rates of weathering rind formation on costa rican basalt weathering rind thicknesses were measured on 200 basaltic clasts collected from three regionally extensive alluvial fill terraces qt 1 qt 2 and qt 3 preserved along the pacific coast of costa rica mass balance calculations suggest that conversion of unweathered basaltic core minerals plagioclase and augite to authigenic minerals in the porous rind kaolinite allophane gibbsite fe oxyhydroxides is iso volumetric and ti and zr are relatively immobile the hierarchy of cation mobility ca na k mg si al fe p is similar to other tropical weathering profiles and is indicative of differential rates of mineral weathering anorthite albite hypersthene orthoclase apatite alteration profiles across the cm thick rinds document dissolution of plagioclase and augite and the growth of kaolinite with subsequent dissolution of kaolinite and precipitation of gibbsite as weathering rinds age the rate of weathering rind advance is evaluated using a diffusion limited model which predicts a parabolic rate law for weathering rind thickness rr as a function of time t rr t and an interface limited model which predicts a linear rate law for weathering rind thickness as a function of time rr kappt in these rate laws is a diffusion parameter and kapp is an apparent rate constant the rate of advance is best fit by the interface model terrace exposures are confined to the lower reaches of streams draining the pacific slope near the coast where the stream gradient is less than 3 m km and terrace deposition is influenced by eustatic sea level fluctuations geomorphological evidence is consistent with terrace deposition coincident with sea level maxima when the stream gradient would be lowest assigning the most weathered regionally extensive terrace qt 1 mean rind thickness 6 9 0 6cm to oxygen isotope stage ois 7 ca 240 ka and assuming that at time 0 rind thickness 0 it is inferred that terrace qt 2 rr 2 9 0 1 cm is coincident with stage 5e ca 125 ka and that qt 3 rr 0 9 0 1 cm is consistent with ois 3 ca 37 ka these assignments yield a value of kapp of 8 6 10 13 cm s 1 r 2 0 99 only this value satisfies both the existing age controls and yields ages coincident with sea level maxima using this value elemental weathering release fluxes across a weathering rind from qt 2 range from 6 0 10 9 mol si m 2 s 1 to 2 5 10 11 mol km 2 s 1 the rate of rind advance for the costa rican terraces is 2 8 10 7 my r 1 basalt rind formation rates in lower temperature settings described in the literature are also consistent with interface controlled weathering with an apparent activation energy of about 50 kj mol 1 rates of rind formation in costa rica are an order of magnitude slower than reported for global averages of soil formation rates copyright 2004 elsevier ltd

upper ocean and subsurface variability in the bay of bengal during cyclone roanu a synergistic view using in situ and satellite observations in this study the upper ocean and subsurface variability during the different phases of the cyclonic storm roanu along the western bay of bengal bob in may 2016 are investigated by using the moored buoys argos hf radar and satellite datasets in the proximity of the cyclone track the moored buoy observations recorded a decrease of sea surface temperature sst by 1 c all over the track whereas increase in salinity by 1 5 psu was detected along with the highest wind speed of 16 m s 1 pressure drop of 14 hpa and air temperature drop of 4 c the cooling at the cyclone centers from the satellite data indicated higher lower sst drops when translation speed of the cyclone was low high and took more less time to recover to its pre cyclone state in southern northern bob mostly higher sst drop was observed along the right side of the cyclone track interestingly the opposite phenomenon occurred before landfall where sst drop was higher on the left due to upwelling in the head bay as observed both from wave rider buoy wrb at digha and satellite sst the wrb near vizag showed the maximum increase in significant wave heights by 2 4 m during the passage of cyclone argos also captured cyclone induced drop in temperature due to upwelling and entrainment reasonably well in the southwestern bay significant upwelling was observed from the argos with drop in temperature and increase in salinity in the upper layers however a strong stratification was observed from argos in the northwestern bob due to lesser salinity and higher precipitation the currents from in situ as well as hf radar datasets measured the increase in current magnitude during the passage of roanu rotary spectral analysis showed strong inertial currents with frequency 2 1 days at bd11 location with higher amplitudes of the clockwise component during the cyclone period

atmospheric storm triggered and intensified by geodynamics case studies from andaman sea and bay of bengal region in the indian ocean the study analyses the possible connection between the onset of cyclone and volcano tectonic seismicity in the andaman region the historical data of the major volcanic seismic and atmospheric events from the region show that several of the geodynamic activities were followed by severe atmospheric disturbances over the region in this study we consider the case of three recent cyclones phailin hudhud and nilam that either originated or were intensified over the andaman sea and bay of bengal and examine their correlation with the volcano tectonic seismic events during the cyclone occurrence the zenith total delay ztd time series derived from global positioning system data from the pbr2 station on andaman island overlapping with the period of the cyclone occurrence were examined to distinguish the onset and intensification of the atmospheric events the comparison of the sharp changes in ztd associated with the cyclone and the seismic events during the period indicates that the atmospheric changes almost coincide or follow the geodynamic activity our study illustrates that volcano tectonics of the region plays a role in the triggering of atmospheric disturbances

synchronous seafloor spreading and subduction at the paleo convergent margin of semail and arabia the semail ophiolite is the largest and best exposed ophiolite having preserved intact record of a precollision system related to neotethyan ocean closure breaking with the alternative models of ophiolite exhumation and emplacement this paper builds on integrating the joined contribution of tectonic evolution of the continental margin in the premise of the ophiolite obduction connecting the along strike segmentation of the ophiolite recorded in the lithospheric flow structure and recent high precision dating results in a 3 d model of evolution of the ophiolite and its continental margin during jurassic cretaceous time among the relevant characteristics newly accounted 1 the contamination of the ophiolite by fluids and magmas of continental origin 2 the discrimination of different types of metamorphics associated to the ophiolite and conventionally classified metamorphic soles 3 the instability of the arabian margin during the late jurassic cretaceous times 4 the new precise ages relating to overlapping of spreading and detachment and 5 the inferred vergence of neotethyan closure during late mesozoic are stressed the complex stem revealed may relate to processes associated with spreading center subduction at ridge trench transform rtt triple junction as documented along a convergent margin the semail ophiolite emplacement on the arabia continental margin would result from a temporary arabian platform directed subduction zone that consumed the southern tethyan plate during late jurassic cretaceous time

chemical weathering in a tropical watershed luquillo mountains puerto rico ii rate and mechanism of biotite weathering abstract samples of soil saprolite bedrock and porewater from a lower montane wet forest the luquillo experimental forest lef in puerto rico were studied to investigate the rates and mechanisms of biotite weathering the soil profile at the top of a ridge in the rio icacos watershed consists of a 50 100 cm thick layer of unstructured soil above a 600 800 cm thick saprolite developed on quartz diorite the only minerals present in significant concentration within the soil and saprolite are biotite quartz kaolinite and iron oxides biotite is the only primary silicate releasing significant k and mg to porewaters although biotite in samples of the quartz diorite bedrock is extensively chloritized chlorite is almost entirely absent in the saprolite phyllosilicates phyllosilicate grains are present as 200 1000 m wide books below about 50 cm depth x ray diffraction xrd and electron microprobe analyses indicate that the phyllosilicate grains contain a core of biotite surrounded by variable amounts of kaolinite lattice fringe images under transmission electron microscope tem show single layers of biotite altering to two layers of kaolinite suggesting dissolution of biotite and precipitation of kaolinite at discrete boundaries some single 14 a layers are also observed in the biotite under tem the degree of kaolinitization of individual phyllosilicate grains as observed by tem decreases with depth in the saprolite this tem work is the first such microstructural evidence of epitaxial growth of kaolinite onto biotite during alteration in low temperature environments the rate of release of mg in the profile calculated as a flux through the soil normalized per watershed land area is approximately 500 mol hectare 1 yr 1 1 6 10 9 molmg msoil 2 s 1 this rate is similar to the flux estimated from mg discharge out the rio icacos 1000 mol hectare 1 yr 1 or 3 5 10 9 molmg msoil 2 s 1 indicating that scaling up from the soil to the watershed is possible for mg release the rate of mg release from biotite normalized to brunauer emmett teller bet surface area is calculated using a mass balance equation which includes the density and volume of phyllosilicate grains porewater chemistry and flux and soil porosity the mean rates of biotite weathering calculated from k and mg release rates are approximately 6 and 11 10 16 molbiotite mbiotite 2 s 1 respectively significantly slower than laboratory rates 10 12 to 10 11 molbiotite mbiotite 2 s 1 the discrepancy in scaling down from the soil to the laboratory is probably explained by 1 differences in weathering mechanism between the two environments 2 higher solute concentrations in soil porewaters 3 loss of reactive surface area of biotite in the saprolite due to kaolinite and iron oxide coatings and or 4 unaccounted for heterogeneities in flow path through the soil

upper ocean variability in the bay of bengal during the tropical cyclones nargis and laila upper ocean variability at different stages in the evolution of the tropical cyclones nargis and laila is evaluated over the bay of bengal bob during may 2008 and may 2010 respectively nargis initially developed on 24 april 2008 intensified twice on 27 28 april and 1 may and eventually made landfall at myanmar on 2 may 2008 laila developed over the western bob in may 2010 and moved westward towards the east coast of india data from the argo profiling floats the research moored array for african asian australian monsoon analysis and prediction rama and various satellite products are analyzed to evaluate upper ocean variability due to nargis and laila the analysis reveals pre conditioning of the central bob prior to nargis with warm 30 c sea surface temperature sst low 33 psu sea surface salinity sss and shallow 30 m mixed layer depths during march april 2008 enhanced ocean response to the right of the storm track due to nargis includes a large sst drop by 1 76 c sss increase up to 0 74 psu mixed layer deepening of 32 m shoaling of the 26 c isotherm by 36 m and high net heat loss at the sea surface during nargis strong inertial currents up to 0 9 ms 1 were generated to the right of storm track as measured at a rama buoy located at 15 n 90 e producing strong turbulent mixing that lead to the deepening of mixed layer this mixing facilitated entrainment of cold waters from as deep as 75 m and together with net heat loss at sea surface and cyclone induced subsurface upwelling contributed to the observed sst cooling in the wake of the storm a similar upper ocean response occurs during laila though it was a significantly weaker storm than nargis

constraints on the magmatic evolution of the oceanic crust from plagiogranite intrusions in the oman ophiolite we present major and trace element as well as sr nd and hf isotope data on a suite of 87 plutonic rock samples from 27 felsic crustal intrusions in seven blocks of the oman ophiolite the rock compositions of the sample suite including associated more mafic rocks range from 48 to 79 wt sio2 i e from gabbros to tonalites the samples are grouped into a ti rich and relatively light rare earth element lree enriched p1 group ce yb n 0 7 resembling the early v1 lavas and a ti poor and lree depleted p2 group ce yb n 0 7 resembling the late stage v2 lavas based on the geochemical differences and in agreement with previous structural and petrographic models we define phase 1 p1 and phase 2 p2 plutonic rocks felsic magmas in both groups formed by extensive fractional crystallization of olivine clinopyroxene plagioclase apatite and ti magnetite from mafic melts the incompatible element compositions of p1 rocks overlap with those from mid ocean ridges but have higher ba nb and th nb trending towards the p2 rock compositions and indicating an influence of a subducting slab the p2 rocks formed from a more depleted mantle source but show a more pronounced slab signature these rocks also occur in the southern blocks with the exception of the tayin block of the oman ophiolite implying that the entire ophiolite formed above a subducting slab initial nd and hf isotope compositions suggest an indian morb type mantle source for the oman ophiolite magmas isotope compositions and high th nb in some p2 rocks indicate mixing of a melt from subducted sediment into this mantle

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

formation and emplacement ages of the masirah ophiolite sultanate of oman hornblende separates from gabbros and biotite separates from crosscutting potassic granites of the masirah ophiolite have been analyzed by conventional k ar techniques the gabbros have late jurassic early cretaceous ages 126 158 ma and the granites have broadly similar ages 124 146 ma because the gabbros are likely to give ophiolite formation ages and the granites ophiolite emplacement ages it can be concluded that the masirah ophiolite was emplaced very soon after formation the late jurassic early cretaceous ages contrast with the middle cretaceous ages 90 95 ma of the semail ophiolite confirming earlier suggestions that the masirah ophiolite cannot simply be a right laterally displaced fragment of the semail ophiolite but is instead an uplifted block of indian ocean crust the formation and emplacement of the masirah ophiolite are discussed in the context of the late mesozoic evolution of the western indian ocean

structural evolution of the northern end of the oman ophiolite and enclosed granulites abstract a combined structural field mapping microstructural and petrographic study has been undertaken to better understand the origin and evolution of the northernmost part of the oman ophiolite khawr fakkan massif in the framework of an oceanic spreading centre emplacement of a sheet of granulite facies metamorphic rocks into the peridotites occurred at temperatures at which the peridotites deformed ductily the metamorphic rocks define the southern extension of a block boundary which separates an eastern peridotite part displaying high temperature fabrics from a western one with porphyroclastic to mylonitic fabrics granitoid intrusions representing partial melts from the metamorphic rocks occur only in the ophiolitic part overlying the metamorphic rocks thus delineating the same boundary between the two mantle blocks this high temperature boundary is not visible on satellite or aerial photographs the granulite facies foliations and lineations in the metamorphic rocks can be correlated with porphyroclastic textures developed at decreasing temperatures in the associated peridotites and to the obduction of the ophiolite the final emplacement of the metamorphic rocks in their present position was accompanied by retrograde hydration decompression and continuous deformation at temperatures ranging from 800 to 300 c the hydration is extended along the wadi ham fault two models are proposed for the emplacement of the metamorphic rocks in the first model the protolith of the metamorphic rocks was deposited in a pull apart basin along a transform fault and then subducted along the transform fault after reversal from transtension to transpression in this model the ophiolite obduction occurred later along another thrust plane in the second model the protolith material descends along an intraoceanic subduction zone and is emplaced into the ophiolite hanging wall along a secondary thrust caused by transpressive or rotational movements during the ophiolite obduction in this case the ophiolite obduction occurred along the same intraoceanic subduction plane

reversed experiments on biotite quartz feldspar melting in the system kmash implications for crustal anatexis melting temperatures of biotite quartz and biotite quartz feldspar assemblages in the system k 2 o mgo al 2 o 3 sio 2 h 2 o have been determined in the pressure range 0 5 18 kbar the subsolidus dehydration of biotite quartz also has been investigated from 300 to 500 bars the melting equilibria studied are phlogopite quartz sanidine vapor liquid o phlogopite quartz vapor enstatite liquid k phlogopite quartz enstatite liquid k v and phlogopite quartz sanidine enstatite liquid v at 10 kbar the o reaction occurs at 700 720 c the k reaction at 780 790 c the k v reaction at 815 850 c and the v reaction at 800 850 c vapor saturated reactions were reversed isobarically in two stage experiments in which the starting assemblage was held at a temperature 10 above the temperature of previously observed melting for a duration equivalent to an initial melting experiment followed by lowering of the temperature below the temperature of initial mel

true k feldspar granites in oceanic crust masirah ophiolite sultanate of oman a upb and smnd isotope study abstract this paper presents u pb and sm nd isotope data of various rock types from the masirah ophiolite sultanate of oman the study aimed at delineating the source and genesis of k feldspar granites which are emplaced in the oceanic crust theses granites clearly intruded the sequence prior to its obduction and show initial pb and nd isotopic compositions which exclude significant continental crust contribution during their generation both geochronological and geochemical data are in conflict with the assumption of a continuous differentiation process for granite generation i e the granites are not the final differentiation chain products of oceanic crust generation their emplacement into previously thinned oceanic crust and their possible genetic relationship with partly explosive alkaline volcanism suggest that the masirah granites were generated by partial melting at depth as a consequence of transtensional movements associated with transform faults these faults may have favored deep hydration of the crust which initiated melting probably enhanced by heat transfer from a nearby hotspot

peraluminous potassium rich granitoids in the semail ophiolite potassic granites are found as dikes and small stocks in the uppermost part of the mantle sequence of the semail ophiolite predominantly in the northern and less frequently in the central and southern part new chemical analyses show that the biotite granites lie on the same evolutionary trend as the quartz diorites and tonalites occurring as late intrusives in the gabboro and mantle sequence based on mineral chemistry the p t conditions of andalusite cordierite bearing pegmatoidal granites were calculated giving pressures of 1 8 2 2 kbar and a solidus within the stability field of andalusite hydrothermal experiments on five natural granite and tonalite compositions gave minimum melting between 650 and 675 c at 2 kbar at 700 c excess h2o there is already 70 80 melt from the granitic starting compositions potassic granites in the ophiolite can be the result of extreme fractional crystallization in the late intrusive series granitic melts can also be produced by a two stage process in which fluids escaping from the underlying metamorphic sole trigger partial melting of the more felsic members in the ophiolite series two mica granites and pegmatites in the underlying metamorphic sole possibly melting products of amphibolites and biotite gneisses are contemporaneous these escaping fluids could also explain the pb and sr isotopic compositions of the leucocratic dikes indicating variable crustal contamination

birth and demise of the bangong nujiang tethyan ocean a review from the gerze area of central tibet abstract reconstructing the evolution of the bangong nujiang tethyan ocean bnto plays an indispensable role in understanding the linkage between gondwana dispersion and tibetan plateau accretion the existence of the bnto is inferred from presence of dismembered ophiolite bodies along the bangong nujiang suture zone which separates lhasa from qiangtang in this paper we present a detailed synthesis of ophiolite metamorphism magmatism lithostratigraphy and tectonism from the western segment gerze area of the lhasa qiangtang collision zone in order to reconstruct the wilson cycle of the bnto our results suggest that the bnto initially opened in the late permian 260 ma as indicated by the earliest record of oceanic crust regionally strong evidence supports a northward subduction of the bnto beneath qiangtang likely initiating in the early jurassic 195 ma as suggested by detrital zircon age spectra from mesozoic arc sourced strata northward oceanic subduction generated three episodes of arc magmatism i e 186 170 ma 169 146 ma and 129 100 ma along the southern qiangtang margin in which the early jurassic magmatism is only sporadically preserved in modern outcrops amdo area meanwhile the recognition of an incomplete arc trench system on the northern lhasa margin supports a southward subduction beneath lhasa as well our new provenance data from lower cretaceous strata on the northern lhasa margin together with available multi disciplinary constraints suggest that final closure of the bnto did not occur until the latest jurassic early cretaceous 150 130 ma therefore the wilson cycle of the bnto is hereby reconstructed providing significant insights into the amalgamation of the tibetan plateau

k ar ages of the metamorphic sole of the semail ophiolite implications for ophiolite cooling history k ar ages have been determined on micas and hornblendes in the basal metamorphic sequence and in metamorphic rocks squeezed into the mantle sequence of the semail ophiolite the hornblende ages of 99 0 5 and 102 0 8 ma and the 90 ma ages of coexisting micas from the high grade metamorphic portion of the sequence are interpreted as cooling stages following the peak of metamorphism t 800 850 c p 6 5 9 kbar the new pressure estimates are based on findings of kyanite in garnet amphibolite and cordierite in quartzitic rocks these data indicate a cooling rate of 10 30 c ma the oldest mica ages of 95 1 ma are observed in the lowest grade greenschists these also largely represent cooling ages but might in part also include formation ages the pattern of the muscovite ages across the metamorphic sole indicates that the cooling front moved from the low grade metamorphic zone through the high grade rocks and into the base of the overlying ophiolite radiometric ages of hornblendes 92 3 0 5 and 94 8 0 6 ma indicate that the crustal gabbro sequence cooled below 500 c later than the base of the ophiolite sequence metamorphism of the sole rocks occurred during subduction of oceanic sediments and volcanic or gabbroic rocks as they progressively came into contact with hotter zones at the base of the overriding plate the peak of metamorphism must have been contemporaneous with the main magmatism in the semail ophiolite one of the dated muscovites yields an age of 81 3 0 8 ma but this is related to discrete deformation zones that were active during late stage emplacement of the ophiolite

constraints on melting and magma production in the crust major intrusions of granitic rocks are found in several tectonic settings and in all cases crustal melts may contribute to the volumes of granitic magma high grade metamorphism and partial melting of the crust take place predominantly under fluid absent conditions we present a model for calculating the amounts of melt that may be formed by fluid absent breakdown of micas and amphiboles in common crustal rock types pelitic quartzofeldspathic intermediate and mafic melt proportions depend mainly on the kind of source rock the pressure at which melting takes place the temperature and the hydrous mineral h2o content of the source as a consequence of the pressure dependence of water solubility in silicate melts any given source rock will produce more melt by a given fluid absent reaction at lower pressure at a given pressure higher temperature reactions can produce more melt from a given source rock based on a survey of the compositions of common rock types we show that the amounts of melt can vary from 50vol thus crustal rocks vary widely in their fertility as magma sources depending on the types and amounts of hydrous phases they contain in general muscovite breakdown in pelites will yield only small quantities of melt and lead to migmatite formation biotite breakdown in pelites occurs at higher temperature and because most high grade pelites below granulite grade are biotite rich can yield up to about 50 vol of granitoid melt rocks of intermediate composition and hornblende rich mafic rocks are potentially highly fertile magma sources also provided that the high temperatures necessary for biotite and hornblende breakdown are realized pyroxene rich mafic rocks and quartzofeldspathic rocks are much less potentially fertile data suggest that mechanisms exist for the efficient segregation of melt and restite in systems with 30and probably 20vol melt the pressure temperature history of a region can greatly influence crustal source fertility through its control over the occurrence of subsolidus dehydration and melting equilibria

the origin of oceanic plagiogranites from the karmoy ophiolite western norway both field relationships and geochemical characteristics indicate two suites of plagiogranitic and related rocks coexisting in the higher parts of the karmoy ophiolite of western norway the plutonic zone of this ophiolite can be subdivided into three complexes the east karmoy igneous complex the visnes high level complex and the veavagen igneous complex and plagiogranitic rocks are well developed in the first two of these within the east karmoy igneous complex plagiogranites are associated with high temperature pre basic dyke shear zones rare earth element modelling indicates that these plagiogranites were derived by anatexis of amphibolite hydrated diabase assuming a starting material consisting of 40 hornblende and 60 plagioclase and that batch melting occurred within the stability field of hornblende in comparison plagiogranite occurs in a number of bodies in the upper part of the visnes high level complex and forms a sandwich horizon together with biotite diorites and epidosites between a roof assemblage of dykes microgabbros and magnetite gabbros and a floor assemblage of layered and non layered gabbros the r e e modelling of the petrogenesis of this series of plagiogranites indicates that they were derived by filter pressing of a differentiated interstitial liquid to the vari textured gabbros although the distribution of highly hygromagmatophile elements such as k rb ba etc cannot be explained satisfactorily by this model alone depletion in these elements appears to be an autometasomatic effect

rapid emplacement of the oman ophiolite thermal and geochronologic constraints in understanding of ophiolite emplacement requires knowledge of the elapsed time between igneous crystallization and intraoceanic thrusting and the rate and duration of that thrusting hornblende 4oar 39ar ages demonstrate that the igneous oceanic crust in oman crystallized and cooled to 825 k in 1 2 m y hornblende ages from metamorphic rocks and from cross cutting dikes require that the basal metamorphic thrust fault beneath the ophiolite also cooled below 825 k in 1 2 m y motion along the sole thrust accounted for 200 km of displacement at a rate of 100 200 mm yr on the basis of age relationships and thermal considerations we favor a two stage model for the initial stages of samall ophiolite emplacement intraoceanic thrusting over 2 m y old lithosphere at 150 km m y parallel to a spreading ridge for 1 2 m y followed by equally rapid and brief thrusting over cold and old lithosphere preservation of the samail ophiolite is a direct result of its young age and positive buoyancy at the time of ocean closure and we propose that all ophiolites that originated near spreading centers and were emplaced onto continents were young at the time of intraoceanic thrusting

a quantitative comparison of soil development in four climatic regimes abstract a new quantitative soil development index based on field data has been applied to chronosequences formed under different climatic regimes the four soil chronosequences developed primarily on sandy deposits have some numeric age control and are located in xeric inland merced calif xeric coastal ventura calif aridic las cruces n mex and udic susquehanna valley pa soil moisture regimes to quantify field properties points are assigned for developmental increases in soil properties in comparison to the parent material currently ten soil field properties are quantified and normalized for each horizon in a given chronosequence including two new properties for carbonate rich soils in addition to the eight properties previously defined when individual properties or the combined indexes are plotted as a function of numeric age rates of soil development can be compared in different climates the results demonstrate that 1 the soil development index can be applied to very different soil types 2 many field properties develop systematically in different climatic regimes 3 certain properties appear to have similar rates of development in different climates and 4 the profile index that combines different field properties increases significantly with age and appears to develop at similar rates in different climates the soil development index can serve as a preliminary guide to soil age where other age control is lacking and can be used to correlate deposits of different geographical and climatic regions

the interaction of supertyphoon maemi 2003 with a warm ocean eddy understanding the interaction of ocean eddies with tropical cyclones is critical for improving the understanding and prediction of the tropical cyclone intensity change here an investigation is presented of the interaction between supertyphoon maemi the most intense tropical cyclone in 2003 and a warm ocean eddy in the western north pacific in september 2003 maemi passed directly over a prominent 700 km 500 km warm ocean eddy when passing over the 22 n eddy rich zone in the northwest pacific ocean analyses of satellite altimetry and the best track data from the joint typhoon warning center show that during the 36 h of the maemi eddy encounter maemi s intensity in 1 min sustained wind shot up from 41 ms 1 to its peak of 77 m s 1 maemi subsequently devastated the southern korean peninsula based on results from the coupled hurricane intensity prediction system and satellite microwave sea surface temperature observations it is suggested that the warm eddies act as an effective insulator between typhoons and the deeper ocean cold water the typhoon s self induced sea surface temperature cooling is suppressed owing to the presence of the thicker upper ocean mixed layer in the warm eddy which prevents the deeper cold water from being entrained into the upper ocean mixed layer as simulated using the coupled hurricane intensity prediction system the incorporation of the eddy information yields an evident improvement on maemi s intensity evolution with its peak intensity increased by one category and maintained at category 5 strength for a longer period 36 h of time without the presence of the warm ocean eddy the intensification is less rapid this study can serve as a starting point in the largely speculative and unexplored field of typhoon warm ocean eddy interaction in the western north pacific given the abundance of ocean eddies and intense typhoons in the western north pacific these results highlight the importance of a systematic and in depth investigation of the interaction between typhoons and western north pacific eddies

submesoscale processes at shallow salinity fronts in the bay of bengal observations during the winter monsoon abstractlateral submesoscale processes and their influence on vertical stratification at shallow salinity fronts in the central bay of bengal during the winter monsoon are explored using high resol

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

from a black to a gray box a mass balance interpretation of pedogenesis we utilize chemical elements as tracers in a mass balance analysis that provides functional relationships among soil chemical composition bulk density and volume change in relation to parent material these analytical functions are based on the principle of conservation of mass and include a term quantifying mass flux into out of the soil and between horizons we apply the technique to the oldest member of a chronosequence developed on marine terraces in northern california it is an alfisol that evolved from beach sand to its present state nearly one third of its weight is composed of secondary clay minerals in about 240 ky aside from large increases in organic carbon desilication is the dominant factor in soil evolution 29 50 83 g cm 2 si was leached from the beach sand during pedogenesis the rate of desilication is roughly 2 1 t km 2 yr 1 0 21 g cm 2 ky 1 an order of magnitude slower than that implied by the si denudation rate calculated for the mattole river watershed weathering of primary minerals and synthesis of secondary minerals is relatively well advanced suggesting that the rate of desilication may be declining the local beach is composed of quartz and sodic plagioclase with smaller amounts of chlorite mica and kaolinite the soil has substantially different mineralogy sand is dominated by quartz and clay is dominated by kaolinite halloysite chloritic intergrades and gibbsite bases are also leached though the total mass was much less 57 2 55 g cm 2 of na in the beach sand was lost as plagioclase weathered by focusing on elemental and mineralogical gains and losses we emphasize the essential connection between the pedologic environment and the external hydrochemical environment

air sea coupling during the tropical cyclones in the indian ocean a case study using satellite observations in the years 1999 and 2001 three intense tropical cyclones formed over the northern indian ocean two over the bay of bengal during 15 19 and 25 29 october 1999 and one over the arabian sea during 21 28 may 2001 we examined the thermal salinity and circulation responses at the sea surface due to these severe cyclones in order to understand the air sea coupling using data from satellite measurements and model simulations it is found that the sea surface temperature sst cooled by about 0 5 0 8 c in the bay of bengal and 2 c in the arabian sea in the bay of bengal this cooling took place beneath the cyclone center whereas in the arabian sea the cooling occurred behind the cyclone only a few days later this contrasting oceanic response resulted mainly from the salinity stratification in the bay of bengal and thermal stratification in the arabian sea and the associated mixing processes in particular the cyclones moved over the region of low salinity and smaller mixed layer depth with a distinct mixed layer deepening to the left side of the cyclone track it is envisaged that daily satellite estimates of sst and sea surface salinity sss using outgoing longwave radiation olr and model simulated mixed layer depth would be useful for the study of tropical cyclones and prediction of their path over the northern indian ocean

evidence for melting mud in earth s mantle from extreme oxygen isotope signatures in zircon evidence for melting mud in earth s mantle from extreme oxygen isotope signatures in zircon

tracking the oman ophiolite to the surface new fission track and u th he data from the aswad and khor fakkan blocks united arab emirates abstract the oman ophiolite in the united arab emirates uae was formed in a supra subduction zone environment at about 95 ma and was almost immediately obducted onto the eastern margin of arabia the timing of obduction is well constrained but the post obduction tectonic uplift and exhumation history of the ophiolite and associated rocks are less well understood we present twenty one new fission track and u th he analyses of apatite and zircon from the hajar mountains the data show that the oman ophiolite had a complex exhumation history to present exposure levels in the khor fakkan and aswad blocks resulting from at least three distinct exhumation events 1 initial ophiolite obduction between ca 93 and 83 ma is characterised by tectonic exhumation and rapid cooling as revealed by zircon u th he and apatite fission track data but it is not associated with major erosional exhumation 2 data from the lower part of the ophiolite and the metamorphic sole document a second exhumation event at ca 45 35 ma interpreted to represent an early phase of the zagros orogeny that led to reactivation of pre existing structures and the differential exhumation of the khor fakkan block along the wadi ham shear zone this event led to significant erosional exhumation and deposition of a thick sedimentary succession in the ras al khaimah foreland basin and 3 neogene exhumation is recorded by ca 20 15 ma apatite u th he data and a single apatite fission track date from the lowermost part of the metamorphic sole this event can be linked to the main phase of the zagros orogeny which is manifested in large fans with ophiolite derived debris barzaman formation conglomerates during this period the metamorphic sole of the masafi window stayed at temperatures in excess of ca 120 c corresponding to ca 4 km of overburden only later to be eroded to present day levels

role of mesoscale eddies on the variability of biogenic flux in the northern and central bay of bengal 1 mesoscale cyclonic eddies cold core are though known to enhance the phytoplankton biomass in the bay of bengal their contribution to the carbon export to the deep ocean are yet to be quantified using biogenic flux data obtained from the sediment traps located at 17 27 n 89 13 e northern bay of bengal trap nbbt and 13 07 n 84 24 e central bay of bengal trap cbbt we explored the variability of biogenic flux in response to cyclonic eddies temporal variation of the biogenic flux at nbbt 1994 1998 and cbbt 1993 1996 showed four distinct peaks with no well defined seasonal pattern the inverse relationship between the high flux events and sea surface height anomaly ssha along with the dominant periodicity of 10 15 weeks from the chi square analysis of ssha confirmed the role of eddies in the observed higher biogenic fluxes during the eddy events enhanced opal flux suggested eddy driven new production while lower carbonate to opal ratio along with high organic carbon indicated large export via diatoms finally we show that 42 of the total organic carbon collected at mid depth 1000 m in the bay of bengal is contributed by eddy driven processes via diatom bloom making it a regional sink for co2