variations of the east asian jet stream and asian pacific american winter climate anomalies in this study the authors apply the ncep ncar reanalysis and other observations to depict the association of the asian pacific american climate with the east asian jet stream eajs with an emphasis on boreal winter seasons and on interannual timescales they analyze the variations of the eajs and their relationships with el nino southern oscillation enso and extratropical north pacific sea surface temperature sst and assess the relative connections of the eajs and enso to the anomalies of atmospheric circulation surface temperature and precipitation in the asian pacific american region it is found that the eajs is coupled to a teleconnection pattern spanning the entire asian pacific american region with the strongest signals over east asia and the western pacific this pattern differs significantly from that associated with enso which influences the earth s climate extensively with a strongest impact on the climate over the central pacific and east a strong eajs is associated with an intensification of the weather and climate systems in asia and over the pacific such as deepening of the east asian trough and the aleutian low and strengthening of the east asian winter monsoon it is linked to colder and drier conditions in east asia and stronger convection over the tropical asia australia sector compared with enso the eajs seems to link to the climate signals of asia and the pacific more strongly an intensified eajs is also associated with anomalies of temperature and precipitation in north america due to the related changes in stationary wave patterns while the eajs does not strongly link to the tropical central eastern pacific sst it is significantly associated with the extratropical north pacific sst more specifically the second most dominant mode of the empirical orthogonal function analysis of the sst in addition a strong weak eajs seems to follow a large small meridional gradient of the western pacific sst associated with warming cooling in the tropics subtropics and cooling warming in the extratropics

deformations of the near surface part of the earth s crust by seismologic and geodetic data obtained on baikal geodynamic polygons abstract the tunkin geodynamic polygon is taken where the deformation tensor components approximately 10 4 for the earth s crust upper layers along with the relative displacements of the blocks in the fault zone have been determined based on the application of the theory of small deformations and on an experimental base of repeated geodetic measurements a comparative analysis of the surface deformation calculated by geodetic measurements with respect to the deep seated deformations obtained from seismic foci mechanisms is given

evidence and causes of the two stage development of the baikal rift abstract the data on the geological and deep seated structures of the baikal rift zone are briefly summarized based on the analysis of the composition of the sedimentary infill in rift basins two stages of the zone development have been recognized 1 1 slow rifting 2 2 fast rifting as a consequence of the study of the deep seated structure and construction of the thermal model of the lithosphere it was assumed that the first stage is associated with a slow uprise of the surface of the asthenospheric upwelling and the second stage connected with sideways flows of the substance involved in this upwelling after the crustal base was reached

pacific and atlantic multidecadal variability in the kiel climate model pacific decadal variability pdv and atlantic multidecadal variability amv the two leading decadal modes of observed northern hemisphere sea surface temperature sst variability are investigated in a multi millennial control integration of the kiel climate model kcm it is shown that the two phenomena are independent modes in the model and can be easily separated by principal oscillation pattern pop analysis of model sst pdvrelated variability covers the whole north pacific with strong signals in both the mid latitude north pacific and the western tropical pacific strong signals are also simulated in the eastern indian ocean sector pdv s memory however resides in the north pacific and is linked to the subtropical gyre the amv mechanism is related to the atlantic meridional overturning circulation amoc a stochastic mechanism applies to both pdv and amv

geometry and kinematics of recent deformation in the mondy tunka area south westernmost baikal rift zone mongolia siberia we used satellite imagery and field data to investigate the south westernmost baikal rift zone we focus our study in the mondy and ikhe ukhgun valleys site of an mw 6 9 seismic event in 1950 surface deformations are observed along the e w trending mondy strike slip fault and along the ikhe ukhgun thrust the mondy fault system is 80 km long and is composed of four segments 10 15 km long these segments are characterized by subvertical planes with left lateral movements the ikhe ukhgun thrust is 20 km long dips 40 to the south and shows reverse movement with a left lateral component these observations are consistent with the present day regional nne ssw compression and with the focal mechanism of the 1950 mondy earthquake that was recently re evaluated these features like those observed in the tunka basin demonstrate a recent change of regional strain regime from transtension to transpression that we place before the late pleistocene

subtropical anticyclones and summer monsoons the summer subtropical circulation in the lower troposphere is characterized by continental monsoon rains and anticyclones over the oceans in winter the subtropical circulation is more strongly dominated by the zonally averaged flow and its interactions with orography here the mechanics of the summer and winter lowertropospheric subtropical circulation are explored through the use of a primitive equation model and comparison with observations by prescribing in the model the heatings associated with several of the world s monsoons it is confirmed that the equatorward portion of each subtropical anticyclone may be viewed as the kelvin wave response to the monsoon heating over the continent to the west a poleward flowing low level jet into a monsoon such as the great plains jet is required for sverdrup vorticity balance this jet effectively closes off the subtropical anticyclone to the east and also transports moisture into the monsoon region the low level jet into north america induced by its monsoon heating is augmented by a remote response to the asian monsoon heating the rossby wave response to the west of subtropical monsoon heating interacting with the midlatitude westerlies produces a region of adiabatic descent it is demonstrated here that a local diabatic enhancement can lead to a strengthening of the descent longitudinal mountain chains act to block the westerly flow and also tend to produce descent in this region below the descent sverdrup vorticity balance implies equatorward flow that closes off the subtropical anticyclone to the west and induces cool upwelling in the ocean through ekman transport feedbacks involving for example sea surface temperatures may further enhance the descent in these regions the conclusion is that the mediterranean type climates of regions such as california and chile may be induced remotely by the monsoon to the east hence it can be argued that the subtropical circulation in summer comprises a set of weakly interacting monsoon systems each involving monsoon rains a low level poleward jet a subtropical anticyclone to the east and descent and equatorward flow to the west in winter it is demonstrated how the nonlinear interaction between the strong zonal mean circulation associated with the winter hadley cell and the mountains can define many of the large scale features of the subtropical circulation the blocking effect of the longitudinal mountain chains is shown to be very important subsequent diabatic effects such as a local diabatic enhancement would appear to be essential for producing the observed amplitude of these features

role of orbital forcing in east asian monsoon climates during the last 350 kyr evidence from terrestrial and marine climate proxies from core rc14 99 proxy records of northeast asian precipitation marine pollen and northwest pacific sea surface temperatures marine fauna contain concentrations of variance frequency peaks coincident with those of orbital variations eccentricity obliquity and precession time series of these monitors of various components of the east asian monsoon system are coherent with changing solar insolation and climate boundary conditions ice volume snow cover albedo at 41 and 23 kyr frequencies winter sea surface temperature wsst maxima are in phase with global ice volume minima at all three milankovitch frequencies 100 41 and 23 kyr periods wsst maxima are also linearly related to summer insolation at 30 n lagging radiation maxima by 55 3 5 kyr across the precessional frequency band 23 kyr period our east asian monsoon rainfall indicator cryptomeria reaches highest values immediately following summer insolation maxima during periods of low ice volume interglacials across the eccentricity frequency band 100 kyr period cryptomeria maxima are in phase with ice volume minima at the higher frequency of orbital precession monsoon rainfall lags both summer radiation maxima 125 8 kyr and ice volume minima 60 3 8 kyr whereas much of the variation in northwest pacific wsst can be attributed to summer radiation forcing and changes in global climate mechanisms driving east asian monsoon precipitation are more complex involving other possibly internal factors

itcz and enso pacing on east asian winter monsoon variation during the holocene sedimentological evidence from the okinawa trough deep sea fan sediments provide an excellent geological archive for paleoenvironment reconstruction grain size clay mineral and elemental ti fe ca compositions were measured for a core retrieved from a submarine fan in the okinawa trough varimax rotated principal component analysis v pca on time evolution of grain size spectrum reveals that since the holocene sediment was transported mainly by the benthic nepheloid layer 33 and upper layers 33 which is driven by the east asian winter monsoon eawm the intensification of the kuroshio current during the holocene masks the fluvial signal of the summer monsoon and obstructs clay minerals derived from the yellow river a major contributor prior to 12 ka bp a new grain size index gsi which represents the eawm well exhibits a negative correlation with the delta o 18 record in dongge cave china during the holocene when sea level was relatively steady this anti correlation suggests the southward migration of the intertropical convergence zone itcz the consistency among our records and rainfall records in peru ti counts in the cariaco basin monsoon records in oman and the averaged summer insolation pattern at 30 degrees n further support the itcz s impact on monsoon systems globally cross correlation analyses for gsi and log ti ca against delta o 18 record in dongge cave reveal a decoupling between the east asian winter and summer monsoon during 5500 2500 cal yr bp with greater complexity in the last 2500 years this can be attributed to exacerbated enso mode fluctuations and possibly anthropogenic interference superimposed on insolation and itcz forcing

the mechanisms that determine the response of the northern hemisphere s stationary waves to north american ice sheets abstractstationary waves describe the persistent meanders in the west east flow of the extratropical atmosphere here changes in stationary waves caused by ice sheets over north america are examin

the influence of continental ice atmospheric co2 and land albedo on the climate of the last glacial maximum the contributions of expanded continental ice reduced atm9spheric co2 and changes in land albedo to the maintenance of the climate of the last glacial maximum lgm are examined a series of experiments is perform ed using an atmosphere mixed layer ocean model in which these changes in boundary conditions are incorporated either singly or in combination the model used has been shown to produce a reasonably reajistic simulation of the reduced temperature of the lgm manabe and broccoli 1985 by comparing the results from pairs of ex periments the effects of each of these envirornnental changes can be determined expanded continental ice and reduced atmospheric co2 are found to have a substantial impact on global mean temperature the ice sheet effect is confined almost ex clusively to the northern hemisphere while lowered co2 cools both hemispheres changes in land albedo over ice free areas have only a minor thermal effect on a global basis the reduction of co2 content in the atmosphere is the primary contributor to the cooling of the southern hemisphere the model sensitivity to both the ice sheet and co2 effects is characterized by a high latitude amplification and a late autumn and early winter maximum

influence of glacial ice sheets on the atlantic meridional overturning circulation through surface wind change coupled modeling studies have recently shown that the existence of the glacial ice sheets intensifies the atlantic meridional overturning circulation amoc however most models show a strong amoc in their simulations of the last glacial maximum lgm which is biased compared to reconstructions that indicate both a weaker and stronger amoc during the lgm therefore a detailed investigation of the mechanism behind this intensification of the amoc is important for a better understanding of the glacial climate and the lgm amoc here various numerical simulations are conducted to focus on the effect of wind changes due to glacial ice sheets on the amoc and the crucial region where the wind modifies the amoc first from atmospheric general circulation model experiments the effect of glacial ice sheets on the surface wind is evaluated second from ocean general circulation model experiments the influence of the wind stress change on the amoc is evaluated by applying wind stress anomalies regionally or at different magnitudes as a boundary condition these experiments demonstrate that glacial ice sheets intensify the amoc through an increase in the wind stress at the north atlantic mid latitudes which is induced by the north american ice sheet this intensification of the amoc is caused by the increased oceanic horizontal and vertical transport of salt while the change in sea ice transport has an opposite though minor effect experiments further show that the eurasian ice sheet intensifies the amoc by directly affecting the deep water formation in the norwegian sea

adjustment of a drainage network to capture induced base level change an example from the sorbas basin se spain abstract quaternary catchments in the south of the sorbas basin se spain have been affected by two regionally significant river captures the river captures were triggered by changes in regional gradients associated with sustained quaternary uplift in the region of 160 m ma 1 the first capture occurred in the early pleistocene and re routed 15 of the original sorbas basin drainage into the carboneras basin to the south the second occurred in the late pleistocene and re routed 73 of the original sorbas basin drainage to the east this latter capture had dramatic consequences for base level in the sorbas basin master drainage local base level was lowered by 90 m at the capture site 50 m at 7 km upstream and 25 m at 13 km upstream of the site the base level change instigated a complex re organisation of the drainage networks in systems tributary to the master drainage over the ensuing period some 100 ka after the capture drainage systems closer to the capture site experienced a tenfold increase in incision rates over most of their network those located some 13 km upstream of the capture site experienced a fivefold increase in incision although in this instance the changes do not appear to have propagated to the headwater regions of the drainage nets the sensitivity of individual catchments was largely governed by geological controls structure and lithology the detailed network evolution in the most sensitive areas can be traced by reconstructing former drainage pathways using abandoned drainage cols and the alignment and degree of incision of the drainage networks three main stages of evolution can be identified which record the progressive spread of base level changes from the master drainage these are stage 1 pre capture original south to north consequent drainage stage 2 early stage post capture aggressive subsequent southwest to northeast and east west drainage developed along structural lineaments first in the east of the area stage 2a and later in the west of the area stage 2b and stage 3 late stage post capture obsequent drainage developing on the topography of the stage 2 drainage all stages of the network evolution are associated with drainage re routing as a function of river capture at a variety of scales the results highlight the complex response of the fluvial system and the very different geomorphological histories of adjacent catchments emphasising the need for regional approaches for examining long term changes in fluvial systems

sea surface temperature and salinity changes in the northwest pacific since the last glacial maximum the oxygen isotope records of both benthic and planktonic foraminifera in five piston cores collected from the region between the oyashio and kuroshio currents near japan clearly show the marked latitudinal shifts of these two currents during the past 25 kyr under the present hydrographic condition a clear relationship between the sea surface temperature sst and oxygen isotope differences from benthic to planktonic foraminifera is observed in this region using this relationship we find decreased ssts of 12 13 c maximum 15 c in the southernmost core site at the last glacial maximum lgm indicating the oyashio current shifted southward the ssts at the southern two core sites abruptly increased more than 10 c at 10 11 ka suggesting the kuroshio current shifted northward over these sites at 10 11 ka in contrast the northern two core sites have remained under the influence of the cold oyashio current for the past 25 kyr with the reasonable estimate of bottom water temperature decrease of 2 5 c at the lgm the ssts estimated by this new method give exactly the same sst values calculated from mg ca ratio of planktonic foraminifera allowing palaeosea surface salinities to be reconstructed the result suggests that the ice volume effect was 1 0 0 1 at the lgm copyright 2004 john wiley sons ltd

morphotectonics of the tunka rift and its bordering mountains in the baikal rift system russia abstract the tunka section of the baikal rift system presents a uniform alternation of the following neostructural forms tilted horsts and asymmetrical block uplifts on the northern flank the central system of the rift valleys and the arched uplift of the southern flank this is a standard set of morphostructural elements for the baikal rift system the main morphological feature of the tunka rift is the strong inclination of its floor ranging from 900 m to 200 km in general elevation above lake baikal such traits of recent geodynamics as volcanism thermal activity and seismicity are also different from other parts of the rift zone all of these features of the tunka rift are related to the deep structure of the rift zone the peculiarities of the neotectonic structure of the tunka rift which are clearly expressed morphologically as is typical of the baikal rift system as well as its unique features are in accordance with deep geodynamic processes of the region on the other hand the development of the rift basin structures of the southwestern area near baikal is complicated by inversion deformations local uplifts followed by deformations of the basin sedimentary cover and inverted morphostructures expressed in relief are fixed against the background of the general subsidence of blocks of the pre cenozoic basement grabens the tunka rift has repeatedly experienced inversion deformations throughout its history the last wave of such deformations involved the southwestern region near baikal in the second half of the late pleistocene during the quaternary the positive component prevailed in the whole range of vertical movements of the inter rift and interbasin blocks since the late neogene these structures have experienced a slow but steady uplift accompanied by their extension at the expense of the bordering basins the remote influence of the india asia collision on the formation of the southwestern section of the baikal rift system is very significant and well pronounced in the development of the morphostructural elements of the tunka rift and its bordering mountains

mid late holocene el nino variability in the equatorial pacific from coral microatolls 1 oxygen isotope ratios in porites microatolls from christmas island in the central pacific provide high resolution proxy records of el nino southern oscillation enso variability since 3 8 thousand years ago ka compared with modern microatolls reconstructions from fossil microatolls imply that interannual variations in enso sea surface temperature and precipitation were less intense 3 8 2 8 ka but more pronounced at 1 7 ka amplification of enso at 2 ka is consistent with precessional changes in insolation seasonality but exceeds model predictions and may reflect stronger rainfall teleconnections through enhanced interaction between the southern oscillation and the pacific intertropical convergence zone

global water balance and atmospheric water vapour transport at last glacial maximum climate simulations with the canadian climate centre for modelling and analysis atmospheric general circulation model a series of new simulations of the climate state at last glacial maximum has been performed using the canadian second generation atmospheric general circulation model and are described herein the

the link between tectonic and paleoclimatic events at 2 8 2 5mabp in the lake baikal region abstract the records of diatom abundance clay fraction content and magnetic susceptibility from lake baikal drill core bdp 96 1 reflect the climate driven plio pleistocene evolution of the lake baikal sedimentation system in addition to the dramatic variations in the proxy records in response to the northern hemisphere ice ages the baikal record also indicates climatic deterioration from 2 8 to 2 5 ma bp with evidence for an early siberian glaciation around the matuyama gauss paleomagnetic reversal boundary the drill core data also allow correlation of this early glacial interval with the basin wide seismic sequence boundary b10 which marks the unconformity produced by the active neotectonic phase in the baikal rift zone at the bdp 96 drill site however the strong b10 acoustic reflection was produced not by an erosional boundary but instead by deposition of glacial clay layers the paleomagnetic age scale of bdp 96 1 constrains the upper age of the neobaikalian uplift subsidence phase in the baikal sayan region at ca 2 5 ma bp the coincident timing of the paleoclimatic and tectonic events recorded in lake baikal sediments suggests a close causal link between regional tectonics and climate and indicate that the late pliocene uplift contributed to the initiation of the early glaciation in southeast siberia between 2 8 and 2 6 ma bp by creating an elevated terrain with lower snowline favorable for alpine glaciation and by changing the heat balance of the region

evolution of the academician ridge accommodation zone in the central part of the baikal rift from high resolution reflection seismic profiling and geological field investigations new high resolution seismic reflection data from the central part of lake baikal provide new insight into the structure and stratigraphy of academician ridge a large intra rift accommodation zone separating the central and north baikal basins four seismic packages are distinguished above the basement a thin top of basement unit seismic stratigraphic unit x seismic stratigraphic unit a and seismic stratigraphic unit b units a and b were cored on selected key locations the four packages are correlated with a series of deposits exposed on the nearby western shores the ularyar sequence oligocene the tagay sequence lower to middle miocene the sasa sequence upper miocene to lower pliocene the kharantsy sequence upper pliocene and the nyurga sequence lower pleistocene based on stratal relationships sedimentary geometries distribution patterns and principal morphostructural elements both onshore and offshore we propose a new palaeogeographic evolution model for the area in this model progressive tectonic subsidence of the baikal basins and successive pulses of uplift of various segments of the rift margins lead to a formation of the ridge as a structural and morphological feature separating the central and north baikal basins during the middle to late miocene b gradual flooding of the main parts of the ridge and establishment of a lacustrine connection between the two rift basins during the late miocene and c total submergence of the top parts of the crest of the ridge during the latest pleistocene this new model helps to better constrain numerous phases in the structural evolution of the baikal rift in which the academician ridge as an accommodation zone plays a crucial role

combined effect of el nino southern oscillation and pacific decadal oscillation on the east asian winter monsoon using long term observational data and numerical model experiments the combined effect of the el nino southern oscillation enso and pacific decadal oscillation pdo on the variability of the east asian winter monsoon is examined in the observations it is found that when the enso and pdo are in phase combinations i e el nino positive pdo phase and la nina negative pdo phase a negative relationship between enso and east asian winter monsoon is significantly intensified in other words when el nino la nina occurs with positive negative pdo phase anomalous warm cold temperatures are dominant over the east asian winter continent on the other hand there are no significant temperature anomalies when the enso and pdo are out of phase combinations i e el nino negative pdo phase and la nina positive pdo phase further analyses indicate that the anticyclone over the western north pacific including the east asian marginal seas plays an essential role in modulating the intensity of the east asian winter monsoon under the changes of enso pdo phase relationship long lasting high pressure and warm sea surface temperature anomalies during the late fall winter and following spring over the western north pacific which appear as the el nino occurs with positive pdo phase can lead to a weakened east asian winter monsoon by transporting warm and wet conditions into the east asian continent through the southerly wind anomalies along the western flank of the anomalous high pressure and vice versa as the la nina occurs with negative pdo phase in contrast the anomalous high pressure over the western north pacific does not show a prominent change under the out of phase combinations of enso and pdo numerical model experiments confirm the observational results accompanying dominant warm temperature anomalies over east asia via strong anticyclonic circulation anomalies near the philippine sea as the el nino occurs with positive pdo phase whereas such warming is weakened as the el nino occurs with negative pdo phase this result supports the argument that the changes in the east asian winter monsoon intensity with enso are largely affected by the strength of the anticyclone over the western north pacific which significantly changes according to the enso pdo phase relationship

three dimensional laboratory modelling of rifting application to the baikal rift russia abstract continental rifting is treated as a mechanical instability developing under horizontal tectonic tension the instability results in strain localization and the formation of a neck which is interpreted as a rift zone at the scale of the whole lithospheric plate this process occurs in plane stress conditions and can therefore be modelled to a first approximation by a one layer plate whose properties represent integral over thickness properties of the real lithosphere we have designed a scaled experimental single layer lithosphere model having elasto plastic rheology and lying upon a liquid substratum to study its behaviour under axial horizontal tension in a homogeneous plate the instability develops along a linear zone oriented at an angle of 60 to the tension axis this orientation is preserved even when the divergent displacement of the plate boundaries is not plain parallel but rotational in the latter case the strain localization zone is rapidly propagating when the plate length to width ratio is less than 2 5 the necking develops along two branches conjugated at an angle of about 120 which is frequently observed in actual rift systems if the model contains a local weak zone hot spot or fault zone the rift junction is located at this zone in the lithospheric models comprising strong cratonic and weak segments strain localization depends on the configuration of the boundary between different lithospheres the necking starts to form within the weak segment in the vicinity of the cratonic promontories and propagates in opposite directions again at an angle of ca 60 to the tension axis in the models containing both a strong lithosphere and local weak zones the rift configuration depends on their shape and relative positions with necking always going through the weak zones in a set of models we have reproduced the geometry of the boundary between the siberian craton and the thermally much younger 100 ma sayan baikal lithosphere in the baikal rift area in these models we were able to obtain the well known three branch configuration of the baikal rift system only by introducing a weak zone in the area of lake baikal such a zone simulates the paleozoic suture existing in this area as in nature two wide outer branches eastern and western are oblique to the regional tension axis whereas the central one is narrow and orthogonal to the tension direction in nature and in the model rifting starts in the central branch corresponding to lake baikal the modelling also predicts the formation of a fourth oblique ns trending branch to the south of baikal although poorly expressed in the field this branch has some seismotectonic and magmatic manifestations the orientations of all four branches with respect to each other and with respect to the regional tension direction are remarkably similar in nature and in the model

multidecadal and multicentennial variability of the meridional overturning circulation the variability of the meridional overturning circulation moc simulated in a multimillenial control integration of the kiel climate model kcm displays enhanced variability relative to the red background at decadal and centennial timescales the multidecadal variability is the model s version of the atlantic multidecadal variability amv often referred to as atlantic multidecadal oscillation amo while multidecadal variability originates in the north atlantic multicentennial variability is driven in the southern ocean both multidecadal and multicentennial variability are associated with considerable changes in sea ice extent this may be important to understand the different evolution of sea ice cover in the northern and southern hemisphere during the most recent decades with a strong decline observed in the north and almost no trend in the south

late pliocene sedimentation in lake baikal implications for climatic and tectonic change in se siberia abstract within the framework of the baikal drilling project bdp a 192 m long sediment core bdp 96 1 was recovered from the academician ridge a submerged topographic high between the north and central basins of lake baikal sedimentological clay mineralogical and geochemical investigations were carried out on the core interval between 90 and 124 m depth corresponding to ca 2 4 3 4 ma the aim was to reconstruct the climatic and tectonic history of the continental region during the intensification of northern hemisphere glaciation in late pliocene time a major climate change occurred in the lake baikal area at about 2 65 ma enhanced physical weathering in the catchment mirrored in the illite to smectite ratio and temporarily reduced bioproduction in the lake reflected by the diatom abundance evidence a change towards a colder and more arid climate probably associated with an intensification of the siberian high in addition the coincident onset of distinct fluctuations in these parameters and in the zr al ratio suggests the beginning of the late cenozoic high amplitude climate cycles at about 2 65 ma fluctuations in the zr al ratio are traced back to changes in the aeolian input with high values in warmer more humid phases due to a weaker siberian high assuming that the sand content in the sediment reflects tectonic pulses the lake baikal area was tectonically active during the entire investigated period but in particular around 2 65 ma tectonic movements have likely led to a gradual catchment change since about 3 15 ma from the western towards the eastern lake surroundings as indicated in the geochemistry and clay mineralogy of the sediments the strong coincidence between tectonic and climatic changes in the baikal area hints at the himalayan uplift being one of the triggers for the northern hemisphere glaciation

paleostress reconstructions and geodynamics of the baikal region central asia part 2 cenozoic rifting abstract investigations on the kinematics of rift opening and the associated stress field present a renewed interest since it has recently been shown that the control of the origin and evolution of sedimentary basins depends to a large extent on the interplay between lithospheric strength and applied stresses it appears that changes of stress field with time are an important factor that either controls or results from the rifting process the object of this paper is to study the changes of fault kinematics and paleostress field with time in the baikal rift system during the cenozoic reduced paleostress tensors were determined by inversion from fault slip data measured in the central part of the rift and its southwestern termination between 1991 and 1995 results show that the stress field varies as well in time as in space two major paleostress stages are determined corresponding broadly to the classical stages of rift evolution late oligocene early pliocene and late pliocene quaternary the first paleostress stage is related to the rift initiation and the second to the major stage of rift development similarities between the recent paleostress field and the present day stress field inverted from focal mechanisms indicate that the second paleostress stage is still active therefore we propose to use proto rift for the late oligocene early pliocene stage and active rift for the late pliocene quaternary stage of rift development during the proto rift stage the stress field was characterized by a compressional to strike slip regime a progressive change from transpression to transtension is suspected for the central part of the rift baikal and barguzin basins during this period in the western termination of the rift sayan massif tunka depression a strongly compressional stress field with oblique thrusting kinematics is well constrained in the late miocene early pliocene interval the active rift stage was initiated by a marked change in fault kinematics and stress regime in the late pliocene in the central part of the rift the stress regime changed into pure extension while in the southwestern extremity it changed into pure strike slip fault kinematics suggests that rifting was initiated by an extrusion mechanism due to the interaction of far field compressional stress on a mechanically heterogeneous crust with the southwards pointing wedge of the siberian craton acting as a passive indentor the cenozoic time space evolution of the stress field is believed to reflect the increasing influence of locally generated buoyancy extensional stresses associated with density anomalies of the lithosphere on intraplate stresses generated by the india eurasia convergence and the west pacific subduction

geology and fauna and preliminary correlation of sediments of the main late cenozoic sites of the transbaikal area abstract the pliocene and pleistocene sediments exposed in eight sections of transbaikalia have been correlated using geological and palynological data together with information on fossil mammals and some paleomagnetic characteristics the most complete sequence of fossiliferous deposits spanning the time interval from the middle pliocene to the late pleistocene is exposed in the tologoi key section the sequence was correlated with other sections primarily on the basis of mammal faunas during deposition of the chikoi suite udunginian chikoian and itantsinian faunal complexes appeared in succession four successive stages in mammal evolution are recognized within the early pleistocene deposition of the krivoyarskaya suite proceeded throughout the time when the tologoi faunistic complex ivolginian and other pleistocene faunas followed each other in the transbaikalian region

insights into the tectonic topography of the present day landscape of the central iberian peninsula spain abstract the landscape of today s central iberian peninsula has been shaped by ongoing tectonic activity since the tertiary this landscape comprises a mountain ridge trending e w to nw se the central system separating two regions of smooth topography the basins of the rivers duero and tajo in this study we explore interrelationships between topography and tectonics in the central iberian peninsula regional landscape features were analysed using a digital elevation model dem slope gradients and slope orientations derived from the dem were combined to describe topographic surface roughness topography trend surfaces inferred from harmonic analysis were used to define regional topographic features low roughness emphasizes the smooth nature of the basins topography where surfaces of homogeneous slope gradient and orientation dominate high roughness was associated with abrupt changes in gradient and slope orientation such as those affecting crests valley bottoms and scarp edges present in the mountain chain and in some deep incised valleys in the basins one of the applications of roughness mapping was its capacity to isolate incised valley segments the area distribution of incised rivers shows their prevalence in the east on a regional scale the topographic surface can be described as a train of ne sw undulations or waves of 20 km wavelength these undulations undergo changes in direction and interruptions limited by n s trending breaks e w and ne sw troughs and ridges clearly mark structural uplifts and depressions within the central system these structures are transverse to the compressive nw se stress field that controlled the deformation of the central iberian peninsula from the neogene to the present they represent the upper crustal folding that accommodates alpine shortening n s breaks coincide with late miocene faults that control the basins sedimentation further associated palaeoseismic structures suggest the recent tectonic activity of n s faults in the eastern part of the tajo basin apatite fission track analysis data for this area suggest the occurrence of a significant uplift episode from 7 to 10 ma which induced the river incisions appearing in the roughness map n s and ne sw faults could be seismogenic sources for the current moderate to low seismic activity of the east tajo basin and southeast central system although n s fault activity has already been established we propose its significant contribution to shaping the landscape

monsoons and the dynamics of deserts the existence of subtropical deserts such as the sahara has often been attributed to the annual mean zonal mean hadley circulation which shows strong descent in the subtropics however the zonal mean hadley circulation shows considerable evolution over the course of the year with very strong subtropical descent during winter but practically no zonal mean subtropical descent during summer when rainfall over the eastern sahara and the mediterranean is least charney 1975 proposed a biosphere albedo feedback mechanism whereby local anthropogenic effects related to over grazing could affect the radiative balance enhancing summertime diabatic descent and leading to desertification of the subtropics in general the present study which uses an idealized model suggests a monsoon desert mechanism for desertification whereby remote diabatic heating in the asian monsoon region can induce a rossby wave pattern to the west integral with the rossby wave solution is a warm thermal structure that interacts with air on the southern flank of the mid latitude westerlies causing it to descend this adiabatic descent is localized over the eastern sahara and mediterranean and over the kyzylkum desert to the south east of the aral sea by the mountains of north africa and south west asia trajectories indicate that the monsoon desert mechanism does not represent a simple walker type overturning cell instead the descending air is seen to be mainly of mid latitude origin it is speculated that the monsoon forced adiabatic descent may result in clear air and therefore a local diabatic enhancement which effectively doubles the strength of descent with this mechanism desertification can be forced by remote changes in monsoon strength rather than by local effects this conclusion is supported by the observed dramatic strengthening of descent over the mediterranean and east sahara during the onset of the asian monsoon and on the longer timescale by relating prehistoric lake levels to milankovitch monsoon forcing the latter may help to explain the perceived discrepancies between the palaeoclimate of the eastern sahara and the strength of a tropic wide monsoon the monsoon desert mechanism may not be confined to the asian monsoon alone and the existence of other monsoon climate regions over the globe may in a similar way explain the observed summertime strengthening of the oceanic sub tropical anticyclones and the existence of western continental deserts and mediterranean type climate regions

northern hemisphere storm tracks during the last glacial maximum in the pmip2 ocean atmosphere coupled models energetic study seasonal cycle precipitation mid latitude eddies are an important component of the climatic system due to their role in transporting heat moisture and momentum from the tropics to the poles and also for the precipitation associated with their fronts especially in winter we study northern hemisphere storm tracks at the last glacial maximum lgm and their influence on precipitation using ocean atmosphere general circulation model oagcm simulations from the second phase of the paleoclimate modelling intercomparison project pmip2 the difference with pmip1 results in terms of sea surface temperature forcing fundamental for storm track dynamics is large especially in the eastern north atlantic where sea ice extends less to the south in oagcms compared to atmospheric only gcms our analyses of the physics of the eddies are based on the equations of eddy energetics all models simulate a consistent southeastward shift of the north pacific storm track in winter related to a similar displacement of the jet stream partly forced by the eddies themselves precipitation anomalies are consistent with storm track changes with a southeastward displacement of the north pacific precipitation pattern the common features of north atlantic changes in the lgm simulations consist of a thinning of the storm track in its western part and an amplification of synoptic activity to the southeast in the region between the azores islands and the iberian peninsula which reflects on precipitation this southeastward extension is related to a similar displacement of the jet partly forced by the eddies in the western north atlantic the synoptic activity anomalies are at first order related to baroclinic generation term anomalies but the mean flow baroclinicity increase due to the presence of the laurentide ice sheet is partly balanced by a loss of eddy efficiency to convert energy from the mean flow moisture availability in this region is greatly reduced due to more advection of dry polar air by stationary waves leading to less synoptic scale latent heat release and hence less precipitation also in terms of seasonality the stormy season is shifted later in the year by a few days to a month depending on the season and the model considered this shift does not directly reflect on the first order seasonal cycle of precipitation which also depends on other mechanisms especially in summer

glacial to holocene evolution of sea surface temperature and surface circulation in the subarctic northwest pacific and the western bering sea it has been proposed that north pacific sea surface temperature sst evolution was intimately linked to north atlantic climate oscillations during the last glacial interglacial transition however during the early deglaciation and the last glacial maximum the sst development in the subarctic northwest pacific and the bering sea is poorly constrained as most existing deglacial sst records are based on alkenone paleothermometry which is limited prior to 15 ka b p in the subarctic north pacific realm by applying the texl86 temperature proxy we obtain glacial holocene sst records for the marginal northwest pacific and the western bering sea our texl86 based records and existing alkenone data suggest that during the past 15 5 ka ssts in the northwest pacific and the western bering sea closely followed millennial scale climate fluctuations known from greenland ice cores indicating rapid atmospheric teleconnections with abrupt climate changes in the north atlantic our sst reconstructions indicate that in the western bering sea ssts drop significantly during heinrich stadial 1 hs1 similar to the known north atlantic climate history in contrast progressively rising sst in the northwest pacific is different to the north atlantic climate development during hs1 similarities between the northwest pacific sst and climate records from the gulf of alaska point to a stronger influence of alaskan stream waters connecting the eastern and western basin of the north pacific during this time during the holocene dissimilar climate trends point to reduced influence of the alaskan stream in the northwest pacific

shrinkage of east asia winter monsoon associated with increased enso events since the mid holocene instrumental records indicate a close relationship between the el nino southern oscillation and the east asian winter monsoon eawm on interannual to decadal time scales however few studies have examined possible links between them on centennial millennial time scales in northeast china modern observations show that the immigration of temperate forest trees such as pinus pine and quercus oak into cold temperate boreal forest is sensitive to changes in winter temperature here we present a continuous high resolution pollen record from lake moon in the central part of the great khingan mountain range northeast china the record reveals increasing contents of pinus and quercus pollen after similar to 6 0 ka cal bp which may indicate a gradual weakening of the eawm it is broadly coupled with an increasing el nino frequency since the middle holocene and we observe a statistically significant correlation between the percentages of pinus and quercus and a time series of el nino events on the centennial to millennial time scale the results of wavelet analysis and band pass filtering show that the occurrence and development of el nino have also promoted a weaker eawm after similar to 6 0 ka cal bp which is inversely correlated with the variation of the ca 500 year cycle originated from changes in solar output these results imply that the climate transition in the mid holocene is caused by the change of variations in solar activity and amplified by ocean circulation el nino southern oscillation to influence the east asian monsoon system especially the eawm and finally change the vegetation in great khingan mountain range

disentangling seasonal signals in holocene climate trends by satellite model proxy integration past sea surface temperatures ssts are routinely estimated from organic and inorganic remains of fossil phytoplankton or zooplankton organisms recovered from sea floor sediments potential seasonal biases of paleo proxies were intensely studied in the past however even for the two most commonly used paleo proxies for sst uk0 37 and mg ca ratios a clear global picture does not yet exist in the present study we combine holocene sst trends derived from uk0 37 and mg ca ratios with results from idealized climate model simulations forced by changes in the orbital conguration which represents the major climate driver over the last 10 kyrs such changes cause a spatio temporal redistribution of incoming solar radiation resulting in a modulation of amplitude and phasing of the seasonal cycle considering that the climate signal recorded by a plankton based paleo proxy may be aected by the seasonal productivity cycle of the respective organism we use the modern relationship between sst and marine net primary production npp both obtained from satellite observations to calculate a seasonality index si as an independent constraint to link modeled sst trends with proxy data although the climate model systematically underestimates holocene sst trends we find that seasonal productivity peaks of the phytoplankton based uk0 37 result in a preferential registering of the warm cold season in high low latitudes as it was expected from the si distribution the overall smoother trends from the zooplankton derived mg ca ssts suggest a more integrated signal over longer time averages which may also carry a seasonal bias but the spatial pattern is less clear based on our ndings careful multi proxy approaches can actually go beyond the reconstruction of average climate trends specifically allowing to resolve the evolution of seasonality

neotectonics and plio quaternary landscape development within the eastern huercal overa basin betic cordilleras southeast spain abstract the huercal overa basin is one of a series of neogene sedimentary basins located within the betic cordillera of southeast spain its geological and geomorphological history has been controlled by tectonic activity culminating in basin inversion during the plio quaternary deformation of the huercal overa basin is associated with left lateral strike slip faulting in relation to its position within the trans alboran shear zone in this paper we focus upon the eastern portion of the huercal overa basin and make the first attempt to reconstruct the long term landscape development during the plio quaternary this is done through integration of geological and geomorphological data obtained through field observations and gis and remote sensing techniques in particular this paper provides a case study that contributes to the understanding of landscape development within tectonically active shear zones within the eastern part of the huercal overa basin the main tectonic activity is associated with the left lateral strike slip lorca alhama fault oriented ne sw during the late pliocene and early pleistocene the interaction of this fault with older miocene ene wsw to e w orientated structures formed a subsiding area with pull apart basin characteristics termed the cubeta del saltador subsidence within the cubeta del saltador enabled sedimentary infilling by braided rivers with sediment being derived from the sierra de las estancias to the north and the sierra de almagro to the south sedimentary deformation has resulted in the development of a series of progressive unconformities angular unconformities and faulting within the alluvial sediments towards the end of this stage of landscape development an increase in tectonic activity resulted in the creation of elevated tectonic highs in the north alto de la garita del diablo and east loma de garcia of the cubeta del saltador from the middle pleistocene onwards a progressive decrease in tectonic activity is recorded alluvial sediments infilled the cubeta del saltador these were dominated by braided river sediments that formed part of a fan shaped alluvial distributary system derived from the sierra de las estancias to the north in contrast smaller debris flow dominated alluvial fans were derived from the sierra de almagro along the southern margin currently the study area presents an asymmetric configuration reflecting the different topographic characteristics of the northern and southern limiting mountain fronts

tectonically driven landscape development within the eastern alpujarran corridor betic cordillera se spain almeria abstract the betic cordillera is a topographic manifestation of miocene to recent collision between the african and the european plates mountain ranges in the internal zone of the betic cordillera are exhumed massifs of metamorphic and sedimentary rocks and are surrounded by low lying sedimentary basins the neogene history of mountain range uplift and basin formation in the betics is well studied but quaternary topographic development and its relation to convergent plate boundary tectonics is less understood deformation rates of stream incision and factors controlling landscape evolution on the flanks of the highest mountains in the betic cordillera are studied to gain insight on the relationship of quaternary tectonics to topographic development specifically geomorphic processes that led to formation of topographic relief within the internal zone of the betic cordillera are assessed this paper is based on a field study conducted in the eastern alpujarran corridor eac which is the eastern half of a 4 6 km wide and 80 km long inverted sedimentary basin the mid to late quaternary history of basin denudation is deduced on the basis of morphostratigraphic geochronologic and structural geologic analyses of oxygen isotope stage 8 time fluvial deposits in the eac results of these analyses indicate that climate and faulting played only a minor role in landscape evolution in the eac instead the eac topographic trough was excavated by a drainage network whose axial stream rio andarax was incising at a rate between 0 3 and 0 7 m ka since oxygen isotope stage 8 this paper demonstrates that these incision rates are the same as regional rock uplift rates in the eac during the mid and late quaternary topographic relief between the eac and adjacent mountain ranges developed largely as a result of fluvial denudation driven by regional uplift the implications of the results of this investigation are used to propose a model of quaternary topographic relief development in the internal zone of betic cordillera topographic relief between internal zone bedrock massifs and adjacent basins formed largely as a result of fluvial denudation driven by regional uplift faulting also played a significant role in areas that are within a few kilometers of crustal scale fault zones

last glacial maximum temperatures over the north atlantic europe and western siberia a comparison between pmip models margo sea surface temperatures and pollen based reconstructions abstract evaluating the ability of models to simulate climates different from the modern one is important for climate prediction here we present a first comparison between results from simulations of the last glacial maximum climate and continental and surface ocean reconstructions for the north atlantic europe and western siberia the simulations include prescribed sea surface temperature sst and slab ocean atmospheric general circulation model runs performed within the pmip1 project and atmosphere ocean fully coupled runs performed after pmip1 and within the pmip2 project the surface ocean reconstructions are from the margo project continental reconstructions are based on pollen data over the north atlantic most models simulate the strengthening of the sst meridional gradient suggested by the reconstructions but most do not reproduce the lgm control sst anomaly at the right location nor with the right amplitude over western siberia the model results are much improved when a new ice sheet reconstruction ice 5g is used to force the models the main discrepancy remains for western europe winter temperatures for which lgm control anomalies are significantly underestimated by all models all models indicate that this region during the lgm experienced significantly higher interannual variability in coldest month temperatures compared to the control runs this increased variability could have conspired to bias the apparently extremely cold pollen based temperature reconstructions

western pacific coral δ18o records of anomalous holocene variability in the el nino southern oscillation 1 skeletal oxygen isotope ratios in holocene porites corals from northern papua new guinea record decreases in sea surface temperature sst and rainfall during el nino events threshold analysis of seven fossil coral 18o records spanning the period 7 6 5 4 ka thousand years ago shows 8 12 el nino events century significantly less than the 23 events century recorded by the nino3 4 index the coral reconstructions also show a 15 reduction in el nino event amplitude for 7 6 5 4 ka compared to today which is greater than the suppression given by model studies in contrast large and protracted el nino events are identified for 2 5 1 7 ka taken together the results indicate a non linear atmospheric response to holocene changes in el nino sst anomalies we propose that small changes in tropical sst gradients the positioning of the intertropical convergence zone and the pacific tradewind climatology modify the impact of el nino events on western pacific rainfall

orbital controls on the el nino southern oscillation and the tropical climate the global synchroneity of glacial interglacial events is one of the major problems in understanding the link between milankovitch forcing and the climate of the late quaternary in this study we isolate a part of the climate system the tropical pacific and test its sensitivity to changes in solar forcing associated with changes in the earth s orbital parameters we use a simplified coupled ocean atmosphere model that is run for the past 150 000 years and forced with milankovitch changes in the solar insolation this system responds primarily to the precessional cycle in solar forcing and is capable of generating a mean response to the changes in the seasonal distribution of solar radiation even while the annual mean insolation is roughly constant the mean response to the precessional forcing is due to an interaction between an altered seasonal cycle and the el nifio southern oscillation enso changes in the enso behavior result in a mean tropical climate change the hypothesis is advanced that such a change in the tropical climate can generate a globally synchronous climate response to milankovitch forcing

last glacial maximum and holocene climate in ccsm3 abstract the climate sensitivity of the community climate system model version 3 ccsm3 is studied for two past climate forcings the last glacial maximum lgm and the mid holocene the lgm approximately 21 000 yr ago is a glacial period with large changes in the greenhouse gases sea level and ice sheets the mid holocene approximately 6000 yr ago occurred during the current interglacial with primary changes in the seasonal solar irradiance the lgm ccsm3 simulation has a global cooling of 4 5 c compared to preindustrial pi conditions with amplification of this cooling at high latitudes and over the continental ice sheets present at lgm tropical sea surface temperature sst cools by 1 7 c and tropical land temperature cools by 2 6 c on average simulations with the ccsm3 slab ocean model suggest that about half of the global cooling is explained by the reduced lgm concentration of atmospheric co2 50 of present day concentrations there is an increase in the antarctic circumpolar current an

influence of the intertropical convergence zone on the east asian monsoon a palaeoclimate record spanning the past 16 000 years with nearly annual time resolution has been obtained from lake huguang maar in china the magnetic properties and titanium content of the lake sediments are thought to reflect changes in the east asian winter monsoon strength thus providing a complement to palaeoclimate archives that record the strength of the rain bearing summer monsoon the records point to an anti correlation between winter and summer monsoon strength best explained by migration of the intertropical convergence zone itcz a belt of low pressure air at the equator interestingly the decline of china s tang dynasty and the mayan civilization broadly coincide with drought periods recorded in lake huguang maar and cariaco basin sediments respectively did major shifts in the position of the itcz catalyse simultaneous events in civilizations on opposite sides of the pacific ocean the asian australian monsoon is an important component of the earth s climate system that influences the societal and economic activity of roughly half the world s population the past strength of the rain bearing east asian summer monsoon can be reconstructed with archives such as cave deposits1 2 3 but the winter monsoon has no such signature in the hydrological cycle and has thus proved difficult to reconstruct here we present high resolution records of the magnetic properties and the titanium content of the sediments of lake huguang maar in coastal southeast china over the past 16 000 years which we use as proxies for the strength of the winter monsoon winds we find evidence for stronger winter monsoon winds before the bolling allerod warming during the younger dryas episode and during the middle and late holocene when cave stalagmites suggest weaker summer monsoons1 2 3 we conclude that this anticorrelation is best explained by migrations in the intertropical convergence zone similar migrations of the intertropical convergence zone have been observed in central america for the period ad 700 to 900 refs 4 6 suggesting global climatic changes at that time from the coincidence in timing we suggest that these migrations in the tropical rain belt could have contributed to the declines of both the tang dynasty in china and the classic maya in central america

structure and formation mechanisms of the northern hemisphere summertime subtropical highs abstract three dimensional structure and dynamics of the climatological mean summertime subtropical highs over the north pacific and atlantic i e the azores high are investigated each of the observed surface highs is accompanied by a meridional vorticity dipole aloft exhibiting barotropic and baroclinic structures in its northern and southern portions respectively in a manner dynamically consistent with the observed midtropospheric subsidence each of the highs develops over the relatively cool eastern ocean where a pronounced near surface thermal contrast exists with a heated landmass to the east the authors demonstrate through numerical experiments that those highs can be reproduced in response to a local shallow cooling heating couplet associated with this thermal contrast although the upper level response is somewhat underestimated the model experiments suggest that the near surface thermal contrasts associated with those surface subtropical highs over the pacific and atlantic can act as s

pacific east asian teleconnection how does enso affect east asian climate observational evidence is presented to show a teleconnection between the central pacific and east asia during the extreme phases of enso cycles this pacific east asian teleconnection is confined to the lower troposphere the key system that bridges the warm cold events in the eastern pacific and the weak strong east asian winter monsoons is an anomalous lower tropospheric anticyclone cyclone located in the western north pacific the western north pacific wind anomalies develop rapidly in late fall of the year when a strong warm or cold event matures the anomalies persist until the following spring or early summer causing anomalously wet dry conditions along the east asian polar front stretching from southern china northeastward to the east of japan kuroshio extension using atmospheric general circulation and intermediate models the authors show that the anomalous philippine sea anticyclone results from a rossby wave response to suppressed convective heating which is induced by both the in situ ocean surface cooling and the subsidence forced remotely by the central pacific warming the development of the anticyclone is nearly concurrent with the enhancement of the local sea surface cooling both the anticyclone and the cooling region propagate slowly eastward the development and persistence of the teleconnection is primarily attributed to a positive thermodynamic feedback between the anticyclone and the sea surface cooling in the presence of mean northeasterly trades the rapid establishment of the philippine sea wind and sst anomalies implies the occurrence of extratropical tropical interactions through cold surge induced exchanges of surface buoyancy flux the central pacific warming plays an essential role in the development of the western pacific cooling and the wind anomalies by setting up a favorable environment for the anticyclone sst interaction and midlatitude tropical interaction in the western north pacific

impact of enso on east asian winter monsoon during interglacial periods effect of orbital forcing orbital forcing influences climate phenomena by changing incoming solar radiation in season and latitude here changes in the el nino southern oscillation enso s impact on the east asian winter monsoon eawm due to orbital forcing especially for three selected time periods in each of two interglacial periods the eemian 126 122 115 ka and holocene 9 6 0 ka are investigated there was a high negative correlation between enso and eawm when the obliquity was low the processional angle was large and especially when accompanied by large eccentricity which corresponds to a weaker monsoon period the correlation was also high when enso variability was high which interestingly corresponded to lower obliquity and higher degree precession periods therefore as both lower obliquity and higher degree precession such as during 115 ka and 0 ka cause the eawm to be weakened through higher winter insolation over northern hemisphere and the enso to be enhanced through an intensified zonal contrast of the equatorial sea surface temperature the relationship between the enso and eawm becomes tighter the opposite case i e during 126 and 9 ka is also true dynamically furthermore the sensitivity of boreal winter precipitation against sea surface temperature sst anomaly over the tropical pacific which depends on mean sst was positively correlated to the strength of the enso eawm correlation implying that the warmer mean ocean surface causes the strong response of atmosphere to change in the sst anomaly thereby enhancing the impact of enso on eawm warmer wintertime tropical sst is attributed to higher insolation over the tropics especially during 115 and 0 ka while cooler ssts occurred during 126 and 9 ka

a numerical study on the atmospheric circulation over the midlatitude north pacific during the last glacial maximum abstract the dynamics of the atmospheric circulation change over the midlatitude north pacific under the boundary conditions during the last glacial maximum lgm have been studied by atmospheric general circulation models gcms with different ocean feedbacks three boundary conditions in the lgm were different from those of the present day pd ice sheet with elevated topography and high albedo atmospheric co2 concentration and insolation the ocean component was treated as follows a full circulation ocean with dynamical and thermal ocean feedback coupled general circulation model cgcm a slab ocean only with thermal feedback used to calculate the surface heat balance slab ocean gcm sgcm and no ocean feedback by fixing sea surface temperature sst with pure atmospheric dynamics agcm both cgcm and sgcm simulated a weakened pacific high pressure system in boreal summer during the lgm compared to the pd and an intensified aleutian low pressure system in winter both in summer and winter t

el nino southern oscillation extrema in the holocene and last glacial maximum 1 the el nino southern oscillation enso is the largest engine of interannual climate variability on the planet yet its past behavior and potential for future change are poorly understood and vigorously contested reconstructions of past enso are indispensable for testing climate models tasked with predicting future enso activity in a warming world but suitable geologic archives are scarce especially for the last glacial period here we reconstruct mean climate and enso variability in the holocene and last glacial maximum lgm from oxygen isotopic ratios 18o of individual foraminifera retrieved from deep sea sediments our results document coordinated adjustments of the tropical pacific enso system between two diametrically opposite states an amplified enso state in the lgm associated with a reduced zonal temperature gradient and a damped enso state in the mid holocene with enhanced gradient orbital precession provided the switch between these states and acted as the dominant external driver of the tropical pacific enso system in the past 25 000 years the linked response of the mean state and variability to orbital forcing provides an integrated framework for testing enso theory and models

pacific east asian teleconnection part ii how the philippine sea anomalous anticyclone is established during el nino development the anomalous philippine sea anticyclone psac conveys impacts of el nino to east asian climate during the mature and decay of an el nino from the winter to ensuing summer it is shown that the anomalous psac forms in fall about one season prior to the peak el nino its strength increases with the el nino intensity and its sign reverses during a la nina the psac formation concurs with abnormal deepening of the east asian trough and with increasing number of northward recurvature of tropical storms in the western pacific the psac establishment is abrupt coupling with a swing from a wet to dry phase of an intraseasonal oscillation iso and often concurrent with early retreat of the east asian summer monsoon the iso becomes inactive after psac establishment the development of the psac is attributed to combined effects of the remote el nino forcing tropical extratropical interaction and monsoon ocean interaction the developing el nino induces off equatorial as cending rossby wave responses and land surface cooling in northeast asia both deepen the east asian trough in fall and induces vigorous tropical extratropical exchange of air mass and heat which enhances the cold air outbreak and initiation of the psac through exciting descending rossby waves the el nino induced indonesian subsidence generates low level anticyclonic vorticity over south asia which is advected by mean monsoon westerly instigating the anomalous psac the iso interacting with the underlying ocean plays a critical role in the abrupt establishment of psac the wind evaporation entrainment feedback tends to amplify suppress iso before after winter northeasterly monsoon commences suggesting the roles of atmosphere ocean inter action and the seasonal march of background winds in changing the philippine sea iso intensity and maintaining psac

how well can we simulate past climates evaluating the models using global palaeoenvironmental datasets abstract global syntheses of palaeoenvironmental data are required to test climate models under conditions different from the present data sets for this purpose contain data from spatially extensive networks of sites the data are either directly comparable to model output or readily interpretable in terms of modelled climate variables data sets must contain sufficient documentation to distinguish between raw primary and interpreted secondary tertiary data to evaluate the assumptions involved in interpretation of the data to exercise quality control and to select data appropriate for specific goals four data bases for the late quaternary documenting changes in lake levels since 30 14 c kyr bp the global lake status data base vegetation distribution at 18 14 c kyr and 6 14 c kyr bp biome 6000 aeolian accumulation rates during the last glacial interglacial cycle dirtmap and tropical terrestrial climates at the last glacial maximum the lgm tropical terrestrial data synthesis are summarised each has been used to evaluate simulations of last glacial maximum lgm 21 calendar kyr bp and or mid holocene 6 cal kyr bp environments comparisons have demonstrated that changes in radiative forcing and orography due to orbital and ice sheet variations explain the first order broad scale in space and time features of global climate change since the lgm however atmospheric models forced by 6 cal kyr bp orbital changes with unchanged surface conditions fail to capture quantitative aspects of the observed climate including the greatly increased magnitude and northward shift of the african monsoon during the early to mid holocene similarly comparisons with palaeoenvironmental datasets show that atmospheric models have underestimated the magnitude of cooling and drying of much of the land surface at the lgm the inclusion of feedbacks due to changes in ocean and land surface conditions at both times and atmospheric dust loading at the lgm appears to be required in order to produce a better simulation of these past climates the development of earth system models incorporating the dynamic interactions among ocean atmosphere and vegetation is therefore mandated by quaternary science results as well as climatological principles for greatest scientific benefit this development must be paralleled by continued advances in palaeodata analysis and synthesis which in turn will help to define questions that call for new focused data collection efforts

a coupled climate model simulation of the last glacial maximum part 2 approach to equilibrium the climate of the last glacial maximum lgm is simulated with a coupled climate model the simulated climate undergoes a rapid adjustment during the first several decades after imposition of lgm boundary conditions as described in part 1 and then evolves toward equilibrium over 900 model years the climate simulated by the coupled model at this period is compared with observationally based lgm reconstructions and with lgm results obtained with an atmosphere mixed layer slab ocean version of the model in order to investigate the role of ocean dynamics in the lgm climate global mean surface air temperature and sea surface temperature sst decrease by about 10 c and 5 6 c in the coupled model which includes ocean dynamics compared to decreases of 6 3 and 3 8 c in slab ocean case the coupled model simulates a cooling of about 6 5 c over the tropics which is larger than that of the climap reconstruction 1 7 c and larger than that of the slab ocean simulation 3 3 c but which is in reasonable agreement with some recent proxy estimates the ocean dynamics of the coupled model captures features found in the climap reconstructions such as a relative maximum of ocean cooling over the tropical pacific associated with a mean la nina like response and lead to a more realistic sst pattern than in the slab model case the reduction in global mean precipitation simulated in the coupled model is larger 15 than that simulated with the slab ocean model 10 in conjunction with the enhanced cooling some regions such as the usa and the mediterranean region experience increased precipitation in accord with proxy paleoclimate evidence the overall much drier climate over the ocean leads to higher sea surface salinity sss in most ocean basins except for the north atlantic where sss is considerably lower due to an increase in the supply of fresh water from the mississippi and amazon rivers and presumably a decrease in salt transport by the weakened north atlantic overturning circulation the north atlantic overturning stream function weakens to less than half of the control run value the overturning is limited to a shallower depth less than 1000 m and its outflow is confined to the northern hemisphere in the southern ocean convection is much stronger than in the control run leading to a stronger overturning stream function associated with enhanced antarctic bottom water formation as a result southern ocean water masses fill the entire deep ocean the antarctic circumpolar current acc transport through the drake passage increases by about 25 the acc transport despite weaker zonal winds is enhanced due to changes in bottom pressure torque the weakening of the overturning circulation in the north atlantic and the accompanying 30 decrease in the poleward ocean heat transport contrasts with the strengthening of the overturning circulation in the southern ocean and a 40 increase in heat transport as a result sea ice coverage and thickness are affected in opposite senses in the two hemispheres the lgm climate simulated by the coupled model is in reasonable agreement with paleoclimate proxy evidence the dynamical response of the ocean in the coupled model plays an important role in determining the simulated and undoubtedly the actual lgm climate

palaeostress reconstructions and geodynamics of the baikal region central asia part i palaeozoic and mesozoic pre rift evolution abstract this paper presents the first palaeostress results obtained for the basement of the baikal rift system in southern siberia russia large scale structural analysis and palaeostress reconstructions show that the palaeozoic mesozoic kinematic history precursor of the baikal cenozoic rifting is characterized by the succession of six regional palaeostress stages stress inversion of fault slip data and earthquake focal mechanisms is performed using an improved right dieder method followed by rotational optimization d delvaux tensor program the results are interpreted in the light of recent developments in the investigation of regional intraplate stress field and used as additional constraints for palaeogeodynamic reconstruction of central asia after the final palaeozoic closure of the palaeo asian ocean on the southern margin of the siberian platform the marginal suture with the sayan baikal caledonian belt was repeatedly and preferentially reactivated during the subsequent palaeozoic and mesozoic history this suture zone also controlled the opening of the baikal rift system in the cenozoic the progressive closure of the palaeo asian and mongol okhotsk oceans generated successive continental collisions which were recorded in the baikal area by brittle ductile and brittle deformations the first two palaeostress stages correspond to the successive collage of precambrian microcontinents and caledonian terranes along the southern margin of the siberian platform 1 late cambrian early ordovician n s compression and 2 late silurian early devonian nw se compression the next two stages are related to the remote effects of the complex evolution of the western palaeo asian ocean southwest of the siberian continent 3 late devonian early carboniferous n s compression recorded only in the altai region and 4 late carboniferous early permian e w compression recorded both in the altai and baikal regions the last stages are the consequences of the mongol okhotsk oceanic closure 5 late permian triassic nw se extension with development of cordilleran type metamorphic core complexes and volcanism along the active margin of the mongol okhotsk ocean 6 initial development of early middle jurassic 10 15 km wide molassic basins in trans baikal and large foredeeps along the southern margin of the siberian platform in probable extensional context but for which no palaeostress data are available and 7 final closure of the mongol okhotsk ocean in the cretaceous this last event results from the collision between the mongol china and the siberian plates and is evidenced by the inversion of the middle mesozoic basins and by late jurassic early cretaceous coal bearing sedimentation in trans baikal this long tectonic history yielded a highly heterogeneous basement in the baikal area precursor of the cenozoic rifting

holocene paleoseismicity of the tunka fault baikal rift russia the tunka fault is a major normal oblique transform fault within the nne trending baikal rift that displays geomorphic evidence of recurrent quaternary movement a flight of six fanhead terraces of the kyngarga river is displaced by several parallel faults and has scarps up to 32 m high at arshan the main fault zone is exposed in an abandoned gravel quarry about 1 km east of the kyngarga river thirteen radiocarbon dates from the quarry a shallow trench in a graben and natural streamcuts constrain the timing of the latest two or three holocene paleoearthquakes the latest earthquake is bracketed by the 1024 1315 calendar years cal year b p age of an unfaulted terrace and by the 1947 2179 cal year b p age of a soil buried by scarp colluvium in the graben trench the penultimate earthquake is also relatively well constrained assuming that the displacement event slightly younger than 7091 7867 cal year b p in the upper quarry exposure is the same as the fissuring event slightly older than 6733 7385 cal year b p in the lower quarry exposure evidence for earlier event s between 9 2 12 7 ka depends on ambiguous stratigraphic evidence in the lower quarry exposure on the basis of only the two well dated earthquakes the recurrence interval at arshan may range from 2 9 to 6 8 ka for earthquake displacements of at least 1 3 m or a slip rate of 0 19 0 44 mm yr intermediate term 100 ka and long term circa 500 ka slip rates computed from terrace age estimates and fault scarp heights are 0 08 0 16 mm yr and 0 07 0 11 mm yr respectively rates that are considerably lower than the late holocene rate and the approximately 0 5 mm yr that might be inferred from the tectonic geomorphology of the tunka range front

late quaternary geology of the tunka rift basin lake baikal region russia abstract the objective of this research is to obtain a better understanding of the evolution of the tunka rift basin part of the baikal rift zone and how it relates to the overall geologic history of the region particular for the quaternary period the tectonically active baikal rift zone began forming over 50 million years ago and continues today in the tunka basin during the oligocene and middle pliocene relatively weak tectonic disturbances took place and thick accumulations of organic rich sands silts and clays were deposited in lacustrine marshy subtropical environments tectonism increased between the miocene and pliocene and thick units of coarse alluvium and floodplain sediments were deposited during the late pliocene quaternary tectonism formed basins that are now filled with a variety of coarse clastic materials early and middle pleistocene sediments are poorly exposed covered by widespread late pleistocene deposits three late pleistocene sedimentary facies dominate boulder pebble gravels proluvial glacial fluvial and alluvial sediments alluvial sand and loess like sediments with associated slope deposits altered by post depositional wind erosion the relationship between these complexes including radiocarbon and other chronological data and fauna and flora remains indicates that they began forming c 70 000 yr ago paleosols glacial deposits and cryogenic material indicate that at times the climate was cool or cold during the early late pleistocene renewed tectonism took place causing increased deposition of coarse sediments the middle late pleistocene deposits consist mostly of sandy floodplain alluvium by the end of the late pleistocene holocene alluviation was reduced and replaced by a high degree of erosion and aeolian deposition

morphotectonic evolution of two depressions at the southern border of the baikal rift system abstract detailed study of two dry depressions in the baikal rift system the e w khoito ghol tunka bistraya depression and the sw ne gusinoje ivolga depression aims to provide a better understanding of tectonic control on the intershoulder relief evolution after the rift opened both depressions are grabens and both feature a suite of 10 20 km wide basins alternating with more or less massive highs field and laboratory analysis shows that this pattern is of recent tectonic origin and that local breaking up and subsidence followed the general sinking which originally formed the grabens the subsidence belts seem to have gradually shifted north and northeastwards geomorphological analysis reveals that in both depressions the highs are remnants of a former pediment which was broken up the young basins display numerous relevant hydrographic anomalies of the secondary channels and a general water logging they also suggest that the subsidence belts have gradually shifted north and northeastwards in the gusinoje ivolga depression evidence was found of a plio pleistocene river course parallel to the selenga river which was later dismantled by the breaking up this depression parallel to the baikal rift and belonging to the mesozoic system of grabens in the caledonian fold belt seems to have been included into the general system of rifts during the pliocene tectonic phase as for the main hydrographic axes the selenga river was set on a palaeogene age planation surface before the first tectonic phase and kept its original course the irkut river flowed in the khoito gol tunka bistraya depression after the first tectonic phase and was not affected by the later breaking up in contrast the secondary drainage network is largely discordant despite their different geotectonic contexts the two depressions show a similar development of relief pattern which poses the question of the style of rift dynamics after the main pliocene tectonic phase

modeling evidence for enhanced el nino southern oscillation amplitude during the last glacial maximum we present a numerical eigenmode analysis of an intermediate el nin o southern oscillation enso model which is driven by present day observed background conditions as well as by simulated background conditions for the last glacial maximum lgm about 21 000 years ago the background conditions are obtained from two lgm simulations which were performed with the national center for atmospheric research climate system model csm1 4 and an earth system model of intermediate complexity ecbilt clio our analysis clearly shows that the leading present day unstable recharge discharge mode changes its stability as well as its frequency during lgm conditions simulated lgm background conditions were favorable to support large amplitude self sustained interannual enso variations in the tropical pacific our analysis indicates that off equatorial climate conditions as well as a shoaling of the thermocline play a crucial role in amplifying the lgm enso mode

the initiation of northern hemisphere glaciation for well over a century scientists have speculated that variations in the atmospheric concentration of radiatively important trace gases such as carbon dioxide could control the earth s climate e g arrhenius 1 896 recent observations of significant glacial interglacial variation in atmo spheric co2 in ice cores put this idea on a firm observational as well as theoretical footing e g barnola et ai1 987 in this century as atmospheric co2 levels creep steadily upwards in response to the burning of fossil fuels and forests the specter of manmade global climate change looms before us ipcc 1990 a possibility that has heightened interest in the natural variability of climate in the past in particular the 3 c warming pre dicted for the next century has stimulated interest in past warm climates such as the middle pliocene around 3 0 million years ma ago an interval that has often been invoked as a greenhouse world budyko et al 1985 in this paper the climate transition from the warm mid pliocene around 3 2 ma to the onset of northern hemisphere ice ages around 2 4 ma is examined evidence for the initiation of significant northern hemisphere glaciation is examined as well as how this event affected climate around the globe while the cause of individual glacial interglacial oscillations is tied to milankovitch variations in the earth s orbit around the sun e g imbrie et ai 1 992 these insolation changes cannot account for the long term cooling trend which culminated in northern hemisphere glaciation in the final section of this paper mechanisms of long term climate change

atlantic meridional overturning circulation response to idealized external forcing the response of the atlantic meridional overturning circulation amoc to idealized external solar forcing is studied in terms of the internal unforced amoc modes with the kiel climate model kcm a coupled atmosphere ocean sea ice general circulation model the statistical investigation of kcm s internal amoc variability obtained from a multi millennial control run yields three distinct modes a multi decadal mode with a period of about 60 years a quasi centennial mode with a period of about 100 years and a multi centennial mode with a period of about 300 400 years most variance is explained by the multi centennial mode and the least by the quasi centennial mode the solar constant varies sinusoidally with two different periods 100 and 60 years in forced runs with kcm the amoc response to the external forcing is rather complex and nonlinear it involves strong changes in the frequency structure of the variability while the control run depicts multi timescale behavior the amoc variability in the experiment with 100 year forcing period is channeled into a relatively narrow band centered near the forcing period it is the quasi centennial amoc mode with a period of just under 100 years which is excited although it is heavily damped in the control run thus the quasi centennial mode retains its period which does not correspond exactly to the forcing period surprisingly the quasi centennial mode is also most strongly excited when the forcing period is set to 60 years the period of the multi decadal mode which is rather prominent in the control run it is largely the spatial structure of the forcing rather than its period that determines which of the three internal amoc modes is excited the results suggest that we need to understand the full modal structure of the internal amoc variability in order to understand the circulation s response to external forcing this could be a challenge for climate models we cannot necessarily expect that the response to external forcing is realistically captured by a model even if only strongly damped modes are not well represented that do not account for much variance under present day conditions

the origin of the subtropical anticyclones abstract the origin of the northern hemisphere summer subtropical anticyclones is investigated using a linear quasigeostrophic model it is found that the broad features in the model solutions forced by realistic heating fields acting on observed zonal flows agree well with those in the observations the realistic features of the model solutions include the subtropical continental lows and oceanic highs in the lower troposphere and continental ridges and midoceanic troughs in the upper troposphere the forced responses are largest near the surface and the tropopause with a vertical node around 500 hpa as observed the results indicate that the model stationary waves owe their existence largely to the asian heat source the authors thus propose that the observed low level subtropical anticyclones over the north pacific and north atlantic oceans be interpreted as a remote response of rossby waves forced by the large scale heat sources over asia the results support the existing theory that the observed low

anti phased response of northern and southern east asian summer precipitation to enso modulation of orbital forcing abstract the timing of orbital scale asian monsoon changes as a direct response of northern summer insolation or remarkably lagged by southern insolation is still unclear in particular various monsoon records obtained in the east asian monsoon region show distinct phase relationships indicating additional forcing feedback mechanisms here monsoon proxies covering the past several precession cycles either from cave stalagmites or from land ocean deposits are first reviewed to present the nearly inverse precipitation responses to the precession forcing between southern and northern east asia modern meteorological observations show that different modes of tropical pacific sea surface temperature sst could lead to an out of phase interannual change in the east asian summer precipitation this enso influence is also found in the precession scale monsoon variability from the long term transient modeling which can explain the phase differences among monsoon proxies at precession maxima the east asian summer monsoon strengthens causing more precipitation in the north and less precipitation in the south the sst precipitation teleconnection is closely associated with a high pressure anomaly due to surface cooling over northwestern pacific therefore the timing of asian paleo monsoon might be significantly influenced by the internal ocean feedbacks and one can not expect all the monsoon proxies are consistently responded to the external insolation forcing

monsoon climate of the early holocene climate experiment with the earth s orbital parameters for 9000 years ago values for the precession and obliquity of the earth 9000 years ago indicate that the global average solar radiation for july 9000 years ago was 7 percent greater than at present when the estimated solar radiation values are used in a low resulation climate model the model simulates an intensified continent scale monsoon circulation this result agrees with paleoclimatic evidence from africa arabia and india that monsoon rains were stronger between 10 000 and 5000 years ago than they are today

baikal rift zone structure and geodynamics abstract the cenozoic baikal rift zone is superimposed on the caledonian baikal fold belt representing the suture between the precambrian siberian craton and several microcontinents the baikal rift zone consists of a system of disconnected fault bounded basins and extensional and wrench faults that straddles a major arch having a topographic relief of 2 3 km rifting activity commenced during the oligocene and is still active as evident from high seismicity of the baikal rift zone across the baikal rift zone upper crustal extension is considerably smaller than would be expected from its crustal thickness which decreases by 8 11 km across the baikal basins as compared to the adjacent unextended areas the discrepancy between upper and lower crustal attenuation could be attributed to intrusion of a major diapir indeed geophysical data indicate that the sayan baikal dome coincides with such a diapir the top of which is located at the crust mantle boundary this intrusion is held responsible for oligocene and quaternary doming of the rift zone development of the intra continental baikal rift system is thought to be related to asthenospheric diapirism active rifting however intra plate stresses in conjunction with the himalayan collision may have played some role

geodynamics of the western part of the mongolia okhotsk collisional belt trans baikal region russia and mongolia abstract after the western edge of the mongolian microcontinent joined the siberian continent in the region of central mongolia in the earliest permian these two continental blocks remained turned at an angle of about 120 with respect to each other and separated on greater extent of their present day boundary by an enormous gulf of the paleopacific called the mongolia okhotsk ocean closure of this ocean at the early middle jurassic boundary led to the complete collision of siberia and mongolia which by then had already become part of the mongolia north china continent this main collisional episode which lasted through the middle and late jurassic involved thrusting folding and magmatism and produced the mongolia okhotsk belt the onon island arc which was located in the mongolia okhotsk ocean was squeezed between the two major continents inasmuch as the third element the island arc was involved in the collision it is reasonable to distinguish two branches of the mongolia okhotsk suture these branches control the spatial distribution of gold mineralization in the trans baikal region on the southeastern periphery of siberia the crust thickened considerably after the collision and a plateau like uplift formed in the early cretaceous when compression ceased the collisional uplift collapsed and the thrusts were transformed into low angle normal faults the motions on which were responsible for the formation of rift basins and exhumation of metamorphic core complexes

seasonally asymmetric transition of the asian monsoon in response to ice age boundary conditions modulation of a monsoon under glacial forcing is examined using an atmosphere ocean coupled general circulation model aogcm following the specifications established by paleoclimate modelling intercomparison project phase 2 pmip2 to understand the air sea land interaction under different climate forcing several sensitivity experiments are performed in response to individual changes in the continental ice sheet orbital parameters and sea surface temperature sst in the last glacial maximum lgm 21 ka to evaluate the driving mechanisms for the anomalous seasonal evolution of the monsoon comparison of the model results in the lgm with the pre industrial pi simulation shows that the arabian sea and bay of bengal are characterized by enhancement of pre monsoon convection despite a drop in the sst encompassing the globe while the rainfall is considerably suppressed in the subsequent monsoon period in the lgm winter relative to the pi anomalies in the meridional temperature gradient mtg between the asian continents minus the tropical oceans become positive and are consistent with the intensified pre monsoon circulation the enhanced mtg anomalies can be explained by a decrease in the condensation heating relevant to the suppressed tropical convection as well as positive insolation anomalies in the higher latitude showing an opposing view to a warmer future climate it is also evident that a latitudinal gradient in the sst across the equator plays an important role in the enhancement of pre monsoon rainfall as for the summer the sensitivity experiments imply that two ice sheets over the northern hemisphere cools the air temperature over the asian continent which is consistent with the reduction of mtg involved in the attenuated monsoon the surplus pre monsoon convection causes a decrease in the sst through increased heat loss from the ocean surface in other words negative ocean feedback is also responsible for the subsequent weakening of summer convection

orbital and millennial scale variations in asian dust transport path to the japan sea abstract orbital and millennial scale variations in the asian monsoon and its probable association with the dansgaard oeschger d o cycles have been demonstrated by previous studies however the origin and nature of such variations are poorly understood the japan sea is located down wind of the arid areas of the eurasian continent and thus receives significant amounts of aeolian dust consequently the hemipelagic sediments of the japan sea are expected to record a continuous aeolian dust accumulation which may provide information about the past variations in asian monsoon grain size flux and provenance of aeolian dust in the sediments were examined using two sediment cores obtained from the northern and southern parts of the japan sea in order to understand the spatial variability of asian monsoon since the silt fraction of the detrital materials in hemipelagic sediments of the japan sea is composed predominantly of aeolian dust the grain size flux and provenance of the silt fraction were examined the taklimakan desert loess plateau and siberia northeast china areas were identified as possible source areas of aeolian dust in the sediments of the japan sea based on the electron spin resonance esr signal intensity and crystallinity of quartz moreover the relative contribution of aeolian dust from each source area was estimated based on the esr signal intensity and crystallinity of quartz aeolian dust fluxes from the two source areas at the southern site were then estimated grain size and flux of eolian dust at the northern site and fluxes of aeolian dust from two source areas at the southern site show orbital scale variations in harmony with the insolation change at 30 n in june these results indicate orbital scale changes in the extent of the arid area and or frequency of dust storms in the taklimakan desert loess plateau and siberia northeast china areas and suggest that southward northward shifts of the westerly jet axis occurred together with either intensified weakened winter monsoon decreased increased winter precipitation in the siberia northeast china area or southeastward northwestward shifts of summer monsoon limit during periods of smaller larger insolation at 30 n in june in addition to these orbital scale variations millennial scale variations possibly associated with the d o cycles are observed in the grain size record of aeolian dust at the two sites based on analogy with orbital scale variations these millennial scale variations are considered to reflect millennial scale changes in the position of the westerly jet axis together with the changes either in winter monsoon intensity winter precipitation or position of summer monsoon limit our results suggest n s oscillations in the westerly jet and summer monsoon limit and changes in the intensity of the winter monsoon on orbital and millennial timescales

remote response of the east asian winter monsoon to tropical forcing related to el nino southern oscillation 1 the mechanism of the east asian winter monsoon variability in response to el nino southern oscillation enso related tropical forcing is investigated using japanese long term reanalysis project data additionally aided by the japan meteorological agency climate data assimilation system there are at least two different responses zonally symmetric and asymmetric of the asian jet over south asia to the enso related tropical convective forcing during the northern hemisphere winter the zonally symmetric response induced by zonally extended anomalous convection from the philippine sea through southern india and sri lanka is pronounced at the mature phase of enso the zonally asymmetric response is intimately associated with anomalous convection localized in the vicinity of the philippine and south china seas accompanied by an anomalous walker circulation cell between the maritime continent and tropical indian ocean when this asymmetric response is prominent enso related anomalous convection can give rise to a change in the east asian winter monsoon system through stationary rossby wave propagation along the south asian waveguide the north atlantic oscillation nao related extratropical forcing is also a crucial factor and contributes not only to the downstream development of subpolar teleconnections across northern eurasia but also to the reinforcement of the zonally asymmetric pattern of the asian jet over south asia resulting in a significant effect on the east asian winter monsoon circulation a combination of the enso and nao related forcing plays a vital role in triggering the occurrence of extraordinary anomalous monsoon circulations such as extremely heavy snowfall in the 2005 2006 winter in japan

synoptic reorganization of atmospheric flow during the last glacial maximum a coupled global atmosphere ocean model of intermediate complexity is used to study the influence of glacial boundary conditions on the atmospheric circulation during the last glacial maximum in a systematical manner a web of atmospheric interactions is disentangled which involves changes in the meridional temperature gradient and an associated modulation of the atmospheric baroclinicity this in turn drives anomalous transient eddy momentum fluxes that feed back onto the zonal mean circulation moreover the modified transient activity weakened in the north pacific and strengthened in the north atlantic leads to a meridional reorganization of the atmospheric heat transport thereby feeding back onto the meridional temperature structure furthermore positive barotropic conversion and baroclinic production rates over the laurentide ice sheets and the far eastern north pacific have the tendency to decelerate the westerlies thereby feeding back to the stationary wave changes triggered by orographic forcing

on the genesis of the equatorial annual cycle abstract a linear theory is proposed that can explain both the period and the westward propagation of the equatorial annual cycles in the sst and zonal wind a coupled model linearized about a mean state of the air sea system is used this model allows the surface winds to directly change the sst through surface evaporation and vertical mixing in contrast to the formulation of the conventional air sea coupling models that emphasize the effects of winds on ocean dynamics it is demonstrated that the characteristics of the equatorial seasonal cycle including its period phase and amplitude are determined to a large extent by the mean state of the air sea coupling system the meridional wind which is specified here is the most important forcing for the annual cycle in sst suggesting that the equatorial annual cycle is the response to an annual solar forcing in the off equatorial regions

the effect of ocean dynamics in a coupled gcm simulation of the last glacial maximum general circulation models gcms of the climate system are powerful tools for understanding and predicting climate and climate change the last glacial maximum lgm provides an extreme test of the model s ability to simulate a change of climate and allows us to increase our understanding of mechanisms of climate change we have used a coupled high resolution ocean atmosphere gcm hadcm3 to simulate the equilibrium climate at the lgm the effect of ocean dynamics is investigated by carrying out a parallel experiment replacing the dynamic three dimensional ocean gcm with a static thermodynamic mixed layer ocean model changes to the ocean circulation and feedbacks between the ocean atmosphere and sea ice have an important influence on the surface response and are discussed the coupled model produces an intensified thermohaline circulation and an increase in the amount of heat transported northward by the atlantic ocean equatorward of 55 n which is at odds with the interpretation of some proxy records such changes which the thermodynamic mixed layer ocean model cannot produce have a large impact around the north atlantic region and are discussed in the study

on the existence of storm tracks abstract given that middle latitude weather systems transport heat in a manner such as to weaken the baroclinicity that is thought to be crucial to their growth it is perhaps surprising that concentrated regions of such eddy activity i e storm tracks are found in the northern hemisphere winter the existence and possible self maintenance of storm tracks is investigated using a linear stationary wave model with storm track region forcings taken from data averaged over a number of winters it is found that the direct thermal effect of the eddies does indeed act against the existence of the storm track their vorticity fluxes lead to some reduction of this effect it is argued that the mean diabatic heating in the storm track region is an indirect eddy effect this heating is found to maintain the mean maximum in baroclinicity in the region further the mean low level flow induced by the eddy effects is such as to enhance the warm western oceanic boundary currents that are crucial to the existence of t

response of quaternary fluvial systems to differential epeirogenic uplift aguas and feos river systems southeast spain the geomorphic expression of two fluvial systems the rio de aguas and the rambla de los feos in southeast spain reflects their adjustment to differential epeirogenic uplift and local tectonic activity during the quaternary regional uplift of a depositional marine surface resulted in the development of a southward flowing drainage network during late pliocene early pleistocene time disruption of this consequent drainage began as the alhamilla cabrera sierras and the sorbas basin were differentially uplifted relative to the surrounding basins the ancestral feos drainage responded by incision across the uplift through a combination of superimposition and antecedence differential uplift of the sorbas basin enhanced headward erosion of strike oriented drainages and promoted capture of the ancestral feos drainage by the rio de aguas during the late pleistocene stratigraphic relations and soil development indicate that epeirogenic uplift and local tectonics together with climatic fluctuations have influenced the development of the drainage systems throughout the quaternary

southern hemisphere climate variability forced by northern hemisphere ice sheet topography an antarctic ice core reveals that during the last ice age the topography of northern hemisphere ice sheets shifted tropical pacific convection eastward increasing climate variability in the high southern latitudes during glacial maxima ice covered vast areas of the northern hemisphere and had a broad influence across the global climate system tyler jones and colleagues show that climate variability in the southern hemisphere was influenced by these large northern hemisphere ice sheets and was about twice as high during the last glacial maximum than in the warmer holocene that followed the ice sheets created more elevated and brighter surfaces than at present and this altered the location of tropical convection and the atmospheric pathways that link the tropics to west antarctica the results reveal the intimate climatic link between the high latitudes and the key role of the tropics as an interhemispheric mediator the presence of large northern hemisphere ice sheets and reduced greenhouse gas concentrations during the last glacial maximum fundamentally altered global ocean atmosphere climate dynamics1 model simulations and palaeoclimate records suggest that glacial boundary conditions affected the el nino southern oscillation2 3 a dominant source of short term global climate variability yet little is known about changes in short term climate variability at mid to high latitudes here we use a high resolution water isotope record from west antarctica to demonstrate that interannual to decadal climate variability at high southern latitudes was almost twice as large at the last glacial maximum as during the ensuing holocene epoch the past 11 700 years climate model simulations indicate that this increased variability reflects an increase in the teleconnection strength between the tropical pacific and west antarctica owing to a shift in the mean location of tropical convection this shift in turn can be attributed to the influence of topography and albedo of the north american ice sheets on atmospheric circulation as the planet deglaciated the largest and most abrupt decline in teleconnection strength occurred between approximately 16 000 years and 15 000 years ago followed by a slower decline into the early holocene

impact of climate and related weathering processes on the authigenesis of clay minerals examples from circum baikal region siberia abstract the widely outcropping igneous and metamorphic rocks of the circum baikal region all contain illite and chlorite resulting from early alteration of primary minerals these rocks were deeply weathered and leached mainly to kaolinite under the warm and mostly wet upper cretaceous and palaeogene climates during the following severely dry and cold pleistocene episodes the glacier cover was restricted allowing the formation of permafrost which is still several hundred metres thick in the northern baikal region while the lowlands of the central and southern regions belong to the so called sporadic permafrost area the lack of glacial abrasion during the cryo arid climate preserved somehow the weathering products of the previous warm periods that presently crop out next to the relics of the periglacial pleistocene weathering these relict deposits derived from the same substrate rocks as those weathered during the warm and wet climate but they differ in the clay composition with the occurrence of a montmorillonite type smectite that is dominant in some sites the varied weathering processes resulting in different clay assemblages emphasize the importance of the climate impact especially the role cryogenic conditions have played on the clay distribution a mineralogical study of the clay fraction extracted from various circum baikal tertiary and pleistocene weathering profiles and deposits confirms that 1 chlorite and illite which represent the initial minerals are most sensitive to cryogenic weathering and were largely destroyed in the alluvial and colluvial deposits 2 smectite formed under periglacial conditions and 3 kaolinite which is the reference clay mineral for the palaeogene formed in a warm and wet tropical climate is still present without alteration features the described smectite authigenesis confirms that geochemical processes are significant in cryogenic environments suggesting that smectite of some present day soils and continental deposits of temperate regions could be inherited as it might have precipitated under periglacial conditions

global glacial isostasy and the surface of the ice age earth the ice 5g vm2 model and grace abstract the 100 kyr quasiperiodic variation of continental ice cover which has been a persistent feature of climate system evolution throughout the most recent 900 kyr of earth history has occurred as a consequence of changes in the seasonal insolation regime forced by the influence of gravitational n body effects in the solar system on the geometry of earth s orbit around the sun the impacts of the changing surface ice load upon both earth s shape and gravitational field as well as upon sea level history have come to be measurable using a variety of geological and geophysical techniques these observations are invertible to obtain useful information on both the internal viscoelastic structure of the solid earth and on the detailed spatiotemporal characteristics of glaciation history this review focuses upon the most recent advances that have been achieved in each of these areas advances that have proven to be central to the construction of the refined model of the global process of glacial isos

morphology of the latest quaternary surface faulting in the gulf of elat region eastern sinai abstract a variety of morphotectonic features bear evidence of neotectonic activity along the gulf of elat these include stepped topography deflected channels fault line grabens sag pond depressions backtilted fan segments faulted gravel bars and debris flow deposits the age of the fault scarps is estimated on the basis of the extent of dissection the amount of rounding of the crest of the scarps the scarp gradient the stage of clast weathering the intensity of the micro relief and the stage of soil and desert pavement development the field data are interpreted and related to the geomorphic time curves suggested by wallace by bucknam and anderson and by nash and the seismic hazard implications are discussed some criteria suggest a recent age with 10 000 yrs b p as a frequently recurrent estimate from the data it is concluded that the gulf of elat has definitely been tectonically highly active during the holocene

palaeoglacial and palaeoclimatic conditions in the nw pacific as revealed by a morphometric analysis of cirques upon the kamchatka peninsula abstract the distribution of glacial cirques upon the kamchatka peninsula far eastern russia is systematically mapped from satellite images and digital elevation model data a total of 3758 cirques are identified 238 of which are occupied by active glaciers the morphometry of the remaining 3520 cirques is analysed these cirques are found to show a very strong n bias in their azimuth orientation likely resulting from aspect related variations in insolation the strength of this n bias is considered to indicate that former glaciation upon the peninsula was often marginal and mainly of cirque type with peaks extending little above regional equilibrium line altitudes this is supported by the fact that s and se facing cirques are the highest in the dataset suggesting that glacier cover was rarely sufficient to allow s and se facing glaciers to develop at low altitudes the strength of these azimuth related variations in cirque altitude is thought to reflect comparatively cloud free conditions during former periods of glaciation it is suggested that these characteristics of marginal glaciation and comparatively cloud free conditions reflect the region s former aridity which was likely intensified at the global last glacial maximum and during earlier periods of ice advance as a result of the development of negative pressure anomalies over the north pacific driven by the growth of the laurentide ice sheet combined with other factors including an increase in the extent and duration of sea ice a reduction in global sea levels cooler sea surface temperatures and the localised growth of mountain glaciers there is published evidence to suggest extensive glaciation of the kamchatka peninsula at times during the late quaternary yet the data presented here appear to suggest that such phases were comparatively short lived and that smaller cirque type glaciers were generally more characteristic of the period

stationary waves of the ice age climate abstract a linearized steady state primitive equation model is used to simulate the climatological zonal asymmetries stationary eddies in the wind and temperature fields of the 18 000 ybp climate during winter we compare these results with the eddies simulated in the ice age experiments of broccoli and manabe who used climap boundary conditions and reduced atmospheric co2 in an atmospheric general circulation model gcm coupled with a static mixed layer ocean model the agreement between the models is good indicating that the linear model can be used to evaluate the relative influences of orography diabatic heating and transient eddy heat and momentum transports in generating stationary waves we find that orographic forcing dominates in the ice age climate the mechanical influence of the continental ice sheets on the atmosphere is responsible for most of the changes between the present day and ice age stationary eddies this concept of the ice age climate is complicated by the sensitivity of t

a simulation of the last glacial maximum climate using the ncar ccsm the national center for atmospheric research community climate system model ncar ccsm is used in a coupled atmosphere ocean sea ice simulation of the last glacial maximum lgm around 21 000 years ago climate in the tropics the simulation shows a moderate cooling of 3 c over land and 2 c in the ocean in zonal average this cooling is about 1 c cooler than the climap sea surface temperatures ssts but consistent with recent estimates of both land and sea surface temperature changes subtropical waters are cooled by 2 2 5 c also in agreement with recent estimates the simulated oceanic thermohaline circulation at the lgm is not only shallower but also weaker than the modern with a migration of deep water formation site in the north atlantic as suggested by the paleoceanographic evidences the simulated northward flow of antarctic bottom water aabw is enhanced these deep circulation changes are attributable to the increased surface density flux in the southern ocean caused by sea ice expansion at the lgm both the gulf stream and the kuroshio are intensified due to the overall increase of wind stress over the subtropical oceans the intensified zonal wind stress and southward shift of its maximum in the southern ocean effectively enhances the transport of the antarctic circumpolar current acc by more than 50 simulated ssts are lowered by up to 8 c in the midlatitudes simulated conditions in the north atlantic are warmer and with less sea ice than indicated by climap again in agreement with more recent estimates the increased meridional sst gradient at the lgm results in an enhanced hadley circulation and increased midlatitude storm track precipitation the increased baroclinic storm activity also intensifies the meridional atmospheric heat transport a sensitivity experiment shows that about half of the simulated tropical cooling at the lgm originates from reduced atmospheric concentrations of greenhouse gases

simulation of the climate of 18 000 years bp results for the north american north atlantic european sector and comparison with the geologic record of north america abstract the large ice sheets in north america and europe and the extensive sea ice cover in the north atlantic at the time of the last glacial maximum must have greatly modified the surface temperature patterns and in turn the location and intensity of the surface winds and jet streams a general circulation model was used to simulate the january and july patterns of temperature precipitation and wind for 18 ka bp boundary conditions for the model consisting of ice sheet location and height sea ice location and sea surface temperature were prescribed from climap 1981 the model results are illustrated and described for the north american north atlantic european sector the jet stream splits around the north american ice sheet and the southern branch strengthens considerably compared to present over the southern portion of the united states the sea ice margin of the north atlantic and the southern edge of the european ice sheet geologic evidence principally from north america of wind temperature and moisture conditions is assessed from sand dune and loess records estimates of snowline depression pollen records and lake level studies the geologic evidence is generally compatible with the model simulation