geochemical characteristics of the eolian deposits in southern china and their implications for provenance and weathering intensity abstract the loess paleosol sequences in the middle lower reaches of the yantgze river are valuable geological records of quaternary environments that bear information about climate change for the subtropical zone of southern china type sections containing eolian deposits in this region mostly include the upper loess soil sequence referred to as xiashu loess formation the middle vermiculated red soil vrs and the underlying fluvial deposits or bedrock in this study xiashu loess paleosol formed in the xiashu loess and the vrs samples from xuancheng xc and jiujiang jj sections were analyzed for their elemental major and trace elements and isotopic sm nd geochemistry and compared with pleistocene loess and paleosol samples from the chinese loess plateau clp in northern china the results show an overall similarity in geochemical characteristics between the southern china loess and the average ucc indicating that the dust materials were derived from well mixed sedimentary protoliths which had undergone numerous upper crustal recycling processes in comparison with the loess of northern china the eolian deposits in southern china have higher tio2 zr hf and lower ba concentrations higher tio2 al2o3 u pb th pb and lower ba rb zr hf eu eu ce yb eu yb ratios and lower end 0 values with relatively greater range these features coincide with the complicated source rock compositions in the middle lower yangtze river which suggests local sources for the eolian deposits in this region the eolian deposits in southern china have experienced the intermediate k removal weathering stage ca sr na mg and k are the main mobile elements in the weathering process in comparison with the xiashu loess formation the vrs has greater depletion of na mg k and mn indicating a stronger weathering intensity or perhaps a longer period of weathering

quantifying lithogenic inputs to the north pacific ocean using the long lived thorium isotopes abstract dissolved 232th is added to the ocean though the partial dissolution of lithogenic materials such as aerosol dust in the same way as other lithogenically sourced and more biologically important trace metals such as fe oceanic 230th on the other hand is sourced primarily from the highly predictable decay of dissolved 234u the rate at which dissolved 232th is released by mineral dissolution can be constrained by a th removal rate derived from 230th 234u disequilibria assuming steady state calculated fluxes of dissolved 232th can in turn be used to estimate fluxes of other lithogenically sourced dissolved metals as well as the original lithogenic supplies such as aerosol dust deposition given the concentration and fractional solubility of th or other metals in the lithogenic material this method is applied to 7 water column profiles from the innovative north pacific experiment inopex cruise of 2009 and 2 sites from the subtropical north pacific the structure of shallow depth profiles suggests rapid scavenging at the surface and at least partial regeneration of dissolved 232th at 100 200 m depth this rapid cycling could involve colloidal th generated during mineral dissolution which may not be subject to the same removal rates as the more truly dissolved 230th an additional deep source of 232th was revealed in deep waters most likely dissolution of seafloor sediments and offers a constraint on dissolved trace element supply due to boundary exchange

transport of u and th series nuclides in a baltic shield watershed and the baltic sea the transport of th ra and 210 pb from a continental source region and through an estuarine environment was investigated unlike previous studies here both short and long lived nuclide data were obtained for river inputs river water and estuarine waters the mire rich kalix river drainage basin was chosen as a typical northern shield area because this river may represent typical waters flowing into the arctic and northern seas groundwaters from bedrock and glacial tills have comparable th isotope concentrations and do not exhibit significant th isotopic shifts relative to host rocks the extensive peat deposits of the basin receive groundwater discharges and concentrate th and u but not ba and ra which cause high 230 th 232 th ratios in mire waters however mire outflows do not have a significant impact on th and ra isotopic compositions of the river overall weathering characteristics for the basin are obtained from the river data the 230 th 232 th 228 ra 226 ra and 226 ra ba river ratios are comparable to those of source rocks consistent with similar release rates of these nuclides from u th and ba bearing minerals river ratios of 230 th 238 u ar and 226 ra 238 u ar are 1 so that th and possibly ra are accumulating in the weathering regions and the weathering profile is still evolving low 228 ra 232 th ar and 226 ra 230 th ar ratios indicate that th is preferentially retained over ra river 234 th 238 u ar ratios are greater than 230 th 238 u ar ratios and suggest that in systems where river inputs are well characterized these ratios can be used to calculate th transit times through the watershed filtration data indicate that although a dominant fraction of the th is transported in the river on particles the rest is almost entirely carried by colloids the kalix river discharges into the baltic sea model calculations for the transport of th and ra isotopes in the baltic sea show that the high ratios of 234 th 238 u ar found here reflect long th residence times relative to particle scavenging of 50 d the water column 232 th budget is dominated by eolian inputs the 226 ra concentrations may be higher than those of water inflows with 60 derived from underlying sediments a greater fraction of 228 ra is derived from sediments to balance the decay of 228 ra within the water column during the 35 yr residence time of water in the baltic the baltic 228 ra 226 ra ar ratios which are relatively constant over a range of salinities are fortuitously similar to those of the river inflows

time scale and conditions of weathering under tropical climate study of the amazon basin with u series the rio solimoes amazonas amazon river and its major tributaries have been analyzed for u series nuclides 238 u 234 u 230 th 226 ra disequilibria have been measured in the dissolved 0 2 lm as well as bed sands u series disequilibria are closely related to major and trace element compositions and therefore reflect elemental fractionation during chemical weathering moreover while the dissolved load records present day weathering suspended particles integrate the erosion his tory over much longer time scales 100 ka lowland rivers are characterized by long time scales of chemical erosion p100 ka result ing in a high weathering intensity moreover exchange between suspended particles and the dissolved load may explain the u series signature for these rivers by combining u series and pb isotopes in suspended particles we show that erosion in the rio madeira basin occurred as a multi step process whereby the pristine continental crust was eroded several hundreds of ma ago to produce sediments that have then been integrated in the cordillera by crustal shortening and are currently eroded in contrast recent erosion of a pristine crust is more likely for the rio solimoes amazonas 10 ka the suspended particles of the rivers draining the andes solimoes ama zonas madeira suggest time scales of weathering ranging between 4 and 20 ka this indicates that suspended particles transported by those rivers are not stored for long periods in the andean foreland basin and the tropical plain the sediments delivered to the ocean have resided only a few ka in the amazon basin 6 3 1 ka for the rio amazonas at obidos nevertheless a large fraction of the sediments coming out from the andes are trapped in the foreland basin and may never reach the ocean erosion in the andes is not operating in steady state u series systematics shows unambiguously that rivers are exporting a lot more sediments than predicted by steady state erosion and that is a consequence of soil destruction greater than production by relating this observation to the short time scales of weathering inferred for the andes a few ka it appears that the erosion regime has been recently perturbed resulting in high denudation rates a possible explanation would be the increase in precipitation less than 5 ka proposed by recent paleoclimatic studies our results indicate that erosion responds rapidly to high frequency climatic fluctuations

precise determination of the open ocean 234u 238u composition uranium has a long residence time in the open oceans and therefore its salinity normalized u concentration and 234u 238u activity ratio expressed herein as 234u the deviation from secular equilibrium are assumed to be uniform the marine 234u 238u activity ratio is currently in radioactive disequilibrium and shows a 15 excess of 234u with respect to the secular equilibrium value due to continuous input from riverine sources knowledge of the marine 234u and how it has evolved through the quaternary is important for validating age accuracy in the u series dating of marine carbonates which is increasingly relied upon for providing a chronological basis in paleoclimate research however accurate and precise measurements of 234u are technically difficult thus existing compilations of the open ocean 234u value vary by up to 10 and the assumed uniformity in the oceanic 234u remains to be confirmed using mc icpms techniques and a suite of multiple faraday cups instead of the typical configurations based on a combined faraday cup multiplier array a long term reproducibility of better than 0 3 2 is achieved for 234u measurements applying these very high precision techniques to open ocean seawater samples an average 234u of 146 8 0 1 2 m n 19 is obtained these high precision seawater measurements yield an external reproducibility of better than 0 4 2 and show that the open oceans have a uniform 234u on the sub level these new data constrain the vertical mixing time of the open oceans to less than 1000 years

230th and 231pa on geotraces ga03 the u s geotraces north atlantic transect and implications for modern and paleoceanographic chemical fluxes abstract the long lived uranium decay products 230th and 231pa are widely used as quantitative tracers of adsorption to sinking particles scavenging in the ocean by exploiting the principles of radioactive disequilibria because of their preservation in the pleistocene sediment record and through largely untested assumptions about their chemical behavior in the water column the two radionuclides have also been used as proxies for a variety of chemical fluxes in the past ocean this includes the vertical flux of particulate matter to the seafloor the lateral flux of insoluble elements to continental margins boundary scavenging and the southward flux of water out of the deep north atlantic in a section of unprecedented vertical and zonal resolution the distributions of 230th and 231pa across the north atlantic shed light on the marine cycling of these radionuclides and further inform their use as tracers of chemical flux enhanced scavenging intensities are observed in benthic layers of resuspended sediments on the eastern and western margins and in a hydrothermal plume emanating from the mid atlantic ridge boundary scavenging is clearly expressed in the water column along a transect between mauritania and cape verde which is used to quantify a bias in sediment fluxes calculated using 230th normalization and to demonstrate enhanced 231pa removal from the deep north atlantic by this mechanism the influence of deep ocean ventilation that leads to the southward export of 231pa is apparent the 231pa 230th ratio however predominantly reflects spatial variability in scavenging intensity complicating its applicability as a proxy for the atlantic meridional overturning circulation

iron manganese and lead at hawaii ocean time series station aloha temporal variability and an intermediate water hydrothermal plume trace metal clean techniques were used to sample hawaii ocean time series hot station aloha on seven occasions between november 1998 and october 2002 on three occasions full water column profile samples were obtained on the other four occasions surface and near surface euphotic zone profiles were obtained together with three other published samplings this site may have been monitored for dissolved 0 4 or 0 2 m fe more frequently than any other open ocean site in the world low fe concentrations 2500 m the concentrations we observe 0 4 0 5 nmol kg 1 are significantly lower than some other deep north pacific stations but are similar to values that have been reported for a station 350 miles to the northeast we attribute these low deepwater values to transport of low fe antarctic bottom water into the basin and a balance between fe regeneration and scavenging in the deep water near surface waters have higher fe levels than observed in the lower euphotic zone significant temporal variability is seen in near surface fe concentrations ranging from 0 2 0 7 nmol kg 1 we attribute these surface fe fluctuations to variable dust deposition biological uptake and changes in the mixed layer depth this variability could occur only if the surface layer fe residence time is less than a few years and based on that constraint it appears that a higher percentage of the total fe must be released from north pacific aerosols compared to north atlantic aerosols surprisingly significant temporal variability and high particulate fe concentrations are observed for intermediate waters 1000 1500 m these features are seen in the depth interval where high 3he from the nearby loihi seamount hydrothermal fields has been observed the total fe 3he ratio implies that the hydrothermal vents are the source of the high and variable fe the vertical profile of mn at aloha qualitatively resembles other north pacific mn profiles with surface and intermediate water maxima but there are some significant quantitative differences from other reported profiles the 0 4 m mn concentration is highest near the surface decreases sharply in the upper 500 m then shows an intermediate water maximum at 800 m and then decreases in the deepest waters these concentrations are higher than observed at a station 350 miles to the northeast that shows similar vertical variations it appears that there is a significant mn gradient throughout the water column from hot towards the northeast compared to the first valid oceanic pb data for samples collected in 1976 pb at aloha in 1997 1999 shows decreases in surface waters and waters shallower than 200 m pb concentrations in central north pacific surface waters have decreased by a factor of 2 during the past 25 yr from 65 to 30 pmol kg 1 surface water pb concentrations in the central north atlantic and central north pacific are now comparable we attribute the surface water pb decrease to the elimination of leaded gasoline in japan and to some extent by the u s and canada we attribute most of the remaining pb in pacific surface waters to asian emissions more likely due to high temperature industrial activities such as coal burning rather than to leaded gasoline consumption a 3 year mixed layer time series from the nearby hale aloha mooring site 1997 1999 shows that there is an annual cycle in pb with concentrations 20 higher in winter months this rise may be created by downward mixing of the winter mixed layer into the steep gradient of higher pb in the upper thermocline pb concentrations double between the surface and 200 m from 200 m to the bottom pb concentrations decrease to levels of 5 9 pmol kg 1 near the bottom for most of the water column thermocline and deepwater pb concentrations do not appear to have changed significantly during the 23 yr interval

iron isotopes in the amazon river system weathering and transport signatures abstract trace metal clean plankton tows river samples aerosol leachates and porewater samples from the amazon river system were measured for their iron isotopic composition the overall isotopic range observed was 1 5 with fe isotopic variability observed between different types of tributaries dissolved fe and suspended load fe from two main channel sites were isotopically similar 0 1 to 0 3 in contrast the dissolved fe and suspended load fe from an organic rich tributary the negro river were isotopically distinct with the dissolved slightly isotopically heavy 0 3 and the suspended load isotopically light 0 9 the isotopically lightest sample from the amazon region was shelf porewater 1 3 in river water seawater mixing experiments the fe isotopic signal of dissolved fe of river water was modified by flocculation of isotopically heavy fe the variability of the fe isotopic composition of natural samples including biological and aqueous samples demonstrates that significant fractionation is associated with fe biogeochemistry in the environment

late pliocene greenland glaciation controlled by a decline in atmospheric co2 levels it is thought that the northern hemisphere experienced only ephemeral glaciations from the late eocene to the early pliocene epochs about 38 to 4 million years ago and that the onset of extensive glaciations did not occur until about 3 million years ago several hypotheses have been proposed to explain this increase in northern hemisphere glaciation during the late pliocene here we use a fully coupled atmosphere ocean general circulation model and an ice sheet model to assess the impact of the proposed driving mechanisms for glaciation and the influence of orbital variations on the development of the greenland ice sheet in particular we find that greenland glaciation is mainly controlled by a decrease in atmospheric carbon dioxide during the late pliocene by contrast our model results suggest that climatic shifts associated with the tectonically driven closure of the panama seaway with the termination of a permanent el nino state or with tectonic uplift are not large enough to contribute significantly to the growth of the greenland ice sheet moreover we find that none of these processes acted as a priming mechanism for glacial inception triggered by variations in the earth s orbit

an overview of dissolved fe and mn distributions during the 2010 2011 u s geotraces north atlantic cruises geotraces ga03 abstract high resolution dissolved fe dfe and dissolved mn dmn distributions were obtained using a trace metal clean rosette during the geotraces ga03 zonal transect cruises usgt10 and usgt11 across the north atlantic ocean this manuscript provides a general overview of the dfe as well as dmn and dissolved al dal distributions that reveal several fe inputs at varying depths across the study region elevated dfe concentrations correlate with elevated dal concentrations in the surface waters of the subtropical gyre indicating a significant atmospheric source of fe in contrast there is no apparent significant dust source for mn in the subsurface waters dfe maxima are a result of the remineralization process as revealed by their correspondence with dissolved oxygen minima within the oxygen minimum the ratio of dfe to apparent oxygen utilization aou is lower than would be expected from the measured fe content of surface water phytoplankton suggesting that a significant amount of dfe that is remineralized at depth 63 90 is subsequently scavenged from the water column the rate of remineralization which is based on the slope of dfe aou plot is similar across a wide area of the north atlantic in addition to the remineralization process sedimentary inputs are apparent from elevated dmn signals in the eastern basin particularly near the african coast in the western basin sedimentary input is also occurring along the advective flow path of the upper labrador sea water ulsw as ulsw transits along the north american continental shelf region the largest dfe anomaly 68 nm which also corresponds to a dmn anomaly up to 33 nm is seen in the neutrally buoyant hydrothermal plume sampled over the mid atlantic ridge and that signal is visible for 500 km to the west of the ridge

a new perspective on boundary scavenging in the north pacific ocean boundary scavenging or the enhanced removal of adsorption prone elements from the ocean in areas of high particle flux is an often cited though not well quantified concept used to understand the oceanic distribution of many trace metals because 230 th and 231 pa are produced uniformly from uranium decay and removed differentially by scavenging the process of boundary scavenging can be elucidated by a more detailed knowledge of their water column distributions to this end filtered seawater was collected across the gradients in particle flux which span the subarctic pacific in the west during the innovative north pacific experiment inopex and in the east along line p lateral concentration gradients of dissolved 230 th are small throughout the subarctic pacific at 12 sites of variable particle flux this contradicts the prediction of the traditional boundary scavenging model a compilation of water column data from throughout the north pacific reveals much larger lateral concentration gradients for 230 th between the subarctic north pacific and subtropical gyre over lateral gradients in scavenging intensity similar to those found within the subarctic this reflects a biogeochemical province aspect to scavenging upper water column distributions of 231 pa and 231 pa 230 th ratio are consistent with the influence of scavenging by biogenic opal while deep waters 42 5 km reveal an additional 231 pa sink possibly related to manganese oxides produced at continental margins or ridge crests

step wise change of asian interior climate preceding the eocene oligocene transition eot abstract understanding the global climate change from greenhouse to icehouse conditions at the eocene oligocene transition eot 34 million years ago requires climatic records from oceanic as well as continental realms of the key late eocene doubthouse period preceding this switch here we report integrated stratigraphic results from well dated late eocene continental mudflat to saline lake paleoenvironments of the xining basin northeastern tibetan plateau western china recording regional and global change cyclostratigraphic analysis strongly suggests continuous dominance of the 41 kyr obliquity cycle in the whole late eocene interval down to the base of polarity chron c18n 2n at 39 ma with additional input of the 100 kyr eccentricity cycle up to the base of chron c13r at 34 7 ma this might imply that high latitude climates dominated the area long before the eot probably related to incipient ice volume fluctuations furthermore our results reveal two paleoenvironmental deterioration steps preceding the eocene oligocene transition the first step occurs in the top of chron c17n 1n at 36 6 ma this age closely corresponds to 1 the high altitude pollen appearance in chron c16 2r at 36 4 ma in the same section 2 the recently dated final retreat of the tarim sea in western china and 3 a shift from precession to obliquity dominance in the atlantic ocean this near co occurrence suggests global change at this time we hypothesize this change is related to an increase in incipient ice sheet volume leading to passing threshold conditions for the high altitude pollen appearance and tarim sea retreat finally leading to decreased moisture availability in the xining basin at the second step in the base of chron c13r at 34 7 ma a substantial increase in clastic sedimentation rates is observed this might relate to increased climate variability preceding the greenhouse to icehouse transition at the eot that prevented landscapes to attain equilibrium configurations

calibration and comparison of the ldgo nephelometer and the osu transmissometer on the nova scotian rise gardner w d biscaye p e zaneveld j r v and richardson m j 1985 calibration and comparison of the ldgo nephelometer and the osu transmissometer on the nova scotian rise in a r m nowell and c d hollister editors deep ocean sediment transport preliminary results of the high energy benthic boundary layer experiment mar geol 66 323 344 during the survey of the hebble high energy benthic boundary layer experiments area two optical instruments were used to determine the spatial and temporal structure of the benthic nepheloid layer both instruments showed a linear response to suspended particle mass and volume over the typical range of concentrations found in the ocean 10 250 ug l at higher concentrations the transmissometer response remains linear but as previously noted and as shown here by theory the nephelometer has a predictable second order response due to multiply scattered light at the low concentrations found in mid water both instruments seem near their limit of sensitivity small differences between instruments at low concentrations may result from variations in response to particle types found in mid water or may be minor second order effects of temperature or pressure on the instruments the comparison made here shows that either instrument can be effectively used to study the nepheloid layer and that data from different study areas using these instruments can consistently be compared the hebble region was ideal for testing the range of these instruments because it yielded the highest concentrations of particles ever recorded in the deep sea

erratum to edward a boyle bridget a bergquist richard a kayser and natalie mahowald 2005 iron manganese and lead at hawaii ocean time series station aloha temporal variability and an intermediate water hydrothermal plume geochimica et cosmochimica acta 69 933 952

dissolved and particulate 231 pa and 230 th in the atlantic ocean constraints on intermediate deep water age boundary scavenging and 231 pa 230 th fractionation 231pa and 230th concentrations were determined in filtered seawater and suspended particulate matter collected from the labrador sea and the equatorial and south atlantic to constrain their application as tracers of intermediate deep water age and atlantic thermohaline circulation distributions of total 231pa and 230th indicate the influence of recently formed north atlantic deep water as evidenced by nearly invariant concentrations below 1000 m in the labrador sea and increasing 231pa and 230th concentrations as deep waters progress southward from northern source regions application of a scavenging mixing model to both tracer distributions indicates an intermediate deep water age of 12 yr in the labrador sea and a 30 140 yr transit time to the low latitude stations we attribute a striking increase in total 230th in the labrador sea from 1993 to 1999 to aging of intermediate waters as a consequence of the cessation of deep convection in the labrador sea since 1993 the temporal change in the 230th age of these waters is consistent with the 6 yr time interval between the observations the average particulate 231pa 230th activity ratio in the labrador sea and low latitude deep waters is 0 057 0 003 significantly below the 231pa 230th production ratio 0 093 and in agreement with excess 231pa 230th ratios in holocene sediments 0 060 0 004 and sediment trap material 0 034 0 012 from the atlantic and model simulations this observation is consistent with the southward transport of deep water strongly attenuating boundary scavenging in the atlantic a latitudinal dependence in particle fractionation of these tracers is also evident with elevated fractionation factors fth pa observed near the equator and south atlantic gyre 11 compared to low values in the labrador sea 3 and southern ocean 2 there also exists a depth dependence in fth pa characterized by low values in surface waters a broad mid depth maximum and decreasing values towards the sea floor the latitudinal and depth variations in fth pa are suggested to reflect differences in the chemical composition of marine particles

late eocene sea retreat from the tarim basin west china and concomitant asian paleoenvironmental change the paleogene sediments of the southwest tarim basin along the west kunlun shan in western china include the remnants of the easternmost extent of a large epicontinental sea this shallow sea once extended across the eurasian continent before it retreated westward and eventually separated as the paratethys sea climate modeling results suggest that this sea retreat is an equally important forcing mechanism as the tibetan plateau uplift in the aridification of the asian continental interior and the intensification of the asian monsoon system the age and paleogeography of the retreat are poorly constrained hindering the understanding of its cause and paleoenvironmental impacts this study reports litho and biostratigraphic results from two sections recording the last major regression out of the tarim basin that is expressed by a regional transition from marine clastics and limestones to continental red beds rich micro and macrofossil assemblages including benthic foraminifera ostracods bivalves calcareous nannofossils and organic walled dinoflagellate cysts dinocysts indicate a shallow proximal and marine environment strong similarity to assemblages known from central asia and europe confirms that surface ocean connections extended across eurasia from the tarim basin to the western tethys during the latest eocene moreover the recovered fossil associations date the last marine sediments as earliest priabonian in age 37 ma overlap between dinoflagellate mps interval zone and calcareous nannofossil zone cp 14 the retreat of the sea from the tarim basin is time equivalent with the sea level lowstand at the bartonian priabonian boundary but pre dates both the oligocene miocene regional uplift of the pamir mountains and kunlun shan and the major eustatic sea level falls of the eocene oligocene transition 34 ma and mid oligocene 30 ma which are usually held responsible for the sea retreat furthermore a concomitant and significant aridification step occurs at 36 6 ma top of chron c17n 1n as recorded by regional sedimentary records of the xining basin along the northeastern tibetan plateau suggesting that the tarim sea served as a significant moisture contributor for the asian interior

238u234u and232th230th in the baltic sea and in river water the concentration c of dissolved238u 234u 232th and230th in fresh and brackish waters from the baltic sea were determined using tims the brackish waters range in salinity from that of sea water sw to 2 5 c238u in oxygen saturated surface waters is well correlated with salinity and shows quasi conservative behavior as does sr samples from the redox water interface show depletion in c238u demonstrating that dissolved u is being removed by femn oxyhydroxides from a simple mixing relationship for the brackish water 234u 1000 was calculated for the fresh water source in the northern baltic a study of the kalixalven river over an annual cycle yields high 234u during spring and summer discharge and lower values during fall and winter showing that different sources contribute to the u load in the river during different seasons c232th and c230th in river water are governed by the discharge reflecting the importance of the increased abundance of small particles 0 45 m for the232th230th load at high discharge 232th 238u in river water is about 40 times less than in detrital material in the brackish water c232th drops 2 orders of magnitude in the low salinity region 5 reaching a value close to that of sea water at a salinity of 7 5 almost all of the riverine232th must be deposited in the low salinity regions of the estuary the230th 232th in river waters is about twice the equilibrium value for232th 238u 3 8 in the brackish waters 230th 232th is greater by a factor of 10 100 than both river water and sw the big increase in230th 232th in the baltic sea waters over the riverine input indicates that the th isotopes enter the estuary as a mixture of two carrier phases we infer that about 96 of232th in river water is carried by detrital particles whereas the other phase solution colloidal has a much higher232th 232th entering the estuary the detrital particles sediment out rapidly whereas the non detrital phase is removed more slowly causing a marked increase in230th 232th in the brackish water in sw 230th 232th is closer to river input and detrital material than in brackish water we conclude that in the deep sea 232th is almost exclusively dominated by windblown dust and can be used to monitor dust flux the230th excess in baltic rivers is produced in u rich 232th poor peatlands and trapped in authigenic particles and transported with the particles time scales for producing the230th excess are 2000 8000 yr this is younger than but comparable to the time of the latest deglaciation which ended some 9000 yr ago when the mires were forming these results have implications for the possible mobility of actinides stored in repositories

how old is the asian monsoon system palaeobotanical records from china the recent discovery of monsoon records in early miocene raised a question of the time when the east asian monsoon system initiated a distinguishing feature of the modern monsoon system is its geographic distribution which disturbs the zonal pattern indigenous to the planetary climate system and the appearance of the monsoonal climate pattern in the geological records should signify the onset of the monsoon system here we present the results of a compilation of palaeobotanical and lithological data from 125 sites over china that has revealed two completely different patterns of climate zones the palaeogene pattern with a broad belt of aridity stretched across china from west to east and the neogene pattern with the arid zone restricted to northwest of china which has persisted until today the reorganization of the climate system around the oligocene miocene boundary provides evidence for the establishment of the modern east asian monsoon since then the neogene has witnessed significant variations of the monsoon system including enhancement of aridity and monsoon intensity at about 15 13 my around 8 my and 3 my the new data do not support the onset of the asian monsoon system around 8 my rather the new data led to a hypothesis that the transition to the monsoon climate system in east asia occurred in the latest oligocene

dissolved gallium in the northwest pacific and the south and central atlantic oceans implications for aeolian fe input and a reconsideration of profiles the distribution of dissolved gallium a less reactive analogue of aluminum has the potential to reveal information about the averaged dust input to the surface ocean and to complement studies using aluminum as a tracer new data are presented here on the distribution of dissolved ga including six profiles in the south and central atlantic as well as seven shallow and two deep profiles from the northwest pacific the atlantic data allow for an estimate of ga in antarctic bottom water 25 30 pmol kg 1 and show reasonably conservative behavior in deep waters in the northwest pacific surface water ga al ratios correlate with chlorophyll concentrations probably reflecting the biogenic removal of dissolved al and suggesting a possible means for estimating variation in surface water al removal times also in the northwest pacific low surface water ga in subpolar surface waters suggests low dust input thereby providing an explanation for the high nutrient low chlorophyll behavior of this environment this low ga subpolar water implies that north pacific intermediate water is low in ga and thus provides an advective explanation for the intermediate water ga minimum observed in the temperate north pacific surprisingly the deepest waters sampled in the north pacific have ga concentrations similar to that estimated for circumpolar waters thus indicating minimal reactivity of ga in its northward transit in the deep pacific

size fractionated major particle composition and concentrations from the us geotraces north atlantic zonal transect the concentration and the major phase composition particulate organic matter caco3 opal lithogenic matter and iron and manganese oxyhydroxides of marine particles is thought to determine the scavenging removal of particle reactive teis particles are also the vector for transferring carbon from the atmosphere to the deep ocean via the biological carbon pump and their composition may determine the efficiency and strength of this transfer here we present the first full ocean depth section of size fractionated 1 51 m 51 m suspended particulate matter spm concentration and major phase composition from the us geotraces north atlantic zonal transect between woods hole ma and lisbon portugal conducted in 2010 and 2011 several major particle features are notable in the section intense benthic nepheloid layers were observed in the western north american margin with concentrations of spm of up to 1648 g l two to three orders of magnitude higher than surrounding waters that were dominated by lithogenic material a more moderate benthic nepheloid layer was also observed in the eastern mauritanian margin 44 g l that had a lower lithogenic content and notably significant concentrations of iron and manganese oxyhydroxides 2 5 each an intermediate nepheloid layer reaching 102 g l an order of magnitude above surrounding waters was observed associated with the mediterranean outflow finally there was a factor of two enhancement in spm at the tag hydrothermal plume due almost entirely to the addition of iron oxyhydroxides from the hydrothermal vent we observe correlations between poc and caco3 in large 51 m particles in the upper 2000 m but not deeper than 2000 m and no correlations between poc and caco3 at any depth in small 51 m particles there were also no correlations between poc and lithogenic material in large particles overall there were very large uncertainties associated with all regression coefficients for mineral ballast carrying coefficients suggesting that mineral ballast was not a strong predictor for poc in this section

u and th concentrations and isotope ratios in modern carbonates and waters from the bahamas the short residence times of th and pa in seawater make them very responsive to changes in the ocean environment we use a new multi ion counting technique to make th and pa isotope measurements in seawaters from a near shore environment in which oceanic chemical tracers are not overwhelmed by terrestrial inputs the bahamas an unusual feature of the bahamas setting is the shallow depth of water residing on the bank tops these waters have significantly lower 232th 230th 10 000 than those immediately adjacent to the banks 24 000 31 000 and a 231pa 230th near the production ratio 0 1 the change in 232th 230th and 231pa 230th on the bank tops is explained by almost quantitative removal of th and pa by scavenging and their replacement with a mixture of 230th and 231pa alpha recoiled from the underlying carbonates together with th from dust dissolution analysis of a water profile in the tongue of the ocean which separates the great and little bahama banks allows us to trace the movement of bank top water to depth a distinct minimum in both 232th 230th 13 000 and 231pa 230th 0 5 is observed at 430 m and is interpreted to reflect density cascading of bank top water with entrained carbonate sediment these results suggest that th and pa can be used as water mass tracers in near shore environments uranium concentration measurements on the same waters demonstrate that u is conservative across a range in salinity of 2 psu with a concentration of 3 33 ppb at a salinity of 35 the incorporation of u and th isotopes into marine carbonates has also been assessed by analyzing carbonate samples from the same location as these bahamas waters such incorporation is critical for u th geochronology u isotope analyses demonstrate that seawater 234u averages 146 6 and does not vary by more than 2 5 o and that carbonates capture this value additional high precision measurements 1 o on modern carbonates confirm that all oceans have identical 234u modern marine carbonates are shown to have 232th 230th ratios that reflect the local seawater in which they formed

impacts of tectonic changes on the reorganization of the cenozoic paleoclimatic patterns in china abstract geologic studies have illustrated that the planetary wind dominant climate in the paleogene is changed into the monsoon dominant one near the oligocene miocene boundary in china the evolution is marked by the changes of regional aridity humidity contrasts the contrasts occur between the south and the north part of china in the eocene and then between east china and central asia near the oligocene miocene boundary indicating the onset of monsoon dominant climate in china the impacts of the himalaya tibetan plateau uplift and or the paratethys sea retreat on the asian monsoon have been well demonstrated however whether or not other factors have affected the above reorganization of paleoclimatic patterns remains a question to be addressed additional factors that should be addressed at least include the indian peninsular drift the south china sea expansion and the east china sea transgression here we use the iap agcm to explore their roles in the above paleoclimatic evolution our experiments demonstrate that the south china sea expansion is another major forcing in addition to the important roles of the paratethys retreat and the himalaya tibetan plateau uplift on the contrary the impacts of the indian peninsular drift and the east china sea transgression are relatively subordinate the himalaya tibetan plateau uplift plays a crucial role in the magnification of the aridity humidity contrasts between the south and the north part of china the paratethys retreat the himalaya tibetan plateau uplift and the south china sea expansion coact to cause the formation of the aridity humidity contrasts between east china and central asia the retreat and the uplift favor the dynamic condition and the expansion provides the water vapor condition for the monsoon dominant climate in china

the middle miocene climatic transition east antarctic ice sheet development deep ocean circulation and global carbon cycling abstract the middle miocene represents a major change in state in cenozoic climatic evolution following the climax of neogene warmth in the late early miocene at 16 ma the early stage of this climatic transition from 16 to 14 8 ma was marked by major short term variations in global climates east antarctic ice sheet eais volume sea level and deep ocean circulation in the later stage from 14 8 to 12 9 ma climatic developments included major growth of the eais and associated antarctic cooling a distinct increase in the meridional temperature gradient large fluctuations in sea level followed by a global sea level fall and important changes in deep water circulation including increased production of southern component water east antarctic ice sheet growth and polar cooling also had large effects on global carbon cycling and on the terrestrial biosphere including aridification of mid latitude continental regions increased stability of the eais after 14 8 ma represents a crucial step in the establishment of late neogene global climate systems what controlled these changes in polar climates and the east antarctic ice sheet deep ocean circulation changes probably played a major role in the evolution and variation in polar climates as they have throughout the cenozoic oxygen and carbon isotopic evidence for warm saline deep water production in the eastern tethyan northern indian ocean indicates that meridional heat transport to the antarctic inhibited cenozoic polar cooling and eais growth during the early middle miocene from 16 to 14 8 ma inferred competition between warm low latitude sources derived from the eastern tethyan northern indian ocean and a cold high latitude source southern component water from 16 to 14 8 ma may have been associated with instability in the antarctic climate and cryosphere reduction of warm saline deep water flow to the southern ocean at 14 8 ma may have decreased meridional heat transport to the antarctic cooling the region and leading to increased production of southern component water these middle miocene climatic and cryospheric changes in the antarctic had profound effects on marine and terrestrial climates as the meridional surface temperature gradient increased boundaries between climatic zones strengthened leading to increased aridification of mid latitude continental regions in australia africa and north and south america enhancing the development of grasslands and stimulating the evolution of grazing mammals

cenozoic climate change in eastern asia part i abstract this special issue provides new studies in the field of cenozoic climate change in eastern asia the papers in this volume are multidisciplinary in nature and examine a range of topics including paleovegetation sedimentology clay mineralogy geochemistry magnetostratigraphy and climate modelling the findings of these studies demonstrate that analysis of terrestrial paleoclimate changes in eastern asia may offer insights into the effects of tibetan plateau uplift and ultimately the dynamic processes of global change that took hold throughout the cenozoic the second part of this special issue to be published later will add a paleoecology component examining how cenozoic climate change has impacted floras and faunas in eastern asia

aridification in continental asia after the middle eocene climatic optimum meco global climate cooling from greenhouse to icehouse conditions occurred across an enigmatic transitional interval during the eocene epoch characterized by incipient polar ice sheet formation as well as short lived warming events of which the middle eocene climatic optimum meco is most noticeable understanding this critical period requires high resolution records that are being gathered in marine basins but are still lacking in the terrestrial realm here we provide a precisely dated terrestrial record crossing the meco time interval from the xining basin nw china we document a rapid aridification step and the onset of obliquity dominated climate cyclicity indicated by lithofacies and pollen records dated at 40 0 ma at the base of magnetochron c18n 2n this shift is concomitant within error with the meco peak warming in ocean drilling program site 1258 for which we reassessed the magnetostratigraphic age at 40 0 ma also at base of magnetochron c18n 2n the rapidity of the shift observed in the xining basin and the region wide aridification and monsoonal intensification reported around 40 ma suggests asian paleoenvironments were responding to global climate changes associated with the meco however the xining records show only the permanent shift but not the transient peak warming observed in marine meco records we thus relate this permanent aridification to occur during the post meco cooling we propose the mechanisms linking global climate to asian paleoenvironments may be eustatic fluctuations driving the stepwise retreat of the proto paratethys epicontinental sea or simply global cooling reducing moisture supply to the continental interior in any case eocene global climate cooling from greenhouse to icehouse conditions seem to have played a primary role in shaping asian paleoenvironments

230th232th systematics in the central pacific ocean the sources and the fates of thorium 232 th and 230 th of unfiltered and filtered sea water samples were measured along a depth profile of the central pacific ocean using isotopic dilution and thermal ionization mass spectrometry the 232 th concentration is rather constant from below 25 m down to over 2000 m 45 60 10 6 atom cm 3 and it then increases rapidly towards the bottom 119 360 10 6 atom cm 3 at 4000 m the 230 th concentration increases linearly with depth from 3 10 3 atom cm 3 at 25 m to 110 10 3 atom cm 3 at 4000 m the reproducibility of replicate analyses and the regularity of the profiles demonstrate the reliability of the procedure however some lack of reproducibility among different samples from the same depth has to be explained by natural variability or by contamination during sample collection due to the very low 232 th concentrations and relatively high 230 th concentrations the 230 th 232 th ratios can be as high as 1 6 10 3 the ratio of the amount of th on particles 0 2 m to the amount of th in solution is significantly higher for 232 th 0 37 than for 230 th 0 18 these data are interpreted in terms of a model that specifically treats particle transport assuming local equilibrium between particles and sea water the relatively high 230 th concentrations and 230 th 232 th ratios measured at 25 m are consistent with a mixed layer of about 100 m the linear increase in 230 th with depth implies that the effect of eddy diffusion is negligible for most of the water column over the th removal time scale this profile is consistent with transport of 230 th by reversible uptake on particles settling with a constant velocity the 232 th data are inconsistent with this model and they suggest that particles carrying 232 th experience 70 of mass loss between the surface and 4000 m and must follow different transport rules this difference in the transport of 230 th and 232 th demonstrates the distinctive behavior of these isotopes during particle formation and subsequent remineralization and repackaging in the water column different speciation of 230 th and 232 th may be explained by their distinctive sources in the ocean as 230 th is produced in solution and 232 th is carried by detrital material and by their respective packaging mechanisms which are not yet known

surface water dissolved aluminum and titanium tracers for specific time scales of dust deposition to the atlantic surface water distributions of dissolved al dal and dissolved ti dti were investigated along a meridional atlantic transect and related to dust deposition estimates in the zone of saharan dust deposition highest dal concentrations occurred in the tropical salinity minimum and suggest increasing al dissolution from saharan aerosols with wet deposition by contrast the dti distribution is not related to precipitation but agrees with the pattern of annual dust deposition in the zone of patagonian dust deposition elevated dti concentrations contrasted with decreased dal concentrations indicating excess dal scavenging onto biogenic particles in surface waters estimated residence times range from months to years for dal and are 10 times higher for dti this suggests that dal reflects seasonal changes in dust deposition while dti is related to longer temporal scales however spatial variations in input and removal processes complicate the quantification of dust deposition from surface water concentrations

geochemical characterization of the luochuan loess paleosol sequence china and paleoclimatic implications abstract chemical major and trace element and isotopic sr nd analyses of the luochuan loess paleosol sequence in china were performed in order to examine the following problems 1 potential source heterogeneity 2 element behavior during pedogenesis 3 paleoclimatic implications and 4 the use of loess data to determine the average composition of the upper continental crust new results clearly indicate that rb sr u and ce abundances are severely depleted in paleosols relative to their parental loess the behavior of these elements is strongly controlled by the breakdown of primary minerals such as carbonate sr or by alteration processes in highly oxidizing environments ce and u the pattern of element variations through the upper section of the luochuan sequence mimics the magnetic susceptibility signal both in position and in intensity thus reinforcing the pedogenesic origin of the enhanced magnetic susceptibility in paleosols all loess samples display highly uniform ree patterns except for ce characterized by the upper continental crust ucc ratios la yb n 10 and eu eu 0 66 the paleosol ree patterns are similar to those of the loess with the same lree hree fractionation but they also show distinct and variable negative ce anomalies nd and sr isotopic compositions are rather uniform in both loess and paleosols and do not vary with stratigraphic position nd 10 5 to 9 2 87 sr 86 sr 0 715 to 0 719 the isotopic homogeneity in the luochuan sequence strongly suggests a uniform source region during the entire period of deposition since 800 ka ago to the present several conclusions may be drawn from the present study 1 1 no geochemical distinction can be made between loess layers l1 to l7 the sources and the dust storm trajectories must have been essendally the same for the last 800 ka 2 2 some elements e g ca rb sr u ce are strongly fractionated by pedogenesis between loess and paleosols ce mobility in soils is clearly demonstrated but the process responsible for this leaching is still poorly understood 3 3 systematic variations of element abundances and ratios between loess and paleosols can be used as chemical indicators for pedogenesic intensity and so for paleoclimatic change these chemical indicators serve a function similar to that of oxygen isotopes in deep sea sediments pelagic foraminifera or that of magnetic susceptibility in loess sequences they are different recorders of paleoclimatic change 4 4 the striking uniformity of ree patterns and la th ratios in the luochuan loess and paleosols as well as in loess worldwide is an excellent starting point for estimating the average composition of the upper continental crust

high resolution characterization of the asian monsoon between 146 000 and 99 000 years b p from dongge cave china and global correlation of events surrounding termination ii abstract speleothem samples from hulu eastern china 32 30 n 119 10 e and dongge southern china 25 17 n 108 5 e caves provide a nearly continuous record of the asian monsoon over the last 160 ka wang y j cheng h edwards r l an z s wu j y shen c c dorale j a 2001 a high resolution absolute dated late pleistocene monsoon record from hulu cave china science 294 2345 2348 yuan d cheng h edwards r l dykoski c a kelly m j zhang m qing j lin y wang y wu j dorale j a an z cai y 2004 timing duration and transitions of the last interglacial asian monsoon science 304 575 578 we have obtained higher resolution data in the interval between 99 and 146 ka b p providing a detailed account of 18o variations over most of mis 5 and the latter portion of mis 6 precise 230th dating has replicated the chronology of the samples within error the higher resolution data set confirms the timing of asian monsoon termination ii the midpoint of the negative shift in 18o marking the onset of the last interglacial asian monsoon placing it at 129 0 0 9 ka b p the bulk of this transition 1 7 took place within approximately 70 years with the total range of the transition being 3 the most abrupt portion of the shift in 18o values 1 1 marking the end of the last interglacial asian monsoon occurred in 120 years the midpoint of which is 120 7 1 0 ka b p the dongge cave monsoon 18o record over late mis 6 exhibits a series of sub orbital millennial scale climate shifts that average 1 3 in magnitude and occur on average every 1 8 ky abrupt shifts in 18o of up to 1 also occurred throughout the last interglacial asian monsoon with periods at multi decadal to centennial timescales similar to the amplitude and periodicities of events found by dykoski et al dykoski c a edwards r l cheng h yuan d cai y zhang m lin y an z revenaugh j 2005 a high resolution absolute dated holocene and deglacial asian monsoon record from dongge cave china earth and planetary science letters 233 71 86 during the holocene in the dongge record these shifts cover more than 1 2 of the amplitude of millennial scale and multi centennial scale interstadial events during the last glacial period wang y j cheng h edwards r l an z s wu j y shen c c dorale j a 2001 a high resolution absolute dated late pleistocene monsoon record from hulu cave china science 294 2345 2348 and millennial scale and multi centennial scale interstadial events during the penultimate glacial period in china this study abrupt decadal to millennial scale climate events therefore appear to be a general feature of both glacial and interglacial climate we demonstrate that monsoon intensity correlates well with atmospheric ch4 concentrations over the transition into the bolling allerod the bolling allerod and the younger dryas in addition we correlate an abrupt jump in ch4 concentration with asian monsoon termination ii on the basis of this correlation we conclude that the rise in atmospheric co2 antarctic warming and the gradual portion of the rise in ch4 around termination ii occur within our weak monsoon interval wmi an extended interval of heavy 18o between 135 5 1 0 and 129 0 1 0 ka b p prior to asian monsoon termination ii and northern hemisphere warming antarctic warming over the millennia immediately preceding abrupt northern warming may result from the bipolar seesaw mechanism as such warming albeit to a smaller extent also preceded asian monsoon termination i the bipolar seesaw mechanism may play a critical role in glacial terminations

quantitative paleoenvironmental and paleoclimatic reconstruction using paleosols abstract paleosols fossil soils are preserved throughout the geologic record in depositional settings ranging from alluvial systems to between basalt flows until recently paleosols were studied using primarily qualitative methods in recent years paleopedology has shifted from a largely qualitative field based on comparisons with modern analogues to an increasingly quantitative endeavor some of this change has been a result of applying existing techniques to new materials but many of the innovations have been the result of applying new techniques to new materials including thermodynamic modeling of soil formation isotope geochemistry and applications of empirical relationships derived from modern soils a variety of semi quantitative and quantitative tools has been developed to examine past weathering and pedogenesis and to reconstruct both paleoenvironmental and paleoclimatic conditions at the time that the paleosols formed though it is often not possible to achieve the same temporal resolution as with marine records for paleoclimatic reconstructions proxies based on paleosols are potentially a much more direct means of making paleoclimatic reconstructions because soils form at the earth s surface in direct contact with the atmospheric and climatic conditions at the time of their formation paleoclimatic and environmental properties that may be reconstructed using the new proxies include provenance weathering intensity mean annual precipitation and temperature during pedogenesis nutrient fluxes into and out of the paleosols the atmospheric composition of important gases including co2 and o2 the moisture balance during pedogenesis the soil gas composition reconstructed vegetative covering and paleo altitude

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

thorium isotopes tracing the iron cycle at the hawaii ocean time series station aloha abstract the role of iron as a limiting micronutrient motivates an effort to understand the supply and removal of lithogenic trace metals in the ocean the long lived thorium isotopes 232th and 230th in seawater can be used to quantify the input of lithogenic metals attributable to the partial dissolution of aerosol dust thus th can help in disentangling the fe cycle by providing an estimate of its ultimate supply and turnover rate here we present time series 1994 2014 data on thorium isotopes and iron concentrations in seawater from the hawaii ocean time series station aloha by comparing th based dissolved fe fluxes with measured dissolved fe inventories we derive fe residence times of 6 12 months for the surface ocean therefore fe inventories in the surface ocean are sensitive to seasonal changes in dust input ultrafiltration results further reveal that th has a much lower colloidal content than fe does despite a common source on this basis we suggest fe colloids may be predominantly organic in composition at least at station aloha in the deep ocean 2 km fe approaches a solubility limit while th surprisingly is continually leached from lithogenic particles this distinction has implications for the relevance of fe ligand availability in the deep ocean but also suggests th is not a good tracer for fe in deep waters while uncovering divergent behavior of these elements in the water column this study finds that dissolved th flux is a suitable proxy for the supply of fe from dust in the remote surface ocean

a lagrangian numerical investigation of the origins and fates of the salinity maximum water in the atlantic the origins and fates of the atlantic salinity maximum water smw formed through excess evaporation in the tropics and subtropics of both hemispheres are studied using monthly mean outputs of a numerical simulation of the world ocean climatological circulation after defining formation domains from the surface salinity field and the vertical stratification a lagrangian technique is used to estimate the formation rates and main pathways in each hemisphere and the role of this water in the framework of the warm water return flow of the meridional overturning cell formation rates around 9 and 11 sv are found in the southern and northern hemispheres respectively while the export of the southern smw from its formation area is realized by the western boundary currents that of the northern smw mainly results from interior subduction equatorward of the formation regions a fraction of each smw variety is entrained in the subtropical cells that connect the subtropics to the equatorial region poleward of them both varieties are seen to feed the regions of subtropical mode water stmw formation around 35 of latitude in both hemispheres the bulk of the transport associated with each variety eventually turns northward this amounts to 6 sv of southern smw gathered in the north brazil undercurrent nbuc and 10 sv of northern smw found in the gulf stream at 35 n of which 8 sv have gone through the caribbean sea of the 13 4 sv northward transport of the meridional overturning cell estimated by the model at 47 n more than 50 6 9 sv is found to have transited through at least one of the smw regions this gives an indication of the likely important role of smw formation in the observed northward salinity increase of the upper atlantic ocean

reconstructing chemical weathering physical erosion and monsoon intensity since 25 ma in the northern south china sea a review of competing proxies reconstructing the changing strength of the east asian summer monsoon has been controversial because different proxies many being indirect measures of rainfall tell contrasting stories about how this has varied over long periods of geologic time here we present new sr isotope grain size and clastic flux data and synthesize existing proxies to reconstruct changing chemical erosion in the northern south china sea since the oligocene using the links between weathering rates and monsoon strength established in younger sediments as a way to infer intensity chemical proxies such as k rb l al and the chemical index of alteration cia together with clay proxies like kaolinite illite chlorite show a steady decline in alteration after a sharp fall following a maximum at the mid miocene climatic optimum mmco 15 5 17 2 ma probably as a result of cooling global temperatures in contrast physical erosion proxies including bulk ti ca and clastic mass accumulation rates mar show peaks at 21 23 ma similar to 19 ma and 15 5 17 2 ma implying faster run off in the absence of drainage capture rates increase again likely driven by slightly increased run off after 13 ma but decrease after 8 ma which is identified as a period of summer monsoon weakening sr isotope composition correlates with hematite goethite and the spectral proxy crat to show stronger weathering linked to more monsoonal seasonality these proxies argue for a strengthening of the east asian monsoon after 22 23 ma followed by an extended period of monsoon maximum between 18 and 10 ma then weakening there is some suggestion that the summer monsoon may have strengthened since 3 4 ma after reaching a minimum in the pliocene c 2014 elsevier b v all rights reserved

stable isotope records of cenozoic climate and topography tibetan plateau and tarim basin we seek to better understand growth of the tibetan plateau and associated climate change by presenting the first regionally extensive set of oxygen isotope data obtained from ca 40 m y of cenozoic strata from a 700 000 km2 area ranging from the northern edge of the tibetan plateau northward across the entire tarim basin our results reveal a previously unrecognized large positive isotope shift from eocene to oligocene which we suggest results from initial topographic growth of the himalayan tibetan system and attendant reorganization of climate by this growing mountain belt a negative isotopic shift recorded in miocene strata may reflect retreat of the neotethyan sea from the tarim basin as well as enhanced elevation of the himalaya tibetan plateau region and the rise of the tian shan which diverted moisture bearing westerlies and deepened aridity in the tarim basin and the northern tibetan plateau

the long term paleomonsoon variation recorded by the loess paleosol sequence in central china abstract the loess paleosol sequence in central china during the last 2 5 ma is a good record of the asian monsoon variation which could be considered as the concrete realization of global paleoclimatic cycles the geological and biological evidence of the loess paleosol sequence indicates that the loess was mainly the dust deposits transported by the northerly wind of winter monsoons and also suffered to some extent from pedogenesis caused by weakened summer monsoons and that the paleosol accreted by the rather slow dust accumulation was closely related to strengthened summer monsoons an alternating occurrence of loess and paleosol in the luochuan section implies the variation history of warm humid climate with a summer monsoon dominance and cold dry climate with a winter monsoon dominance the magnetic susceptibility of loess and paleosol can be regarded as a proxy index of asian monsoon variation an analysis of the susceptibility curve and structure characters of luochuan section shows that the asian monsoon circulation was strengthened from early pleistocene to late pleistocene and the 500 ka bp point and 1200 ka bp point seem to be a threshold and a turning point respectively in terms of the long term paleomonsoon variation in asia

tracing the amazon component of surface atlantic water using 228ra salinity and silica high 228ra 226ra activity ratios characteristic of waters in the amazon estuary provide a sensitive indicator of the presence of these waters in the atlantic ocean a conservative mixing model utilizing the 228ra 226ra activity ratio ar tied to absolute measurements in the estuary allows us to estimate that 20 34 of the surface water east of the antilles during june 5 9 from the same area during december and 15 20 of the eastern caribbean surface water during december are derived from the amazon estuary differences in 228ra input occur in response to variable stratification of water near the river mouth during high discharge intense vertical mixing enriches the water in the estuary in 22sra a large fraction of this water moves to the north and east of the antilles where its relatively high 22sra 226ra ar distinguishes it over 1500 km from its source during low discharge northern hemisphere fall a significant fraction of river water passes northwest of the zone of intense mixing into a vertically stratified region where 228ra gain is lower this water is transported by the guiana current along the coast of south america and into the caribbean

investigating the use of 232th 230th as a dust proxy using co located seawater and sediment samples from the low latitude north atlantic abstract the thorium isotope ratio 232 th 230 th can be measured in seawater and sediment samples and has been used as a proxy to reconstruct lithogenic fluxes to the oceans for the modern day and the pleistocene there has not yet been a systematic study testing the proxy using the 232 th 230 th ratio in seawater and the ratio recorded in the underlying sediment in this study we use co located core top sediments and seawater samples from five seamount sites spanning the tropical north atlantic to investigate the link between seawater and sediment 232 th 230 th ratios across a range of water depths our results indicate that a broad correlation exists between seawater and sedimentary 232 th 230 th ratios both seawater and sedimentary 232 th 230 th ratios record a signal consistent with decreasing lithogenic input east to west from africa to south america however calculated 232 th fluxes for the core top sediment samples indicate a strong dependence on depth with up to a factor of 4 difference from shallow 2900 m this depth dependence is likely caused by either a deficit of 230 th burial at depth compared to the production in the overlying water column through addition of 232 th or by a combination of the two by comparing seawater and sedimentary 232 th 230 th ratios we derive an apparent fractional solubility of 232 th of 29 3 in reasonable agreement with the upper end of existing estimates

evolving history of the east asian summer monsoon intensity during the mis5 inconsistent records from chinese stalagmites and loess deposits as an important component of the global monsoon system the intensity of east asian summer monsoon easm influences lives and economic development of more than 2 billion people the last interglacial period also known as marine isotope stage 5 mis 5 has been thoroughly investigated due to its similarity to the modern interglacial period mis 1 according to records from chinese stalagmites and loess deposits evolving history of easm intensity during mis5 can be divided into 5 sub stages i e 5a 5e however during the 3 warm sub stages 5a 5c and 5e evolving history of easm intensity recorded by chinese stalagmites and loess deposits is apparently different oxygen isotope 18o records of stalagmites demonstrate that the easm intensity during mis5e 5c and 5a is not obviously different on the other hand easm intensity apparently decreased from mis5e to 5c and 5a based on chinese loess deposits records the discrepancy between chinese stalagmite and loess deposits reveals that 18o records of stalagmites may not be a pure indicator of easm intensity the relationship between 18o and easm intensity is not linear based on 18o data of modern precipitation from 21 weather stations within major monsoon area in china mmac ca 110 e to 122 e 18 n to 41 n we speculate that chinese stalagmite 18o values recorded changes of 18o of summer precipitation as well as adjustment from 18o of winter precipitation inconsistent records from chinese stalagmites and loess deposits indicate that further investigations are needed to study the mechanism and fractionation of 18o in stalagmites collected in china

aeolian origin of the red earth in southeast china a clay like deposit known as red earth is widely distributed over the terraces and high lands of the yangtze river valley in southeast china its typical pedo stratigraphical features have attracted the interest of pedologists and geologists for many years although its origin is still debated here we report an analyses of the grain size distributions rare earth element bee patterns and upper continental crust ucc normalised major elemental composition of the red earth and compare them with those of the loess and other aeolian deposits in northern china the results show that the red earth in southeast china has two or three end member grain size distributions similar to the sedimentary characteristics and geochemical composition of aeolian deposits found in northern china together with other evidence from field observations these results suggest that the red earth is probably of acolian origin on the basis of these data we suggest that thick aeolian dusts were also deposited in the wet subtropics and that the effect of the winter monsoonal winds upon the dust transport in eastern china was more important than previously believed copyright c 2002 john wiley sons ltd

stability of the sargasso sea subtropical frontal zone abstract recent studies suggest that eddy properties are significantly influenced by the mean current shear associated with the western sargasso sea subtropical frontal zone sfz between 19 and 34 n the mean density structure is characterized by three layers separated by a climatologically permanent upper seasonal thermocline that shoals and a lower main thermocline that deepens toward the north the thermoclines are separated by the wedge shaped southern part of the subtropical mode water pool the sfz is evident as a zonal band between about 26 and 32 n where subtropical frontogenesis between the westerlies and trades enhances the slope of the mean seasonal thermocline classical linear as well as more recent nonlinear stability theories predict that the mean sfz flow should be unstable the linear eigenvalue problem suggests that the most unstable perturbations have wavelengths between 150 and 200 km analysis of a channel version of the miami isopycnic coordinate primitive equation numeri

what triggers the transition of palaeoenvironmental patterns in china the tibetan plateau uplift or the paratethys sea retreat abstract geological research has illustrated the transition of palaeoenvironmental patterns by the earliest miocene from a planetary wind dominant type to a monsoon dominant type indicating that the east asian monsoon became markedly intensified and played a leading role in the east asian climate from a modeling point of view the pioneering research using the reduced number of scenarios had demonstrated that both the tibetan plateau uplift and the paratethys sea retreat were important for understanding the asian monsoon evolution however the sensitivity of the paratethys retreat to the east asian climate still needs further studies based on the more detailed scenarios thirty numerical experiments under the six paratethys sea and the five tibetan plateau conditions illustrate the shifts from zonal climate to the monsoon climate in east asia the results confirm again that both the paratethys retreat and the tibetan plateau uplift play important roles in the formation of the monsoon dominant environmental pattern and show that the paratethys retreat can strengthen the east asian monsoon and greatly increase humidity and aridity respectively in the monsoon areas and northwest china which is similar to the impact of the tibetan plateau uplift on the east asian climate furthermore the fact that the paratethys sea retreats to the turan plate is found to be the key criterion for the palaeoenvironmental patterns transition in china the shrinkage of paratethys sea leads to the reconstructions of the pressure system and the atmospheric circulations which result in the variations of precipitation and the transition of palaeoenvironmental patterns

constraints on the early uplift history of the tibetan plateau the surface uplift history of the tibetan plateau and himalaya is among the most interesting topics in geosciences because of its effect on regional and global climate during cenozoic time its influence on monsoon intensity and its reflection of the dynamics of continental plateaus models of plateau growth vary in time from pre india asia collision e g 100 ma ago to gradual uplift after the india asia collision e g 55 ma ago and to more recent abrupt uplift 7 ma ago and vary in space from northward stepwise growth of topography to simultaneous surface uplift across the plateau here we improve that understanding by presenting geologic and geophysical data from north central tibet including magnetostratigraphy sedimentology paleocurrent measurements and 40ar 39ar and fission track studies to show that the central plateau was elevated by 40 ma ago regions south and north of the central plateau gained elevation significantly later during eocene time the northern boundary of the protoplateau was in the region of the tanggula shan elevation gain started in pre eocene time in the lhasa and qiangtang terranes and expanded throughout the neogene toward its present southern and northern margins in the himalaya and qilian shan

the tracing of riverine u in arctic seawater with very precise 234u 238u measurements abstract the riverine flux of u that enters the deep oceans is not well constrained since the net losses during estuarine mixing are difficult to quantify riverine dissolved u normally has a higher 234 u 238 u activity ratio 234 u 238 u ar than the uniform value that characterizes open ocean seawater and could be used as a tracer of riverine inputs if one could resolve subtle variations in seawater composition using new mass spectrometry techniques we achieve a long term reproducibility 0 3 on 234 u 238 u ar which permits the tracing of riverine u in seawater samples from the arctic a partially restricted basin that is ideal for such a study we find that surface waters from the arctic basins carry elevated 234 u 238 u ar when compared with deep ocean seawater samples from the canada basin have a significant freshwater component and provide evidence that the mackenzie river loses 65 of its u in the mackenzie shelf estuary zone before entering the deeper basin this is in contrast to samples from the makarov basin which provide evidence that all of the freshwater input is derived from the major yenisey river alone despite the proximity of the lena and ob rivers the differing behaviour of u between the mackenzie and yenisey rivers is most likely a consequence of the strong binding of u to dissolved organic matter doc or secondary phases in these rivers the yenisey river appears to transport the majority of the doc through the shelf and into the makarov basin in contrast the mackenzie river appears to lose a significant amount of doc 50 in the estuary shelf zone which may lead to loss of associated u these findings offer a more detailed picture of the fresh riverine water flow patterns in the arctic ocean when compared to other geochemical proxies the non conservative behaviour of u in the mackenzie river through the shelf estuaries has important implications for u input into oceans and the total marine budget

thorium isotopes in the western mediterranean sea an insight into the marine particle dynamics we present a detailed view of the 230 th 232 th systematics in the western mediterranean sea in order to constrain water and particle fluxes the conclusions obtained at the regional scale are also relevant at a more global scale although they may be more difficult to establish in the open ocean 230 th and 232 th were analyzed in size fractionated seawater and marine particle samples collected in the ligurian alboran and ionian seas the 230 thxs 230 th produced by the radioactive decay of 234 u in seawater profiles at dyfamed and in the alboran sea site are not linear due to the formation of deep waters the difference of 230 thxs concentration between these two sites is related to the aging of the water masses and to different scavenging conditions the 230 th 232 th ratio is used as a tracer during mixing processes to provide information on the pathways followed by the matter in the water column at dyfamed filtered 6 0 2 wm and ultrafiltered 6 1 kda solutions have similar 230 th 232 th ratios suggesting that an equilibrium exists between truly dissolved and colloidal th the change of the th flux and of the 230 th 232 th ratio of trapped particles observed in august between 200 m and 1000 m is best explained by aggregation of filtered large particles on the trapped particles the residence time of filtered large particles with respect to aggregation on trapped particles is of the order of 8 80 days the combined budget of 230 th and 232 th inputs to the western mediterranean sea requires the dissolution of 3 5 of the th associated with all the continental particulate inputs including particles sequestered in margins suggesting that eolian inputs are not the only source of refractory elements to the mediterranean sea and may be to the whole ocean fl 2002 elsevier science b v all rights reserved

thorium distributions in high and low dust regions and the significance for iron supply thorium and uranium isotopes 232th 230th 238u and 234u were investigated to refine their use for estimating mineral dust deposition and fe delivery to the ocean u concentrations and isotope ratios were consistent with conservative behavior and can safely be described using published u salinity relationships and global average seawater isotopic composition near barbados waters affected by the amazon outflow contained elevated 232th this signals one region where the thorium dust method is inaccurate because of a confounding continental input dissolved 232th fluxes in this region suggest that amazonian fe supply to the adjacent open ocean is much larger than local atmospheric deposition the colloidal content of dissolved th south of bermuda was found to be quite small 2 6 similar to that found north of hawaii despite the order of magnitude higher dust deposition in the atlantic this finding supports the assumption that dissolved 232th and 230th are scavenged at the same rate despite their different sources and also sheds light on the increase of dissolved 232th fluxes with integrated depth outside the region influenced by amazon river waters dissolved 232th fluxes are compared with bermudan aerosol fe deposition to estimate that fractional th solubility is around 20 in this region finally new dissolved and soluble fe mn and cr data from the subtropical north pacific support the idea that fe concentrations in the remote ocean are highly buffered whereas 232th has a larger dynamic range between high and low dust regions

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

randomly interstratified illite vermiculite from weathering of illite in red earth sediments in xuancheng southeastern china abstract mixed layer illite vermiculite i v clays of the xuancheng red earth were investigated using x ray diffraction xrd fourier transform infrared ftir spectrometer and high resolution transmission electron microscopy hrtem methods the xrd results indicated that the mixed layer i v clays were characterized by the broad 10 14 a peak with a maximum intensity at 12 a in air dried sample which decomposed into two peaks at 10 a and 14 a peaks respectively after ethylene glycol treatment after k saturation the 14 a peak changed to 10 a which reverted back to 14 a after saturation with mg 2 with a notable decrease in intensity of the 10 a peak the broad 10 14 a peak collapsed to 10 a on heating to 400 c these suggested that the broad 10 14 a peak resulted from randomly interstratified illite vermiculite clays together with discrete illite and also vermiculite hrtem observation showed that straight 10 a illite layers were interstratified with 12 a vermiculite layers suggesting that transformation of illite to vermiculite involves an exchange of k by hydrated cations associated with a swelling of the illite the 060 spacing of i v clay is 1 50 a indicating a dioctahedral precursor of illite and thus reinforcing the transformation from illite to vermiculite ftir analysis suggested that most band positions of vermiculite and illite in mixed layer i v did not change in comparison with those of the discrete clay species indicating that the basic crystal structure of mixed layer illite vermiculite remains the same as the discrete clays the interlayer cations in the interlayer region of vermiculite layers of the i v clays are mainly ca and minor mg al and fe the abundant ca makes the i v clays to behave like i s on glycolated and thermal treatment while the mg al and fe complex ions in the interlayer region cause the vermiculite layer to lose its expandability and to behave like chlorite the mixed layer i v clays were widely formed in late quaternary alluvial fans in subtropical to tropical areas where the sediments experienced synchronous pedogenic modification the syndepositional pedogenesis process leads to an incomplete transformation of illite to vermiculite and causes the formation of metastable intermediates of mixed layer illite vermiculite

clay mineralogy and geochemistry and their palaeoclimatic interpretation of the pleistocene deposits in the xuancheng section southern china a red soil profile in xuancheng anhui province southern china in the middle to lower reaches of the yangtze river was investigated using x ray diffraction x ray fluorescence spec trometer and scanning electron microscopy the mobile components k2o and na2o and trace elements ba and sr of the xuancheng section exhibit a general trend of decrease downward along the red soil profile together with an increase downward of chemical index of alteration cia values suggesting more intense depletion in the lower portion than in the upper portion the major components sio2 a l 2o3 and fe2o3 as well as sio2 al2o3 sio2 fe2o3 and al2o3 fe2o3 ratios show notable fluctuations along the soil profile indicating intense climatic oscillations in the area during the pleistocene age the clay mineral assemblage of the xuancheng section can be generally subdivided into three groups suggesting a general trend of three stages of climate changes the lower portion of 10 4 6 3 m depth has a lower illite content and higher abundance of kaolinite and illite smectite i s clays indicating that a warm and wet climate prevailed over the episode of ca 600 350 ka bp a decrease in abundance of kaolinite and i s clays and increase in illite content at a depth of 6 3 2 2 m probably indicate a transition stage of climate change from warm humid to cool dry in the period ca 350 80 ka bp the higher illite content and lower abundance of kaolinite and i s clays in the upper portion of 2 2 0 m depth suggest that a relatively cool and dry climate dominated since ca 80 ka bp based on changes in clay mineralogy and chemical indices of the sediments seven warm cold fluctuations were determined in the area since the middle pleistocene climate changes documented in the xuancheng section are in agreement with the d 18 o records of sediments from the equatorial pacific core v28 238 and the loess palaeosol sequences in the loess plateau of northwestern china correlated to the episode of s4 and s5 soil units in the loess plateau the period of ca 600 350 ka bp in the xuancheng area was dominated by the particularly strong east asia summer monsoon as indicated by its most abundant kaolinite and i s clays fluctuations in clay mineralogy along the xuancheng soil profile were mainly controlled by both the east asia summer and winter monsoons in response to the global changes in the middle late pleistocene copyright 2009 john wiley sons ltd

dry deposition of trace elements to the western north atlantic 1 data for al fe na sb se v and zn in aerosol particles from bermuda are used in combination with parameterized dry deposition velocities to investigate trace element recycling on atmospheric sea salt during july and august which are in the high dust season 10 of the monthly mean aerosol na can be ascribed to crustal sources rather than sea salt but in general the contribution of mineral dust to na dry deposition is small 1 relative to that from sea salt in fall and winter 10 to 20 of the aerosol al a commonly used indicator of mineral dust is attributable to recycled sea salt but the dust fluxes then are small and longer term averages show a recycling effect of only 1 to 5 on dry deposition the percentage of recycled fe appears to be even less than for al noncrustal non sea salt nc nss sources account for 70 of the aerosol sb se v and zn but differences in the dry deposition velocities for three particle types strongly affect their air sea exchange dust can account for more than half of the new dry deposition inputs of v and zn while the amounts of sb and se recycled on sea spray approach or exceed their new inputs from dust and the nss nc sources

timing of the tianshan mountains uplift constrained by magnetostratigraphic analysis of molasse deposits abstract the tianshan mountains lie in the actively deforming part of the india asia collision zone the thrust faulting and folding of the neogene and quaternary sediments forming linear roughly east west anticlines at the northern and southern borders of the orogenic belts indicate crustal shortening and thickening in late cenozoic time detailed magnetostratigraphic studies of the molasse deposits of the folded neogene and quaternary strata in the northern edge of the tianshan mountains indicate that the onset of uplift occurred at 7 ma deposition of the thick conglomerates between 7 and 2 58 ma in the studied region was mainly in response to the tectonic uplift while the accumulation of the early pleistocene conglomerates xiyu formation was mostly controlled by both tectonics and climatic cooling our results indicate that the present high relief of the tianshan mountains is the result of two dominant phases of uplift occurring at about 7 2 58 ma and the early pleistocene

reactive trace metals in the stratified central north pacific abstract vertical concentration profiles of the dissolved and suspended particulate phases were determined for a suite of reactive trace metals al fe mn zn and cd during summertime at a station in the center of the north pacific gyre during summer the euphotic zone becomes stratified forming a shallow 0 25 m oligotrophic mixed layer overlying a subsurface 25 140 m strongly stratified region the physical biological and chemical structure within the euphotic zone during this period enhanced the effect of atmospheric inputs of al fe and mn on mixed layer concentrations for example the concentration of dissolved fe in the surface mixed layer was eighteen times that observed at a depth of 100 m the observed aeolian signature of these metals matched that predicted from estimates of atmospheric input during the period between the onset of stratification and sampling the distributions of suspended particulate al fe and mn all exhibited minima in the euphotic zone and increased with depth into the main thermocline particulate al and fe were then uniform with depth below 1000 m before increasing in the near bottom nepheloid layer average particulate phase concentrations in intermediate and deep waters of the central north pacific were 1 0 0 31 and 0 055 nmol kg 1 for al fe and mn respectively the distribution of particulate cd exhibited a maximum within the subsurface euphotic zone particulate zinc also exhibited a surface maximum albeit a smaller one concentrations of particulate zn and cd in intermediate and deep waters were 17 and 0 2 pmol kg 1 substantial interbasin differences in particulate trace metals occur concentrations of suspended particulate al fe and mn were three to four times lower in the central north pacific than recently reported for the central north atlantic gyre consistent with differences in atmospheric input to these two regions concentrations of suspended particulate cd and zn were enriched in the north pacific relative to the north atlantic an observation consistent with their assimilation by plankton reactive trace metals exhibit a range of biogeochemical behaviors that can be characterized by two endmembers nutrient type and scavenged type nutrient type metals best exemplified by zn and cd are primarily removed from surface waters by biogenic particles and then remineralized at depth internal biogeochemical cycles together with physical mixing and circulation patterns control the distributions of nutrient type metals scavenged type metals best exemplified by al continue to be removed onto particles in intermediate and deep waters as well as at the surface external inputs such as the deposition of aeolian dust control the concentrations and distributions of scavenged type metals other metals such as fe exhibit a mixture of the characteristic behaviors of these two endmembers

controls on seawater 231pa 230th and 232th concentrations along the flow paths of deep waters in the southwest atlantic measurements of dissolved th 230 pa 231 and th 232 were made for twelve full depth profiles along a southwest atlantic section during geotraces cruise ga02s sampling captures all the main atlantic deep water masses along their meridional flow paths and allows insight into the control on th and pa in a setting where waters are flowing in opposing directions with direct relevance to understanding the use of pa 231 th 230 as an ocean circulation proxy water column th 230 increases linearly with depth in line with expected reversible scavenging models pa 231 increases from the surface to similar to 1200 1500 m but is invariant or decreases with greater depth deviating from the behavior expected for reversible scavenging dissolved pa 231 th 230 ratios display a mid water column maximum at similar to 1000 2000 m which is broadly coincident with upper circumpolar deep water below 2000 m nuclide distributions and ratios exhibit no dependence on water mass nor any indication of progressive change within a water mass challenging the use of pa 231 th 230 as a past circulation tracer in the south atlantic calculation of horizontal transport of th 230 and pa 231 by ocean circulation indicates a net southward export out of the atlantic of 19 of the pa 231 and 3 of the th 230 produced in that ocean this removal is all from the north atlantic while in the south atlantic removal to sediment equals production simple one dimensional modeling can simulate th 230 profiles but not the mid water column maximum observed in pa 231 profiles suggesting an additional source of pa 231 perhaps lateral transport from the margin or removal at depth due to bottom scavenging near seafloor minima in concentrations indicates bottom scavenging of th 230 and 231 pa which is enhanced in the presence of nepheloid layers particularly for 231pa this additional scavenging fractionates th 230 and pa 231 and in the presence of nepheloid layers may lead to an increase in sedimentary pa 231 th 230 ratios th 232 concentrations were paired with th 230 derived residence times in the upper 250 m of the water column to test the application of th as a tracer of dust deposition maxima in th 232 indicate high dust input from the african and possibly south american continents

the elevation history of the tibetan plateau and its implications for the asian monsoon abstract the determination of the evolving palaeoaltitude of the tibetan plateau since the india eurasia collision underpins our understanding of how orography in central asia affects the intensity of the monsoon and hence global climate change palaeoaltitudes however cannot be measured directly and need to be inferred from proxy observations that are usually model dependent differing tectonic models for the behaviour of the lithosphere during continental collision have contrasting implications for the elevation of the plateau however two techniques recently employed for determining palaeo elevation are independent of tectonic models the first involving the variation with altitude of oxygen isotopes in precipitation and the second involving the change of leaf morphology with moist static energy of the atmosphere elevation studies have focused on southern tibet largely due to the relative ease of access to the region there is a remarkable unanimity amongst the diverse techniques applied that the altitude of the southern plateau has not significantly changed since at least the mid miocene ca 15 ma arguing for an onset of the monsoon system during or before the early miocene a range of tectonic studies suggest that the northern and eastern parts of the plateau are younger geomorphological features but there are few quantitative constraints of the timing of elevation from these regions of tibet since both the elevation and the surface area of the plateau impact on atmospheric circulation palaeoaltitude studies need to be extended to chart the increasing areas of elevated land surface through time

geochemical evidence for the provenance of middle pleistocene loess deposits in southern china the provenance of middle pleistocene loess in the middle and lower reaches of the yangtze river the most intensively investigated loess deposits outside the loess plateau region in china remains controversial identification of the provenance will provide crucial insight into the environmental implications of this valuable sedimentary archive and into the potential role of the east asian winter monsoon in transporting the dust from deserts in the asian interior in this study geochemistry was used to compare the provenance of loess in the lower reaches of the yangtze river in southern china with that inferred for loess deposits on the loess plateau in northern china compared with samples from the loess plateau the 20 mm fraction in the loess deposits of southern china has higher tio2 al2o3 zr nb zr al zr ti zr hf y al and lan smn ratios and lower eu eu th nb y nb and al nb ratios the clear distinction in immobile element ratios between samples from the two regions indicates that the loess deposits in the two regions have different provenances the inferred difference in source area is also supported by variations in the major element composition of bulk samples obtained in this study and collected from published data these lines of evidence indicate that the deserts in the asian interior are not the primary provenance for the southern loess it is suggested that the adjacent floodplains to the north of yangtze river are the dominant dust sources and the occurrence of sustained loess deposits in the lower reaches of the yangtze river currently an area of northern subtropical climate is an indication of local aridification and strengthened winter monsoon activity during glacial periods as a regional response to the middle pleistocene climate transition around 0 8 ma the role of the east asian winter monsoon in transporting the dust from northern deserts to southern china has been overestimated in previous studies

geochemical constraints on provenance of the mid pleistocene red earth sediments in subtropical china abstract the source of mid pleistocene red earth sediments in the middle to lower reaches of the yangtze changjiang river was investigated based on their geochemical characteristics the xuancheng and jiujiang red earth sediments have similar major and trace element distribution patterns compared to the loess and paleosol deposits of the chinese loess plateau the upper continental crust ucc and the post archean australian average shale paas the sediments display notable depletion of cao mgo na2o and accumulation of tio2 al2o3 and fe2o3 t the trace element distribution patterns of the red earth sediments are also different from those of loess and the paas but are similar to those of the loess deposits except for lower values of mobile trace elements sr ba and ni and higher values of zr and y the red earth samples have uniform la th ratios of 2 8 compatible with those of the ucc loess and paleosol they also have similar chondrite normalized ree patterns characterized by enriched lree and relatively flat hree profiles and consistent negative eu anomalies similar to those of the ucc the loess and paleosol and the yangtze deposits these results suggest that the red earth sediments have been subject to considerable mixing prior to deposition and strong subsequent chemical weathering the sediments have very uniform 143nd 144nd and 147sm 144nd ratios this points to well mixed and multi recycled sediments the 143nd 144nd and 87sr 86sr values of the red earth sediments match well with those of the deposits in the middle to lower reaches of the yangtze river but are different from those of the loess and paleosols this suggests that the red earth sediments are derived from the drainage basins of the middle to lower yangtze river and might have experienced more intense chemical weathering relative to the yangtze deposits as reflected by their higher rb sr ratios intense depletion of mobile elements and accumulation of immobile elements as well as their well developed net like structure

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

the influence of particle composition on thorium scavenging in the mediterranean sea abstract sediment trap data are crucial for the study of marine biochemical cycles but they need careful validation by thorium th isotopes in the present study 230th 232th uranium u aluminum al barium ba and manganese mn were analyzed in sinking particles collected by moored sediment traps in the ligurian sea dyfamed site in order to determine the collection efficiency of the traps and to constrain which particulate phase s carries th isotopes in a region with strong lithogenic inputs the 230thxs evaluation was based on the u content of each sample rather than on the 232th content of each sample and the average 238u 232th ratio of the continental crust because the latter method introduced too much uncertainty in the calculation high trapping efficiencies 187 85 at 200 m and 87 11 at 1000 m indicated no evidence of particle under collection by the traps the lack of correlation between 230thxs and the carbonate or the organic matter fraction suggests that these phases are not major 230thxs carrying phases in the deep ocean for most samples of the time series the 230thxs concentration is correlated with the lithogenic fraction and the mn concentration but pulses of particles with high lithogenic and mn content and low 230thxs concentration occur in winter assuming that 230thxs is only carried by lithogenic particles we estimate kd lithoth ranges from 0 42 0 04 107 ml g to 0 8 0 2 107 ml g assuming that 230thxs is only carried by authigenic mn oxide precipitates mno2 we estimate that kd mno2th ranges from 0 6 0 1 1010 ml g to 1 1 0 4 1010 ml g the relative variation of kd mno2th a factor 7 between different oceanic sites is significantly lower than the relative variation of kd lithoth a factor 50 suggesting that 230thxs has a tighter link with mno2 rather than with lithogenic particles and hence that 230thxs may be more likely scavenged by mno2 than by lithogenic particles the unambiguous determination of the particles carrying 230thxs remains to be done

geochemical evidence for african dust inputs to soils of western atlantic islands barbados the bahamas and florida 1 we studied soils on high purity limestones of quaternary age on the western atlantic ocean islands of barbados the florida keys and the bahamas potential soil parent materials in this region external to the carbonate substrate include volcanic ash from the island of st vincent near barbados volcanic ash from the islands of dominica and st lucia somewhat farther from barbados the fine grained component of distal loess from the lower mississippi river valley and wind transported dust from africa these four parent materials can be differentiated using trace elements sc cr th and zr and rare earth elements that have minimal mobility in the soil forming environment barbados soils have compositions that indicate a complex derivation volcanic ash from the island of st vincent appears to have been the most important influence but african dust is a significant contributor and even mississippi river valley loess may be a very minor contributor to barbados soils soils on the florida keys and islands in the bahamas appear to have developed mostly from african dust but mississippi river valley loess may be a significant contributor our results indicate that inputs of african dust are more important to the genesis of soils on islands in the western atlantic ocean than previously supposed we hypothesize that african dust may also be a major contributor to soils on other islands of the caribbean and to soils in northern south america central america mexico and the southeastern united states dust inputs to subtropical and tropical soils in this region increase both nutrient holding capacity and nutrient status and thus may be critical in sustaining vegetation

climatically driven glacial interglacial variations in c3 and c4 plant proportions on the chinese loess plateau high resolution 13c records of bulk organic matter om from three loess paleosol successions from the central chinese loess plateau document systematic fluctuations in c3 and c4 plant abundance for certain intervals during the past 620 k y measured 13c values of om in paleosols are less negative by 0 5 4 and total organic carbon toc contents are higher by up to 0 5 wt relative to corresponding values in loess deposits the 13com and toc decrease from peak values in paleosols progressively into overlying and underlying loess deposits integrated 13com toc and magnetic susceptibility rec ords indicate an increase in c4 vegetation to 50 during peak paleosol formation and a decrease in c4 vegetation to 30 during loess deposition for three of the past glacial interglacial cycles these results indicate that c4 plant abundance declined during glacials in this mid latitude region driven primarily by a shift to enhanced winter precipitation and lower temperatures and further contribute to the rapidly growing body of evidence that low p co2 during pleistocene glacials was insufficient to trigger c4 plant expansion without coincident favorable climatic conditions

effect of orogeny plate motion and land sea distribution on eurasian climate change over the past 30 million years the eurasian climates of today 10 million and 3o million years ago are simulated using an atmospheric general circulation model that incorporates realistic continental geography and epicontinental sea distributions the resulting climates compare well with various palaeoclimate records the retreat of the paratethys an epicontinental sea shifts the central asian climate from temperate to continental conditions and plays as important a role as uplift of the himalayan tibetan plateau in driving the asian monsoon changes

late quaternary intensified monsoon phases control landscape evolution in the northwest himalaya the intensity of the asian summer monsoon circulation varies over decadal to millennial time scales and is reflected in changes in surface processes terrestrial environments and marine sedi ment records however the mechanisms of long lived 2 5 k y intensified monsoon phases the related changes in precipitation distribution and their effect on landscape evolution and sedimen tation rates are not yet well understood the arid high elevation sectors of the orogen correspond to a climatically sensitive zone that currently receives rain only during abnormal i e strength ened monsoon seasons analogous to present day rainfall anom alies enhanced precipitation during an intensified monsoon phase is expected to have penetrated far into these geomorphic threshold regions where hillslopes are close to the angle of failure we as sociate landslide triggering during intensified monsoon phases with enhanced precipitation discharge and sediment flux leading to an increase in pore water pressure lateral scouring of rivers and ov ersteepening of hillslopes eventually resulting in failure of slopes and exceptionally large mass movements here we use lacustrine deposits related to spatially and temporally clustered large land slides 0 5 km 3 in the sutlej valley region of the northwest him alaya to calculate sedimentation rates and to infer rainfall patterns during late pleistocene 29 24 ka and holocene 10 4 ka inten sified monsoon phases compared to present day sediment flux measurements a fivefold increase in sediment transport rates re corded by sediments in landslide dammed lakes characterized these episodes of high climatic variability these changes thus em phasize the pronounced imprint of millennial scale climate change on surface processes and landscape evolution

partitioning of dissolved iron and iron isotopes into soluble and colloidal phases along the ga03 geotraces north atlantic transect abstract the size partitioning of dissolved fe dfe 56 fe of 1 3 to 1 5 relative to dfe 56 fe 0 5 in the surface ocean where sfe and cfe cycle independently and identical sfe and dfe isotope ratios below 250 m where sfe and cfe are constantly partitioned and exchanged

combining seawater 232th and 230th concentrations to determine dust fluxes to the surface ocean abstract aeolian dust is a significant source of iron and other nutrients to the surface ocean but constraining the size of this flux is difficult chemical tracers such as al are useful but are limited by lack of information about their rate of removal from surface seawater in this study we test the use of th isotopes as an improved tracer of dust input by measuring 232 th and 230 th concentrations of upper ocean seawater at six stations along a meridional atlantic section that spans the saharan dust plume open ocean 232 th like al is dominantly derived from dust dissolution while 230 th is produced in seawater by u decay and provides an assessment of th removal rates the highest 232 th concentrations and 232 th 230 th ratios particularly in the surface waters are observed at stations expected to be influenced by input of saharan dust the pattern of 232 th concentration is in agreement with dissolved al distributions and seawifs aerosol imagery supporting the use of 232 th as a proxy for short term dust addition deeper in the water column 232 th concentration may also reflect longer term dust inputs in addition lateral input of 232 th from mediterranean outflow water is detected at 1000 m in the north atlantic surface water residence times are calculated separately from 230 th and 234 th using a simple scavenging model and values from the two isotopes are generally consistent with one another th 230 residence times appear to reflect the longer term value however rather than exhibiting the strong seasonal influence seen for 234 th these th residence times allow dust flux to the surface ocean to be calculated using the known concentration of th in dust and assumed values for the solubility of dust th in seawater resulting dust fluxes show good agreements with models of dust deposition if th solubility is 1 to 5 in the north atlantic yielding fluxes of 0 4 19 2 g m 2 yr 1 and 5 to 10 in the south atlantic fluxes of 0 2 0 7 g m 2 yr 1 despite the need for better constraints on the fractional solubility of dust th this study demonstrates the power of combining th isotope measurements to constrain dust fluxes to the surface ocean

geology and ore enrichment factors at the radiore mine quebec the radiore cu zn massive sulfide deposit occurs in archean metavolcanic rocks of the abitibi greenstone belt in northwestern quebec the ore forms a stratiform lens between a massive rhyolite flow and a unit of mixed basaltic and intermediate flows intrusions of thick dykes of gabbro diorite quartz diorite and granodiorite and of the bell river igneous complex closely surround the ore lens all the volcanic rocks the quartz diorite grandiorite and the igneous complex are tholeiitic whereas the gabbro diorite is of calc alkaline affinity sedimentary structures are prevalent in the ore and heavily chloritized and biotitized rocks form a stratiform alteration zone mainly below the ore indicating a distal type deposit

glacial interglacial indian summer monsoon dynamics the modern indian summer monsoon ism is characterized by exceptionally strong interhemispheric transport indicating the importance of both northern and southern hemisphere processes driving monsoon variability here we present a high resolution continental record from southwestern china that demonstrates the importance of interhemispheric forcing in driving ism variability at the glacial interglacial time scale as well interglacial ism maxima are dominated by an enhanced indian low associated with global ice volume minima in contrast the glacial ism reaches a minimum and actually begins to increase before global ice volume reaches a maximum we attribute this early strengthening to an increased cross equatorial pressure gradient derived from southern hemisphere high latitude cooling this mechanism explains much of the nonorbital scale variance in the pleistocene ism record