holocene history of fire vegetation and land use from the central pyrenees france located on a mountain pass in the west central pyrenees the col d ech peat bog provides a holocene fire and vegetation record based upon nine 14c ams dates we aim to compare climate driven versus human driven fire regimes in terms of frequency fire episodes distribution and impact on vegetation our results show the mid holocene 8500 5500 cal yr bp to be characterized by high fire frequency linked with drier and warmer conditions however fire occurrences appear to have been rather stochastic as underlined by a scattered chronological distribution wetter and colder conditions at the mid to late holocene transition 4000 3000 cal yr bp led to a decrease in fire frequency probably driven by both climate and a subsequent reduction in human land use on the contrary from 3000 cal yr bp fire frequency seems to be driven by agro pastoral activities with a very regular distribution of events during this period fire was used as a prominent agent of landscape management

palaeo moisture evolution in monsoonal central asia during the last 50 000 years abstract the late quaternary climate history of monsoonal central asia was inferred from 75 palaeoclimatic records which provide information about moisture conditions in the last 50 ka or part of this period wet conditions occurred during middle and late marine isotope stage 3 while the last glacial maximum lgm was characterized by dry climate conditions in the region a stepwise climate amelioration is suggested by the climate records following the lgm several climate signals of this period which were reported from high latitude ice core records are preserved in archives from monsoonal central asia as well during the early holocene high effective moisture was inferred from most records from the area dominated by the indian monsoon e g the tibetan plateau suggesting that holocene optimal climate conditions occurred there during this period in contrast areas which are dominated by the south east asian monsoon se monsoon and the westerlies in north western and north central china mongolia do not uniformly show an early holocene climate optimum for this area optimal conditions prevailed during the mid holocene these apparent contradictions can possibly be explained by the regional uplift and descent of air masses in the holocene during the early holocene strengthened insolation possibly caused an enhanced low level convergence over the tibetan plateau which led to the intensification of the summer monsoon the strong air uplift caused intensified precipitation and air divergence in the upper troposphere over the tibetan plateau the areas adjacent to the north therefore experienced an intensified descent of air masses and consequently increased aridity the majority of the palaeoclimatic records suggest reduced effective moisture since the late holocene in the region

rate of outward growth of the mediterranean ridge accretionary complex abstract the position as a function time of the deformation front on the southwest flank of the mediterranean ridge accretionary complex is constrained as follows 1 a the deformation front is now active 2 b the site of core ban84 05gc was still near the abyssal plain when displaced shallow water benthic foraminifera of inferred african provenance were redeposited within an upper pliocene age unit 3 c the site of core ban84 05gc on the outer flank of the mediterranean ridge was already within the topographically rugged accretionary complex when a pliocene debris flow was emplaced 4 d dsdp site 125 had already been uplifted into a topographically elevated position when lower pliocene pelagic ooze was deposited 5 e a gypsum bearing breccia in dsdp site 125 requires that the site was either on the abyssal plain or within the tectonically active outer perimeter of the accretionary complex during the messinian salinity crisis 6 f dsdp site 377 had already been uplifted into a topographically elevated position when middle miocene age pelagic marl was deposited 7 g dsdp site 377 was still on or near the abyssal plain when early to lower middle miocene age smectite bearing turbidites of inferred african provenance were deposited and 8 h the mediterranean ridge began to grow by offscraping against a backstop formed by the alpine nappes of the hellenic arc at the time that subduction began 33 ma together these constraints define a range of potential growth curves for the mediterranean ridge with a rate of outward growth of approximately 0 5 to 2 cm yr this growth rate is faster than that inferred for most other modern accretionary prisms both as an absolute value and as a fraction of the subduction velocity an unusually thick incoming section and or an unusually weak evaporitic decollement may contribute to the rapid growth rate the inferred age of accretion does not increase linearly with distance from the deformation front rather there is an apparent acceleration of the rate of outward growth through time this observation may reflect a true acceleration of growth rate in response to the onset of back arc extension in the overriding plate aegean sea and or in response to the development of a weak basal decollement following the introduction of halite into the incoming stratigraphic section alternatively the non linearity of the age vs distance curve may indicate that shortening of the offscraped sediments continues across the breadth of the mediterranean ridge rather than being confined to the outer flank

a study of cleaning procedures used for foraminiferal mg ca paleothermometry the various cleaning steps required for preparation of foraminiferal samples for mg ca and sr ca analysis are evaluated for their relative importance and effects on measured elemental ratios it is shown that the removal of silicate contamination is the most important step for the measurement of mg ca ratios in an example bulk sample mg ca decreases from 10 5 to 2 5 mmol mol 1 during clay removal oxidation of organic material causes a lowering of sample mg ca in the order of 10 or approximately 1 c when converted to temperature use of dilute acid leaching to remove adsorbed contaminants causes partial dissolution of the sample carbonate and a corresponding decrease in mg ca reductive treatment also causes dissolution of the sample and a decrease in the mg ca ratio of up to 10 15 sample preparation for sr ca analysis does not require the same degree of rigor as is necessary for mg ca work the within run reproducibility of the method described here for g ruber in a core top sample from the arabian sea was 1 8 mean sample ratio was 4 72 mmol mol 1 when converted to temperature this becomes 28 0 2 c the equivalent result for sr ca was 0 5 mean ratio 1 44 mmol mol 1

from foreland to forearc domains new multichannel seismic reflection survey of the mediterranean ridge accretionary complex eastern mediterranean abstract the mediterranean ridge of the eastern mediterranean sea is a huge accretionary wedge emplaced as a consequence of the africa aegean plate convergence that has a rate estimated at 40 mm yr processing of recent multichannel seismic data and integration with previous results seismic profiling swath bathymetry sonar have facilitated the study of the overall deformation pattern of the area which includes three distinct major structural domains facing various forelands 1 1 the outer domain is bounded southward by the present day wedge toe and towards the north by topographic slope breaks and clear changes in deformational style beneath the ionian and levantine mediterranean ridge branches the base of messinian evaporites seems to act as a major decollement level 2 2 the central or crestal domain the shallowest one shows evidence of mud diapiric and mud volcano activity and is overthrusting northward over the inner domain facing the libyan margin this area which displays spectacular mud volcano fields appears much wider and shallower 3 3 the less deformed inner domain is bounded northward by the hellenic trench system beneath its ionian inner area seismic velocities characteristic of continental crust have been recorded while within its levantine region it is made of a series of disconnected and uplifted basement blocks strabo seamounts along the matapan and pliny trenches structures which could be caused by transpressive deformation are locally observed we believe that both the north south structural arrangement and the clear west east lateral variations of the mediterranean ridge relate to its progressive collision against the libyan margin promontory this event which may have initiated 5 6 myr ago may have induced a a differentiated paleogeography of messinian evaporites later available for tectonic accretion leading to the further lateral structural variations of the outer domain and b strain partitioning between the central mediterranean ridge and the hellenic trench system

postglacial vegetation and fire history eastern klamath mountains california usa pollen and high resolution charcoal data from bluff lake and crater lake california indicate simi lar changes in climate vegetation and fire history during the last 15 500 years pollen data at bluff lake suggest that the vegetation between c 15 500 and 13 100 cal bp consisted of subalpine parkland with scattered pinus and abies after 13 100 cal bp a relatively closed forest of p monticola p contorta and abies developed and fire event frequency was low the inferred climate then was cooler and wetter than present pinus and quercus vaccinifoliadominated at both sites during the early holocene when conditions were warm and dry as climate became wetter and cooler in the late holocene abies spp at both sites and tsuga mertensi ana at crater lake increased in importance displacing pinus and quercus the two lake records have similar trends in fire history with high event frequencies at c 8400 4000 and 1000 cal bp and low values at c 4800 cal bp the fire and vegetation history at both sites suggests a similar response to large scale changes in climate during the holocene

holocene fire history in eastern monsoonal region of china and its controls abstract for the first time we synthesized the fire history for the eastern monsoonal region of china during the holocene through the combined analyses of paleofire indices including both charcoal and black carbon records from 14 localities available at present our results show that in eastern china fire activity was relatively higher before 9500 cal yr bp very low between 9500 and 7500 cal yr bp and evidently increased since 7500 cal yr bp reaching its maximum at about 2000 cal yr bp this general pattern of fire activity closely follows the holocene effective moisture evolution in the eastern monsoonal china at an orbital timescale i e more fires occurred during drier conditions while less fire occurred during more humid conditions these results suggest that the fire activity in eastern china were primarily driven by climate changes i e variations of past moisture conditions and monsoon related changes in vegetation communities ultimately forced by the northern hemisphere insolation nhi on orbital timescales over the holocene our data also show that the fire activity increased concurrently with significant human development from the mid to late holocene possibly suggesting an intensified trend of human induced fire activities since about 7500 years ago moreover the fire activity in eastern china closely parallels the atmospheric co2 concentration inferred from antarctica ice cores our synthesis will help to better understand the relationship between fire climate and human activity at a variety of geographical scales

paleogene calcite compensation depth in the eastern subtropical pacific answers and questions 1 ocean drilling program leg 199 drilled a north south transect across the eocene paleoequator in the eastern pacific permitting reconstruction the calcite compensation depth ccd since earliest eocene time the ccd was relatively shallow near the early eocene pacific equator 3200 m and unlike modern latitudinal ccd gradients deepened to the north to 3600 m paleolatitude 10 n at 41 ma the ccd underwent a brief sharp transient deepening of 700 m then remained shallow until the eocene oligocene boundary at the e o boundary the ccd deepened by 1200 m in less than 300 kyr this rapid deepening served to more than double the area of seafloor subject to caco3 deposition sea level fall associated with ice volume buildup and ensuing shelf basin fractionation is unlikely to be the sole cause of the increased deep ocean caco3 burial rather a sudden rapid increase in the amount of ca entering the ocean appears necessary to explain the observations

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

the structure of the kythira antikythira strait offshore sw greece 35 7 36 6 n the kythira antikythira strait within the sw hellenic arc forms a 100 km long nnw sse trending ridge between peloponnesus and crete and represents the submarine continu ation of the hellenic alpine belt in order to present the shallow as well as the deeper structure of kythira antikythira strait we studied five seismic sections oriented either parallel or perpendicu lar to the inner part of the hellenic arc this information was complemented with velocity analyses from a dense network of seismic lines and information concerning the bathymetry contractional structures recognized on the seismic profiles indicate that this part of the gavrovo tripolitza geo tectonic zone was involved in the miocene shortening related to the westward propagation of the hellenic fold and thrust system east dipping thrust faults which root in the top of the crystalline basement were identified on the seismic profiles the deepest reflector identified on the profiles cor responds to the crystalline basement shallower reflectors include those corresponding to the con tacts between the mesozoic miocene upper miocene lower pliocene and pliocene pleistocene sedimentary sequences the upper cenozoic to quaternary sequence rests unconformably upon mesozoic carbonates messinian intrusions forming small scale domes deform the pliocene quaternary sedimentary succession west and east dipping normal faults were also recognised both within the palaeozoic and cenozoic successions and are related to regional extension during sedimentation

atmospheric carbon dioxide through the eocene oligocene climate transition geological and geochemical evidence1 2 3 indicates that the antarctic ice sheet formed during the eocene oligocene transition4 33 5 34 0 million years ago modelling studies5 6 suggest that such ice sheet formation might have been triggered when atmospheric carbon dioxide levels fell below a critical threshold of 750 p p m v but the timing and magnitude of relative to the evolution of the ice sheet has remained unclear here we use the boron isotope ph proxy7 8 on exceptionally well preserved carbonate microfossils from a recently discovered geological section in tanzania9 10 to estimate before during and after the climate transition our data suggest that a reduction in occurred before the main phase of ice growth followed by a sharp recovery to pre transition values and then a more gradual decline during maximum ice sheet growth was between 450 and 1 500 p p m v with a central estimate of 760 p p m v the ice cap survived the period of recovery although possibly with some reduction in its volume implying as models predict11 a nonlinear response to climate forcing during melting overall our results confirm the central role of declining in the development of the antarctic ice sheet in broad agreement with carbon cycle modelling12 and help to constrain mechanisms and feedbacks associated with the earth s biggest climate switch of the past 65 myr

the geometry and rates of microplate motions in the eastern mediterranean sea quantitative constraints by using anoxic basins as piercing points abstract anoxic conditions encountered in small basins on the flanks of the mediterranean ridge are due to the formation of brine pools caused by exposure of messinian evaporites seismic reflection profiles and structural data indicate young active strike slip faulting and thrusting due to collision between microplates to be responsible for the continued isolation of the basins an estimate of 100 000 years for the age of initiation of the tyro and kretheus basins using a finite microplate rotation model for the central and eastern mediterranean sea is in close agreement with coring results in the kretheus basin rates of relative motion with respect to africa of more than 8 cm a 1 along the western strabo trench are supported by these results this study indicates that regional deformation resulting from active plate convergence appears to bear a simple relation to a few finite rotation poles for relative movement between plates and microplates

structural sketch of the hellenic continental margin between the western peloponnesus and eastern crete a structural sketch of the hellenic continental margin and adjacent areas based on numerous seismic profiles obtained in the past few years shows two distinct structural domains an inner extensional domain characterizes most of the continental margin the offshore regions as well as the cretan sea an outer compressional domain extends over the trenches and part of their outer slope we believe that this perplexing pattern is related to the presence of an underlying evaporitic series progressively deformed and piling up against a resistant continental margin the completion of subduction and subsequent continental collision are also involved in this structural framework

a fluid model for the shape of accretionary wedges in this paper the accretionary wedges landward of most oceanic trenches are modelled assuming a newtonian fluid rheology it is shown that lubrication theory is applicable and that the addition of material to the wedges can be neglected in determining the shape of the wedges the predicted shape of the wedges is in good agreement with bathymetric profiles across the kurile ryukyu and aleutian wedges from the shape of the above wedges it is deduced that accretionary sediments have viscosities between 1018 and 1019 poise

a continuous record of fire covering the last 10 500 calendar years from southern sweden the role of climate and human activities a high resolution continuous 10 500 cal yrs long macroscopic charcoal record from a peat and lake sediment deposit at storasjo in the hemiboreal vegetation zone of southern sweden is presented

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

asynchronous marine terrestrial signals of the last deglacial warming in east asia associated with low and high latitude climate changes a high resolution multiproxy record including pollen foraminifera and alkenone paleothermometry obtained from a single core dg9603 from the okinawa trough east china sea ecs provided unambiguous evidence for asynchronous climate change between the land and ocean over the past 40 ka on land the deglacial stage was characterized by rapid warming as reflected by paleovegetation and it began ca 15 kabp consistent with the timing of the last deglacial warming in greenland however sea surface temperature estimates from foraminifera and alkenone paleothermometry increased around 20 19 kabp as in the western pacific warm pool wpwp sea surface temperatures in the okinawa trough were influenced mainly by heat transport from the tropical western pacific ocean by the kuroshio current but the epicontinental vegetation of the ecs was influenced by atmospheric circulation linked to the northern high latitude climate asynchronous terrestrial and marine signals of the last deglacial warming in east asia were thus clearly related to ocean currents and atmospheric circulation we argue that i early warming seawater of the wpwp driven by low latitude insolation and trade winds moved northward via the kuroshio current and triggered marine warming along the ecs around 20 19 kabp similar to that in the wpwp and ii an almost complete shutdown of the atlantic meridional overturning circulation ca 18 15 kabp was associated with cold heinrich stadial 1 and delayed terrestrial warming during the last deglacial warming until ca 15 kabp at northern high latitudes and hence in east asia terrestrial deglacial warming therefore lagged behind marine changes by ca 3 4 ka

temporally constant quaternary uplift rates and their relationship with extensional upper plate faults in south crete greece constrained with 36cl cosmogenic exposure dating in order to investigate how active upper plate faults in crete influence uplift above the hellenic subduction zone we mapped deformed late quaternary marine terraces along 17 profiles across strike of the south central crete fault sccf identified and dated palaeoshorelines using in situ 36cl exposure dating on wave cut platforms correlated them with the quaternary sea level curve and calculated uplift rates we identified 16 distinct palaeoshorelines from field observations and study of digital elevation models dems located along the footwall and hangingwall of the sccf and the footwall of the offshore ptolemy trench fault cosmogenic dating constrains the ages of three palaeoshorelines as 76 100 and 125 ka we use these dates to guide a correlation of other mapped palaeoshorelines with quaternary sea level highstands between 200 and 980 ka with results implying that the uplift rate is constant through time at each of the 17 profile locations elastic half space modelling implies that uplift in both the hangingwall and footwall of the sccf is influenced by uplift related to offshore upper plate faults in addition to background regional uplift perhaps from the subduction interface by correlating palaeoshorelines across the active south central crete fault we derive a throw rate of 0 41 mm yr for this fault which can also be expressed as a slip rate of 0 58 mm yr the fault specific earthquake recurrence interval assuming repetition of 1 1 m slip events is approximately 2700 years for the sccf

millennial scale variability in biomass burning covering the interval 41 000 7050 cal bp in the tropical leizhou peninsula south china abstract here we present a well dated terrestrial charcoal chronology covering the interval 41 000 7050 cal bp and identifying the millennial scale variability in biomass burning for the tropical leizhou peninsula south china our results show that changes in biomass burning closely followed regional temperature and precipitation variations on orbital timescales i e more biomass burning occurred during the warm wet marine isotope stage mis 3 and less biomass burning occurred during the cold dry mis 2 superimposed on this general trend our charcoal record shows millennial scale variability in biomass burning corresponding to the rapid climate changes associated with dansgaard oeschger d o cycles i e biomass burning increased during d o warming events whereas biomass burning decreased during intervals of rapid cooling terminated by heinrich events during the cooler drier periods low biomass burning can be explained by the decline of vegetation productivity whereas the warmer wetter periods are characterized by higher biomass burning related to increasing fuel availability therefore climate control can be considered as the major forcing factor of biomass burning from 41 000 7050 cal bp on both orbital and millennial timescales in the northern leizhou peninsula

changes in fire regimes since the last glacial maximum an assessment based on a global synthesis and analysis of charcoal data fire activity has varied globally and continuously since the last glacial maximum lgm in response to long term changes in global climate and shorter term regional changes in climate vegetation and human land use we have synthesized sedimentary charcoal records of biomass burning since the lgm and present global maps showing changes in fire activity for time slices during the past 21 000 years as differences in charcoal accumulation values compared to pre industrial there is strong broad scale coherence in fire activity after the lgm but spatial heterogeneity in the signals increases thereafter in north america europe and southern south america charcoal records indicate less than present fire activity during the deglacial period from 21 000 to 11 000 cal yr bp in contrast the tropical latitudes of south america and africa show greater than present fire activity from 19 000 to 17 000 cal yr bp and most sites from indochina and australia show greater than present fire activity from 16 000 to 13 000 cal yr bp many sites indicate greater than present or near present activity during the holocene with the exception of eastern north america and eastern asia from 8 000 to 3 000 cal yr bp indonesia and australia from 11 000 to 4 000 cal yr bp and southern south america from 6 000 to 3 000 cal yr bp where fire activity was less than present regional coherence in the patterns of change in fire activity was evident throughout the post glacial period these complex patterns can largely be explained in terms of large scale climate controls modulated by local changes in vegetation and fuel load

a late pleistocene and holocene vegetation and environmental record from shuangchi maar hainan province south china abstract shuangchi is a maar in the volcanic province of tropical northern hainan island south china a radiocarbon dated record of pollen charcoal organic carbon and some fossil algae provides a discontinuous record from its sediments covering the last 20 000 years the fossil record is broken in places by abrupt pulses of inorganic material washed into the basin from the crater walls presumably during periods of high magnitude storms last glacial maximum was marked by forest but with a high component of grassland suggesting a drier and cooler climate than today forest recovery was rapid from about 9500 years ago and a peak in tropical rainforest taxa persisted until about 5000 years ago and this appears to represent peak warming in the region from about 5000 years ago until present there is evidence of human impact and fire was a tool used to clear forest the human impact signal varies across hainan which suggests that the level of human resource use was localised at least for several millennia human impact signals appear to be widespread from about 2000 years ago

holocene wildfires related to climate and land use change over the weihe river basin china abstract charcoal particles preserved in the loess palaeosol profiles provide records of wildfires during the holocene total organic carbon magnetic susceptibility and charcoal analysis and osl dating were carried out in the holocene loess palaeosol profiles at two sites in the weihe river basin the analytical results show that natural wildfires occurred frequently during the last glaciation when climate was dominated by northwest continental monsoon and steppe vegetation expanded southerly to the weihe river basin wildfire occurrence decreased during climatic amelioration in the early holocene during the holocene climatic optimum between 8500 b p and 3100 b p natural wildfire occurrence was reduced greatly pedogenic alteration to the accumulated dust was intensified because of the humid warm climate brought on by southeast maritime monsoon localized fire events in connection with human activities of the neolithic occurred in several episodes over the region during the late holocene when climate become drier wildfire occurrence over the upland hills shows a pattern different from that in the guanzhong basin over the upland hills in the north charcoal concentrations show a decreasing trend in the recent loess and topsoil it indicates infrequent biomass burning during the last 3100 years this is attributable to nomadic occupation of the loess hills during the bronze age and the development of a land use pattern of livestock farming in most part of the history over the loess tableland in the guanzhong basin in the south abruptly increased charcoal concentrations in the recent loess and topsoil show very high level of biomass burning this is attributable to the increasingly intensified land reclamation for cereal cultivation from the bronze age this study provides new insights into wildfires over the semi arid and sub humid regions in connection with climate and land use change

the prina complex in eastern crete and its relationship to possible miocene strike slip tectonics abstract the basal neogene formations in the ierapetra region eastern crete are strongly influenced by a late serravallian tectonic phase which resulted in the breakup of pre existing palaeogeographic patterns important vertical movements caused the southward emplacement of neogene sediments together with parts of the underlying pre neogene nappe pile the resulting chaotic association of exotic blocks and sediments known as the prina complex has the properties of a sedimentary melange it can be traced for more than 15 km from north to south in the north a relatively coherent accumulation of large slide masses overlies deformed neogene coarse clastics and pre neogene rocks distally it comprises a poorly stratified sequence of breccias and intermixed finer grained sediments which locally contains olistostromes and debris flows and interfingers to the south with submarine fan deposits the intricate relation of faulting and gravity sliding in a rapidly subsiding basin can be explained by generation in a strike slip setting it is suggested that the ierapetra basin and its offshore extension the south cretan trough were initiated by sinistral movements along a ne sw oriented fault zone implications of this model for the geodynamic evolution of the south aegean area are discussed

eocene oligocene ocean de acidification linked to antarctic glaciation by sea level fall one of the most dramatic perturbations to the earth system during the past 100 million years was the rapid onset of antarctic glaciation near the eocene oligocene boundary some 34 million years ago this climate transition was accompanied by a deepening of the calcite compensation depth the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution but the mechanism linking glaciation to the deepening of calcite compensation depth remains unclear merico et al use a global biogeochemical box model to test competing hypotheses put forward to explain the eocene oligocene transition they find that only shelf to deep sea carbonate partitioning can explain the observed changes in both carbon isotope composition and calcium carbonate accumulation at the sea floor this work sheds new light on the mechanisms linking glaciation and ocean acidity change during this important climate transition a global biogeochemical box model is used to test competing hypotheses put forward to explain the eocene oligocene transition it is found that only shelf to deep sea carbonate partitioning is capable of explaining the observed changes in both carbon isotope composition and calcium carbonate accumulation at the sea floor this work sheds new light on the mechanisms linking glaciation and ocean acidity change across the climate transition of the cenozoic one of the most dramatic perturbations to the earth system during the past 100 million years was the rapid onset of antarctic glaciation near the eocene oligocene epoch boundary1 2 3 34 million years ago this climate transition was accompanied3 by a deepening of the calcite compensation depth the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution changes in the global carbon cycle4 rather than changes in continental configuration5 have recently been proposed as the most likely root cause of antarctic glaciation but the mechanism linking glaciation to the deepening of calcite compensation depth remains unclear here we use a global biogeochemical box model to test competing hypotheses put forward to explain the eocene oligocene transition we find that of the candidate hypotheses only shelf to deep sea carbonate partitioning is capable of explaining the observed changes in both carbon isotope composition and calcium carbonate accumulation at the sea floor in our simulations glacioeustatic sea level fall associated with the growth of antarctic ice sheets permanently reduces global calcium carbonate accumulation on the continental shelves leading to an increase in pelagic burial via permanent deepening of the calcite compensation depth at the same time fresh limestones are exposed to erosion thus temporarily increasing global river inputs of dissolved carbonate and increasing seawater 13c our work sheds new light on the mechanisms linking glaciation and ocean acidity change across arguably the most important climate transition of the cenozoic era

a 400 000 year record of vegetational and climatic changes from a volcanic basin leizhou peninsula southern china abstract the tianyang lake in leizhou peninsula is an enclosed crater formed during the early to middle pleistocene over 200 m of diatomaceous mud and clay were deposited in the last 400 000 years providing a continuous middle and late quaternary lacustrine sequence for paleoenvironmental studies the pollen record spans the last four glacial interglacial cycles equivalent to oxygen isotope stages ois 10 to 1 during most of the glacial phases fagaceous monsoon forest was replaced by altitudinal vegetation indicating a regional landscape transformation on the peninsula the montane forest reached down to the lowland by at least 600 m during the ois 6 and 8 in a cool and relatively wet condition with temperature estimated to be more than 4 c lower than present a further lowering of the montane forest belts by about 800 1000 m occurred in the ois 4 2 as implied by the appearance of many temperate elements during the last glacial maximum this mixed forest subsequently gave way to the poaceae grassland a savanna vegetation type favored by drier and cooler climatic conditions this drastic change implies a more significant drop in temperature and precipitation than the previous three glacial periods ois 10 8 and 6 it is thus inferred that the weakening of summer monsoon was more significant towards the end of the late pleistocene particularly during the last glacial maximum lgm

postglacial vegetation climate and fire history along the east side of the andes lat 41 42 5 s argentina abstract the history of the low elevation forest and forest steppe ecotone on the east side of the andes is revealed in pollen and charcoal records obtained from mid latitude lakes prior to 15 000 cal yr bp the vegetation was characterized by steppe vegetation with isolated stands of nothofagus the climate was generally dry and the sparse vegetation apparently lacked sufficient fuels to burn extensively after 15 000 cal yr bp a mixture of nothofagus forest and shrubland steppe developed fire activity increased between 13 250 and 11 400 cal yr bp contemporaneous with a regionally defined cold dry period huelmo mascardi cold reversal the early holocene period was characterized by an open nothofagus forest shrubland mosaic and fire frequency was high in dry sites and low in wet sites the data suggest a sharp decrease in moisture eastward from the andes a shift to a surface fire regime occurred at 7500 cal yr bp at the wet site and at 4400 cal yr bp at the dry site preceding the expansion of austrocedrus by 1000 1500 yr the spread of austrocedrus is explained by a shift towards a cooler and wetter climate in the middle and late holocene the change to a surface fire regime is consistent with increased interannual climate variability and the onset or strengthening of enso the present day mixed forest dominated by nothofagus and austrocedrus was established in the last few millennia

calibration of mg ca thermometry in planktonic foraminifera from a sediment trap time series 1 paired mg ca and 18o measurements on planktonic foraminiferal species g ruber white g ruber pink g sacculifer g conglobatus g aequilateralis o universa n dutertrei p obliquiloculata g inflata g truncatulinoides g hirsuta and g crassaformis from a 6 year sediment trap time series in the sargasso sea were used to define the sensitivity of foraminiferal mg ca to calcification temperature habitat depths and calcification temperatures were estimated from comparison of 18o of foraminifera with equilibrium calcite based on historical temperature and salinity data when considered together mg ca mmol mol of all species except two show a significant r 0 93 relationship with temperature t c of the form mg ca 0 38 0 02 exp 0 090 0 003 t equivalent to a 9 0 0 3 change in mg ca for a 1 c change in temperature small differences exist in calibrations between species and between different size fractions of the same species o universa and g aequilateralis have higher mg ca than other species and in general data can be best described with the same temperature sensitivity for all species and pre exponential constants in the sequence o universa g aequilateralis g bulloides g ruber g sacculifer other species this approach gives an accuracy of 1 2 c in the estimation of calcification temperature the 9 sensitivity to temperature is similar to published studies from culture and core top calibrations but differences exist from some literature values of pre exponential constants different cleaning methodologies and artefacts of core top dissolution are probably implicated and perhaps environmental factors yet understood planktonic foraminiferal mg ca temperature estimates can be used for reconstructing surface temperatures and mixed and thermocline temperatures using g ruber pink g ruber white g sacculifer n dutertrei p obliquiloculata etc the existence of a single mg thermometry equation is valuable for extinct species although use of species specific equations will where statistically significant provide more accurate evaluation of mg ca paleotemperature

the pliny strabo trench region a large shear zone resulting from slab tearing the eastern part of the hellenic subduction zone is composed of the pliny and strabo trenches that have been regarded as a zone of convergence between the subducting african lithosphere and the overriding anatolian aegean plate in the pliny and strabo trenches the oblique relative plate motion is generally thought to be accommodated by a typical strain partitioning consisting of strike slip and convergence components notwithstanding the occurrence of strike slip motion parallel with the pliny strabo trenches trench normal thrusting is not observed so far therefore we conducted a detailed analysis to investigate the deformation mechanisms of the eastern part of the hellenic trench system our analyses of offshore faulting and mechanisms of earthquakes in the overriding aegean lithosphere show that the region of the pliny and strabo trenches obeys the mechanics of the sinistral shear zone model of tchalenko 1970 we propose that the trench perpendicular convergence is taken up by the rhodes fold and thrust belt which has been postulated off the southeast coast of rhodes several regional p wave tomography results give indications of a slow seismic anomaly under this zone which is interpreted as a tear between the hellenic and cyprus subduction zones the primary reason for such tear and its propagation is the ongoing rollback of the subducted part of the african lithosphere also referred to as the aegean slab our work elucidates the surface expression of this tearing process in the form of the development of a shear zone between the aegean lithosphere in the nw and the african lithosphere in the se the pliny strabo shear zone

natural and anthropogenic forest fires recorded in the holocene pollen record from a jinchuan peat bog northeastern china abstract pollen and charcoal particles from a jinchuan peat northeastern china were examined to investigate the fire origin and interaction between climate vegetation fire and human activity during the holocene pollen results show that i a broadleaved deciduous forest was dominant during the early holocene ii from 5500 cal yr b p there was a gradual increase in coniferous trees mainly pinus and a decrease in broadleaved deciduous trees e g quercus juglans and ulmus zelkova iii after 4200 cal yr b p the deciduous forest was replaced by a mixed forest of coniferous and deciduous trees iv coniferous trees including pinus abies and picea further increased after 2000 cal yr b p reflecting a cooler and drier climate after 5500 4200 cal yr b p two layers of abundant microfossil charcoal particles 250 10 m and the coexistence of macrofossil particles 2 mm suggest two local fires fire event 1 5120 66 cal yr b p and fire event 2 1288 8 cal yr b p ad 662 8 charcoal layer 1 with a large amount of monolete psilate spores is superimposed on the long term trend of vegetation changes indicating a natural origin for fire event 1 that was probably facilitated by drying environmental conditions since the mid holocene cerealia type pollen and a low percentage of monolete psilate spores were observed in charcoal layer 2 indicating that fire event 2 was caused by clearing we suggest that fire event 2 may be related to the spread of the han farming culture accompanied by the territorial expansion of the tang dynasty to the studied area in ad 668

changes in c3 and c4 plant abundances reflect climate changes from 41 000 to 10 000yr ago in northern leizhou peninsula south china abstract organic carbon stable isotopes 13 c org have been widely used to estimate past c 3 and c 4 vegetation changes as the relative abundance of c 3 and c 4 plants can normally be affected by multiple factors including atmospheric co 2 concentrations acc and climatic conditions e g temperature aridity the relative importance of these factors is still debated and may differ greatly in different regions by using the 13 c org records from a peat sequence in the tropical leizhou peninsula south china we estimate the past c 3 and c 4 plant abundances ccpa from 41 000 cal bp to 10 000 cal bp the results indicate that lower 13 c org values and thus more c 3 plants generally occurred during marine isotope stage 3 mis 3 whereas higher 13 c org values and thus more c 4 plants generally occurred during mis 2 moreover several short positive excursions of 13 c org records indicating expansions of c 4 plants also occurred corresponding with the known yd and h1 h4 events in high latitudes we conclude that the ccpa in northern leizhou peninsula is mainly controlled by precipitation which in turn is associated with the east asian summer monsoon easm intensity both on orbital time scales and suborbital time scales the acc may have slightly affected the long term variation trend of ccpa on orbital time scales it is likely that the temperature threshold which is normally an important factor in high latitudes may have less important influence on the ccpa in tropical south china our results provide the quantitative estimations of ccpa from the tropical leizhou peninsula and more studies are necessary in low latitudes to examine possible connections between past vegetation changes and potential controlling factors on shorter timescales

charcoal records of fire history in the holocene loess soil sequences over the southern loess plateau of china abstract charcoal preserved in accretionary loess soil profiles within the southern part of the loess plateau has recorded fire history and landscape evolution connected with climatic variations and human activities local wildfires occurred frequently during the late last glacial period and the early holocene before 8500 years bp when steppe vegetation expanded from the inner mongolian plateau southerly over the loess plateau during the holocene climatic optimum between 8500 years bp and 3100 years bp natural wildfires were largely reduced pedogenesis of the luvisols and isohumisols was intensified because of the increased monsoonal precipitation and soil moisture localized fires in connection with human activities occurred in different patterns at the study sites fire seems to have been applied to vegetation clearance for land reclamation for millet cultivation at many places during the neolithic and early bronze age levels of biomass burning were very high during the late holocene when the climate became drier and historical land use became more intensive at some sites the intensity of human disturbance by fire and cultivation increased continuously during the last 3100 years at the other sites local fires occurred most frequently between 3100 years bp and 1500 years bp during the major period of land reclamation for cereal cultivation human burning of the landscape has been reduced since then

the neotectonics of the aegean an alternative view minor reverse faults in widely dispersed neogene outcrops in the central aegean have led several people to suggest that the regional extension which started in the lower pliocene or earlier was interrupted by short periods of compression the durations of these postulated compressional episodes are short compared to the time scale on which convective forces acting on the base of the lithosphere can change thus possible mechanisms for driving such motions are limited in this paper we offer alternative explanations for these observations and in particular show that these apparently compressional episodes are probably not regional in extent and may not be truly compressional in origin in some places they are more likely to be a consequence of the considerable rotation that is found in extensional terranes the plio quaternary paleogeography of the central aegean is satisfactorily explained by uplift in the footwall blocks of normal faults and does not require regional compression studies of the faulting associated with recent large earthquakes suggest that the sort of microtectonic analysis which is typically carried out on small faults in surficial sediments is more likely to reflect the internal deformation of blocks bounded by major fault structures than be a reliable indicator of regional stress patterns

active faults deformation rates and quaternary paleogeography at kyparissiakos gulf sw greece deduced from onshore and offshore data abstract kyparissiakos gulf forms a 45 km long zone located at 70 80 km east from the hellenic trench with a general direction nnw sse onshore studies show the existence of several neotectonic horsts and grabens bounded by e w trending normal faults thrust sheets of the underlying hellenides crop out within the horst areas and younger sediments mostly lower pleistocene have been deposited in the grabens the age of the marine sediments is mostly lower pleistocene throw rate on the normal faults varies between 0 7 and 1 0 mm yr accommodating extension in the n s direction subsidence rates during early pleistocene are between 0 1 and 0 3 mm yr whereas uplift rates during middle pleistocene present are between 0 18 and 0 50 mm yr offshore data were obtained using bathymetric and air gun litho seismic profiles the shelf has been disrupted by active faults with several meters of throw average holocene throw rates are 0 4 0 6 mm yr but in some areas adjacent filiatra and olympia values greater than 3 mm yr are detected holocene and upper pleistocene marine sediments thicken gradually to the north as do the marine lower pleistocene sediments onshore a nnw sse offshore longitudinal fault parallel to the kyparissiakos coast with throw rate above 3 mm yr is the dividing structure between the uplifted coastal area and the present day gulf this indicates a major change in paleogeography between early and middle pleistocene present day transition from e w compression in the hellenic trench to e w extension in the kyparissiakos gulf and to n s extension in western peloponnesus is discussed the development of e w structures in western peloponnesus since latest pliocene may be related to the central hellenic shear zone which accommodates differential gps rates between northern greece and southern peloponnesus

a high resolution absolute dated late pleistocene monsoon record from hulu cave china oxygen isotope records of five stalagmites from hulu cave near nanjing bear a remarkable resemblance to oxygen isotope records from greenland ice cores suggesting that east asian monsoon intensity changed in concert with greenland temperature between 11 000 and 75 000 years before the present yr b p between 11 000 and 30 000 yr b p the timing of changes in the monsoon as established with 230th dates generally agrees with the timing of temperature changes from the greenland ice sheet project two gisp2 core which supports gisp2 s chronology in this interval our record links north atlantic climate with the meridional transport of heat and moisture from the warmest part of the ocean where the summer east asian monsoon originates

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

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

the pliny and strabo trenches eastern mediterranean integration of seismic reflection data and seabeam bathymetric maps abstract data from a recent seismic reflection survey which covers a segment of the south hellenic trench system comprising the pliny and strabo trenches are compared with older seismic data and morphostructural interpretations of surface structures detected on seabeam maps the pliny trench consists of an en echelon series of elongated depocenters whose geometry reflects left lateral transform motion along the trench axis continental rocks form the alpine basement of late cenozoic deposits on both sides of the pliny trench and are locally outcropping along the steep walls thus deformation takes place within the aegean continental margin which demonstrates that former or present day subduction along this trench is improbable inclined older seismic horizons observed in the trench wall are interpreted to result from rotational deformation along listric normal faults the strabo trench which appears to be extending to the southwest is characterized by discontinuous highly disturbed sedimentary basins the plateau situated in between the pliny and strabo trenches is less affected by normal faulting and incorporates sedimentary basins arcuate swells of diapiric origin and culminations of continental rocks the presence of faulted crustal rocks of the south aegean continental margin in the south hellenic trenches supports recent views on the geodynamics of the eastern mediterranean the thinned continental margin can be interpreted to function as a crustal wedge in the deformation zone at the african eurasian convergent boundary leading to the formation of an accretionary prism of tectonized sediments the mediterranean ridge

heinrich events massive late pleistocene detritus layers of the north atlantic and their global climate imprint 1 millennial climate oscillations of the glacial interval are interrupted by extreme events the so called heinrich events of the north atlantic their near global footprint is a testament to coherent interactions among earth s atmosphere oceans and cryosphere on millennial timescales heinrich detritus appears to have been derived from the region around hudson strait it was deposited over approximately 500 250 years several mechanisms have been proposed for the origin of the layers binge purge cycle of the laurentide ice sheet jokulhlaup activity from a hudson bay lake and an ice shelf buildup collapse fed by hudson strait to determine the origin of the heinrich events i recommend 1 further studies of the timing and duration of the events 2 further sedimentology study near the hudson strait and 3 greater spatial and temporal resolution studies of the layers as well as their precursory intervals studies of previous glacial intervals may also provide important constraints

the gamburtsev mountains and the origin and early evolution of the antarctic ice sheet the manner in which the antarctic ice sheet first formed at a time of rapid global climate change about 34 million years ago has been the subject of considerable speculation several lines of evidence point to central antarctic mountain ranges as the site of the initial ice sheet but our knowledge of the present ice sheet topography is highly restricted in the very zone where ice sheet initiation is most likely along the subglacial gamburtsev mountain range at the centre of the present ice sheet now a detailed survey and analysis of the morphology of the gamburtsev mountains has been performed based on an ice penetrating radar study conducted over two seasons the data reveal a mountain landscape initially incised by rivers then over deepened by ice movement the topography beneath up to 3 000 metres of ice resembles an exploded version of classic alpine valley topography and seems to have developed more than 34 million years ago when mean summer temperatures were about 3 c the nature of initial glaciation on antarctica about 34 million years ago is a mystery results from an intensive radar survey now show that the gamburtsev mountains at dome a at the centre of the present ice sheet were initially incised by rivers and then subsequently overdeepened by ice movement this is suggestive of topographical development before 34 million years ago when mean summer temperatures were about 3 c ice sheet development in antarctica was a result of significant and rapid global climate change about 34 million years ago1 ice sheet and climate modelling suggest reductions in atmospheric carbon dioxide less than three times the pre industrial level of 280 parts per million by volume that in conjunction with the development of the antarctic circumpolar current led to cooling and glaciation paced by changes in earth s orbit2 based on the present subglacial topography numerical models point to ice sheet genesis on mountain massifs of antarctica including the gamburtsev mountains at dome a the centre of the present ice sheet2 3 our lack of knowledge of the present day topography of the gamburtsev mountains4 means however that the nature of early glaciation and subsequent development of a continental sized ice sheet are uncertain here we present radar information about the base of the ice at dome a revealing classic alpine topography with pre existing river valleys overdeepened by valley glaciers formed when the mean summer surface temperature was around 3 c this landscape is likely to have developed during the initial phases of antarctic glaciation according to antarctic climate history estimated from offshore sediment records the gamburtsev mountains are probably older than 34 million years and were the main centre for ice sheet growth moreover the landscape has most probably been preserved beneath the present ice sheet for around 14 million years

deposition models for chronological records abstract long term sedimentary sequences provide a wealth of useful information for research into the palaeo environment especially in relation to past climate change shorter records provide similar information in many archaeological contexts however if such records are to be used to provide precise timing of events and more critically the relative timing between different records methods are needed to provide accurate and precise age depth models for these sequences given the imprecision of individual calibrated radiocarbon determinations it is necessary to use the information we have about the deposition process to refine our chronologies and also to provide interpolation between dated levels in any sequence even with layer counted chronologies the uncertainties are sometimes hard to quantify this paper outlines a range of bayesian models for deposition which have been implemented in the computer programme oxcal these models can be used to combine information from the sediments themselves with radiocarbon or other direct dating information such models have the potential to integrate information between different records and provide a coherent chronology on which to base environmental or archaeological research