instability waves in the equatorial atlantic ocean abstract evidence is presented for the generation of planetary waves by barotropic instability within the cyclonic shear region of the atlantic ocean s south equatorial current sec immediately following the springtime intensification of the southeast trade wind which accelerates the sec westward a packet of waves with central periodicity of around 25 days is observed lasting for about three cycles independent wavenumber analyses on 1983 and 1984 data give newly identical zonal wavelengths and phase speed estimates of around 1100 km and 50 cm s 1 the waves are anisotropic and spatially inhomogeneous with generation confined primarily to the mixed layer an energetics analysis using 1983 data centered upon the equator at 28 w shows a rapid increase in total perturbation energy tpe reaching values of 2000 erg cm 3 within two weeks the subsequent decrease in tpe at this location is due primarily to meridional pressure work divergence baroclinic instability is negligible because both the meridional

the northeast southwest oscillating equatorial mode of the tropical instability wave and its impact on equatorial mixing the tropical instability waves tiws in the eastern pacific consist of waves with central periods of about 33 and 17days while the former manifest as vortices north of the equator and are known to modulate diapycnal mixing at their southern edge the latter remain largely unexplored here the structure of the 17 day tiws and the mechanism through which they may influence equatorial mixing are investigated based on long term in situ measurements and reanalysis data different from the well recognized meridional velocity oscillation the 17 day tiws are found to induce northeast southwest ne sw velocity oscillations they are confined within but asymmetric about the equator differing from free yanai waves which they were commonly assumed to resemble the vertical shear associated with the westward anomalous velocity superimposes on the shear of the mean flow resulting in the strongest shear in the upper thermocline that is expected to facilitate diapycnal mixing therein plain language summary observed from satellites the tropical instability wave tiw in the eastern tropical pacific ocean is a 1 000 km long gigantic combination of waves and vortexes it emerges between the energetic zonally interleaving equatorial currents impacts the atmosphere and transfers enormous energy to the western pacific ocean and to the deep ocean as wellone of the research foci for both physical oceanographers and meteorologists however the structures of its huge body and the associated complicated smaller scale processes remain unrevealed primarily because the measurements that have been conducted usually by research vessels are too limited to derive a full picture here based on long term observations at a hotspot of tiw and 4 d numerical model outputs we identify the structure of tiw at the equator which manifests as a pair of slanted clockwise and anticlockwise vortexes and induces strong east west oscillations we also find the most efficient mechanism for the tiw to strengthen vertical velocity shear shear instability and ocean turbulent mixing the findings therefore are important for understanding the tiw dynamics tiws signatures in atmosphere ocean interactions and their impact on vertical heat transport from warmer sea surface to colder subsurface layers of the ocean

equatorial subthermocline currents across the pacific recent sections crossing the equator at nine longitudes from 146 e to 86 w show zonal currents below 400 m similar to those found in a 16 month mean section on 159 w from the pacific equatorial ocean dynamics pequod program in 1982 1983 most of the new measurements were made with a lowered acoustic doppler current profiler eastward current extrema north and south intermediate countercurrents are found in all sections about 2 from the equator in the depth range 500 1500 m with the possible exceptions of 146 e where topography complicates the picture south of the equator and 150 e where the sections extend only from 1 s to 2 n poleward of the intermediate countercurrents westward flow is found near 3 from the equator in most of the sections on the equator from 250 500 m depth a westward equatorial intermediate current is found in many but not all of the sections similarly it is present in the pequod mean but not in all synoptic sections below the intermediate currents and countercurrents an eastward current near 3000 m was found at and south of the equator in the pequod mean and in the new sections from 150 e to 110 w near 4000 m there is westward flow south of the equator in the pequod mean and near the equator in the new sections from 179 e to 135 w geostrophic currents calculated from an 8 year mean hydrographic section at 165 e also resemble the pequod mean although not conclusive the evidence presented here indicates that these currents are basin scale components of the general circulation perhaps involving vigorous horizontal recirculation in a set of basin wide elongated gyres within a few degrees of the equator

potential vorticity dynamics of tropical instability vortices abstracttropical instability vortices tivs in the equatorial pacific exhibit energetic horizontal and vertical circulation characterized by regions of high rossby number and low richardson number their strong anticyclonic vorticity and vertical shear can influence the broader scale circulation by driving lateral mixing and vertical exchange between the ocean surface and interior the authors use a set of nested high resolution simulations of the equatorial pacific with a finest grid size of 3 km to examine the vortex dynamics associated with tiv core water formation tiv cores are characterized by low values of the ertel potential vorticity pv as the relative vorticity is anticyclonic with magnitude comparable to the local coriolis parameter a study of the variation of pv and other scalars along lagrangian fluid parcel tracks entering the tivs shows that the low pv water in their cores is a mix of equatorial undercurrent euc water and north equatorial counter current necc water the euc water

tropical instability wave energetics observations from the tropical instability wave experiment ocean velocity data from an array of subsurface moorings deployed from may 1990 to june 1991 during the tropical instability wave experiment are used to study the energetics of planetary waves in the vicinity of the equator at 1408w such waves observed from august to december 1990 were initiated by barotropic instability arising primarily from the cyclonic shear region of the south equatorial current and equatorial undercurrent just north of the equator subsequently local barotropic production continued to maintain and modulate these tropical instability waves through a combination of cyclonic shear and meridional velocity component divergence just north of the equator the end of the wave season coincided with the propagation past the array of a large intraseasonal kelvin wave

an analysis of tropical instability waves in a numerical model of the pacific ocean 2 generation and energetics of the waves this work was supported by the department of com merce noaa under grant na56gp0026 one of the au thors sm was partially supported by a nasa global change fellowship ngt 30288 another author ab was supported by a ucar postdoctoral fellowship

late cretaceous cenomanian maastrichtian calcareous nannofossils from goban spur dsdp sites 549 551 implications for the palaeoceanography of the proto north atlantic abstract the early late cretaceous cenomanian early turonian is thought to have been one of the warmest periods of the phanerozoic this period was characterised by tropical sea surface temperatures of up to 36 c and a pole to equator gradient of less than 10 c the subsequent turonian maastrichtian was characterised by a continuous climatic cooling peaking in the maastrichtian this climatic cooling and the resulting palaeoceanographic changes had an impact on planktic primary producer communities including calcareous nannofossils in order to gain a better understanding of these cenomanian maastrichtian palaeoceanographic changes calcareous nannofossils have been studied from the proto north atlantic goban spur dsdp sites 549 551 in order to see potential differences between open oceanic and shelf dwelling nannofossils the data from goban spur have been compared to findings from the european shelf northern germany a total of 77 samples from goban spur were studied for calcareous nannofossils revealing abundant mean 6 2 billion specimens g sediment and highly diverse mean 63 species sample nannofossil assemblages the dominant taxa are watznaueria spp mean 30 7 prediscosphaera spp mean 18 3 zeugrhabdotus spp mean 8 3 retecapsa spp mean 7 2 and biscutum spp mean 6 6 the cenomanian assemblages of both goban spur open ocean and wunstorf shelf are characterised by elevated abundances of high fertility taxa like biscutum spp zeugrhabdotus spp and tranolithus orionatus early turonian to maastrichtian calcareous nannofossil assemblages of goban spur are however quite different to those described from european sections oceanic taxa like watznaueria spp retecapsa spp and cribrosphearella ehrenbergii dominate in goban spur whereas the fertility indicators biscutum spp and t orionatus are more abundant in the european shelf assemblages this shift from a homogeneous distribution of calcareous nannofossils in the cenomanian towards a heterogeneous one in the turonian maastrichtian implies a change of the ocean circulation the eddy ocean system of the cenomanian was replaced by an oceanic circulation similar to the modern one in the turonian maastrichtian caused by the cooling the increased pole to equator gradients resulted in an oceanic circulation similar to the modern one

weathering of the new albany shale kentucky usa i weathering zones defined by mineralogy and major element composition abstract comprehensive understanding of chemical and mineralogical changes induced by weathering is valuable information when considering the supply of nutrients and toxic elements from rocks here minerals that release and fix major elements during progressive weathering of a bed of devonian new albany shale in eastern kentucky are documented samples were collected from unweathered core parent shale and across an outcrop excavated into a hillside 40 year prior to sampling quantitative x ray diffraction mineralogical data record progressive shale alteration across the outcrop mineral compositional changes reflect subtle alteration processes such as incongruent dissolution and cation exchange altered primary minerals include k feldspars plagioclase calcite pyrite and chlorite secondary minerals include jarosite gypsum goethite amorphous fe iii oxides and fe ii al sulfate salt efflorescence the mineralogy in weathered shale defines four weathered intervals on the outcrop zones a c and soil alteration of the weakly weathered shale zone a is attributed to the 40 a exposure of the shale in this zone pyrite oxidization produces acid that dissolves calcite and attacks chlorite forming gypsum jarosite and minor efflorescent salt the pre excavation active weathering front zone b is where complete pyrite oxidation and alteration of feldspar and organic matter result in increased permeability acidic weathering solutions seep through the permeable shale and evaporate on the surface forming abundant efflorescent salt jarosite and minor goethite intensely weathered shale zone c is depleted in feldspars chlorite gypsum jarosite and efflorescent salts but has retained much of its primary quartz illite and illite smectite goethite and amorphous fe iii oxides increase due to hydrolysis of jarosite enhanced permeability in this zone is due to a 14 loss of the original mass in parent shale denudation rates suggest that characteristics of zone c were acquired over 1 ma compositional differences between soil and zone c are largely attributed to illuvial processes formation of additional fe iii oxides and incorporation of modern organic matter

fe cycling in the shale hills critical zone observatory pennsylvania an analysis of biogeochemical weathering and fe isotope fractionation abstract during weathering fe in primary minerals is solubilized by ligands and or reduced by bacteria and released into soil porewaters such fe is then removed or reprecipitated in soils to understand these processes we analyzed fe chemistry and isotopic composition in regolith of the shale hills watershed a critical zone observatory in central pennsylvania overlying iron rich shale of the rose hill formation elemental concentrations were measured in soil from a well drained catena on a planar hillslope on the south side of the catchment based upon x ray diffraction and bulk elemental data loss of fe commences as clay begins to weather 15 cm below the depth of auger refusal more fe iii was present than fe ii in all soil samples from the ridge top to the valley floor both total and ferrous iron are depleted from the land surface of catena soils relative to the bedrock loss of ferrous fe is attributed mostly to abiotic or biotic oxidation loss of fe is most likely due to transport of micron sized particles that are not sampled by porous cup lysimeters but which are sampled in stream and ground waters the isotopic compositions 56 fe relative to irmm 014 of bulk fe and 0 5 n hcl extracted fe operationally designed to remove amorphous fe oxyhydr oxides range between 0 3 and 0 3 with 56 fe bulk extractable values between 0 2 and 0 4 throughout the soils along the catena 56 fe signatures of both bulk fe and hcl extracted fe become isotopically lighter as the extent of weathering proceeds the isotopic trends are attributed to one of two proposed mechanisms one mechanism involves fe fractionation during mobilization of fe from the parent material due to either fe reduction or ligand promoted dissolution the other mechanism involves fractionation during immobilization of fe oxyhydr oxides if the latter mechanism is true then shale which comprises one quarter of continental rocks could be an important source of isotopically heavy fe for rivers

the impact of eastern pacific versus central pacific el ninos on the north equatorial countercurrent in the pacific ocean 1 using a three dimensional ocean reanalysis data product the influence of two types of the el ninos on the north equatorial countercurrent necc across the pacific basin is examined in this study eastern pacific el ninos ep el ninos exert a significant impact on the interannual changes of the necc whereas central pacific el ninos cp el ninos have little influence from the developing to mature phase of the ep el ninos that occursfrequently in the latter half of a calendar year the necc tends to intensify and shift southward while the ep el nino related position changes of the necc is out of phase with its seasonal position changes the ep el nino related intensity variability of the necc is in phase with its seasonal modulation during both types of el ninos the el nino modulated wind stress curl forcing changes the upper ocean thickness modifying the necc intensity and central position the weaker and shorter fluctuations of wind stress curl forcing during the cp el nino events induce irregular and insignificant changes of the necc

the three dimensional structure of an upper ocean vortex in the tropical pacific ocean in the equatorial pacific ocean easterly trade winds and the earth s rotation combine to drive surface currents away from the equator thereby causing cold nutrient rich subsurface water to upwell the front1 that forms between this upwelled water and warmer waters north of the equator is sometimes visible as a spectacular line in the sea 2 between 2 and 6 n westward propagating cusp shaped disturbances observed along this front3 have been attributed to the effect of dynamical instabilities in the system of zonal equatorial currents4 11but the connection between these phenomena remains unclear here we report extensive measurements from shipboard sensors satellite and drifting buoys which reveal the three dimensional structure of an anticyclonic eddy or vortex 500 km in diameter and centred at 4 n we suggest that cusp shaped disturbances of the front are caused by trains of large amplitude vortices which are driven by instability of the mean zonal shear we show that these vortices not only play an important role in the meridional transport of heat salt and momentum but are also associated with regions of intense horizontal convergence along the front where dramatic concentrations of marine life are observed

tropical instability wave variability in the pacific and its relation to large scale currents abstract shipboard acoustic doppler current profiler adcp derived zonal currents from 170 to 110 w are assembled into composite seasonal and enso cycles to produce detailed representations of large scale ocean flow regimes that favor tropical instability waves tiws the instability favorable portion of these cycles namely the august october period of the seasonal cycle and the pre december period of the enso cold phase both have intense westward flow in the south equatorial current most particularly the branch north of the equator secn and strengthened eastward flows in the north equatorial countercurrent necc and the equatorial undercurrent euc taken together these flows enhance current shear in the two regions generally associated with tiw activity namely the cyclonic and anticyclonic shear regions located to the south and north of the secn respectively direct correlation of adcp currents and ctd densities to an instability index derived from equatorial 13 30 day meridional velocit

the role of meridional flow asymmetry in the dynamics of tropical instability the role of asymmetry of zonally and temporally invariant equatorial zonal flow on the structure and dynamics of tropical instability is investigated in a continuously stratified plane model while more strongly developed flow in the northern hemisphere leads to a northern hemisphere enhancement of the instability consistent with observational data asymmetry is not found to dramatically change the internal dynamics of tropical instability we find that both sides of the northern branch of the south equatorial current are potentially unstable with the relative level of meridional shear on the two sides of the flow playing a role in determining the location of the dominant source region consideration of the structure of the energy conversions however demonstrates the strong dynamical importance of the surface of zero meridional isopycnal potential vorticity gradient in setting the phase speed and controlling the structure of the instability this control can be clearly understood through the dynamical framework provided by the wave geometry construct

upper equatorial pacific ocean current and salinity variability during the 1996 1998 el nino la nina cycle the recent el nino la nina cycle exhibited striking patterns of current and salinity variability in the upper equatorial pacific ocean this evolution is described from mid 1996 through 1998 using a remarkable data set of 35 meridional conductivity temperature depth ctd acoustic doppler current profiler adcp sections along with buoy data the sections nominally from 8 s to 8 n between 165 e and 95 w were occupied over the course of 27 months a wide range of current variability was sampled with currents that appeared or disappeared some time during the cycle including an equatorially trapped eastward surface current the equatorial undercurrent the northern branch of the south equatorial current and the north equatorial countercurrent basin wide interannual changes in upper ocean and pycnocline zonal transports were as large as 64 32 106 m3 s 1 changes in the salinity structure included a deep and fresh mixed layer in the central equatorial pacific that built up during the el nino and was then disrupted by upwelled salty water with the onset of la nina a very fresh mixed layer observed in the eastern equatorial pacific late in the el nino and a reduction in the strength of the meridional equatorial salinity gradient within the pycnocline to one third of the usual value during the el nino finally the zonal transports above the thermocline from 5 s to 5 n were well correlated with the rate of change of warm water volume west of the individual ctd adcp sections

variability and linkages of new guinea coastal undercurrent and lower equatorial intermediate current abstract velocity at depths of 700 800 m was measured between september 1998 and october 2002 at 2 5 s 142 e off the new guinea coast and at 0 138 e to examine the new guinea coastal undercurrent ngcuc and the current on the equator carrying antarctic intermediate water aaiw velocity characteristics before november 1999 were markedly different from those after november 1999 the typical state occurred during the second period the intermediate ngcuc and the lower equatorial intermediate current leic varied markedly with an annual cycle in opposite phases in austral winter the ngcuc flowed west northwestward strongly 14 cm s 1 285 t especially in may july during which the leic disappeared and eddylike equatorial variations with periods of 20 60 days were significant in austral summer the leic flowed westward strongly 12 cm s 1 270 t especially in october december whereas the ngcuc reversed its direction repeatedly to flow east southeastward in november february thus the intermediat

quantification of loss of calcite pyrite and organic matter due to weathering of toarcian black shales and effects on kerogen and bitumen characteristics abstract comparison of geochemical data on posidonia shale early toarcian from a shallow unweathered core and from adjacent weathered exposures of the same fades was performed results revealed that quantitatively the most affected petrographic constituent is pyrite and that organic matter and carbonate were also altered by weathering due to this process of weathering the bulk composition of organic matter especially the molecular composition of soluble organic matter and the fluorescence colour of organic particles are changed estimates of weathering rates reveal that the annual release of sulphur and organic carbon from black shales may significantly add to anthropogenic pollution

soil patterns in weathering clay translocation and podzolisation on hilly and steep land at port underwood marlborough sounds new zealand classification and relation to landform and altitude abstract six soil profiles ranging in altitude from 30 m to 580 m at port underwood in the marlborough sounds new zealand are described classified and discussed in terms of their morphology chemistry and mineralogy the soils are formed from greywacke on hilly and steep land under a climate ranging from mild and humid at lower elevations to cool and superhumid at the highest elevation the profiles show distinct altitudinal patterns in weathering clay translocation leaching and podzolisation differences in weathering are related mainly to geomorphic history whereas differences in leaching and podzolisation are attributed mainly to the effects of climate weathering has been strongest at altitudes below about 200 m where the soils are dominated by kaolinitic clay minerals parent materials were probably inherited from late pleistocene interglacial or interstadial weathering at higher altitudes less weathered soils containing mainly vermiculite clays are formed from parent materials exposed by widespread periglacial erosion and deposition during the last glaciation and from periodic erosion and deposition during the holocene clay translocation as evidenced by the presence of argillic horizons has been most active at lower altitudes where the soils are older and the climate is drier than at higher elevations field and laboratory data show that the 2 profiles at the highest elevation are podzolised they have substantial accumulations of illuvial amorphous minerals and mineral organic complexes in subsoils and one profile also has morphological eluvial features with an underlying placic horizon neither the new zealand genetic classification nor soil taxonomy satisfactory classifies the podzolised soils we think that they would be better classified as spodosols or as spodic subgroups of inceptisols

eddy energetics in the upper equatorial pacific during the hawaii to tahiti shuttle experiment abstract eddy energetics in the central equatorial pacific ocean is examined using acoustic doppler current profiler velocities and ctd densities collected during the hawaii to tahiti shuttle experiment in 1979 80 three distinct sources of eddy energy are identified with varying degrees of statistical reliability and are interpreted as evidence for three separate instabilities of the mean flow field an instability at and just north of the equator occurs primarily in boreal summer and fall it arises from the cyclonic shear between the equatorial undercurrent and the south equatorial current sec north of the equator the instability is present only when and where both currents are well developed and there is little involvement of the shear between the sec and the north equatorial countercurrent necc the instability is characterized by local maxima in zonal and meridional eddy velocity variance strong u v reynolds stress and large mean flow to eddy kinetic energy conversion despite seasonal va

tropical instability waves at 0 n 23 w in the atlantic a case study using pilot research moored array in the tropical atlantic pirata mooring data temperature salinity velocity and wind from a mooring at 0 n 23 w are used along with satellite data for sea surface temperature and sea level to examine the contribution of tropical instability waves tiws to the energy and heat balance of the equatorial atlantic mixed layer the tiws appear as periodic 20 30 day fluctuations of currents temperature and salinity which intensify beginning in june and peak in late boreal summer the intensification occurs in phase with strengthening of the southeasterly trade winds and the seasonal appearance of the equatorial tongue of cold mixed layer temperatures in 2002 these waves which warm the mixed layer by 0 35 c during summer months are maintained by both barotropic and baroclinic conversions that are of comparable size salinity fluctuations previously neglected increase the magnitude of baroclinic energy conversion

direct measurements of upper ocean currents and water properties across the tropical pacific during the 1990s abstract meridional sections of upper ocean zonal currents potential temperature and salinity are estimated at ten longitudes from 143 e to 95 w using conductivity temperature depth and acoustic doppler current profiler data from 172 synoptic sections taken in the tropical pacific between 138 e and 86 w mostly in the 1990s data reduction is carried out in a potential isopycnal and mixed layer framework to preserve a sharp pycnocline a mixed layer water property extrema and velocity extrema mean zonal currents potential temperatures and salinities are produced at each longitude the seasonal cycles of these fields are also estimated as well as a simple el nino southern oscillation enso cycle zonal sections along the equator are also presented properties of the near equatorial zonal currents including transports temperatures and salinities are estimated separately from the synoptic sections the seasonal cycles of these quantities and their correlations with the southern oscillation index are investigated the work is distinguished from most existing literature in that direct estimates of zonal velocity are combined with contemporaneous temperature and salinity data allowing trans pacific estimates of near equatorial current transports and properties including those of the northern branch of the south equatorial current the new guinea coastal undercurrent and the equatorial undercurrent

dynamics of intraseasonal sea level and thermocline variability in the equatorial atlantic during 2002 03 abstract satellite and in situ observations in the equatorial atlantic ocean during 2002 03 show dominant spectral peaks at 40 60 days and secondary peaks at 10 40 days in sea level and thermocline within the intraseasonal period band 10 80 days a detailed investigation of the dynamics of the intraseasonal variations is carried out using an ocean general circulation model namely the hybrid coordinate ocean model hycom two parallel experiments are performed in the tropical atlantic ocean basin for the period 2000 03 one is forced by daily scatterometer winds from the quick scatterometer quikscat satellite together with other forcing fields and the other is forced by the low passed 80 day version of the above fields to help in understanding the role played by the wind driven equatorial waves a linear continuously stratified ocean model is also used within 3 s 3 n of the equatorial region the strong 40 60 day sea surface height anomaly ssha and thermocline variability result mainly from the

distinct 17 and 33 day tropical instability waves in subsurface observations abstract tropical instability waves tiws within a half degree of the equator in the pacific ocean have been consistently observed in meridional velocity with periods of around 20 days on the other hand near 5 n tiws have been observed in sea surface height ssh thermocline depth and velocity to have periods near 30 days tropical atmosphere ocean tao project moored equatorial velocity and temperature time series are used to investigate the spatial and temporal structure of tiws during 3 years of la nina conditions from 1998 through 2001 along 140 w where the tiw temperature and velocity variabilities are at their maxima these variabilities include two distinct tiws with periods of 17 and 33 days rather than one broadbanded process as predicted by modeling studies the 17 day tiw variability is shown to occur not only in meridional velocity at the equator but also in subsurface temperature at 2 n and 2 s while the 33 day tiw variability is observed primarily in subsurface temperature at 5

limited iron isotope variations in recent lateritic soils from nsimi cameroon implications for the global fe geochemical cycle laterites are oxidized fe rich soils covering one third of the continents and are drained by half of the continental waters they therefore represent a key component of the iron geochemical cycle at the earth s surface yet no iron isotope study has been conducted on recent laterites so far building on previous integrated morpho pedological studies of soils located in an equatorial rainforest southern cameroon we have undertaken a mineralogical elemental and isotopic study of iron in two lateritic profiles one is a borehole 3620 cm deep going to the parent granodioritic rock located at the top of a hill whereas the other is 675 cm deep and is located downhill mossbauer spectroscopy reveals that typically geq 96 of the soil s iron is held in nanocrystalline hematite and goethite iron isotope measurements performed by plasma source mass spectrometry show that fe isotopic equilibrium was rarely reached between these iron oxide and hydroxide despite their small size overall it is found that most samples display iron isotope signatures very close to the mean crustal value with a maximum range of 0 2 in delta 57 fe given that lateritic soils evolve over millions of years show large variations in fe concentrations and mineralogical abundances this range is surprisingly small when compared to other fe isotope studies of soils from different climatological contexts that can easily show delta 57 f e ranges in excess of 1 at the bulk sample scale the most likely explanation of this finding is that despite notable vertical and lateral fe mobility in the studied laterites from cameroon as computed using the open system mass fraction transport function tau fe w iron remained mostly in the oxidized form as shown by mossbauer pectroscopy this probably results from the strong bioturbation and pedoturbation of these lateritic soils that lead them to remain porous over a large thickness and facilitated the flow of oxygenated waters from the surface down to the saprolite horizon this study therefore reveals that soils that remained as an open system for iron do not necessarily show large fe isotopic variations it is suggested that the fe drained from such lateritic soils should have delta 57 fe values within sim 0 1 of that of the continental crust this is in contrast with previous soil studies notably from sites located at higher latitudes that imply that these soils should release isotopically more variable fe to surface waters such possible contrasted isotopic signatures from different surface waters will likely lead to an isotopically heterogeneous ocean given the short residence time of fe in seawater

iron isotope fractionation during microbial reduction of iron the importance of adsorption in experiments investigating the causes of fe isotope fractionation the d 56 54 fe value of fe ii remaining in solution fe ii aq after reduction of fe iii goethite by shewanella putrefaciens is 21 2 relative to the goethite in agreement with previous research the addition of an electron shuttle did not affect fractionation suggesting that fe isotope fractionation may not be related to the kinetics of the electron transfer furthermore in abiotic anaerobic fecl2 aq experiments in which approximately one third of fe ii aq is lost from solution due to adsorption of fe ii onto goethite the d 56 54 fe value of fe ii aq remaining in solution is shifted by 20 8 relative to fecl 2 this finding demonstrates that anaerobic nonbiological interaction between fe ii and goethite can generate signif icant fe isotope fractionation acid extraction of sorbed fe ii from goethite in experi ments reveals that heavy fe preferentially sorbs to goethite simple mass balance modeling indicates that the isotopic composition of the sorbed fe ii pool is 11 5 to 12 5 heavier than fe in the goethite 2 7 3 7 heavier than aqueous fe ii mass balance is also consistent with a pool of heavy fe that is not released to solution during acid extraction

iron isotope systematics in estuaries the case of north river massachusetts usa abstract recent studies have suggested that rivers may present an isotopically light fe source to the oceans since the input of dissolved iron from river water is generally controlled by flocculation processes that occur during estuarine mixing it is important to investigate potential fractionation of fe isotopes during this process in this study we investigate the influence of the flocculation of fe rich colloids on the iron isotope composition of pristine estuarine waters and suspended particles the samples were collected along a salinity gradient from the fresh water to the ocean in the north river estuary ma usa estuarine samples were filtered at 0 22 m and the iron isotope composition of the two fractions dissolved and particles were analyzed using high resolution mc icp ms after chemical purification dissolved iron results show positive 56 fe values with an average of 0 43 0 04 relative to the irmm 14 standard and do not display any relationships with salinity or with percentage of colloid flocculation the iron isotopic composition of the particles suspended in fresh water is characterized by more negative 56 fe values than for dissolved fe and correlate with the percentage of fe flocculation particulate 56 fe values vary from 0 09 at no flocculation to 0 1 at the flocculation maximum which reflect mixing effects between river borne particles lithogenic particles derived from coastal seawaters and newly precipitated colloids since the process of flocculation produces minimal fe isotope fractionation in the dissolved fe pool we suggest that the pristine iron isotope composition of fresh water is preserved during estuarine mixing and that the value of the global riverine source into the ocean can be identified from the fresh water values however this study also suggests that 56 fe composition of rivers can also be characterized by more positive 56 fe values up to 0 3 relative to the crust than previously reported in order to improve our current understanding of the oceanic iron isotope cycling further work is now required to determine the processes controlling the fractionation of fe isotopes during continental run off

a semidiscrete finite volume formulation for multiprocess watershed simulation 1 hydrological processes within the terrestrial water cycle operate over a wide range of time and space scales and with governing equations that may be a mixture of ordinary differential equations odes and partial differential equations pdes in this paper we propose a unified strategy for the formulation and solution of fully coupled process equations at the watershed and river basin scale the strategy shows how a system of mixed equations can be locally reduced to ordinary differential equations using the semidiscrete finite volume method fvm domain decomposition partitions the watershed surface onto an unstructured grid and vertical projection of each element forms a finite volume on which all physical process equations are formed the projected volume or prism is partitioned into surface and subsurface layers leading to a fully coupled local ode system referred to as the model kernel the global ode system is assembled by combining the local ode system over the domain and is then solved by a state of the art ode solver the unstructured grid based on delaunay triangulation is generated with constraints related to the river network watershed boundary elevation contours vegetation geology etc the underlying geometry and parameter fields are then projected onto the irregular network the kernel based formulation simplifies the process of adding or eliminating states constitutive laws or closure relations the strategy is demonstrated for the shale hills experimental watershed in central pennsylvania and several phenomena are observed 1 the enslaving principle is shown to be a useful approximation for soil moisture water table dynamics for shallow soils in upland watersheds 2 the coupling shows how antecedent moisture i e initial conditions can amplify peak flows 3 the coupled equations predict the onset or threshold for upland ephemeral channel flow and 4 the model shows how microtopographic information controls surface saturation and connectivity of overland flow paths for the shale hills site the open source code developed in this research is referred to as the penn state integrated hydrologic model pihm

a model for assessing quantifying and correcting for index element mobility in weathering studies evidence shows that high field strength hfs elements commonly used to index chemical weathering are variably mobile this mobility may be linked to redistribution of suspended solids a mass balance model is presented that can quantify such redistribution without assuming immobility for any single element two tropical weathering profiles on quartz diorite and basalt are examined and redistribution of the hfs elements zr and ti is documented along with potential corrections for the resulting changes in measured concentrations

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

behavior of re and os during low temperature alteration results from himalayan soils and altered black shales re os analyses were performed on five soil profiles developed on silicate lithologies in the narayani drainage basin of the himalayas as well as on several altered black shales and associated alteration phases the results indicate that all of these samples have lost large amounts of re this re loss approached 100 in the black shale derived soils which also most probably lost substantial quantities of os the near constancy of os and re concentrations with depth indicates that this loss occurred quite early in the alteration process rather than progressively during the course of soil development a slight decrease in 187os 188os was observed toward the surface of the two black shale soil profiles possibly indicating a minor preferential mobility of radiogenic 187os for this lithology in the black shale derived saprolite and soils the loss of re and os was related to the loss of organic carbon the importance of this phase is underscored by the fact that organic material separated from a black shale sample accounted for nearly all of the os contained in the whole rock analysis of alteration phases from the surface of a weathered black shale showed that os liberated during alteration was partially reprecipitated in fe oxides with os isotopic compositions very similar to that of the original rock whereas re was removed with the fluid phase these results demonstrate the disproportionately large role that black shale weathering may play in determining the re and os contents of continental runoff and thus ultimately of seawater but they also emphasize the possible complexity of this process the data suggest that a large fraction of the os contained in black shales is released during chemical alteration which is apparently not the case for most other silicate rocks therefore the potential contribution of black shales to the dissolved os budget of runoff and river water may be even greater than that expected from the high os concentrations of these rocks the extent to which this os will affect the seawater os composition depends on how efficiently it is recaptured by secondary phases such as fe mn oxides in situ or during transport these results also underscore the high mobility of re with respect to os at every stage in the erosional process thus explaining the order of magnitude increase in re os ratio from the black shale source rocks to seawater

tropical instability wave kinematics observations from the tropical instability wave experiment the kinematics of planetary waves originating from instability of the nearsurface equatorial currents are reported on using velocity measurements from an array of acoustic doppler current profilers deployed in the equatorial pacific during the tropical instability wave experiment a distinctive wave season was observed from august to december 1990 with wave energy confined primarily above the core of the equatorial undercurrent particle motions in the horizontal plane are described by eccentric ellipses oriented toward the north but tilting into the cyclonic shear of the south equatorial current the tilt is maximum near the surface just north of the equator and decreases to the south and with depth the distribution of wave variance is narrowband in both frequency and zonal wavenumber with central period zonal wavelength and westward directed phase propagation estimated to be 500 hours 1060 km and 59 cm s 1 respectively neither the meridional nor the vertical wavenumber component is statistically different from zero these results generally agree with previous findings on tropical instability waves from the atlantic and pacific oceans and in the undersampled arena of geophysical measurements they provide an example where statistical inference is supported by an ensemble of independent measurements

iron isotope fractionation during leaching of granite and basalt by hydrochloric and oxalic acids abstract transport of iron fe within hydrothermal and soil environments involves the transferral into aqueous solutions by leaching of complex polyminerallic rocks understanding the isotope fractionation mechanisms during this process is key for any application of the fe isotope system to biogeochemical studies here we reacted biotite granite and tholeiite basalt with 0 5 m hydrochloric acid and 5 mm oxalic acid solutions at ambient temperature solution aliquots were recovered over a seven day period and analysed for major and trace element concentrations and fe isotopic compositions in all experiments fe initially released into solution was isotopically lighter with 56fesolution rock as low as 1 80 in the granite hydrochloric acid system the oxalic acid experiments showed similar patterns but smaller fractionation in all experiments the 56fesolution rock reduced over time which would be in line with the formation of a leached layer as proposed before brantley s l liermann l j guynn r l anbar a icopini g a and barling j 2004 fe isotopic fractionation during mineral dissolution with and without bacteria geochim cosmochim acta 68 15 3189 3204 granite and basalts reacting with hydrochloric acid reached apparent steady state values of 0 60 0 15 and 0 40 0 20 respectively whilst experimental values with oxalic acid were 1 0 0 15 and 0 50 0 15 during the granite experiments alteration of biotite to chlorite followed by dissolution of chlorite were likely the dominant processes whilst in the basalt experiments dissolution of pigeonite was likely the principal source of fe variations in ph during the hydrochloric acid experiments were minimal remaining below 0 5 at all times in oxalic acid solutions the ph increased to over 4 leading likely to precipitation of secondary minerals and adsorption co precipitation of fe onto mineral surfaces these processes could contribute to the greater fractionation observed in the final stages of the oxalic acid experiments our results highlight the importance of mineralogy and fluid composition on the fe isotope systematics during weathering the fractionation processes identified for granites and basalts are in line with those inferred from field observations in soils sediments groundwater and hydrothermal deposits and from laboratory studies of single mineral leaching

worldwide distribution of continental rock lithology implications for the atmospheric soil co2 uptake by continental weathering and alkalinity river transport to the oceans 1 the silicate rock weathering followed by the formation of carbonate rocks in the ocean transfers co2 from the atmosphere to the lithosphere this co2 uptake plays a major role in the regulation of atmospheric co2 concentrations at the geologic timescale and is mainly controlled by the chemical properties of rocks this leads us to develop the first world lithological map with a grid resolution of 1 1 this paper analyzes the spatial distribution of the six main rock types by latitude continents and ocean drainage basins and for 49 large river basins coupling our digital map with the gem co2 model we have also calculated the amount of atmospheric soil co2 consumed by rock weathering and alkalinity river transport to the ocean among all silicate rocks shales and basalts appear to have a significant influence on the amount of co2 uptake by chemical weathering

geochemical behaviors of different element groups during shale weathering at the susquehanna shale hills critical zone observatory major and trace element concentrations were measured in bedrock regolith and stream sediments from a first order catchment developed entirely on grey shale in central pennsylvania usa these elements can be classified into five major groups based on statistical data analysis the presence of different elemental groups is due to the mineralogical origin cycling processes and geochemical properties of these elements during soil formation a better understanding of the behaviors of these elements during chemical weathering would allow for their possible use as natural tracers in critical zone processes

monthly period oscillations in the pacific north equatorial countercurrent monthly period oscillations in temperature and velocity in the vicinity of the north equatorial countercurrent along 140 w are examined using moored time series data collected during 1988 1989 these oscillations which presumably derive their energy from instability of the large scale shear of the zonal equatorial current system are found to be energetic across a broad band of periods of about 15 50 days along 7 n wavelike motions at these periods propagate westward with a phase speed of about 30 40 cm s 1 and a zonal wavelength of 750 1150 km the oscillations are approximately in geostrophic balance with the thermal field with the velocity vector rotating anticyclonically around westward propagating high sea level centers zonal volume transport variations associated with these waves between 5 and 9 n at 20 180 m depth have a standard deviation of about 4 1 sv with peak to peak changes in some instances approaching 20 sv maximum temperature variance along 140 w occurs between 5 and 7 n at 100 150 m depth in a region of strong mean vertical and meridional temperature gradient associated with a thermocline sloping upward to the north at the surface maximum temperature variability occurs from 2 to 5 n in the vicinity of the strong sea surface temperature front north of the equator analysis of the upper ocean temperature balance at 7 n 140 w reveals that meridional advection is important both in the surface layer and in the thermocline vertical advection estimated using vertical velocity calculated from a simplified linear vorticity balance is also important in the thermocline where it contributes a variance comparable to that of meridional advection zonal advection is likely to be significant in the upper 80 m below which it is probably of secondary importance compared to meridional and vertical advection one consequence of advection in the temperature balance is that variance is shifted toward lower frequencies in temperature vis a vis velocity spectra this red shift may account for the apparent difference between periods for instability waves inferred from near equatorial meridional velocity spectra and slightly longer periods reported for oscillations of the sea surface temperature front north of the equator based on satellite imagery

pausing of the enso cycle a case study from 1998 to 2002 abstract the heat balance of the surface mixed layer is analyzed at the eastern equatorial pacific ocean 0 140 w in order to examine the transition from the 1998 la nina to the 2002 el nino the data used are observations from the tropical atmosphere ocean triangle trans ocean buoy network tao triton results show that interannual variation of eddy heat flux due to tropical instability waves slows the transition from la nina to el nino previous studies have described this slow transition as a pausing period of the enso cycle that is la nina lingers and el nino does not immediately appear despite a deepened thermocline heat balance analysis shows that the vertical heat advection anomaly and surface heat flux anomaly warm the mixed layer from 1999 to 2002 these warming anomalies cause the rise of the mixed layer temperature anomaly in the transition from la nina to el nino in contrast a cooling anomaly of the horizontal heat advection reduces the warming anomaly and slows down the transition fr