relative weathering intensity of calcite versus dolomite in carbonate bearing temperate zone watersheds carbonate geochemistry and fluxes from catchments within the st lawrence and danube river basins 1 calcite and dolomite solubilities in open weathering environments are proportional to pco2 and inversely proportional to temperature and dolomite solubility is progressively greater than calcite below 25 c the continent scale weathering budget reveals the significance of the northern hemisphere nh to globally integrated riverine fluxes of ca2 mg2 and hco3 the nh contributes 70 of the global hco3 flux while only 54 of the riverine discharge we present results of a comparative hydrogeochemical study of carbonate mineral equilibria and weathering fluxes in two nh carbonate rich river basins surface water geochemistry and discharge were determined for headwater streams in michigan and slovenia within the st lawrence and danube river basins michigan watersheds are established atop carbonate bearing glacial drift deposits derived from erosion of paleozoic strata with thick soil horizons 100 300 cm slovenia watersheds drain mesozoic bedrock carbonates in alpine and dinaric karst environments with thin soil horizons 0 70 cm carbonate weathering intensity is a parameter that normalizes river runoff and hco3 concentration to catchment area meq hco3 km 2 s 1 summing calcite and dolomite contributions and is used to gauge the effects of climate land use and soil thickness on organic inorganic carbon processing rates importantly michigan riverine discharge is one tenth of slovenian rivers providing the opportunity to evaluate the kinetics of carbonate mineral equilibration the study rivers are hco3 ca2 mg2 waters supersaturated for calcite at pco2 values in excess of the atmosphere as discharge varies hco3 concentrations differ by less than 20 for any location and mg2 ca2 remains relatively fixed for michigan 0 5 and slovenia streams 0 4 requiring that dolomite dissolution exceed calcite on a mole basis the ability of calcite and dolomite dissolution to keep pace with increased discharge indicates carbonate weathering is limited only by water flux and temperature dependent solubility in these watersheds carbonate weathering intensity in michigan and slovenia exceeds the world average by factors between 2 and 20 and dolomite weathering intensity estimated from riverine mg2 fluxes exceeds the world average by factors between 2 and 15 thus global fluxes of carbonate related weathering products appear heavily skewed toward carbonate bearing environments at higher latitudes with relatively low mean annual temperatures and high discharge

biotic and abiotic controls on co2 partial pressure and co2 emission in the tigris river turkey abstract rivers act not only as vectors from the terrestrial biosphere to the ocean but also as significant sources of co2 to the atmosphere which plays a key role in the global carbon cycle in this study dissolved inorganic carbon dic and carbon dioxide partial pressure pco2 in the tigris river were investigated the alkalinity concentrations of the tigris river ranged from 1718 to 4995 eq l with an average of 3064 eq l median 2877 eq l 2 3 times the global median value of 1256 eq l higher alkalinity values occurred in autumn and winter months that were due to carbonate rock weathering pco2 values varied from 95 6 to 16 001 8 atm with a total average of 1277 1883 atm 80 of samples had pco2 above atmospheric equilibrium 390 atm the highest levels of pco2 occurred at stations diyarbakir bismil and cizre which are categorized as polluted stations the lowest levels of pco2 generally occurred in the wet season october april due to dilution effect of rainfall the estimated water to air co2 degassing flux from the tigris river was around 39 mol m2 y thus 0 15 tg c y as co2 released from the river to the atmosphere about 0 6 fold the riverine dic flux 0 25 tg c y correlative analyses demonstrated that population density and air temperature increased pco2 while slope degree decreased pco2 pco2 also had positive correlations with cod nh4 n po4 p so4 cl phytoplankton abundance and number of phytoplankton taxa while negative correlations with do saturation and ph

a multi proxy climatic record from the central tengger desert southern mongolian plateau implications for the aridification of inner asia since the late pliocene abstract aridification of the asian interior is one of the most significant paleoenvironmental events during the cenozoic however continuous paleoclimatic records from desert interiors are scarce because of the lack of outcrops erosion and discontinuous sediment accumulation here we report a multi proxy climatic record for the last 3 55 ma from paleomagnetically dated drilling core wedp01 from the central tengger desert which is one of the most important sediment source areas for northern hemisphere atmospheric dust and the chinese loess plateau analysis of grain size components indicates the onset of continuous dust deposition at 2 6 ma and desert formation at 0 9 ma in addition analysis of major element content and sediment color reveals a stepwise process of increasing aridification and significant cooling in the tengger desert area simultaneous aridification events in northwest china during the quaternary were probably induced by the uplift of the tibetan plateau northern hemisphere glaciation may have been another important factor for asian aridification meanwhile the increased dust emission from sources such as the tengger desert may provide a positive feedback mechanism for global cooling

chronology and paleoenvironmental records of a drill core in the central tengger desert of china abstract the desertification history of inland asia provides most direct evidence for asian drying history but the formation ages of the most asian deserts are not clear due to the lack of outcrops the tengger desert one of the main proximal deserts of the chinese loess plateau clp is of special paleoclimatic significances for its dust emission and environmental affection here we report lithofacies paleomagnetic ages and paleoenvironmental proxy indexes of the first drill core wedp01 from the central tengger desert paleomagnetism measurements reveal that the core spans from 3 55 ma to present consistent with the electron spin resonance esr dating results the strata of the central desert consist of alluvial fluvial deposits lacustrine fluvial deposits mixed with dust and eolian sand from bottom to top sedimentary analysis reveals that continuous eolian sand started by 0 9 ma marking the initial formation of the tengger desert and the domination of eolian sand in the strata with similar characters of the modern desert appeared by 0 68 ma indicating expansion of the tengger desert the proximal deserts formation and simultaneous increase of dust accumulation in the clp and the north pacific ocean in mid pleistocene demonstrate the role of proximal deserts for the dust loading of northern china and even northern hemisphere our analysis suggests the uplift of tibetan plateau in the mid pleistocene probably played the main role for this drying event and desert formation while global cooling may strength the arid environment of the proximal deserts

characteristics of δ13cdic in lakes on the tibetan plateau and its implications for the carbon cycle dissolved inorganic carbon isotope 13cdic is an important tool to reveal the carbon cycle in lake systems however there are only few studies focusing on the spatial variation of 13cdic of closed lakes here we analyze the characteristics of 13cdic of 24 sampled lakes mainly closed lakes across the qiangtang plateau qtp and identify the driving factors for its spatial variation the 13cdic value of these observed lakes varies in the range of 15 0 to 3 2 with an average value of 1 2 the 13cdic value of closed lakes is close to the atmospheric isotopic equilibrium value much higher than that in rivers and freshwater lakes reported before the high 13cdic value of closed lakes is mainly attributed to the significant contribution of carbonate weathering in the catchment and the evasion of dissolved co2 induced by the strong evaporation of lake water the 13cdic value of closed lakes has a logarithmic correlation with water chemistry tds dic and pco2 also suggesting that the evapo concentration of lake water can influence the 13cdic value the 13cdic value shows two opposite logarithmic correlations with lake size depending on the 13cdic range this study suggests that the 13c in carbonates in lacustrine sediments can be taken as an indicator of lake volume variation in closed lakes on qtp copyright 2011 john wiley sons ltd

late pliocene establishment of exorheic drainage in the northeastern tibetan plateau as evidenced by the wuquan formation in the lanzhou basin abstract the fluvial archives in the upper reach yellow river basins provide important information about drainage history of the northeastern tibetan plateau tp associated with geomorphologic evolution and climate change however the pliocene fluvial strata within this region have not been studied in detail hence limiting the understanding of the late cenozoic development of regional fluvial systems in this paper we present the results of a study of the geochronology sedimentology and provenance of the fluvial sequence of the wuquan formation in the lanzhou basin in the northeastern tp magnetostratigraphic and cosmogenic nuclide burial ages indicate that the wuquan formation was deposited during 3 6 2 2 ma furthermore sedimentary facies gravel composition paleocurrent data and detrital zircon u pb age spectra reveal that the fluvial sequence resembles the terraces of the yellow river in terms of source area flow direction and depositional environment our results indicate that a paleo drainage system flowing out of the northeastern tp was established by ca 3 6 ma and that the upstream parts of the yellow river must have developed subsequently from this paleo drainage system the late pliocene drainage system fits well with the dramatic uplift of the northeastern tp an intensified asian summer monsoon and global increase in erosion rates which may reflect interactions between geomorphic evolution tectonic deformation and climate change

sulfuric acid as an agent of carbonate weathering constrained by δ13cdic examples from southwest china abstract rock weathering by carbonic acid is thought to play an important role in the global carbon cycle because it can geologically sequestrate atmospheric co 2 current model of carbon cycle evolution usually assumes that carbonic acid is the major weathering agent and that other acids are not important here we use carbon isotopic evidence and water chemistry of springs and rivers from the beipanjiang river basin guizhou province southwest china to demonstrate that sulfuric acid is also an important agent of rock weathering the 13 c of dissolved inorganic carbon dic in the water samples ranges from 13 1 to 2 4 and correlates negatively to hco 3 ca 2 mg 2 ratios and positively to so 4 2 ca 2 mg 2 ratios these relationships are interpreted as mixing diagrams between two reactions of carbonate weathering using carbonic acid and sulfuric acid as a proton donor respectively mixing proportions show that around 42 of the divalent cations in the spring water from guizhou are originated from the interaction between carbonate minerals and sulfuric acid it is shown that 40 of this sulfuric acid is derived from the atmosphere and has an anthropogenic origin the remaining 60 are derived from the oxidative weathering of sulfide minerals in sedimentary rocks our results show the positive action of sulfuric acid on the chemical weathering of carbonate particularly we show that sulfuric acid generated by coal combustion has increased by almost 20 the weathering rates of carbonate in southwest china this is a clear evidence that human activities are changing the weathering rates of rocks and demonstrates a negative feedback on the acidification of the ocean by greenhouse gases because of the involvement of sulfuric acid in weathering reactions 63 of the alkalinity exported by rivers is derived from carbonate instead of 50 when atmospheric co 2 is the only acid involved in chemical weathering of carbonate in the guizhou province the weathering of carbonate is thus at least transiently a net source of co 2 to the atmosphere when extrapolated at global scale sulfuric acid induced carbonate weathering could counterbalance a significant part of the co 2 consumed by silicate weathering this paper highlights the competition between silicate weathering by carbonic acid and carbonate weathering by sulfuric acid for the regulation of the atmospheric co 2 level

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

magnetostratigraphy and its paleoclimatic significance of the pl02 borehole in the yinchuan basin abstract the basin sediment provides an important means of studying regional tectonic actives however regional climate factors overlaying tectonic actives affect the sedimentary process in the basin because of the lack of long term scales data the research on climate change in the arid and semi arid region is limited the pl02 core located in the center area of deposition in the yinchuan basin has a thick deposit with a higher resolution and sedimentation rate making itself practical for the reconstruction of the paleoclimate and the coupling relationship between regional tectonic activities and climate change the study of the 720 m borehole near pingluo county is presented in this paper the chronostratigraphic sequence of the core is established by palaeomagnetic dating the magnetostratigraphic correlation to the geomagnetic polarity timescale shows that the pl02 core recorded the brunhes matuyama gauss jaramillo olduvai kaena and mammoth polarity chron or subchron the sedimentation rate and the magnetostratigraphic of the core indicate that the onset of the pl02 core in this section occurred at 3 4 ma bp the analysis of the core established a detailed chronological framework for regional geological research at the stage of 3 22 3 04 ma 2 581 1 95 ma and after 0 012 ma the sedimentation rate increases gradually which archive three regional tectonic subsidence events the frequency dependent susceptibility of the sediment is used to reconstruct the paleoclimatic change the frequency dependent susceptibility is more effective than the magnetic susceptibility on reflecting regional climate change in the basin from 3 4 to 0 467 ma the gradual decrease of frequency dependent susceptibility reflects the regional climate change from warm and humid to cold and dry since 0 467 ma the gradual increase of the frequency dependent susceptibility corresponds to the climate becoming warm and humid again

formation of recent martian gullies through melting of extensive water rich snow deposits the observation of gullies on mars indicates the presence of liquid water near the surface in recent times1 2 which is difficult to reconcile with the current cold climate gullies have been proposed to form through surface runoff from subsurface aquifers1 3 or through melting of near surface ice under warmer conditions4 but these gullies are observed to occur preferentially in cold mid latitudes2 where the presence of liquid water is less likely and on isolated surfaces where groundwater seepage would not be expected making both potential explanations unsatisfactory here i show that gullies can form by the melting of water rich snow that has been transported from the poles to mid latitudes during periods of high obliquity within the past 105 to 106 years refs 5 6 melting within this snow7 can generate sufficient water to erode gullies in about 5 000 years my proposed model for gully formation is consistent with the age and location of the gullies and it explains the occurrence of liquid water in the cold mid latitudes as well as on isolated surfaces remnants of the snowpacks are still present on mid latitude pole facing slopes and the recent or current occurrence of liquid water within them provides a potential abode for life

cosmogenic burial ages reveal sediment reservoir dynamics along the yellow river china burial dating using cosmogenic al 26 and be 10 is an emerging technique for establishing chronologies of fluvial deposits ranging in age from ca 0 5 ma to 5 ma the determination of burial age however requires an assumption that sediment is buried with a known initial al 26 be 10 ratio using a sequence of well dated fluvial terraces along the yellow river in lanzhou china we demonstrate that this assumption may be violated when upstream sediment sources include neogene sedimentary basins samples of fluvial gravel from six terraces yield burial ages ranging from ca 0 83 ma to 2 81 ma comparison of these results to independent ages determined from magneto stratigraphic and loess paleosol studies demonstrates a high degree of correspondence between ages in the lower three terraces in the higher terraces however burial ages are systematically too old implying a previous burial history these results can be exploited to place quantitative constraints on the provenance of sediment in the terrace deposits our results reveal that rapid incision and excavation of late neogene sedimentary basins ca 1 7 ma led to injection of fluvial sediment with low initial al 26 be 10 ratios dilution of this source through time occurred as incision progressed into upstream bedrock ranges our results suggest that cosmogenic nuclides can illuminate the timing of long term storage and remobilization of sediment in continental scale river systems

inversion of bedrock channel profiles in the daqing shan in inner mongolia northern china implications for late cenozoic tectonic history in the hetao basin and the yellow river evolution abstract many studies indicate the hetao basin in inner mongolia northern china controlled the erosion base level of the upper yellow river before 1 5 ma the late cenozoic extensional rifting in the hetao basin in response to the northeastward growth of the tibetan plateau may be an plausible mechanism that initiated the headward erosional signal along the yellow river at the northeastern margin of tibetan plateau 1 8 ma ago however little attention has been paid to establish the relationship between the late cenozoic tectonic evolution in the hetao basin and integration of the upper yellow river in this paper we explore the tectonic mechanism that can drive headward erosion along the yellow river and the timescales over which it occurred by reconstructing the late cenozoic tectonic history in the hetao basin we applied linear inversion of bedrock channel profiles and late cenozoic sedimentary strata in the daqing shan to explore the late cenozoic tectonic evolution in the hetao basin results show that the accelerated vertical slip between the daqing shan and the hetao basin initiated at 2 8 0 8 ma and the average relative uplift rate was 0 18 0 04 mm yr since 2 8 ma the lowering of erosion base level in the hetao basin since 2 8 0 8 ma produced a headward erosional signal along the yellow river that initiated fluvial incision at the northeastern margin of the tibetan plateau 1 8 ma ago that indicates the accelerated extensional rifting in the hetao basin has been responsible for the integration of the upper yellow river since the late pliocene our study improved understanding how the yellow river responds to the late cenozoic rifting around the ordos block as well as the northeastward growth of the tibetan plateau meanwhile these tectonic processes were also linked together by the yellow river evolution

inorganic carbon isotope systematics in soil profiles undergoing silicate and carbonate weathering southern michigan usa abstract the upper midwest usa features glacial derived till materials enriched in carbonate minerals but with the uppermost soil layer progressively leached of carbonates in the interval since glaciation groundwaters and groundwater fed surface waters are profoundly influenced by carbonate mineral dissolution stable carbon isotope compositions of soil waters and groundwaters in two southern michigan watersheds huron and kalamazoo were studied as a function of ph 13cco2 types of weathering reactions silicate vs carbonate and degree of isotope equilibration this comprehensive study of carbon isotope biogeochemistry in the vadose zone including soil gas soil water groundwater and soils organic matter carbonate phases elucidates relations between the chemical weathering rates and co2 fluxes in the soil zone such information is important to evaluate responses of terrestrial ecosystems to global climate change in shallow soil zones where only silicate weathering was occurring respiratory co2 was the major source of soil water dic with little addition from the atmospheric co2 isotopic equilibration between 13cdic and 13cco2 occurred in an open system with respect to soil co2 in the deeper soil horizons carbonate dissolution dominated soil water chemistry and saturation with respect to calcite and dolomite was attained rapidly mass balance calculation showed that large amounts of soil co2 were consumed by carbonate dissolution such that the deeper soil zone may not have been an open system with respect to co2 constant 13cdic values 11 were observed in these deep soil waters and also in shallow groundwaters of the huron watershed thus isotopic equilibrium might not be reached between dic and co2 possibly due to a rapid kinetics of carbonate dissolution and limited gas water exchange in the soils if so dic was equally contributed by carbonate minerals 13ccaco3 0 in reaction with soil co2 13cco2 22 soils beneath an agricultural site with a wheat corn soybean rotation the kalamazoo watershed displayed a wide range in 13cco2 values 22 to 12 and the 13cdic of deeper soil waters in contact with carbonate minerals was controlled by seasonal variations of 13cco2 as well as by strong acids produced by nitrification and to a lesser degree by pyrite oxidation both of which could react to dissolve carbonate minerals in addition to carbonic acid dissolution

carbon cycle in st lawrence aquatic ecosystems at cornwall ontario canada seasonal and spatial variations abstract seasonal studies of a cross section through the upper st lawrence river in 1995 and 1996 revealed strong biogeochemical gradients between a wetland a creek embayments and the main river near the city of cornwall ontario canada these local differences are much more pronounced than over the entire length of the main river indicating the importance of near shore ecosystems in the riverine carbon cycle the aqueous pco2 ranged from atmospheric equilibrium to values as high as 5450 ppmv reflecting a gradient from the great lakes dominated main river to the peripheral ecosystems with active biological recycling the isotopic composition of dissolved inorganic carbon fits this observation with 13 c dic values ranging from 2 2 to 13 7 from the main river to near shore ecosystems warm season samples of embayments revealed active photosynthesis with po2 values up to 50 higher than those of the atmosphere and pco2 below atmospheric equilibrium while photosynthetic activity was mostly caused by phytoplankton as indicated by chlorophyll a up to 63 0 mg l an active periphyton and macrophyte community also contributed to oxygen oversaturations in the littoral zone in situ respiration dominated in the wetland particularly during winter and spring when dissolved organic carbon up to 17 3 mg l was transformed into co2 leading to 13 c dic values as low as 12 3 the creek was the only ecosystem with a respiratory signal inherited from near shore baseflow as indicated by its 18 o h 2 o composition that was similar to local groundwater during peak runoff periods its peak doc concentrations of 38 3 mg l the highest amongst the studied ecosystem may have resulted in further enhanced respiratory activity

carbon and oxygen dynamics in the laurentian great lakes implications for the co2 flux from terrestrial aquatic systems to the atmosphere abstract we collected samples in lakes superior erie and huron including georgian bay in mid summer during the stratified period to determine the relative importance of production respiration and atmospheric exchange to carbon dynamics in the lakes in all lakes sampled oxygen saturation averaged 107 2 significantly greater than the atmospheric equilibrium and the isotopic composition of dissolved oxygen 18odo averaged 22 8 0 1 significantly less than the isotopic composition of dissolved atmospheric oxygen suggesting that biological production was greater than respiration in the epilimnion during the summer months while lakes worldwide are commonly oversaturated in carbon dioxide average pco2 in the epilimnion of the lake studied was 342 42 atm and the isotopic composition of dissolved inorganic carbon 13cdic was 0 2 0 2 both values not significantly different from expected atmospheric co2 equilibration n 65 p 0 89 n 64 p 0 81 this trend is atypical approximately ninety percent of lakes globally are oversaturated in carbon dioxide the atmospheric equilibrium observed in the laurentian great lakes and other studies suggest that pco2 in large lakes is depleted relative to smaller lakes this is also the case for rivers that are sourced from or flow though large lakes and they can be expected to have lower pco2 downstream from the lakes and lower per unit area carbon fluxes than other rivers an improved understanding of the global carbon cycle mandates that this be taken into account when considering co2 fluxes from aquatic ecosystems

isotopic composition of dissolved inorganic carbon in a large polluted river the vistula poland abstract the vistula is a large lowland temperate river receiving high loads of pollutants from a densely populated catchment on the other hand the river is to a relatively small extent affected by channelisation and damming this study is the first attempt to characterise stable isotope aspects of dissolved inorganic carbon in the vistula which is a major source of pollution to the baltic sea isotopic composition of dic and other chemical properties were measured biweekly at the upper reach and monthly at the mouth of the river two longitudinal samplings were performed in hydrological summer and winter conditions short term and short range observations were carried out in an anthropogenically influenced urban reach at cracow most water samples from the vistula and its tributaries analysed in this study had 13 c dic values around the range 12 to 11 typical for european lowland rivers fed by groundwaters on carbonate areas variablity of 13 c dic in this river system is limited except for the impoundments and the specific hydrological conditions the few impoundments that exist on the vistula intensify the photosynthesis respiration cycle as well as the exchange of co 2 with the atmosphere enhanced contribution of biogenic carbon during floods is reflected by lowering of 13 c dic low flows facilitate photosynthetic assimilation and evasion of co 2 into the atmosphere resulting in positive shifts of 13 c dic principal component analysis confirmed that 13 c dic variability at the fixed cross section in cracow reflected releases and withdrawals of co 2 from the riverine dic pool the apparent 13 c dic variability depends to some extent on the spatio temporal context of observations diurnality can be very pronounced in the impounded anthropogenically influenced reaches in warm periods interpretation of the observed riverine 13 c dic patterns can be difficult as the spatial and temporal variabilities combine resulting in convoluted isotopic signals isotopic investigations into the nature of riverine carbon cycling should be supplemented by discharge records and by observations of the parameters influenced by the photosynthesis respiration cycle dissolved oxygen ph p co 2 and of those conservative with respect to biological processes electrical conductivity stable isotope composition of water

seasonal changes in the sources and fluxes of dissolved inorganic carbon through the st lawrence river isotopic and chemical constraint the st lawrence river ranks 16 th in the world rivers for its freshwater discharge into the ocean but its particulate fluxes are relatively low due the upstream presence of the great lakes system using notably 13 c measurements in total dissolved inorganic carbon dic at several stations along stream earlier studies provided information on dissolved inorganic carbon dic fluxes through the st lawrence with some constraints on spatial trends with respect to the in situ dic metabolism here we further document annual dic fluxes and seasonal changes in dic supplies and dic metabolism downstream chemical and isotopic measurements were performed in 1998 on a biweekly basis at four different sites these sites represent respectively the great lakes outflow into the st lawrence system supplies from two tributaries one with a silicate rich precambrian bedrock the other with a carbonate rich paleozoic bedrock and the st lawrence outflow into the maritime estuarine system the 1998 survey yielded a total annual dic flux of 6 10 12 to 7 10 12 g of carbon at the quebec city outlet about 40 higher than estimates from earlier studies this represents about 1 5 of the world river dic supplies to the ocean very strong seasonal variations are observed between the summer low water levels when water supplies from the great lakes into the riverine system may represent up to 80 of the total outflow of the st lawrence river and the spring snowmelt period when tributaries may provide up to 80 of this outflow d 13 c dic values respond to this seasonal cycle with near isotopic equilibrium values with atmospheric co2 during summer and strongly depleted values in other seasons notably during the spring high outflow period this seasonal isotopic cycle is more pronounced at the quebec city outlet where the influence of 13 c depleted dic supplies from tributaries is stronger than upstream the low d 13 c dic values observed from fall to spring may be due to a combination of the following factors i enhanced supplies of 13 c depeleted dic from soils and ground waters from watersheds ii higher oxidation rates of dissolved or particulate 13 c depleted organic carbon and iii a reduced incidence of the in situ photosynthetic activity the outflow and isotopic seasonal cycles result notably in a strong negative correlation between d 13 c dic values and discharge rates estimates of dic supplies from tributaries vs those from the great lakes were calculated using either chemical or isotopic approaches dic supplies from tributaries vary between 5 and 60 of total dic examination of pco2 data indicates a negligible seasonal variability at the great lakes outlet with a mean annual value near equilibrium with atmospheric co2 i n contrast strong seasonal changes are observed downstream at quebec city with minimum pco2 values in summer and a mean

stable oxygen and carbon isotope record from a drill core from the hetao basin in the upper reaches of the yellow river in northern china and its implications for paleolake evolution abstract knowledge of the evolution of the paleolakes that developed intermittently within the hetao basin in northern china is important for understanding both the evolution of the upper and middle reaches of the yellow river drainage system and the spatio temporal evolution of regional water vapor transport associated with the east asian summer monsoon however the long term history of these lakes and the driving mechanisms are poorly understood in this study we reconstructed the history of the paleolakes within the hetao basin over the past 1 68 myr based on 18o and 13c records from lacustrine authigenic carbonates in a 274 60 m long drill core from the centre of the hetao basin the absence of covariation of carbonate 18o and 13c during the intervals of 1 47 1 30 ma and 1 17 1 07 ma suggests the existence of a hydrologically open lake system in the hetao basin the relatively low and invariant carbonate 18o values are similar to those of the modern yellow river water suggesting that the paleolakes formed when the lakes and the yellow river were connected the moderately high correlation r 0 61 of carbonate 18o and 13c during 0 68 0 60 ma suggests an intermittently open hydrology of the lake probably with a tendency towards closure within certain intervals the low correlation during 0 47 0 28 ma suggests a hydrologically open lake while the relatively high 18o values suggest a longer residence time of the lake water the high correlation r 0 92 of carbonate 18o and 13c from 0 28 ma to the last interglacial suggests a hydrologically closed lake although the yellow river may have flowed through the hetao basin at that time the interaction of the tectonically controlled relative height of the basin spill point and the climatically driven sediment and water supply of the yellow river was responsible for the long term evolution of the paleolake within the hetao basin strong regional tectonic activity which induced the uplift of the eastern part of the hetao basin and jinshan gorge and raised the relative height of the spill point was the primary cause of the formation of a hydrologically closed lake within the basin

rapid fluvial incision along the yellow river during headward basin integration the onset of fluvial erosion in an area of tectonic uplift is thought to reflect the timing of the uplift geomorphological data from the yellow river in tibet indicate that the rapid incision of this river channel occurred as a result of climate change at least six million years after the onset of plateau uplift

handbook of environmental isotope geochemistry vol 1 the terrestrial environment a p fritz and j ch fontes editors elsevier amsterdam 1980 xii 532 pp u s 90 25 dfl 185 00

testing contrasting models of the formation of the upper yellow river using heavy mineral data from the yinchuan basin drill cores the upper yellow river drains the central and northeastern tibetan plateau understanding the origin of this river is essential for unraveling the interplay between fluvial incision basement uplif

carbon 14 in streams as a tracer of discharging groundwater summary quantification of the volume of groundwater discharge to streams and the source aquifer of that discharge is required to adequately manage the impacts of groundwater use on stream ecosystems this has been achieved through longitudinal surveys of gaseous tracers but their effectiveness can be limited by rapid equilibration between the stream and the atmosphere here we develop the use of carbon 14 in dissolved inorganic carbon dic in a stream as a tracer of groundwater discharge a controlled equilibration experiment was conducted during which groundwater with an initial 14c activity of 5 5 pmc was allowed to equilibrate with the atmosphere over 72 days the effective transfer velocity for 14c was measured as 0 013 m d 1 the method was then tested at an artificial groundwater discharge location where the effective transfer velocity was measured as 0 025 m d 1 in these simple systems the ratio of the effective 14c transfer velocity to the co2 gas transfer velocity is a function of ph and proportional to the fraction of dic present as co2 the method was then applied along a reach of the daly river australia where groundwater discharge is known to occur a decrease of 7 pmc was observed across the major spring discharge zone with subsequent equilibration with the atmosphere occurring over at least tens of kilometres this allowed for the effective transfer velocity to be estimated at between 0 09 and 0 15 m d 1 and for the 14c activity of groundwater discharge to be estimated at between 60 and 66 pmc the equilibration of 14c in stream dic is in the order of 10 times slower than for gas tracers which may allow for the detection of smaller groundwater discharge fluxes than is possible with gas tracers if the total groundwater discharge flux is known measurements of 14c in stream dic can also be used to infer the 14c activity of discharging groundwater this method may be a useful alternative to direct groundwater sampling particularly in remote basins with few groundwater wells

a 1000 year record of dry conditions in the eastern canadian prairies reconstructed from oxygen and carbon isotope measurements on lake winnipeg sediment organics a short sediment core 162cm covering the period ad 920 1999 was sampled from the south basin of lake winnipeg for a suite of multi proxy analyses leading towards a detailed characterisation of the recent millennial lake environment and hydroclimate of southern manitoba canada information on the frequency and duration of major dry periods in southern manitoba in light of the changes that are likely to occur as a result of an increasingly warming atmosphere is of specific interest in this study intervals of relatively enriched lake sediment cellulose oxygen isotope values d 18 ocellulose were found to occur from ad 1180 to 1230 error range ad 1104 1231 to 1160 1280 1610 1640 error range ad 1571 1634 to 1603 1662 1670 1720 error range ad 1643 1697 to 1692 1738 and 1750 1780 error range ad 1724 1766 to 1756 1794 regional water balance inferred from calculated lake winnipeg water oxygen isotope values d 18 oinf lw suggest that the ratio of lake evaporation to catchment input may have been 25 40 higher during these isotopically distinct periods associated with the enriched d 18 ocellulose intervals are some depleted carbon isotope values associated with more abundantly preserved sediment organic matter d 13 com these suggest reduced microbial oxidation of terrestrially derived organic matter and or subdued lake productivity during periods of minimised input of nutrients from the catchment area with reference to other corroborating evidence it is suggested that the ad 1180 1230 1610 1640 1670 1720 and 1750 1780 intervals represent four distinctly drier periods droughts in southern manitoba canada additionally lower magnitude and duration dry periods may have also occurred from 1320 to 1340 error range ad 1257 1363 1530 1540 error range ad 1490 1565 to 1498 1572 and 1570 1580 error range ad 1531 1599 to 1539 1606 copyright 2009 john wiley sons ltd

evaluating the role of climate and tectonics during non steady incision of the yellow river evidence from a 1 24 ma terrace record near lanzhou china abstract the competing roles of bedrock uplift and climatic change in the formation of fluvial terraces remain uncertain most of recent studies have attributed terrace formation to climatic changes and held that even in tectonically active settings climate variations control cycles of terrace planation and abandonment based on field investigations of loess paleosol sequences magnetostratigraphy and optically stimulated luminescence osl dating we develop a new chronology for a spectacular flight of terraces along the yellow river near lanzhou china over past 1 24 ma all the terraces are strikingly similar in that they have several meters of paleosol developed directly above fluvial deposits on the terrace treads suggesting that the abandonment of each terrace due to river incision occurs during the transition from glacial to interglacial climates however the ages of terraces cluster in two relatively short time periods 1 24 0 86 ma and 0 13 ma present during the intervening time between 0 86 ma and 0 13 ma terraces either did not form or were not preserved we suggest that this record indicates that rock uplift rates varied through time and influenced terrace formation preservation thus our results demonstrate the utility of deep chronologic records from fluvial terraces for deconvolving the effects of tectonics and climate on fluvial incision

heavy mineral assemblages and sedimentation rates of eastern central asian loess paleoenvironmental implications abstract central asian loess deposits record the evolution of aridification across the asian interior however paleoclimatic proxies are strongly influenced by the variation of the dust source and accumulation process in order to decipher the paleoenvironmental changes a sensitive paleoclimatic proxy with clear source and accumulation process will be needed in this study heavy mineral assemblages and sedimentation rates were investigated in a 30 kyr loess section in the ili basin xinjiang northwestern china during marine isotope stage mis 2 trends in dust sedimentation rate were similar to those of the chinese loess plateau clp in anti phase with northern hemisphere summer insolation nhsi at 65 n amphibole epidote ratios contents and mean grain size were low during cold phases such as the late last glacial maximum lgm and heinrich event h 1 their ratios were higher during adjacent warm periods this was attributed to aeolian sorting during transportation namely greater sorting between amphibole and epidote occurred in warmer phases and weaker sorting occurred in colder phases the amphibole epidote ratio could serve as a proxy for wind intensity and thus the siberian high sh intensity amphibole epidote ratio was a more appropriate proxy to record wind intensity than dust sedimentation rate which was also influenced by sediment availability a higher amphibole epidote ratio corresponded to a more negative east asian stalagmite 18o indicating an anti phase relationship between the sh and east asian summer monsoon easm during the mis 2

the carbonate system geochemistry of shallow groundwater surface water systems in temperate glaciated watersheds michigan usa significance of open system dolomite weathering we present here a field geochemical study of controls on carbonate weathering within rapidly circulating shallow groundwater surface water systems in the glaciated mid continent region groundwaters and surface waters in three watersheds spanning the upper to lower peninsulas of michigan consist of ca 2 mg 2 hco 3 solutions derived from the open system dissolution of calcite and dolomite in soils developed on mixed mineralogy glacial drift the thermodynamic stabilities of calcite and dolomite both decrease with decreasing temperature with dolomite more strongly affected thus the low mean annual temperature of these temperate weathering environments maximizes the absolute solubility of dolomite as well as its solubility relative to calcite many groundwaters in the study area approach equilibrium with respect to the more soluble dolomite and are moderately supersaturated with respect to calcite groundwaters in each watershed have distinct and relatively narrow ranges of carbon dioxide partial pressure p co 2 values which increase significantly from north to south log p co 2 of 3 0 to 2 2 atm suggesting that there are landscape level differences in carbon transformation rates in soil weathering zones increases in weathering zone p co 2 values produce hco 3 concentrations that vary by a factor of five but the mg 2 ca 2 and mg 2 hco 3 ratios of all groundwaters are similar suggesting relatively constant weathering input ratios of calcite and dolomite although surface waters commonly are between 2 and 10 times supersaturated with respect to calcite the mg 2 hco 3 ratios of surface waters are very close to initial groundwater values suggesting that back precipitation of calcite is not a significant process in these systems the enhanced solubility of dolomite at low temperatures coupled with the landscape level differences in carbon cycling suggest that temperate zone weathering reactions in glaciated terrains are significant contributors to continent scale fluxes of both mg 2 and hco 3

the origins and behaviour of carbon in a major semi arid river the murray river australia as constrained by carbon isotopes and hydrochemistry abstract 13 c values of dissolved inorganic c dic dissolved organic c doc and particulate organic c poc together with 18 o and 2 h values of water 34 s values of dissolved so 4 and major ion concentrations were measured in the murray river and its tributaries between november 2005 and april 2007 to constrain the origins and behaviour of riverine c 13 c dic values in the murray river vary between 9 5 and 4 7 with a range of 13 c dic values of the tributaries are 11 0 to 5 1 dic concentrations of the murray river increase from 25 mg l in the middle and upper reaches of the river to 45 55 mg l in the lower reaches however the mass ratio of dic as a proportion of the total dissolved solids tds decreases from 0 6 0 7 in the headwaters to 0 2 0 3 in the lower reaches of the river with similar downstream changes in dic cl ratios this precludes simple evaporative concentration of dic and is interpreted as the river evading co 2 this interpretation is consistent with p co 2 values that are in the range 550 11 200 ppm volume ppmv which are far higher than those in equilibrium with the atmosphere 360 ppmv the 13 c dic values are similar to those that would be produced by the weathering of marine limestone 13 c 0 however the lack of marine limestones cropping out in the murray darling basin and the relatively uniform 13 c dic values of the murray river even in upland reaches where the dominant rock types are metamorphosed silicates and granites make this unlikely rather the high p co 2 values and 13 c dic values are best explained by a combination of mineralisation of low 13 c organic c and evasion to the atmosphere the rate of these two processes may attain near steady state and control both dic concentrations and 13 c values

use of 13c to trace origin and cycling of inorganic carbon in the rhone river system dissolved inorganic carbon dic and particulate inorganic carbon pic were sampled at 20 sites on the rhone and its main tributaries from switzerland to the mediterranean in march september and july flood event 1996 flux estimation and dic and pic values are used to trace watershed inputs and fluvial processes affecting the inorganic carbon budget dic concentration and values vary between 1 mm at 5 near the rhone s source and 3 mm at 10 near its mouth with tributaries draining lowland carbonate dominated areas at 3 8 mm and 11 there is an inverse relationship between river dic concentration and dic the headwaters are characterized by high dic values and low dic indicating a minor input of respired co2 dic should be mainly produced through the reaction of carbonate with atmospheric co2 or organic sulfuric acids in lowland carbonate dominated areas values of 11 are consistent with production of dic by weathering of limestone c 1 with co2 derived from the oxidation of organic matter 21 5 the evolution of the rhone s dic concentration and appear to be largely determined by mixing between the rhone and its main tributaries the co2 fluxes and dic mass balance calculated for the different segments of the rhone point to a net but very limited input of fluvial respired co2 from the oxidation of organic c 5 the pic represents a small but quite variable fraction of the inorganic carbon 3 except on alpine catchments and during floods in these cases it can be up to 10 of the dic concentration and export the carbon and oxygen isotopic composition of pic from the rhone during a flood and from alpine tributaries falls within the range of limestones 2 6 relatively light pic isotopic composition indicate mixing of sedimentary rocks and carbonate precipitated in situ data for the rhone system are typical of watersheds presenting high chemical weathering rates for hco3 and alpine lowland conditions

response of dissolved inorganic carbon dic and δ13cdic to changes in climate and land cover in sw china karst catchments abstract monthly hydrochemical data and 13c of dissolved inorganic carbon dic in karst water samples from september 2007 to october 2012 were obtained to reveal the controlling mechanisms on dic geochemistry and 13cdic under different conditions of climate and land cover in three karst catchments banzhai dengzhanhe and chenqi in guizhou province sw china dic of karst water at the banzhai site comes mainly from carbonate dissolution under open system conditions with soil co2 produced by root respiration and organic carbon decomposition with lowest 13c values under its dense virgin forest coverage weaker carbonate bedrock dissolution due to sparse and thin soil cover results in lower 13cdic pco2 dic and ec and lower cation and anion concentrations at the chenqi site larger soil co2 input from a thick layer of soil results in high pco2 and dic and low ph sic and 13cdic in the karst water at the dengzhanhe site a lesser soil co2 input due to stronger karst rock desertification and strong gypsum dissolution contribute to higher 13cdic high ec and high cation and anion concentrations soil co2 inputs controlled by biological activity and available soil moisture carbonate bedrock dissolution dilution and degassing effects vary seasonally following rainfall and temperature changes consequently there are seasonal cycles in hydrochemistry and 13cdic of the karst water with high pco2 and low ph ec sic and 13cdic values in the warm and rainy seasons and vice versa during the cold and dry seasons a strongly positive shift 3 in 13cdic occurred in the drought year 2011 indicating that 13cdic in groundwater systems can be an effective indicator of environmental and or climate changes

carbon fluxes pco2 and substrate weathering in a large northern river basin canada carbon isotope perspectives abstract isotopic composition of dissolved inorganic carbon 13 c dic in the ottawa river basin is about 8 and 16 for lowland carbonate and upland silicate tributaries respectively this suggests that 1 the source of dic to the ottawa river is soil respiration and carbonate weathering 2 exchange with the atmosphere is unidirectional or volumetrically unimportant and 3 in river respiration and photosynthesis are not significant influences on the river carbon budget accepting these constraints chemical and isotopic data are used to reconstitute soil pco2 for tributary catchments averages for upland silicate mixed and lowland carbonate basins are calculated to be roughly 2000 5000 and 30 000 ppm respectively these values are used as input to model the pathway of carbon through the watershed rain water to soil water to river water the flux of carbon from the ottawa river as dic is calculated to be 4 3 1010 mol c a utilizing carbon isotopes 75 and 25 of the ca2 mg2 flux is calculated to originate from carbonate and silicate weathering respectively and 61 of the dic is calculated to originate from organic respiration the latter represents some 6 of respired carbon in the basin assuming an average respiration rate of 0 5 mmol c m 2 h 1 based on a diffusion model co2 evasion to the atmosphere from the ottawa river and its tributaries is estimated to be 1 3 1010 mol c a or 30 of the dic flux

chemical dynamics of the st lawrence riverine system δdh2o δ18oh2o δ13cdic δ34ssulfate and dissolved 87sr 86sr chemical and stable isotope analyses of the st clair detroit niagara and st lawrence rivers st lawrence system and their tributaries show that the chemical and isotopic compositions of the waters are strongly controlled by the geology of their drainage basins tributaries draining the canadian shield have very low tds hco3 so42 ca2 mg2 no3 sr2 higher si and fetotal and high 87sr 86sr ratios 0 710 0 713 the grand and thames rivers that drain paleozoic limestones dolostones and evaporites are characterized by opposite attributes the st lawrence and the tributaries draining the canadian appalachians fall between these two endmembers the st clair detroit and niagara rivers do not show any pronounced seasonal variations in major component chemistry due to buffering by the great lakes in contrast pronounced seasonal variations characterize the lower st lawrence mainly because of significant tributary inputs into the overall water budget the d and 18o in the st lawrence range from 60 9 to 44 5 and from 8 5 to 6 1 smow respectively much heavier than the comparative values measured for the tributaries 92 8 to 58 3 and 13 1 to 8 5 this is a consequence of evaporative loss that over the residence time of water of 102 years equals about 7 of the water volume in the great lakes the strontium and sulfur isotopic values for the st lawrence system are relatively uniform with measured values from 0 70927 to 0 71112 for 87sr 86sr and from 4 3 to 5 6 for sulfate 34s their seasonal variations are also minor the strontium and sulfur fluxes of the st lawrence river are calculated to be 7 84 108 and 1 09 1011 mol a respectively the relative contributions of the great lakes tributaries and other sources to these fluxes are 73 16 11 for strontium and 64 13 23 for sulfur isotopic composition of dissolved inorganic carbon 13cdic in the st lawrence system ranges from 4 7 to 0 7 considerably heavier than the values for the tributaries 16 5 to 6 7 the light 13cdic values for the tributaries suggest that co2 from bacterial respiration plays an important role in the isotopic composition of riverine dic however in the main stem river s this bacterial signal is masked by isotopic equilibration with atmospheric co2 due to the long residence time of water in the great lakes seasonally the main stem river s have heavier 13c values in the fall than in the spring a consequence of preferential 12c consumption by photosynthetic plants in the epilimnion of the great lakes during the growth season in the down stream portion of the st lawrence river influx of isotopically light tributary waters causes progressive 13c depletion from 1 3 to 2 0 and 1 4 to 3 0 in the fall and spring respectively the total dic carbon flux of the st lawrence river is calculated to be 3 9 1011 mol a mass balance calculations show that the relative contributions of the great lakes tributaries decay of organic matter exchange with the atmosphere and dissolution of carbonates to this total dic flux are 81 13 2 6 10 in the spring and 83 15 2 4 0 in the fall respectively

the co2 consumption potential during gray shale weathering insights from the evolution of carbon isotopes in the susquehanna shale hills critical zone observatory abstract shale covers about 25 of the land surface and is therefore an important rock type that consumes co 2 during weathering we evaluated the potential of gray shale to take up co 2 from the atmosphere by investigating the evolution of dissolved inorganic carbon dic concentrations and its carbon isotopic ratio 13 c dic along water flow paths in a well characterized critical zone observatory susquehanna shale hills catchment in this catchment chemical weathering in shallow soils is dominated by clay transformation as no carbonates are present and soil pore waters are characterized by low dic and ph in shallow soil porewaters the dic dominated by dissolved co 2 is in chemical and isotopic equilibrium with co 2 in the soil atmosphere where pco 2 varies seasonally to as high as 40 times that of the atmosphere the degradation of ancient organic matter is negligible in contributing to soil co 2 the chemistry of groundwater varies along different flowpaths as soil pore water recharges to the water table and then dissolves ankerite or secondary calcite under the valley floor weathering of carbonate leads to much higher concentrations of dic 2500 mol l and divalent cations ca 2 and mg 2 in groundwaters than soil waters the depth to the ankerite weathering front is hypothesized to be roughly coincident with the water table but it varies due to heterogeneities in the protolith composition groundwater chemistry therefore shows different saturation indices with respect to ankerite depending upon location along the valley the 13 c dic values of these groundwaters document mixing between the ankerite and soil co 2 the major element concentrations dic and 13 c dic in the first order stream incising the valley of the catchment are derived from groundwater and soil waters in proportions that vary both spatially and temporally the co 2 degassed slightly in the stream but little evidence of c isotopic equilibration with the atmosphere is observed due to the short length of the stream and short contact time with air the ankerite reaction front also lies close to the pyrite dissolution front pyrite oxidation in bedrock likely released sulfuric acid and played a minor role in the ankerite dissolution shifting groundwater 13 c dic slightly above the expected mixing values at the catchment scale the stream so 4 2 is also dominantly derived from wet deposition as stream has 34 s so4 values around 3 well within the range of acid deposition a mass balance calculation shows that silicate and ankerite dissolution of the rose hill shale at shale hills consumes co 2 at a rate of 44 and 42 48 mol m 2 ky 1 respectively while degradation of ancient organic matter releases co 2 at a rate of 1 3 mol m 2 ky 1 silicate dissolution at the shallow soils is facilitated by low ph and high soil pco 2 as ankerite dissolution and organic matter oxidation are shown to occur early during shale alteration co 2 consumption by shale weathering is thus limited by initiation of rock disintegration e g fractures and exposure of fresh surface area to infiltrating co 2 and o 2 rich water

mars orbiter camera geodesy campaign during the geodesy campaign in may and june 1999 the wide angle system of the mars global surveyor mars orbiter camera imaged the visible surface of mars from latitudes 70 s to 90 n over 90 of this portion of the planet was covered at two viewing angles to obtain side looking stereo at a resolution of 250 m pixel and convergence angles of 21 27 continuous radiometric spacecraft tracking during this period provided precise orbit determination of spacecraft location this data set will become the basis of a new image mosaic of mars with the potential to exceed the geodetic precision and image quality of those presently available

formation of recent martian debris flows by melting of near surface ground ice at high obliquity the observation of small gullies associated with recent surface runoff on mars has renewed the question of liquid water stability at the surface of mars the gullies could be formed by groundwater seepage from underground aquifers however observations of gullies originating from isolated peaks and dune crests question this scenario we show that these landforms may result from the melting of water ice in the top few meters of the martian subsurface at high obliquity our conclusions are based on the analogy between the martian gullies and terrestrial debris flows observed in greenland and numerical simulations that show that above freezing temperatures can occur at high obliquities in the near surface of mars and that such temperatures are only predicted at latitudes and for slope orientations corresponding to where the gullies have been observed on mars

terrestrial and fluvial carbon fluxes in a tropical watershed nyong basin cameroon abstract the nyong watershed with an area of 27 800 km2 and a mean annual discharge of 390 m3 s 1 is the second largest river in cameroon the nyong watershed serves as an outstanding study area for the examination of carbon fluxes in humid tropical environments because of its limited anthropogenic impact and homogeneous silicate bedrock between april 2005 and april 2007 we sampled water at seven stations from the small watershed of the mengong 0 6 km2 to the nyong at edea 24 500 km2 and monitored temperature ph dissolved inorganic carbon dic and dissolved organic carbon doc contents as well as the isotopic composition of dic 13cdic and doc 13cdoc we estimated terrestrial net ecosystem productivity in the nyong river watershed and measured fluvial fluxes of carbon to the ocean and the atmosphere the nyong river basin sequesters significant amounts of carbon on an annual basis 7 920 000 t c year 1 300 g c m 2 year 1 the combined dissolved organic dissolved inorganic and atmospheric fluxes of carbon from the nyong river only export 3 of this flux from the basin on an annual basis this includes a minimum co2 outgassing of 1487 g c m 2 year 1 comparable to 115 of the annual flux of doc and four times greater than the flux of dic

liquid co2 breakout and the formation of recent small gullies on mars we show that the action of a co2 suspended flow could have produced the recent small gullies on mars and hence that liquid water is not required the model involves the build up of a liquid co2 aquifer behind and below a dry ice barrier dam cap rock in the pore spaces a few meters into the rock from the cliff face and on order of a hundred meters below the top of the cliff brink surface seasonal or obliquity cycle seasonal heating causes pinching out of the dry ice barrier and rapid release of the liquid co2 erosion of the gullies occurs as the rapid vaporization of the liquid co2 with entrainment of rock and clathrate hydrate ice produces a density flow analogous to a terrestrial nue ardente

incision rate of the yellow river in northeastern tibet constrained by 10be and 26al cosmogenic isotope dating of fluvial terraces implications for catchment evolution and plateau building unlike other large rivers flowing out of tibet the yellow river escapes from the plateau towards the ne crossing no less than five nw se striking actively growing ranges and intervening basins thick plio quaternary deposits and fluvial terraces testify to a phase of aggra dation and sediment infill up to the average surface elevation 3200 3250 m a s l of the gonghe guide and qinghai lake basins a set of seven main terraces across the gonghe basin suggests progressive down cutting of the yellow river carving the 500 m deep longyang gorge at the basin exit 10be and 26al concentrations in quartz of surface and sub surface samples of four terraces constrain the timing of incision by determining the burial age of the deposit and the exposure age of its surface modelling the depth dependence of the 10be concentration and the 26al 10be ratio allows us to constrain the onset of the ongoing phase of incision to 120 250 ka these ages suggest long term incision rates between 2 6 mm a together with the present morphology of the yellow river terraces across the gonghe basin and the longyang gorge our results imply rapid river catchment evolution and interaction between river dynamics tectonic and climate in northeastern tibet

formation and evolution of the badain jaran desert north china as revealed by a drill core from the desert centre and by geological survey abstract the deserts in north china are regarded as direct records of the process of inland asian aridification amongst these deserts those proximal to the chinese loess plateau clp are especially important because of their role as sediment source areas in order to investigate the formation history of the badain jaran desert the largest desert proximal to the clp a 310 m long drill core was obtained from the desert centre which reached the underlying basement rock the lithology of the core consists of an upper layer of aeolian sand with three intercalated layers of lacustrine sediments overlying alluvial fluvial deposits which are developed unconformably over red coloured basement rock a geological survey indicates that the lower red coloured basement rock is of late cretaceous age and is cut by a mesozoic erosion surface widely developed over the badain jaran area on the basis of optically stimulated luminescence and electron spin resonance dating and stratigraphic correlation a preliminary chronological framework was established which was improved by tuning the aeolian sand proportion of the drill core to earth orbital obliquity and precession this final chronology suggests that 1 the basal age of the desert strata is at least 1100 ka corresponding to the formation of the badain jaran desert and 2 that the formation of the erosion surface terminated and the surface had begun to subside by at least 1200 ka the formation of the desert can be summarized as follows the alluvial fluvial fan formed by the heihe river draining the qilian mountains provided sufficient sedimentary material to form the desert under an arid climate while the asian winter monsoon and the westerlies entrained the clastic sediments from the fan area which finally accumulated downwind more distant sediment transport was prevented by the intervening mountainous terrain these coupled processes were driven by tibetan plateau uplift and ongoing global climatic cooling after initial formation of the desert three humid phases occurred in mis 13 15 mis 5 and the holocene during which extensive lakes developed the sequential drying out of the lakes may reflect inter relationships between global climate and the intensity of the asian summer monsoon and the westerlies

present day impact cratering rate and contemporary gully activity on mars the mars global surveyor mars orbiter camera has acquired data that establish the present day impact cratering rate and document new deposits formed by downslope movement of material in mid latitude gullies on mars twenty impacts created craters 2 to 150 meters in diameter within an area of 21 5 106 square kilometers between may 1999 and march 2006 the values predicted by models that scale the lunar cratering rate to mars are close to the observed rate implying that surfaces devoid of craters are truly young and that as yet unrecognized processes of denudation must be operating the new gully deposits formed since august 1999 are light toned and exhibit attributes expected from emplacement aided by a fluid with the properties of liquid water relatively long extended digitate distal and marginal branches diversion around obstacles and low relief the observations suggest that liquid water flowed on the surface of mars during the past decade

the co2 system in rivers of the australian victorian alps co2 evasion in relation to system metabolism and rock weathering on multi annual time scales abstract the patterns of dissolved inorganic c dic and aqueous co2 in rivers and estuaries sampled during summer and winter in the australian victorian alps were examined together with historical 1978 1990 geochemical data this study provides for the first time a multi annual coverage of the linkage between co2 release via wetland evasion and co2 consumption via combined carbonate and aluminosilicate weathering 13c values imply that carbonate weathering contributes 36 of the dic in the rivers although carbonates comprise less than 5 of the study area baseflow interflow flushing of respired c3 plant detritus accounts for 50 and atmospheric precipitation accounts for 14 of the dic the influence of in river respiration and photosynthesis on the dic concentrations is negligible river waters are supersaturated with co2 and evade 27 7 106 mol km2 a to 70 9 106 mol km2 a co2 to the atmosphere with the highest values in the low runoff rivers this is slightly higher than the global average reflecting higher gas transfer velocities due to high wind speeds evaded co2 is not balanced by co2 consumption via combined carbonate and aluminosilicate weathering which implies that chemical weathering does not significantly neutralize respiration derived h2co3 the results of this study have implications for global assessments of chemical weathering yields in river systems draining passive margin terrains as high respiration derived dic concentrations are not directly connected to high carbonate and aluminosilicate weathering rates

controlling factors on heavy mineral assemblages in chinese loess and red clay abstract heavy mineral analysis is a sensitive technique in constraining provenance of sandstone but has rarely been applied to loess here we report a heavy mineral study of selected samples from the luochuan xifeng and caoxian loess red clay sections on the chinese loess plateau based on the novel qemscan quantitative evaluation of minerals by scanning electron microscopy technique we found that heavy mineral assemblages of loess deposited through the past 500 kyr are similar and unchanged by post depositional chemical dissolution in contrast in samples deposited from 900 ka to 3 ma the relative proportion of stable minerals tends to increase down section in addition the xifeng samples consistently display higher contents of unstable ferromagnesian minerals than the luochuan samples detailed analysis of surface textures displayed by different minerals by optical methods indicates that such a compositional difference can be ascribed to more effective diagenetic dissolution for the luochuan section explained by more extensive percolation of interstitial waters in wetter climatic conditions interestingly heavy mineral assemblages in the underlying upper miocene red clay from xifeng deposition age 7 ma are similar to those of recent loess deposited since 500 ka this similarity indicates that climate and or local preservation conditions hampered dissolution reactions thus helping to preserve an original provenance signal that remained largely unchanged throughout the considered time period our study demonstrates that climatically and time controlled diagenesis plays a key role in determining the composition of heavy mineral assemblages contained in loess deposited several hundreds of thousands years ago we also show that by using both qemscan and traditional optical techniques on the same samples we can obtain fundamental complementary information for a correct interpretation of the heavy mineral assemblage

geochemistry of dissolved inorganic carbon and carbonate weathering in a small typical karstic catchment of southwest china isotopic and chemical constraints abstract the sources of dissolved inorganic carbon dic and rock weathering processes were studied in the houzhai catchment a typical karstic catchment in the changjiang river basin southwest china the carbon isotopic compositions 13 c dic of dic in the samples collected from the catchment vary from 13 5 to 6 9 with a mean value of 9 8 the dic in the catchment is thereby considered to be mainly derived from soil co 2 and weathering of carbonate rocks the dic concentrations and the 13 c dic values show pronounced seasonal variations with the lowest values being observed during the high flow season from may to october the logpco 2 values in the waters were positively correlated with the dic contents and negatively correlated to the saturation index of calcite sic and 13 c dic values these observations indicate that co 2 derived from organic matter oxidation plays an important role in the dissolution of carbonate for this typical karstic environment based on a chemical mass balance the weathering rate of carbonate rocks in the houzhai catchment was estimated to be approximately 133 t km 2 year or 584 10 3 mol km 2 year in terms of co 2 consumption rate which is higher than the reported values for other rivers in southwest china

how and when did the yellow river develop its square bend the current course of the yellow river china involves an unusual 1500 km long angular bend around the ordos tectonic block although sedimentary evidence suggests that the river once followed a more direct path eastward into the bohai sea geologic evidence reveals that the yellow river formed in the eocene as an eastward draining river and developed its square bend around the ordos block in late miocene early pliocene time as a result of folding and uplift that are most probably related to the collision and penetration of india into eurasia as well as rifting around the ordos block the change in course of the yellow river predates flat lying pliocene pleistocene sediment deposits that unconformably overlie folded eocene miocene strata the yellow river provides a typical example of tectonic controls on the size morphology and longevity of rivers

origin of particulate organic carbon in the upper st lawrence isotopic constraints abstract seven sampling locations in the upper st lawrence river near the city of cornwall ontario canada including the main river and six near shore ecosystems a creek embayments and a wetland were studied in order to determine the origin of particulate organic carbon parameters studied included chlorophyll a chl a particulate organic carbon poc and dissolved inorganic carbon dic as well as the isotopic compositions of the latter two 13cpoc 13cdic the results show that in situ photosynthesis and detrital inputs are both significant contributors to the poc pool in the isolated embayments the former dominates during warm seasons with poc concentrations up to 2663 g l and chl a concentrations up to 26 1 g l near shore ecosystems have a wide range of 13cpoc values 31 5 to 16 3 but this variability is not reflected in the main channel there the 13cpoc signal is uniformly close to 27 in accord with estimates from earlier studies on the river s estuary this suggests that the poc contribution from near shore ecosystems is minor although the main channel has low chl a concentrations model calculations suggest that most of its poc originates from photosynthetic activity probably within the great lakes

dissolved inorganic carbon export by mountainous tropical rivers of the western ghats india abstract large rivers that are known for carrying huge fluxes are few in numbers nevertheless the contributions of thousands of small mountainous coastal rivers to global biogeochemical cycles is also measured to be equally important small catchment sizes high channel gradients yet high water discharge are prominent characters of the coastal rivers draining the western ghats wg of india three geo tectonic divisions namely southern granulite terrain sgt in southern western darwar craton wdc in central and deccan traps dt in the north constitute the entire western ghats based on the seasonal sampling of 70 coastal rivers draining into the arabian sea this study provides a comprehensive discharge weighted estimate of dic for the western ghats wg region the concentration of bicarbonate measured in situ using gran plot method fluxes and yields were calculated using seasonal discharge and area of respective rivers the discharge weighted dic concentration of wg region is 629 m which is slightly higher than the average global dic concentration for the low latitude

martian cratering vi crater count isochrons and evidence for recent volcanism from mars global surveyor this paper develops a methodology to establish absolute martian ages by deriving isochrons on a plot of martian impact crater density vs crater diameter calibrated by lunar crater age data the isochrons illustrated here are based on a mars moon cratering ratio of 1 6 at constant size but there is a factor of 2 to 4 uncertainty in this ratio and the consequent model ages martian crater diameter distributions are determined in several areas down to diameter d 16 45 m the shapes of the curves in young areas are found to be close to that of the predicted isochrons and close to the standard production function found by neukum the youngest areas studied here display the lunar like production function down to d 30 m where saturation equilibrium sets in model crater retention ages of several volcanic units are found to be a few hundred million years or less with estimated uncertainties ranging from a factor of 2 lower to a factor of 4 higher the results are consistent with martian meteorite ages volcanism on mars has probably persisted into the last 10 to 15 of the planet s history and is likely ongoing because surfaces as young as a few hundred million years have reached crater saturation equilibrium at d 60 to 100 m mars is likely to have widespread impact produced regoliths at least a few meters deep and this may contribute to the widespread mobile dust and boulder fields of mars

observations of martian gullies and constraints on potential formation mechanisms abstract the discovery of presumably geologically recent gully features on mars malin and edgett 2000 science 288 2330 2335 has spawned a wide variety of proposed theories of their origin including hypotheses of the type of erosive material to test the validity of gully formation mechanisms data from the mars global surveyor spacecraft has been analyzed to uncover trends in the dimensional and physical properties of the gullies and their surrounding terrain we located 106 mars orbiter camera moc images that contain clear evidence of gully landforms distributed in the southern mid and high latitudes and analyzed these images in combination with mars orbiter laser altimeter mola and thermal emission spectrometer tes data to provide quantitative measurements of numerous gully characteristics parameters we measured include apparent source depth and distribution vertical and horizontal dimensions slopes orientations and present day characteristics that affect local ground temperatures we find that the number of gully systems normalized to the number of moc images steadily declines as one moves poleward of 30 s reaches a minimum value between 60 63 s and then again rises poleward of 63 s all gully alcove heads occur within the upper one third of the slope encompassing the gully and the alcove bases occur within the upper two thirds of the slope also the gully alcove heads occur typically within the first 200 meters of the overlying ridge with the exception of gullies equatorward of 40 s where some alcove heads reach a maximum depth of 1000 meters while gullies exhibit complex slope orientation trends gullies are found on all slope orientations at all the latitudes studied assuming thermal conductivities derived from tes measurements as well as modeled surface temperatures we find that 79 of the gully alcove bases lie at depths where subsurface temperatures are greater than 273 k and 21 of the alcove bases lie within the solid water regime most of the gully alcoves lie outside the temperature pressure phase stability of liquid co2 based on a comparison of measured gully features with predictions from the various models of gully formation we find that models involving carbon dioxide melting ground ice in the upper few meters of the soil dry landslide and surface snowmelt are the least likely to describe the formation of the martian gullies although some discrepancies still exist between prediction and observation the shallow and deep aquifer models remain as the most plausible theories interior processes involving subsurface fluid sources are generally favored over exogenic processes such as wind and snowfall for explaining the origin of the martian gullies

δ13c pattern of dissolved inorganic carbon in a small granitic catchment the strengbach case study vosges mountains france abstract the transfers and origins of dissolved inorganic carbon dic were studied for a year in a soil spring stream system in the strengbach catchment vosges mountains france this 80 ha experimental research basin is located on the eastern side of the mountains at an altitude ranging from 883 to 1146 m a s l and is mainly covered by spruce 80 brown acid and podzolic soils developed on a granitic basement and as a result the dic originates solely from co2 generated by oxidation of soil organic matter the 13 c dic in catchment waters is highly variable from about 22 in the springs and piezometers to about 12 in the stream at the outlet of the catchment in the springs pronounced seasonal variations of 13 c dic exist with the dic in isotopic equilibrium with the soil co2 that has estimated 13 c of about 24 in winter and 20 in summer these seasonal variations reflect an isotopic fractionation that seems only induced by molecular diffusion of soil co2 in summer in stream water seasonal variations are small and the relatively heavy dic 12 on average is a result of isotopic equilibration of the aqueous co2 with atmospheric co2