eolian deposition in the northeast pacific ocean cenozoic history of atmospheric circulation the mass accumulation rate and grain size distribution of the total eolian component of north pacific pelagic clays have been used to evaluate changes in eolian sedimentation and in the intensity of atmospheric circulation that have occurred during the past 70 m y eolian deposition was relatively low approximately 12 mg cm2 1 000 yr in the late cretaceous and paleocene reflecting an increasingly humid environment a peak in accumulation rates across the paleocene eocene boundary may be the result of episodic volcanism in mexico a sharp decrease in grain size across the paleocene eocene boundary is not readily interpreted fine eolian grain size and the low accumulation rates averaging 8 mg cm2 1 000 yr in the eocene and early oligocene are in agreement with low early tertiary thermal gradients and less vigorous atmospheric circulation large increases in grain size between 37 and 30 m y ago 20 and 10 m y ago and 5 m y ago to the present suggest that atmospheric circulation intensified by a factor of 1 5 1 8 and 1 4 respectively at these times eolian accumulation rates increased from 8 mg cm2 1 000 yr at the eocene oligocene boundary to approximately 25 mg cm2 1 000 yr at the end of the miocene with significant changes at 25 and 13 m y ago increased rates about 25 m y ago probably reflect movement of the core site into the influence of the westerlies and the increase 13 m y ago appears to be a response to steepening thermal gradients and intensifying atmospheric circulation resulting from major expansion of antarctic ice in the mid miocene along with a general increase in global aridity in the late cenozoic an order of magnitude increase in eolian accumulation rates 25 to 226 mg cm2 1 000 yr in pliocene pleistocene time coincides with the onset of northern hemisphere glaciation and consequent climatic deterioration the large increase in accumulation rates in pliocene pleistocene time coincides with a relatively smal increase in the intensity of atmospheric circulation compared to that in oligocene and miocene time suggesting that the increased deposition rates were the result of an increase in global aridity in glacial times rather than a further increase in the vigor of the global wind systems

geostatistical characterization of snow depth structures on sea ice near point barrow alaska a contribution to the amsr ice03 field validation campaign the objective of this paper is to characterize spatial properties of snow depth structures and their role as indicators of sea ice properties and sea ice morphogenetic processes and to provide quantitative measures of sea ice properties that may be utilized in analyses of passive microwave data snow depth data collected near point barrow alaska as part of the amsrice03 field validation campaign for advanced microwave scanning radiometer amsr e sea ice products from nasa earth observing systems satellite aqua are analyzed and compared to p 3 polarimetric scanning radiometer psr data a proxy for amsr e brightness temperatures the approach taken in the analysis is geostatistical characterization various functions of first and second order are calculated for the snow depth profiles then geostatistical classification parameters are extracted and combined into feature vectors on which the characterization is based the complexity of sea ice requires a generalization of the method by introduction of the hyperparameter concept results include a quantitative characterization of sea ice provinces from field transects in the beaufort sea chukchi sea and elson lagoon which represent a good subset of arctic sea ice types an internal segmentation of the longer profiles and a derivation of surface roughness length and of sea ice type complexity psr data reflect complexity of spatial snow depth structures as captured in multidimensional feature vectors and less directly snow depth and surface roughness length these results indicate that passive microwave data in general may be affected by spatial snow depth and surface roughness with a dependence on scale and quantified by geostatistical classification

empirical relationships among seismic velocity effective pressure porosity and clay content in sandstone we use a multivariate analysis to investigate the influence of effective pressure pe porosity and clay content c on the compressional velocity vp and shear velocity vs of sandstones laboratory measurements on water saturated samples of 64 different sandstones provide a large data set that was analyzed statistically for each sample relationships between effective pressure and vp and vs have been determined all samples were well fit by relationships that have an exponential increase in velocity at low pe tapering to a linear increase with pe for pe greater than 0 2 kbar there are differences in the pressure dependences of velocity for different rocks particularly at very low pressures however the differences cannot be attributed to or c for the combined set of measurements from all samples the best fitting formulations are vp 5 77 6 94 1 73c 0 446 pe e 16 7pe and vs 3 70 4 94 1 57c 0 361 pe e 16 7pe while this is admittedly a very simplified parameterization it is remarkable how well

the paleoclimatic record provided by eolian deposition in the deep sea the geologic history of wind the mineral component of pelagic sediment is brought to the deep sea by transport in the wind extraction and analysis of this dust allows estimation of the past aridity of the eolian source region via flux determinations and of the intensity of the transporting winds from grain size data these two parameters the grain size and mass flux of dust vary independently there are three significant sources of modern dust eastern and central asia northwest africa and arabia all in the northern hemisphere as the rainfall associated with the intertropical convergence zone is an effective barrier to southerly transport of dust the northern hemisphere is an order of magnitude more dusty than is the southern an asymmetry that has characterized most of the cenozoic eolian flux data show that most of the northern hemisphere was more arid during glacial maxima with 3 to 5 times as much dust transported during glacial stages than during interglacials only northwestern south america varied in the opposite sense the periodicity of quaternary variation in both eolian flux and eolian grain size data is strongly influenced by the milankovitch cycles of orbital variability wind intensities vary on a shorter time scale than the general 100 kyr cycles of glaciation and general aridity eolian grain sizes display forcing at precessional 19 and 23 kyr tilt 41 kyr and at approximately 30 kyr periodicities as a result the generalization that winds are uniformly stronger during glacial times is not valid whole cenozoic records show that the largest change in dust flux an order of magnitude increase occurred in the northern hemisphere and reflects continental drying associated with the late pliocene onset of northern hemisphere glaciation southern hemisphere eolian records show no sign of paleoclimatic changes in the late pliocene the most important change in cenozoic atmospheric circulation was a severalfold reduction in wind intensity that occurred at the time of the paleocene eocene boundary before then latest cretaceous and paleocene winds were essentially as strong as those of the late cenozoic this shift appears to be one of several climatic responses to a change in the nature and amount of global heat transport at about 55 ma

stable and clumped isotopes in shell carbonates of land snails cathaica sp and bradybaena sp in north china and implications for ecophysiological characteristics and paleoclimate studies knowledge of ecophysiological characteristics of different land snail species is crucial for defining climatic significance of snail faunal assemblages however little work has been done in this aspect hindering our obtaining unambiguous paleoclimatic information using these proxy indicators here we document for the first time the different ecophysiological characteristics of cathaica sp and bradybaena sp land snails using the stable isotopes and clumped isotope 47 of the shell carbonates the 47 derived temperatures for both species revealed a robust correlation with environmental temperatures moreover the temperatures for cathaica sp are 3 5 c higher than those for bradybaena sp land snails indicating different ecophysiological adaptations or growing seasons of the two species specifically cathaica sp snails prefer living in a warm humid summer whereas bradybaena sp snails are active in the relatively cool arid spring and or autumn the result testifies to the 47 in snail shell carbonates as a promising paleothermometer in monsoonal region and presents new insight into paleoclimatic explanation of these land snail species this finding highlights the importance of climatic seasonality in the changes of the faunal assemblages of land snails

climate change and tectonic activity during the early pliocene warm period from the ostracod record at lake qinghai northeastern tibetan plateau abstract the early pliocene warm period epwp 5 3 ma is sometimes thought to be a useful analogue for a future warmer world and thus the boundary conditions and drivers of climate in the epwp may provide valuable lessons for understanding how a future warmer world might unfold lake qinghai is located on the northeastern margin of the tibetan plateau tp and is affected by both monsoon climate and westerlies circulation it is sensitive to the climate drivers of these systems its sediments accumulated over the cenozoic period are a rich source of information for climate tectonics and environmental changes of the period we present a high resolution ostracod record from a lake qinghai sediment core with a record of the period 5 10 2 60 ma thus covering the epwp ostracods appear at 4 63 ma and are most abundant until 3 58 ma while a body of water was present at the core site this suggests a phase of humid climate and an intensified asian summer monsoon asm which is consistent with a warmer and wetter climate in the early pliocene within this period the ostracod record shows some variabilities in lake level with deeper periods suggesting more intense asm compared to those with shallower water the disappearance of ostracods at 3 58 ma may provide evidence for the uplift of qinghai nanshan south of qinghai lake since this is when the asm intensified

a brief study of applications of the generalized reciprocal method and of some limitations of the method an analysis of the generalized reciprocal method grm developed by palmer for the interpretation of seismic refraction investigations has been carried out the aim of the present study is to evaluate the usefulness of the method for geotechnical investigations in connection with engineering projects practical application of the grm is the main object of this study rather than the theoretical mathematical aspects of the method the studies are partly based on the models and field examples presented by palmer for comparison some other refraction interpretation methods and techniques have been employed namely the abc method the abem correction method the mean minus t method and hales method the comparisons showed that the results i e the depths and velocities determined by palmer are partly incorrect due to some errors and misinterpretations when analysing the data from field examples due to the limitations of the grm some of which are mentioned here stated by palmer in his various publications and other shortcomings of the method e g the erasing of valuable information the grm must be regarded as being of limited use for detailed and accurate interpretations of refraction seismics for engineering purposes

the mechanisms of sea ice melt pond formation and evolution 1 a series of observations were made on melting first year landfast arctic sea ice near barrow alaska to explore the seasonal evolution of melt pond coverage observations of pond coverage albedo and ice properties are combined with terrestrial lidar measurements of surface topography and meltwater balance to quantitatively identify the timing and role of mechanisms driving pond coverage the formation of interposed fresh ice is found to eliminate meltwater percolation through early pond formation and allow widespread ponding well above sea level pond drainage to sea level occurs principally by horizontal meltwater transport over the ice surface to macroscopic flaws freeboard loss caused by buoyancy decline as the ice thins controls pond growth late in the melt season after percolation begins the majority of the macroscopic flaws that drain melt ponds to sea level are observed to develop from brine drainage channels within the ice a simple thermodynamic model of meltwater percolation illustrates that fresh meltwater inflow causes pores in the ice to either shrink and freeze shut or enlarge based on initial size and ice temperature this threshold behavior of pore diameter controls both the blockage of smaller pores with interposed ice and the enlargement of larger brine drainage channels to allow meltwater drainage the results identify links between the temporal evolution of pond coverage and ice temperature salinity and thickness providing new opportunities to realistically parameterize ponds and summer ice albedo within sea ice models

marked ecological shifts during 6 2 2 4 ma revealed by a terrestrial molluscan record from the chinese red clay formation and implication for palaeoclimatic evolution abstract a new molluscan fossil record from the late miocene pliocene xifeng red clay sequence in the central loess plateau northern china reveals the process of ecological environmental changes during 6 2 2 4 ma three marked ecological shifts in mollusk assemblages occurred at about 5 4 4 5 and 3 4 ma which reflect changes in the east asian monsoon circulation a predominantly cold aridiphilous group reveals an extremely cold dry climate due to strengthened east asian winter monsoon during 6 2 5 4 ma a predominantly thermo humidiphilous group from 5 4 4 5 ma indicates a strengthening of the east asia summer monsoon circulation the marked occurrence of meso xerophilous taxa during 4 5 3 4 ma implies mild climatic conditions from 3 4 ma the cold aridiphilious species again became dominant in the fossil assemblages indicating that the winter monsoon was gradually intensifying towards the quaternary glaciations climate changes in this region were characterized by stepwise cooling from 5 4 to 2 4 ma with a 1 ma rhythmicity the cooling trend is in good agreement with the general global cooling trend during this period as documented by marine 18o records the formation and development of the northern hemisphere ice sheets during the late pliocene accelerated the climate deterioration towards the quaternary glaciations the history of environmental changes revealed by the red clay molluscan fossils is coupled in phase with the process of tibetan plateau uplift which may be the major cause and forcing mechanism of late miocene pliocene environmental changes in the loess plateau

assessment of the palaeoclimate during 3 0 2 6 ma registered by transition of red clay to loess palaeosol sequence in central north china abstract a continuously accumulated section the yanyu section of red clay and loess palaeosol sequence from the southernmost chinese loess plateau was selected for this study of palaeoclimate of the late pliocene to early pleistocene period termination of the red clay accumulation and onset of loess deposition was coincident with the beginning of extensive northern hemisphere glaciation at 2 6 ma field observations and compositional analyses suggest an aeolian origin for the red clay much like the processes experienced by the loess palaeosol sequence pedogenic analysis indicates that the late pliocene red clay first experienced complete decalcification and illuviation mechanical translocation of clays in all horizons including the present carbonate precipitation zones but other chemical alterations have been rather weak and even weaker than experienced by the overlying loess derived palaeosols in great contrast to the pleistocene climate characterised by frequent and large amplitude fluctuations between cold dry and warm wet a relatively steady warm dry climate condition is implied for the late pliocene dustfall rate assessment indicates a much lower accumulation rate during the late pliocene than in the early pleistocene in agreement with a notable systematic coarsening from the red clay to the overlying loess and palaeosols together these features suggest that the dust transport agent the northwesterly winds were weaker over the late pliocene the transition from red clay to loess possibly marked a significant and rapid shift in the climatic system in east asia

the coal mine roof rating cmrr a decade of experience abstract the coal mine roof rating cmrr was developed 10 years ago to fill the gap between geologic characterization and engineering design it combines many years of geologic studies in underground coal mines with worldwide experience with rock mass classification systems like other classification systems the cmrr begins with the premise that the structural competence of mine roof rock is determined primarily by the discontinuities that weaken the rock fabric however the cmrr is specifically designed for bedded coal measure rock since its introduction the cmrr has been incorporated into many aspects of mine planning including longwall pillar design roof support selection feasibility studies extended cut evaluation and others it has also become truly international with involvement in mine designs and funded research projects in south africa canada and australia this paper discusses the sources used in the development of the cmrr describes the cmrr data collection and calculation procedures and briefly presents a number of practical mining applications in which the cmrr has played a prominent role

influence of late cenozoic mountain building on ocean geochemical cycles in a steady state ocean input fluxes of dissolved salts to the sea must be balanced in mass and isotopic value by output fluxes for the elements strontium calcium and carbon rivers provide the primary input whereas marine biogenic sedimentation dominates removal dissolved fluxes in rivers are related to rates of continental weathering which in turn are strongly dependent on rates of uplift the largest dissolved fluxes today arise in the himalayan and andean mountain ranges and the tibetan plateau during the past 5 m y uplift rates in these areas have increased significantly this suggests that weathering rates and river fluxes may have increased also the oceanic records of carbonate sedimentation level of the calcite compensation depth and delta sup 13 c and delta sup 87 sr in biogenic sediments are consistent with a global increase in river fluxes since the late miocene the cooling of global climate over the past few million years may be linked to a decrease in atmospheric co sub 2 driven by enhanced continental weathering in these tectonically active regions

sediment transport by sea ice in the chukchi and beaufort seas increasing importance due to changing ice conditions abstract sediment laden sea ice is widespread over the shallow wide siberian arctic shelves with off shelf export from the laptev and east siberian seas contributing substantially to the arctic ocean s sediment budget by contrast the north american shelves owing to their narrow width and greater water depths have not been deemed as important for basin wide sediment transport by sea ice observations over the chukchi and beaufort shelves in 2001 02 revealed the widespread occurrence of sediment laden ice over an area of more than 100 000 km2 between 68 and 74 n and 155 and 170 w ice stratigraphic studies indicate that sediment inclusions were associated with entrainment of frazil ice into deformed multiple layers of rafted nilas indicative of a flaw lead environment adjacent to the landfast ice of the chukchi and beaufort seas this is corroborated by buoy trajectories and satellite imagery indicating entrainment in a coastal polynya in the eastern chukchi sea in february of 2002 as well as formation of sediment laden ice along the beaufort sea coast as far eastward as the mackenzie shelf moored upward looking sonar on the mackenzie shelf provides further insight into the ice growth and deformation regime governing sediment entrainment analysis of radarsat synthetic aperture sar imagery in conjunction with bathymetric data help constrain the water depth of sediment resuspension and subsequent ice entrainment 20 m for the chukchi sea sediment loads averaged at 128 t km 2 with sediment occurring in layers of roughly 0 5 m thickness mostly in the lower ice layers the total amount of sediment transported by sea ice mostly out of the narrow zone between the landfast ice edge and waters too deep for resuspension and entrainment is at minimum 4 106 t in the sampling area and is estimated at 5 8 106 t over the entire chukchi and beaufort shelves in 2001 02 representing a significant term in the sediment budget of the western arctic ocean recent changes in the chukchi and beaufort sea ice regimes reduced summer minimum ice extent ice thinning reduction in multi year ice extent altered drift paths and mid winter landfast ice break out events have likely resulted in an increase of sediment laden ice in the area apart from contributing substantially to along and across shelf particulate flow an increase in the amount of dirty ice significantly impacts sub ice algal production and may enhance the dispersal of pollutants

the late miocene and pliocene climate in east asia as recorded by grain size and magnetic susceptibility of the red clay deposits chinese loess plateau abstract grain size characteristics of the aeolian red clay sediment series in china demonstrate the existence of warm cool alternations during the late miocene and pliocene from the dissimilarity between the temporal patterns of grain size and magnetic susceptibility it is inferred that the finest grain size fraction in the red clay clay and very fine silt is transported by the wind as is the case of the coarser silty component relatively cool climatic conditions are indicated by increased loess supply represented by the silty component from the nw caused by a stronger winter monsoon as in the overlying quaternary system it is striking that at the same time the amounts of clay also increased probably due to transportation by intensified westerly circulation relatively warm periods are characterized by opposite grain size properties these warm cool alternations on the asian continent dated by palaeomagnetic analyses correlate well with already established changes in sea level and ice sheet volumes up to 6 ma in addition time series analysis of the grain size signal points to an orbitally forced climatic cyclicity precession eccentricity and weak obliquity

intensified aridity in northern china during the middle piacenzian warm period abstract dryland areas are predicted to expand significantly due to global climate change and such expansion would reduce carbon sequestration and enhance warming forming a positive feedback however a contrasting theory is that earth s thermal equator will move northward in a warm climate resulting in precipitation increase and dryland shrinking a study of past warm periods analogous to future climate can help distinguish between these predictions the middle piacenzian warm period during 3 3 3 ma is the best pre quaternary analog to late 21st century climate but pliocene terrestrial paleoclimatic records that can resolve orbital timescale variations are scarce here we present a pedogenic carbonate oxygen isotope record spanning the entire pliocene from the chinese loess plateau the record reveals intensified evaporation induced aridity during the warm phases of the middle piacenzian period these records provide the first evidence demonstrating that intensified evaporation in northern china counteracted any precipitation increase associated with thermal equator migration during the warm periods these results suggest that asian drylands will likely expand with future warming requiring a revision of model simulation which predicts increases in humidity

10be in continental sediments from north china probing into the last 5 4 ma 10be in continental sediments from north china probing into the last 5 4 ma 10be in continental sediments from north china probing into the last 5 4 ma continental sediments from north china probing into the last 5 4 ma 10be in continental sediments from north china probing into the last 5 4 ma

tertiary oxygen isotope synthesis sea level history and continental margin erosion tertiary benthic and planktonic foraminiferal oxygen isotope records are correlated to a standard geomagnetic polarity time scale making use of improved chronostratigraphic control and additional oligocene isotope data synchronous changes in both benthic and planktonic 18o values which occurred in the oligocene to miocene 36 5 2 ma are interpreted in part to represent ice growth and decay the inferred ice growth events correlate with erosion on passive continental margins as interpreted from seismic and chronostratigraphic records this association is consistent with a link between oligocene to miocene erosional events and rapid 15 m m y glacioeustatic lowerings of about 50 m high benthic foraminiferal 18o values suggest the presence of continental ice sheets during much of the oligocene to recent 36 0 ma substantially ice free conditions probably existed throughout the paleocene and eocene 66 36 ma the mechanisms and rates of sea level change apparently were different between the early and late tertiary with glacioeustatic changes restricted to the past 36 m y pre oligocene erosion on passive continental margins was caused by eustatic lowerings resulting from global spreading rate changes we apply a model which suggests that large areas of the continental shelves were subaerially exposed during such tectonoeustatic lowstands stimulating slope failure and submarine erosion the different mechanisms and rates of eustatic change may have caused contrasting erosional patterns between the early and late tertiary on passive continental margins this speculation needs to be confirmed by examination of data from several passive margins

pliocene pleistocene stable isotope and paleoceanographic changes in the northern south china sea abstract based on the stable isotopic analysis of planktonic and benthic foraminifers from ocean drilling program core 1148 of the northern south china sea scs pliocene pleistocene isotope stratigraphy and events have been reconstructed the benthic foraminiferal 18o record shows that the pacific intermediate water had a greater influence upon the scs or the pacific deep water above 2600 m was warmer before 3 2 ma than at present after that the benthic 18o conspicuously increased during the 3 2 2 5 ma period in correspondence to the formation of the northern hemisphere ice sheet whereas the planktonic 18o signal suggests a stepwise overall decrease of sea surface temperature during the 2 2 0 9 ma period compared to the equatorial pacific records the decrease in planktonic globigerinoides ruber 13c during the 3 2 2 2 ma period is particularly striking suggesting that fertility of surface water increased noticeably according to the modern 13c distribution of g ruber in the northern scs it is inferred that the east asian winter monsoon strengthened during this interval afterwards there were several conspicuous decreases of g ruber 13c at 1 7 1 3 0 9 0 45 and 0 15 ma bp that is about every 0 4 ma suggesting that the east asian winter monsoon became episodically stronger this is confirmed by changes in relative abundance of planktonic foraminifer species neogloboquadrina dutertrei a typical east asian winter monsoon proxy the deep water 13c of the scs is close to that of the pacific but lighter than that of the atlantic implying that the pattern of deep water originating mainly from the atlantic and through the pacific entering the scs existed at least since the early pliocene after 1 4 ma the benthic 13c signal decreased conspicuously but with a periodicity of 100 ka suggesting that the deep water ventilation of the scs was reduced probably corresponding to a decrease of the north atlantic deep water and or further isolation of the scs deep basin from the pacific during glaciations

c3 c4 vegetation evolution over the last 7 0 myr in the chinese loess plateau evidence from pedogenic carbonate δ13c the stable carbon and oxygen isotopic compositions of soil carbonate were measured on an eolian loess and red clay sequence at lingtai the chinese loess plateau this sequence is composed of 130 m of tertiary red clay deposits with a basal age of 7 05 ma overlain by 175 m of pleistocene loess in the field we identified ca 110 carbonate nodule horizons in the red clay and 27 nodule horizons in the loess these carbonate nodule horizons are formed by leaching and re precipitation of carbonate from the eolian material the d13c record of soil carbonate indicates a major expansion of c 4 plants at ca 4 0 myr in the loess plateau this event is comparable in timing with the expansion of c 4 plants in northern north america cerling et al 1997 nature 389 153 158 but is ca 3 million years later than the c 4 biomass expansion in pakistan quade et al 1989 nature 342 163 166 the pedogenic characteristics of the soils and the d18o record in the red clay suggest that the c 4 plant expansion in the loess plateau was not driven by local climatic changes which may support cerling et al s 1997 assertion that the decline of atmospheric co 2 levels in the neogene is responsible for this global vegetation change our record also implies that the tibetan plateau could have been uplifted to a critical height in the late miocene thus resulting in the formation of the atmospheric great east asia trough 2000 elsevier science b v all rights reserved

past co2 changes and tropical sea surface temperatures the relationship between past co2 variations and tropical climate change on time scales of millions of years is reviewed explanations for cretaceous and early cenozoic climate change often involve higher atmospheric co2 levels climate models predict that such increases should have been associated with warmer tropical sea surface temperatures ssts however sparse mid cretaceous 18o based sst estimates from low latitude calcareous plankton are 1 0 1 5 heavier than predicted initial evaluations indicate that changes in salinity may not alleviate model data discrepancies for calcareous 18o and that interpretation of altered latitudinal 18o gradients in terms of increased poleward heat transport due to warm saline bottom water wsbw formation would require very large levels of wsbw production at least 60 sv calcareous 18o records may not always record true sst patterns as 18o analyses from phosphatic groups which are less sensitive to diagenesis indicate ssts 5 c higher this latter conclusion is supported by a number of other fossil groups which indicate temperatures warmer than those estimated from calcareous 18o in order to more rigorously test the paleo co2 hypothesis and indeed the models used to forecast future climates it is desirable to intensify investigations of past climate change in low latitudes in order to determine whether these preliminary conclusions stand the test of further scrutiny

late neogene evolution of the east asian monsoon revealed by terrestrial mollusk record in western chinese loess plateau from winter to summer dominated sub regime article i nfo more and more evidence indicates that the onset of the east asian ea monsoon can be traced back to the oligocene miocene boundary at about 23 ma however the process of its evolution is still less well known until now here we investigate its late neogene evolution by analyzing a terrestrial mollusk sequence from the chinese loess plateau clp covering the period between 7 1 and 3 5 ma considering the modern ecological requirements of these organisms we were able to define two groups of cold aridiphilous ca and thermo humidiphilous th species representing the ea winter and summer monsoon variations respectively as previously defined in the quaternary glacial interglacial cycles variations in these two groups indicate two different monsoon dominated periods during 7 1 3 5 ma first between 7 1 and 5 5 ma the ea winter monsoon with a 100 kyr periodicity was dominant second between 5 1 and 4 ma the ea summer monsoon dominated with a 41 kyr periodicity furthermore our mollusk record yields valuable evidence for a late miocene pliocene transition of about 400 kyr from winter monsoon dominated towards summer monsoon dominated associated with a periodicity transition from weak 100 kyr to 41 kyr the strengthened winter monsoon interval with a 100 kyr periodicity is coeval with orbital scale global ice volume changes in conjunction with the uplift of the tibetan plateau which probably reinforced the winter monsoon sub regime conversely closures of the panama and indonesian seaways associated with changes in obliquity between 5 1 and 4 ma are probably major forcing factors for the observed dominant summer monsoon with 41 kyr frequency favoring heat and moisture transports between low and high latitudes to allow th mollusks to grow and develop in the clp

spatial and temporal patterns of grain size and chemical weathering of the chinese red clay formation and implications for east asian monsoon evolution abstract palaeoclimatic interpretation of the red clay in the chinese loess plateau is particularly important for understanding of the east asian monsoon evolution from pliocene to the quaternary in this study a n s transect involving five loess red clay sections across the loess plateau was selected for detailed investigation with analyses of grain size and major element geochemistry in order to address the spatial pattern results indicate that the red clay contains large amount of coarse 16 m fraction and shows a prominent n s decreasing gradient much similar to that of the overlying loess suggesting that the dust transport was dominantly by low level northerly northwesterly winds compared with overlying loess the red clay is markedly fine and rather constant through all the sections implying a distant and steady dust source area about 200 km further north during most of the pliocene time pedogenic leaching intensities inferred from geochemical data display a clear decreasing trend from south to north both for the red clay and the loess suggesting that the modern spatial pattern of the east asian monsoon regime has been maintained at least for the past 5 ma the n s spatial gradient however might be smaller during the pliocene than the quaternary period temporally two short periods of climatic deterioration implied by marked grain size coarsening and low weathering intensity occurred at 5 3 and 3 5 ma respectively which divide the pliocene into two major stages the 5 3 3 5 ma stage is characterized by a steady state climate through the entire region consistent with other records in the 3 5 2 7 ma stage the red clay in the jingbian section shows a noticeable coarsening in grain size than the previous stage indicating some southward extension of the deserts in agreement with mass accumulation rate record in the north pacific but the eolian dust deposition remained relatively stable in major part of the loess plateau until 2 7 ma the red clay deposition was then terminated by massive and coarse loess deposition in the entire region suggesting dramatic intensification of the winter monsoon in response to the onset of extensive glaciation of northern hemisphere

active geologic processes in barrow canyon northeast chukchi sea abstract circulation patterns on the shelf and at the shelf break appear to dominate the barrow canyon system the canyon s shelf portion underlies and is maintained by the alaska coastal current a c c which flows northeastward along the coast toward the northeast corner of the broad chukchi sea offshelf and onshelf advective processes are indicated by oceanographic measurements of other workers these advective processes may play an important role in the production of bedforms that are found near the canyon head as well as in processes of erosion or non deposition in the deeper canyon itself coarse sediments recovered from the canyon axis at 400 to 570 m indicate that there is presently significant flow along the canyon the canyon hooks left at a point north of point barrow where the a c c loses its coastal constriction the left hook as well as preferential west wall erosion continues down to the abyssal plain of the canada basin at 3800 m a possible explanation for the preferential west wall erosion along the canyon at least for the upper few hundred meters is that the occasional upwelling events which cause nutrient rich water to flow along the west wall would in turn cause larger populations of burrowing organisms to live there than on the east wall and that these organisms cause high rates of bioerosion this hypothesis assumes that the dominant factor in the canyon s erosion is biological activity not current velocity sedimentary bedforms consisting of waves and furrows are formed in soft mud in a region on the shelf west of the canyon head their presence there perhaps reflects a the supply of fine suspended sediments delivered by the a c c from sources to the south probably the yukon and other rivers draining northwestern alaska and b the westward transport of these suspended sediments by the prevailing beaufort gyre which flows along the outer shelf

wind blown origin of the pliocene red clay formation in the central loess plateau china abstract in order to determine the depositional processes of the pliocene red clay formation deposited directly beneath the plio pleistocene loess in the chinese loess plateau four red clay sections spanning over 400 km are studied grain size analysis of closely spaced samples in the sections shows that the particles of the red clay are very fine with the sand fraction 63 m being negligible and that all the curves indicating changes in different grain size parameters have a similar pattern the grain size records in the upper part of the four sections are almost identical with the median grain size centered at 4 8 m the ree patterns of 28 samples from the jiaxian red clay section are all characterized by lree enrichments relatively flat hree and slight negative eu anomaly being similar to those of eolian loess and the average upper continental crust these lines of evidence point to a wind blown origin of the red clay deposits accumulation of the loess soil sequences in the chinese loess plateau during the past 2 6 ma can be therefore regarded as the continuation of the pliocene atmospheric dust deposition observations of spatial grain size changes in the loess plateau suggest that the eolian red clay might be transported mainly by the westerlies differing significantly from the overlying loess that was transported essentially by the east asia winter monsoonal winds

forcing of late cenozoic northern hemisphere climate by plateau uplift in southern asia and the american west geologic evidence indicates that net vertical uplift occurred on a large kilometer scale and at accelerating rates during the middle and late cenozoic in plateaus of southern asia and the american west based on this evidence general circulation model sensitivity tests were run to isolate the unique effects of plateau uplift on climate the experiments simulated significant climatic changes in many places some far from the uplifted regions the basic direction of most of these simulated responses to progressive uplift is borne out by changes found in the geologic record winter cooling of north america northern europe northern asia and the arctic ocean summer drying of the north american west coast the eurasian interior and the mediterranean winter drying of the north american northern plains and the interior of asia and changes over the north atlantic ocean conducive to increased formation of deep water the modeled changes result from increased orographic diversion of westerly winds from cyclonic and anticyclonic surface flow induced by summer heating and winter cooling of the uplifted plateaus and from the intensification of vertical circulation cells in the atmosphere caused by exchanges of mass between the summer heated and winter cooled plateaus and the mid latitude oceans disagreements between the geologic record and the model simulations in alaska and the southern rockies and plains may be related mainly to the lack of narrow mountain barriers in the model orography taken together the observed regional trends comprise much of the pattern of late cenozoic climatic deterioration in the northern hemisphere that culminated in the plio pleistocene ice ages the success of the uplift sensitivity experiment in simulating the correct pattern and sign of most of the observed regional climatic trends points to uplift as an important forcing function of late cenozoic climatic change in the northern hemisphere at time scales longer than orbital variations however the modest amplitude of the uplift induced cooling simulated at high latitudes indicates a probable need for additional climatic forcing

magnetostratigraphy and palaeoclimatic significance of late tertiary aeolian sequences in the chinese loess plateau summary the aeolian red clay sequence in the central part of the chinese loess plateau was investigated in an attempt to obtain magnetostratigraphic and palaeoclimatic records from the results we deduce that aeolian dust accumulation and the related east asia palaeomonsoon system began at least 7 6 myr ago and that the tibetan plateau had reached a significant elevation by that time the late tertiary palaeoclimatic history of the red clay as reflected by magnetic susceptibility is reconstructed for the time period 7 6 2 5 ma increases in aeolian dust accumulation for the last 7 6 myr appear to have a close relation with the uplift processes of the tibetan plateau the remarkable increase of aeolian dust accumulation beginning at 3 2 ma appears to reflect the influence of an increasing global ice volume on the east asian monsoon and aeolian dust accumulation

a short circuit in thermohaline circulation a cause for northern hemisphere glaciation the cause of northern hemisphere glaciation about 3 million years ago remains uncertain closing the panamanian isthmus increased thermohaline circulation and enhanced moisture supply to high latitudes but the accompanying heat would have inhibited ice growth one possible solution is that enhanced moisture transported to eurasia also enhanced freshwater delivery to the arctic via siberian rivers freshwater input to the arctic would facilitate sea ice formation increase the albedo and isolate the high heat capacity of the ocean from the atmosphere it would also act as a negative feedback on the efficiency of the conveyor belt heat pump

northeastward growth of the tibet plateau deduced from balanced reconstruction of two depositional areas the qaidam and hexi corridor basins china we address the problem of late cenozoic uplift erosion and growth of northeastern tibet by reconstructing from isopach maps and drill holes the volumes and masses of sediments deposited in the qaidam and hexi corridor basins since 35 myr ago the mass budget is based on simple geometrical assumptions such as regional similarity of the thickness ratios between strata of different ages in the qaidam where our record extends back to the oligocene the budget shows a huge rise of the accumulation rates after the beginning of the pliocene 5 3 ma the early pliocene seems to be the period of maximum deposition with accumulation rates in excess of 1 mm yr 1 2 7 kg m 2 yr 1 of compacted rocks throughout the basin there also seems to be a southeastward shift of the largest depocenters between the upper pliocene 3 4 1 6 ma and the quaternary in the hexi corridor sedimentation is confined to small foreland flexural depressions associated with the frontal thrusts of the qilian shan and occurs at an average rate one order of magnitude smaller than in the qaidam basin the accumulation rate is maximum in the quaternary the sedimentation history appears to support a plateau building mechanism resulting from the combination of two geologicallly common processes crustal scale thrusting and sedimentary basin infilling the time needed to completely fill the qaidam basin and make its catchment a plateau closely resembling that of the highest part of tibet qangtang is of the order of 9 myr the mechanism now at work north of the kunlun which involves rapid infilling of broad flat areas separated by relatively narrow mountain ranges has thus probably been important in producing the high smooth topography that characterizes much of central tibet

response of deep ocean circulation to initiation of northern hemisphere glaciation 3 2 ma carbon isotopic records from benthic foraminifera are used to map patterns of deep ocean circulation between 3 and 2 million years ago the interval when significant northern hemisphere glaciation began the 18o and 13c data from four atlantic sites 552 607 610 and 704 and one pacific site 677 show that global cooling over this interval was associated with increased suppression of north atlantic deep water nadw formation however the relative strength of nadw production was always greater than is observed during late pleistocene glaciations when extreme decreases in nadw are observed in the deep north atlantic our data indicate that an increase in the equator to pole temperature gradient associated with the onset of northern hemisphere glaciation did not intensify deepwater production in the north atlantic but rather the opposite occurred this is not unexpected as it is the warm high salinity characteristic rather than the low temperature of thermocline waters that is critical to the deepwater formation process in this region today

late cenozoic history of the polar north atlantic results from ocean drilling abstract dsdp odp drilling in the northern north atlantic reveals that so far the onset of northern hemisphere cooling deduced from the occurrence of ice rafted debris ird in deep sea sediments can be traced back to the middle miocene the greenland ice sheet has probably the longest history on the northern hemisphere leg 151 site 909 fram strait recovered a unique continuous sediment record dating from early middle miocene the composition of the coarse fraction indicates that the oldest ird pulses are documented around 14 ma in the fram strait site 909 and around 12 6 ma on the voring plateau leg 104 site 642 in the norwegian greenland sea fram strait site 909 indicates a further stepwise increase of northern hemisphere cooling by serveral ird pulses during late miocene between 10 8 and 8 6 ma around 7 2 6 8 and 6 3 ma which ultimately led to a drastic intensification of northern hemisphere glaciation during plio pleistocene the deep sea sediment records show that plio pleistocene strengthening of ird pulses have been observed since approximately 4 0 ma in the westernmost norwegian greenland sea and labrador sea by contrast strengthening of ird pulses are observed at approximately 3 2 2 7 ma on the eastern side of the norwegian greenland sea including the barents sea margin sediment composition and physical properties of the drilled mostly terrigenous sections reveal that orbital parameters have controlled major aspects of shallow and deep water environments with frequency domains related to 41 ka periods of obliquity dominant in the pre glacial miocene pliocene and early quaternary and to 100 ka periods of eccentricity dominant during the past 600 000 700 000 years the stratigraphy of ice rafted material reveals a frequently and rapidly changing history of the dynamics of various segments in ice sheets around the norwegian greenland sea it is particularly evident from the composition of the ice rafted material that the eurasian ice sheets delivered ird to the eastern part of the norwegian greenland sea whereas greenland source areas are represented in the drill sites of the east greenland continental margin and in the labrador sea the stratigraphic sequences on the yermak plateau suggest that the svalbard ice sheet may have extended far to the north prior to oxygen isope stage 16 but not since then invasions of temperate atlantic waters during interglacials can be observed as short lived and rather irregular events it never reached the area off eastern greenland except during the pliocene interval when tundra floras were able to develop on north eastern greenland and planktonic foraminifers suggesting the presence of temperate water masses in the fram strait as been documented in the drill sites from the yermak plateau

geotechnical evaluation of coal deposits based on the geophysical strata rating abstract in exploration programs for coal mining geophysical logging of boreholes is mainly undertaken to reveal seam locations and the basic lithological section through the introduction of the geophysical strata rating gsr this paper develops new geotechnical applications for geophysical logs the gsr is an empirical rating scheme based on p wave velocity data from sonic logs and estimates of the clay content and porosity derived from natural gamma and density logs in coal measure strata gsr values range between 0 and 100 with values of given that geophysical logging data are obtained at closely spaced intervals within boreholes and that coal measure strata are usually laterally persistent between boreholes geophysical results such as the clay content and the gsr can be modelled in two and three dimensions this allows geotechnical information to be viewed in a geological context examples are provided of the log analysis and modelling geotechnical applications in risk identification hazard assessment and design optimisation are also discussed these applications exist in both underground and open cut mining

a new molluscan record of the monsoon variability over the past 130 000 yr in the luochuan loess sequence china this paper presents a new record of monsoon changes that occurred in china during the late pleistocene study of terrestrial mollusks from the loess sequence in luochuan indicates alternating strengthened summer and winter paleomonsoons these variations based on the content of xerophilous hygrophilous and oriental species are in very good agreement with the variation inferred from pedology sedimentology and climate modeling the three occurrences of currently southeastern species in the sequence indicate that the climate conditions were warmer and wetter than today at about 88 60 and 10 ka the main occurrence of xerophilous taxa between 75 and 65 ka is interpreted as drier than today in agreement with other proxy data these results demonstrate that fossil terrestrial mollusk data can provide reliable information on past monsoon variability in asia

a new coal mine floor rating system and its application to assess the potential of floor heave abstract several underground coal mines have reported floor heave associated with the buckling mechanism however studies on the coal mine floor especially the buckling failure mechanism in the floor and relevant analysis techniques are still insufficient this paper introduces a new floor classification system the coal mine floor rating based on the underlying failure mechanisms the new floor mass rating system quantifies the stability of floor strata by considering two main factors uniaxial compressive strength and discontinuity spacing of the floor units the coal mine floor rating is incorporated into an empirical method the floor heave index developed by statistical analysis of a database obtained from actual floor failure cases the floor heave and non floor heave cases are determined depending on the coal mine floor rating and the horizontal stress rating a proxy that represents the magnitude of horizontal stress while obtaining underground floor data is challenging the new floor classification system and the empirical method help assess the potential of significant floor heave on development in underground coal mine roadways for new mining projects or future workings

overview on the application of geophysics in coal mining abstract since their introduction to the coal mining industries of the united kingdom and west germany in the 1970s geophysical methods are now utilised in coal mining around the world the range of applications in both surface and underground mining is extensive applications include coal seam mapping and geological fault detection lithological mapping geotechnical evaluation assessment of the rock mass response to mining detection of voids location of trapped miners and guidance of drills and mining equipment the range of techniques that can be employed is also extensive and includes geophysical borehole logging the potential field methods seismic reflection 2d and 3d resistivity electromagnetics and microseismic monitoring using active and passive sources this paper discusses the major applications and the geophysical methods that can be applied it also discusses future trends and suggests that the future motives for applying geophysics will not only include the current motivations of mine safety and productivity but will also include an increased emphasis on environmental management the monitoring of sequestration activities and the provision of sensors to enable autonomous mining

orbit related long term climate cycles revealed in a 12 myr continental record from lake baikal quaternary records of climate change from terrestrial sources such as lake sediments1 2 and aeolian sediments3 4 in general agree well with marine records5 6 but continuous records that cover more than the past one million years were essentially unavailable until recently when the high sedimentation rate site of lake baikal was exploited1 2 7 8 because of its location in the middle latitudes lake baikal is highly sensitive to insolation changes9 and the entire lake remained uncovered by ice sheets throughout the pleistocene epoch making it a valuable archive for past climate here we examine long sediment cores from lake baikal that cover the past 12 million years our record reveals a gradual cooling of the asian continental interior with some fluctuations spectral analyses reveal periods of about 400 kyr 600 kyr and 1 000 kyr which may correspond to milankovitch periods reflecting orbital cycles our results indicate that changes in insolation were closely related to long term environmental variations in the deep continental interior over the past 12 million years

4 ma coarsening of sediments from baikal chinese loess plateau and south china sea and implications for the onset of nh glaciation abstract intense tectonic movement occurred along the northeastern margin of the tibetan plateau 3 4 ma during the same time period global climate changed from a period of stability to a period of frequent and abrupt changes which prevented fluvial and glacial systems from establishing a state of equilibrium thus it is difficult to directly attribute the 3 4 ma coarse grained sediment accumulation in east asia to climate change or tectonic activity this study compares late cenozoic multi proxy records from the chinese loess plateau clp to the low latitude grain size sea level and benthic 18 o records from the south china sea scs and the high latitude grain size record from lake baikal all records suggest a steady and persistent cooling since 4 ma which correlates well with those cooling records from other regions around the world this coincided in timing with the modeling results that the closure of the central american seaway cas initiated strengthening of atlantic meridional overturning circulation between 4 8 and 4 0 ma which led to both warming of the northern hemisphere nh and cooling of the southern hemisphere sh cooling of the sh would induce a marked development of the antarctic ice sheets at 4 ma pushing the intertropical convergence zone itcz northward this was superimposed on warming of the nh and brought more precipitation to the middle latitudes of the nh resulting in increases in coarse grained sediments in the sikouzi section from the western clp since 4 2 ma notably the absence of coarse grained sedimentation in the sikouzi section during 3 0 2 1 ma and the gradual decrease in coarse grained peaks since 2 1 ma reflected by the sikouzi grain size record probably resulted from stepwise increase in the nh ice volume pushing the itcz southward on the other hand development of the antarctic ice sheets would induce global cooling and enhancement of physical weathering initiating increases in sedimentation rates as well as increases in grain size from lake baikal to the clp to the scs therefore the closure of the cas during 4 8 4 0 ma and its influence on ocean heat transport was possibly the major forcing factor for global cooling since 4 ma a persistent and steady cooling during 4 3 ma probably made a significant contribution to the establishment of the nh ice sheets at 2 75 ma ago

mid pliocene warmth stronger greenhouse and stronger conveyor abstract three million years ago prior to the onset of northern hemisphere glaciation global mean temperatures may have been as much as 3 5 c warmer than at present we present evidence based on the carbon isotopic composition of marine organic matter that atmospheric co2 levels at this time were on average only about 35 higher than the preindustrial value of 280 ppm we also present carbon isotopic evidence for stronger thermohaline circulation in the atlantic ocean during the warmest intervals and propose that the north atlantic conveyor belt may act as a positive feedback to global warming by enhancing sea ice retreat and decreasing high latitude albedo based on our results it seems unlikely that the mid pliocene warm period was a doubled co2 world

low latitude hydro climatic changes during the plio pleistocene evidence from high resolution alkane records in the southern south china sea abstract high resolution records of long chain n alkane biomarkers from the southern south china sea reveal tightly response of n alkane distribution to hydro climate changes over the past 5 ma with increasing longer chain n c31 alkanes indicating a correlation with drier conditions and increasing shorter chain n c27 alkanes with wetter conditions the variations of the c31 c27 ratio or the alkane chain length index imply humid conditions before 2 9 ma progressively reduced moisture since then and to bigger fluctuations between wet and dry conditions since 1 2 ma this long term hydro climate trend is superimposed by glacial dry and interglacial wet patterns over the plio pleistocene glacial cycles combined with other proxy records our results indicate that precipitation over the tropical asia pacific strengthened before the onset of the northern hemisphere glaciation and the mid pleistocene climate transition at about 1 2 ma these dramatic humidity changes over major climate transitions imply a crucial role of tropical hydrology dynamics on global climate change in the late cenozoic

stable carbon and oxygen isotopic evidence for late cenozoic environmental change in northern china abstract stable carbon and oxygen isotope ratios of 311 enamel samples from a diverse group of herbivorous mammals including equidae rhinocerotidae bovidae rodentia and ochotonidaewere were analyzed in order to reconstruct the late cenozoic history of vegetation and environmental change in the yushe basin in north china the 13c values of bulk and serial enamel samples from large mammals show a wide range of variation from 13 3 to 1 4 with a mean of 7 4 3 5 n 294 this indicates that large herbivorous mammals in the area had a variety of diets since 6 5 ma ranging from pure c3 to mixed c3 c4 and pure c4 diets in contrast the 13c values of small mammals vary from 11 9 to 7 6 with a mean of 9 7 1 1 n 17 indicating that rodents and ochotonids were feeding mostly on c3 plants variations in 13c values within and between species reflect the variations in the habitat and the vegetation consumed by the animals in general horses had higher amounts of c4 grasses in their diets than other contemporary taxa such as bovids rhinos rodents and deer suggesting that horses exploited more open habitats such as grasslands while deer rhinos and rodents may have preferred more c3 vegetation which is more indicative of forested environments the carbon isotope data show that c4 grasses have been an important component of horses diets and of local ecosystems since 6 5 ma confirming that the late miocene c4 expansion occurred in north china as it did in africa indian subcontinent and the americas this supports a global factor as a main driver of the late miocene c4 expansion the combined carbon and oxygen isotope data reveal major shifts in climate to drier and or warmer conditions after 5 8 4 1 3 3 and 2 5 ma and significant shifts to relatively wetter and or cooler conditions after 6 4 5 3 5 ma the shifts to drier and or warmer climate after 5 8 ma and 2 5 ma coincide with two major fauna turnover events intra tooth 13c and 18o values are negatively correlated within individual modern teeth and some fossil teeth displaying the characteristic pattern of the summer monsoon regime and confirming a strong monsoon influence in the area since at least the early pliocene the data also suggest that the c4 abundance in the area has fluctuated over the past 6 5 ma in response to changes in climate with more c4 grasses during warmer and or drier periods and a reduced c4 component at cooler and or wetter times

in situ estimation of roof rock strength using sonic logging sonic travel time logging of exploration boreholes is routinely used in australia to obtain estimates of coal mine roof rock strength because sonic velocity logs are relatively inexpensive and easy to obtain during exploration the technique has provided australian underground coal mines with an abundance of rock strength data for use in all aspects of ground control design however the technique depends upon reliable correlations between the uniaxial compressive strength ucs and the sonic velocity this paper describes research recently conducted by niosh aimed at developing a correlation for use by the u s mining industry from two coreholes in illinois two from pennsylvania and one each from colorado western kentucky and southern west virginia sonic velocity logs were compared with ucs values derived from point load tests for a broad range of coal measure rock types for the entire data set the relationship between ucs and sonic travel time is expressed by an exponential equation relating the ucs in psi to the travel time of the p wave in s ft the coefficient of determination or r squared for this equation is 0 72 indicating that a relatively high reliability can be achieved with this technique the strength estimates obtained from the correlation equation may be used to help design roof support systems the paper also addresses the steps that are necessary to ensure that high quality sonic logs are obtained for use in estimating ucs

a long term increasing aridification and cooling trend at the chinese loess plateau during the pliocene the development of asian aridification and cooling is a research hotspot nowadays loess red clay sequence in the chinese loss plateau provides an excellent terrestrial archive of such paleoclimatic evolution this paper applied the magnetic unmixing technique to isolate the magnetic components of the red clay sequence for the first time the jiaxian section in the north edge of chinese loess plateau is sensitive to paleoclimate changes because it is in the transitional zone of the monsoon and non monsoon area systematic magnetic measurements and xrd analysis consistently indicate that the magnetic components of red clay are predominantly magnetite maghemite and hematite the strongly developed paleosols exhibit high content of soft magnetic minerals higher ms and mrs and lower bc and bcr while the weakly developed paleosols and loess samples display the opposite features with increasing alternating field the contributions of soft components to sirmx mt are cleaned gradually sirm is the saturation isothermal remanent magnetization sirmx mt represents the residual sirm after alternating field demagnetization at x mt the significant contributor to sirm100 mt is hematite an indication of the intensity of chemical weathering variations in the ratios of sirm100 mt sirm sirm100 mt sirm60 mt and sirm100 mt sirm30 mt document a long term up section decreasing trend during the last 5 2 6 ma with similar trends to the long term up section increase in 18o values of marine records decreased hematite content indicates weakened chemical weathering which further implies an increasing aridification and cooling and a gradually weakened summer paleomonsoon mainly in the depositional area chinese loess plateau in some loess layers where hematite is mainly of aeolian origin the mineral magnetic signals may indicate aridification and cooling in the asian interior source region this long term aridification and cooling trend is probably attributed to the comprehensive activity of ongoing global cooling progressive uplift of the tibetan plateau and changes in land sea distribution

late cenozoic eolian deposition in the north pacific asian drying tibetan uplift and cooling of the northern hemisphere a newly constructed record of eolian dust accumulation from the central north pacific shows that dust deposition increased by an order of magnitude quite rapidly at 3 6 ma we associate this sudden drying with the uplift of at least the northern portion of the tibetan plateau shutting off the indian ocean moisture source to central and western china this ten fold increase in atmospheric dust loading appears to be associated with the 1 m y long shift toward heavy 18o values that occurred at 3 6 2 6 ma the dust grain size record of wind intensity begins its late cenozoic coarsening a million years before the drying event at 4 5 ma the northern hemisphere cooling that results in intensification of the subpolar westerly winds may have as its ultimate cause the drawdown of atmospheric co2 in the latest miocene and the early pliocene closing of the panamanian seaway

the structure and development of the baikal rift depression abstract the baikal rift depression located in southeastern siberia is one of the best investigated intra continental rift structures in the world in addition to being the site of comprehensive studies by russian geo scientists for decades the baikal depression is now the subject of new international investigations using advanced technical means and technologies the present paper summarizes the principal results concerning the morphostructure of the baikal rift the stratigraphy of the cenozoic deposits and the stages of the baikal depression development based on cross sections which exhibit the impact of both tectonic and climatic processes the development of the baikal depression occurred through two stages i the pre crypto rift stage of the late cretaceous eocene and ii active rifting of the oligocene recent the second stage is divided into several steps and substeps separated by tectonic phases formation of the baikal rift zone appears to be related to the indo eurasian plate collision related to a model of passive rifting the uplifted shoulders of the depression have a complex morphostructure overlain by cenozoic deposits which are thin and restricted in area the near marginal zones of the rift are largely defined by the system of longitudinal blocks of different width surfaces of the blocks are inclined either to the uplifted shoulder of the rift bound by listric faults typical for western edges of the depression or to the axis of the depression cenozoic deposits on the blocks consist of accumulative plains composed primarily of thick lacustrine sequences

correlation of nearshore ice movement with seabed ice gouges near barrow alaska nearshore patterns of ice motion near barrow alaska were monitored between 1973 and 1979 with a sea ice radar system side scan sonar surveys of the seafloor were made at the same location during the summers of 1977 and 1978 the two data sets provide information on ice motion ice gouging and the rate and character of seabed deformation by ice four ice stages open water freeze up winter and breakup can be defined on the basis of the frequency and patterns of ice motion and ice cover processes as recorded by the radar system in all four ice stages the dominant ice motion was nearly parallel to the coast side scan sonar surveys show that the principal ice gouge directions nearshore were at a high angle to the coast and to the predominant direction of ice drift in both years gouge density was greatest in a narrow zone centered about the 10 m isobath which reflects the distribution of deep ice keels and the pattern of reworking of the seafloor by waves and currents we believe the majority of observed gouges were formed by keels of multiyear ice floes during an event that occurred in july 1975 2 years before the first seabed survey persistence of the gouge pattern from 1975 until 1977 is attributed to persistence of the ice cover and limited reworking by waves and currents or additional gouging the observed decrease in gouge density between 1977 and 1978 is attributed to 1 seafloor reworking and gouge infilling by storms and 2 the absence of ice conditions that were conducive to creating fresh gouges

magnetostratigraphy and paleoclimatic interpretation of a continuous 7 2 ma late cenozoic eolian sediments from the chinese loess plateau an almost 300m thick eolian sequence of late cenozoic sediments which includes 162 5m of quaternary loess paleosols and 126m of late tertiary eolian red clay from the central part of the chinese loess plateau was investigated to determine the magnetostratigraphy the results show that eolian dust accumulation and by inference the related east asia paleomonsoon had begun by 7 2ma as paleomonsoon are largely controlled by the tibetan plateau this implies that the plateau had reached some critical elevation by 7 2ma the section also documents a rapid increase in eolian dust accumulation in the late cenozoic at 3 2ma that is probably due to the influence of global ice volume on the east asian monsoon

major changes in east asian climate in the mid pliocene triggered by the uplift of the tibetan plateau or global cooling since the mid pliocene east asian climates have experienced significant changes one view suggests that significant uplift of the tibetan plateau during this period could have been responsible for these dramatic changes in the strength of the east asian monsoon and for asian interior acidification while some other authors attribute these changes to the ongoing global cooling and rapid growth of the arctic ice sheet up to the present which factor dominates the major changes of east asian climate in the mid pliocene is still a contentious issue this study presents an analysis of several climate proxies including grain size cao na2o mgo tio2 ratio na ka ratio and dust accumulation rates of the xifeng red clay sequence in the eastern chinese loess plateau and the xihe pliocene loess soil sequence in west qinling they reveal that aridity in the continental interior and winter monsoon circulation both intensified whereas the east asian summer monsoon showed a weakening rather than intensifying trend since the mid pliocene these changes are also supported by the other multi proxy records from various regions in east asia previous numerical modeling studies have demonstrated that uplift of the tibetan plateau would have simultaneously enhanced continental scale summer and winter monsoon strength as well as central asian aridity the mid pliocene climate changes in east asia are therefore unlikely to be a response to plateau uplift on the contrary our recent modeling results give support to the view that ongoing cooling could have intensified both the aridity of the interior and the strength of the winter monsoon but weakened the summer monsoon in east asia c 2012 elsevier ltd all rights reserved

geochemical evidence supporting t c chamberlin s theory of glaciation in 1899 t c chamberlin proposed that the co sub 2 content of the atomsphere decreased during times of enhanced continental erosion ultimately resulting in glacial epochs he ascribed the increase in the rate of chemical weathering relative to the rate of supply of co sub 2 from earth s interior to increased orogenic activity and globally higher average elevations which promoted rapid chemical erosion of silicates the oceanic record of strontium isotopes preserved in marine sediment supports his suggestion that glacial climates during the phanerozoic are in part linked to increases in the rate of global chemical erosion relative to outgassing from earth s interior further the close correspondence of the major tectonic episodes of the late cenozoic to times of increased continental erosion and glaciation suggests that chamberlin s hypothesis of the cause of glacial periods should be revived

development of asian monsoon revealed by marked ecological shift during the latest miocene in northern pakistan carbon isotopes from soil carbonate1 4 and soil organic matter5 6 yield palaeoecological information because the carbon in the soil carbonate forms in isotopic equilibrium with local soil co2 refs 1 7 the isotopic composition of which is in turn determined by local plant cover siwalik group sediments in northern pakistan contain a well exposed palaeosol record spanning the past 18 myr here we report on stable carbon isotope results from associated pedogenic carbonate which indicate a dramatic ecological shift from to dominated floodplain biomass beginning 7 4 7 0 myr ago the earlier c3 floodplain biomasses were probably mainly composed of trees and shrubs whereas c4 grasslands dominated in the plio pleistocene oxygen isotopes also exhibit a shift in the latest miocene probably corresponding to a major climate change which may have induced the forest to grassland transition this dramatic ecological shift in the latest miocene may mark the inception or a marked strengthening of the asian monsoon system

aeolian origin and palaeoclimatic implications of the red clay north china as evidenced by grain size distribution the red clay is an important deposit underlying the quaternary loess palaeosol sequence in the chinese loess plateau being regarded as an excellent record of palaeoclimate changes in the late tertiary several properties of the red clay have been measured previously in order to derive climatic information however the sedimentary processes involved and the origin of the materials remain controversial here we present results of grain size analyses of the red clay from four representative sites in the chinese loess plateau in particular their grain size distribution is compared with that of typical quaternary aeolian loess palaeosol as well as lacustrine and fluvial sediments it appears from the sedimentological evidence that the major part of the red clay is of aeolian origin it is rather similar in some of its properties to the quaternary loessic palaeosols the dust forming the red clay was transported by a wind system that was weaker than that involved in the accretion of the quaternary loess furthermore the red clay sediment has been modified by post depositional weathering copyright 2001 john wiley sons ltd

initial intensification of east asian winter monsoon at about 2 75 ma as seen in the chinese eolian loess red clay deposit 1 the loess paleosol red clay sequence in the chinese loess plateau provides a record of the evolution of atmospheric circulation and monsoon climate over east asia during the last 7 8 ma detailed analyses of the baishui and jingchuan sections show that the grain size of eolian loess increased abruptly at about 2 75 ma which is accompanied with a reversal of depositional pattern from the red clay to loess paleosol deposits suggesting that the dust transporting circulation was reorganized this is the earliest clear expression of the east asian winter monsoon intensification at the pliocene pleistocene climate transition coincident with the initiation of major northern hemisphere glaciation over the eurasian arctic and northeast asia implying that at the early stage of the pliocene pleistocene global cooling the east asian winter monsoon circulation had been closely linked with the build up of ice sheet and climate changes over the high latitudes of northern hemisphere the intensified winter monsoon winds would have in turn acted as an important positive feedback in strengthening global cooling by increasing albedo and dust loading

sea ice scouring on the inner shelf of the southeastern canadian beaufort sea abstract about 2200 ice scours were observed and analyzed over a distance of approximately 500 km on the inner shelf of the southeastern canadian beaufort sea ice scours were divided into two types based on their morphology multiple scours consisting of a series of parallel scours and ridges and single scours single scours are the dominant type representing more than 85 of the total observations the mean scour depth and width are 0 3 m and 11 m respectively but scour depths of more than 2 m and a scour width up to 345 m were documented the magnitude of ice scouring processes increases with water depth in water depths less than 10 m less than 25 of the seafloor surface is reworked by ice scours this percentage increases significantly seaward of the 10 m isobath being more than 75 in water depths in excess of 12 m a break in the seabed slope at about 10 to 12 m water depth marks a boundary between a nearshore zone moderately influenced by ice processes and an outer zone affected by intense ice scouring this morphological boundary could be due to intense erosion by the keels of pressure ice ridges at the inner edge of a zone of grounded ice ridges most of the observed ice scours appear to be reworked especially in water depths of less than 10 m and represent small scale sediment sinks inshore of the 10 m isobath scour reworking is believed to be mainly due to frequent bottom disturbance by wave orbital currents and mean near bottom flows during the open water season scour orientations show that the dominant motion of ice during scouring events is east or west which is subparallel to the bathymetric contours and coastline scour terminal push mounds however suggest a dominant east to southeast movement that may contribute to onshore sediment transport during ice push events

elastic and shear moduli of coal measure rocks derived from basic well logs using fractal statistics and radial basis functions abstract gamma ray density sonic and core logs obtained from two boreholes drilled over a longwall panel in southwestern sw pennsylvania were analyzed for formation boundaries log derived porosities and densities and for rock elastic properties from sonic transit times gamma ray gr and density logs dl were analyzed using univariate statistical techniques and fractal statistics for similarity and ordering of the log data in depth a fourier transformation with low pass filter was used as a noise elimination filtering technique from the original logs filtered data was tested using basic univariate and fractal statistics rescaled range r s and power spectrum ps analysis to compare the information characteristics of the filtered logs with the original data the randomness of log data in depth was analyzed for fractional gaussian noise fgn or fractional brownian motion fbm character a new prediction technique using radial basis function rbf networks was developed to calculate shear and young s moduli of the formations when sonic logs are not available for this approach the filtered logs were used as input to an rbf based upon a combination of supervised and unsupervised learning the network was trained and tested using rock elastic properties calculated from the sonic log of one of the boreholes the network was used to predict the elastic and shear moduli of the coal measure rocks over a longwall coal mine in sw pennsylvania this approach demonstrated that it could be used for prediction of elastic and shear moduli of coal measure rocks with reasonable accuracy

iron geochemistry of loess and red clay deposits in the chinese loess plateau and implications for long term asian monsoon evolution in the last 7 0 ma abstract recently some groups of authors have demonstrated that the tertiary red clay deposits underlying the pleistocene loess paleosol sequence in the chinese loess plateau are wind blown in origin thus extending the eolian record in the plateau from 2 6 ma back to about 7 0 ma and providing a good opportunity to reconstruct long term monsoon changes as magnetic susceptibility the widely used paleomonsoon proxy of loess deposits is problematic in reconstructing the monsoon history recorded in the red clay the development of other proxies is urgently needed in this study we analyzed the ratios of citrate bicarbonate dithionite cbd extractable fe2o3 to total fe2o3 concentrations in four loess sections along a north south transect of the loess plateau and in the lingtai loess red clay sequence of 305 m thick the fe2o3 ratio in the loess sections clearly shows higher values in soil units than in loess horizons and a southward increase in this ratio is also remarkable along the transect these are in good agreement with the temporal spatial variations in the east asia summer monsoon intensity identified by other monsoon proxies and soil development observations the fe2o3 ratio thus attests to being a good proxy indicator of the summer monsoon evolution the lingtai fe2o3 ratio record shows high values over three time intervals 4 8 4 1 ma 3 4 2 6 ma and during the interglacial periods of the past 0 8 ma the increase in summer monsoon intensity over the three intervals also coincides with the well developed soil characteristics it is therefore concluded that the east asia summer monsoon has experienced a non linear evolution since the late miocene the occurrence of a monsoon prime at about 4 8 4 1 ma implies that the tibetan plateau one of the most important boundary conditions in maintaining the monsoon circulation must have been uplifted to a critical height at that time

nearshore erosion by combined ice scouring and near bottom currents in eastern hudson bay canada abstract a study of nearshore sedimentary processes was carried out in manitounuk sound a sheltered environment protected by rocky islands along eastern hudson bay high resolution seismic profiles suggest that up to 10 m of holocene sediments were eroded in less than 15 m water depth although these shallow depths are affected by low energy waves and currents according to our measurements of near bottom currents at 3 7 and 5 6 m water depths the threshold velocity for sediment motion 20 cm s 1 is only seldom exceeded and consequently the significant erosion of the nearshore deposits can hardly be explained by hydraulic processes alone geophysical data seismic and echosounding profiles suggest that the observed erosion is mainly due to bottom scouring by dragging ice keels these data show that the zone of maximum ice scouring between 8 and 12 m water depths corresponds to the zone of maximum erosion of holocene sediments because ice scouring in this area occurs when the sea is largely ice free wind induced near bottom currents probably contribute to the dispersal of the sediments resuspended by ice

pedostratigraphy and paleomagnetism of a 7 0 ma eolian loess red clay sequence at lingtai loess plateau north central china and the implications for paleomonsoon evolution abstract a 305 m thick loess red clay sequence was discovered recently at lingtai which is located in the middle part of the chinese loess plateau it consists of a complete pleistocene loess soil sequence with a thickness of about 175 m and 130 m of tertiary red clay deposits the red clay sequence at lingtai is the thickest one presently known in the loess plateau field observations show that the lingtai red clay contains over 110 couplets of pedogenic b horizons and horizontal carbonate nodule horizons and that it can be regarded as an extremely thick soil complex paleomagnetic studies of 680 samples suggest that the basal age of the lingtai loess red clay sequence is about 7 05 ma grain size analysis of samples taken at 3 3 cm intervals indicates that the red clay has the same sedimentological characteristics as those observed in the loess thus suggesting a wind blown origin of the tertiary red clay and continuous atmospheric dust deposition in the loess plateau during the last 7 05 ma the pedogenic characteristics of the paleosols within the pleistocene loess and the b horizons in the red clay suggest that the east asia summer monsoon in the latest miocene may have already been slightly stronger than that during the holocene this implies that at about 7 5 ma bp the tibetan plateau could have been uplifted to a critical height in maintaining the east asia summer monsoon system observations of the loess red clay sequence also suggest that the long term changes in the east asia summer monsoon strength have been nonlinear since the latest miocene

reconstruction of glaciation over the past 6 myr from ice borne deposits in the norwegian sea it is well known that a significant intensification of northern hemisphere glaciation occurred 2 5 myr ago in contrast to the much earlier onset 35 myr of glaciation in antarctica1 3 much less is known about the behaviour of the climate before 2 5 myr and it has remained unclear when sizeable glaciers first started to develop in the northern hemisphere here we deduce the history of high northern latitude glaciation over the past 6 myr from records of ice borne deposits in deep sea sediments of the norwegian sea we find that glaciers large enough to reach sea level were present in the norwegian sea area as early as 5 5 myr three million years before the intensification of glaciation at 2 5 myr fluctuations in ice volume can be deduced from the oxygen isotope record but this provides only a global average which may not reflect the history of ice sheet growth in specific regions from a comparison of the oxygen isotope records with the record of ice rafted material we derive an estimate of the relative contributions of southern and northern hemisphere glaciation to global variations in ice volume

pliocene uplift of the northern tibetan plateau neogene redbeds passing upward into upward coarsening conglomerate and debris flow deposits at the foot of the kunlun mountains record the change in paleoslope related to uplift of the surface of the northern tibetan plateau detailed magnetostratigraphy of a 4 5 km section near yecheng in the western kunlun mountains shows that the change from deposition on distal alluvial plains to proximal alluvial fans occurred during the gilbert reversed chron 4 5 3 5 ma the change in depositional facies was accompanied by an increase in sedimentation rate from an average 0 15 mm yr between the earliest oligocene and the earliest pliocene to 1 4 mm yr in the gauss normal chron 3 6 2 6 ma we interpret the change in depositional facies and increase in sedimentation rate as indicating that the main uplift of the northwestern tibetan plateau began ca 4 5 ma

late cenozoic environmental changes and uplift on the northern side of the central himalaya a reappraisal from field data abstract the extreme view that uplift of the tibetan plateau and the adjacent himalayan range occurred mainly during the quaternary cannot be further sustained as discussed in the light of available field data palaeobiogeography sedimentary environments and tectonic evidence comparison with other independent sources such as the loess records of central china and data on the post orogenic sedimentation and geochronology of the himalayan and south asian oceanic fans shows that the tibetan plateau certainly reached an elevation close to its present one before the climatic changes of the quaternary as such this elevated himalaya tibet ensemble was probably one of the major causes of the late tertiary general cooling of the northern hemisphere as suggested by global modelling of climate palaeoenvironmental changes observed during the quaternary were certainly governed by orbital parameters yet they were also regionally influenced by both the uplift of the greater himalaya with respect to tibet and by the disruption of the northern himalaya and south tibet into horsts and grabens uncertainty still surrounds the periods during which critical elevations were achieved to induce both the monsoon circulation and e w extension

late cenozoic magnetochronology and paleoenvironmental changes in the northern foreland basin of the tian shan mountains 1 the folded neogene deposits in the northern foreland basin of the tian shan mountains provide important information about tectonic history and environmental changes of northwestern china on the basis of lithostratigraphic and magnetostratigraphic evidence we develop a new chronology for the previous studied kuitun he section our palynological study on the late miocene pliocene sediment of the dushanzi section yields new information about vegetation and climate change during the period of 8 7 2 58 ma the results indicate that steppe taxa artemisia and chenopodiaceae were generally dominant in the studied areas between 8 7 and 2 58 ma implying that a dry climate has occurred in the inland basins of northwestern china at least since 8 7 ma ago although the general climate pattern indicated by our palynological results displays to some extent of drought a warm and humid phase occurred at 5 8 3 9 ma ago this climatic optimum is comparable with the other records from the chinese loess plateau central japan the sub himalayan zone and the marine eustatic sea level rise implying this seems to be at least a regional climatic optimum

onset of asian desertification by 22 myr ago inferred from loess deposits in china the initial desertification in the asian interior is thought to be one of the most prominent climate changes in the northern hemisphere during the cenozoic era1 2 3 4 but the dating of this transition is uncertain partly because desert sediments are usually scattered discontinuous and difficult to date here we report nearly continuous aeolian deposits covering the interval from 22 to 6 2 million years ago on the basis of palaeomagnetic measurements and fossil evidence a total of 231 visually definable aeolian layers occur as brownish loesses interbedded with reddish soils this new evidence indicates that large source areas of aeolian dust and energetic winter monsoon winds to transport the material must have existed in the interior of asia by the early miocene epoch at least 14 million years earlier than previously thought3 5 regional tectonic changes and ongoing global cooling are probable causes of these changes in aridity and circulation in asia

origin of the miocene pliocene red earth formation at xifeng in northern china and implications for paleoenvironments abstract in the eastern loess plateau region of northern china the quaternary loess soil sequences of the last 2 6 ma are underlain by the hipparion red earth formation magneto stratigraphic studies suggest that it is a near continuous terrestrial record for the period from 7 to 2 6 ma bp and therefore has great potential for the study of asian paleoclimates the origin of this formation is controversial and needs further study in this work the xifeng red earth section a type section for the eastern loess plateau region was studied using optical microscopic analysis grain size measurements and both major and trace element geochemical properties to address questions of its origin and environmental implications the results show that this formation consists of three parts the lower part 6 2 ma bp is a water reworked deposit related to alluvial and slope processes the middle part from 6 2 to 3 6 ma bp was derived from in situ eolian dust deposition but was significantly affected by groundwater oscillations and the upper part from 3 6 to 2 6 ma bp is an eolian formation similar to the quaternary loess soil sequence the grain size of the upper part is significantly coarser than for the middle part but finer than for the overlying loess because the eolian dust deposits in the middle reaches of the yellow river were mainly transported from the deserts in northern china by the northwesterly winter monsoon wind and the westerlies we interpret the eolian origin of the middle and upper red earth formation beginning approximately at 6 2 ma bp as an indication of the strengthening of the aridification of the asian continent desert lands in central asia must have been formed at or by that time to provide a significant source of dust however the generally finer grain size of the red earth suggests a weaker transporting wind and or a more remote source the latter implies a smaller extent of deserts than in the quaternary the high degree of similarity between the geochemical properties of the red earth and loess samples seems to suggest a rather similar source areas and comparable dust transporting trajectories the removal of the dust deposits from groundwater influence and the increase in grain size at 3 6 ma bp are attributable to both tectonic and climatic causes the initiation of these phenomena corresponds to an intensive uplift of the tibetan plateau and also to a simultaneous uplift of the sedimentary basins in the surrounding areas it is also approximately synchronous with an increase in eolian mass accumulation rate in the north pacific both suggesting an increased continental aridity in the asian dry lands and an increasing intensity of transporting winds

predicting rock mechanical properties of carbonates from wireline logs a case study arab d reservoir ghawar field saudi arabia abstract four hundred plug samples from the arab d carbonate reservoir ghawar field were tested for acoustic and mechanical properties at increasing triaxial stress the results show that the rock mechanical parameters are primarily functions of porosity and to a lesser degree of mineralogy texture and pore fabric in order of degree of impact from higher to lower the rock mechanical parameters of the intact matrix rock show no significant changes with stress under reservoir condition the study enabled the generation of general and layer specific correlation formulae of porosity with p wave velocity s wave velocity static and dynamic constants and the angle of internal friction the formulae were then applied to a key well in the ghawar using the compressional wave slowness from a multipole array acoustic log mac baker atlas to derive rock mechanical pseudo logs on reservoir scale referred to here as general and on individual reservoir zone scale referred to here as layer specific comparison made between the general and the layer specific pseudo logs shows good agreement for each of the elastic constants with matching peaks and troughs throughout the logs in addition the laboratory derived rock mechanical constants show a good agreement with the pseudo logs where there is some difference between the general and layer specific pseudo logs the layer specific log shows better correlation with the laboratory derived constants it can be concluded that the porosity correlation is an accurate representative and cost effective method of obtaining a rock mechanical profile of the arab d reservoir the derived formulae have been implemented as predictive tools in reservoir development and management e g hydrofracturing and underbalanced drilling and new prospect evaluation the rock mechanical layering scheme shows higher resolution in the prolific part of the arab d reservoir than the saudi aramco conventionally used zonation each of zones 2b and 3a consists of two rock mechanical layers furthermore the least prolific zones lower part of 3a the whole of 3b and 4 form one rock mechanical layer

african climate change and faunal evolution during the pliocene pleistocene abstract environmental theories of african faunal evolution state that important evolutionary changes during the pliocene pleistocene interval the last ca 5 3 million years were mediated by changes in african climate or shifts in climate variability marine sediment sequences demonstrate that subtropical african climate periodically oscillated between markedly wetter and drier conditions paced by earth orbital variations with evidence for step like 0 2 ma increases in african climate variability and aridity near 2 8 ma 1 7 ma and 1 0 ma coincident with the onset and intensification of high latitude glacial cycles analysis of the best dated and most complete african mammal fossil databases indicates african faunal assemblage and perhaps speciation changes during the pliocene pleistocene suggesting more varied and open habitats at 2 9 2 4 ma and after 1 8 ma these intervals correspond to key junctures in early hominid evolution including the emergence of our genus homo pliocene pleistocene shifts in african climate vegetation and faunal assemblages thus appear to be roughly contemporary although detailed comparisons are hampered by sampling gaps dating uncertainties and preservational biases in the fossil record further study of possible relations between african faunal and climatic change will benefit from the accelerating pace of important new fossil discoveries emerging molecular biomarker methods for reconstructing african paleovegetation changes tephra correlations between terrestrial and marine sequences as well as continuing collaborations between the paleoclimatic and paleoanthropological communities

coastal landfast sea ice decay and breakup in northern alaska key processes and seasonal prediction 1 seasonal breakup of landfast sea ice consists of movement and irreversible ice detachment in response to winds or oceanic forces in the late stages of ice decay the breakup process of landfast sea ice in the chukchi sea at barrow alaska was analyzed for the years 2000 through 2010 on the basis of local observations of snow and ice conditions weather records image sequences obtained from cameras coastal x band marine radar and satellite imagery we investigated the relation of breakup to winds tides and nearshore current measurements from a moored acoustic doppler current profiler two breakup modes are distinguished at barrow on the basis of the degree of ice decay mechanical breakup due to wind and oceanic forces follows ablation and weakening of the ice thermal breakup is the result of ice disintegration under melt ponds requiring little force to induce dispersion grounded pressure ridges are pivotal in determining the breakup mode the timing of thermal breakup of the nearshore ice cover was found to correlate with the measured downwelling solar radiation in june and july this linkage allows for the development of an operational forecast of landfast ice breakup results from forecasts during 2 years demonstrate that thermal breakup can be predicted to within a couple of days 2 weeks in advance the cumulative shortwave energy absorbed by the ice cover provides for a measure of the state of ice decay and potential for disintegration discriminating between the two modes of breakup bears the potential to greatly increase forecasting skill

increased seasonality and aridity drove the c4 plant expansion in central asia since the miocene pliocene boundary abstract continuous and high resolution records of the content mass accumulation rate mar and 13 c values of black carbon obtained from integrated ocean drilling program iodp site u1430 in the southwestern japan sea have been established and combined with previous results obtained from central asia the main objective of this work is to reconstruct the historical changes in vegetation types c3 c4 and to constrain the driving force of c4 plant expansion over the last 13 ma the stable carbon isotope value of black carbon 13 c bc shows a major shift since the miocene pliocene boundary 5 3 ma suggesting significant expansion of c4 plants in broad areas of central asia including the inland basins of northwestern china and the loess plateau however a decline in the content and mar of black carbon reveals the absence of any link between fire and c4 plant expansion in central asia due to the dramatic decrease in biomass under a drying regime on a global scale asynchronous expansion of c4 plants suggests that regional hydroclimatic change rather than decline in co 2 concentration was the most important factor to influence c4 expansion we propose that the increased seasonality and the enhanced long term aridity driven by the concurrent decline in winter westerly vapor and increase in east asian summer monsoon precipitation were the main driving forces of c4 plant expansion in broad areas of central asia variations in winter westerly moisture have played a significant role in changes of regional climate and vegetation in central asia since the late miocene