magma chamber scale liquid immiscibility in the siberian traps represented by melt pools in native iron magma unmixing i e separation of a homogeneous silicate melt into two or more liquids is responsible for sudden changes in the evolution of common melts element fractionation and potential formation of orthomagmatic ore deposits although immiscible phases are a common phenomenon in the mesostasis of many tholeiitic basalts evidence of unmixing in intrusive rocks is more difficult to record because of the transient nature of immiscibility during decompression cooling and crystallization in this paper we document a clear case of liquid immiscibility in an intrusive body of tholeiitic gabbro in the siberian large igneous province using textures and compositions of millimeter sized silicate melt pools in native iron the native iron crystallized from a metallic iron liquid which originated as disseminated globules during reduction of the basaltic magma upon interaction with coal bearing sedimentary rocks in the siberian craton the silicate melts entrapped and armored by the native iron are composed of two types of globules that represent the aluminosilicate 60 77 wt sio2 and silica poor fe ti ca p rich in wt sio2 15 46 feo 15 22 tio2 2 7 cao 11 27 p2o5 5 30 conjugate liquids different proportions and the correlated compositions of these globules in individual melt pools suggest a continuously evolving environment of magmatic immiscibility during magma cooling these natural immiscible melts correspond extremely well to the conjugate liquids experimentally produced in common basaltic compositions at 1025 c our results show that immiscibility can occur at large scale in magma chambers and can be instrumental in generating felsic magmas and fe ti ca p rich melts in the continental igneous provinces

cross shelf transport of terrestrial al enhanced by the transition of northeasterly to southwesterly monsoon wind over the east china sea aluminum al is one of the key parameters of geotraces in spring 2011 we examined the distribution of dissolved al in the east china sea ecs to assess the potential passage of coastal water across the shelf to the western pacific measurement of dissolved al in coastal shelf and shelf break waters indicated decreasing concentrations with distance from the coast however the northward increase of dissolved al in the upper 100 m along the shelf break transect corresponding to the northward flow of kuroshio water along the okinawa trough from the north of taiwan to the tokara strait indicates contributions of terrestrial material the presence of an al plume indicated cross shelf transport at the subsurface at a potential density of 23 3 24 0 kg m3 this plume originates from the near bottom layer along the coast off zhejiang and fujian provinces and first moves southeastward to the north of taiwan and then northeastward to shelf break with export at 29 n 127 e we calculated the cross shelf fluxes of water and dissolved al based on simulation results of the 3 d massachusetts institute of technology general circulation model mitgcm the calculated cross shelf fluxes of al at the subsurface layer indicate that the ecs is highly efficient in pumping al rich coastal waters northward to the japan sea east sea and or eastward into the western pacific we also identified an important role of the monsoon with a change from northeasterly wind to southwesterly wind in spring on the cross shelf transport of al by use of numerical tracer experiments

trace elements in magnetite from massive iron oxide apatite deposits indicate a combined formation by igneous and magmatic hydrothermal processes iron oxide apatite ioa deposits are an important source of iron and other elements e g ree p u ag and co vital to modern society however their formation including the namesake kiruna type ioa deposit sweden remains controversial working hypotheses include a purely magmatic origin involving separation of an fe p rich volatile rich oxide melt from a si rich silicate melt and precipitation of magnetite from an aqueous ore fluid which is either of magmatic hydrothermal or non magmatic surface or metamorphic origin in this study we focus on the geochemistry of magnetite from the cretaceous kiruna type los colorados ioa deposit 350 mt fe located in the northern chilean iron belt los colorados has experienced minimal hydrothermal alteration that commonly obscures primary features in ioa deposits laser ablation inductively coupled plasma mass spectroscopy la icp ms transects and electron probe micro analyzer epma wavelength dispersive x ray wdx spectrometry mapping demonstrate distinct chemical zoning in magnetite grains wherein cores are enriched in ti al mn and mg the concentrations of these trace elements in magnetite cores are consistent with igneous magnetite crystallized from a silicate melt whereas magnetite rims show a pronounced depletion in these elements consistent with magnetite grown from an fe rich magmatic hydrothermal aqueous fluid further magnetite grains contain polycrystalline inclusions that re homogenize at magmatic temperatures 850 c smaller inclusions 500 ppm concentrations

the contrasting biogeochemistry of iron and manganese in the pacific ocean abstract vertical and horizontal distributions of dissolved and suspended particulate fe and mn and vertical fluxes of these metals obtained with sediment traps were determined throughout the pacific ocean in general dissolved fe is low in surface and deep waters 0 1 to 0 7 nmol kg with maxima associated with the intermediate depth oxygen minimum zone 2 0 to 6 6 nmol kg vertical distributions of dissolved mn are similar to previous reports exhibiting a surface maximum a subsurface minimum a mn maximum layer coincident with the oxygen minimum zone and lowest values in deep waters near shore removal processes are more intense for dissolved fe than for dissolved mn dissolved mn in the surface mixed layer remains elevated much farther offshore than dissolved fe elevated near surface dissolved mn concentrations occur in the north pacific equatorial current suggesting transport from the eastern boundary near surface mixed layer dissolved mn concentrations are higher in the north pacific gyre reflecting enhanced northern hemisphere aeolian sources residence time estimates for the settling of refractory paniculate fe and mn from the upper water column are 62 220 days fe and 105 235 days mn in contrast residence times for the scavenging of dissolved fe and mn are 2 13 years fe and 3 74 years mn scavenging residence times for dissolved mn based on horizontal mixing in the surface mixed layer of the northeast pacific are 0 4 years nearshore to 19 years 1000 km offshore there is no evidence for in situ fe redox dissolution within sub oxic waters in the eastern tropical north pacific dissolved fe appeared to be controlled by dissolution from sub oxic sediments with oxidative scavenging in the water column or upper sediment layers however in situ mn dissolution within the oxygen minimum zone was evident

fluvial and hydrothermal input of manganese into the arctic ocean abstract a total of 773 samples were analysed for dissolved manganese mn in the arctic ocean aboard r v polarstern during expedition ark xxii 2 from 28 july until 07 october 2007 from tromso norway to bremerhaven concentrations of mn were elevated in the surface layer with concentrations of up to 6 nm over the deep basins and over 20 nm in the laptev sea the general distribution of mn through the water column is consistent with previous studies but there are differences in the absolute concentrations that are most likely related to differences in sample area sampling and filtration the elevated concentrations of mn in the surface layer are related to fresh water input this was visible in the strong negative correlations observed between dissolved mn and salinity the correlation between mn and salinity and the correlation between mn and the quasi conservative trace water mass tracer po4 showed fluvial and melt water input and the pacific and atlantic origin of the surface waters a large portion of the mn delivered by the arctic rivers is removed in the shelf seas and does not pass into the central basins most likely a benthic flux is at the origin of the elevated concentrations of mn near the sediments in the barents and kara seas these elevated concentrations of mn apparently affected the deep basins as well as maxima in the concentrations of mn were observed that corresponded with lowered transmission over the continental slope a maximum in the concentration of mn in the deep basin corresponded with anomalies in light transmission potential temperature and dissolved iron confirming the hydrothermal origin the hydrothermal plume was observed throughout the nansen basin and over the deep gakkel ridge around 2500 m depth and a smaller plume was observed around 3200 m the concentration of mn at the mn maximum around 2500 m depth decreased exponentially consistent with a first order scavenging model the concentrations of mn were extremely low in the deep makarov basin 0 05 nm and slightly higher in the eurasian basin 0 1 nm outside the influence of the hydrothermal activity

the diffusive tortuosity of fine grained unlithified sediments abstract use of fick s first law to estimate solute fluxes is arguably the most common and important calculation related to the geochemistry and environmental chemistry of fine grained unlithified sediments in such porous media the diffusion coefficient in this law must be reduced by the square of the tortuosity to account for the longer diffusive paths experimental methods to estimate tortuosity are specialized or time consuming and not routinely done an analysis of available data shows that tortuosity is accurately correlated to readily measured porosity values through the simple relation 2 1 l n 2

distribution of dissolved manganese in the peruvian upwelling and oxygen minimum zone abstract the geochemistry of manganese mn in seawater is dominated by its redox chemistry as mn ii is soluble and mn iv forms insoluble oxides and redox transformations are mediated by a variety of processes in the oceans dissolved mn dmn accumulates under reducing conditions and is depleted under oxidizing conditions thus the peruvian upwelling region characterized by highly reducing conditions over a broad continental shelf and a major oxygen minimum zone extending far offshore is potentially a large source of mn to the eastern tropical south pacific in this study dmn was determined on cruises in october 2005 and february 2010 in the peruvian upwelling and oxygen minimum zone to evaluate the relationship between mn oxygen and nitrogen cycle processes dmn concentrations were determined using simple dilution and matrix matched external standardization inductively coupled mass spectrometry surprisingly dmn was depleted under the most reducing conditions along the peruvian shelf concentrations of dissolved mn in surface waters increased offshore indicating that advection of mn offshore from the peruvian shelf is a minor source subsurface mn maxima were observed within the oxycline rather than within the oxygen minimum zone omz indicating they arise from remineralization of organic matter rather than reduction of mn oxides the distribution of dmn appears to be dominated by non redox processes and inputs from the atmosphere and from other regions associated with specific water masses lower than expected dmn concentrations on the shelf probably reflect limited fluvial inputs from the continent and efficient offshore transport this behavior is in stark contrast to fe reported in a companion study which is very high on the shelf and undergoes dynamic redox cycling

flux and fate of yangtze river sediment delivered to the east china sea numerous cores and dating show the yangtze river has accumulated about 1 16 x 10 12 t sediment in its delta plain and proximal subaqueous delta during holocene high resolution seismic profiling and coring in the southern east china sea during 2003 and 2004 cruises has revealed an elongated similar to 800 km distal subaqueous mud wedge extending from the yangtze river mouth southward off the zhejiang and fujian coasts into the taiwan strait overlying what appears to be a transgressive sand layer this distal clinoform thins offshore from similar to 40 in thickness between the 20 and 30 m water depth to 1 2 in between 60 and 90 m water depth corresponding to an across shelf distance of less than 100 km total volume of this distal mud wedge is about 4 5 x 10 11 m 3 equivalent to similar to 5 4 x 10 11 t of sediment most of the sediment in this mud wedge comes from the yangtze river with some input presumably coming from local smaller rivers thus the total yangtze derived sediments accumulated in its deltaic system and east china sea inner shelf have amounted to about 1 7 x 10 12 t preliminary analyses suggest this longshore and across shelf transported clinoform mainly formed in the past 7000 yrs after postglacial sea level reached its mid holocene highstand and after re intensification of the chinese longshore current system sedimentation accumulation apparently increased around 2000 yrs bp reflecting the evolution of the yangtze estuary and increased land erosion due to human activities such as fanning and deforestation the southward flowing china coastal current the northward flowing taiwan warm current and the kuroshio current appear to have played critical roles in transporting and trapping most of yangtze derived materials in the inner shelf and hence preventing the sediment escape into the deep ocean c 2006 elsevier b v all rights reserved

western pacific coastal sources of iron manganese and aluminum to the equatorial undercurrent 1 we present results from the first zonal transect of iron aluminum and manganese conducted from the western source region of the equatorial undercurrent euc to the central equatorial pacific trace metals were elevated along the slope of papua new guinea and within the new guinea coastal undercurrent ngcu which is the primary southern hemisphere entry path of water to the euc subsurface maxima in total acid soluble iron aluminum and manganese were evident in the euc these maxima were generally greatest in the western equatorial pacific and decreased in magnitude eastward maxima in iron and aluminum persisted to 140 w maxima in manganese extended to 175 w iron and manganese maxima were deeper 25 75 m than aluminum maxima and located in the lower euc which undergoes less interior ocean mixing than shallower waters the depth of the aluminum subsurface maxima correlated strongly r 0 88 with the depth of the euc velocity maximum surface waters were enriched in aluminum and manganese offshore of papua new guinea surface metal concentrations decreased eastward throughout the western warm pool up to the longitude 180 w of the salinity front detrital sediment input from either direct riverine input or sediment resuspension appeared to be the primary mechanism of supplying metals to the ngcu we estimated eastward fluxes of metals in the euc and found greatest fluxes in the western equatorial pacific between 160 e and 165 e except for aluminum fluxes of aluminum and to a lesser extent manganese increased concurrently with water volume transport in the central equatorial pacific iron transport in the euc remained constant east of the dateline apparently due to the combined effects of dilution by meridional entrainment and scavenging iron was mobilized in a highly active western boundary current region and transported eastward in the lower euc

the dynamics of estuarine manganese cycling seasonal observations of dissolved managnese in the tamar estuary south west england have demonstrated pronounced temporal and spatial variability in the distribution of this component simultaneous observations of physical and physico chemical properties of the estuarine system together with kinetic measurements of dissolved managenese behaviour in isolated samples have demonstrated that the observed distributions are the instantaneous product of dynamic interactions involving external sources and internal input and removal processes dissolved manganese is mobilized internally from reduced sedimentsduring advective resuspension of bed material so that this input is regulated by temporal and spatial variations in tidal stress manganese is returned to the sediments by continuous uptake on to suspended particles the rate of this process is responsive to changes in suspended particulate load ionic strength ph and temperature the reaction changes from zero order kinetics in freshwater to first order kinetics characteristic of the saline medium with marked deceleration in effective removal rate following small increases in salt concentration relative changes in the first order removal rate throughout the estuary are consistent but there are considerable temporal variations in the absolute rates this is partially attributable to variations in the quality as well as the quantity of the suspended particles these results indicate that changes in the relative effectiveness of both the input and removal mechanisms which lead to internal cycling of manganese and to variable distributions of dissolved managanese within the estuary are closely coupled to the internal behaviour of particles and hence to the tidally induced oscillations in bed stress this observation has been confirmed by sequential recordings of dissolved manganese distributions through a spring tide to neap tide period furthermore climatic events producing enhanced disturbance of bed sediment have been shown to induce a similar sequence of events to that arising from tidally induced net mobilization of bed material

dissolved aluminium in the tamar estuary southwest england abstract distributions of dissolved al in the tamar estuary have been recorded through spring neap tidal cycles in winter and summer dissolved al is a highly reactive constituent in this estuary undergoing net removal in the very low salinity region and net input to the mid estuary the extent of both the depletion and the augmentation varied systematically with tidal energy input indicating that tidal sediment disturbance was the principal controlling agency these field data supported by the results of laboratory simulations show that the removal is regulated by sorption onto resuspended sediment particles which dominates kinetically over authigenic aluminosilicate formation removal of dissolved al by flocculation of riverborne colloids is not significant the mid estuarine input is consistent with dissolution of authigenic aluminosilicate following net remobilization of estuarine sediment the internal cycling of al in the estuary generated by these processes alters both the time course and the soluble particulate balance of the riverine discharge of al to the adjacent coastal water

magnetostratigraphy in pursuit of missing links since the last quadrennial report magneto stratigraphy has continued to flourish the primary issues have been 1 refinements to the geomagnetic reversal time scale grts including recalibrations correlation of biostratigraphic data to the crts and revision of the terminology 2 use of magnetostratigraphic data for estimating rates of such processes as sediment accumulation evolution and faunal migration and 3 magnetic mineralogy and the origin of remanence for convenience we have divided the publications into studies of continental and marine sediments and highlight the most exciting issues within each of these sub headings in the first section of this review we will concentrate on the development of the geomagnetic reversal time scale grts with particular emphasis on refinements from the last few years we then turn our attention to applications of magnetostratigraphy in marine and continental sequences

source and development of large manganese enrichments above eastern mediterranean sapropel s1 1 the residual dark unit of the most recent eastern mediterranean sapropel s1 is usually overlain by sediments with enhanced concentrations of mnox in two separated layers the variability and magnitude of the mn enrichment at different locations and water depths indicate that mn must have been added preferentially to sediments at intermediate 1 2 km water depths we propose a two stage mechanism for the mn enrichment that involves decreasing oxygenation with increasing water depth this mechanism involves the loss of reduced mn2 from the deepest sediments 2 km water depth into overlying anoxic waters and a variable gain of mnox in sediments in contact with oxygenated waters at shallower depth in the s1 unit that receives the extra mnox input an upper higher mn enriched zone 3 wt is maintained continuously at the top of the accumulating s1 unit because the pore waters are anoxic at shallow sediment depth while bottom waters are oxic to some degree in a reactive transport model the mn enrichment in the upper zone could not be supported by normal sediment diagenesis thus the mnox in the upper mn horizon must have formed mainly in the water column the mnox in the upper mn enriched zone adsorbed mo and li from seawater in a similar manner as other mn enriched oxic sediments nodules and crusts with a mn mo ratio of 600 1 a mn li ratio of 750 1 and a 98 95momomo of 2 5

a comparative study of manganese dynamics in the water column and sediments of intertidal systems of the north sea abstract the dynamics of the redox sensitive trace metal manganese mn and its response to biological activity were investigated in the water column and shallow pore waters of the german wadden sea southern north sea in 2008 and 2009 two systems one from the southern backbarrier area of spiekeroog island and one from the eastern part sylt romo wadden sea of the german bight were compared the major aim was to examine to which extent biogeochemical findings are specific for a particular tidal basin or transferable to other basins of the german wadden sea although both study areas reveal hydrodynamical sedimentological and ecological differences qualitatively pronounced similarities in mn dynamics are observed thus complex cycling of dissolved mn with increasing values in spring and late summer due to elevated biological activity as well as a depletion period in early summer were observed in both study areas this finding suggests a seasonal behaviour of mn being generally representative for the tidal basins of the southern north sea quantitative differences are significant as the backbarrier area of spiekeroog island shows much higher concentrations of dissolved mn in the water column especially during spring we suggest that this difference is due to a larger sediment area water volume ratio in the spiekeroog backbarrier area combined with a higher release of dissolved mn from the tidal flat sediments as seen in pore water profiles from surface sediments site specific differences are also seen in further tidal systems of the north frisian wadden sea which are characterised by individual hydrodynamical and sedimentological conditions several transects leading from offshore locations towards the coast also revealed a highly variable mn level overall the north frisian wadden sea most likely represents a less important source for dissolved mn than the east frisian wadden sea furthermore our data suggest that site specific properties of the different tidal basins have to be considered in budget calculations for the entire wadden sea

submarine thermal springs associated with young volcanoes the teahitia vents society islands pacific ocean abstract hydrothermal solutions were sampled close to two summits of teahitia a submarine volcano from the southern extension of the society volcanic chain the temperatures measured within two vents were 30 c the vent solutions have a ph value around 5 3 and are enriched in fe mn si ba li and rees relative to ambiant seawater but show only a small decrease in mg and so4 concentrations the lowest measured 87sr 86sr is 0 70867 while the end is identical to those of the surrounding alkali basalt 2 5 the vent solutions from teahitia have chemical characteristics similar to pele s vents loihi seamount another mid plate volcano the exact temperature of seawater basalt interaction is difficult to constrain however the absence of positive eu anomaly in the fluids the particles and in the hydrothermal deposits from teahitia seems to exclude the participation of a high temperature component comparable as those involved in mid ocean ridge axis vents

geochemical behavior of dissolved manganese in the east china sea seasonal variation estuarine removal and regeneration under suboxic conditions to better understand the geochemical cycle of dissolved manganese mn in the east china sea ecs the distribution of dissolved mn across the ecs was investigated during three field studies in 2011 may august and november the concentration of dissolved mn decreased across the ecs with distance from the coast mn rich ecs shelf waters could export to the kuroshio waters and had the potential to influence the northwest pacific ocean as well as the japan sea the kuroshio waters were devoid of dissolved mn so its incursion could be tracked as it entered the ecs continental shelf region approximately 50 m isobath seasonal variations of dissolved mn in the ecs were significant with the highest concentrations occurring in summer dissolved mn in the changjiang estuary was nonconservative and significant quantities were removed by net sorption onto suspended particulate matter a model describing the sorption processes was applied to data for the changjiang estuary regeneration of dissolved mn took place in near bottom waters of the suboxic zone in august 2011 following extensive consumption of oxygen the benthic flux of dissolved mn was estimated based on mn concentrations in the overlying waters and the near bottom waters a preliminary box model was established to develop a dissolved mn budget for the ecs based on the dissolved mn content in the ecs and the total input flux a residence time of 76 350 days for dissolved mn in the ecs was inferred

spatial and temporal variations of the kuroshio east of taiwan 1982 2005 a numerical study 1 a 1 8 east asian marginal seas model nested to a larger domain north pacific ocean model is implemented over a span of 24 years from 1982 to 2005 to investigate the spatial and temporal variations of the kuroshio east of taiwan between 22 and 25 n the mean state and variability of the kuroshio such as the two paths observed in the trajectories of surface drifters southeast of taiwan and the branching of the kuroshio northeast of taiwan are well reproduced by the model southeast of taiwan the kuroshio is mostly in the top 300 m in the inshore path but extends to 600 m in the offshore path northeast of taiwan the kuroshio follows the shelf edge in the east china sea but may branch along a path south of the ryukyu islands the latter path often meanders southward and a significant portion of the kuroshio transport may be diverted to this path the kuroshio extends from the coast to 123 123 5 e between 22 and 25 n with currents reaching a depth of 1000 m at some latitudes the kuroshio transports averaged over five sections east of taiwan are 28 4 5 0 sv and 32 7 4 4 sv with and without the contribution from the countercurrent respectively

yttrium and rare earth elements in fluids from various deep sea hydrothermal systems rare earth element ree and yttrium y concentrations were measured in fluids collected from deep sea hydrothermal systems including the mid atlantic ridge mar i e menez gwen lucky strike tag and snakepit the east pacific rise epr i e 13 n and 17 19 s and the lau vai lili and manus vienna woods pacmanus desmos back arc basins bab in the south west pacific in most fluids y is trivalent and behaves like ho chondrite normalized y ree y reen concentrations of fluids from mar epr and two bab sites i e vai lili and vienna woods showed common patterns with lree enrichment and positive eu anomalies ree analysis of plagioclase collected at lucky strike strengthens the idea that fluid ree contents are controlled by plagioclase phenocrysts other processes however such as ree complexation by ligands cl f so42 secondary phase precipitation and phase separation modify ree distributions in deep sea hydrothermal fluids ree speciation calculations suggest that aqueous ree are mainly complexed by cl ions in hot acidic fluids from deep sea hydrothermal systems ree concentrations in the fluid phases are therefore influenced by temperature ph and duration of rock fluid interaction unusual y reen patterns found in the pacmanus fluids are characterized by depleted lree and a positive eu anomaly the demos fluid sample shows a flat y reen pattern which increases regularly from lree to hree with no eu anomaly these manus basin fluids also have an unusual major element chemistry with relatively high mg so4 h2s and f contents which may be due to the incorporation of magmatic fluids into heated seawater during hydrothermal circulation ree distribution in pacmanus fluids may stem from a subseafloor barite precipitation and the ree in demos fluids are likely influenced by the presence of sulfate ions

fluid inclusion and stable isotope study of the esfordi apatite magnetite deposit central iran a reply sir we are pleased that our recent paper in economic geology jami et al 2007 presenting the geologic setting a description of the mineralization fluid inclusion and o isotope analyses of the esfordi p fe oxide deposit in central iran has been of interest to aftabi and his colleagues aftabi et al 2009 the opportunity to discuss further some aspects of our paper is appreciated including support for a hydrothermal dominated depositional model for esfordi aftabi et al 2009 focus their comments on the question of the affinity of the esfordi p fe oxide deposit in particular they argue that esfordi and by inference other diverse fe oxide deposits within the bafq district of central iran should be considered rapitan type banded iron formations i e bif klein 2005 rather than kiruna type hitzman 2000 in discussing our results and conclusions in the light of previous work particularly forster and jafarzadeh 1994 aftabi et al 2009 have misconstrued our interpretation of some of the textural and isotopic data as providing support for an orthomagmatic model for the esfordi p fe oxide deposit based on the structure relationships between mineralization and host rocks fluid inclusion and isotopic data we concluded that esfordi exhibits strong evidence of hydrothermal origin though we did not preclude some component of precursor orthomagmatic processes in formation of the p fe mineralisation it is noted that some examples of the kiruna end member of the continuum of fe oxide deposits discussed by hitzman 2000 are controversial particularly in regard to their evolution sillitoe and burrows 2002 henriquez et al 2003 we have shown that esfordi has a number of features typical of the kiruna type deposits and does not exhibit features consistent with an affinity to rapitan type fe oxide deposits this evidence will be discussed briefly with further data

suboxic trace metal geochemistry in the eastern tropical north pacific abstract we analyzed al ti fe mn cu ba cd u mo v and re in water column settling particulate and sediment 0 to 22 cm samples from the intense oxygen minimum zone omz of the eastern tropical north pacific near mazatlan mexico the goal was to determine how the geochemistry of these elements was influenced by suboxic water column conditions and whether the sediments have a unique suboxic geochemical signature the water column was characterized by a mn maximum reaching 8 nmol kg 1 at 400 m concentrations of cu ba cd mo re u and v were unaffected by the low o2 conditions and were comparable to those of the open ocean sinking particles were composed of lithogenic particles of detrital origin and nonlithogenic particles of biogenic origin al ti and fe were mostly at least 79 lithogenic about 75 of the mn was nonlithogenic significant amounts at least 58 of cu ba cd and mo were nonlithogenic sediment geochemistry varied across the continental shelf and slope cadmium u and re have prominent maxima centered at 310 m with 12 3 ppm 10 9 ppm and 68 3 ppb respectively at the core top high values of mo averaging 6 8 ppm and v averaging 90 ppm are seen in omz surface sediment additional down core enrichment occurs for all redox sensitive elements in the top 10 cm for u mo v and re surface sediments are a poor indicator of metal enrichment comparison of the nonlithogenic composition of sediments with sinking particles suggests that direct input of plankton material enriched in metals makes a significant contribution to the total composition especially for cd u and mo we evaluated re mo and cd u ratios as tracers for redox environments rhenium and mo concentrations and re mo ratios do not lead to consistent conclusions concurrent enrichments of re and mo are an indicator of an anoxic depositional environment in contrast high re mo ratios are an indicator of suboxic conditions cadmium is enriched in surface sediments while u has considerable down core enrichment the concentrations of cd and u and the cd u ratio do not follow patterns predicted from thermodynamics though the water column is suboxic these four redox sensitive elements indicate that the sediments are anoxic the implication for paleostudies is that a trace metal sediment signature that indicates anoxic conditions is not necessarily attributable to an anoxic water column

processes controlling the distribution and cycling of manganese in the oxygen minimum zone of the arabian sea abstract vertical and horizontal distributions of dissolved and particulate manganese were investigated in the arabian sea northwestern indian ocean during the 1995 spring intermonsoon period march april us jgofs process cruise 2 tn045 the region is characterized by an intense basin wide oxygen minimum zone omz that strongly influences the manganese distribution in the omz two distinct dissolved mn d mn maxima were observed at depths of 200 300 m and 600 m respectively the latter peak displayed concentration maxima of approximately 6 nanomolar and was largely confined to stations north of 19 n latitude stations n2 n7 this mid depth maximum was associated with the low oxygen core of the omz o 2 saager et al 1989 geochimica et cosmochimica acta 53 2259 2267 this signal was largely absent at stations along the southern transect likely due to oxidative scavenging of d mn to the suspended particulate phase mid depth particulate mn maxima at some southern stations stations s4 s11 appear to be remnants of this feature the upper d mn maximum 200 300 m depth was more widely distributed than the 600 m peak with d mn concentrations of 3 to as high as 8 nm at most stations east of about 62 e longitude the signal was everywhere correlated with the secondary nitrite maximum at stations within the main denitrification zone delineated by naqvi 1991 nepheloid layers presumably bacterial also were associated with this depth interval particulate mn profiles displayed corresponding concentration minima and low mn al and reactive refractory mn ratios for this same depth interval suggesting reductive dissolution of mn oxyhydroxides these observations imply that in situ microbially mediated processes may be the predominant source of d mn in the upper omz while horizontal advection is more important deeper in the water column

the continental margin is a key source of iron to the hnlc north pacific ocean here we show that labile particulate iron and manganese concentrations in the upper 500m of the western subarctic pacific an iron limited high nutrient low chlorophyll hnlc region have prominent subsurface maxima between 100 200 m reaching 3 nm and 600 pm respectively the subsurface concentration maxima in particulate fe are characterized by a more reduced oxidation state suggesting a source from primary volcagenic minerals such as from the kuril kamchatka margin the systematics of these profiles suggest a consistently strong lateral advection of labile mn and fe from redox mobilized labile sources at the continental shelf supplemented by a more variable source of fe from the upper continental slope this subsurface supply of iron from the continental margin is shallow enough to be accessible to the surface through winter upwelling and vertical mixing and is likely a key source of bioavailable fe to the hnlc north pacific

immiscible iron and silica rich melts and magnetite geochemistry at the el laco volcano northern chile evidence for a magmatic origin for the magnetite deposits abstract the pliocene el laco volcano northern chile hosts a large iron oxide deposit that occurs as stratiform bodies with underlying feeder zones dykes hosted by hydrothermally altered andesite lava flows phenocrysts in the andesite hosting the mineralization have abundant melt inclusions displaying strong evidence for melt immiscibility most of the pyroxene and the plagioclase phenocrysts contain abundant fe rich melt inclusions with low ti magnetite pyroxene apatite and minor anhydrite the glassy groundmass of these melt inclusions is chemically similar to sub alkaline rhyolitic rocks e g 70 sio 2 si al k na rich large resorbed plagioclase phenocrysts also host another group of melt inclusions with a similar silica rich groundmass but hosting evenly distributed immiscible and complex fe rich spheroidal globules that are enriched in ti p mg ca and s these immiscible globules and the ti poor magnetite daughter crystals in the melt inclusions in pyroxene phenocrysts are thought to be the parental iron oxide melt liquid after which their coalescence leads to the formation of magnetite melts from which the magnetite that formed the el laco iron oxide deposits crystallized and were emplaced the mineralogy and chemistry of these melt inclusions tracks the chemical evolution of the fe ox melts and supports a magmatic origin for the el laco magnetite this is mainly recognized by the continuum of compositions between volcanic separate immiscible fe oxide melts and magnetite ores the trace element composition of the fe rich melt inclusions and of the magnetite in the host andesite and the ore bodies reveals a systematic depletion in most of the elements that are compatible in magnetite the ti content of the magnetite also records the separation and crystallization of the iron rich melt typically the magnetite in the orebodies and the melt inclusions is ti poor compared with titanomagnetite found in the andesite groundmass and that hosted by the hydrothermally altered andesite that is interpreted as being attributed to its crystallization under oxidizing and sulfur rich conditions the cause of this unusual chemical behaviour is probably due to the mechanism s governing the crystallization of the iron rich melt including the temperature changes in chemistry prior to eruption and an increase in the redox conditions of the silicate melt magma oxidation facilitates the prevalence of ferric iron and formation of ti poor magnetite preventing the incorporation of ti in the exsolving iron rich melt the likely reason for the formation of these large ti poor magnetite deposits is likely the contamination of the parental andesitic magma by oxidized crustal rocks and concomitant crystallization of magnetite under oxidizing conditions something that had a significant impact on the elemental distribution

reply to discussion by a aftabi and s mohseni on combined igneous and hydrothermal source for the kiruna type bafq magnetite apatite deposits in central iran trace element and oxygen isotope studies of magnetite by mehdipour ghazi et al ore geology reviews 105 2019 590 604 abstract in this reply we emphasize on some geological and geochemical evidence that indicate most of the studied deposits choghart chadormalu and sechahun have magmatic origin and they are not related to bif deposits as declared by aftabi and mohseni 2019 field studies reveal the existence of at least three types of iron mineralization in the posht e badam block 1 stratiform fe oxide ologist sublayers within the neoproterozoic meta sedimentary units 2 iron lenses within the early cambrian volcano sedimentary unit and 3 massive magnetite deposits we assume that studies by aftabi and mohseni 2019 were focused on iron deposits mainly belonging to type 2 iron mineralization above we proposed contamination of primary silicate magma with older units similar to ediacaran bands of magnetite reported by aftabi and mohseni 2019 that include iron phosphor and sodium which were responsible for triggering immiscibility of fe rich melt from silicate magma and formation of the studied massive iron deposits

combined igneous and hydrothermal source for the kiruna type bafq magnetite apatite deposit in central iran trace element and oxygen isotope studies of magnetite abstract the main deposits of the bafq district choghart se chahun and chadormalou deposits are magnetite apatite ore bodies with early cambrian age hosted by early cambrian volcano sedimentary rocks showing lava flow structure with miarolitic cavities and occasional brecciation the texture and geochemistry trace elements and o isotope of the studied magnetite crystals show three types of magnetite with different proportions in different parts of the district and the deposits these are primary ignious magnetite and high temperature hydrothermal magnetite in the massive parts of the deposits and foam like magnetite in the veins or in the fractures of the massive part the lack of zonation high ti fe ratios and 18o values 2 than the massive magnetites the magmatic origin for the main part of the ores in the bafq is more plausible contamination of the primary magmas of the bafq magmatic rocks with crustal phosphorus and evaporate units was the major agent for triggering iron rich melt immiscibility from the original magma concentration of volatiles in the iron rich melt involving in crystallization of the primary magnetite and nucleation of the aqueous fluid bubbles on magnetite surfaces led to ascending the buoyant fluid bubble magnetite aggregates this caused continuation of the magmatic magnetite microlites growth from the iron rich magmatic hydrothermal fluid and formed high temperature hydrothermal magnetite formation of hypersaline fluid due to crystallization of iron rich melt at shallow depth led to crystallization of titanite and th u ree bearing minerals and sodic calcic alteration related to magnetite mineralization microscopic evidence replacement of magnetite by hematite and filling of fractures of thorite by magnetite show that degassing continued at shallow depth which led to re crystallization of the primary magnetites and formation of the foam like magnetites

paleogene magnetic stratigraphy in umbrian pelagic carbonate rocks the contessa sections gubbio the umbrian sequence of pelagic carbonate rocks provides an opportunity for precise correlation between paleogene biostratigraphy and geomagnetic polarity history the red to pink paleocene to middle eocene scaglia rossa limestone the varicolored upper eocene scaglia variegata limestone and the gray green oligocene scaglia cinerea marlstone form a 250 m thick continuous exposure in the contessa valley near gubbio italy magnetostratigraphic lithostratigraphic and biostratigraphic investigations in three sections covering the entire paleogene have confirmed and dated the geomagnetic reversal sequence for most of this period the ferromagnetic mineral in the scaglia cinerea is magnetite and af demagnetization to peak fields of 20 mt is sufficient to define the characteristic remanent magnetization the scaglia variegata and pink scaglia rossa samples contain an additional hematite component which is very pronounced in dark red paleocene scaglia rossa samples changes of magnetic mineralogy take place in these limestones during heating especially above 500 c however thermal demagnetization is effective in isolating the characteristic remanence vectors which form almost antipodal clusters of directions representing normal and reversed polarities the directions are rotated counterclockwise partly due to post oligocene tectonism paleontological zonations of planktic foraminifera and calcareous nannofossils were hampered by poor preservation but the major epoch and stage 29 as in the gubbio bottaccione section paleocene eocene just above anomaly 25 eocene oligocene between anomalies 13 and 15 oligocene miocene just below anomaly 6c these correlations require slight modifications to previous conclusions on paleogene sea floor spreading rates

dissolved manganese in the atlantic sector of the southern ocean the first comprehensive dataset 492 samples of dissolved mn in the southern ocean shows extremely low values of 0 04 up to 0 64 nm in the surface waters and a subsurface maximum with an average concentration of 0 31 nm n 20 s d 0 08 nm the low mn in surface waters correlates well with the nutrients po4 and no3 and moderately well with si oh 4 and fluorescence furthermore elevated concentrations of mn in the surface layer coincide with elevated fe and light transmission and decreased export th 234 u 238 deficiency and fluorescence it appears that mn is a factor of importance in partly explaining the hnlc conditions in the southern ocean in conjunction with significant controls by the combination of fe limitation and light limitation no input of mn from the continental margins was observed this is ascribed to the protruding continental ice sheet that covers the shelf and shuts down the usual biological production microbial breakdown and sedimentary geochemical cycling the low concentrations of mn in the deep ocean basins 0 07 0 23 nm were quite uniform but some elevations were observed the highest deep concentrations of mn were observed at the bouvet triple junction region and coincided with high concentrations of fe and are deemed to be from hydrothermal input the deep basins on both sides of the ridge were affected by this input in the deep weddell basin the input of weddell sea bottom water appears to be the source of the slightly elevated concentrations of mn in this water layer c 2010 elsevier ltd all rights reserved

mean residence time of the shelf water in the east china and the yellow seas determined by 228ra 226ra measurements increasing attention of oceanographers has recently been paied on east asian marginal seas regarding their role on the global environment yet geochemical investigations have been few to date we here report new data on the distribution of 228ra and 226ra in the surface water of the east china and the yellow seas in an effort to constrain the time necessary for the coastal and shelf waters to exchange with offshore waters such information is needed in evaluating the exchange of heat and water across the air sea interface that affects the local climate and the fate of pollutants nutrients and weathering products supplied from the continent based on the ra isotope signals we have estimated that the shelf water component contributes 20 of the tsushima current water passing through the tsushima strait and the mean residence time for the shelf water to mix with the kuroshio surface water is 2 3 years as many of materials derived from the continent such as heavy metals and the nutrients have their mean residence times less than a few months in the nearshore and shelf waters they must largely deposit on the shelf sediments prior to the transport from the shelf to the open sea by mixing

magnetic polarity stratigraphy and 40 k 40 ar dating of late miocene and early pliocene continental deposits catamarca province nw argentina magnetostratigraphic and 40 k 40 ar data on a 2300 m thick sequence of continental sediments at puerta de corral quemado in catamarca province nw argentina permit calibration of land mammal faunas of late tertiary huayquerian and montehermosan age the sequence represents from oldest to youngest the chiquimil a araucanense and corral quemado formations paleomagnetic samples were collected from 99 stratigraphic levels strong field thermomagnetic and isothermal remanent magnetization experiments indicate that the dominant ferrimagnetic mineral is magnetite progressive alternating field af and themal demagnetization of the natural remanent magnetism nrm demonstrates that af demagnetization to 20 mt peak field is sufficient to isolate the primary nrm which is of depositional origin the resulting paleomagnetic data provide a well defined magnetic polarity zonation although sampling is less dense in the upper half of the section 40 k 40 ar data obtained from mineral separates of fo

reply to discussion by sadegh mohseni and alijan aftabi of significance of apatite ree depletion and monazite inclusions in the brecciated se chahun iron oxide apatite deposit bafq district iran insights from paragenesis and geochemistry by bonyadi z davidson g j mehrabi b meffre s ghazban f chemical geology 281 2011 253 269

increased dissolved terrestrial input to the coastal ocean during the last deglaciation 1 here we present the first downcore results for a new paleoproxy the mn ca ratio of foraminiferal calcite applied to sediment accumulated in the extreme eastern tropical north pacific etnp over the last 30 000 years the mn ca results are compared to oxygen isotopes and sea surface temperature calculated from mg ca we determined metal ratios using flow through time resolved analysis to minimize the effects of secondary mineralization the foraminiferal species used for this study calcify at different depths core top ratios of these variant species change in proportion to the concentration of dissolved manganese in the water column at the depth of calcification since terrestrial input and oxidation reduction reactions control the levels of dissolved mn in the oceans today it therefore should be possible to use the mn ca ratios of foraminifera as a proxy for these processes in the past mn ca of a mixed layer species g ruber suggest that dissolved terrestrial input to the surface waters of the etnp during the last glacial maximum was lower than today but began to increase with initial sea level rise and reached a maximum at 15 ka b p before coming down to present day levels at the end of sea level rise in the mid holocene 7 5 ka ratios of a deeper calcifying species n dutertrei mimic those of g ruber over this same time period consistent with shoaling of the 18 c thermocline mn ca of a benthic species u peregrina does not show a maximum at 15 ka suggesting that mn was efficiently remineralized in the water column during deglaciation assuming that the period from the last glacial until the mid holocene was a time of increased productivity as elevated mn might imply the oxygen minimum zone omz was at least as well developed during deglaciation as it is today expansion of the omz may have contributed to the mn ca trends we observe through time