ferromanganese nodules and micro hardgrounds associated with the cadiz contourite channel ne atlantic palaeoenvironmental records of fluid venting and bottom currents abstract ferromanganese nodule fields and hardgrounds have recently been discovered in the cadiz contourite channel in the gulf of cadiz 850 1000 m this channel is part of a large contourite depositional system generated by the mediterranean outflow water ferromanganese deposits linked to contourites are interesting tools for palaeoenviromental studies and show an increasing economic interest as potential mineral resources for base and strategic metals we present a complete characterisation of these deposits based on submarine photographs and geophysical petrographic mineralogical and geochemical data the genesis and growth of ferromanganese deposits strongly enriched in fe vs mn av 39 vs 6 in this contourite depositional system result from the combination of hydrogenetic and diagenetic processes the interaction of the mediterranean outflow water with the continental margin has led to the formation of late pleistocene holocene ferromanganese mineral deposits in parallel to the evolution of the contourite depositional system triggered by climatic and tectonic events the diagenetic growth was fuelled by the anaerobic oxidation of thermogenic hydrocarbons 13 c pdb 20 to 37 and organic matter within the channel floor sediments promoting the formation of fe mn carbonate nodules high 87 sr 86 sr isotopic values up to 0 70993 0 00025 observed in the inner parts of nodules are related to the influence of radiogenic fluids fuelled by deep seated fluid venting across the fault systems in the diapirs below the cadiz contourite channel erosive action of the mediterranean outflow water undercurrent could have exhumed the fe mn carbonate nodules especially in the glacial periods when the lower core of the undercurrent was more active in the study area the growth rate determined by 230 th excess 232 th was 113 11 mm ma supporting the hypothesis that the growth of the nodules records palaeoenvironmental changes during the last 70 ka ca rich layers in the nodules could point to the interaction between the mediterranean outflow water and the north atlantic deep water during the heinrich events siderite rhodochrosite nodules exposed to the oxidising sea bottom waters were replaced by fe mn oxyhydroxides slow hydrogenetic growth of goethite from the seawaters is observed in the outermost parts of the exhumed nodules and hardgrounds which show imprints of the mediterranean outflow water with low 87 sr 86 sr isotopic values down to 0 70693 0 00081 we propose a new genetic and evolutionary model for ferromanganese oxide nodules derived from ferromanganese carbonate nodules formed on continental margins above the carbonate compensation depth and dominated by hydrocarbon seepage structures and strong erosive action of bottom currents we also compare and discuss the generation of ferromanganese deposits in the cadiz contourite channel with that in other locations and suggest that our model can be applied to ferromanganiferous deposits in other contouritic systems affected by fluid venting

micrometer and nanometer sized platinum group nuggets in micrometeorites from deep sea sediments of the indian ocean abstract we examined 378 micrometeorites collected from deep sea sediments of the indian ocean of which 175 180 and 23 are i type s type and g type respectively of the 175 i type spherules 13 contained platinum group element nuggets pgns the nuggets occur in two distinct sizes and have distinctly different elemental compositions micrometer m sized nuggets that are 3 m contain dominantly ir os and ru iridium platinum group element or ipge and sub m or nanometer sized 1 m nuggets which contain dominantly pt rh and pd palladium pge or ppge the m sized nuggets are found only one per spherule in the cross section observed and are usually found at the edge of the spherule by contrast there are hundreds of nanometer sized nuggets distributed dominantly in the magnetite phases of the spherules and rarely in the wustite phases both the nugget types are found as separate entities in the same spherule and apparently nugget formation is a common phenomenon among i type micrometeorites however the m sized nuggets are seen in fewer specimens 2 5 of the observed i type spherules in all we analyzed four nuggets of m size and 213 nanometer sized nuggets from 13 i type spherules for platinum group elements chemically the m sized pgns contain chondritic ratios of os ir but are depleted in the more volatile pge pt rh and pd relative to chondritic ratios on the other hand the nanometer sized nuggets contain dominantly pt and rh importantly the refractory pges are conspicuous by their absence in these nanometer nuggets palladium the most volatile pge is highly depleted 1 1 with respect to chondritic ratios in the m sized pgns and is observed in only 17 of 213 nanometer nuggets with concentrations that are just above the detection limit 0 2 distinct fractionation of the pge into ipge ir os ru and ppge seems to take place during the short span of atmospheric entry these observations suggest several implications 1 the observation of fractionated pge in an fe ni system gives rise to the possibility that earth s core could contain fractionated pge 2 the present data support the processes suggested for the fractionated pge patterns observed in the ejecta of ancient meteorite impacts 3 meteoric metals released in the troposphere could contain fractionated pgns in large numbers

uptake of elements from seawater by ferromanganese crusts solid phase associations and seawater speciation marine fe mn oxyhydroxide crusts form by precipitation of dissolved components from seawater three hydrogenetic crust samples one phosphatized and two hydrothermal mn oxide samples were subjected to a sequential leaching procedure in order to determine the host phases of 40 elements those host phase associations are discussed with respect to element speciation in seawater the partitioning of elements between the two major phases mn oxide and fe oxyhydroxide can in a first order approximation be explained by a simple sorption model related to the inorganic speciation of the elements in seawater as has been proposed in earlier models free and weakly complexed cations such as alkali and alkaline earth metals mn co ni zn tl i and partly y are sorbed preferentially on the negatively charged surface of the mno2 in hydrogenetic crusts the driving force is a strong coulombic interaction all neutral or negatively charged chloro cd hg tl carbonate cu y pb and u and hydroxide be sc ti fe zr nb in sn sb te hf ta bi th and tl iii complexes and oxyanions v cr as se mo and w bind to the slightly positively charged surface of the amorphous feooh phase while coulombic interaction can explain the sorption of the negatively charged species the binding of neutral species is based on specific chemical interaction organic complexation of elements in deep ocean water seems to be at most of minor importance surface oxidation can explain some strong metal associations e g of co and tl with the mno2 and te with the feooh sorption reactions initially driven by coulombic forces are often followed by the formation of specific bonds between the adsorbate and the atoms of the oxide surface differences in the associations of some metals between the non phosphatized and phosphatized hydrogenetic crusts and between the hydrogenetic and the hydrothermal samples reflect the different physico chemical environments of formation and speciations in oxic seawater vs less oxic fluids especially for the redox sensitive metals such as mo and v these environmental related differences indicate that the methodology of chemical speciation used here in combination with spectroscopic methods may allow for the detection of changes in paleoceanographic conditions recorded during the several tens of millions of years of crust growth

in situ filtration and preliminary molecular analysis of microbial biomass from the rainbow hydrothermal plume at 36 15 n on the mid atlantic ridge abstract elevated microbial biomass levels play a significant role in altering the chemical composition of hydrothermal plumes in this work a procedure was developed for collecting sufficient quantities of microbial biomass from a hydrothermal plume to allow the extraction of dna suitable for use in molecular analyses of the plume microbial populations during a geophysical survey along 200 km of the mid atlantic ridge mar southwest of the azores triple junction several new sites of hydrothermal activity were identified including the rainbow hydrothermal plume at 36 15 n the strongest such feature yet reported from the mar during the survey in situ filtration systems were used to collect microbial biomass from the water column onto 293 mm diameter 0 2 m pore membrane filters by pumping large volumes 300 500 l of seawater through the filters filter samples were collected from both the neutrally buoyant portion of the rainbow plume at a depth of 2050 m and from above it in the water column at 1500 m microgram quantities of genomic dna were extracted and purified from the biomass on these filters the suitability of the purified dna for use in molecular analyses was demonstrated by polymerase chain reaction pcr amplification of the small subunit ribosomal rrna ssu rrna gene from the two primary prokaryotic domains the bacteria and the archaea as indicated by the binding of domain specific oligonucleotide hybridisation probes to the purified dna the plume microbial populations contained a higher proportion of members of the domain archaea than the populations in the surrounding ambient sea water

dense microbial community on a ferromanganese nodule from the ultra oligotrophic south pacific gyre implications for biogeochemical cycles abstract during integrated ocean drilling program iodp expedition 329 a deep sea ferromanganese nodule and surrounding sediment were collected from the south pacific gyre the most oligotrophic oceanic environment on earth using a combination of cryo sectioning and fluorescence based cell counting techniques we determined that the microbial cell density at the very surface of the nodule was 108 cells cm 3 three orders of magnitude higher than that in the surrounding sediment analysis of bacterial and archaeal 16s rrna gene sequences 1400 bp indicated that the taxonomic composition of the nodule associated community differed markedly from that of the sediment associated community members of marine group i mgi thaumarchaeota are potentially crucial for sustaining the high cell density because both ammonia and cu were available on the nodule surface making it suitable for ammonia oxidizing chemolithoautotrophy mediated by copper enzymes combined cryo sectioning and synchrotron analysis of the nodule surface revealed both hexagonal birnessite resembling mno2 and triclinic birnessite minerals characteristic of biogenic oxide and its secondary product respectively regardless of these possible biogenic features only one gene sequence exhibited some similarity to previously identified manganese oxidizing bacteria on the other hand mgi thaumarchaeota were assumed as potential candidate of manganese oxidizers because they have multi copper oxidase that is utilized by most known manganese oxidizers therefore this archaeal group is considered to play a significant ecological role as a primary producer in biogeochemical elemental cycles in the ultra oligotrophic abyssal plain

field characteristics of laterally emplaced dikes anatomy of an exhumed miocene dike swarm in reydarfjordur eastern iceland abstract many dikes of the tertiary breiddalur dike swarm in reydarfjordur have a great lateral extent but are vertically upward and or downward discontinuous field relationships indicate that they are not the feeders of the lava pile they intrude their characteristics can be best interpreted as them constituting the fossil expression of lateral magma emplacement analogous to that occurring in the actively spreading krafla volcanic center of the neovolcanic zone average dike thickness increases clearly with depth and the thickness versus depth relationship is different from that described for other tertiary dike swarms in eastern iceland it is suggested that dikes represent the extent of finite spreading which at higher levels in the crust is expressed by fissures and other extensional structures

chloride depletions and enrichments in seafloor hydrothermal fluids constraints from experimental basalt alteration studies na k ca cl fluid was reacted with diabase at 400 and 425 c 400 bars and fluidrock mass ratio of 0 5 to assess the relative mobility of dissolved cl fluids from the present experiments reveal relatively large time and temperature dependent decreases in cl temperature increase enhances cl removal whereas reaction progress has the opposite effect these changes are not due to boiling and or phase separation at 400 and 425 c 400 bars cl removal from solution is accompanied by ca and na fixation respectively both experiments produced mixed layer chlorite smectite clinozoisite and albite olivine was not detected by x ray diffraction or petrographic analysis of run products from either experiment however we propose that the time dependent changes in dissolved cl result from olivine replacement by an fe hydroxy chloride phase followed by hydration effects quenched and washed alteration products however did not reveal anomalous cl which suggests that the cl bearing phase is characterized by retrograde solubility this is consistent with the relative magnitude of cl fixation observed for experiments at both temperatures and from results of an isobaric cooling experiment the experiments provide evidence for the non conservative behavior of cl during hydrothermal alteration of basalt the data are particularly important in light of the cl depleted nature of some ridge crest hot spring fluids and suggest temperatures of formation for these fluids of approximately 410 c assuming sub seafloor pressure of 400 bars in addition the retrograde solubility of the cl bearing phase responsible for cl fixation during high temperature basalt alteration may help to explain cl enrichment in hot spring fluids which have conductively cooled below 350 c

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

geophysical characterisation of active thermogenic oil seeps in the salt province of the lower congo basin part ii a regional validation abstract the lower congo basin is known to discharge a substantial volume of oil towards the sea surface from more than one hundred seafloor seep sites distributed throughout the deep province of the lower congo basin a large geochemical coring survey confirmed the presence of oil on the seabed the combination with the seismic data considerably improved the identification of the origin of the oil slicks on the seabed multiple specific geophysical characteristics of thermogenic hydrocarbon seep sites were highlighted in a previous detailed analysis of seismic datasets this study aims to test the characteristics previously identified at regional scale the active discharge zone is limited to the distal province of the basin it is characterised by strong compression shortening due to the sliding of the post salt super sequence resulting in numerous salt diapirs that control the location of seafloor oil seep sites the paper describes the bathymetric reflectivity amplitude and sub bottom profiler characteristics of a group of thermogenic seep sites they correspond essentially to submarine mounds or pockmarks of complex and irregular shape surrounded by hummocky mounds active oil pockmarks are systematically associated with positive amplitude anomalies on the seabed and are linked to vertical high amplitude columns rooted in the seismic reflector and associated with the base of the gas hydrate stability zone the sub bottom profiler data shows that the hummocky mounds are connected by a network of faults to high amplitude bodies buried under a consistent sediment thickness based on the definition of specific geophysical features seafloor mounds complex shape and irregular pockmarks positive anomalies of seafloor amplitude high amplitude vertical pipes we identified a series of potential oil seep sites at basin scale the mounds are particularly recognizable using the seismic curvature attribute we have identified 2946 individual hummocks that are grouped in 50 zones with a density of 35 240 per km2 they are believed to be associated with asphalt storage on the seafloor and related to the biodegradation of heavy oils during hydrocarbon dysmigration through the sedimentary pile unusual double bsrs occur over the study area these are also a specific feature of thermogenic seep sites barely half of the potential sites identified on the seismic datasets are associated with recurrent oil slicks at the sea surface the proportion of remaining anomalies may be associated with inactive seep sites over the period of satellite based monitoring or gas dominated seep sites

fast growing shallow water ferro manganese nodules from the western baltic sea origin and modes of trace element incorporation abstract ferro manganese nodules of the western baltic sea reveal enhanced heavy metal concentrations since the end of the 19th century and are therefore potentially useful for retrospective monitoring of the heavy metal pollution history however only zn shows a significant rise even though cu is also introduced to the western baltic sea by natural and anthropogenic sources this study focused on geochemical considerations to evaluate the mechanism responsible for the predominance of zn in ferro manganese nodules compared to cu the particulate and dissolved metal fractions in the water column in the fluffy layer an approximately 2 cm thick sediment layer situated at the sediment water interface and in the pore water adjacent to ferro manganese nodules were studied the analysis of the dissolved fraction and speciation studies were carried out using cathodic stripping voltammetry csv the particulate fraction and the pore water were analyzed via graphite furnace atomic absorption spectroscopy gf aas and inductively coupled plasma optical emission spectroscopy icp oes the fluffy layer provides high quantities of mn fe zn and cu to the dissolved fraction of the bottom water during the stratification period hence the signal manifested in the ferro manganese nodules consists of newly emitted elements on top of the amount collected in the fluffy layer over many years and remobilized throughout the stratification trace elements with the tendency to form weak inorganic complexes in the water column like zn are more likely to be incorporated in ferro manganese nodules and therewith document the anthropogenic metal input while elements which tend to form strong organic complexes such as cu are scavenged by particulate organic matter in the water column and the fluffy layer

geochemistry of north cleft segment vent fluids temporal changes in chlorinity and their possible relation to recent volcanism hydrothermal vent fluids from the north cleft segment of the juan de fuca ridge between 44 54 and 45 00 n were sampled in 1988 1990 1991 and 1992 in 1988 chloride depleted relative to seawater diffuse fluids with low dissolved metal concentrations relative to other mid ocean ridge mor fluids were sampled over a distance of 10 km along axis in 1990 and 1991 both high temperature 200 c and diffuse vents were consistently metal and chloride enriched the end member compositions of high temperature vents and nearby diffuse vents were very similar there were small but significant correlated changes in diffuse and high temperature composition from 1990 to 1991 the large scale but temporary venting of low chlorinity fluids over the entire north cleft segment provides a resolution to the apparent mass imbalance implied by observations of continuous venting of chloride enriched fluids it is possible that a volcanic event along the north cleft segment prior to 1987 for which there is firm geologic evidence initially caused a boiling event which resulted in the preferential venting of vapor enriched fluids through 1988 followed by a transition to brine enriched fluids by 1990 high iron low sodium and low sr ca ratios in the high chlorinity fluids suggest that the brine phase has continued to react and approach reequilibration with an alteration mineral assemblage after the phase separation event the absence of chloride depleted fluids from 1990 onward and the systematics of lithium boron and manganese with chloride in the high temperature fluids from north cleft suggest that the evolution toward lower chlorinity at monolith vent from 1990 to 1992 is caused by progressive dilution of a brine with hydrothermal seawater

salinity variations in submarine hydrothermal systems by layered double diffusive convection various mechanisms have been proposed to explain the salinity variations in vent fluids of seafloor geothermal systems new experiments reacting diabase and evolved seawater were carried out to reproduce earlier published observations of cl depletions attributed to formation of an ephemeral cl bearing mineral the absence of any cl depletions in the present study suggests that the formation of cl bearing minerals is not sufficiently widespread to account for the observed salinity variations in the vent fluids a re evaluation of both field and laboratory evidence has led to a new model for subseafloor circulation that accounts for salinity variations as well as other chemical and mineralogic observations in place of a simple single pass convection system we propose that the seafloor systems consist of two vertically nested convection cells in which a brine layer at depth heats and drives an overlying seawater cell such layering of salinities a process known in fluid mechanics as double diffusive conve

hydrothermal venting and the apparent magmatic budget of the juan de fuca ridge the fact that vigorous hydrothermal discharge occurs on ridge segments with a variety of spreading rates and morphological characteristics makes it difficult to discern the large scale geological controls on the distribution of hydrothermal venting along the mid ocean ridge we undertook to simplify this problem by mapping the distribution of hydrothermally produced thermal and light attenuation anomalies along the crest of the juan de fuca ridge a medium rate spreading center with segments of markedly differing morphology hydrothermal anomalies were detected by towing a high precision conductivity temperature depth transmissometer ctdt package in a sawtooth pattern through the lowermost 1000 m of the water column above each segment these surveys conducted between 1985 and 1989 have produced the first quantitative and continuous visualizations of hydrothermal plumes along a multisegment portion of the mid ocean ridge hydrothermal discharge is strongest on those segments or portions of segments where the apparent magmatic budget is highest as indicated by the degree of along axis inflation and other morphological characteristics this correspondence implies that magma is episodically delivered in small and spatially discontinuous bodies of melt rather than by the constant resupply of a steady state magma chamber we propose that the probability of discharge occurring at any point on the mid ocean ridge is proportional to the spreading rate this probability scaled by the observation that significant plumes presently emanate from 20 of the juan de fuca ridge is expected to range from 5 on the slowest spreading ridge to 50 on the fastest spreading ridge

ferromanganese nodules from manop sites h s and r control of mineralogical and chemical composition by multiple accretionary processes abstract the chemical composition of ferromanganese nodules from the three nodule bearing manop sites in the pacific can be accounted for in a qualitative way by variable contributions of distinct accretionary processes these accretionary modes are 1 1 hydrogenous i e direct precipitation or accumulation of colloidal metal oxides in seawater 2 2 oxic diagenesis which refers to a variety of ferromanganese accretion processes occurring in oxic sediments and 3 3 suboxic diagenesis which results from reduction of mn 4 by oxidation of organic matter in the sediments geochemical evidence suggests processes 1 and 2 occur at all three manop nodule bearing sites and process 3 occurs only at the hemipelagic site h which underlies the relatively productive waters of the eastern tropical pacific a normative model quantitatively accounts for the variability observed in nearly all elements zn and na however are not well explained by the three end member model and we suggest that an additional accretionary process results in greater variability in the abundances of these elements variable contributions from the three accretionary processes result in distinct top bottom compositional differences at the three sites nodule tops from h are enriched in ni cu and zn instead of the more typical enrichments of these elements in nodule bottoms in addition elemental correlations typical of most pelagic nodules are reversed at site h the three accretionary processes result in distinct mineralogies hydrogenous precipitation produces mno2 oxic diagenesis however produces cu ni rich todorokite and suboxic diagenesis results in an unstable todorokite which transforms to a 7 a phase birnessite upon dehydration the presence of cu and ni as charge balancing cations influence the stability of the todorokite structure in the bottoms of h nodules which accrete dominantly by suboxic diagenesis na and possibly mn 2 provide much of the charge balance for the todorokite structure limited growth rate data for h nodules suggest suboxic accretion is the fastest of the three processes with rates at least 200 mm 106 yr oxic accretion is probably 10 times slower and hydrogenous 100 times slower since these rates predict more suboxic component in bulk nodules than is calculated by the normative analysis we propose that suboxic accretion is a non steady state process variations in surface water productivity cause pulses of particulate flux to the sea floor which result in transient mn reduction in the surface sediments and reprecipitation on nodule surfaces

composition and textures of chromite and platinum group minerals in chromitites of the western ophiolitic belt from pampean ranges of cordoba argentina abstract chromitite bodies hosted in the neoproterozoic western ophiolitic belt of pampean ranges of cordoba argentina were studied at los congos and los guanacos ultramafic bodies with regard to the composition and textures of the chromite and platinum group minerals primary chromite composition is only preserved in some massive chromitites from the los guanacos ultramafic body and is similar to al rich ophiolitic chromitites suggesting that they crystallized from melts with back arc basin basalts babb affinity in the suprasubduction mantle subsequently these chromitites underwent a prograde metamorphism chromites from chromitites and associated metamorphosed ultramafic rocks show complex replacement and exsolution textures mineral chemistry and texture indicate that the chromite composition records two main metamorphic trends a first trend defined by chromite from massive chromitite in which there is an enrichment in fe3 and fe2 cr remain relatively constant and slightly depleted in al mg a second trend is defined by chromite from disseminated chromitite and metamorphosed dunite and harzburgite in which a fe rich phase is replacing the al rich chromite this alteration trend is characterized by enrichment in the total iron content fe3 fe2 and a strong depletion in al and mg the chemical composition of all analyzed spinels from los guanacos and los congos as plotted on the ternary fe3 cr al diagram correlates well with the cr spinels from the upper amphibolite to granulite facies metamorphism platinum group minerals pgm identified include native osmium laurite erlichmanite irarsite platinum and a number of inadequately identified phases such as an oxide or hydroxide of ru pt and ir ru pt telluride ir ru as se and ir ru ti compounds native osmium was the only pgm which remained unaltered other pgm underwent mineralogical reworking during metamorphism although it is difficult to establish the extent of platinum group element mobilization based on mineralogical observation our results suggest that the ru os ir pgm in the los guanacos and los congos chromitites were modified in situ producing re distribution of these pge on a small scale the presence of rare pt and pge as se minerals was possibly related to remobilization of pt as and se by fluids during the alteration processes

bacterial incorporation of relict carbon in the hydrothermal environment of guaymas basin abstract radiocarbon analyses of bulk carbon and individual organic compounds are presented for the hydrothermal environment of the rebecca s roost vent in the southern trough of the guaymas basin hydrothermal field the 14 c values of co 2 and ch 4 in the hottest hydrothermal fluids 317 c are nearly radiocarbon dead 944 and 923 respectively in contrast the 14 c values of sediments and individual fatty acids 418 to 227 obtained from a bacterial mat located south of the vent site are similar to values previously reported for hydrothermal petroleum in this environment and are more depleted in 14 c than overlying waters hydrothermal fluids moving through the sediments appear to supply 14 c of intermediate age to the bacteria this carbon may take the form of or may be supplied by processes similar to the generation of hydrothermal petroleum although the bacterial mat visibly was dominated by beggiatoa spp such mats are known to include numerous other species individual compound data show that preaged carbon is being consumed by the integrated bacterial assemblage values of 13 c and 14 c indicate that petroleum derived carbon is incorporated directly into fresh bacterial biomass subsequently some of this newly synthesized material also is consumed by heterotrophs as eukaryotic sterols from the same sample also have 14 c depleted values 14 c 136 to 110 therefore the entire system may operate as a complex consortium to transform relict carbon back into biomass bacterial consumption of relict carbon occurs despite the ample supply of fresh carbon delivered from the productive overlying water column

systematics of and postulated controls on submarine hydrothermal solution chemistry the chemical compositions of seafloor hydrothermal solutions from the galapagos spreading center 21 n and 13 n on the east pacific rise the southern juan de fuca ridge and the guaymas basin gulf of california are examined for systematic variations several elemental ratios elemental products and empirical geothermometers show much consistency among the various areas in spite of large absolute differences in elemental concentrations the results suggest that most of the major cations in these solutions are solubility controlled with respect to a similar phase assemblage at all of the sites examination of the solution chemistry in conjunction with experimental results and seafloor rock alteration data permits identification of phases which may be important in controlling the solution chemistry as potassium appears to be solubility controlled its use to calculate water rock ratios is inappropriate lithium appears to be a better element to use in these calculations a model to explain the observed solution chemistries as a result of three component mixing is discussed all of the solutions are postulated to be either the result of mixing between a seawater hydrothermal solution which has not undergone a phase separation and is hence gas containing a gas rich vapor phase and a gas poor brine phase or any one of these individual components alone the vapor and brine phases are the result of phase separation which may have occurred at some time in the past essentially all of the reported data fall within the field defined by these three components the solutions apparently have had sufficient time after the mixing event s to reequilibrate with the rock this is true for quartz as well as other chemical components the best test of this model is chloride together with gas and isotropic data as the model predicts that solutions with elevated chlorinities will be depleted in gases and enriched in 18 o and low chlorinity solutions will have elevated gas contents and lower 18 o

the influence of suboxic diagenesis on the formation of manganese nodules in the clarion clipperton nodule belt of the pacific ocean abstract polymetallic nodules and a single fe mn crust from the clarion and clipperton zone ccz of the equatorial eastern pacific have been analyzed to determine their chemical and mineralogical compositions icp oes analyses of bulk nodules from the ccz indicate that the nodules formed under oxic diagenetic conditions with typical mn fe ratios of 4 6 ni cu values of 2 3 wt co contents of 0 12 0 17 wt however detail analyses of individual growth layers by electron microprobe analyses empa reveal much larger chemical heterogeneity of individual layers with mn fe ratios ranging from 800 two different genetic types of layers can be distinguished layer type 1 dense layer with average mn fe ratios of 1 80 average ni cu of 0 81 wt co contents of 0 30 wt hydrogenetic metal precipitation from oxic waters these layers consist of fe vernadite mno2 epitaxially intergrown with feroxyhyte feooh nanoparticles layer type 2 growth structures dendritic growth structures and dense layers with average mn fe ratios of 96 ni cu of 3 9 wt co contents of 0 08 wt and a distinct ni cu maximum of 6 51 wt at a mn fe ratio of 56 suboxic diagenetic metal precipitation from suboxic pore waters type 2 layers mainly consist of turbostratic phyllomanganates such as 10 a vernadite 7 a vernadite and todorokite are minor compounds mixed layer type 3 these layers can occur as zones of low reflectivity in the transition from layer type 1 to 2 or build up inhomogeneous growth structures of nm thin layers of low or high reflectivity the mn fe ratios of this material range between 3 and 11 ni cu of 1 4 6 wt and co contents are between 0 02 and 0 77 wt in most cases these growth structures represent a mixture of type 1 and 2 layers x ray photoelectron spectroscopy xps of the recent outermost nm layers of nodules top rim and bottom side indicates hydrogenetic accretion processes under recent oxic conditions both from seawater and pore water the mixed type ccz nodules are interpreted to consist of an oxic hydrogenetic and a suboxic diagenetic end member calculations of the proportions of the individual layer end members show that suboxic layers make up about 50 60 of the chemical inventory of the ccz nodules whereas oxic hydrogenetic layers comprise about 35 40 the remaining part 5 10 consists of incorporated sediment particles occurring along cracks and pores these results demonstrate that suboxic conditions alternate with oxic conditions during the growth of nodules in the eastern ccz this is probably due to fluctuating bioproductivity in the equatorial pacific surface waters during glacial interglacial periods which led to changing organic carbon flux to the sediment and changing oxygen consumption in near surface sediments furthermore reduced ventilation of the deep ocean during glacial periods may have led to suboxic conditions in near surface sediments our investigations prove that bulk chemistry data of whole nodules only provides an average of individual layers that build up the nodules and is inappropriate for genetic interpretation

controls on the chemical composition of ferromanganese nodules in the clarion clipperton fracture zone eastern equatorial pacific abstract ferromanganese nodules have long been considered an attractive source for mn co ni and cu and potentially for the rare earth elements and yttrium rey sixteen exploration contracts have recently been granted for the clarion clipperton fracture zone ccfz in the eastern equatorial pacific and because of concern about the environmental impacts of seafloor mining some parts of the ccfz have been designated areas of particular environmental interest apei from which mining will be excluded as the apeis were selected based on surface ocean characteristics and seafloor topography estimated from satellite altimetry the abundance and composition of nodules in these areas are unknown and as a result their relevance as an intended baseline for mining disturbance has not been demonstrated to fill this gap we have undertaken a detailed study of the chemical composition of nodules and seafloor sediments in the uk contract area in the ccfz and its closest apei apei 6 there are distinct differences between the two sites nodules from the uk contract area are larger 10 15 cm in diameter compared to those from apei 6 2 4 cm diameter and they have faster growth rates 11 vs 3 mm ma nodules from apei 6 have on average higher contents of fe 7 2 vs 5 7 wt co 0 28 vs 0 13 wt and total rey 1120 vs 715 ppm relative to those from the uk contract area analyses of individual growth layers reveal that nodules from the uk contract area contain a greater proportion of mn rich phases that are also enriched in ni and cu although pore waters in the uppermost sediments are oxygen replete today these layers likely precipitated from suboxic sediment pore waters indicating that the supply of organic material to the sediments in this area has been higher in the past sediments from the uk contract area in turn have higher mn al ratios compared to sediments from apei 6 and have a higher proportion of mn in easily reducible phases nodules from apei 6 have a greater proportion of fe rich layers that are also enriched in co and the rey and likely precipitated from seawater these differences in the chemical composition of nodules from the uk contract area and apei 6 as well as differences in the oxygen penetration depth in the sediments mean that apei 6 does not provide a relevant geochemical baseline for mining disturbance in the uk contract area or for many other contract areas within the ccfz

deep ocean mineral deposits as a source of critical metals for high and green technology applications comparison with land based resources abstract ferromanganese fe mn crusts are strongly enriched relative to the earth s lithosphere in many rare and critical metals including co te mo bi pt w zr nb y and rare earth elements rees fe mn nodules are strongly enriched in ni cu co mo zr li y and rees compared to fe mn crusts nodules are more enriched in ni cu and li with subequal amounts of mo and crusts are more enriched in the other metals the metal ions and complexes in seawater are sorbed onto the two major host phases feo oh with a positively charged surface and mno 2 with a negatively charged surface metals are also derived from diagenetically modified sediment pore fluids and incorporated into most nodules seafloor massive sulfides sms especially those in arc and back arc settings can also be enriched in rare metals and metalloids such as cd ga ge in as sb and se metal grades for the elements of economic interest in sms cu zn au ag are much greater than those in land based volcanogenic massive sulfides however their tonnage throughout the global ocean is poorly known and grade tonnage comparisons with land based deposits would be premature the clarion clipperton fe mn nodule zone ccz in the ne pacific and the prime fe mn crust zone pcz in the central pacific are the areas of greatest economic interest for nodules and crusts and grades and tonnages for those areas are moderately well known we compare the grades and tonnages of nodules and crusts in those two areas with the global terrestrial reserves and resources nodules in the ccz have more tl 6000 times mn te ni co and y than the entire global terrestrial reserve base for those metals the ccz nodules also contain significant amounts of cu mo w li nb and rare earth oxides reo compared to the global land based reserves fe mn crusts in the pcz have significantly more tl 1700 times te 10 times more co and y than the entire terrestrial reserve base other metals of significance in the pcz crusts relative to the total global land based reserves are bi reo nb and w ccz nodules and pcz crusts are also compared with the two largest existing land based ree mines bayan obo in china and mountain pass in the usa the land based deposits are higher grade but lower tonnage deposits notably both land based deposits have

fe mn nodule morphotypes from the ne clarion clipperton fracture zone pacific ocean comparison of mineralogy geochemistry and genesis abstract ferromanganese nodules are polymetallic ore deposits considered to be archives of paleoceanographic proxies and targets of deep sea mining in the present paper nodules and underlying sediments from a claim area uk 1 within the eastern clarion clipperton fracture zone ccfz and from area of particular environmental interest apei 6 were analyzed in each area nodules are characterized by contrasting morphology mineralogy geochemistry and abundance the obtained results reveal three types of fe mn nodules type 1 smooth irregular nodules with sizes of 1 1 5 cm containing mainly 10 a phyllomanganates and phillipsite mn fe 2 50 high trace metal abundances co ni cu 2 10 high rare earth element and yttrium rey concentrations 1515 ppm positive ce anomaly hydrogenetic origin type 2 smooth discoidal nodules with sizes of 2 4 cm composed of 10 a phyllomanganates and buserite i mn fe 3 65 high trace metal enrichment co ni cu 2 35 positive ce anomaly mainly formed by hydrogenous precipitation type 3 nodules 3 15 cm with botryoidal surfaces and well defined concentric zonality mn fe 5 1 trace metal content co ni cu 2 42 the textural and chemical characteristics of nodules suggest that they acquire metals as a result of both hydrogenetic and diagenetic processes during nodule growth in alternating oxic suboxic conditions scanning electron microscopy sem in conjunction with energy dispersive x ray spectroscopy eds reveals abundant pseudomorphs which is considered possible evidence for biomineralization within the nodules the morphology mineralogy and geochemistry of the studied nodules are strongly affected by post accretional diagenetic processes which are closely linked to biomineralization

an overview of biomineralization processes and the problem of the vital effect biomineralization links soft organic tissues which are compositionally akin to the atmosphere and oceans with the hard materials of the solid earth it provides organisms with skeletons and shells while they are alive and when they die these are deposited as sediment in environments from river plains to the deep ocean floor it is also these hard resistant products of life which are mainly responsible for the earth s fossil record consequently biomineralization involves biologists chemists and geologists in interdisciplinary studies at one of the interfaces between earth and life leadbeater and riding 1986 biomineralization refers to the processes by which organisms form minerals the control exerted by many organisms over mineral formation distinguishes these processes from abiotic mineralization the latter was the primary focus of earth scientists over the last century but the emergence of biogeochemistry and the urgency of understanding the past and future evolution of the earth are moving biological mineralization to the forefront of various fields of science including the earth sciences the growth in biogeochemistry has led to a number of new exciting research areas where the distinctions between the biological chemical and earth sciences disciplines melt away of the wonderful topics that are receiving renewed attention the study of biomineral formation is perhaps the most fascinating truly at the interface of earth and life biomineralization is a discipline that is certain to see major advancements as a new generation of scientists brings cross disciplinary training and new experimental and computational methods to the most daunting problems it is however by no means a new field the first book on biomineralization was published in 1924 in german by w j schmidt schmidt 1924 and the subject has continued to intrigue a dedicated community of scientists for many years until the early 1980s the field was known as

local variations in distribution and composition of ferromanganese nodules in the clarion clipperton nodule province abstract local variations in nodule distribution and composition are discussed based on investigations in seven areas surveyed during five soviet expeditions beteween 1968 and 1988 to the clarion clipperton nodule province variations in nodule abundance are related to seafloor topography and to local changes in sedimentation rates caused both by bottom current activity and by carbonate dissolution below the lysocline and ccd most variations in nodule composition can be attributed to the two principal mechanisms of nodule growth hydrogenetic and diagenetic which create three genetic types of nodules differing in morphology mineralogy inner structure and chemistry hydrogenetic nodules relatively enriched in fe co and pb poor in mn cu ni and mo and with low mn fe ratios were found both on abyssal hills where they are associated with siliceous marly ooze and on the abyssal basin floor where they are associated with radiolarian ooze rugged bottom topography favours their occurrence and high abundance hydrogenetic nodules are though to be formed under distinct stable bottom current conditions diagenetic nodules enriched in mn cu ni and mo and with a high mn fe ratio occur on clayey radiolarian ooze on the abyssal basin floor below the ccd these nodules are deposited in high densities and are found predominantly on gentle slopes where upper quaternary clayey radiolarian ooze is only a few tens of centimetres thick and is unconformably underlain by pre quaternary pelagic clay we assume that the diagenetic growth of hydroxides is favoured by long term oscillations of bottom currents which lead to periodical redeposition of the soft unstable diagenetically active surface layer of radiolarian ooze the latter serves as a direct source of metals for nodule growth

authigenic phillipsite in deep sea manganese nodules from the clarion clipperton area ne equatorial pacific abstract occurrence optical properties chemical composition crystal structure and formation environments of the phillipsite within deep sea manganese nodules were systematically investigated phillipsite occurs in manganese nodules as nuclei along consolidated bottom sediments weathered volcanic debris and interstitial grains in all layers of manganese encrustments phillipsite is predominantly a pseudomorph of volcanic shards and occurs as white to pale yellow lath shaped and equant crystals they show prismatic blocky and bladed aggregations 2 to 20 m long and 2 to 5 m thick the chemical formula of phillipsite in a microprobe analysis is ca0 1mg0 3na1 1k1 5 fe0 3al4 2si11 8 o32 10h2o indicating a relatively siliceous and alkalic composition the si al fe3 ratio is 2 37 to 2 78 alkalis greatly exceed the divalent exchangeable cations and the na k ratio is 0 59 to 0 81 the mineral is monoclinic p2 1 m with the unit cell parameters a 10 005 a b 14 129 a c 8 686 a 124 35 and v 1013 6 a 3 phillipsites in manganese nodules formed apparently authigenically at a temperature less than 10 c and they crystallized at a pressure of less than 0 7 kbar and ph of about 8 due to deep sea environments

mineralogy and crystal chemistry of mn fe co ni and cu in a deep sea pacific polymetallic nodule minor element concentrations in marine ferromanganese nodules are primarily controlled by the mineralogy which itself depends on redox conditions at the sediment water interface results are presented for the first in depth x ray microstructural and microspectroscopic investigation of a mixed hydrogenetic diagenetic nodule which is representative of ferromanganese deposits on abyssal plains the measurements were conducted by micro x ray diffraction and x ray absorption spectroscopy both xanes and exafs on hydrogeneous and diagenetic regions of the nodule the hydrogenetic diagenetic interface was imaged by x ray microfluorescence after which regions of interest were chosen to represent mineralogical and chemical transformations that occurred at the early stage of suboxic diagenesis in the hydrogenetic nodule oxic environment mn is speciated as fe vernadite a nanocomposite material composed of intergrown feroxyhite feooh and monodispersed phyllomanganate layers having no interlayer mn vernadite in the diagenetic nodule suboxic environment mn is speciated dominantly as mg rich 10 a vernadite which consists of a random intergrowth of vernadite and its transformation product todorokite the authigenic 10 a vernadite precipitated from the components of vernadite in fe vernadite that were dissolved in suboxic microenvironments of the sediment direct evidence supporting a redox driven dissolution reaction is provided by the valence composition of mn as measured by micro xanes which is 0 69mn4 0 24mn3 0 07mn2 average 3 62 0 04 v u for fe vernadite and 0 61mn4 0 23mn3 0 16mn2 average 3 28 0 04 v u for 10 a vernadite ni and cu derived mainly from dissolved vernadite and oxidized organic matter replace structural mn3 4 in both the mno2 layer and todorokite domains of 10 a vernadite pure todorokite in highly diagenetic regions of the nodule has an average formula of mg2 0 167 mn4 0 783 mn3 0 099co3 0 002ni2 0 076cu2 0 040 o2 n h2o with an atomic ratio of cu ni co mn 0 13 which is slightly lower than 0 167 1 6 the maximum metal uptake capacity reported for marine nodules by analogy with synthetic todorokites we infer that mg2 which has a hydrated diameter close to that of the 3 3 tunnel size of todorokite and mn3 and cu2 which prefer jahn teller distorted octahedra play a crucial role in templating the topotactic transformation of 10 a vernadite to todorokite and stabilizing todorokite in suboxic marine sediments

volcanic eruption of the mid ocean ridge along the east pacific rise crest at 9 45 52 n direct submersible observations of seafloor phenomena associated with an eruption event in april 1991 in april 1991 we witnessed from the submersible alvin a suite of previously undocumented seafloor phenomena accompanying an in progress eruption of the mid ocean ridge on the east pacific rise crest at 9 45 n 52 n the volume of the eruption could not be precisely determined although comparison of pre and post eruption seabeam bathymetry indicate that any changes in ridge crest morphology resulting from the eruption were 10 m high effects of the eruption included 1 increased abundance and redistribution of hydrothermal vents disappearance of numerous vent communities and changes in characteristics of vent fauna and mineral deposits within the eruption area since december 1989 2 murkiness of bottom waters up to tens of meters above the seafloor due to high densities of suspended mineral and biogenic particulates 3 destruction of a vent community by lava flows mass wasting and possible hydrovolcanic explosion at a site known as tubeworm barbecue in the axial summit caldera asc at 9 50 6 n 4 near critical temperatures of hydrothermal vent fluids ranging up to 403 c 5 temporal variations over a 2 week interval in both temperatures and chemical isotopic compositions of hydrothermal fluids 6 unusual compositions of end member vent fluids with ph values ranging to a record low of 2 5 salinities ranging as low as 0 3 wt nacl one twelfth that of seawater and dissolved gases reaching high concentrations 65 mmol l for both co2 and h2s 7 venting at temperatures above 380 c of visually detectable white vapor that transformed to plumes of gray smoke a few centimeters above vent orifices 8 disorganized venting of both high temperature fluids black and gray smoke and large volumes of cooler diffuse hydrothermal fluids directly from the basaltic seafloor rather than from hydrothermal mineral constructions 9 rapid and extensive growth of flocculent white bacterial mats species unknown on and under the seafloor in areas experiencing widespread venting of diffuse hydrothermal fluid and 10 subseafloor downslope migration of magma normal to the ridge axis in a network of small scale 1 5 m diameter lava tubes and channels to distances at least 100 200 m outside the asc we suggest that in april 1991 intrusion of dikes in the eruption area to 200 m beneath the asc floor resulted in phase separation of fluids near the tops of the dikes and a large flux of vapor rich hydrothermal fluids through the overlying rubbly cavernous lavas low salinities and gas rich compositions of hydrothermal fluids sampled in the eruption area are appropriate for a vapor phase in a seawater system undergoing subcritical liquid vapor phase separation boiling and phase segregation hydrothermal fluids streamed directly from fissures and pits that may have been loci of lava drainback and or hydrovolcanic explosions these fissures and pits were lined with white mats of a unique fast growing bacteria that was the only life associated with the brand new vents the prolific bacteria which covered thousands of square meters on the ridge crest and were also abundant in subseafloor voids may thrive on high levels of gases in the vapor rich hydrothermal fluids initially escaping the hydrothermal system white bacterial particulates swept from the seafloor by hydrothermal vents swirled in an unprecedented biogenic blizzard up to 50 m above the bottom the bacterial proliferation of april 1991 is likely to be a transient bloom that will be checked quickly either by decline of dissolved gas concentrations in the fluids as rapid heat loss brings about cessation of boiling and or by grazing as other organisms are re established in the biologically devastated area

geochemistry of hydrothermal fluids from axial seamount hydrothermal emissions study vent field juan de fuca ridge subseafloor boiling and subsequent fluid rock interaction hydrothermal fluids collected from the ashes vent field in 1986 1987 and 1988 exhibit a very wide range of chemical composition over a small area 60 m in diameter compositions range from a 300 c gas enriched 285 mmol kg co2 low chlorinity 33 of seawater fluid to a 328 c relatively gas depleted 50 mmol kg co2 high chlorinity 116 of seawater fluid the entire range of measured compositions at ashes is best explained by a single hydrothermal fluid undergoing phase separation while rising through the ocean crust followed by partial segregation of the vapor and brine phases other mechanisms proposed to produce chlorinity variations in hydrothermal fluids precipitation dissolution of a chloride bearing mineral or crustal hydration cannot produce the covariation of chlorinity and gas content observed at ashes there is good agreement of the measured fluid compositions with compositions generated by a simple model of phase separation in which gases are partitioned according to henry s law and all salt remains in the liquid phase significant enrichments in silica lithium and boron in the low chlorinity fluids over levels predicted by the model are attributed to fluid rock interaction in the upflow zone depletions in iron and calcium suggest that these elements have been removed by iron sulfide and anhydrite precipitation at some time in the history of the low chlorinity fluids the distribution of low and high chlorinity venting is consistent with mechanisms of phase segregation based on differential buoyancy or relative permeability the relatively shallow depth of the seafloor 1540 m and the observed chemistry of ashes fluids are consistent with phase separation in the sub critical or near critical region

the occurrence of platinum group element and gold minerals in the bon accord ni oxide body south africa two samples from the enigmatic ni oxide body of bon accord barberton greenstone belt south africa have been investigated with the hydroseparation technique to obtain heavy mineral concentrates the concentrates contain abundant pt pd and gold minerals never reported before from the bon accord ni oxide body the grains occur as 1 minute inclusions 3 m in trevorite ideally nife3 o4 and 2 larger 5 70 m free aggregates liberated from the host phase the first group comprises several pgm compounds of pd sb pd sb as pd cu sb pt sb pt as s ru as s ru s along with free grains of ni fe as the second consists of sperrylite ptas2 members of the sobolevskite kotulskite series and electrum these results are in good agreement with previous analyses of pge au in bulk rock paragenetic relationships indicate that the pgm and electrum are of secondary origin probably generated during low temperature metamorphism of the ni rich mineralization they have a terrestrial origin and are related with a low sulfidation regime that usually accompanies hydrothermally driven serpentinization of mafic ultramafic bodies the ligands in the newly formed pgm as sb bi te and o probably proceed from the same source of the hydrothermal solutions in this model the metals ni pge au were original components of the primary mineral assemblage of the bon accord precursor whereas as sb bi te and o might have been contributed by the metasomatizing fluids during near surface evolution of the ore body the data on the high grade heavy mineral concentrates obtained by hydroseparation have provided new knowledge about the mineral deportment of pd pt and au

cobalt in ferromanganese crusts as a monitor of hydrothermal discharge on the pacific sea floor ferromanganese oxide crusts which accumulate on unsedimented surfaces in the open ocean1 6 derive most of their metal content from dissolved and particulate matter in ambient bottom water7 8 in proportions modified by the variable scavenging efficiency of the oxide phase for susceptible ions9 they differ in this respect from abyssal nodules much of whose metals are remobilized from host sediments here we present maps of cobalt concentration and inferred accumulation rate of ferromanganese crusts from the pacific ocean we propose that depletion of cobalt in pacific crusts measures the location and intensity of submarine hydrothermal discharge use of the cobalt chronometer an algorithm inversely relating cobalt content and crust growth rate permits mapping of the accumulation rate of ferromanganese crusts with only indirect recourse to radioactivity based dating methods these maps show that crusts in hydrothermal areas grow from two to more than four orders of magnitude faster than in the central pacific ocean cobalt enriched crusts are found where water masses are most isolated from continental coastal and hydrothermal sources of metals now and in the past this relationship can resolve the problem of cobalt enrichment in crusts without recourse to hypotheses invoking special cobalt sources or enrichment mechanisms

critical metals in manganese nodules from the cook islands eez abundances and distributions abstract the cook islands cis exclusive economic zone eez encompasses 1 977 000 km2 and includes the penrhyn and samoa basins abyssal plains where manganese nodules flourish due to the availability of prolific nucleus material slow sedimentation rates and strong bottom currents a group of cis nodules was analyzed for mineralogical and chemical composition which include many critical metals not before analyzed for cis nodules these nodules have varying sizes and nuclei material however all are composed predominantly of mno2 and x ray amorphous iron oxyhydroxide the mineralogy fe mn ratios rare earth element contents and slow growth rates mean 1 9 mm 106 years reflect formation primarily by hydrogenetic precipitation the paucity of diagenetic input can be explained by low primary productivity at the surface and resultant low organic matter content in seafloor sediment producing oxic seafloor and sub seafloor environments the nodules contain high mean contents of co 0 41 ni 0 38 ti 1 20 and total rare earth elements plus yttrium rey 0 167 and also high contents of mo nb v w and zr compiled data from a series of four cruises by the japan international cooperation agency and the mining agency of japan from 1985 to 2000 were used to generate a map that defines the statistical distribution of nodule abundance throughout the eez except the manihiki plateau the abundance distribution map shows a belt of high nodule abundance 19 45 kg m2 that starts in the southeast corner of the eez runs northwest and also bifurcates into a sw trending branch small isolated areas contain abundances of nodules of up to 58 kg m2 six 20 000 km2 areas of particularly high abundance were chosen to represent potential exploration areas and maps for metal concentration were generated to visualize metal distribution and to extrapolate estimated metal tonnages within the six sites and the eez as a whole grades for mn cu and ni are low in cis nodules in areas of high abundance however ti co and rey show high contents where nodule abundances are high of the six areas identified to represent a range of metal contents one at the northern end of the n s abundance main belt optimizes the most metals and would yield the highest dry metric tons for mn 61 002 292 ni 1 247 834 mo 186 166 v 356 247 w 30 215 and zr 195 323 when compared with the clarion clipperton zone the cis nodules show higher nodule abundances 25 kg m2 over 123 844 km2 and are more enriched in the green tech high tech and energy metals co ti te nb rey pt and zr the cis eez shows a significant resource potential for these critical metals due to their high prices high demand and the high nodule abundance which will allow for a smaller footprint for a 20 year mine site and therefore smaller environmental impact

ferromanganese oxide deposits from the central pacific ocean ii nodules and associated sediments bulk chemical mineralogical and selective leach analyses have been made on a suite of abyssal ferromanganese nodules and associated sediments from the s w equatorial pacific ocean compositional relations between nodules sediment oxyhydroxides and nearby ferromanganese encrustations are drawn assuming that the crusts represent purely hydrogenetic ferromanganese material crusts mno2 rich nodules and sediment oxyhydroxides are compositionally similar and distinct from diagenetic todorokitebearing nodules compared to fe mn crusts sediment oxyhydroxides are however slightly enriched relative to mn and ni in fe cu zn ti and al and depleted in co and pb reflecting processes of non hydrogenous element supply and diagenesis mno2 nodules exhibit compositions intermediate between fe mn crusts and sediment oxyhydroxides and thus are considered to accrete oxides from both the water column and associated sediments deep ocean vertical element fluxes associated with large organic aggregates biogenic calcite silica and soft parts have been calculated for the study area fluxes associated with organic aggregates are one to three orders of magnitude greater than those associated with the other phases considered are in good agreement with element accumulation rates in sediments and are up to four orders of magnitude greater than element accumulation rates in nodules metal release from labile biogenic material in surface sediments can qualitatively explain the differences between the composition of fe mn crusts and sediment oxyhydroxides todorokite rich diagenetic nodules are confined to an eastwards widening equatorial wedge it is proposed that todorokite precipitates directly from interstitial waters since the transition metal chemistry of interstitial waters is controlled dominantly by reactions involving the breakdown of organic carbon the supply and degradation rate of organic material is a critical factor in the formation of diagenetic nodules the wide range of trace metal mn ratios observed in marine todorokite reflects a balance between the release of trace metals from labile biogenic phases and the reductive remobilisation of mn oxide both of which are related to the breakdown of organic carbon

biogenic signature and ultra microfossils in ferromanganese nodules of the central indian ocean basin abstract theories related to the precipitation mechanism of the metallic elements in marine manganese nodules have remained controversial between two schools of thoughts 1 chemical oxidation abiotic origin and 2 deposition of the metals through microbial enzymatic processes biogenic origin one of the most important evidence in support of the biogenic origin is the occurrence of fossilized microbes however well documented literature in this regard is either lacking or very scanty in case of indian ocean nodules using high resolution feg sem we have recorded various biogenic signatures and ultra microfossils in the ferromanganese nodule samples from central indian ocean basin ciob that are presented in this paper the microfossils are mostly protozoans belonging to varieties of bacteria diatoms and foraminifera some of the features recorded in this study have perhaps never been reported before from any manganese nodules the chemical compositions of these ultra microfossils indicate a high level of manganese precipitation in and around them in comparison to the distant surrounding areas while clumpy microbes are enriched with nickel the rod shaped bacteria are rich in copper up to 4 70 wt nickel and 5 31 wt cu have been recorded in the fossilized microbe bodies the high abundance of biogenic features as well as microfossils in the ferromanganese nodules and their chemical compositions support arguments in favor of a dominant role of the microorganisms in the construction of the nodules of the ciob

geochemical variations of ferromanganese nodules and crusts from different provinces of the pacific ocean and their genetic control abstract the chemical composition of nodule samples from the northeast pacific nodule belt and from the northern part of the nazca plate in the southeast pacific have been investigated ni and cu contents increase with increasing mn fe ratio up to a value of 5 in samples from both provinces the nodules from the southeast pacific show a decrease in ni and cu contents when the mn fe ratio increases above a value of 5 nodules with a mn fe ratio of 5 have the highest concentrations of ni and cu a similar relationship cannot clearly be observed in nodules from the northeast pacific where the mn fe ratio does not exceed values of 7 4 the observed decrease in the ni and cu contents at mn fe ratios greater than 5 is a consequence of an enhanced supply of mn2 ions within the pore water environment of the upper centimeters to decimeters of the sediment column this leads to the incorporation of mn2 ions instead of ni2 and cu2 ions in the intermediate layers of the todorokite lattice increased amounts of organic matter in the sediment deposits below the equatorial zone of high biological productivity result in a decrease in the redox potential within the uppermost part of the sediment column which promotes the mobilization of mn nodules grow faster under these conditions and are enriched in mn and depleted in ni and cu the co contents of the nodules from the southeast pacific decrease in general with rising mn fe ratio considering three phase diagrams the geochemical discrimination of different genetic types of nodules is possible plotting only co vs mn and fe in a three phase diagram it can be elucidated that ferromanganese deposits richest in co only occur at mn fe ratios between 1 and 2 however the individual co values show a great range of variation in the case of early diagenetic nodules the samples from the southeast pacific show on the average lower concentrations of co than the nodules from the northeast pacific

a new discrimination scheme for oceanic ferromanganese deposits using high field strength and rare earth elements abstract ferromanganese fe mn deposits constitute a ubiquitous mineral type in oceanic settings with metal cu ni zn co pt and rare earth element ree enrichments of potential economic interest routine analysis of trace elements by icp ms has advanced our understanding of the impact of hydrogenetic diagenetic and hydrothermal processes on the mobility and interaction of high field strength elements hfse zr and ti and ree and yttrium rey with fe mn oxyhydroxides recent discoveries in the french exclusive economic zone eez of wallis and futuna southwest pacific ocean have brought new insight into the formation of low temperature lt hydrothermal mn deposits and lead us to reconsider the classification and discrimination diagrams for fe mn deposits and ore forming processes using a suite of lt hydrothermal fe mn crusts from wallis and futuna we investigate how contrasting genetic processes influence the distribution of metals mn fe cu ni and co hfse and rey in hydrogenetic diagenetic hydrothermal and mixed type deposits from different environments in the global ocean the interaction of the different metal oxide forming processes indicates that i enrichment of co hfse and rey is favored by hydrogenetic precipitation ii diagenetic processes produce higher mn cu and ni concentrations with oxic remobilization in the sedimentary column while suboxic conditions promote greater mn and fe remobilization that competes with the incorporation of cu and ni ions in nodules hfse and rey derived from seawater are usually low in diagenetic precipitates which discriminate between hydrogenetic and diagenetic inputs within nodules iii hydrothermal fe mn deposits show strong depletion in hfse and rey due to rapid formation and high contents of either fe or mn oxides we present a new discrimination scheme for the genetic types of fe mn deposits using a 10 cu ni co 100 zr y ce fe mn 4 ternary diagram the use of hfse and rey in the classification allows for a more robust discrimination of i each ore forming process with well delimited fields without overlap of metal rich hydrothermal samples and hydrogenetic samples ii oxic and suboxic diagenesis within nodules iii trends between hydrogenetic and diagenetic end members forming a continuum and iv mixed genetic types such as the presence of hydrothermal particles within hydrogenetic crust layers alternatives are also explored to adapt our discriminative diagram to elements measurable by on board instruments to aid in exploration at sea

critical metal enrichment mechanism of deep sea hydrogenetic nodules insights from mineralogy and element mobility abstract the micro nano textural features major and trace element compositions of ferromanganese nodule from the marcus wake seamount group of the western pacific ocean were documented in this study the ferromanganese nodules genetically comprise a core and three types of layers the core is made up of porous quartz and locally fe mn oxides layer close to the core layer i mantle ii and rim iii are featured by a massive dense layer with stromatolite like structure laminated and detrital and dendritic rim respectively these layers contain mainly birnessite goethite and quartz the mn fe ratios 1 0 4 1 mean 1 9 demonstrate a hydrogenetic genesis for these nodules the nodules have moderate enrichments 1000 10 000 ppm of na mg al p k ti co ni and cu with minor enrichments 100 1000 ppm of v zn as sr y zr nb mo ba and pb whereas other elements li sc cr ge se rb sn cs hf w bi th and u have concentrations of several tens of ppm based on the growth rate calculated by co concentration layer i has the lowest mean growth rate 1 8 mm myr followed by layer ii 2 3 mm myr and then layer iii 2 7 mm myr integrating the previous marine nodule studies in the south china sea we suggest that the massive dense layers were possibly resulted from a slow growth rate the conduits of various scales may have promoted the post depositional processes as they enlarged the surface area for fluid dissolution and reprecipitation nickel enrichment is associated with birnessite and promoted by the post depositional processes as evidenced by the higher ni content in the early formed layer i and its decreasing trend from core to rim cobalt may have associated with mn3 and has less effect by post depositional accumulation the fe content which may have related to goethite fe3 o oh shows good correlations with the rey ree y contents this correlation demonstrates the scavenging of reys by hydrothermal fe oxyhydr oxides reys are likely released during the post deposition as the rey contents are decreasing from the core to rim and negatively correlated with the accumulation time the similarity of rey distribution pattern between hydrothermal nodule and goethite bearing and mn oxides free banded iron formation bif may suggest hydrothermal fe may have linked to rey enrichments in deep sea sediments these micro nano sized conduits are well developed in either type i ii or iii layer which likely served as fluid circulating conduits and facilitate post depositional processes

compositions and transport of lipid biomarkers through the water column and surficial sediments of the equatorial pacific ocean abstract a systematic investigation of fluxes and compositions of lipids through the water column and into sediments was conducted along the u s jgofs egpac transect from l2 n to l5 s at 140 w fluxes of lipids out of the euphotic zone varied spatially and temporally ranging from 0 20 0 6 mmol lipid c m 2 day 1 lipid fluxes were greatly attenuated with increasing water column depth dropping to 0 002 0 06 mmol lipid c m 2 day 1 in deep water sediment traps sediment accumulation rates for lipids were 0 0002 0 00003 mmol lipid c m 2 day 1 lipids comprised 11 23 of corg in net plankton 10 30 in particles exiting the euphotic zone 2 4 particles in the deep egpac and 0 1 1 in sediments lipids were in general selectively lost due to their greater reactivity relative to bulk organic matter toward biogeochemical degradation in the water column and sediment qualitative changes in lipid compositions through the water column and into sediments are consistent with the reactive nature of lipids fatty acids were the most labile compounds with polyunsaturated fatty acids pufas being quickly lost from particles branchedchain c15 and c17 fatty acids increased in relative abundance as particulate matter sank and was incorporated into the sediment indicating inputs of organic matter from bacteria long chain c39 alkenones of marine origin and long chain c20 c30 fatty acids alcohols and hydrocarbons derived from land plants were selectively preserved in sediments compositional changes over time and space demonstrate the dynamic range of reactivities among individual biomarker compounds and hence of organic matter as a whole a thorough understanding of biogeochemical reprocessing of organic matter in the oceanic water column and sediments is thus essential for using the sediment record for reconstructing past oceanic environments