plio pleistocene megacycles record of climate and tectonics abstract paleoclimatic records from the deep sea floor show that in the last 3 m y more than 100 oscillations of mild and cool global climate took place with a larger amplitude than any experienced during the holocene variations of dry and wet climates in the chinese loess plateau and in the loess belt of central europe have similar frequency it has been convincingly proved that the periodicity of the past gross climate changes agrees with that of the earth s orbital perturbations however while the amplitude of the orbital cycles and of the oceanic oxygen isotope variations is relatively uniform several of the cold climate episodes recorded on land appear more severe than the remainder they correspond to chinese loess units l1 l2 l5 l6 and l9 correlating with central european loess of cycles b c f h and j these units correspond to oxygen isotope stages 2 6 12 16 and 22 and to the weichselian saalian and elsterian ice advances in addition chinese loess layers l13 l15 wl1 wl2 wl3 and wl4 appear to represent exceptionally dry and cold episodes apparently correlative with the inter bavelian cooling and with menapian eburonian and praetiglian glacials of the rhine delta based on this observation we propose to distinguish within the last 2 5 m y ten megacycles describe them in the chinese loess sequences and name them in the order of increasing age mc1 mc10 each megacycle starts with an unusually thick loess unit interpreted as a deposit of an exceptionally severe glaciation and terminates with a cluster of well developed soils indicative of warm humid climates interrupted by relatively mild glacials the megacycles of the last 2 5 m y lasted between 200 and 340 millennia each with an average duration of 255 thousand years when correlated with the stratigraphic record of the chinese loess plateau the wurm terrace as well as the saale glacier advances the eem marine transgression the weichsel ice advance and the holocene correspond to a still incomplete megacycle mc1 the riss terrace the elster ice advance holstein transgression and subsequent mild and cool intervals ending with the schoningen interglacial sensu urban 1992 belong to the megacycle mc2 recognition of four megacycles within brunhes resolves the long standing discrepancy between the limited number of classical continental glacial and interglacial units and the frequent climate oscillations recorded in the deep sea sediments and the loess sequences only in the holsteinian and eemian interglacials was the crustal rebound delayed enough to permit oceanic transgressions reaching deep inland there is no apparent astronomic reason for the exceptional intensity and deep southward penetration of continental ice sheets during only some of the cold intervals since the differences are much more pronounced on land than in the ocean and since the major ice advances are closely linked with terraces it seems that the megacycles were preconditioned by tectonic movements intermittent pulses of rapid uplift of mountain ranges could have impacted climate worldwide by deflecting atmospheric circulation in the sense of ruddiman and raymo 1988 it is also probable that the tectonically changing shape of the sea floor sills reoriented the oceanic circulation which then could have affected plio pleistocene climates world wide the loess covered terraces in the lanzhou area demonstrate that the tectonic movements in the northern part of the tibet plateau correlate closely with the advances of continental ice in europe suggesting that the uplift of the tibet plateau significantly contributed to the gradual climate deterioration of the last million years

seagrass on the rocks posidonia oceanica settled on shallow water hard substrata withstands wave stress beyond predictions abstract a multidisciplinary approach was applied to investigate the role of abiotic constraints in the settlement of posidonia oceanica on shallow rocks in two coastal areas of the ligurian sea italy nw mediterranean meadows developed very shallow upper limits at 1 5 m depth in both areas and with a distinctive morphology of stripes growing on rocky outcrops orthogonal to the coastline application of a predictive model to indicate the reference condition zone for the meadow upper limit already validated on meadows developing on soft bottoms was not adequate for these rocky substrata as the meadow upper limits were found shallower than model predictions 5 m depth geological and geomorphological characteristics of the rocky shores were analysed through geomechanic and petrographic analyses i e thin sections sem analyses rock hardness tests whilst the shape and the features of the meadows i e shoot density and maximum leaf length were assessed through scuba diving surveys among the different lithotypes occurring at the sites in the alternating and interbedded outcrops p oceanica was passively selected i e due to the seedlings survival and settlement there on the strongest i e less erodible lithotypes whilst the comparatively weaker and more erodible rocks remained unvegetated and covered by a layer of soft sediments p oceanica settling on specific rocky substrata with favourable lithological and geomechanical characteristics is able to establish outside the theoretical reference zone predicted by the model for soft sediments due to greater attachment strength and possible resistance to hydrodynamic forces combining biological ecological mineralogical geological and geomorphological approaches was effective for explaining the primary role of substratum nature in the spatial variability of seagrass meadows with geomechanical and lithological characteristics of the rocks being equally important abiotic factors than sedimentological features

much damage for little advantage field studies and morphodynamic modelling highlight the environmental impact of an apparently minor coastal mismanagement while coastal management activities have long been known to exert a strong influence on the health of marine ecosystems neither scientists nor administrators have realized that small interventions may lead to disproportionately larger impacts this study investigated the broad and long lasting environmental consequences of the construction of an ill planned although small only 12 m long jetty for pleasure crafts on the hydrodynamic conditions and on the meadow of the seagrass posidonia oceanica of an embayed cove in the ligurian sea nw mediterranean there p oceanica used to develop on a high 1 5 m matte a lignified terrace causing seafloor elevation in which the leaves reach the surface and form a compact natural barrier to waves in front of the beach such a so called fringing reef of p oceanica is today recognized of high ecological value and specific conservation efforts are required the construction of the jetty implied the cutting of the matte which directly destroyed part of the fringing reef in addition meadow mapping and sedimentological analyses coupled with morphodynamic modelling showed that the ecosystem of the whole cove had been greatly altered by the jetty we used the geometric planform approach a proper tool in the study of headland controlled embayment both to characterise the present situation of prelo cove and to simulate the original one before the jetty was built in the long term such a small jetty completely altered the configuration and the hydrodynamic conditions of the whole cove splitting the original pocket beach into two smaller ones and creating strong rip currents flowing seaward along the jetty these rip currents enhanced erosion of residual shallow portions of the meadow and further modified the sedimentary fluxes in shallow waters a century after the construction of the jetty an irreversible environmental damage has occurred as the slow growing rate of p oceanica implies that the high matte terrace and the fringing reef will hardly form again even after the removal of the jetty the lesson learnt from this study is that even such small and therefore reputed intrinsically innocent interventions on the coastal zone require accurate planning based on interdisciplinary studies to understand and respect the delicate interplay among morphological hydrodynamic and ecological components

geomorphology and ecology unifying themes for complex systems in biogeomorphology the interaction of geomorphic and ecologic landscape components has been largely conceptualized as independent in one direction geomorphic processes and landforms shape the distribution of biota conversely in the other direction biota modify geomorphic processes and landforms increasingly the interactions between geomorphic and ecological components are more circular and developmentally intertwined in this paper i integrate these two independent perspectives within the framework of complexity theory i outline four themes that characterize complex systems in biogeomorphology multiple causality and the concept of recursivity the influence of organisms that function as ecosystem engineers the expression of an ecological topology and ecological memory implicit in all of these themes is the recognition that biogeomorphic systems are open and path dependent they may exhibit a range of assembly states from self reinforcing stability domains to more transient configurations of organisms and environment

geological control of beach morphodynamic state the concept of beach morphodynamic states has achieved widespread acceptance in the coastal geological literature since its inception in the mid 1980s and expansion in the 1990s much of the pioneering work was undertaken in australia under a range of environmental conditions in microtidal environments and a close empirical relationship between beach 3 dimensional morphology and the dean s parameter h b wst was established subsequently the relative tidal range parameter h b tr was extended to beaches of all tidal ranges in this paper observations are presented from 25 beaches around the north coast of ireland these beaches exist on an environmental gradient that encompasses marked tidal and wave energy variability micro to macrotidal and low to high wave energy each beach was visually categorised into one of several established beach states described in the literature on the basis of field observations for each beach the rtr and dean s parameter were calculated for the immediately antecedent period and used to predict the beach state using published relationships observed and predicted beach states were then compared comparison of observed and predicted beach states showed that while beaches with observed dissipative morphology typically matched the expected criteria most other beach states did not lack of agreement between predicted and observed beach states has been reported elsewhere and attributed to failings in the rtr and dean s parameter in addition this study identifies geological factors as important constraints on actual beach state in the majority of beaches studied inherited geological factors appear to be more important determinants of beach morphology than contemporary dynamics c 2005 elsevier b v all rights reserved

east asian winter monsoon evolution since the late pliocene based on a pollen record from lake xingkai northeast asia a 328 58 m drill core xk12 was recovered from lacustrine alluvial sediments in the xingkai basin northeast china with the aim of obtaining a high resolution pollen record of east asian winter monsoon eawm evolution since 3 6 ma an index based on the pollen record of thermophilous trees and terrestrial herbs is used as an indicator of winter temperature conditions controlled by the eawm at the glacial interglacial scale primary age control was established based on lithostratigraphy and magnetostratigraphy and then the pollen index was correlated to the lr04 global benthic 18 o record and finally tuned to earth orbital obliquity to produce a high resolution astronomical time scale the pollen record indicates that the eawm underwent two stepwise enhancements at 2 8 and 1 6 ma these events are consistent with paleoclimatic records of mean quartz grain size from the chinese loess plateau and they are also in accord with the initiation and intensification of northern hemisphere glaciation our findings suggest that the variability of the eawm since 3 6 ma was primarily controlled by changes in global ice volume and climatic cooling

the santa rosa event 40ar 39ar and paleomagnetic results from the valles rhyolite near jaramillo creek jemez mountains new mexico the jaramillo event was originally defined by doell and dalrymple in 1966 on the basis of k ar ages from sanidine in the normally transitionally and reversely magnetized rhyolite domes named cerro del abrigo cerro santa rosa i and cerro santa rosa ii respectively that erupted following collapse of the archetypal valles caldera new mexico we have collected new paleomagnetic data from the three domes and new 40 ar 39 ar laser fusion and furnace incremental heating experiments on sanidine crystals from the cerro santa rosa i rhyolite step wise alternating field and thermal demagnetization techniques applied to 52 samples from seven sites indicate that the original paleomagnetic results of doell and dalrymple science 152 1966 1060 1061 are valid cerro del abrigo is normally magnetized whereas the santa rosa i dome is transitional with an inclination of 363 toward the east and the santa rosa ii dome is of reversed polarity twenty five laser fusion experiments on sanidine crystals from the the cerro santa rosa i dome together with the saddle shaped spectrum obtained by incrementally heating the sanidine in a furnace reveal that this rhyolite contained a small but significant component of excess argon prior to eruption our preferred age of 936 8 ka 2c for the santa rosa i rhyolite is based on the concordant laser fusion isochron and incremental heating plateau ages this age is significantly older than was inferred on the basis of earlier laser fusion 40 ar 39 ar results that suggested a trapped component characterized by a 40 ar 36 ar ratio lower than the atmospheric value of 295 5 our new age distinguishes the santa rosa i dome by 65 kyr from the termination of the jaramillo normal subchron 1001 10 ka and by 37 kyr from basaltic lavas at haleakala and tahiti which record the kamikatsura event 899 6 ka moreover this determination is a factor of three more precise than the best previous estimate for a proposed geomagnetic event in this time period the cerro santa rosa i rhyolite dome once intimately linked with the end of the jaramillo event and the acceptance of plate tectonic theory now defines a highly resolved feature the santa rosa event in a terrestrial geomagnetic reversal time scale that is consistent with the global record of magnetic field intensity from marine sediments fl 2002 elsevier science b v all rights reserved

driving mechanisms of holocene coastal evolution in the bonifacio strait western mediterranean abstract we produced a new suite of sea level data which allowed assessing the holocene evolution of the bonifacio strait a key coastal sector of the mediterranean sea which experienced significant morphological changes since the last glacial maximum squeezed between corsica and sardinia islands this strait connects the two major basins of the western mediterranean due to its peculiar geographic and morphological setting the bonifacio strait is affected by extreme meteomarine conditions characterized by severe winds waves and currents the millennial sea level changes were reconstructed through multiproxy investigations made of sediment coring and underwater beachrock sampling carried out on both sides of the strait these data provided fresh insights into the timing of the progressive opening of the bonifacio strait which followed the last glacial maximum when corsica and sardinia were connected forming the largest mediterranean island major palaeogeographic changes occurred before 7 ka bp since that period the significant decrease of the northern ice sheet melting triggered a significant sea level stabilization which induced only minor modifications in the palaeogeography of the strait in the late holocene the isostatic related subsidence became the dominant factor controlling the sea level changes which rose with rates 0 35 mm a 1 in the last four millennia our data have also an important archaeological implication because they indicate that the bonifacio strait has not represented a significant geographical barrier along the early neolithic migration path which connected mainland italy to northern corsica and finally to sardinia this further confirms the ability of early neolithic communities to navigate not also across large sea stretches but also maritime areas characterized by extremely complex meteomarine conditions

fine tuning of age integrating magnetostratigraphy radiocarbon dating and carbonate cyclicity example of lacustrine sediments from heqing basin yunnan china covering the past 1 myr abstract high resolution magnetostratigraphy wavelength spectra of carbonate cyclicities and ams radiocarbon dating are integrated to establish an optimum age model for a 168 m long drill core of lacustrine sediments from heqing basin yunnan province southwestern china a 14c age of 51 62 2 42 1 85 kyr bp is obtained at a depth of 7 3 m remanent magnetization is carried by maghemite and partly in addition by magnetite both showing the same direction the polarity sequence clearly reveals the brunhes matuyama b m boundary at 141 5 m blake event is found between 16 3 and 17 5 m and the upper boundary of jaramillo is indicated at 167 0 m carbonate content and magnetic susceptibility were used for spectral analysis fourier analysis was done on the depth section for sliding windows with different window lengths the spectra within the range of window centers 30 140 m show a dominant long wavelength which changes from about 18 5 m in the lower part 65 m depth to about 14 5 m in the upper part

uplift events of the qinghai tibetan plateau and environmental evolution of the southwest monsoon since 2 7 ma recorded in a long lake sediment core from heqing china abstract the tectonic sedimentary cycles and environmental evolution in the southwest monsoon area since 2 7 ma were reconstructed based on the analysis of lithology grain size carbonate content loss on ignition loi and pollen in a 737 72 m sediment core from heqing basin china the results indicated that the lake basin was formed in about 2 7 ma continuous lacustrine sediment was preserved since 2 7 ma three stages of tectonic sedimentary cycle were revealed 2 7 1 5 ma 1 5 0 9 ma and 0 9 0 ma the environmental evolution in heqing area was influenced by the uplift of the qinghai tibetan plateau the resulting variation of southwest monsoon and the earth orbital scale periodicity

ionospheric responses to the october 2003 superstorm longitude local time effects over equatorial low and middle latitudes 1 ionospheric responses to the major magnetic storm disturbances of october 2003 are investigated using database selected in the brazilian and japanese asian longitude sectors data obtained from latitudinally spaced digisondes in the equatorial and low latitude sites in brazil and from the asian and japanese ionosonde network the total electron content data from the extensive japanese gps receiver chain and magnetometer data from the pacific equatorial electrojet stations are analyzed during the period 28 31 october prompt penetrating pp dawn dusk polar cap electric fields produce large f region plasma uplift on the dayside and eveningside while the associated westward electric field on the nightside produces large downdraft of the f region plasma and causes development of westward electrojet current observed for the first time episodes of pp electric field effects appear to be of larger intensity over brazil than over asian longitudes equatorial anomaly development due to undershielding as well as overshielding electric fields was observed in the brazilian and in the asian sectors disturbance dynamo electric field causes large nighttime f layer uplifts that are modulated by strong meridional winds in both sectors the disturbance electric field local time variation patterns are compared with the results of recent global model mtiegcm simulation by richmond et al 2003 and validated in some cases transients of transequatorial winds flipping direction from southward to northward in the widely separated longitude sectors were diagnosed to be present toward the final recovery phase of the storm these results are presented and discussed in this paper

climate variations in europe over the past 140 kyr deduced from rock magnetism rapid shifts in climate during the last glacial are now well documented particularly from the oxygen isotope records of the two greenland ice cores grip1 2 and gisp23 in the grip record1 2 these climate events are also seen during the preceding eemian interglacial which may be an analogue for the future climate warmed by the greenhouse effect but these shifts are not found in the eemian section of the gisp2 core3 casting doubt on whether the rapid shifts in the grip oxygen isotope record really do represent a climate signal here we present magnetic susceptibility pollen and organic carbon records from maar lake deposits in the massif central france these data provide an independent record of past climate and we find that they correlate well with the ice core records during the last glacial during the eemian two rapid cooling events seen in our record also correlate with those seen in the grip ice core supporting the idea that rapid climate change did occur in the eemian interglacial and demonstrating that it extended to continental europe

pleistocene climates in china dated by magnetic susceptibility the magnetic susceptibility of loess and interbedded soils in central china varies with the degree of pedogenesis and serves as a proxy measure of climate the concentration of magnetic minerals in the sediment is inversely proportional to sedimentation rates throughout the brunhes epoch susceptibility measurements combined with the reversal stratigraphy provide a time scale that is independent of astronomic chronology on this scale the susceptibility record closely parallels the oxygen isotope fluctuations in deep sea sediments suggesting a close interdependence of the chinese dust falls the volume of land based ice and global climate

evidence for the kamikatsura and santa rosa excursions recorded in eolian deposits from the southern chinese loess plateau 1 a detailed paleomagnetic investigation of a loess paleosol sequence in baoji southern chinese loess plateau reveals two distinct geomagnetic excursions accompanied by inferred relative paleointensity minima in the late matuyama chron rock magnetic experiments demonstrate that the sediments of the excursion intervals in loess unit l9 have the same magnetic properties as those from surrounding normal and reversed polarity intervals assuming constant sedimentation rate between the jaramillo matuyama and matuyama brunhes magnetic polarity boundaries the midpoint ages and durations for these two excursions are estimated at 0 89 ma and 16 kyr and 0 92 ma and 7 kyr respectively in addition these two events are separated by an interval with fully reversed polarity that had a duration of 16 kyr these estimates are supported by paleoclimatologically inferred age constraints the two excursions are probably correlated with the kamikatsura and santa rosa excursions respectively

chronology and correlation of quaternary magnetostratigraphy and nannofossil biostratigraphy in norwegian greenland sea sediments paleomagnetic analyses of a series of sediment cores from the norwegian greenland sea document the existence of seven short lived geomagnetic events during the last about 500 000 years calcareous nannofossil biostratigraphy correlated to oxygen isotope chronostratigraphy provides a time framework to infer age and duration of these periods of extreme divergence of the earth s magnetic paleofield from the regular normal polarity configuration of the brunhes chron the geomagnetic events typically extend over 5 to 10 kyr two events are observed within the oxygen isotope stage 2 4 interval a short event is recorded at the stage 4 5 boundary and another just below the stage 5 6 boundary additional three geomagnetic events are identified in oxygen isotope stage 6 at the stage 9 10 boundary and near the top of oxygen isotope stage 13 respectively

sediment retention by a mediterranean posidonia oceanica meadow the balance between deposition and resuspension the role of posidonia oceanica in promoting sediment stability and accretion was studied in a 15 m deep meadow at fanals point nw mediterranean spain by comparing particle deposition within the meadow and adjacent bare sediment small sediment traps were used to measure deposition within and above the meadow and over bare sand a model based on measurements of particle deposition at increasing distances from the bottom was used to partition the total depositional flux between primary sediment particles deposited for the first time at the measuring site and resuspended deposition sediment particles that have been previously deposited at the measuring site measurements were conducted monthly over a year to establish the magnitude and seasonality of deposition and to form a balance of particle transport at the annual time scale significant differences in total deposition were found over time ranging from 1 5 to 500 g dw m 2 d 1 including those between bare and vegetated sediments the effect of p oceanica in increasing primary deposition at an annual scale was modest however p oceanica significantly buffered sediment resuspension which was reduced more than three fold compared to the unvegetated bottom the annual flux of deposition was dominated by settling of resuspended materials which represented 85 of the total flux within the meadow but 95 of the total deposition on bare sand thus seagrass meadows reduce resuspension in the nw mediterranean littoral thereby contributing to increased sediment retention and therefore reducing erosion in the coastal zone

palaeoclimatic changes over the past 1 million years derived from lacustrine sediments of heqing basin yunnan china abstract a 168 m long core of mostly fine grained lacustrine sediments was recovered from heqing basin yunnan province southwestern china the area is located at the south eastern margin of the tibetan plateau and is mainly affected by the sw monsoon magnetostratigraphy of this core indicates that it spans the last one million years spectral analysis of carbonate and magnetic susceptibility and a rough correlation of with the marine oxygen isotope record suggest that the climatic record of this area is consistent with the global climatic pattern pollen data from hq indicate alternations between temperate arid and cold humid climatic conditions as a typical regional palaeoclimatic pattern the highs and lows of can be related to warm and cold periods respectively maghemite and magnetite dominate the magnetic mineralogy maghemite is distributed throughout the whole core whereas magnetite occurs additionally in samples with higher deposited during arid periods the magnetic and non magnetic variations clearly show a change at 65 m corresponding to ca 410 ka indicating a change in the depositional system related to a climatic and or tectonic event

a new approach to an absolute timescale from measurements of orbital cycles and sedimentary microrhythms when the sedimentary microrhythms of two groups of jurassic zones forming part of the chronostratigraphical scale are analysed against recent radiometric age scales there is good agreement with present day cycles resulting from the obliquity of the ecliptic sedimentary microrhythms resulting from orbital forcing can be used to establish either the relative or the true length of chronostratigraphical zones and thus provide a new approach towards an absolute timescale such a scale will be powerful in the analysis of other cycles and perturbations in the geological record

diatom response to climatic and tectonic forcing of a palaeolake at the southeastern margin of the tibetan plateau during the late pleistocene between 140 and 35 ka bp abstract the heqing basin is located in yunnan province south western china near the southeastern edge of the tibetan plateau a region that is strongly influenced by the asian monsoon its long sedimentary record represents an archive of global importance for palaeoclimate research this study presents the results of diatom analysis of the last 140 35 ka of the record dated using ams 14 c and magnetostratigraphy diatoms are generally well preserved apart at the top of the sequence after 35 ka bp in which diatoms were too few to be counted the diatom data provide a detailed history of palaeoenvironmental changes during the late pleistocene and demonstrate the sensitivity of diatoms to changes in climate and hydrology in particular they provide proxy evidence for water depth and indirect evidence for temperature changes that are characterized by glacial interglacial shifts between planktonic and benthic diatoms and variations in the percentage of the warm water and eutrophic species aulacoseira granulata respectively in the heqing sequence remarkably high proportions of benthic diatoms coincide with warm and wet conditions suggesting that at this site the diatom signal is mediated by climate catchment vegetation processes such as the concentration of nutrient and runoff from the catchment from 132 ka bp however the tectonic uplift of the basin caused a change in the hydrological setting of the lake pollen and geochemical data are then used to help interpreting the diatom sequence and disentangle the direct effects of climate from those mediated by the conditions on the catchment such as the influence of glacier melt water

paleomagnetic record at odp site 980 feni drift rockall for the past 1 2 myrs 1 a detailed record of variations in the direction and intensity of the geomagnetic field over the past 1 2 myrs has been obtained from an 120 m thick sedimentary section cored at odp site 980 on the feni drift north atlantic the record has high resolution due to high mean sedimentation rates 11 3 cm kyr for the brunhes chron and 5 5 cm kyr for the matuyama chron paleomagnetic measurements every 1 cm along u channel samples and high quality isotopic age control the iceland basin event is manifest by virtual geomagnetic poles crossing the equator at 190 ka the base of the recovered section lies immediately below the cobb mountain subchronozone that occurs within marine isotope stage 35 normalized remanence data can be correlated to paleointensity records from odp sites 983 and 984 700 km to the nw from site 980 and with lower resolution paleointensity data from the pacific ocean differences between the site 980 paleointensity record and the pacific records are attributed to variable sedimentation rates variable quality age control and inadequacies in the normalization procedure used to derive the paleointensity proxies

lake baikal record of continental climate response to orbital insolation during the past 5 million years the sedimentary record of biogenic silica from lake baikal in south central siberia suggests that this region of central asia was impacted by two major cooling episodes at 2 8 to 2 6 and 1 8 to 1 6 million years ago the spectral evolution of this continental interior site parallels the evolutionary frequency spectra for various marine oxygen isotope records in the baikal record the 41 000 year obliquity cycle is particularly strong from 1 8 to 0 8 million years ago variance in the 100 000 year eccentricity band increases during the past 0 8 million years the expected precession frequency of 23 000 years is highest during the past 400 000 years the modulation of the predicted 23 000 and 41 000 year insolation forcing by the 100 000 and 400 000 year eccentricity bands indicates that the transfer of variance from the precession and obliquity frequencies to the eccentricity part of the spectrum occurred in the eurasian continental interior as well as in tropical and high latitude ocean sites

indian summer monsoon variations and competing influences between hemispheres since 35 ka recorded in tengchongqinghai lake southwestern china abstract the southwestern yunnan province of china which is located at the southeastern margin of the tibetan plateau and close to bay of bengal is significantly influenced by the indian summer monsoon ism in this study we reconstruct proxies for the ism from 35 to 1 ka through detailed analysis of grain size distribution geochemical composition and environmental magnetism from a 7 96 m sediment core from tengchongqinghai lake yunnan province china globally recognized abrupt climatic events including heinrich events 0 3 h0 h3 and the bolling allerod b a warm period are identified in most of our proxies and the long term trend is consistent with other published records such as stalagmite oxygen isotopes 18o from sangxing cave northern hemisphere nh temperature which is influenced by nh solar insolation is commonly suggested to play a dominant role in controlling the ism a comparison of our record with the 18o variations of ice cores from greenland and antarctica a sea surface temperature sst record from the bay of bengal and summer solar insolation at 25 n latitude demonstrates that the general pattern of ism change does follow variations in summer insolation however the ism lags summer insolation by thousands of years while the ism fluctuations are highly correlated with nh temperature on shorter timescales centennial millennial the gradually weakened ism from 22 5 ka until the last glacial maximum lgm indicates a close relationship with the rise of southern hemisphere sh temperature and the relatively cold background of the sh our record expands on the findings of ism records from heqing paleolake basin in southwestern china and the arabian sea sediments suggesting that the nh and sh have a competitive influence on ism by controlling the cross equatorial pressure gradient this relationship means that when nh temperatures are relatively high it has a stronger influence on the ism than sh influences in contrast when the sh temperature is relatively low it has a dominant influence on ism in addition we speculate that the change of sh temperature not only influences the cross equatorial pressure gradient directly but also likely modulates the circulation system of ocean energy by influencing the atlantic meridional overturning circulation amoc

intermontane basin development in the past 4 myr in the north west himalaya the through the combined use of magnetic polarity stratigraphy with fission track dating of volcanic ashes a new chronology spanning 4 myr has been developed for the intermontane basin of kashmir in the northwestern himalaya

paleomagnetic calibration of milankovitch cyclicity in lower cretaceous sediments abstract bedded pelagic limestones of early to mid cretaceous age may record cyclic climate variability driven by changes in the earth s orbit milankovitch cycles if properly calibrated the lithologic cycles could provide sedimentary chronometry at far shorter time scales than biostratigraphy and magnetic stratigraphy the lower cretaceous maiolica formation of northern and central italy displays rythmic bedding in sections whose magnetic reversal sequence is clearly correlated to the upper m series marine anomalies the magnetic reversals divide measured sections into 0 5 2 myr increments in which sedimentation rate assuming continous deposition can be measured to 15 25 accuracy paleomagnetically estimated sedimentation rates over a number of polarity zones establish with one exception a narrow range in periods of the carbonate cycles carbonate couplets have an estimated mean period of 23 5 kyr and prominent modulations in bedding thickness bundling have a mean period of 117 kyr kent and gradstein 1985 time scale the close match of sedimentary periodicities to orbital repeat times implies that the carbonate cycles reflect a combination of professional and eccentricity climatic forcing comparison of measured sections from different locations shows that bed to bed correlations are possible regionally cosistent with the milankovitch hypothesis episodes of barremian black shale deposition occur in the troughs of the short eccentricity cycle as roughly one half of the carbonate marl couplet or about 10 kyr duration it is possible to estimate both the timing relative to the top of reversed chron m 0 and duration of a period of unusual organic carbon rich deposition selli horizon in the early part of the cretaceous long normal magnetic polarity interval by tracing the sedimentary cycles up from the barremian strata