to localised down slope mass movements on the slope and floor high levels of mn li and elevated u li ratios demonstrate a strong concentration of mn in organic poor sediment the mn redoxcline is present at 10 cm depth the high ba li 500 ppm in the forearc floor core reflects some limited enhanced productivity source sediment for the forearc may in part be derived from the northwest weddell abyssal plain based on the 206 207pb isotope ratios reflecting transport by weddell sea bottom water

holocene paleoclimatic reconstruction based on mud deposits on the inner shelf of the east china sea abstract we present a paleoclimatic reconstruction of the mid holocene by geochemical analysis of a sediment core mz01 retrieved from the mud area of the inner continental shelf of the east china sea ecs our results show that the downcore geochemical variations in the sediments of the core provide a link to historical climate changes relatively higher ratios of cia ba sr and a lower ratio of cao mgo coincide with major regional warm and humid climate episodes and vice versa therefore these geochemical indicators are useful in reconstructing the paleoclimate in eastern china using the geochemical records of core mz01 which are well constrained by ams 14c dating we found that from 8300 yr bp to 4200 yr bp the regional climate was moderately warm and humid and from 4200 yr bp to 2300 yr bp the climate was cool and dry with large fluctuations between cool dry 3700 yr bp 2850 yr bp and 2400 yr bp and warm wet 3250 yr bp and 2650 yr bp since 2300 yr bp our records indicate that the climate has gradually become warmer although a cold event centered at around 250 yr bp the little ice age lia interrupted this warming trend we also found significant 238 yr cycles in our cia records that imply a possible solar influence on the regional climate changes since the mid holocene

holocene vegetation and climate dynamics of ne china based on the pollen record from sihailongwan maar lake abstract high resolution palynological analysis on annually laminated sediments of sihailongwan maar lake shl provides new insights into the holocene vegetation and climate dynamics of ne china the robust chronology of the presented record is based on varve counting and ams radiocarbon dates from terrestrial plant macro remains in addition to the qualitative interpretation of the pollen data we provide quantitative reconstructions of vegetation and climate based on the method of biomization and weighted averaging partial least squares regression wa pls technique respectively power spectra were computed to investigate the frequency domain distribution of proxy signals and potential natural periodicities pollen assemblages pollen derived biome scores and climate variables as well as the cyclicity pattern indicate that ne china experienced significant changes in temperature and moisture conditions during the holocene within the earliest phase of the holocene a large scale reorganization of vegetation occurred reflecting the reconstructed shift towards higher temperatures and precipitation values and the initial holocene strengthening and northward expansion of the east asian summer monsoon easm afterwards summer temperatures remain at a high level whereas the reconstructed precipitation shows an increasing trend until approximately 4000 cal yr bp since 3500 cal yr bp temperature and precipitation values decline indicating moderate cooling and weakening of the easm a distinct periodicity of 550 600 years and evidence of a mid holocene transition from a temperature triggered to a predominantly moisture triggered climate regime are derived from the power spectra analysis the results obtained from shl are largely consistent with other palaeoenvironmental records from ne china substantiating the regional nature of the reconstructed vegetation and climate patterns however the reconstructed climate changes contrast with the moisture evolution recorded in s china and the mid latitude semi arid regions of n china whereas a clear insolation related trend of monsoon intensity over the holocene is lacking from the shl record variations in the coupled atmosphere pacific ocean system can largely explain the reconstructed changes in ne china

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

sea level changes at the lgm from ice dynamic reconstructions of the greenland and antarctic ice sheets during the glacial cycles abstract new experiments were performed with three dimensional thermomechanical models of the greenland and antarctic ice sheets to simulate their behaviour during the glacial cycles to reconstruct their thickness and extent at the last glacial maximum lgm and to estimate their glacio eustatic contribution to the global sea level stand the calculations used improved ice dynamic and isostatic treatments updated datasets on higher grid resolutions and refined climatic treatments based on newly calibrated transfer functions between ice core records and climatic perturbations results are discussed from a reference run with standard parameters that is compared with available glacial geological observations and from a series of sensitivity experiments focusing on isostatic adjustment thermomechanical coupling climatic forcing mass balance changes and basal melting rates and viscosity changes of antarctic ice shelves for the antarctic ice sheet we find that volume changes are closely linked with grounding line changes of the west antarctic ice sheet at the lgm the grounding line extended close to the continental shelf break almost everywhere ice over central east antarctica was generally thinner than today and varied mainly in accordance with accumulation fluctuations for the greenland ice sheet melting is important only during interglacial periods and the most sensitive period concerns the size of the ice sheet during the eemian at the lgm the greenland ice sheet extended beyond the present coastline to cover at least the inner continental shelf and thinned by up to several hundred meters in central areas for a plausible range of parameters the experiments indicate that at the time of maximum sea level depression 21 kyr bp the antarctic ice sheet contributed 14 18 m to the sea level lowering and the greenland ice sheet 2 3 m significantly less than the older climap reconstructions whereas both ice sheets were at 21 kyr bp close to their maximum extent the experiments also indicate that their maximum volumes were reached only by 16 5 kyr bp greenland and 10 kyr bp antarctica equal to an additional sea level lowering of respectively 0 4 and 3 7 m holocene retreat was essentially complete by 5 kyr bp in greenland but is found to still continue today in west antarctica before reversing to growth during the next millenium the models were found to reproduce gross features of the ice sheet s history since the lgm in reasonably good agreement with available glacial geological data although observational control on ice thickness changes remains very limited

is there a distinct continental slope fauna in the antarctic abstract the antarctic continental slope spans the depths from the shelf break usually between 500 and 1000 m to 3000 m is very steep overlain by warm 2 2 5 c circumpolar deep water cdw and life there is poorly studied this study investigates whether life on antarctica s continental slope is essentially an extension of the shelf or the abyssal fauna a transition zone between these or clearly distinct in its own right using data from several cruises to the weddell sea and scotia sea including the andeep antarctic benthic deep sea biodiversity colonisation history and recent community patterns i iii biopearl biodiversity phylogeny evolution and adaptive radiation of life in antarctica 1 and easiz ecology of the antarctic sea ice zone ii cruises as well as current databases sombase scar marbin four different taxa were selected i e cheilostome bryozoans isopod and ostracod crustaceans and echinoid echinoderms and two areas the weddell sea and the scotia sea to examine faunal composition richness and affinities the answer has important ramifications to the link between physical oceanography and ecology and the potential of the slope to act as a refuge and resupply zone to the shelf during glaciations benthic samples were collected using agassiz trawl epibenthic sledge and rauschert sled by bathymetric definition these data suggest that despite eurybathy in some of the groups examined and apparent similarity of physical conditions in the antarctic the shelf slope and abyssal faunas were clearly separated in the weddell sea however no such separation of faunas was apparent in the scotia sea except in echinoids using a geomorphological definition of the slope shelf slope abyss similarity only changed significantly in the bryozoans our results did not support the presence of a homogenous and unique antarctic slope fauna despite a high number of species being restricted to the slope however it remains the case that there may be a unique antarctic slope fauna but the paucity of our samples could not demonstrate this in the scotia sea it is very likely that various ecological and evolutionary factors such as topography water mass and sediment characteristics input of particulate organic carbon poc and glaciological history drive slope distinctness isopods showed greatest species richness at slope depths whereas bryozoans and ostracods were more speciose at shelf depths however significance varied across weddell sea and scotia sea and depending on bathymetric vs geomorphological definitions whilst the slope may harbour some source populations for localised shelf recolonisation the absence of many shelf species genera and even families in a poorly dispersing taxon from the continental slope indicate that it was not a universal refuge for antarctic shelf fauna

the behavior of biologically important trace elements across the oxic euxinic transition of meromictic fayetteville green lake new york usa abstract trace elements are central components of enzymes that catalyze many of the essential reactions mediated by life the redox sensitive nature of trace elements also permits their use as a record of ancient ocean conditions preserved in the geologic record trace element geochemistry in modern stratified systems is often used as a proxy for the redox state of the ancient oceans which are thought to have been largely anoxic in the present study we examined trace element behavior of simultaneously collected samples at a heretofore unprecedented depth resolution 1 0 25 m intervals throughout the redox stratified water column of fayetteville green lake n y fgl a 53 m deep meromictic lake under euxinic conditions similar to those thought to have been prevalent in proterozoic oceans among characterized proterozoic ocean analogs fgl represents an understudied proxy in terms of trace elements with characteristics of low salinity and high sulfate in the fgl water column spikes in the concentration of dissolved mn fe and co are coincident with the transition from oxic to euxinic conditions and are associated with a decrease in dissolved mo concentration in contrast the concentration of dissolved ni did not vary across this transition despite the dramatic shift in redox state from these data we present a one dimensional model for element transport and cycling through the water column to the sediments collectively this comprehensive analysis of water column geochemistry provides insight into the effects of biogeochemical cycling in stratified systems on dissolved trace element concentrations in the water column this study in concert with characterization of other early earth analogs will greatly enhance the use of trace elements in interpreting the geologic record

water masses and distribution of physico chemical properties in the western bransfield strait and gerlache strait during austral summer 1995 96 in the framework of the fruela project two oceanographic surveys were conducted by r v hesperides in the eastern bellingshausen sea western basin of the bransfield strait and gerlache strait area during december 1995 and january 1996 the main hydrographic structures of the study domain were the southern boundary of the acc and the bransfield front the characteristics and zonation of local water masses are discussed in terms of temperature salinity dissolved oxygen nutrient and inorganic carbon concentrations concentration intervals for water mass labelling on the basis of chemical parameters in addition to the common s based classification are defined silicate seems to be a very good discriminator for local water masses

a high resolution absolute dated holocene and deglacial asian monsoon record from dongge cave china abstract we present a continuous record of the asian monsoon over the last 16 ka from 18o measurements of stalagmite calcite over 900 oxygen isotopic measurements providing information on shifts in monsoon precipitation are combined with a chronology from 45 precise 230th dates 18o and therefore asian monsoon intensity generally follows changes in insolation although changes in 18o are generally accommodated in abrupt shifts in contrast to smoothly varying insolation indicating that threshold effects may be important 18o decreased dramatically 3 at the start of the holocene 11 5 ka and remained low for 6 ka four positive 18o events centered at 11225 97 yr bp 1 05 10880 117 yr bp 1 15 9165 75 yr bp 1 4 and a double event centered at 8260 64 yr bp 1 1 and 8080 74 yr bp 1 0 punctuated this period of high monsoon intensity all four events correlate within error with climate changes in greenland ice cores thus the relationship between the asian monsoon and the north atlantic observed during the glacial period appears to continue into the early holocene in addition three of the four events correlate within error with outburst events from lake agassiz the decline of monsoon intensity in the mid late holocene is characterized by an abrupt positive shift in 18o which occurs at 3550 59 yr bp 1 1 in 100 yr in addition the holocene is punctuated by numerous centennial and multi decadal scale events amplitudes 0 5 to 1 up to half the amplitude of the glacial interstadial events seen in the last glacial period thus holocene centennial and multi decadal scale monsoon variability is significant although not as large as glacial millennial scale variability the monsoon shows a strong connection with northern south american hydrological changes related by changes in itcz position spectral analysis of the 18o record shows significant peaks at solar periodicities of 208 yr and 86 yr suggesting variation is influenced by solar forcing however there are numerous other significant peaks including peaks at el nino frequencies observed for high resolution portions of the record between 8110 and 8250 yr which suggest that changes in oceanic and atmospheric circulation patterns in addition to those forced by solar changes are important in controlling holocene monsoon climate in addition for this high resolution portion we observe a distinctive biennial oscillation of the asian monsoon which has been associated with the tropospheric biennial oscillation tbo

seismic facies and sedimentary processes on the continental rise off wilkes land east antarctica evidence of bottom current activity abstract the slope and rise areas off wilkes land east antarctica encompass three large scale composite sediment ridges dissected by two broad deep sea valleys jussieu canyon and wega channel large scale depositional architecture revealed from multi channel seismic profiles acquired during the wilkes basin glacial history wega cruise indicates a wide temporal and spatial variability in the dominant depositional processes delivering or redistributing sediments on the slope and rise all three sediment ridges are built on a flat seafloor and resulted from the growth of a thick sediment section at least 2 km with a depositional relief in the order of hundreds of meters on the adjacent deep sea valleys the sediment ridges show their maximum internal complexity in areas shallower than 3000 m where they are also substantially thicker as much as 1 1 5 s in two way travel time high amplitude sediment waves typically 20 30 m and up to 50 70 m have wavelengths ranging from 1500 to 3500 m and occur in the deepest sectors of the continental rise where the sediment ridges toe out in the lower rise the sediment waves display a consistent decrease in wavelength with increasing water depth on seismic profiles the relief of the sediment waves decreases from older to younger sequences possibly indicating a decrease in bottom current intensity throughout their formation sediment waves occur also at the seafloor which is dominated elsewhere by irregular topography and widespread evidence of erosion however no conclusion can be drawn on the possible modern activity of these large scale bedforms in shallower upper rise areas where the sediment ridges are thicker sediment waves are evident in the upper stratigraphic units while the remaining section is characterized by the development of channel levee complexes seen as small scale erosional channels bordered by depositional reliefs consisting of variable amplitude reflector packages wedging out away from the channels channel levee complexes are locally associated with poorly developed sediment waves the origin of these features is likely related to transport by turbidity flows from the edge of the antarctic shelf and implies the presence of a more temperate glacial regime than the one dominating since the late miocene the formation of the sediment waves both in this more proximal area and on the deep rise is indicative of the impact of bottom hugging currents during intervals of the cenozoic history of the margin no constrains are available at present on the nature of these currents nor on the timing of their activity down slope turbidity currents downwelling dense waters or slope parallel contour currents are possible mechanisms despite this substantial uncertainty the observed progressive upward attenuation of the wave amplitudes indicates that substantial variations of sediment delivery and dispersal occurred through time we suggest that the interval of more complex depositional geometry in the proximal areas reflects higher bottom current velocity and or increased sediment input perhaps during conditions of temperate wet based ice sheet on the continent these conditions were conducive to high rates of melt water production formation of dense plumes and enhanced sediment input

a continuous record of vegetation and climate change over the past 50 000years in the fujian province of eastern subtropical china abstract a 425 cm core has been collected from the gantang subalpine peat bog in pingnan county fujian province of southern china high resolution pollen analysis of the core has allowed for the reconstruction of past vegetation and climate changes over the last 50 000 years today fujian province is located in the eastern part of middle subtropical zone where the dominant vegetation is evergreen broadleaved forest that receives its precipitation from the east asian monsoon the pollen record testifies that the vegetation in fujian varied between subtropical evergreen and warm temperate deciduous forests during the last glacial interglacial cycle it appears that during marine oxygen isotope stage 3 this area was covered with broadleaved forest suggesting warm and wet subtropical condition whereas the flora was quite different with many ancient elements the last glacial maximum is distinguished by an increase in warm temperate deciduous taxa particularly fagus and alnus accompanied by abundant ericaceae implying a spatial shift of zonal vegetation during this coldest episode in the world local swamp developed soon after the younger dryas event coinciding with the formation of peatlands in the northern hemisphere possibly linked with atmospheric carbon accumulation a rapid increase in evergreen broadleaved taxa that dominated the local forest occurred at ca 8 2 cal ka bp indicating the inception of the regional thermal maximum during the holocene which was generally characterised by more humid conditions the middle to late holocene sees a progressive decline in arboreal elements and an increase in grasses and ericaceae these changes beginning from around 4 ka cal bp were concordant with the general weakening of the east asian monsoon during the holocene corresponding with an orbitally induced reduction of boreal summer insolation this is the first terrestrial high resolution record from eastern part of middle subtropical areas that evaluates the forest changes through the last glacial interglacial cycle