analysis and modeling of atmospheric gravity waves observed in radarsat sar images four case studies of radarsat synthetic aperture radar sar observations of atmospheric gravity waves are presented to demonstrate sar s capability to measure associated near surface wind field variations a brief review of the main characteristics and scales of atmospheric gravity waves agws first establishes their importance in atmospheric dynamics the shape and scale of the wave patterns observed in successive sar images are compared with those calculated from agw models there is agreement between the small scale wind variations across wave patterns in sar images and the larger scale wind field that plays a role in the generation of the observed waves

the stabilisation and transportation of dissolved iron from high temperature hydrothermal vent systems iron fe binding phases in two hydrothermal plumes in the southern ocean were studied using a novel voltammetric technique this approach reverse titration competitive ligand exchange adsorptive cathodic stripping voltammetry showed that on average 30 21 of dissolved fe in the hydrothermal plumes was stabilised by chemically labile binding to ligands the conditional stability constant log k fel of the observed complexes was 20 61 0 54 mean 1 sd for the two vent sites intermediate between previous measurements of deep ocean ligands 21 4 23 kondo et al 2012 and dissolved weak estuarine ligands 20 gerringa et al 2007 our results indicate that approximately 7 5 of all hydrothermal fe was stabilised by complexation with ligands furthermore 47 26 of the dissolved fe in the plume existed in the colloidal size range 0 02 0 2 m our data suggests that a portion 7 5 of hydrothermal fe is sufficiently stabilised in the dissolved size fraction 0 2 m to make an important impact on deep ocean fe distributions lateral deep ocean currents transport this hydrothermal fe as lenses of enhanced fe concentrations away from mid ocean ridge spreading centres and back arc basins

sulfate minerals control dissolved rare earth element flux and nd isotope signature of buoyant hydrothermal plume emso azores 37 n mid atlantic ridge abstract while hydrothermal vents are now thought to be a major source of dissolved iron to the oceans they have always been considered to be a sink for the dissolved rare earth elements drees however true dissolved ree observations in hydrothermal plumes are still lacking here we report for the first time the dree concentrations and neodymium isotopic compositions dend of buoyant hydrothermal fluids at lucky strike mid atlantic ridge we find that 27 to 62 of total hydrothermal drees are rapidly scavenged by anhydrite precipitation at the onset of buoyant plume formation after this initial loss all drees behave quasi conservatively within the buoyant plume dissolved phase end dend in the evolving plume are identical to black smoker dend of 9 0 and contrast radically with dend of the local deep water mass at 12 0 plume dend as low as 6 6 may be reconciled by dissolution of newly formed barite in the local environment and carrying seawater dend signature we find based on the first plume dree observations that hydrothermal plumes are in fact a source of dree to the north atlantic deep water precipitation dissolution processes of hydrothermally derived minerals i e sulfates in the buoyant plume and fe oxy hydroxide in the non buoyant plume will likely affect the fate of other trace metals and their isotopic composition

stable isotope and rare earth element evidence for recent ironstone pods within the archean barberton greenstone belt south africa there is considerable debate about the mode and age of formation of large up to 200 m long hematite and goethite ironstone bodies within the 3 2 to 3 5 ga barberton greenstone belt we examined oxygen and hydrogen isotopes and rare earth element ree concentrations of goethite and hematite components of the ironstones to determine whether these deposits reflect formation from sea floor vents in the archean ocean or from recent surface and shallow subsurface spring systems goethite d 18 o values range from 0 7 to 1 0 and dd from 125 to 146 which is consistent with formation from modern meteoric waters at 20 to 25 c hematite d 18 o values range from 0 7 to 2 0 which is consistent with formation at low to moderate temperatures 40 55 c from modern meteoric water ree in the goethite and hematite are derived from the weathering of local sideritic ironstones silicified ultramafic rocks sideritic black cherts and local felsic volcanic rocks falling along a mixing line between the eu eu and shale normalized hreeavg lreeavg values for the associated silicified ultramafic rocks and felsic volcanic rocks contrasting positive ce ce of 1 3 to 3 5 in hematite and negative ce ce of 0 2 to 0 9 in goethite provides evidence of oxidative scavenging of ce on hematite surfaces during mineral precipitation these isotopic and ree data taken together suggest that hematite and goethite ironstone pods formed from relatively recent meteoric waters in shallow springs and or subsurface warm springs

chemical processes in buoyant hydrothermal plumes on the east pacific rise near 21 n hydrothermal plume water containing suspended particles of precipitated black smoke has been sampled from three hydrothermal vent fields on the east pacific rise near 21 n the samples were taken within the lower 22 m of the buoyant plumes directly above 273 350 c black smoker vents using go flo bottles mounted on the submersible alvin based on li as a conservative tracer of the high temperature endmember solution mixing ratios of 102 to 104 g seawater g vent water are achieved within the lower 22 m of the plumes the particle concentrations sampled in the lower 13 m of the plumes are much larger than predicted for these mixing ratios suggesting that the particles are settling within the lower part of the plume the major minerals in the smoke are pyrrhotite fe rich sphalerite pyrite unidentified fe s si and fe si s phases chalcopyrite amorphous silica sulfur fe oxyhydroxides including goethite and anhydrite present in trace quantities are barite isocubanite wurtzite covellite marcasite and unidentified silicates and alsilicates organic matter is common the composition of the plume solutions indicates that 35 25 of the hydrothermally injected fe remains in dissolved form i e 0 45 m within the lower 22 m of the plume in spite of a 3 to 9 fold excess of h2s in the vent solutions nearly all of the mn and si and most of the ba also remain in solution h2s by contrast has been largely 70 100 removed by precipitation as sulfides and sulfur but mainly by oxidation to dissolved species with intermediate oxidation states its early removal implies that 50 30 of the injected fe will eventually precipitate as primary oxides rather than as sulfides and that fe can be fractionated from the other chalcophile metals during sulfide precipitation compared with the vent water the particles are enriched in cu co ag cd al zn pb and ni by factors of 4 to 20 relative to fe and depleted in ba s si and mn scavenging from seawater may play a role in co and cu enrichment at the ngs field and for ag cd and ni at all three fields but is negligible for pb and zn these results indicate that two distinct metalliferous components are delivered to the distal regions of a plume as a result of reactions in the lower part of the buoyant plume 1 1 a dissolved component that includes about half the fe and all of the mn and will eventually precipitate as oxides and 2 2 a particulate component consisting of fine grained sulfide minerals that are enriched in ore metals by factors of 4 to 20

tracking oceanic nonlinear internal waves in the indonesian seas from geostationary orbit abstract nonlinear internal waves nliws in the ocean are observable from passive satellite radiometers the surface manifestations of these internally propagating waves are curvilinear bands demarcating relatively smooth and rough surface waters providing a means for their detection via observations of sunglint typical horizontal scales of nliws are such that traditionally only high resolution

opposing authigenic controls on the isotopic signature of dissolved iron in hydrothermal plumes iron is a scarce but essential micronutrient in the oceans that limits primary productivity in many regions of the surface ocean the mechanisms and rates of fe supply to the ocean interior are still poorly understood and quantified iron isotope ratios of different fe pools can potentially be used to trace sources and sinks of the global fe biogeochemical cycle if these boundary fluxes have distinct signatures seafloor hydrothermal vents emit metal rich fluids from mid ocean ridges into the deep ocean iron isotope ratios have the potential to be used to trace the input of hydrothermal dissolved iron to the oceans if the local controls on the fractionation of fe isotopes during plume dispersal in the deep ocean are understood in this study we assess the behaviour of fe isotopes in a southern ocean hydrothermal plume using a sampling program of total dissolvable fe tdfe and dissolved fe dfe we demonstrate that 56fe values of dfe 56dfe within the hydrothermal plume change dramatically during early plume dispersal ranging from 2 39 0 05 to 0 13 0 06 2 sd the isotopic composition of tdfe 56tdfe was consistently heavier than dfe values ranging from 0 31 0 03 to 0 78 0 05 consistent with fe oxyhydroxide precipitation as the plume samples age the dfe present in the hydrothermal plume includes stabilised dfe species with potential to be transported to the deep ocean we estimate that stable dfe exported from the plume will have a 56fe of 0 28 0 17 further we show that the proportion of authigenic iron sulfide and iron oxyhydroxide minerals precipitating in the buoyant plume exert opposing controls on the resultant isotope composition of dissolved fe passed into the neutrally buoyant plume we show that such controls yield variable dissolved fe isotope signatures under the authigenic conditions reported from modern vent sites elsewhere and so ought to be considered during iron isotope reconstructions of past hydrothermalism from ocean sediment records

synthetic aperture radar observation of the sea surface imprints of upstream atmospheric solitons generated by flow impeded by an island 1 two cases of upstream propagation of atmospheric solitons generated by atmospheric flow over topography were identified on two radarsat 1 synthetic aperture radar sar images acquired near st lawrence island in the bering sea on 7 september 1997 and 6 june 2001 respectively in both cases a group of solitons was shown as three dark bright linear features on the sar images the soliton width and peak to peak distance measured from the two sar images are about 3 km and 4 5 km respectively simultaneous radiosonde measurements a surface weather map and operational weather model results confirm that these waves did not propagate on the lee side of the island as is commonly observed with island lee waves but indeed propagated against the flow in the upstream direction in the second case the same group of solitons was also identified as a wave like cloud pattern on a modis image taken about 4 5 hours later in this modis image the soliton train propagated further upstream with the leading crest reaching about 30 km north of the island and the number of crest trough features increased from three to seven in this study we describe the generation and evolution of upstream atmospheric solitons using the force kdv fkdv model with radiosonde and island topography data the numerical solution of the fkdv exhibits a sequence of solitons propagating upstream of the island both temporal and spatial scales of the solitons are in good agreement with that estimated from the successive sar and modis satellite images

the formation of terrains antipodal to major impacts abstract in 1975 schultz and gault suggested that seismic energy from a major impact could extensive could cause crystal fracturing and surface disruption on the part of the planet directly opposite the impact disrupted terrains of this type have been identified on mercury antipodal to the caloris impact basin and on the moon antipodal to imbrium large impact basins are found on many icy satellites herschel on mimas valhalla on callisto odysseus on tethys and others antipodal disruption from these impacts might appear as a fractured surface or as a resurfaced area the simplified arbitrary lagrangian eulerian sale code was used to calculate the antipodal pressures generated by large impacts into stylized icy satellites and planets that have different compositions and core sizes it was found that in a planet with a high density core sorrounded by a lower density mantle the incident pressure wave is refracted away from the antipode by the core and the generated antipodal pressure will be low in a planet with a low velocity core sorrounded by a mantle with a higher wave speed the core will focus the wavefront and the antipodal pressure will be high in both cases for equal impacts the magnitude is dependent upon the size of the core relative to the planet we also modeled specific impact basins on the moon mercury and several icy satellites to determine whether the impacts were capable of producing the observed antipodal surface features we found surface accelerations and pressures which exceed the strength of surface materials for the caloris impact on mercury imbrium on the moon odysseus on tethys and the herschel impact on mimas images of the surface antipodal to all of these impacts except herschel show a morphology which could be interpreted as impact induced seismically disrupted terrain

fluxes to sediments underlying the rainbow hydrothermal plume at 36 14 n on the mid atlantic ridge abstract a geochemical investigation has been conducted of a suite of four sediment cores collected from directly beneath the hydrothermal plume at distances of 2 to 25 km from the rainbow hydrothermal field as well as a large biogenic component 80 caco3 these sediments record clear enrichments of the elements fe cu mn v p and as from hydrothermal plume fallout but only minor detrital background material systematic variations in the abundances of hydrothermal elements are observed at increasing distance from the vent site consistent with chemical evolution of the dispersing plume further pronounced ni and cr enrichments at specific levels within each of the two cores collected from closest to the vent site are indicative of discrete episodes of additional input of ultrabasic material at these two near field locations radiocarbon dating reveals mean holocene accumulation rates for all four cores of 2 7 to 3 7 cm kyr 1 with surface mixed layers 7 to 10 cm thick from which a history of deposition from the rainbow hydrothermal plume can be deduced deposition from the plume supplies elements to the underlying sediments that are either directly hydrothermally sourced e g fe mn cu or scavenged from seawater via the hydrothermal plume e g v p as holocene fluxes into to the cores surface mixed layers are presented which typically are an order of magnitude greater than background authigenic fluxes from the open north atlantic one core collected closest to the vent site indicates that both the concentration and flux of hydrothermally derived material increased significantly at some point between 8 and 12 14c kyr ago the preferred explanation is that this variation reflects the initiation intensification of hydrothermal venting at the rainbow hydrothermal field at this time perhaps linked to some specific tectonic event in this fault controlled hydrothermal setting

discriminating between different genetic types of marine ferro manganese crusts and nodules based on rare earth elements and yttrium marine ferro manganese fe mn crusts and nodules are metal rich chemical sediments that are archives of paleoceanographic proxies and potential metal resources and targets of deep sea mining traditionally crusts and nodules are subdivided into hydrogenetic diagenetic and hydrothermal types because these are characterized by different compositions and hence economic resource potential a useable genetic classification is not only a tool for geochemical studies but may also help to characterize potential exploration targets we propose two easy to use yet robust discrimination diagrams based on geochemical relationships controlling the rare earths and yttrium rey inventory of marine fe mn oxyhydr oxide deposits the rey are a set of trace elements that show coherent behavior are routinely determined in geochemical studies and for which the analytical quality can easily be evaluated graphs of ce anomaly vs nd concentration and ce anomaly vs y anomaly effectively discriminate between the different types of precipitates regardless of their diverse mineralogical composition both hydrogenetic crusts and nodules show positive ce anomalies negative y anomalies and high nd concentrations of 100 mg kg 1 although nodules tend to have slightly lower nd concentrations than crusts in marked contrast hydrothermal deposits generally yield negative ce anomalies positive y anomalies and low nd concentrations of 10 mg kg 1 in spite of their large geochemical mineralogical and sedimentological diversity diagenetic nodules show negative ce anomalies negative y anomalies and intermediate nd concentrations between 10 and 100 mg kg 1 we discuss the geochemical background of these diagrams the respective sources of rey in the different precipitates and address the processes that control their rey inventory besides the three end members we also use rey systematics to define mixed type diagenetic hydrogenetic nodules and classify well studied international reference standards

hydrothermal scavenging at the mid atlantic ridge radionuclide distributions we have carried out a study of u series radionuclide distributions in the neutrally buoyant plume overlying the tag hydrothermal vent field at 26 n mid atlantic ridge limited uptake of u accompanies the formation of fe oxyhydroxide particulate material within the hydrothermal plume the particulate u concentrations are too small for measurable dissolved u anomalies to be produced within the water column at plume height however such uptake followed by deposition in the underlying sediments could account for 10 of the u enrichment that has been reported previously for metalliferous ridge crest sediments particulate 234th 230th and 228th activities in the tag hydrothermal plume represent 65 of total th activities typical of the deep ocean low dissolved th activities coincide with the high particulate th activities indicating that hydrothermal scavenging strongly affects th isotope distributions in the water column close to hydrothermal vents much of the scavenging occurs during the initial formation of fe rich hydrothermal precipitates but some further scavenging continues as the material is dispersed away from its source distributions of particulate 210pb and 231pa activities in the neutrally buoyant plume are also extremely high 7 12 dpm 102 l and 30 160 dpm 106 l respectively like th 210pb and231pa show evidence for scavenging within the hydrothermal plume total th activities at plume height are 50 higher than background this focusing of th into the plume is consistent with the entrainment and re emplacement at plume height of particulate material recycled from beneath the neutrally buoyant plume

oxyanions in metalliferous sediments tracers for paleoseawater metal concentrations abstract the concentration of carbon fe mn s p v cr as mo cd u and re were determined in sediment core y 71 7 53p near an active hydrothermal location on the southern east pacific rise crest 10 s the goal was to determine the usefulness of hydrothermal iron oxides as carriers of elemental tracers of seawater concentrations the sediments are 70 carbonate and about 1 3 detrital material with the remainder having a hydrothermal origin rhenium concentrations are at detrital levels suggesting little anaerobic diagenesis beyond manganese remobilization however u cd and mo concentrations all indicate alteration after deposition oxyanion fe ratios of p v and as in surface sediments are lower than the ratios in plume particles and covary with fe content downcore the probable explanation for these variations is variable efficiency of incorporation of these metals during iron oxide formation or early diagenetic processes after deposition the p fe ratio in the core sediment is about half that in the plume particles among the oxyanion ratios only the v as ratio in the sediments is relatively constant at the present plume particle ratio during the past 60 70 kyr changes in sediments older than this could reflect variability in the incorporation efficiency or changes in v as ratio in seawater this study demonstrates the difficulties of using hydrothermal sediment element enrichments as tracers of past seawater chemistry changes in this core it appears that all oxyanion ratios change for reasons other than seawater metal concentration changes with the possible exception of the v as ratio

effective use of cerium anomalies as a redox proxy in carbonate dominated marine settings abstract rare earth elements and yttrium rey have a distinct distribution pattern in seawater and this pattern may be faithfully preserved in carbonate sediments and rocks anomalous concentrations of redox sensitive cerium ce compared with neighbouring rey originate in oxic water column conditions and as such ce anomalies can provide a potentially useful redox proxy in carbonate dominated marine settings the methods used to extract rey from carbonates vary widely and may suffer from widespread leaching of rey from accessory non carbonate minerals and organic matter limiting the application of ce anomalies for palaeo redox reconstruction we have systematically compared different methods on 195 carbonate samples with varying purity carbonate from both modern and ancient environments we used sequential leaching experiments in nitric acid to identify the most seawater like portion of the carbonate sample where contributions from non carbonate minerals and organic matter are minimised we also compared the results of sample dissolution in different types and strengths of acid our results confirm that rey concentrations can be inadvertently contaminated by partial leaching of clays and fe oxyhydr oxides during a single step digestion and we suggest a pre leach of 20 of the sample followed by a partial leach of 40 of the sample to selectively dissolve carbonate we suggest that rey studies are optimised in carbonates with 85 caco 3 and show that dolomites behave differently during the leaching process and must be treated separately we present rey patterns for modern carbonate rich sediments from a range of environments and show that seawater rey are faithfully preserved in some non skeletal carbonate but modified leaching procedures are necessary for impure unlithified or organic rich carbonate sediments we combine rey with fe speciation data to identify how fe oxides and clays contribute to the rey signal and explore how the two proxies can be used together to provide a complex and high resolution redox reconstruction in carbonate dominated marine environments

coexistence of atmospheric gravity waves and boundary layer rolls observed by sar abstractboth atmospheric gravity waves agw and marine atmospheric boundary layer mabl rolls are simultaneously observed on an environmental satellite envisat advanced synthetic aperture radar asar image acquired along the china coast on 22 may 2005 the synthetic aperture radar sar image covers about 400 km 400 km of a coastal area of the yellow sea the sea surface imprints of agw show the patterns of both a transverse wave along the coastal plain and a diverging wave in the lee of mount laoshan 1133 m peak which indicate that terrain forcing affects the formation of agw the agw have a wavelength of 8 10 km and extend about 100 km offshore model simulation shows that these waves have an amplitude over 3 km finer scale 2 km brushlike roughness features perpendicular to the coast are also observed and they are interpreted as mabl rolls the fft analysis shows that the roll wavelengths vary spatially the two way interactive triply nested grid 9 3 1 km weather research and forecasti

hydrothermal sediments as a potential record of seawater nd isotope compositions the rainbow vent site 36 14 n mid atlantic ridge 1 geochemical compositions and sr and nd isotopes were measured in two cores collected 2 and 5 km from the rainbow hydrothermal vent site on the mid atlantic ridge overall the cores record enrichments in fe and other metals from hydrothermal fallout but sequential dissolution of the sediments allows discrimination between a leach phase easily leachable and a residue phase refractory the oxy anion and transition metal distribution combined with rare earth element ree patterns suggest that 1 the leach fraction is a mixture of biogenic carbonate and hydrothermal fe mn oxy hydroxide with no significant contribution from detrital material and 2 99 5 of the ree content of the leach fraction is of seawater origin in addition the leach fraction has an average 87sr 86sr ratio indistinguishable from modern seawater at 0 70916 although we lack the nd value of present day deep water at the rainbow vent site we believe that the ree budget of the leach fraction is predominantly of seawater origin we suggest therefore that the leach fraction provides a record of local seawater nd values nd isotope data from these cores span the period of 4 14 ka 14c ages and yield nd values for north east atlantic deep water neadw that are higher 9 3 to 11 1 than those observed in the nearby madeira abyssal plain from the same depth 12 4 0 9 this observation suggests that either the iceland scotland overflow water isow and lower deep water contributions to the formation of neadw are higher along the mid atlantic ridge than in the surrounding basins or that the relative proportion of isow was higher during this period than is observed today this study indicates that hydrothermal sediments have the potential to provide a higher resolution record of deep water nd values and hence deepwater circulation patterns in the oceans than is possible from other types of sediments

ocean vector winds retrieval from c band fully polarimetric sar measurements we present an efficient algorithm for retrieving the ocean surface wind vector from c band radar satellite radarsat 2 fully polarimetric synthetic aperture radar sar measurements based upon the copolarized geophysical model function i e cmod5 n and the cross polarized ocean backscatter model i e c 2po the analysis of fine quad polarization mode single look complex sar data and collocated in situ moored buoy observations reveals that the polarimetric correlation coefficient between co and cross polarization channels has odd symmetry with respect to the wind direction this characteristic is different from the feature that normalized radar cross sections for quad polarization have even symmetry regarding the wind direction we first use the c 2po model to directly retrieve wind speeds without any external wind direction and radar incidence angle inputs subsequently the retrieved wind speeds along with incidence angles and cmod5 n are employed to invert the wind direction still with ambiguities the odd symmetry property is then applied to remove the wind direction ambiguities thus it is shown that fully polarimetric sar measurements provide complementary directional information for the ocean surface wind fields this method has the potential to improve wind vector retrievals from space

flow and mixing in the rift valley of the mid atlantic ridge high levels of diapycnal mixing and geothermal heating near midocean ridges contribute to the buoyancy fluxes that are required to close the global circulation in topographically confined areas such as the deep median valleys of slow spreading ridges these fluxes strongly influence the local hydrography and dynamics data from a segment scale hydrographic survey of the rift valley of the mid atlantic ridge and from an array of current meters deployed there during an entire year are analyzed in order to characterize the dominant hydrographic patterns and dynamical processes comparison with historic hydrographic data indicates that the temporal variability during the last few decades has been small compared to the observed segment scale gradients the rift valley circulation is characterized by inflow from the eastern ridge flank and persistent unidirectional alongsegment flow into a cul de sac therefore most of the water flowing along the rift valley upwells within the segment with a mean vertical velocity 1025 ms 21 the observed streamwise hydrographic gradients indicate that diapycnal mixing dominates the rift valley buoyancy fluxes by more than an order of magnitude in spite of the presence of a large hydrothermal vent field supplying several gigawatts of heat to the water column hydrographic budgets in the rift valley yield diffusivity values of order 5 3 1023 m2 s 21 consistent with estimates derived from statically unstable overturns the largest of which were observed downstream of topographic obstacles in the path of the along segment flow this suggests vertical shear associated with cross sill flows as the dominant contributor to the mechanical mixing in the rift valley

composition and dissolution of black smoker particulates from active vents on the juan de fuca ridge during two atlantis ii alvin cruises to the juan de fuca ridge in 1984 active high temperature 140 284 c vents were sampled for black smoker particulates using the grassle pump individual mineral phases were identified using standard x ray diffraction and petrographic procedures in addition elemental compositions and particle morphologies were determined by x ray energy spectrometry and scanning electron microscope x ray energy spectrometry techniques the vent particulates from the southern juan de fuca ridge vent sites were highly enriched in s si fe zn and cu and were primarily composed of sphalerite wurtzite pyrite pyrrhotite barite chalcopyrite cubanite hydrous iron oxides and elemental sulfur two additional unidentified phases which were prevalent in the samples included an fe si phase and a ca si phase the grain sizes of the individual particle phases ranged from 100 m for the fe si particles grain size and current meter data were used in a deposition model of individual phase dispersal for many of the larger sulfide and sulfate particles the model predicts dispersal to occur over length scales of only several hundreds of meters the high temperature black smokers from the more northerly endeavour segment vents were highly enriched in fe s ca cu and zn and were primarily composed of anhydrite chalcopyrite sphalerite barite sulfur pyrite and other less abundant metal sulfide minerals the grain sizes of the individual particles ranged from 10 m to slightly larger than 500 m the composition and size distributions of the mineral phases are highly suggestive of high temperature mixing between vent fluids and seawater a series of field and laboratory studies were conducted to determine the rates of dissolution of several sulfate and sulfide minerals the dissolution rates ranged over more than 3 orders of magnitude from 3 2 10 8 cm s 1 for anhydrite to 1 2 10 12 cm s 1 for chalcopyrite the results indicate that for some minerals particularly anhydrite and marcasite total dissolution occurs within a few hours to a few weeks of their formation for other more stable minerals including pyrite sphalerite and chalcopyrite the time required for total dissolution is much longer and consequently individual crystals may be expected to persist in the sediments for considerable periods of time after deposition

a dual origin for the hydrothermal component in a metalliferous sediment core from the mid atlantic ridge a highly metalliferous sediment core collected from tag 26 n mid atlantic ridge has been analyzed for uranium series isotopes rare earth elements ree and radiogenic isotopes two types of deposition of hydrothermal material have been identified and characterized the first is sulfide material which has been rapidly deposited and is sometimes clearly turbiditic this material exhibits high u fe and eu sm ratios and low 230th fe and ree fe ratios it is proposed that u is incorporated into the sulfides by diffusion through the oxidized coating with reductive fixation near the sulfide oxide boundary the second hydrothermal component is particulate fallout from the neutrally buoyant plume which is diluted by the background pelagic sedimentation this component exhibits u fe ratios around 2 10 5 an order of magnitude greater than reported plume particulate levels but the 230th fe ree fe and eu sm ratios are similar to plume values nd and pb isotopes have been used to differentiate the hydrothermal and pelagic end members within this sediment core

the trace metal composition of suspended particles in the oceanic water column near bermuda trace metal partitioning between seawater and particles both suspended and sinking must be determined to understand and model oceanic trace metal scavenging processes in order to improve the oceanic particulate trace metal data base a newin situ pump was developed and deployed to collect suspended particles from 0 4000 m in the sargasso sea near bermuda these particles were analyzed for al fe mn co zn cu ni cd and pb major particulate carrier phases were estimated from ca opaline si and p cd is the only trace element of this group with a particulate maximum in near surface waters the other metals have low particulate concentrations mol l in near surface waters and increase with depth into the upper thermocline particulate al and fe are then uniform with depth below about 1000 m until increasing in the bottom nepheloid layer the remaining elements mn co zn cu ni and pb decrease from the mid thermocline values to lower and relatively uniform concentrations in deep waters the similarities among the vertical profiles for these metals suggest that authigenic mn oxides influence their uptake from the dissolved pool although an important or dominant role for other host phases specifically particulate organic matter is not ruled out by the data mean intermediate and deep water concentrations are al 3600 fe 1200 mn 146 co 1 5 zn 7 4 cu 15 ni 6 0 cd 0 06 and pb 2 1 pmol l these particulate al and mn values agree with previous measurements in this region but the other elements are lower by a factor of 3 fe co to 30 zn suggesting that earlier data were compromised by contamination the suspended metal data are used in a simple steady state two flux model to evaluate the role of suspended particles in determining the vertical flux of metals in the sargasso sea the model calculations indicate that removal of suspended particles in the deep 500 m water column contributes less than half of the total deep flux for all of the elements investigated except for cd this result implies that uptake of these metals onto particles in the deep central ocean is a minor factor in their oceanic mass balance if this finding is generally true for oligotrophic ocean environments whole ocean residence times for these elements must be governed largely by processes occurring either in near surface waters or at ocean margins

the relationship between p fe and v fe ratios in hydrothermal precipitates and dissolved phosphate in seawater a strong positive relationship between the molar p fe ratio in fresh hydrothermal fe ferrihydrite precipitates and seawater dissolved phosphate has been demonstrated using samples from the atlantic and pacific oceans we ascribe this relationship to scavenging of dissolved phosphate from seawater during the formation of hydrothermal fe rich particles above hydrothermal vents in contrast molar v fe ratios in hydrothermal particles are inversely correlated with dissolved phosphate these results indicate that inter ocean variations in dissolved phosphate control the p fe and v fe ratios in hydrothermal fe precipitates one of the precursors of metalliferous sediment

gap winds and wakes sar observations and numerical simulations the nature of terrain induced gap winds and wakes in the atmosphere is examined using surface wind data from synthetic aperture radar sar and the shallow water equations the shallow water model is used to predict the types of wake jet wind patterns that might occur behind an idealized pair of bell shaped hills with a gap between them a regime diagram is constructed based on the width of the gap and the upstream froude number specific predictions of the model are found to compare moderately well with sar data from four examples of airflow near unimak island in the aleutian chain the model predicts the observed wakes and jets including jets that exceed the upstream speed theoretical analysis considers the relative importance of rising terrain and narrowing valley walls in the acceleration of gap winds wind speeds in the wake region are controlled by the bernoulli function and regional pressure gap winds therefore are streams of air that have avoided bernoulli loss over the terrain by passing through gaps the speed of gap winds can exceed the upstream speed only in ridgelike situations when the regional leeside pressure is lower than the upstream pressure

an ers 1 synthetic aperture radar image of atmospheric lee waves an ers 1 synthetic aperture radar sar image of the island hopen shows a distinct 7 6 km wavelength wave phenomenon near the island this wave phenomenon is interpreted as the surface imprint on open water of atmospheric lee waves the pattern is visible in the sar image since the lee waves modulate the horizontal wind speed near the ocean surface which in turn modulates the surface roughness and the radar cross section the physical setting for the observation is presented and discussed the lower bound on horizontal wind speed modulation is estimated to range from 3 2 ms 1 for the wind speed minima to 12 2 ms 1 for the wind speed maxima based upon the observed radar cross section modulation and the ers 1 scatterometer wind retrieval model cmod4 the wavelength and wind speed modulation are consistent with linear lee wave model predications the model uses an atmosphere with an exponential profile of the scorer parameter ratio of buoyancy frequency to wind speed to represent a shallow ground based inversion layer observed at bear island and a bell shaped barrier to represent the forcing effects of hopen

major and trace elements in mid eocene lacustrine oil shales of the fushun basin ne china concentration features and paleolimnological implications abstract mid eocene tectonic subsidence of the pull apart fushun basin ne china accommodated an up to 300 m thick oil shale succession within the lacustrine jijuntun formation lutetian based on sedimentary records and bulk element geochemistry accumulation of this oil shale succession is modeled to evaluate the principal controls on enrichment patterns of organic matter om and trace metals in lacustrine organic facies the jijuntun formation consisting primarily of massive oil shale and interbedded siltstone and sandstone that grade rapidly upward into well laminated oil shale records an overall evolution from lacustrine deltaic facies associations to profundal facies associations sedimentological characteristics of the oil shale succession display a gradual change of moderately overfilled to balanced fill lake fill mode consistent with the up section drop in siliciclastic inputs reflected by detrital proxies like decreased si al and k na ratios variations in the sedimentary fill states are accompanied by increasing hydrographic restriction of the jijuntun paleo lake in agreement with low mo toc consistently

co diagenesis of iron and phosphorus in hydrothermal sediments from the southern east pacific rise implications for the evaluation of paleoseawater phosphate concentrations abstract we present a detailed study of the co diagenesis of fe and p in hydrothermal plume fallout sediments from 19 s on the southern east pacific rise three distal sediment cores from 340 1130 km from the ridge crest collected during dsdp leg 92 were analysed for solid phase fe and p associations using sequential chemical extraction techniques the sediments at all sites are enriched in hydrothermal fe oxyhydr oxides but during diagenesis a large proportion of the primary ferrihydrite precipitates are transformed to the more stable mineral form of goethite and to a lesser extent to clay minerals resulting in the release to solution of scavenged p however a significant proportion of this p is retained within the sediment by incorporation into secondary goethite by precipitation as authigenic apatite and by readsorption to fe oxyhydr oxides molar p fe ratios for these sediments are significantly lower than those measured in plume particles from more northern localities along the southern east pacific rise and show a distinct downcore decrease to a depth of 12 m molar p fe ratios are then relatively constant to a depth of 35 m the fe and p speciation data indicate that diagenetic modification of the sediments is largely complete by a depth of 2 5 m and thus depth trends in molar p fe ratios can not solely be explained by losses of p from the sediment by diffusion to the overlying water column during early diagenesis instead these sediments are likely recording changes in dissolved p concentrations off the sepr possibly as a result of redistribution of nutrients in response to changes in oceanic circulation over the last 10 million years furthermore the relatively low molar p fe ratios observed throughout these sediments are not necessarily solely due to losses of scavenged p by diffusion to the overlying water column during diagenesis but may also reflect post depositional oxidation of pyrite originating from the volatile rich vents of the southern east pacific rise this study suggests that the molar p fe ratio of oxic fe rich sediments may serve as a proxy of relative changes in paleoseawater phosphate concentrations particularly if fe sulfide minerals are not an important component during transport and deposition

the effect of hydrothermal processes on midwater phosphorus distributions in the northeast pacific abstract the distributions of dissolved particulate and sedimentary phosphorus were measured in the region of the juan de fuca ridge to determine the impacts of hydrothermal processes on the phosphorus cycle in the oceans significant negative dissolved phosphate anomalies ranging from 0 to 60 nmol l were observed in the water column at depths between 1900 and 2300 db the largest anomalies

hydrothermal plumes along the east pacific rise 8 40 to 11 50 n particle distribution and composition the discovery of a volcanic eruption at the 9 45 52 n site on the east pacific rise epr led us to investigate how the composition of suspended matter in hydrothermal plumes may be used to provide a better understanding of the relative age and vent fluid characteristics of a ridge crest system during surface ship surveys during the troughs tropical ridge observations of underwater geochemical hydrothermal signals expedition we collected hydrothermal plume particles along a 350 km section extending from approximately 8 40 n to 11 50 n of the epr north and south of the clipperton transform fault over the segment south of the clipperton transform fault the sfe ratio in the particles ranged from about 0 9 to 10 with the highest values immediately over the new vent field at the 9 45 52 n site these enrichments exactly coincide with the elevated 3he heat and ch4mn ratios in the plumes over the same vent field the s rich particles are primarily organic and may be related to the bacteria blizzard associated with the eruption in addition very high cufe and znfe ratios were observed in the hydrothermal plumes south of the clipperton transform fault these high ratios are indicative of the predominance of high temperature h2s rich vents between 9 35 n and 9 50 n in contrast the samples from the segment north of clipperton transform fault had sfe ratios which ranged from 0 04 to 0 82 typical of mature fe rich hydrothermal plumes these results suggest that the gas rich vent fluids at the 9 45 52 n site produced the sulfur enriched particles in the water column gas rich plumes and sulfur enriched plume particles were also observed underneath the 1986 megaplume on the juan de fuca ridge jdfr suggesting a similar mode of formation north of the clipperton transform fault the hydrothermal particles are dominated by fe rich oxyhydroxide particles characteristic of mature high temperature vent fields the plume maximum is centered at 11 08 n the fe oxyhydroxide particles scavenge ca si p v cr and as from seawater for p and v the mean element fe ratios in the epr hydrothermal particles are intermediate between jdfr and tag hydrothermal systems for as the mean element fe ratios of all three systems are about the same new evidence for si scavenging by hydrothermal fe oxyhydroxide particles indicates that this sink for dissolved si in the oceans is small

geology age and origin of supracrustal rocks at akilia west greenland new mapping geochronology and geochemistry of the supracrustal enclave and associated orthogneisses at akilia west greenland support a 3825 6 ma age for the sequence and a chemical sedimentary origin for the controversial fe rich quartz pyroxene gneisses lithologies of the enclave comprise laterally continuous mappable units of mafic amphibolite ultramafic rocks and two fe rich quartz pyroxene units a minor anthophyllite garnet rock with chemical characteristics suggesting a sedimentary protolith was identified the earliest foliation parallels lithologic contacts this foliation was isoclinally folded about a steep hinge surface and then tightly refolded about a steep ns hinge plane the latest folding produced limbs exhibiting contrasting strains the full deformation history is shared by all lithologies of the enclave two previously unidentified orthogneiss sheets preserve deformed magmatic crosscutting relations with amphibolite and ultramafic units in the low strain limb the supracrustal anthophyllite garnet rock experienced zircon growth at 3600 and 2700 ma in common with amphibolites these ages are interpreted to reflect metamorphism at granulite and amphibolite facies respectively consistent with independent regional evidence the crosscutting orthogneiss sheets preserve a complex history of zircon growth but only earliest cores indicate th u exchange equilibrium with the bulk rock at magmatic conditions weighted mean 207 pb 206 pb ages of cores of 3730 7 ma and 3825 6 ma date the crystallization ages of the sheets indicating that the akilia supracrustal rocks were deposited 3819 ma quartz pyroxene rocks on akilia have been interpreted as metamorphosed chemical sediments that may preserve carbon isotope evidence for life at the time of their formation an alternative proposal is an origin by metasomatic alteration our results show that these rocks experienced a history of deformation and zircon growth identical to other lithologies of the supracrustal body metamorphic zircons give a minimum 207 pb 206 pb age of 3589 13 ma regardless of origin the two models of formation of quartz pyroxene rocks were evaluated using field petrologic and geochemical tests the distribution of the units the absence of field or petrologic indicators of metasomatism and geochemistry oxygen and nontraditional stable isotopes immobile elements and ree together support a sedimentary but not a metasomatic origin because their protolith was sedimentary the quartz pyroxene rocks are a primary part of the supracrustal sequence and have the same minimum age despite strong deformation and polymetamorphism the akilia supracrustal enclave contains information about terrestrial surficial processes at 3819 ma

hydrothermal scavenging at the mid atlantic ridge modification of trace element dissolved fluxes abstract we have carried out an icp ms study of the distributions of trace elements fe ca mg al mn cu zn v as cr co pb y mo ag sn cd and be in particulate material collected from the tag hydrothermal plume 26 n mid atlantic ridge to examine the extent to which fluxes of dissolved trace elements emitted from hydrothermal vent fluids are balanced by the precipitation of associated particulate phases comparison of particulate trace element distributions with particulate fe concentrations within the neutrally buoyant plume reveals that the distribution of trace elements within the plume is controlled by the following processes i co precipitation from vent fluids ii scavenging from seawater and iii preferential settling from the plume and oxidative dissolution within the water column for y and be continuous scavenging from seawater appears to be important whereas for v as and cr it appears that conditions suitable for uptake into particles may be restricted to the buoyant portion of the hydrothermal plume from a comparison of trace element fe ratios in the particles and associated mid atlantic ridge vent fluids it appears that for many elements e g cu co ag pb al cd be and zn the flux of dissolved material from vent fluids is matched closely by the precipitation of hydrothermal particulate phases of the various elements studied here hydrothermal activity only appears to act as a significant source for dissolved ca and dissolved mn

chemical evolution of mid ocean ridge hot springs abstract chemical analyses yielding elemental concentrations of major and minor elements of four hot springs on the east pacific rise at 21 n and 10 hot springs from the southern trough of the guaymas basin gulf of california provide a basis for thermodynamic modeling of conductive cooling of the hydrothermal endmembers mixing of the hydrothermal endmember with seawater and reaction of an epr type fluid with sediment of bulk chemical composition corresponding to unaltered sediment from dsdp hole 477 in the guaymas basin results of the calculations indicate that conductive cooling of endmember fluids within closed chimneys and conduits accounts for the solution composition of one vent on the east pacific rise and several vents in guaymas basin mixing of the hydrothermal fluids with seawater yields a prediction of mineral assemblages closely approximating those observed in samples of chimneys from the east pacific rise and drill cores in guaymas basin the hypothesis that guaymas basin hydrothermal fluids result from interaction of an epr type fluid with sediment cover in guaymas basin is supported by calculations which predict an increase in ph to a value similar to guaymas basin fluids an order of magnitude decrease in metal concentrations and an excellent agreement between predicted mineral assemblages as a function of extent of interaction with sediment and observed mineral assemblage distribution with depth

soluble iron conservation and colloidal iron dynamics in a hydrothermal plume abstract iron fe limits or co limits primary productivity and nitrogen fixation in large regions of the world s oceans and the supply of fe from hydrothermal vents to the deep ocean is now known to be extensive however the mechanisms that control the amount of hydrothermal fe that is stabilized in the deep ocean and thus dictate the impact of hydrothermal fe sources on surface ocean biogeochemistry are unclear to learn more we have examined the dispersion of total dissolvable fe tdfe dissolved fe dfe and soluble fe sfe in the buoyant and non buoyant hydrothermal plume above the beebe vent field caribbean sea we have also characterized plume particles using electron microscopy and synchrotron based spectromicroscopy we show that the majority of dfe in the beebe hydrothermal plume was present as colloidal fe cfe dfe sfe during ascent of the buoyant plume a significant fraction of particulate fe pfe tdfe dfe was lost to settling and exchange with colloids conversely the opposite was observed in the non buoyant plume where pfe concentrations increased during non buoyant plume dilution cfe concentrations decreased apparently due to colloid aggregation elemental mapping of carbon oxygen and iron in plume particles reveals their close association and indicates that exchanges of fe between colloids and particles must include transformations of organic carbon and fe oxyhydroxide minerals notably sfe is largely conserved during plume dilution and this is likely to be due to stabilization by organic ligands in contrast to the more dynamic exchanges between pfe and cfe this study highlights that the size of the sfe stabilizing ligand pool and the rate of iron rich colloid aggregation will control the amount and physico chemical composition of dfe supplied to the ocean interior from hydrothermal systems both the ligand pool and the rate of cfe aggregation in hydrothermal plumes remain uncertain and determining these are important intermediate goals to more accurately assess the impact of hydrothermalism on the ocean s carbon cycle this article is part of a special issue entitled cycles of trace elements and isotopes in the ocean geotraces and beyond edited by tim m conway tristan horner yves plancherel and aridane g gonzalez

oceanic spreading center generated basaltic crust and associated sulfidic and carbonate rich hydrothermal deposits in the archean ca 3 ga north spirit lake greenstone belt ontario canada detailed mapping of a portion of the north spirit lake greenstone belt reveals a basal basaltic volcanic unit ca 3 ga with a komatiitic component and strong major and trace element geochemical affinity with typical mid ocean ridge basalts e g n morb the overlying transitional unit includes basaltic tuffs which have close geochemical affinity to the underlying basalts and to n morb interbedded with and overlying the tuffs is a thin laterally continuous sulfide rich unit with chert interbeds which is in turn overlain by interbedded carbonate chert and iron rich sedimentary rocks the chemical sedimentary rocks of the transitional unit display rare earth element ree patterns and positive eu anomalies consistent with derivation from fluids associated with submarine hydrothermal vent fields the sulfide unit is interpreted to represent proximal hydrothermal vent deposits derived from black smoker activity near a spreading center the overlying carbonate and chert mounds and beds are interpreted as hydrothermal deposits formed at lower temperatures in a more distal setting relative to the spreading center the carbonate deposits may have formed in an environment analogous to that of the lost city hydrothermal field kelley et al 2001 where abundant chimneys dendrites and beds of carbonate are produced 15 km from the mid atlantic rift axis the basal volcanic unit consequently is interpreted as ocean floor basalts formed at an archean spreading center with the basaltic tuffs representing the last volcanic emanations and with the chemical sediments representing hydrothermal vents deposits both proximal and distal to the spreading center the capping siliciclastic unit likely is part of an accretionary wedge possibly representing ocean closure after a protracted seafloor spreading episode the sedimentary rocks were derived in part from a weathered tonalite trondhjemite granodiorite source the supracrustal rocks of the north spirit lake greenstone belt provide an unusually clear window into some tectonic activity on the primitive earth including evidence for the existence of ocean floor basalts proximal and distal hydrothermal activity and possibly a protracted cycle of ocean opening and destruction

temporal variability of the hydrothermal plume above the kairei vent field 25 s central indian ridge 1 continuous profiling of the nonbuoyant plume above a hydrothermal vent site can be used to determine the interaction between the plume formed by venting high temperature fluids and changing background temperature salinity and current fields over a tidal cycle we have conducted a 12 hour monitoring of the nonbuoyant plume above the kairei vent field 25 s central indian ridge the depth of the plume particle maximum varies significantly in the water column from 2150 m to 2350 m but remains strongly associated with the 2 36 987 potential density isopycnal we have used the interaction between two unrelated physical oceanographic phenomena to isolate the section of the time series record most suitable for determining the heat flux of the kairei source on the basis of the rise height of the plume to neutral buoyancy at the start of the time series internal waves are observed with a period similar to the calculated buoyancy period n 1 about 3 hours no consistent relationship is observed between the rise height of the plume and the calculated heat flux for the last 6 hours of the time series isopycnal surfaces are compressed above a strongly developed nonbuoyant plume such that the calculated buoyancy period is less than that of the internal waves a more constant heat flux can be calculated on the basis of the plume rise height from this part of the record

particle geochemistry in the rainbow hydrothermal plume mid atlantic ridge we report the analysis of 18 large volume 500 1500 l in situ filtered samples of particulate material from the largest hydrothermal plume on the mid atlantic ridge overlying the ultramafic hosted rainbow hydrothermal field at 36 deg 14 n measured particulate iron concentrations reach 614 nm high concentrations of particulate fe oxyhydroxides result from the extremely high fe concentration 24 mm and fe h2s ratio 24 of the vent fluids and persist to at least 10 km away from the vent site due to the advection of plume material with the ambient along axis flow two of the nine pairs of pump deployments appear to have intercepted the buoyant or otherwise very young portion of the hydrothermal plume these samples are characterized by anomalously compared to neutrally buoyant plume samples high concentrations of mg u and chalcophile elements and low concentrations of mn ca v y and the rare earth elements ree within the neutrally buoyant plume elemental distributions are largely consistent with previously observed behaviors preferential removal of chalcophile elements conservative behavior of oxyanions p v and u and continuous scavenging of y and the ree this consistency is particularly significant in light of the underlying differences in fluid chemistry between rainbow and other studied sites chalcophile elements are preferentially removed from the plume in the order cd zn co cu phosphorus iron and vanadium iron ratios for the neutrally buoyant plume are consistent with global trends with respect to the concentration of dissolved phosphate in ambient seawater comparison of buoyant and neutrally buoyant plume ratios with data from hydrothermal sediments underlying the rainbow plume cave et al 2002 indicates however that while p fe ratios are indeed constant v fe ratios increase progressively from early stage plume particles to sediments ree distributions in the buoyant and neutrally buoyant plume appear most consistent with a continuous scavenging process during dispersion through the water column

sources of ree in sediment cores from the rainbow vent site 36 14 n mar a geochemical investigation was carried out on two sediment cores collected at 2 and 5 km from the rainbow hydrothermal vent site bulk sediment compositions indicate that these cores record clear enrichments in fe cu mn v p and as from hydrothermal plume fallout cave et al 2002 cave r r german c r thomson j nesbitt r w 2002 fluxes to sediments underlying the rainbow hydrothermal plume at 36 14 n on the mid atlantic ridge geochim cosmochim acta 66 11 1905 1923 sequential dissolution of the bulk sediments has been used to discriminate between a leach biogenic and oxy hydroxide component and a residual phase detrital and sulphide sulphate fractions major element data al fe ti mn mg ca si and index reveal that the hydrothermal input as recorded in the leach phase is much stronger than apparent from bulk sediment analyses alone ree patterns for the leach phase record contributions from both biogenic carbonate mimicking seawater ree patterns and hydrothermal oxy hydroxides with the latter exhibiting positive eu anomalies hydrothermal derived and negative ce anomalies seawater derived based on major element and ree data the residue contains contributions from aeolian dust input local morb material and a hydrothermal component ternary ree mixing calculations indicate that most of the ree within the residual fraction 80 is derived from hydrothermal material while detrital contributions to the ree budget as deep sea clay and volcanic debris are

processes affecting the isotopic composition of dissolved iron in hydrothermal plumes a case study from the vanuatu back arc abstract hydrothermal discharge is one of multiple fe sources contributing to the marine dissolved fe budget but its relative importance remains controversial and largely unconstrained isotopic characterization of fe sources and mass balance calculations are considered as a potential tool to unravel the complex interplay of various fe fluxes but require a more profound knowledge of the processes that fractionate fe isotopes in hydrothermal plumes we present dissolved fe isotope data from two buoyant plumes and profiles traversing the non buoyant plume above the nifonea vent field in the vanuatu back arc our findings support opposing controls from precipitation of fe sulfides and fe oxyhydroxides that either enrich the heavy or the light isotopes within the residual dissolved fe fraction but also suggest significant influence from size partitioning of oxidized fe following precipitation as well as potential effects from organic complexation at low aggregation of precipitated fe oxyhydroxides or stabilization of significant fe iii aq dissolved 56 fe is only marginally affected by fe ii oxidation which strengthens the role of fe sulfide precipitation during early plume rise in determining the isotope signature of hydrothermal fe exported to the open ocean dissolved 56 fe range from 0 73 0 05 to 0 16 0 05 and suggest that sulfide rich basalt hosted hydrothermal systems and slow oxidation kinetics in the pacific favor export of stabilized dissolved fe with heavier 56 fe values than the true vent fluids 56 fe of 0 5

uranium enrichment in metalliferous sediments from the mid atlantic ridge abstract previous studies of metal rich sediments at mid ocean ridge spreading centres have suggested that u fe ratios are relatively constant from site to site a suite of cores from the mid atlantic ridge has been analysed for u and fe content and most samples exhibit constant u fe ratios sulphide bearing parts of one core however contain excess u compared with that observed in other metalliferous sediments but apparently only during oxidative alteration of pyrite phases fission track registration has demonstrated that this excess u is intimately associated with sulphide grains in the sediment scanning electron microscope examination indicates that this u enrichment is limited to very small areas within the oxidation layer and is associated with an enhanced p concentration ion probe analyses allow semi quantitative analyses of various elements through a u rich grain the observed distribution of u coupled with its specific enrichment suggests that microbial mediation might be controlling this enrichment u fe ratios in fully oxidised tag sediments are constant and approximately an order of magnitude higher than in young plume particulates this discrepancy is attributed to a second type of post depositional u enrichment producing an homogeneous distribution of u throughout the sediment

composition and sedimentation of hydrothermal plume particles from north cleft segment juan de fuca ridge in 1990 and 1991 particles from buoyant and neutrally buoyant hydrothermal plumes above hydrothermal vents at the north cleft segment of the juan de fuca ridge were sampled to study their changing composition and fluxes away from the vent field in the rising buoyant plume 75 of the p v cr and as scavenging from seawater by hydrothermal precipitates occurs in the first 50 m above the vent cu and zn are most enriched in buoyant plume particles collected from the first few meters above the vent however the degree of enrichment decreases very rapidly with increased height above the vents due to sedimentation of the more dense cu and zn rich sulfide phases using the plume data coupled with the results of our analysis of sediment trap samples we estimated that more than 99 and 99 9 respectively of the total hydrothermal fe and mn produced at the vent field are transported beyond the vent field and dispersed in the open ocean

uptake and fractionation of rare earth elements on hydrothermal plume particles at 9 45 n east pacific rise abstract particulate samples 0 45 m from a neutrally buoyant hydrothermal plume at 9 45 n on the northern east pacific rise were collected using large volume in situ filtration and analyzed for fe al mn ni and fourteen rare earth elements ree the sm fe ratio a proxy for overall ree fe and nd er light heavy ree fractionation increased moderately with decreasing particulate fe chemically the sense of these relationships matched that documented previously in the tag plume on the mid atlantic ridge german et al 1990 although particulate fe was about 10 fold lower at 9 45 n spatial trends relative to the vent source however were opposite of expectation because slow fe ii oxidation and fe iii colloid aggregation over this interval led to increased particulate fe 10 26 nm with distance from source field and sherrell submitted after subtraction of non plume background particle composition plume particles at 9 45 n and tag had indistinguishable ranges of light ree enriched fractionation relative to ambient seawater and had very similar sm fe therefore kd for fe oxyhydroxides demonstrating that plume particles in both oceans reflect to a first degree the local seawater ree composition within plume ree variations at 9 45 n were investigated using a simple mixing model which accounts for the bulk fe al mn variations in the plume using two endmembers fresh hydrothermal oxyhydroxide precipitates and ridge crest background particles composed largely of locally resuspended sediment sm fe and nd er plot linearly with mixing ratio r 0 96 implying that the observed ree trends result from mixing of these two endmembers extrapolation to the composition of pure hydrothermal precipitates suggests that nd er is fractionated relative to seawater by a factor of 1 8 during adsorption onto fresh fe oxyhydroxide particles the ridge crest background particles are 5 fold higher in sm fe and nd er is 2 49 relative to seawater partly a result of enriched terrigenous component in the resuspended matter a reinterpretation of ree at tag reveals that positive curvature in ree vs fe plots argued previously to reflect continuous ree uptake i e increasing kd german et al 1990 may result from local depletion of the dissolved ree pool by partitioning onto fe particles at fe 100 nm similar drawdown effects could contribute to the variable degrees of curvature observed for all seawater source particle reactive species in plumes that are sampled at high particulate fe concentration in sum ree behavior in hydrothermal plumes is more consistent with equilibrium adsorption and mixing of distinct particle types than with kinetic uptake control precise measurements of rees in modern ridge crest metalliferous sediments could be compared to the endmember composition calculated from the plume data to evaluate long term changes in ree of the hydrothermal component

coastal katabatic winds imaged by sar 1 sea surface imprints of coastal katabatic winds are observed on a radarsat 1 synthetic aperture radar sar standard mode image off the u s west coast taken on january 21 2003 the katabatic wind pattern is shown in the sar image as a striking finger like bright dark region that mirrors the coastal mountain topography we simulate the low level atmospheric circulation using the numerical weather model mm5 with a triply nested grid technique the model simulation reproduces the finger like katabatic wind pattern at the sar imaging time katabatic wind is strongest in the morning when the surface temperature gradient between ocean and land reaches a maximum the sea surface wind simulated by the mm5 model and that derived from the calibrated sar normalized radar cross section are in good agreement the katabatic wind variation along the coastline is between 5 8 ms 1 and the longest wind finger stretches over 20 km offshore

global environmental effects of large volcanic eruptions on ocean chemistry evidence from hydrothermal sediments odp leg 185 site 1149b a sr nd pb isotope investigation has been carried out on sediments overlying the cretaceous oceanic crust at odp leg 185 site 1149b the sediments biogenic carbonate and siliceous clays contain two horizons with high excess concentrations of fe zn cu and pb these horizons are both characterized by rare earth element patterns that are concave upwards and exhibit both negative ce and positive eu anomalies comparable to those from modern hydrothermal plume particles and sediments however pb isotope signatures differ significantly between the two metal rich horizons metal rich sediments in the lower part of unit iv have pb isotopes that lie on a mixing line between seawater and local oceanic crust end members which is consistent with a hydrothermal fall out originating from a local oceanic spreading centre in contrast sediments from the upper part of unit iv have much more radiogenic pb isotope ratios that cannot be related readily to local end members off axis hydrothermal vent clays oceanic crust or large igneous provinces lip their age corrected pb isotope compositions do however overlap with basalts from the parana etendeka lip evidence for related environmental effects include a drastic biotic change higher oceanic 13c values and more radiogenic seawater 87sr 86sr we estimate that the parana etendeka lip released 1 1019 g of carbon into the atmosphere as co2 corresponding to pb and s degassing fluxes of 1 109 g a 1 and 15 1012 g a 1 respectively the study demonstrates that pb isotopes when combined with other geochemical parameters are ideal tools for detecting and tracing lip volcanism in the marine geological records

sar observation and numerical simulation of mountain lee waves near kuril islands forced by an extratropical cyclone several groups of atmospheric gravity waves agws were observed on a sentinel 1a synthetic aperture radar sar image acquired near the kuril islands in the northwest pacific ocean on june 1 2015 during the passage of an extratropical cyclone etc these waves occurred on the lee side of the mountains located on the islands both diverging and transverse waves with wavelengths ranging between 20 and 30 km are shown as alternating bright dark patterns in the sar image for the diverging waves there exists a prominent asymmetry in the wave motions of the two arms the moderate resolution imaging spectroradiometer and landsat 7 enhanced thematic mapper plus images acquired 5 7 h prior to the sentinel 1a pass also contain the same groups of agws the mesoscale weather research and forecasting model simulation confirms that the agws are lee waves triggered by the airflow over the islands agws are aligned perpendicular to the wind direction and locked on the lee side of the islands the life span of the waves is about two days consistent with that of the etc over the region the numerical model also successfully reproduces the main characteristics of the lee waves simulation results demonstrate that the variation in the wave parameters i e wavelength amplitude orientation wedge angle of the diverging wave and vertical propagation characteristic and the wave asymmetry of the diverging wave are mainly caused by the wind and stratification changes the smaller amplitude of the diverging wave seems to be associated with a smaller froude number

bioavailability of zinc in marine systems through time zinc is a marine nutrient that may have been limited in the early oceans estimates of marine zinc availability through time suggest that values were instead near modern during the proterozoic eon

trace element behaviour at cold seeps and the potential export of dissolved iron to the ocean seawater samples were collected by submersible above methane seeps in the gulf of guinea regab and baboon pockmarks in order to investigate the behaviour of iron fe manganese mn and rare earth elements ree during fluid seepage our aim was to determine whether cold seeps may represent potential sources of dissolved chemical species to the ocean dissolved 0 45 m filtered samples and total dissolvable unfiltered samples concentrations were determined over 50 m long vertical transects above the seafloor and at various discrete locations within the pockmarks we show that substantial amounts of fe and mn are released into seawater during seepage of methane rich fluids mn is exported almost quantitatively in the dissolved form more than 90 of total mn mean mndiss 12 11 nmol kg 12 11 nmol kg although a significant fraction of fe is bound to particulate phases the dissolved iron pool still accounts on average for approximately 20 percent of total iron flux at vent sites mean fediss 22 11 nmol kg 22 11 nmol kg this dissolved fe fraction also appears to remain stable in the water column in contrast there was no evidence for any significant benthic fluxes of pore water ree associated with fluid seepage at the studied sites overall our results point towards distinct trace element behaviour during fluid seepage with potential implications for the marine geochemical budget the absence of any dissolved ree enrichments in bottom waters clearly indicates effective removal in sub surface sediments most likely precipitation of authigenic mineral phases at cold seeps i e carbonates represents a net sink for these elements while mn appears to behave near conservatively during fluid seepage the observed relative stability of dissolved fe in the water column above seepage sites could be explained by complexation with strong organic ligands and or the presence of fe bearing sulfide nanoparticles as reported previously for submarine hydrothermal systems considering the ubiquitous occurrence of methane vents at ocean margins cold seeps could represent a previously unsuspected source of dissolved fe to the deep ocean

tracing dust input to the mid atlantic ridge between 14 45 n and 36 14 n geochemical and sr isotope study abstract a geochemical and sr isotope study was carried out on sediment cores collected from the logatchev hydrothermal vent site 14 45 n on the mid atlantic ridge with the aim of identifying aeolian inputs into the overlying water column the logatchev vent site lies beneath the ne trade winds which transport large amounts of detrital material across the north atlantic sequential dissolution of the sediments has been used to discriminate the detrital fraction from other types of sediment ree patterns for the acetic acid fraction at the logatchev site record contributions from biogenic carbonate seawater like ree pattern and oxy hydroxides which exhibit positive eu and negative ce anomalies typical of hydrothermal origin the logatchev site leach fractions have similar major element compositions to terrigenous al fe mn oxides whose ree patterns show strong positive ce and negative eu anomalies that are comparable to those of preformed fe mn oxides of continental origin based on major element and ree data and 87sr 86sr ratios 0 7197 0 7236 the residue fractions at the logatchev site contain a significant contribution from aeolian sources whose chemical composition is virtually identical to oligotrophic settling particles in the equatorial atlantic ocean in comparison residues from the rainbow hydrothermal site 36 14 n have geochemical composition controlled by hydrothermal anhydrite chavagnac v german c r milton j a palmer m r 2005 sources of ree in sediment cores from the rainbow vent site 36 14 n mar chem geol 216 329 352 they are characterised by 87sr 86sr ratios of 0 7087 0 7093 which are significantly less radiogenic than those of the saharan dust hence the data suggest 1 a significant contribution of aeolian material to the sediments at 14 45 n that is not present at 36 14 n 2 that this material is most likely of north african origin and 3 that this source of aeolian material has remained relatively constant over the last 13 kyr

on polarimetric characteristics in sar images of mesoscale cellular convection in the marine atmospheric boundary layer 1 convection is an important phenomenon in the marine atmospheric boundary layer mabl previous spaceborne radar studies of such have been limited to single polarization data and therefore their focus was on the variation in intensity of the radar return which was constrained by the existence of a single polarization image pattern representing different atmospheric and oceanic phenomena in this paper we study the polarimetric characteristics of mesoscale cellular convection mcc in the mabl using high resolution data from fully polarimetric hh vv hv and vh radarsat 2 rs 2 synthetic aperture radar sar images in conjunction with closely collocated mesoscale atmospheric model simulations to identify the mcc signatures to compare the polarimetric characteristics of mcc with those of the ocean surface our analysis also includes 641 open ocean surface quad polarization rs 2 sar images collocated with 52 national data buoy center buoys the open ocean surface sar images exhibit different polarimetric characteristics from those of mcc thus we differentiate mcc from other open ocean phenomena based on identifiable polarimetric sar characteristics

iron isotope fractionation in a buoyant hydrothermal plume 5 s mid atlantic ridge fe isotopes are a potential tool for tracing the biogeochemical redox cycle of fe in the ocean specifically it is hypothesized that fe isotopes could enable estimation of the contributions from multiple fe sources to the dissolved fe budget an issue that has received much attention in recent years the first priority however is to understand any fe isotope fractionation processes that may occur as fe enters the ocean resulting in modification of original source compositions in this study we have investigated the fe inputs from a basalt hosted deep sea hydrothermal system and the fractionation processes that occur as the hot chemically reduced and acidic vent fluids mix with cold oxygen rich seawater the samples collected were both end member vent fluids taken from hydrothermal chimneys and rising buoyant plume samples collected directly above the same vents at 5 s mid atlantic ridge our analyzes of these samples reveal that for the particulate fe species within the buoyant plume 25 of the fe is precipitated as fe sulfides the isotope fractionation caused by the formation of these fe sulfides is fe ii fes 0 60 0 12 the source isotope composition for the buoyant plume samples collected above the red lion vents is calculated to be 0 29 0 05 this is identical to the value measured in end member vent fluids collected from the underlying tannenbaum chimney the resulting isotope compositions of the fe sulfide and fe oxyhydroxide species in this buoyant plume are 0 89 0 11 and 0 19 0 09 respectively from mass balance calculations we have been able to calculate the isotope composition of the dissolved fe fraction and hypothesize that the isotope composition of any stabilised dissolved fe species exported to the surrounding ocean may be heavier than the original vent fluid such species would be expected to travel some distance from areas of hydrothermal venting and hence contribute to not only the dissolved fe budget of the deep ocean but also it s dissolved fe isotope signature

observation and interpretation of wave clouds over macquarie island images obtained from two noaa avhrr overpasses of macquarie island in october 1985 show pronounced cloud bands associated with trapped lee waves one image reveals striking evidence of an abrupt change in the propagating wave mode the structure and evolution of the waves is interpreted using a linear wave model coupled with radiosonde data obtained from the island the model successfully forecasts the mode change and accurately predicts the associated wavelengths an interpretation of the difference between the amplitudes of the two modes is also provided infrared channel measurement of the temperature of the cloud in the wave crests yields a useful constraint on the cloud height

geochemistry of vent fluid particles formed during initial hydrothermal fluid seawater mixing along the mid atlantic ridge we present geochemical data of black smoker particulates filtered from hydrothermal fluids with seawater dilutions ranging from 0 99 results indicate the dominance of sulphide minerals fe cu and zn sulphides in all samples taken at different hydrothermal sites on the mid atlantic ridge pronounced differences in the geochemistry of the particles between logatchev i and 5 s hydrothermal fields could be attributed to differences in fluid chemistry lower metal sulphur ratios me h2s 1 compared to logatchev i result in a larger amount of particles precipitated per liter fluid and the occurrence of elemental sulphur at 5 s while at logatchev i fe oxides occur in larger amounts systematic trends with dilution degree of the fluid include the precipitation of large amounts of cu sulphides at a low dilution and a pronounced drop with increasing dilution moreover fe sulphides or oxides precipitation increases with dilution of the vent fluid by seawater geochemical reaction path modeling of hydrothermal fluid seawater mixing and conductive cooling indicates that cu sulphide formation at logatchev i and 5 s mainly occurs at high temperatures and low dilution of the hydrothermal fluid by seawater iron precipitation is enhanced at higher fluid dilution and the different amounts of minerals forming at 5 s and logatchev i are thermodynamically controlled larger total amounts of minerals and larger amounts of sulphide precipitate during the mixing path when compared to the cooling path differences between model and field observations do occur and are attributable to closed system modeling to kinetic influences and possibly to organic constituents of the hydrothermal fluids not accounted for by the model

evidence for episodic oxygenation in a weakly redox buffered deep mid proterozoic ocean abstract over the last two decades popular opinion about prevailing conditions in the mid proterozoic deep ocean has evolved from fully oxygenated to globally euxinic sulfidic to a more heterogeneous stratified water column with localized pockets of euxinia existing in predominantly iron rich ferruginous deep waters the animikie basin in the lake superior region has been essential in shaping our view of marine redox evolution over this time period in this study we present a multi proxy paleoredox investigation of previously unanalyzed strata of the late paleoproterozoic animikie basin using drill cores through the 1 85 ga stambaugh formation paint river group in the iron river crystal falls district of the upper peninsula of michigan usa based on previous tectonic reconstructions and analysis of sedimentary regimes the iron river crystal falls section captures strata from among the deepest water facies of the animikie basin in contrast to previous work on sedimentary rocks in this basin we find evidence from iron speciation trace metal and mo isotope data for episodes of at least local deep water oxygenation within a basin otherwise dominated by ferruginous and euxinic conditions while trace metal enrichments and iron speciation data suggest predominantly anoxic conditions the occurrence of mn rich intervals up to 12 3 wt mno containing abundant mn fe carbonate and a wide range of mo isotope data with extremely negative values 98 95mo 1 0 to 1 1 record the shuttling of mn oxides from surface waters through oxic or suboxic waters to the sediment water interface we propose that such conditions are analogous to those of locally restricted modern and holocene basins in the baltic sea which receive episodic inflow of oxygenated water producing similar geochemical signatures to those observed for the animikie basin we argue that the mid proterozoic was characterized by a lack of a strong redox buffer low sulfide ferrous iron and oxygen contents and thus was vulnerable to dramatic and at least local redox shifts including briefly oxygenated bottom waters a refined view of the mid proterozoic ocean is emerging one that was still predominantly anoxic but marked by regional heterogeneities and short term redox variability that may in part reflect a transitional state between prevailingly anoxic archean and predominantly oxic phanerozoic oceans

an estimate of the efficiency of the iron and manganese driven dissolved inorganic phosphorus trap at an oxic euxinic water column redoxcline 1 geochemical records suggest the ocean has undergone periods of at least partial deeper ocean anoxia or euxinia two counteracting feedback loops involving redox control of the dynamics of the phytoplankton nutrient dissolved inorganic phosphorus dip might coexist helping to stabilize the redox state of the atmosphere and oceans this concept implies that during deeper ocean anoxia the dip transfer from the deep anoxic into the oxic surface ocean is uninhibited by processes taking place at the redoxcline this implicit assumption requires testing because iron fe and manganese mn dynamics at oxic anoxic water column redoxclines have the potential to form a dip trap inhibiting dip transport from anoxic deep into oxic surface waters using a time series data set of fe mn dip and dissolved oxygen distributions in the eastern gotland basin of the baltic sea we provide estimates of the efficiency of this fe and mn driven dip trap this efficiency was estimated by calculating the ratios of 1 the downward flux of dip adsorbed onto and or coprecipitated into the settling authigenic fe and mn rich particles just above the redoxcline and 2 the upward turbulent diffusive dip flux across the redoxcline depending on the assumed particle densities we find average 1 sd trapping efficiencies of 0 38 0 29 and 0 63 0 45 the efficiencies are significant in that they seem to impact cyanobacterial dynamics in the central baltic sea we discuss possible implications of the trapping mechanism for and propose two hypotheses relating to the potential importance of fe controlled dip trapping at redoxclines during ocean anoxic events

surface sediment geochemistry and hydrothermal activity indicators in the dragon horn area on the southwest indian ridge abstract the fluids found in sulfide producing hydrothermal vents are rich in ore forming elements these elements usually precipitate as solid particles that are dispersed by the plumes and deposited as sediments around the hydrothermal field to assess how the geochemical features of such sediments may be used in seafloor sulfide exploration this study analyzed the surface sediment geochemistry in the dragon horn area on the southwest indian ridge the results indicate that the sediments are mainly composed of pelagic material basalt and ultramafic debris mn fe oxyhydroxides and mn oxides hydrothermal components the debris content in this area is lower than that in sediments found at fast and medium spreading mid ocean ridges with relatively high amounts of ultramafic components indicating that ultramafic rock outcrops are present in the study area precipitated hydrothermal elements in the sediments exhibit zonation in the spatial distributions of zn cu fe and mn the sediments proximal to the hydrothermal field display high cu zn and fe contents and low mn contents hydrothermal cu and zn phases occurred within a limited range of the hydrothermal field and zn was found to precipitate earlier than cu during dispersal from the plume hydrothermal fe distributed similarly with cu spatially but with a larger dispersion distance hydrothermal mn was able to migrate beyond the ridge valley to precipitate in the ridge flank sediments two hydrothermal cu and zn anomalies were identified on the south ridge flanks which suggest the presence of undiscovered hydrothermal field the sediments in the study area are additionally characterized by relatively low mn contents and high fe mn molar ratios the relatively reducing environment of the plume may facilitate the migration of hydrothermal mn over large distances which probably accounts for the lower mn contents in the sediments the cu cu fe molar ratio model was proposed to identify mafic and ultramafic related hydrothermal field the low cu fe molar ratios and ree characteristics of the sediments suggest that ultramafic rocks are likely not the only source of the ore forming element for hydrothermal mineralization low temperature diffuse flow on the ridge flanks of the study area probably results from serpentinization of ultramafic rocks

geology and lithogeochemistry of hydrothermal mudstones from the upper block near the duck pond volcanogenic massive sulfide vms deposit newfoundland canada evidence for low temperature venting into oxygenated mid cambrian seawater pyrite and pyrrhotite rich mudstones are spatially associated with cambrian 512 509 ma volcanogenic massive sulfide vms deposits throughout the tally pond group central newfoundland canada at the duck pond mine sulfide rich mudstones are hosted within a weakly mineralized upper block that structurally overlies the deposit but is older 513 versus 509 ma the mudstones are laminated 10 30 cm thick and pyrite and pyrrhotite rich and occur along pillow lava selvages or in between pillow lavas rhyolite flows and volcaniclastic rocks the mudstones are laterally extensive and proximal to the mudstone host rocks are hydrothermally altered to epidote quartz chlorite basalt host and sericite quartz rhyolite host lithogeochemical data for the sulfide rich mudstones reflect the varying contributions of elements from sedimentary detritus hydrothermal discharge and hydrogenous scavenging from middle cambrian seawater the mudstones have minor detrital element abundances and significant hydrothermal element enrichments i e elevated fe2o3 s pb zn cu and ba concentrations high fe al ratios the hydrothermal mudstones are also enriched in oxyanions i e p2o5 u v cr ni co and hg interpreted to have been enriched via oxidative scavenging from seawater by fe oxide oxyhydroxide particles the mudstones also have ree y signatures similar to modern oxygenated seawater with high y ho and negative ce anomalies ce ce 0 40 0 86 average 0 58 which correlate with adsorbed oxyanion concentrations the low eu eu 1 02 1 86 average 1 22 in the mudstones suggest that they were deposited from low temperature 250 c fe rich hydrothermal fluids that likely formed a buoyant plume into an oxygenated water column the ree y oxyanion signatures suggest that the particles within the hydrothermal plume had sufficient residence time to scavenge oxyanions from seawater and inherit a middle cambrian seawater signature the predominant seawater ree y oxyanion signature in the duck pond upper block sulfide rich mudstones suggests that they are distal hydrothermal sedimentary rocks that could have formed up to 10 km from their original vent sources correspondingly to utilize hydrothermal mudstones as vectors to mineralization in the tally pond belt and similar belts globally it is critical to identify vent proximal samples that have hydrothermal signatures i e high fe al base metals ba s with subdued seawater and adsorption signatures i e chondritic y ho low p2o5 ni u co cr v and hg indicating minimal residence time in the water column and deposition proximal to the vent

near field variability of the tag non buoyant plume 26 n mid atlantic ridge we report the initial results of a nine hour monitoring of the non buoyant plume above the tag hydrothermal vent field at 26 n on the mid atlantic ridge a ctd conductivity temperature and pressure and nephelometer particle sensor were continuously raised and lowered through the non buoyant plume for nine hours at a site situated 100 m south of the hydrothermal mound this method permits a detailed record of the variability of the non buoyant plume close to the vent field to be made our results show that the particulate maximum of the non buoyant plume appears 150 m lower in the water column at the start and end of the record compared with profiles recorded towards the middle of the record a corresponding structure also appears in the temperature and salinity records with the result that the plume particle maximum resides on the 27 8035 isopycnal throughout modelling of the rise height of an axisymmetric plume can only account for 95 m of the variability in the final level of neutral buoyancy plume bending due to currents is a likely explanation for the recorded temporal variability

the geochemistry of atlantic hydrothermal particles particles were collected from the dilute portion of neutrally buoyant hydrothermal plumes from four mid atlantic ridge sites mark 23 n tag 26 n broken spur 29 n lucky strike 37 n comparison of data from proximal portions of the tag atlantic german et al 1991 this study and north cleft pacific feely et al 1994 plumes show that oxyanion e g v scavenging is more efficient at tag possibly due to a higher proportion of fe removed as sulfides at north cleft and or the more vigorous mixing in the high energy tag buoyant plume chalcophile elements e g cu show two stage removal they are precipitated as sulfides during initial mixing of vent fluids with seawater and are sedimented from the buoyant plume in the dilute plume they are scavenged from seawater by fe oxyhydroxides the ree show continued scavenging in the neutrally buoyant plume and lower levels in 1993 samples compared to 1988 samples german et al 1990 suggesting that the amount of scavenging is related to particle recycling

hydrography and high temperature heat flux of the rainbow hydrothermal site 36 14 n mid atlantic ridge on the basis of an extensive set of conductivity temperature depth lowered acoustic doppler current profiler ladcp and nephelometry profiles and tow yos the hydrography flow field and particle plume of the rainbow hydrothermal site on the mid atlantic ridge are analyzed in the rift valley the water column is less dense and stratified than both eastern and western off ridge water with t s characteristics consistent with inflow across a sill from the east the buoyant hydrothermal plumes rise into a strong boundary current flowing along the slope of a topographic high which partially blocks the rift valley below 1950 m the bulk of the neutrally buoyant plume is advected across a sill which forms both the narrowest and the shallowest part of the valley and acts as a hydraulic control point for the flow below 2000 m large amplitude internal waves consistent with tidal forcing are observed near the sill but ladcp measurements suggest that the tidal signal is not strong enough to lead to flow reversal at plume depth above 2000 m the mean current across the topography generates lee waves which radiate energy upward and downstream density averaged light scattering profiles show the hydrothermal particle plume to be gaussian in depth even in the near field where many of the individual profiles are characterized by multiple peaks and the horizontal variability is highest the temperature anomalies associated with the mean near source particle plume are of order 5 10 3 c that is the plume is cold fresh as expected from the background hydrography of the deep atlantic using the flow field light scattering and hydrographic anomaly observations the heat flux associated with the hydrothermal particle plume at rainbow is estimated to lie between 1 and 5 gw

field and laboratory studies of metal uptake and release by hydrothermal precipitates data for suspended particles from hydrothermal plumes on the mid atlantic ridge mar support uptake of dissolved v and as during formation of fe oxides and release of cu and cd during alteration of sulfides to complement these field observations we carried out laboratory time series experiments to determine the stability of v as cu and cd in precipitates from hydrothermal plumes on the mar and juan de fuca ridge for v and as the metal fe ratio in plume particles remained uniform after sampling in contrast to v and as particulate cu and cd values decreased relative to fe over time in laboratory studies using both plume particles and mound derived sulfides the combined field and laboratory results show that scavenging is an important removal mechanism for seawater v and as whereas oxidative dissolution of hydrothermal precipitates in seawater adds cu and cd to the ocean

synergistic use of satellite observations and numerical weather model to study atmospheric occluded fronts synthetic aperture radar sar images reveal the surface imprints of atmospheric occluded fronts an occluded front is characterized as a low wind zone located between and within two zones of higher winds blowing in the opposite directions on the left and right sides of the occluded front a group of four sar images reveal that the width of an individual occluded frontal zone and the wind magnitudes outside fronts vary greatly from case to case in this paper we performed a case study to analyze an occluded front observed by an environmental satellite envisat advanced sar and ascat scatterometer along the west coast of canada on november 24 2011 the two way interactive triply nested grid 9 3 1 km weather research and forecasting wrf model was utilized to simulate the evolution of the occluded front the occluded front moved toward the east during a 24 h model simulation and the movement between 18 00 and 21 00 utc matched the occluded front positions derived from the concurrently collected surface weather maps from the national oceanic and atmospheric national weather service archives the wrf simulated low wind zone associated with the occluded front and ocean surface wind speed match well with the sar and scatterometer wind retrievals high wind outside the front zone became weaker during the front evolution whereas the width of the occluded frontal zone was contracted laterally analysis of the wrf model derived potential temperature field suggests that the occlusion process occurred below the 800 mb level the structure of the occluded front studied here not only follows the conventional conceptual model and also supports the findings of a novel wrap up conceptual model for an atmospheric frontal occlusion process

the rainbow hydrothermal plume 36 15 n mar the rainbow hydrothermal plume was discovered during a recent geophysical survey along 200 km of the mid atlantic ridge mar sw of the azores triple junction in which at least seven new sites of hydrothermal activity were identified here we present the first hydrographic study of the rainbow plume 36 15 n the strongest of the features located during that survey the plume is detectable from real time in situ nephelometer anomalies and extends 10 15km w e in a non transform discontinuity ntd between two adjacent ridge segments maximum anomalies in the rainbow plume indicate particle enrichments at least as large as those seen directly above the trans atlantic geotraverse tag vent field 26 n mar analysis of hydrographic data indicates a vent source at rainbow with a thermal output of up to 98 mw representing 140 of the thermal output previously attributed to tag both lines of evidence indicate the rainbow plume to be the strongest such feature yet found on the mar

sea surface imprints of coastal mountain lee waves imaged by synthetic aperture radar 1 a group of mountain lee waves is observed on an envisat advanced synthetic aperture radar sar image on the lee side of mountain laoshan 1133 m along the yellow sea coast of china the lee waves are shown as alternating bright and dark patterns on the sar image indicating the ocean surface wind oscillation associated with the atmospheric wavefield the horizontal wind variation between wave crest and trough is from 7 to 17 m s a moderate resolution imaging spectroradiometer image acquired about 8 5 h prior to the sar pass also showed the same group of standing lee waves the cloud pattern matches the high wind pattern in the sar derived wind image the mesoscale weather research and forecasting wrf model is used to simulate the lee wave phenomenon we run the triply nested grid model with the highest horizontal resolution of 1 km the wrf model successfully captures the characteristics of the lee wave the waves are generated by the terrain forcing and the wave induced perturbation propagates very strongly upward to the 500 hpa level the event lasts about 24 h based on the wrf model wind results we run a radar imaging model to simulate the sar observation the normalized radar cross section nrcs variations induced by the lee wave are compared between the radar simulation and the actual sar observation reasonable agreement is reached

analysis of coastal lee waves along the coast of texas observed in advanced very high resolution radiometer images we examine a group of wave like cloud patterns that occurred along the coast of texas on a national oceanic and atmospheric administration satellite advanced very high resolution radiometer ir images taken on january 22 1999 these wave like cloud patterns were interpreted to be signatures of a coastal lee wave packet on the basis of simultaneous field observations and theories developed by zheng et al 1998a the wave packet contains 13 waves with crest lines generally parallel to the coastline the lengths of leading wave crest lines are longer than 500 km the average wavelength is 9 5 km ranging from 6 2 to 14 7 km the width of the horizontal distribution band of the wave packet is as wide as 113 km this case represents the most energetic coastal lee wave packet that has ever been reported

hydrothermal sediments record changes in deep water oxygen content in the se pacific the distribution of redox sensitive metals in sediments is potentially a proxy for past ocean ventilation and productivity but deconvolving these two major controls has proved difficult to date here we present a 740 kyr long record of trace element concentrations from an archived sediment core collected at 15 s on the western flank of the east pacific rise epr on 1 1 myr old crust and underlying the largest known hydrothermal plume in the world ocean the downcore trace element distribution is controlled by a variable diagenetic overprint of the inferred primary hydrothermal plume input two main diagenetic processes are operating at this site redox cycling of transition metals and ferrihydrite to goethite transition during aging the depth of oxidation in these sediments is controlled by fluctuations in the relative balance of bottom water oxygen and electron donor input organic matter and hydrothermal sulfides these fluctuations induce apparent variations in the accumulation of redox sensitive species with time subsurface u and p peaks in glacial age sediments in this and other published data sets along the southern epr indicate that basin wide changes in deep ocean ventilation in particular at glacial interglacial terminations ii iii iv and v alter the depth of the oxidation front in the sediments these basin wide changes in the deep pacific have significant implications for carbon partitioning in the ocean atmosphere system and the distribution of redox sensitive metals in ridge crest sediment can be used to reconstruct past ocean conditions at abyssal depths in the absence of alternative proxy records

hydrothermal scavenging on the juan de fuca ridge 23othxs 10be and rees in ridge flank sediments abstract we have investigated the geochemistry of a hydrothermally enriched sediment core recovered from the western flank of the n cleft segment juan de fuca ridge 8km west of the megaplume area previously identified near 45 n the core contains varying biogenic lithogenic and hydrothermal components as reflected in caco3 al and fe contents respectively horizons of pronounced hydrothermal input in core top sediments and at depth exhibit increased concentrations of fe cu zn and pb and shifts in pb isotopic compositions toward nonradiogenic morb hydrothermal values ree concentrations co vary with hydrothermal fe down core and shale normalised ree distribution patterns exhibit both negative ce anomalies and positive eu anomalies indicative of input from plume particle fall out unsupported 230thxs activities down core are consistent with continuous slow sediment accumulation rates of 0 54 cm ky for 200 ky since the deposition of the deeper fe rich horizon 10be 0 and 9be isotope concentrations also co vary with hydrothermal fe down core and exhibit 10 be o 9 be ratios which approach that of pacific ocean deep water indicative of a seawater scavenging source 10 be 0 230 oth xs 0 ratios throughout most of core gc88 6 are greater than mean pacific ocean values indicating that hydrothermal scavenging can lead to significant net removal of dissolved 10be into ridge flank sediments

the rainbow vent fluids 36 14 n mar the influence of ultramafic rocks and phase separation on trace metal content in mid atlantic ridge hydrothermal fluids fluids were collected from the rainbow vent field 36 14 n on the mid atlantic ridge mar during the 1997 diving flores cruise this vent field in ultramafic rocks at a depth of 2300 m is composed of 10 black smokers emitting acidic ph 2 8 fluids at 365 c the low ph of the hot temperature rainbow fluids likely results from seawater ultramafic rock interaction that releases h ions into reducing hydrothermal fluids fluid chemistry is strongly influenced by phase separation generating cl rich brines clem 750 mm strongly enriched with mn fe co ni cu zn ag cd cs pb y and rare earth elements ree ree and transition metal abundance particularly fe and mn in the rainbow fluids is dramatically higher than in other mar fluids the abundance of trace element and ree enrichment is due to the greater solubility of these elements that is strongly favored by cl complexation at low ph and high temperature conditions chondrite normalized ree patterns show strong lree enrichment with evidence of the typical eu anomaly this ree partitioning suggests that either 1 ultramafic rocks represent only a part of rocks leached during hydrothermal alteration and or 2 that the unique rainbow fluid temperature ph and redox state issued from the ultramafic character of leached substratum can produce unique ree partitioning

topographic control of a dispersing hydrothermal plume deep sea hydrothermal vents represent a major source of heat and chemicals to the oceans and support endemic chemosynthetic biological communities to fully understand the impact of hydrothermal activity upon the oceans however requires investigation of both the physical and the biogeochemical processes which are active in hydrothermal plumes and which serve to determine the net hydrothermal flux to the oceans we have recently conducted a detailed multidisciplinary study of the lateral dispersion of the hydrothermal plume emitted from the rainbow vent site near 36 15 n mid atlantic ridge combining velocity measurements from a lowered adcp optical back scatter measurements from a deep tow ctd and methane measurements from bottle samples we are able for the first time in the atlantic to trace a neutrally buoyant plume for a distance of over 50 km the path of the plume is seen to be heavily controlled by the local topography with a general northeast movement of water both particle and methane concentrations decrease downstream over the length of the observed plume the dataset provides an excellent opportunity to study the mixing and biogeochemical processes active in a hydrothermal plume and estimate fluxes of biogeochemical constituents

ree fe variations in hydrothermal sediments implications for the ree content of seawater seafloor hydrothermal vent solutions exhibit rare earth element ree enrichments ranging between one to three orders of magnitude greater than average seawater to assess the impact of these hydrothermal inputs on ocean chemistry we have examined the behavior of rees for hydrothermal sediments collected adjacent to two pacific spreading ridge sites the east pacific rise at 19 s and the southern juan de fuca ridge at 4s n in general the ree fe ratios for both proximal and distal hydrothermal sediments are greater than vent solutions by a factor of 2 to 500 and these ratios increase with increasing distance away from the ridge axis an evaluation of these results in the context of previous models of ree behavior indicates that in fact seawater experiences a net depletion in rees as a result of hydrothermal activity this is due primarily to the large scavenging capacity of iron oxyhydroxides which precipitate from these solutions such an interpretation explains why the ree content of seawater collected in the vicinity of hydrothermal vents is anomalously lower than normal seawater sampled from a comparable depth

phosphate removal by oceanic hydrothermal processes an update of the phosphorus budget in the oceans abstract we present a compilation of dissolved phosphate and solid phase p data from the oceanic crust to evaluate the effects of hydrothermal processes on the oceanic budget of p concentrations of phosphate in fluids that emanate from ridge axis hydrothermal systems are less than that in bottom seawater the extent of removal in these fluids is at least 30 and in some hydrothermal systems dissolved phosphate is removed completely from the circulating fluid evidence for the removal of phosphate in each of six ridge flank hydrothermal systems is based on systematic variations in porewater profiles of phosphate and speeds of porewater flow the extent of removal is 80 in these ridge flank systems these removal processes are recorded in the basaltic crust as an increase in p concentration that coincides with an increase in extent of alteration and content of ferric iron phosphate also is removed in hydrothermal plumes by coprecipitation with fe oxyhydroxide particles which eventually deposit on the seafloor each of these hydrothermal processes results in a flux of p into the oceanic crust bottom seawater flow through ridge axis hydrothermal systems removes at most 0 4 of the preindustrial dissolved riverine flux of p while ridge flanks remove at least 5 but less than 50 of the dissolved riverine flux consistent with p data from deep sea drilling project dsdp sites 417 and 418 removal of phosphate by coprecipitation with fe rich particles in hydrothermal plumes along ridge axes accounts for 18 33 of the dissolved riverine flux thus hydrothermal systems remove about 50 of the preindustrial dissolved riverine flux of phosphate we have included these new estimates in a revised budget for oceanic p

hydrothermal deposition on the juan de fuca ridge over multiple glacial interglacial cycles abstract hydrothermal systems play an important role in modern marine chemistry but little is known about how they may have varied on 100 000 year timescales here we present high resolution records of non lithogenic metal fluxes within sediment cores covering the last 500 000 years of hydrothermal deposition on the flanks of the juan de fuca ridge six adjacent gridded cores were analyzed by x ray fluorescence for fe mn and cu concentrations corrected for lithogenic inputs with ti and normalized to excess initial 230 th to generate non lithogenic metal flux records that provide the longest orbitally resolved reconstructions of hydrothermal activity currently available fe fluxes vary with global sea level over the last two glacial cycles suggesting higher hydrothermal deposition during interglacial periods the observed negative relationship between fe and mn indicates variable sediment redox conditions and diagenetic remobilization of sedimentary mn over time thus mn fluxes may not be a reliable indicator for hydrothermal activity in the juan de fuca ridge sediment cores cu fluxes show substantial high frequency variability that may be linked to changes in vent temperature related to increased magmatic production during glacial periods deglacial hydrothermal peaks on the juan de fuca ridge are consistent with previously published records from the mid atlantic ridge and the east pacific rise moreover on the juan de fuca ridge the deglacial peaks in hydrothermal activity are followed by relatively high hydrothermal fluxes throughout the ensuing interglacial periods relative to the previous glacial period

mineralogy and geochemistry of silicate sulfide and oxide iron formations in norway evidence for fluctuating redox states of early paleozoic marine basins laterally extensive silicate and sulfide iron formation associated with jasper hematitic chert beds and volcanogenic massive sulfide vms deposits in norway provide evidence of early mineral assemblages and redox conditions within coeval early paleozoic seawater calculated detrital free compositions record mixed hydrothermal e g fe cu and seawater biogenic e g si ni s ree p components rare earth element ree patterns are characterized by small to large negative ce anomalies and insignificant to locally large positive eu anomalies reflecting seawater ree carried to the seafloor by fe p rich particles later modified by diagenetic processes protoliths of silicate iron formation precipitated in anoxic and intermittently euxinic deep waters by the diagenetic modification of amorphous si fe oxyhydroxides and or si fe ooh gels based on possible modern analogues in the red sea diagenetic minerals include nontronite greenalite stilpnomelane magnetite manganosiderite apatite and iron sulfides in sulfide iron formation a local predominance of pyrrhotite over pyrite records highly reducing conditions caused by organic material the geochemical data provide evidence for mn fe p shuttle and redox processes in a stratified basin with oxic or suboxic shallow waters and silica concentrations much higher than those of modern seawater hydrothermal plume derived fe present within the anoxic layer and near the chemocline formed mixed valence oxyhydroxides and silicates and intermittently sulfides by reaction with aqueous si and h2s respectively the latter derived from bacterial reduction of seawater sulfate at the chemocline major sustained fluxes of hydrothermally derived reductants fe2 mn2 h2s h2 produced from large seafloor systems such as lokken may have changed the redox state of seawater in local and possibly regional basins from weakly or moderately oxic to intermittently anoxic or euxinic conditions

tracking the dispersal of hydrothermal plumes from the juan de fuca ridge using suspended matter compositions in 1988 and 1989 particles from on and off axis neutrally buoyant plumes over the juan de fuca ridge were sampled to study their changing composition with distance from the ridge crest plume depth and particle composition in off axis hydrothermal plumes were used to identify plume sources and trajectories iron and phosphorus concentrations and in particular p fe molar ratios were found to be sensitive indicators of hydrothermal phases in the suspended matter phosphorus vanadium and arsenic are scavenged from solution where dissolved iron from hydrothermal vents oxidizes in seawater and forms submicrometer sized particles of fe oxyhydroxide the p fe molar ratio 0 23 is essentially the same for vent fields along cleft and endeavour segments indicating that the scavenging processes are the same for both regions high p fe ratios are observed over the south and north cleft segment vent fields and to the west along the vance seamount chain the seamounts evidently function as a barrier bathymetrically steering the hydrothermal plumes to the west away from the ridge crest since particles from the endeavour vent field are greatly enriched in copper relative to hydrothermal plumes from other vent fields along the juan de fuca ridge copper concentrations in the plumes can be used to distinguish plume sources based on water column depth and elemental composition hydrothermal plume particles from specific vent fields on the juan de fuca ridge may be tracked as much as several tens of kilometers from their source using particle compositions

iodine records from the ediacaran doushantuo cap carbonates of the yangtze block south china abstract late neoproterozoic cap carbonates formed following the cryogenian glaciations may record information about the significant climate change and ocean chemistry evolution immediately after the snowball earth events large negative carbon isotope anomalies and enigmatic sedimentary structures have been identified from the post marinoan cap carbonates across the globe but their formation mechanism remains debatable due to difficulties of distinguishing overlapped chemical signatures and diagenetic alterations in this study we present i ca mg profiles of four sections from a shallow to deep water transect of the basal doushantuo cap carbonates one of the most extensively studied ediacaran units in south china most samples have i ca mg values lower than 1 mol mol with a few exceptions in the shelf sections up to 2 5 mol mol all calcite samples with extremely low 13c have iodine signal below detection limit suggesting carbonate precipitation from anoxic seawater or diagenetic fluids among the four sections the slope section has the lowest i ca mg values suggesting that it may have experienced more extensive fluid buffered diagenesis and more severe loss of io3 in combination with available major trace rare earth element and isotope data the temporal i ca mg variations support freshwater mixing and deep water upwelling in proximal sites and transient oxidation during deposition of the doushantuo cap carbonates