erosional and climatic effects on long term chemical weathering rates in granitic landscapes spanning diverse climate regimes abstract we used cosmogenic nuclide and geochemical mass balance methods to measure long term rates of chemical weathering and total denudation in granitic landscapes in diverse climatic regimes our 42 study sites encompass widely varying climatic and erosional regimes with mean annual temperatures ranging from 2 to 25 c average precipitation ranging from 22 to 420 cm year 1 and denudation rates ranging from 23 to 755 t km 2 year 1 long term chemical weathering rates range from 0 to 173 t km 2 year 1 in several cases exceeding the highest granitic weathering rates on record from previous work chemical weathering rates are highest at the sites with rapid denudation rates consistent with strong coupling between rates of chemical weathering and mineral supply from breakdown of rock a simple empirical relationship based on temperature precipitation and long term denudation rates explains 89 95 of the variation in long term weathering rates across our network of sites our analysis shows that for a given precipitation and temperature chemical weathering rates increase proportionally with fresh material supply rates we refer to this as supply limited weathering in which fresh material is chemically depleted to roughly the same degree regardless of its rate of supply from breakdown of rock the temperature sensitivity of chemical weathering rates is two to four times smaller than what one would expect from laboratory measurements of activation energies for feldspar weathering and previous inter comparisons of catchment mass balance data from the field our results suggest that climate change feedbacks between temperature and silicate weathering rates may be weaker than previously thought at least in actively eroding unglaciated terrain similar to our study sites to the extent that chemical weathering rates are supply limited in mountainous landscapes factors that regulate rates of mineral supply from erosion such as tectonic uplift may lead to significant fluctuations in global climate over the long term

chemical weathering indices applied to weathering profiles developed on heterogeneous felsic metamorphic parent rocks abstract chemical weathering indices are commonly used for characterizing weathering profiles by incorporating bulk major element oxide chemistry into a single metric for each sample generally on homogeneous parent rocks weathering indices change systematically with depth however the weathering of heterogeneous metamorphic rocks confounds the relationship between weathering index and depth in this paper we evaluate previously defined chemical weathering indices for their suitability in characterizing weathering profiles developed on felsic heterogeneous metasedimentary bedrock from coweeta hydrologic laboratory north carolina usa among the weathering indices evaluated here the weathering index of parker wip is the most appropriate for application to weathering profiles on heterogeneous and homogeneous parent rock because the wip includes only the highly mobile alkali and alkaline earth elements in its formulation it yields values that differ greatly from those of the parent rock in addition the wip allows for aluminum mobility unlike other weathering indices these characteristics combine to make the weathering index of parker the most applicable index for studying the weathering of heterogeneous metasedimentary rocks however the wip should be applied judiciously as alkali and alkaline earth metals may be readily depleted during weathering in addition to reflecting weathering the chemical index of alteration cia chemical index of weathering ciw plagioclase index of alteration pia and vogt s residual index v may be sensitive to subtle geochemical changes such as hydrothermal alteration along a fault and or alteration at the water table weathering indices that include iron in their calculations were not included in this study because they do not distinguish between ferric and ferrous iron the oxidation state and distribution of iron in a weathering profile is influenced by the proportion of oxidation states in the pre weathered metamorphic rock and interaction with groundwater during weathering

mountain drag along the gotthard section during alpex abstract an estimate of the time variation of the pressure drag component across the inner portion of the st gotthard section of the alps is derived for the special observational period march april 1982 of the alpex project surface pressure data obtained from a purpose designed mesoscale array of microbarograph stations are used and the results indicate that this drag component amounted to a value per unit area that varied on the order of 5 pa with a mean 0 78 pa it is shown that the phase variations of the time trace of the drag are directly related to synoptic scale flow developments however the magnitude of the drag is substantially influenced by mesoscale effects further an indication is given of the contribution to the drag of the effects of diurnal variation vertically propagating buoyancy waves and low level flow blocking deflection the order of magnitude of these drag values notwithstanding the potential errors in the estimates indicates that the alps exert a substantial influenc

the frequency and distribution of recent landslides in three montane tropical regions of puerto rico landslides are common in steep mountainous areas of puerto rico where mean annual rainfall and the frequency of intense storms are high each year landslides cause extensive damage to property and occasionally result in loss of life average population density is high 422 people km2 and is increasing this increase in population density is accompanied by growing stress on the natural environment and physical infrastructure as a result human populations are more vulnerable to landslide hazards the blanco cibuco and coamo study areas range in surface area from 276 to 350 km2 and represent the climatologic geographic and geologic conditions that typify puerto rico maps of recent landslides developed from 1 20 000 scale aerial photographs in combination with a computerized geographic information system were used to evaluate the frequency and distribution of shallow landslides in these areas several types of landslides were documented rainfall triggered debris flows shallow soil slips and slumps were most abundant hillslopes in the study area that have been anthropogenically modified exceed 12 in gradient are greater than 300 m in elevation and face the east northeast are most prone to landsliding a set of simplified matrices representing geographic conditions in the three study areas was developed and provides a basis for the estimation of the spatial controls on the frequency of landslides in puerto rico this approach is an example of an analysis of the frequency of landslides that is computationally simple and therefore may be easily transferable to other settings

lithological correction of chemical weathering proxies based on k rb and mg contents for isolation of orbital signals in clastic sedimentary archives abstract the extraction of palaeoenvironmental palaeoclimatic signals from the chemical composition of siliciclastic sediments is valuable for the reconstruction of past environments particularly in continental basins here we test novel weathering proxies which are less sensitive to lithological control than the previously used raw element ratios k al k ti and k rb 1 local enrichment factors of k al mg al and k rb i e the element ratios corrected for grain size and matrix composition using local background functions al si fe and ca as explanatory variables and ordinary regression and 2 robust regression residuals of those element ratios based on isometric log ratio coordinates of the most relevant lithogenic elements ca fe rb si zr in the chemical composition chemical weathering proxies can be obtained from departures of chemical composition of sedimentary profiles from relationships with other chemical elements in particular those with grain size control the resulting weathering proxies were examined for the miocene deposits from the most basin the czech republic which recorded one of the major warm episodes of the cenozoic time the miocene climatic optimum the performance of weathering proxies has been checked by 1 comparison of individual proposed proxies in one drill core hk930 2 detailed analysis of orbital signals in the relevant compositional functions in hk930 and 3 lateral correlation of three cores hk930 du7 and do565 of the same basin the novel proxies show lateral stability and orbital signatures of short eccentricity obliquity and precession confirming their usefulness in palaeoenvironmental studies corrections for grain size and carbonate contents should help to isolate climatic content from the weathering proxies although in the studied sediments it weakened the precession component in the orbital signal as grain size proxies and other compositional data also carried orbital signals we propose to consider these proxy ideas in palaeoclimatic reconstructions based on chemical weathering proxies

grain size control of river suspended sediment geochemistry clues from amazon river depth profiles residual solid products of erosion display a wide range of size density shape mineralogy and chemical composition and are hydrodynamically sorted in large river channels during their transport we characterize the chemical and isotopic variability of river sediments of the amazon basin collected at different water depths as a function of grain size absolute chemical concentrations and sr and nd isotopic ratios greatly varies along channel depth the al si ratio tightly linked to grain size distribution systematically decreases with depth mostly reflecting dilution by quartz minerals a double normalization diagram is proposed to correct from dilution effects elements define fan shaped patterns and can be classified in three different groups with respect to hydrodynamic sorting during transport in the amazon 1 poorly sorted insoluble elements like al fe th and rees 2 well sorted insoluble elements like zr and ti mainly carried by heavy minerals and 3 alkali na to cs and alkali earth elements mg to ba for which a large variety of patterns is observed related for alkali to their variable affinity for phyllosilicates sr isotopes show that the amazon river at the mouth is stratified the madeira and solimoes derived sediments being preferentially transported near the channel surface and at depth respectively the comparison between the solimoes and madeira rivers shows how the interplay between grain sorting weathering and crustal composition controls the composition of the suspended river sediments

the applicability of the chemical index of alteration as a paleoclimatic indicator an example from the permian of the parana basin brazil abstract the chemical index of alteration cia was expressed as cia molar to become a more sensitive measure of the degree of chemical weathering the cia molar has the value of 1 for fresh feldspars and for unweathered non peraluminous igneous rocks but increases towards infinity as chemical weathering progresses the utility of this index as a humidity indicator for both modern and ancient muds was tested a database comprising 281 entries with chemical data for modern and ancient sediments deposited under arid semi arid semi humid and humid climate was assembled from the literature and used to calibrate the relationship between humidity and cia molar values for both modern and ancient sediments the histograms display a shift towards higher values with increasing geological indicators of humidity whereas sediments deposited under conditions inferred to be arid from other geological indicators show values tightly clustered around 1 the permian of the parana basin was then used as an example of the applicability of the cia molar for paleoclimatic studies major element analyses al2o3 k2o na2o cao were performed on 55 claystones and shales from three drill cores in a stratigraphic succession spanning the early to late permian the cia molar for these rocks accorded with expectations based on sedimentologic and paleontologic evidence discriminating well between arid and humid conditions in the basin independently determined from sedimentological and paleontological indicators the use of the cia molar as a paleo humidity indicator however can be limited by the presence of carbonate rich sediments the occurrence of post depositional k addition metasomatism metamorphism diagenetic illitization as well as by inheritance of clays from sedimentary rocks in the source area nevertheless with appropriate caution the cia molar is a useful tool for the assessment of the humidity conditions in the rock record

influences of tropical monsoon climatology on the delivery and dispersal of organic carbon over the upper gulf of thailand abstract organic carbon cycling in se asia is data sparse and poorly studied although high sediment yield and organic carbon intensity occur in the tropical region in the present study we evaluated the role of tropical monsoon pertaining to fluvial discharge sediment load coastal current and water stratification on seasonal organic carbon dynamics during four sampling campaigns in the upper gulf of thailand ugot this study demonstrates that particulate organic carbon poc is closely correlated with the river influx of suspended sediment which is generally regulated by the local rainfall higher poc is found near the large estuarine section chao phraya river chao during southwest monsoon period and the small estuarine section mae klong river mk during november 2013 when tropical cyclones impacted poc in the estuarine sections is more significantly influenced by the seasonal shift compared with the coastal sections land derived organic matter prevails in the small estuarine and coastal sections while marine derived organic matter dominates in the estuarine sections impacted by chao and mk anthropogenic inputs and dam regulation also influences the river export of organic matter during the high precipitation periods total organic carbon toc however displays less significant seasonal monsoon variations than poc further toc tends to accumulate in the sub silt fraction of sediments which mainly occurs in the small estuarine and eastern coastal sections and is more obviously influenced by marine derived factors toc in sediment of the chao and mk influenced sections however displays more seasonal variations with prevailing river input evidenced by coarser sediment and higher c n ratios moreover the almost year round water stratification across the region acts as the barrier in retaining organic carbon in the estuaries and their vicinities from dispersal into the lower portion of gulf of thailand high sedimentation rate 1 1 cm yr 1 further facilitates the organic carbon burial in the study area the delivery dispersal and burial of organic carbon are closely associated with the climate controlled precipitation and thus the tropical monsoon climatology under the global warming in particular is an important factor influencing the organic carbon in the ugot

areal melt and discharge modelling of storglaciaren sweden a grid based glacier melt and discharge model was applied to storglaciaren a small valley glacier 3 km 2 in northern sweden for the melt seasons of 1993 and 1994 the energy available for melt was estimated from a surface energy balance model using meteorological data collected by automatic weather stations on the glacier net radiation and the turbulent heat fluxes were calculated hourly for every grid point of a 30 m resolution digital terrain model using the measurements of temperature humidity wind speed and radiative fluxes on the glacier two different bulk approaches were used to calculate the turbulent fluxes and compared with respect to their impact on discharge simulations discharge of storglaciaren was simulated from calculated meltwater production and precipitation by three parallel linear reservoirs corresponding to the different storage properties of firn snow and ice the performance of the model was validated by comparing simulated discharge to measured discharge at the glacier snout depending on which parameterization of the turbulent fluxes was used the timing and magnitude of simulated discharge was in good agreement with observed discharge or simulated discharge was considerably underestimated in one year

redox stratification of an ancient lake in gale crater mars introduction the primary goal of nasa s curiosity rover mission is to explore and quantitatively assess a local region on mars surface as a potential habitat for past or present life a necessary component of that assessment involves an investigation of the surface chemical conditions and paleoclimate of ancient mars gale crater was selected as the landing site for curiosity it hosts a 5 km tall mountain of layered sedimentary rock the rocks of mount sharp preserve a long duration record of martian environmental conditions geological reconstructions from curiosity rover data have revealed an ancient habitable lake environment that was sustained for tens of thousands to tens of millions of years by rivers draining into the crater rationale we seek to constrain the chemical environment within the lake in gale crater as well as short and long term climate variations in and around gale crater we focus on fine grained sedimentary rocks that carry information about sediment provenance the environment of deposition the conversion of sediment to rock during burial i e lithification and the chemical conditions of later modification i e diagenesis these were investigated during the first 1300 martian solar days sols of rover operations in gale crater using bulk geochemical and mineralogical analysis techniques combined with high resolution color imagery at a variety of scales results two mudstone units have been recognized both deposited in lakes the sheepbed member of the yellowknife bay formation an older set of strata defining the base of the stratigraphic section and the murray formation of relatively younger age and positioned higher in the stratigraphic section the chemical index of alteration cia paleoclimate proxy increases by up to 10 to 20 cia units expressed in from the sheepbed member to the murray formation on the basis of mineralogy geochemistry textural properties and stratigraphic relationships the murray formation can be subdivided into two sedimentary associations or facies the hematite phyllosilicate hp facies and the magnetite silica ms facies the hp facies is characterized by abundant fe 3 oxides accompanied by phyllosilicates as well as indications of mn oxidation and trace metal concentration these properties are consistent with deposition in an oxidizing environment the ms facies is recognized by a near complete absence of pure fe 3 minerals and high concentrations of silica accompanied by magnetite consistent with deposition in an anoxic environment both facies were affected by a saline overprint after burial and lithification conclusion the observed variations in cia are consistent with modest short term fluctuations in the ancient climate between cold dry conditions and relatively warmer wetter conditions these changes occurred during the deposition of lake bed mudstones in an environment that was conducive to the presence of a long lived lake in gale crater we propose that the distinct properties of the two murray facies were developed as a result of i fractionation of river borne detritus into coarser denser materials in shallow water close to shore and finer lower density materials offshore in deeper water as a result of deceleration of river flow as it entered the lake and ii redox stratification of the lake water body caused by depth dependent variations in the concentration of atmospheric oxidants and dissolved groundwater derived solutes resulting in oxidizing conditions in shallow water and anoxia in deeper water the addition of saline minerals during a later phase of brine migration through the section records longer term changes in martian climate at gale crater perhaps driven by global atmospheric escape processes the recognition of redox stratification in the lake in gale crater adds new detail to our understanding of ancient martian aquatic environments previously reported detections of organic carbon compounds nitrogen phosphate minerals and fe and s minerals in a variety of redox states combined with the evidence presented here for relatively stable climate conditions and gradients in fluid oxidation state provide compelling evidence that all of the physical chemical and energetic conditions necessary to establish a habitable environment were present on mars between 3 8 billion and 3 1 billion years ago

late quaternary sediment fluxes from tropical watersheds abstract inherited saprolite stores and continued weathering in quaternary time juxtapose abundant clay and fresh rock in tropical landscapes this influences sediment fluxes and affects the interpretation of sediment sequences derived from tropical watersheds detrital kaolinites derive from inherited saprolite sources as well as from soil clays and appear in delta and ocean sediments these sediments appear to correspond with sub milankovitch millennial scale cycles of climate change but may also record century scale episodes of rapid warming dansgaard oeschger events destabilisation of sediment sources and increased sediment fluxes in the late quaternary followed millennia of climatic deterioration cooling aridity and vegetation change and led to altered patterns of sedimentation during the last glacial maximum lgm sediment yield from slopes increased 10 around the lgm when rainfall was reduced by 30 60 and led to fan building and braided channels rainfall increased 40 80 from the lgm to the early holocene maximum and this led to channel cutting and major sediment fluxes to delta and ocean sinks vegetation recovery lagged the rapid warming by several millennia and was interrupted by younger dryas yd aridity influencing slope and stream behaviour holocene sedimentation has been by both vertical and lateral accretion increasing floodplain sediment stores

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

surface roughness and bulk heat transfer on a glacier comparison with eddy correlation more than 100 simultaneously measured profiles of wind speed and temperature were analyzed to determine the aerodynamic and thermal roughness lengths of glacier ice the results proved to be extremely sensitive to measurement height which is difficult to define precisely on the hummocky terrain of a glacier therefore aerodynamic roughness lengths were estimated from the microtopography of the surface yielding 2 46 mm for ice and 5 5 mm for snow despite the indeterminate nature of the profile analysis it did support the view that the thermal roughness length must decrease as the roughness reynolds number increases a relationship which has been modelled in the literature good agreement between bulk transfer estimates and eddy correlation measurements of fhe sensible heat flux density on melting ice and snow was obtained by combining the aerodynamic roughness length with a suitable model for thermal roughness length

reconnaissance study of glacier energy balance in north greenland 1993 94 reconnaissance energy balance studies were made for the first time at two sites in north greenland to compare with conditions in west greenland the field expe e planned to save weight because it is expensive operate in north greenland the larger energy components incoming radiation and ablation were measured for 55 days altogether and the smaller components were evaluated by indirect methods c g turbulent fluxes are calculated from air temperature humidity and w ind speed to save the weight of inst ruments the energy balance model is tuned by choosing surface roughness and albedo to reduce the mean error between measured ablation and modelled daily melting the error standard deviation for ablation is only 5 kg m 2 d 1 which is much lower than found in west greenland due to better instruments and modelling in the presen study net radiation is the main energy source for melting in north greenland but ablation is is relatively low because sublimation and conductive heat fluxes use energy that would otherwise be available for melting there is a strong diurnal variation in ablation mainly forced by variations in shortwave radiation and reinforced by nocturnal cooling of the ice surface by outgoing longwave radiation and sublimation the model frequently predicts a frozen glacier surface at night even when air temperatures are positive

weathering and global denudation a negative correlation between sediment yield and weathering history as measured by the chemical alteration cia of the suspended sediment is observed for many of the world s major rivers and other regions of denudation the weathering history is a first order control on the sediment yield of such areas termed equilibrium denudation regions for other areas data scatter with either apparent increases or decreases of sediment yield for given cia values these areas are termed nonequilibrium denudation regions low sediment yields can be attributed to moderated erosion either natural or human induced and or the incorporation of unweathered glacial debris accelerated erosion resulting in high sediment yield is primarily human induced and results from cultivation and other land use each of these effects has a profound influence on global sediment discharge from the continents pre human suspended sediment discharge from the continents is estimated to be 12 6 times 10 15 g yr or about 0 6 the

a simple energy balance model to calculate ice ablation at the margin of the greenland ice sheet apres avoir etabli les relations donnees climatiques taux d enlevement de la glace dans 2 glaciers du groenland un modele simple de bilan energetique est effectue pour calculer le taux d enlevement de la glace aux bordures du glacier

sub surface melting in a seasonal snow cover the ability of solar radiation to penetrate into a snow cover combined with the low thermal conductivity of snow can lead to a sub surface temperature maximum this elevated sub surface temperature allows a layer of wet snow to form below the surface even on days when the air temperature remains subfreezing a high resolution frequency modulated continuous wave fmcw radar has been used to detect the onset of sub surface melting in a seasonal snow cover the experimental observation of sub surface melting is shown to be in good agreement with the predictions of a one dimensional mass and energy balance model the effects of varying snow characteristics and solar extinction parameters on the sub surface melt characteristics are investigated using model simulations

on the role of subsurface heat conduction in glacier energy balance modelling we discuss the inclusion of the subsurface heat conduction flux into the calculation of the energy balance and ablation at the glacier atmosphere interface data from automatic weather stations are used to force an energy balance model at several locations on alpine glaciers and at one site in the dry andes of central chile the heat conduction flux is computed using a two layer scheme assuming that 36 of the net shortwave radiation is absorbed by the surface layer and that the rest penetrates into the snowpack we compare simulations conducted with and without subsurface heat flux results show that assuming a surface temperature of zero degrees leads to a larger overestimation of melt at the sites in the accumulation area 10 4 13 3 than in the ablation area 0 5 2 8 due to lower air temperatures and the presence of snow the difference between simulations with and without heat conduction is also high at the beginning and end of the ablation season up to 29 for the first 15 days of the season when air temperatures are lower and snow covers the glacier surface while they are of little importance during periods of sustained melt at all the locations investigated

chemical weathering of monsoonal eastern china implications from major elements of topsoil major element compositions of 36 bulk samples and 41 clay samples which were obtained from 47 topsoils collected in monsoonal eastern china were investigated with conventional wet chemistry and x ray fluorescence xrf spectrometry respectively based on major element analyses the mobility of major elements and latitudinal distributions of sio2 al2o3 ratio chemical index of alteration cia chemical index of weathering ciw and weathering index of parker wip were analyzed meanwhile the suitability of these chemical weathering indices to topsoils in monsoonal eastern china and its controls were discussed these investigations indicate that na k ca mg and si are relatively depleted while mn p fe and ti are relatively enriched in topsoils of the study area by comparison with their contents in the upper continent crust ucc and that alkali metal na k and alkaline earth metal ca mg elements are generally easier to be depleted from their parent materials than other major elements during chemical weathering the latitudinal distributions of cia ciw and wip show that they are suitable to both bulk and clay samples but sio2 al2o3 is only suitable to clay samples not suitable in bulk ones all these investigations indicate a significant dependence of grain size in major element abundance and latitudinal distributions of sio2 al2o3 cia ciw and wip but parent rock type has little effect on them except its impact on the latitudinal distribution of wip in clay samples the significant grain size dependence probably indicates the presence of unaltered minerals in bulk samples thus we suggest that clay samples are more suitable to investigating chemical weathering of sediments on continents than bulk samples the trivial effect of parent rock type probably indicates a relatively uniform chemical weathering on various parent rocks correlation analyses indicate that climate is the dominant control of chemical weathering of topsoils in the study area and the significant latitude effect indicated by the spatial distributions of chemical weathering indices actually reflect the climate control on chemical weathering of topsoils chemical weathering indices actually reflect the integrated weathering history in the study area besides the dominant control of climate other factors like tectonics parent rock biology landform and soil depth and age might also have some effect on the chemical weathering of topsoils in the study area which needs further research c 2013 elsevier ltd all rights reserved

paleopedologic and paleohydrologic records of precipitation seasonality from early pennsylvanian underclay paleosols u s a underclays in the crooked fork group lower pennsylvanian atokan langsettian in eastern tennessee u s a are paleosols associated with fourth order depositional sequences that record changing paleohydrologic conditions during their formation climate changes possibly milankovitch driven resulted in evolution of soil landscapes from well drained seasonally wet floodplains and delta plains dominated by vertic vertisol like paleosols to very poorly drained everwet swamps dominated by sideritic gley paleosols coals paleohistosols cap most underclays and record peat swamp development during everwet conditions followed by marine submergence pedogenic slickensides and angular blocky ped structures in conjunction with illuviated clay pore fillings and sepic plasmic microfabric indicate an initial better drained phase of paleosol development stage i gley overprinting characterized by drab low chroma paleosol colors fe reduction in upper portions of paleosols sideritic rhizocretions sphaerosiderite and pyrite nodules extensive leaching and translocation of alkali and alkaline earth elements and kaolinitization of smectites and hydroxy interlayer vermiculite hiv indicate a later poorly drained stage of paleosol development characterized by saturated conditions moderate to low eh and low ph stage ii as well as peat swamp development lastly burial and juxtaposition of marine facies on top of terrestrial deposits terminated paleosol and peat development stage iii paleosols likely formed under conditions of marked seasonality of rainfall judging from both modern analog systems in sumatra and pennsylvanian paleoclimate models the chemical index of alteration without potash cia k was used as a proxy for atokan paleoprecipitation estimated as 1300 mm yr this estimate is comparable with mean annual precipitation map in modern tropical to subtropical rainy environments

a distributed surface energy balance model for a small valley glacier i development and testing for haut glacier d arolla valais switzerland this paper describes the development and testing of a distributed surface energy balance model used to calculate rates of surface melting at haut glacier d arolla valais switzerland the model uses a digital elevation model dem of the glacier surface and surrounding topography together with meteorological data collected at a site in front of the glacier to determine hourly or daily totals of the energy balance components and hence of melting over the entire surface of the glacier with a spatial resolutio of 20 m the model can also be used to determine temporal and spatial variations in snow depth snow line position and glacier surface albedo calculations from the model are compared with observations made along the glacier centre line in 1990 and in general the model performs very well the correlation coefficients between calculated and measured snow line elevation albedo and ablation are 0 99 0 85 and 0 81 respectively the main source of error between modelled and measured values of these variables is probably inadequacies in the parameterization of albedo used in the model

climatic cycles during a neoproterozoic snowball glacial epoch the profound glaciations of the neoproterozoic cryogenian period ca 850 544 ma represent an extreme climatic mode when it is claimed earth was fully or almost completely covered with ice for millions of years we show that the geochemistry and mineralogy of fine grained neoproterozoic sedimentary rocks in oman are best explained by climatic oscillations that drove variations in the intensity of chemical weathering on contemporary land surfaces the cold climate modes of the cryogenian were therefore cyclical punctuated with well defined warm humid interglacial periods the hydrological cycle and the routing of sediment were active throughout the glacial epoch which requires substantial open ocean water this reconstruction represents a significantly different target for numerical climate models at this critical time in the evolution of earth s biosphere

effects of a tectonically triggered wave of incision on riverine exports and soil mineralogy in the luquillo mountains of puerto rico we document the long term response of a tropical mountain stream to tectonics and show how this response exerts a first order spatial control on the delivery of weatherable minerals to forest soils in its catchment these minerals in turn affect nutrient availability and biogeochemical cycles the luquillo mountains is a rainforest covered isolated massif on puerto rico island instead of displaying typical concave up long profiles of most mountain streams the rivers draining the southern flank of these mountains display a systematic downstream increase in gradient using concentrations of in situ produced cosmogenic 10be in quartz from river sediments we find that the downstream steepening is due to the propagation of an erosion wave along the rivers from the coastal plain upstream toward the headwaters decreased 10be concentration along the steepened reaches knickpoint faces or knickzones results from faster denudation of the valley sides around the steepened reaches the upper portions of the steepened reaches knickpoint lips cluster in elevation around the altitude of a flat lying dissected surface traceable around the luquillo mountains inspection of similar platforms over other parts of puerto rico and in the surrounding seas suggests that the dissected surface is an uplifted shore platform formed in the early pliocene 4 my ago upstream of the knickpoints rivers possess alluvial reaches still graded to this uplifted platform they represent relict profiles of the rivers that once drained an island that was surrounded by the now uplifted platform we conclude that the knickpoints initiated when the platform started to rise above the caribbean sea the knickpoints then started propagating upstream defining the front of a slow moving wave of erosion 10be derived catchment scale denudation rates measured above and below the knickpoints indicate a 30 210 increase in denudation associated to the passage of the knickpoints mineralogical analysis of the soils show that soils upstream of the knickpoints overlie deeply depleted saprolite and only contain recalcitrant minerals whereas soils downstream of the knickpoints experience an input of fresh weatherable minerals this influx considerably increases nutrient availability porder et al 2015 in a forest where atmospheric inputs are otherwise the main source of nutrients mcdowell et al 1990 zarin and johnson 1995 pett ridge 2009

chemical weathering in a tropical watershed luquillo mountains puerto rico i long term versus short term weathering fluxes abstract the pristine rio icacos watershed in the luquillo mountains in eastern puerto rico has the fastest documented weathering rate of silicate rocks on the earth s surface a regolith propagation rate of 58 m ma 1 calculated from iso volumetric saprolite formation from quartz diorite is comparable to the estimated denudation rate 25 50 ma 1 but is an order of magnitude faster than the global average weathering rate 6 ma 1 weathering occurs in two distinct environments plagioclase and hornblende react at the saprock interface and biotite and quartz weather in the overlying thick saprolitic regolith these environments produce distinctly different water chemistries with k mg and si increasing linearly with depth in saprolite porewaters and with stream waters dominated by ca na and si such differences are atypical of less intense weathering in temperate watersheds porewater chemistry in the shallow regolith is controlled by closed system recycling of inorganic nutrients such as k long term elemental fluxes through the regolith e g si 1 7 10 8 moles m 2 s 1 are calculated from mass losses based on changes in porosity and chemistry between the regolith and bedrock and from the age of the regolith surface 200 ma mass losses attributed to solute fluxes are determined using a step wise infiltration model which calculates mineral inputs to the shallow and deep saprolite porewaters and to stream water pressure heads decrease with depth in the shallow regolith 2 03 m h2o m 1 indicating that both increasing capillary tension and graviometric potential control porewater infiltration interpolation of experimental hydraulic conductivities produces an infiltration rate of 1 m yr 1 at average field moisture saturation which is comparable with libr tracer tests and with base discharge from the watershed short term weathering fluxes calculated from solute chemistries and infiltration rates e g si 1 4 10 8 moles m 2 s 1 are compared to watershed flux rates e g si 2 7 10 8 moles m 2 s 1 consistency between three independently determined sets of weathering fluxes imply that possible changes in precipitation temperature and vegetation over the last several hundred thousand years have not significantly impacted weathering rates in the luquillo mountains of puerto rico this has important ramifications for tropical environments and global climate change

earth s oldest reported glaciation physical and chemical evidence from the archean mozaan group 2 9 ga of south africa the pongola supergroup is a thick succession of archean 2 9 ga supracrustal rocks in the eastern part of the kaapvaal craton of southern africa its upper part the mozaan group 5000 m thick includes diamictites with a highly varied suite of clasts some of which are striated and faceted clasts in associated stratified siltstones are interpreted as ice rafted debris a glacial origin is also supported by geochemical investigation of diamictite matrix materials and associated mudstones plots of sio2 al2o3 and tio2 al2o3 suggest that these rocks underwent little chemical weathering an interpretation confirmed by calculation of a chemical index of alteration with low values typical of other glacial deposits the analyzed rocks are rich in fe average fe2o3 t is 24 wt like rocks of many other glaciomarine successions the diamictites and associated mudstones of the mozaan group have low th sc ratios suggesting preferential incorporation of mafic materials into the diamictite matrix material

statistical empirical index of chemical weathering in igneous rocks a new tool for evaluating the degree of weathering abstract chemical weathering indices are useful tools in characterizing weathering profiles and determining the extent of weathering however the predictive performance of the conventional indices is critically dependent on the composition of the unweathered parent rock to overcome this limitation the present paper introduces an alternative statistical empirical index of chemical weathering that is extracted by the principal component analysis pca of a large dataset derived from unweathered igneous rocks and their weathering profiles the pca analysis yields two principal components pc1 and pc2 which capture 39 23 and 35 17 of total variability respectively the extent of weathering is reflected by variation along pc1 primarily due to the loss of na 2 o and cao during weathering in contrast pc2 is the direction along which the projections of unweathered felsic intermediate and mafic igneous rocks appear to be best discriminated therefore pc1 and pc2 represent independent latent variables that correspond to the extent of weathering and the chemistry of the unweathered parent rock subsequently pc1 and pc2 were then mapped onto a ternary diagram mfw diagram the m and f vertices characterize mafic and felsic rock source respectively while the w vertex identifies the degree of weathering of these sources independent of the chemistry of the unweathered parent rock the w index has a number of significant properties that are not found in conventional weathering indices first the w index is sensitive to chemical changes that occur during weathering because it is based on eight major oxides whereas most conventional indices are defined by between two and four oxides second the w index provides robust results even for highly weathered sesquioxide rich samples third the w index is applicable to a wide range of felsic intermediate and mafic igneous rock types finally the mfw diagram is expected to facilitate provenance analysis of sedimentary rocks by identifying their weathering trends and thereby enabling a backward estimate of the composition of the unweathered source rock

global changes during carboniferous permian glaciation of gondwana linking polar and equatorial climate evolution by geochemical proxies the most prevalent phanerozoic glaciation occurred during the carboniferous permian on the southern hemisphere gondwana supercontinent sediments from the pennsylvanian dwyka group deposited in the karoo basin of south africa provide a complete record of glaciation and deglaciation phases the direct correlation of glaciation events in southern gondwana basins with the well studied climate evolution of equatorial regions was previously hampered by lack of precise radiometric dating as dating has now become available for the karoo basin the gondwana glaciation can be viewed in a global paleoclimatic framework with high temporal resolution element geochemical proxies cia chemical index of alteration zr ti rb k v cr record three confined shifts in climate and paleoenvironment of the karoo basin these shifts were induced by changes in sea level weathering rate provenance and redox conditions because of the low availability and diagenetic overprint of carbonates ocean and atmosphere pco 2 variations had to be reconstructed from 1 3 c o r g values of marine organic matter the 1 3 c o r g signatures are affected by variable proportions of marine versus terrestrially derived organic matter and its state of preservation organic geochemical investigations toc total organic carbon c n lipid biomarkers indicate the organic matter in the central karoo basin was primarily of algal origin in agreement with element proxies the varying 1 3 c o r g values mirror shifts in pco 2 rather than variations of organic matter type a covariation trend between carbon isotope signatures of equatorial carbonates and 1 3 c o r g values from the karoo basin argues against local forcing factors and instead implies a global climate control mechanism the 5 7 m y duration of a complete glacial cycle is not in tune with any known orbital frequency processes such as changes in equator pole temperature gradients or newly developing atmosphere ocean circulation pathways can be regarded as controlling factors

investigation of in situ weathering of quartz diorite bedrock in the rio icacos basin luquillo experimental forest puerto rico abstract the rio icacos basin in puerto rico is the site of the highest measured chemical solute fluxes for a catchment on granodiorite this is partly attributable to high annual rainfall 4300 mm high average temperature 23 c and moderate relief the bulk of these fluxes is contributed by dissolution of plagioclase and amphiboles in zones of partially weathered rock 0 5 1 5 m thick underlying saprolite these zones are characterized by systems of onion skin rindlets each 3 10 cm thick in which porosity development is dominated by weathering of plagioclase to kaolinite fe bearing aluminosilicate minerals hornblende augite and biotite persist in the weathered rock after plagioclase has weathered to completion but hornblende and augite disappear between the porous rindlet systems and saprolite a new watershed scale solute mass balance corroborates earlier studies and yields an overall reaction stoichiometry that closely resembles complete weathering of the rock except quartz and biotite to kaolinite and fe3 oxides our findings indicate that steady state assumptions are reasonable and useful in studying weathering at this site estimated steady state sediment yields based on net solute fluxes and average bedrock composition of 3 24 10 9 to 3 60 10 9 kg m 2 s 1 are smaller than measured values indicating that sediment generation is currently accelerated with respect to steady state however sediment generation has recently been closer to steady state since weathering within the rindlet systems occurs on multiple fronts moving upward and downward two new steady state conceptual models are developed to account for 1 multiple parallel weathering fronts and 2 differential rates of advance of weathering fronts due to porosity development based on these models in situ weathering rates for plagioclase at two sample locations of 2 7 10 15 and 5 0 10 15 mol na g 1 s 1 are calculated values comparable to bet surface area normalized rates of 2 7 10 16 to 5 0 10 15 mol na m 2 s 1