ferromanganese oxide deposits from the central pacific ocean i encrustations from the line islands archipelago abstract chemical and mineralogical analyses of a well controlled suite of ferromanganese encrustations from the line islands archipelago central pacific suggest that they represent purely hydrogenous deposits i e they have formed through the slow accumulation of trace metal enriched oxides directly from the water column mineralogically they consist predominantly of mno2 and amorphous feoohxh2o compositionally they are similar to mno2 nodules from adjoining basinal areas but are enriched in both mn mean 20 4 max 29 3 and co mean 0 55 max 1 57 mno2 is the most important trace metal bearing phase strong associations are noted between it and co mo ni zn and cd whilst only be is associated specifically with feooh v sr and pb are partitioned between the authigenic oxide phases whilst ti most probably occurs as tio2xh2o cu is contained in both aluminosilicate contaminant phases and fe oxide phases these relations are considered to reflect the differing scavenging behaviour of mn and fe oxides in the water column crusts from 1 2 km are enriched in mn and the mn related elements and exhibit higher mn fe ratios than deeper crusts which are compositionally constant the higher mn fe ratios may result from a supply of mn from continental borderland sediments at these depths which is transported horizontally by advective diffusive processes since manganophile elements are enriched relative to mn in the 1 2 km crusts it is considered that the supply of mn is scavenged by existing oxides is oxidised and effectively occludes them a higher proportion of oxide particles thus exhibit mn oxide scavenging properties in the 1 2 km depth zone the increased vertical flux of mn resulting from the supply at 1 2 km is not reflected by higher mn fe ratios in deeper crusts so that the vertical flux of oxides is not simply related to the standing crop the mn fe ratios of the crusts thus reflect the composition of suspended oxides at similar depths

thermospheric circulation temperature and compositional structure of the southern hemisphere polar cap during october november 1981 thermospheric temperature composition and winds at f region heights over the southern hemisphere polar cap have been measured by the dynamics explorer 2 de 2 satellite during october november 1981 perigee of the de 2 satellite during this period was over the southern hemisphere polar cap and measurements made along 0900 2100 local time polar passes are used to determine the average universal time dependence of thermospheric properties for this local time slice the f region wind vector is derived from the meridional wind component measured by the fabry perot interferometer fpi and the zonal wind component measured by the wind and temperature spectrometer wats instruments on board de 2 the neutral gas temperature is derived from fpi and wats measurements and the compositional structure is determined from the neutral atmosphere composition spectrometer instrument the measured temperature composition and winds along the 0900 2100 local time polar passes all display a universal time dependence that is due to the displacement between geomagnetic and geographic poles the temperature and molecular nitrogen densities are enhanced and the atomic oxygen density is reduced in the magnetic polar cap in comparison with lower latitude regions the neutral wind pattern follows the pattern of ion drift associated with magnetospheric convection the national center for atmospheric research thermospheric general circulation model tgcm is used to calculate the temperature composition and winds over the southern hemisphere polar cap region for conditions similar to those of october 1981 the tgcm includes displaced geomagnetic poles the temperature composition and winds are determined along the de 2 satellite track for various universal times the calculated winds are in general agreement with the observed winds both having a two cell pattern of magnetospheric convection the calculated and observed composition patterns are also in general agreement with predictions made by the mass spectrometer and incoherent scatter radar 1983 empirical model when models and observations are normalized to the same constant pressure surface the calculated and observed maximum compositional variations in the magnetic polar cap occur near 0900 ut when the dawn sector of the auroral oval passes over the south geographic pole the overall pattern of the calculated temperature variation is similar to that observed except for the period between 1300 and 1500 ut better agreement with temperature in this time range is obtained with the inclusion of auroral particle precipitation within the magnetospheric cusp

fenicu sulfides in tectonite peridotites from the maqsad district sumail ophiolite southern oman implications for the origin of the sulfide component in the oceanic upper mantle abstract forty samples of harzburgites and dunites from the maqsad oceanic mantle diapir southern oman have been investigated for the cu fe ni sulfide component and analyzed for sulfur the residual harzburgites contain less than 180 ppm of s the sulfide component is considered to be residual and to have survived the partial melting event giving rise to s saturated morb type magma the primary sulfide assemblage is closely associated with orthopyroxene dominated by pentlandite and chalcopyrite and very poor in pyrrhotite it has been partly altered into secondary sulfides and native metals awaruite and native copper by serpentinization related reducing fluids residual peridotites infiltrated by silicate melts subsequent to plastic deformation are strongly enriched in sulfur this applying especially to the dunites which contain up to 570 ppm s in this case the sulfide component has a metasomatic origin as demonstrated by its close association with the impregnation silicates clinopyroxene and to a lesser degree plagioclase and with cr spinel re equilibrated with the percolating silicate melts moreover the sulfide assemblage of the impregnated rocks differs from that of the harzburgites by virtue of a high cu ni bulk ratio the primary sulfide assemblage included in cr spinel has resisted low temperature alteration and is composed of pentlandite chalcopyrite bornite and very small amounts of pyrrhotite the metasomatic sulfide component of impregnated rocks is ascribed to s saturated silicate melts coming from deeper parts of the mantle and trapped at the top of the mantle diapir nevertheless sulfide precipitation differs from a simple gravity settling model and seems to be dependent on the precipitation of fe mg non sulfide minerals probably because the latter were capable of modifying the fe activity of the silicate melt which controls the s solubility

ionospheric effects during the total solar eclipse over southeast asia pacific on 9 march 2016 part 1 vertical movement of plasma layer and reduction in electron plasma density

the distribution of rare earth and minor elements in manganese nodules and sediments from the equatorial and s w pacific abstract 62 manganese nodules and 17 associated sediments from the equatorial and s w pacific have been analyzed for a number of elements including the rare earth elements ree by instrumental neutron activation sc co as hf th and ree occur in higher concentrations in s w pacific than in equatorial pacific nodules reflecting the higher iron content of the s w pacific nodules these elements are probably incorporated nondiscriminantly into the iron oxyhydroxide structure by direct sorption from seawater because they are too large to be incorporated into the manganese oxide structure the highest ce la ratios are also found in the s w pacific nodules this may result from the fact that these nodules lie beneath the path of the fast flowing well oxygenated antarctic bottom water aabw which facilitates oxidation of ce to the tetravalent state if so this supports the idea that the ce la ratio of manganese nodules is an important redox indicator negative cerium anomalies were noted for nodules from areas f and g can be interpreted on the same model the ree contents in equatorial pacific siliceous oozes and s w pacific red clays are similar on a carbonate free basis the ce la ratio of the s w pacific red clays is however much higher than that of the equatorial pacific sediments possibly reflecting the preferential oxidation of ce to the tetravalent state beneath the aabw there appears to be no systematic relationship between the ree abundance in the nodules and their associated sediments although absolute ree abundances are higher in nodules than in their associated sediments nodules with the highest ce la ratios are however found on sediments with the highest ce la ratios the principal difference in the ree distribution pattern of the nodules and sediments lies in the well known cerium anomaly which is positive to slightly negative for nodules and always negative for sediments

geomagnetic effects due to an eclipse induced low conductivity ionospheric spot 1 the solar eclipse on 11 august 1999 was quite unique due to its totality belt coverage of the territory of central europe where the facilities for the geophysical monitoring are most dense ionospheric and geomagnetic observations during the eclipse allowed us to study the eclipse induced effects more precisely a mathematical model based on the classical ashour chapman model is considered to show that the decrease up to 40 of the ionospheric total electron content in the region of the totality belt leads finally to geomagnetic disturbances quantitatively dependent on the position of both the quasi circular spot of the ionospheric conductivity decrease and given geomagnetic observatory location the model is generalized for the anisotropic ionosphere the theoretical estimates are compared with observational data from european geomagnetic observatories furstenfeldbruck nagycenk tihany and hurbanovo the last one being nearby the totality belt

growth rate variations of manganese nodules and crusts induced by paleoceanographic events time markers at about 3 ma 6 5 ma and 14 ma are common to 16 manganese nodules and crusts from different localities in the world oceans these time markers correspond to variations in the growth rates in the inner structure and in the chemistry of the samples the observed time markers could be related to 1 changes of the bottom water velocity and 2 variations in the manganese and iron contents in the deep ocean the time markers were determined by high resolution 10be dating applying the accelerator mass spectrometry facility at the eidgenossische technische hochschule zurich

marine os isotopic fluctuations in the early eocene greenhouse interval as recorded by metalliferous umbers from a tertiary ophiolite in japan abstract the mineoka umbers occur within the tertiary accretionary complex of central japan immediately overlying 53 7 ma tholeiitic basalts the associated tholeiitic basalts exhibit typical normal mid ocean ridge basalt n morb type geochemical signatures and are interpreted to be a remnant of tertiary oceanic crust centimeter resolution bulk rock chemical analyses were performed to cover the entire section of the 35 cm thick umber deposit there are striking similarities in major element trace element re and os contents between the umbers and modern metalliferous sediments along the east pacific rise these results demonstrate that the mineoka umbers are ancient counterparts of mor metalliferous sediments that are plume fall out ferromanganese precipitates scavenging various seawater derived elements including p v y rees and os and confirm that the umbers subaerially exposed in the accretionary complex generally preserve their primary geochemical signatures at the time of deposition the marine 187 os 188 os ratios inferred from the mineoka umbers gradually increase up section with moderate fluctuations the 187 os 188 os composition ranging from 0 47 to 0 54 is significantly higher than that of the prior period post paleocene eocene thermal maximum petm 187 os 188 os 0 38 this was probably the result of an increase in the chemical weathering rate of continental crust caused by the long duration of noticeably warm climate during the early eocene greenhouse interval several fluctuations observed in the marine 187 os 188 os record during this interval are most likely related to petm like brief hyperthermals supporting the suggestion that the intensity of continental crustal weathering controlled by climatic changes can fluctuate on timescales of 10 5 yr

comparison of the geochemistry of ophiolitic pyroxenites with a strongly fractionated dyke of pyroxenite from the sakhakot qila ophiolite pakistan abstract exceptionally strong fractionation has been found amongst the pyroxenite dykes crosscutting the ultramafic rocks of the sakhakot qila ophiolite pakistan one such dyke an fe websterite is particularly fractionated and anomalously feenriched and mg depleted this is supported by the data from whole rock analyses of major trace and rare earth elements as well as by the mineral chemistry of the constituent chromian spinel olivine clinopyroxene orthopyroxene and magmatic amphibole secondary sulphides of the fe websterite include troilite pentlandite instead of the awaruite heazle woodite pentlandite assemblage typical of all the other ultramafic rocks of the host ophiolite the non cumulate parent liquid of the magnesian pyroxenites crystallized in an initial episode when the surrounding cumulates were still hot in a belated second episode the fe websterite may have crystallized in isolated pockets after its differentiation to an extent much greater than that known from most pyroxenite dykes in ophiolites

a rise in the carbonate compensation depth of western tethys in the carnian late triassic deep water evidence for the carnian pluvial event the upper triassic of the lagonegro basin southern apennines southern italy is represented by hemipelagic cherty limestones of the calcari con selce formation deposited in an oceanic setting two stratigraphic sections petina chiana and pignola 2 representative of the evolution of the lagonegro basin during the carnian have been studied in detail with a multidisciplinary approach in the pignola 2 section within the calcari con selce formation a unique interval composed of green shales and radiolarites has been identified the absence of carbonate deposition within this interval is interpreted as evidence of a contemporaneous shallowing of the carbonate compensation depth conodont and palynomorph biostratigraphy constrain the age of this interval to the julian tuvalian lower carnian upper carnian boundary the age and characteristics of this interval suggest correlation with a putative climatic event known as the carnian pluvial event which has also been recognized in continental and shallow marine successions from different european localities this event is thus now documented also in a deep marine setting like the continental and shallow water settings it is characterized by a sudden input of siliciclastics petina chiana and pignola 2 integrate current knowledge of the carnian distribution of conodonts paragondolella praelindae kozur to date known only from the lower tuvalian has now been documented from the uppermost julian moreover a drastic turnover was recorded between julian and tuvalian conodont assemblages which is clearly associated with the carnian pluvial event thus a biotic crisis oceanographic changes associated with the rise of the carbonate compensation depth increased rainfall and an anomalous siliciclastic input occur contemporaneously at the time of the carnian pluvial event a similar pattern is associated with perturbations of the carbon cycle that occur during the jurassic and cretaceous e g in the early aptian thus it is hypothesized that the carnian pluvial event may have analogous causes

marine ferromanganese oxide a potentially important sink of light chromium isotopes abstract marine ferromanganese oxides are widely distributed in oxic marine sediments and are a sink for a range of metal elements derived from seawater their potential as a sink of chromium cr isotopes has yet to be investigated and may have important implications for our understanding of the cr isotope system in this study we reported cr isotope data of modern oceanic fe mn crusts for the first time the 53cr values of the surface scrapings of the fe mn crusts from the central north pacific seamounts range from 0 85 to 0 15 with an average of 0 42 0 34 2 n 11 which are lower than published data from pacific seawater 0 53 1 43 with an average of 0 79 these results reveal preferential removal of light cr isotopes from seawater into fe mn crusts with an isotopic fractionation 53cr 53crfe mn crust 53crseawater estimated from 2 3 to 0 7 averaging at ca 1 2 we suggest that such significant negative isotopic fractionation may have been reached through adsorption of dissolved cr vi oxyanions in the oxic water column onto the surface of mn oxide phases during the precipitation of fe mn crusts however our modelling results imply that the deposition of mn oxide sediments would make insignificant contribution to elevation of the global seawater average 53cr value

micromorphological characteristics of a marine ferromanganese crust abstract marine ferromanganese oxide crust fragments sampled from a massive equatorial pacific ocean crust deposit exhibit distinct micromorphological features and a microchemical distribution which have not been previous reported black shiny upper layers of the crust display a prismoidal microstructure and a unique crystallite habit expressed by a mosaic like design of hexagonal and pentagonal columns this columnar arrangement which has been previously reported on a scale of a few millimeters in other marine fe mn deposits extends vertically for several centimeters and is observed throughout the entire horizontal plane of growth of the crust and is the largest scale of morphological regularity observed in marine fe mn deposits to date the polygonal columnar structures which constitute the crust are mainly composed of mn fe and ti oxides aluminium and si rich intercolumnar space lamellae surrounds individual columns and sharply defines each polyhedron additionally the chemical composition of the crust fragments exhibits an unusual uniformity over several centimeters which to our knowledge has not been previously observed in marine fe mn minerals

hydrothermal altered serpentinized zone and a study of ni magnesioferrite magnetite awaruite occurrences in wadi hibi northern oman mountain discrimination through aster mapping abstract economic important minerals and ore deposits are common in hydrothermal altered serpentinized zone advanced spaceborne thermal emission and reflection radiometer aster satellite sensor is capable of discrimination of such hydrothermal mineralized zone and detection of hydrothermal altered minerals in the present study the hydrothermal altered serpentinized harzburgites of wadi hibi area of northern oman mountains have been discriminated by using aster vnir swir spectral bands by image processing methods and the occurrences of ni magnesioferrite magnetite awaruite in the rocks are studied the color composite rgb image developed using aster spectral bands 8 4 and 1 mapped well the occurrence of weathered peridotites by pale green to dark blue in colors and discriminated the hydrothermally altered serpentinized rocks by pale brown to dark blue colors due to the strong absorption of oh and mg oh molecules that occurred in the serpentine minerals of the rocks in the study area the aster band ratios 4 7 4 1 and 2 3 4 3 rgb images studied are capable of discrimination of hydrothermal mineralized areas more clear by pale blue to purple colors due to the strong absorption of such hydroxyl bearing serpentine minerals the studied image processing methods are evaluated by applying to the region of wadi sarami situated in the semail ophiolite oman in addition to that the occurrence of serpentine minerals namely lizardite and antigorite in the hydrothermally altered serpentinized region are detected qualitatively and quantitatively using spectral angle mapper sam supervised classification image processing method and studied the interpreted images are verified in the field and checked for the occurrences of minerals including ni magnesioferrite magnetite pentlandite and awaruite and are confirmed through laboratory studies petrographic study of serpentinized harzburgites shows that the rocks consist predominantly of antigorite and lizardite serpentines olivine and have the opaque minerals assemblage of ni magnesioferrite magnetite awaruite pentlandite developed during serpentinization of the rock the occurrences of such minerals are confirmed by xrd electron microprobe analyses and spectral measurements in the laboratory aster sensor proved its capability in discriminating the hydrothermal altered serpentinized zone and detecting the mineral occurrences and thus the study recommends the technique to the exploration geologists scientists and mining geologists for mapping of such rocks and minerals in the similar arid region

ionospheric effects of the solar eclipse of march 9 1997 as deduced from gps data this paper presents data from first measurements of total electron content tec and its gradient during the solar eclipse of march 9 1997 obtained with the gps radio interferometer at irkutsk the interferometer consists of three receivers one turbo rogue snr 8000 and two ashtech z 12 located at the vertices of a triangle and spaced by about 3 5 km the measured tec variations are indicative of profound changes in the ion production process in the ionosphere attendant on the solar eclipse simultaneously in a large volume of space with a radius of at height 300 km at 300 km altitude the delay of a minimum value of tec with respect to the maximum phase of eclipse at 300 km altitude was about 10 min and the depression depth of tec growth varies from l 3 1016m 2 by analyzing the data on tec gradient variations one is led to conclude that the depression of tec growth during the eclipse is essentially independent of the longitude and of the latitude within the observation ranges 52 6 n and 104 11 e

application of the ce anomaly as a paleoredox indicator the ground rules much attention has been paid in recent years to the potential application of the ce anomaly measured in various marine phases as a paleoceanographic indicator of widespread marine anoxia in this paper we present and discuss results from recent studies of present day rare earth element ree distributions and hence ce anomaly distributions in the marine environment which are particularly pertinent to paleoceanography subsequently we review and discuss the validity of the recent literature in which ce anomalies have been employed as paleoredox indicators

rare earth element geochemistry of ferromanganese crusts from the hawaiian archipelago central pacific abstract the rare earth element ree composition of ferromanganese deposits from the hawaiian archipelago was determined as part of a geochemical investigation into the origin and environment of deposition of crusts most samples exhibit shale normalized ree patterns which are typical of hydrogenous ferromanganese deposits patterns of two todorokite and manjiroite rich crusts are significantly different from those of the other samples the range of concentrations in typical hawaiian crusts sum of ree 0 15 0 25 wt is in the uppermost portion of that reported for deep sea fe mn nodules shallow water 2000 m as well as slightly greater ree fractionation large positive ce anomalies attributed to the oxidative scavenging at the mno 2 surface are observed on all samples except one the slight light ree lree depletion in shallow water crusts relative to deeper samples is discussed in terms of variations in the ree concentrations in the water column and the relative complexing behavior of the ree no significant trend in ce concentration with depth is observed partition coefficient calculations suggest that concentrations of trivalent ree in crusts are affected by their availability in seawater to a greater extent than by the composition of the scavenging ferromanganese oxide flocs

variations in the fine scale composition of a central pacific ferromanganese crust paleoceanographic implications a 47 to 60 mm thick fe mn crust from horizon guyot water depth 1800 1780 m central pacific was used to evaluate the potential of crusts as recorders of neogene paleoceanographic and paleoclimatic conditions the chemical composition was determined by microprobe for 16 elements from a polished thin section three analyses were made per millimeter and averaged to give the composition of each millimeter the age of the crust was determined by measuring the strontium isotope composition of the crust and comparing it with the tertiary seawater curve the crust represents 18 5 m y of growth of fe and mn oxyhydroxides the crust is composed of alternating botryoidal and laminated layers the botryoidal layers formed during the same time intervals that widespread neogene deep sea hiatuses were forming in bottom sediments the botryoidal layers represent growth during times of intensified deepwater flow whereas the laminated intervals represent more quiescent conditions the correspondence between the botryoidal layers and the neogene hiatuses is so strong that we were able to choose a variable growth rate model over a constant growth rate model for the crust chemical changes in the crust take two forms the first is represented by broad changes in the composition defined chiefly by fourth order polynomial fits to the chemical profiles of each element with depth in the crust the second is high frequency changes in composition the broader changes occurred primarily at about 15 11 5 7 4 6 4 5 2 and 4 6 ma which may correlate with major changes in paleoceanographic circulation and development of ice caps at the poles the periods of the high frequency changes may reflect climatic changes that resulted from orbital forcing these high frequency changes may correspond to the high order eccentricity periods of 3 47 2 04 and 1 31 m y

late cretaceous and cenozoic paleoceanography from north east atlantic ferromanganese crust microstratigraphy abstract oceanic hydrogenetic ferromanganese fe mn crusts precipitate directly from ambient seawater over millions of years their very slow growth rates and physio chemical properties mean that they adsorb numerous elements from seawater as such they provide condensed records of seawater evolution through time that can be used for paleoceanographic reconstruction here we present the results of a high resolution stratigraphic textural and geochemical investigation of a core sample obtained from a fe mn crust pavement located on the summit of tropic seamount in the tropical north east atlantic ocean a number of observations and interpretations are proposed within the context of a well constrained age model spanning the last 75 2 myr this core has textural stratigraphic coherence with pacific fe mn crusts formed since the late cretaceous highlighting that global oceanic and climatic phenomena exert first order controls on fe mn crust development all major hiatuses observed in the fe mn crusts are contemporaneous with erosion events occurring throughout the atlantic ocean high resolution geochemical data indicate that there is variability in the composition of fe mn crusts at the cm to m scale the dominant factors controlling this include major oceanographic events mineral textures and micro topography

marine cobalt resources ferromanganese oxides in the open oceans are more enriched in cobalt than any other widely distributed sediments or rocks concentrations of cobalt exceed 1 percent in ferromanganese crusts on seamounts ocean ridges and other raised areas of the ocean the cobaltrich crusts may be the slowest growing of any earth material accumulating one molecular layer every 1 to 3 months attention has been drawn to crusts as potential resources because they contain cobalt manganese and platinum three of the four priority strategic metals for the united states moreover unlike abyssal nodules whose recovery is complicated by their dominant location in international waters some of the most cobalt rich crusts occur within the exclusive economic zone of the united states and other nations environmental impact statements for crust exploitation are under current development by the department of the interior

the influence of the carbonate dissolution rate on the growth and composition of co rich ferromanganese crusts from central pacific seamount areas abstract the metal composition of oceanic ferromanganese deposits occurring in seamount regions line islands chain and mid pacific mountains varies with water depth and age the results of metal determinations of carbonate plankton samples suggest that carbonate dissolution in the water column might have an important influence on the accretion and composition of hydrogenetic precipitates two ferromanganese crust generations of different age have been observed the precipitation of the older crust took probably place during early oligocene the younger crust began to form during middle miocene between the two crust generations periods of carbonate sedimentation and of phosphorite deposition occur the hydrogenetic formation of the crusts is controlled by the metal supply from the water column according to the laws of colloidal surface chemistry dissolution experiments with carbonate plankton samples show that the main fe source for the hydrogenetic crust formation are colloidal fe hydroxide particles being released in the water column from the dissolution of carbonate plankton skeletons in the case of mn maximum dissolved mn occurs in the oxygen minimum zone as the result of in situ break down of organic matter and the in situ reduction of mn bearing solid phases closely beneath the oxygen minimum zone a fe supply mobilized within the oxygen minimum zone has also to be taken into account in the water column below the oxygen minimum zone a mixture of colloidal particles of mn fe oxyhydroxide and colloidal al fe silicate precipitate together on the surface of substratum rocks the mixing ratio of these colloidal phases controlling the metal composition of the ferromanganese precipitates is depth dependent and shows also temporal variations in general mn fe ratio ni and co contents decrease with depth down to the calcite compensation depth the most probable mechanism for the ultimate removal of co and ni from the water column might be a surface reaction mno2 is specifically able to absorb hydrous co2 and ni2 ions because of the surface enrichment of co and the strong electrical field of mn iv a subsequent oxidation of co2 to co3 takes place leading to higher enrichment of co in comparison to ni the most important factor governing the high co enrichment in the ferromanganese crusts is the growth rate the lower the growth rate the higher the co content maximum values of up to 2 co occurring in samples from water depths between 1500 and 1100 m 1 are related to lower carbonate dissolution rates and corresponding lower fe supply the metal supply from the water column is strongly related to distinct environmental factors such as bio productivity range of lysocline and calcite compensation depth rate of carbonate dissolution and activity of the antarctic bottom water thus our model shows that the growth periods and the metal composition of hydrogenetic seamount crusts are controlled by changes in the paleoceanography and reflect distinct environmental conditions

the midlatitude ionosphere during the total solar eclipse of march 9 1997 the total solar eclipse of march 9 1997 was visible from some regions of china mongolia and east siberia during 0045 0130 ut the eclipse coincided with a relatively long geomagnetically quiet period during the total solar eclipse the observations included oblique incidence ionograms recording also measurement the total electron content along specified directions to the visible global positioning system satellites and the doppler sounding on various hf ray paths over the region under consideration were carried out this paper presents results derived from studying the spatial pattern of midlatitude ionospheric response to this eclipse on the basis of a numerical simulations calculations have been executed using a model for ionosphere plasmasphere coupling comparison of model results with data of all measurements showed a good qualitative and quantitative agreement it is shown that by and large the behavior of the ionosphere during the eclipse manifests itself as a short lasting l hour rearrangement to nighttime conditions with the ion flow directed downward from the plasmasphere as a rise of the f2 layer maximum by about 20 km and as a twofold increase in electron density at the height of the maximum during the eclipse s totality phase the electron temperature decreases by 200 400 k while the ion temperature drops only slightly it is found that changes in the spatial distribution of electron density along the hf ray paths during the eclipse give rise to variations of doppler frequency shift with amplitudes of about 1 hz and a duration of about 120 min the findings reported in this paper do not validate the hypothesis that solar eclipses generate atmospheric gravity waves and associated traveling ionospheric disturbances

processes controlling the heavy metal distribution in pacific ferromanganese nodules and crusts the ferromanganese precipitates existing in deep sea waters of the pacific consist of two types of deposits 1 nodules mainly are distributed in pelagic basins beneath the ccd calcite compensation depth where the rate of sedimentation is low 2 polymetallic encrustations are formed on exposed seamount rocks where currents prevent normal sediment accumulation nodules being formed in areas bordering the equatorial zone of high biological productivity grow by two different processes a early diagenetic growth by supply of metals and metal compounds from pore water and b hydrogenetic growth by supply of colloidal particles from near bottom seawater these processes lead to different kinds of oxide and different metal contents

mineralogical and geochemical constraints on the origin of ferromanganese crusts from the rivera plate western margin of mexico abstract marine hydrogenetically precipitated ferromanganese crusts are widespread in the pacific ocean they occur as pavements coating volcanic or sedimentary hard rock substrates mainly on the slopes of seamounts plateaus and hills in ocean basins and continental margins we studied three ferromanganese crusts from one dredge haul from the rivera plate western margin of mexico which are up to 15 mm thick and grow directly on a substrate of pillow basalt fragments they consist of laminated botryoidal porous aggregates mostly of fe and mn oxyhydroxides and up to 10 silicates xrd analysis showed the predominance of poorly crystallized mineral phases in the crusts that include mn feroxyhyte and vernadite and an authigenic smectite like clay detrital minerals probably derive from granodiorites of the eastern wall of the neighboring middle america trench scattered barite grains occur on the crust surface and suggest plume fall out derived from hydrothermal vents although a possible pelagic source cannot be dismissed ratios between major fe mn si and trace co ni cu elements reveal that such crusts are predominantly hydrogenetic in origin although they show a hydrothermal influence that increases in the outer layers iron contents range from 16 2 to 25 2 wt and manganese from 3 4 to 14 5 wt the fe mn ratio ranges from 1 6 to 7 0 the sio 2 al 2 o 3 ratio ranges from 4 3 to 6 6 indicating the presence of biogenic silica radiolarians the concentrations of copper up to 383 ppm and cobalt up to 534 ppm are significantly below those of the typical hydrogenetic crusts whereas ni up to 1320 ppm is about the same or slightly lower ree normalized profiles and ree values 486 to 732 ppm match those reported for hydrogenetic crusts but suggest a hydrothermal contribution for the later crust layers the inferred crust growth rates using the co chronometer 44 and 229 mm myr are higher than those reported for pure hydrogenetic crusts mostly 1 to 6 mm myr thus indicating an increasing hydrothermal influence the highest growth rate 229 mm myr corresponding to the outer crust layers suggests a regional hydrothermal input of iron and manganese to seawater the intensification of regional submarine hydrothermal activity began about 13 000 yr ago and may be related to the tectonic activity in the complex junction of the rivera cocos pacific and north america plates

cobalt and platinum rich ferromanganese crusts and associated substrate rocks from the marshall islands abstract ferromanganese crusts cover most hard substrates on seafloor edifices in the central pacific basin crust samples and their associated substrates from seven volcanic edifices of cretaceous age along the ratak chain of the marshall islands are discussed the two most abundant substrate lithologies recovered were limestone dominantly fore reef slope deposits and volcanic breccia composed primarily of differentiated alkalic basalt and hawaiite clasts in a phosphatized carbonate matrix the degree of mass wasting on the slopes of these seamounts is inversely correlated with the thickness of crusts crusts are generally thin on limestone substrate away from areas of active mass wasting processes and large atolls crusts may be as thick as 10 cm maximum the dominant crystalline phase in the marshall islands crusts is mno 2 vernadite high concentrations of cobalt platinum and rhodium strongly suggest that the marshall islands crusts are a viable source for these important metals many metals and the rare earth elements vary significantly on a fine scale through most crusts thus reflecting the abundances of different host mineral phases in the crusts and changes in seawater composition with time high concentrations of cobalt nickel titanium zinc lead cerium and platinum result from a combination of their substitution in the iron and manganese phases and their oxidation potential

interelement relationships in ferromanganese crusts from the central pacific ocean their implications for crust genesis the fine scale chemical variations in ferromanganese fe mn crusts from the central pacific ocean were investigated using a variety of techniques in order to elucidate their genesis thirty seven major minor and trace elements were determined by icp oes and icp ms in sub samples collected at approximately 2 mm intervals throughout the crust sequences an inverse relationship is observed between the logarithm of the elemental distribution coefficients log cmncsw and the mean residence time tr of elements in seawater these associations provide evidence supporting the strong link between seawater and fe mn crust chemistry results of factor analysis reveal that elements in crusts can generally be partitioned into four major groups with selected elements displaying associations with several groups these statistical associations are interpreted to represent hydrogenetic mn ni co cu ce zn biogenic ba zn cu pt fe detrital al si fe and carbonate fluorapatite ca p ree groups a comparison between elemental associations in fine scale data from individual crust sequences and bulk compositional data from samples collected in separate locations reveals very similar elemental associations the similar elemental associations in bulk samples and in fine scale subsamples from individual crusts are consistent with the notions that hydrogenetic crusts exhibit no significant post depositional remobilization of elements and that elemental distributions within crusts reflect the chemistry of oceanic water during the period in which they accreted chemical paleotracks are proposed based on factor scores derived from chemical variations as a function of depth in individual crusts our results show that there is internal consistency between the chemical evolution previously proposed seamount paleotracks and nanofossil biostratigraphy dating results

cufenis mineral assemblages in upper mantle peridotites from the table mountain and blow me down mountain ophiolite massifs bay of islands area newfoundland their relationships with fluids and silicate melts abstract plastically deformed ultramafic rocks in the table mountain and blow me down mountain ophiolites comprise a basal unit of slightly depleted iherzolites an intermediate sequence of strongly depleted harzburgites and an upper zone of dunites also referred to as a transition zone intensively percolated by basaltic melts or magmatic fluids thirty five samples including all of the above rock types have been investigated on 100 polished thin sections for cu fe ni s mineral assemblages most of them contain traces of cu fe ni sulfides native metals and locally ni arsenide compositional features of opaque assemblages as well as their textural sites in the rocks indicate that the present cu fe ni s minerals derive from an upper mantle sulfide component through extensive subsolidus re equilibration down to 100 c the primitive component predominant pentlandite minor pyrrhotite and chalcopyrite is preserved as sulfide inclusions in chromites of the transition zone due to a subsolidus re equilibration in a closed system on the contrary sulfide assemblages interstitial to silicates and spinel have extensively reacted with reducing serpentinizing fluids to produce sulfur deficient sulfides such as heazlewoodite and mackinawite and native metals native copper and awaruite microscale variations of redox conditions and the removal of fe from the silicate during serpentinization may account for the peculiar grain by grain equilibrium state of intergranular assemblages in spite of low temperature alteration a gradual depletion in sulfide component has been recognized from the basal lherzolites to the intermediate harzburgites while the sulfide content gradually increases in the transition zone up to 0 2 by volume the first pattern is consistent with the low melting nature of the sulfide component in mantle melting processes microstructural criteria such as the absence of sulfide inclusions in olivine neoblasts demonstrate that the sulfide component postdates plastic deformation of the transition zone the sulfide enrichment pattern is thus ascribed to the percolation of a sulfur saturated basaltic magma into residual dunites

age determinations and growth rates of pacific ferromanganese deposits using strontium isotopes abstract 87 sr 86 sr ratios trace element and ree compositions and textural characteristics were determined for three hydrogenetic fe mn crusts one hydrothermal deposit and two mixed hydrothermalhydrogenetic crusts from the pacific the sr isotope data are compared to the sr seawater curve for the cenozoic to determine the ages and growth rates of the crusts the 87 sr 86 sr in the crusts does not increase monotonically with depth as expected if the sr were solely derived from seawater and perfectly preserved since deposition this indicates post depositional exchange of sr or heterogeneous sources for the sr originally contained in the crusts textures of hydrogenetic crusts generally correlate with sr isotopic variations the highest porosity intervals commonly exhibit the highest 87 sr 86 sr ratios indicating exchange with younger seawater intervals with the lowest porosity commonly have lower 87 sr 86 sr and may preserve the original sr isotopic ratios minimum ages of crust growth inception were calculated from dense low porosity intervals growth of the hydrogenetic crusts began at or after 23 ma although their substrates are cretaceous estimated average growth rates of the three hydrogenetic crusts vary between 0 9 and 2 7 mm ma consistent with published rates determined by other techniques within the marshall islands crust growth rates for individual layers varied greatly between 1 0 and 5 4 mm ma for one crust very low 87 sr 86 sr ratios occurred in detrital rich intervals hydrothermal fe mn oxide from the active lau basin back arc spreading axis valu fa ridge has an 87 sr 86 sr ratio with a predominantly seawater signature 87 sr 86 sr 0 709196 indicating a maximum age of 0 9 ma one crust from an off axis seamount west of gorda ridge may have begun precipitating hydrogenetically at 0 5 ma 0 709211 and had increasing hydrothermal or volcanic input in the top half of the crust indicated by a significantly lower 87 sr 86 sr ratio 0 709052

molybdenum isotopes in hydrothermal manganese crust from the ryukyu arc system implications for the source of molybdenum abstract a high concentration of molybdenum mo is a striking feature of modern marine hydrothermal manganese mn crusts from both low and high temperature hydrothermal systems however the origin of that mo is poorly constrained in this study we analyzed mo isotopic composition 98 95mo in a mn crust collected from the ryukyu arc system and assessed the possible use of 98 95mo to constrain the origin of mo in hydrothermal mn crusts along with mo isotope analysis we also measured the abundance of major and trace elements and the re os isotopic composition the mn crust sample had a high mn content 42 47 and was low in fe 0 2 0 5 among the manganophile elements co ni cu zn and mo only mo showed high concentrations 550 ppm we also found low contents of os 35 ppt with an isotopic composition of 187os 188os 1 00 these results are consistent with previously reported chemical compositions of hydrothermal mn crusts 98 95mo values in the sample ranged from 0 56 to 0 66 which are 2 7 lighter than the present day seawater 98 95mo but similar to those in modern hydrogenous fe mn crusts and mn nodules although current data do not preclude the possible contribution of hydrothermally derived mo the light 98 95mo values can be explained by isotope fractionation associated with a change in coordination number during the adsorption of mo from seawater onto mn oxides we suggest that the 98 95mo data are useful for constraining the source of mo in hydrothermal mn crusts

thermospheric response to the june 11 1983 solar eclipse the ncar thermospheric general circulation model tgcm that includes coupling of dynamics and composition is used to calculate the time dependent thermospheric response to the june 11 1983 total solar eclipse the path of totality originated at sunrise in the indian ocean near 35 s and 60 e the path moved equatorward passing through indonesia near 5 s latitude 125 e longitude and ending near 20 s latitude and 165 e longitude in the vicinity of the solomon islands although the path of totality is relatively small the area of partial shadow is relatively large and the total flux incident on the dayside earth decreases by about 7 during the total eclipse the tgcm calculates the time dependent response of the winds temperature and mass mixing ratios of the major constituents throughout the thermosphere perturbations follow the path of totality with maximum deviations occurring near 0530 ut at about 350 km the winds converge from all directions toward the shadow at speeds reaching 60 m s 1 in the upper thermosphere the maximum temperature anomaly 70 k and vertical wind anomaly 8 m s 1 occur near the center of the shadow the mass mixing ratio at n2 along a constant pressure surface decreases by up to 2 and that of o increases by up to 2 in response to the sudden thermospheric cooling caused by the shadow passing over the dayside of the earth at a constant altitude of 300 km the n2 and o number densities both decrease by about 6 the time dependent calculation shows that disturbances are generated during the onset of the eclipse with the largest perturbations following the path of totality

preferential dissolution of benthic foraminiferal calcite during laboratory reductive cleaning we have investigated the effect of cleaning procedures on eight element ca ratios in three widely used benthic foraminifera species from core top and down core sediments two cleaning techniques were employed 1 comparison between mg cleaning and cd cleaning methods and 2 comparison between the various constituent reagents li ca b ca and sr ca ratios remained unchanged for samples subjected to different treatments but mg ca mn ca zn ca cd ca and u ca were substantially decreased when foraminifera shells were cleaned with reagents containing citrate in contrast no significant decreases in element ca ratios were observed for samples cleaned in n2h4 without citrate indicating that the role of n2h4 was insignificant during reductive cleaning and that citrate is responsible for decreases of mg ca mn ca zn ca cd ca and u ca decreases in these ratios are most likely due to 1 removal of contaminant particles enriched in mg mn zn cd and u and or 2 preferential leaching of caco3 by the formation of stable metal complexes through chelation between citrate and metals heterogeneously distributed in foraminiferal shells due to the negligible effect of n2h4 and preferential dissolution of caco3 during reductive cleaning it is suggested that the reductive cleaning step should be omitted and the mg cleaning method barker et al 2003 could be employed to clean foraminiferal shells for trace element measurements

tectonic and paleoceanographic conditions during the formation of ferromanganese nodules from the northern south china sea based on the high resolution geochemistry mineralogy and isotopes abstract deep water ferromanganese fe mn nodules cumulate trace elements from the underlying sediment pore water and seawater during the concentric mineral layers growth process over millions of years they can record long term tectonic movements and paleoceanographic changes to systematically ascertain paleoceanographic evolution of the deep south china sea scs since the last 3 2 ma we comprehensively investigated microstructure mineralogy geochemical element concentrations as well as sr nd and pb isotopic compositions in the fe mn nodules nearby the dongsha islands in the northern scs results indicate that these deposits were formed in a continental marginal environment by a mixture of diagenetic and hydrogenetic processes overall the studied nodules can be divided into three stages with different microstructures and chemical compositions which indicate different formation environments stage 1a is the innermost and oldest layer with a porous mottled texture and has the lowest mn fe ratio cu ni and zn which implies comparatively high oxidization conditions in contrast the mn mineralogy of stage 2 shows conditions similar to those of buserite formed under less oxidative conditions between stage 1a and 2 stage 1b represents a mixture of stage 1a and 2 and has inhomogeneous growth structures based on the nd and sr isotopic composition of the detrital phases and pb isotopes three potential terrigenous source regions including south china luzon and taiwan that discharge into the northern scs from 3 2 ma to 1 06 ma after 1 06 ma the terrigenous fraction in the fe mn deposits on the northern slope of the scs is a two end members mixture of fluvial input from taiwan islands and eolian dusts from the chinese loess our study indicates that scs bottom water variation occurred at 3 2 ma 2 1 ma and 1 06 ma respectively which could be attributed to global cooling and the influence of luzon arc forearc uplift

calcareous nannofossil biostratigraphic dating of a ferromanganese crust from schumann seamount abstract calcareous nannofossil biostratigraphy was employed to determine the age and growth rates of the different layers within ferromanganese crusts from schumann seamount 200 miles north of the island of kauai hawaii this work is part of a study to reconstruct the paleoceanographic history of crusts using various geochemical indicators the methods are based on the identification of coccolith imprints not actual coccolith remains age constraints on the time span of a particular horizon are defined either 1 by the presence of a species which was extant for only a limited geological time interval or 2 by the presence of two organisms whose time ranges overlapped age resolution is optimized by short time ranges or narrow overlaps in the crust studied there was considerable inter horizon variability in the preservation of coccolith imprints in imprint abundance and in species diversity some of the crust layers examined were narrowly constrained temporally 1 4 myr while others were less so 10 myr our results indicate that the minimum age for the interval at 27 mm depth is at least eocene this is the maximum age many believe any crust can be the position of this interval however is only about one half of the way through the crust while the data support previous estimates of average crust growth rates 0 5 mm myr the actual apparent growth rate appears to have varied by an order of magnitude 0 1 to 2 mm myr

a comparative analysis of compositional variations in and between marine ferromanganese nodules and crusts in the south pacific and their environmental controls abstract regional variation of mn fe co ni and cu in ferromanganese oxides nodules and crusts in the central south pacific is related to primary productivity oxygen minimum layer and calcium carbonate compensation depth the largely latitudinal influence of these environmental parameters on nodule and crust composition reflects their predominantly latitudinal variation primary productivity is the principal regional environmental control influencing diagenetic enrichment of these elements in nodules through its effect mediated by the ccd on supply and concentration of labile organic matter vs carbonate remains to the sediments it influences hydrogenetic enrichment of these elements in nodules and crusts through its effect mediated by the oxygen minimum layer mainly in the case of crusts on their export from surface waters the elements varying susceptibility to being scavenged or organically bound influences the contrasting composition of diagenetic vs hydrogenetic ferromanganese oxides which is further influenced by depth hydrogenesis is the fundamental process governing nodule and crust formation superimposed on which is diagenesis under specific circumstances both are subject to intermittent interruption diminution and augmentation by changes in environmental parameters application of regionally operative environmental controls locally explains local compositional variations and helps refine exploration criteria for economically viable nodules and crusts

rare earth elements in the phosphatic enriched sediment of the peru shelf abstract apatite enriched materials from the peru shelf have been analyzed for their major oxide and rare earth element ree concentrations the samples consist of 1 the fine fraction of sediment mostly clay material 2 phosphatic pellets and fish debris which are dispersed throughout the fine grained sediment 3 tabular shaped phosphatic crusts which occur within the uppermost few centimeters of sediment and 4 phosphatic nodules which occur on the seafloor the bulk ree concentrations of the concretions suggest that these elements are partitioned between the enclosed detrital material and the apatite fraction analysis of the fine grained sediment with which the samples are associated suggested that this detrital fraction in the concretions should have shale ree values the analysis of the fish debris suggested that the apatite fraction might have seawater values the seawater contribution of ree s is negligible in the nodules and crust in which the apatite occurs as a fine grained interstitial cement that is the concentration of ree s and the ree patterns are predominantly a function of the amount of enclosed fine grained sediment by contrast the ree pattern of the pelletal apatite suggests a seawater source and the absolute ree concentrations are relatively high the ree p 2 o 5 ratios of the apatite fraction of these samples thus vary from approximately zero in the case of the crust and nodules to as much as approximately 1 2 10 3 in the case of the pellets the range of this ratio suggests that rather subtle variations in the depositional environment might cause a significant variation in the ree content of this authigenic fraction of the sediment pelletal glauconite was also recovered from one sediment core its ree concentrations closely resemble those of the fish debris

major and trace element geochemistry and os isotopic composition of metalliferous umbers from the late cretaceous japanese accretionary complex 1 metalliferous umbers and red shales occur as unique products of the kula pacific ridge forearc collision in the late cretaceous shimanto supergroup an accretionary complex in japan these umbers are closely associated with greenstones of mid ocean ridge basalt morb origin and are regarded as hydrothermal metalliferous precipitates related to mor type volcanism the umbers and red shales were deposited in the trench area where both terrigenous detritus from land and hydrothermal metalliferous particulates from a mor were supplied simultaneously besides a predominance of fe and mn the umbers exhibit remarkable enrichments in p v co ni zn y mo rare earth elements rees and os relative to continental crustal abundances the x fe x mn p v co ni zn y and rees ratios and paas normalized ree patterns of the umbers are very similar to those of modern hydrothermal plume fallout precipitates deposited on flanks of mor this indicates that the umbers preserve primary geochemical signatures of hydrothermal metalliferous sediments that scavenged seawater derived elements and thus can be used as a proxy for late cretaceous seawater the marine 187os 188os ratios reconstructed from the late maastrichtian umbers range from 0 42 to 0 56 and are very consistent with recent data obtained from the pacific and atlantic pelagic carbonates that record an abrupt decline from 0 55 to 0 4 during the period between 67 0 ma and 65 7 ma

paleoredox variations in ancient oceans recorded by rare earth elements in fossil apatite abstract rare earth element concentrations in biogenic apatite of conodonts fish debris and inarticulate brachiopods were determined in over 200 samples from cambrian to modern sediments tests for experimental bias caused by the chemicals used to separate fossils from the rock matrix and for interlaboratory interexperiment or interspecies related variations clearly show that no resolvable fractionation of ree occurs incorporation of ree in biogenic apatite of recent fish debris occurs near the sediment water interface soon after deposition and reflects characteristics of seawater the original ree signature apparently survives subsequent burial and diagenesis cerium variations in fish debris from modern environments are controlled by redox potential ce is fractionated by co precipitation with metallic oxides under oxidizing conditions this fractionation produces a negative ce anomaly ce anom in seawater that is reflected in the sedimented fish debris conversely no fractionation of ce occurs under reducing conditions resulting in ce concentrations that are normal to enriched in anoxic seawater and fish debris deposited under local or basinwide anoxic conditions extrapolation of observations of the redox control of ce anom in modern oceans to fossil apatite indicates that anoxic conditions were prevalent in lower paleozoic and lower triassic oceans whereas in the upper paleozoic the world ocean was generally oxidizing

mineralogy of the groote eylandt manganese oxides a review abstract the mineralogy and genesis of the tetravalent manganese oxides present in the groote eylandt ore are discussed on the basis of recent mineralogical concepts their mechanisms of formation on groote eylandt are described in terms of primary sedimentation formation of vernadite romanechite pyrolusite todorokite diagenesis formation of pyrolusite supergene processes formation of cryptomelane and lithiophorite and pedogenic processes formation of chalcophanite and birnessite these geochemical processes have resulted in the formation of deposits of metallurgical ore of a cryptomelane pyrolusite mineralogy and a battery active ore of vernadite todorokite pyrolusite mineralogy

mechanisms to explain the platinum concentration in ferromanganese seamount crusts abstract ferromanganese seamount crusts cover large areas of hard substrates of sea floor edifices in the central pacific they can be distinctly enriched in pt and show pt pd ratios which are several orders of magnitude greater than those orders of magnitude greater than those of seawater thirty four selected samples of the younger and the older crust generation were analyzed for mn fe ni co and pt the bulk pt concentration varies between 0 14 and 1 02 ppm and averages to 0 51 0 24 ppm the older generation is generally somewhat richer in pt 0 63 0 25 ppm than the younger one 0 39 0 15 ppm compared to the earth s upper continental crust the ferromanganese material contains about 100 times more pt in the studied depth range between 1100 and 3800 m the pt concentration is controlled by the water depth in addition to the bulk data the distribution of pt and pd is recorded through a complete ferromanganese crust profile the average pd value amounts to 16 2 8 ppb for the younger and 16 4 8 ppb for the older generation two immediate sources may be responsible for the pt concentration in the ferromanganese crusts seawater and cosmic spherules the presented thermodynamic approaches are based on the presumption that the pt tetrachlorocomplex is the prevailing species under seawater conditions precipitation of pt in seawater may take place if this complex is decomposed by reduction of pt 2 to the elemental state on the other hand the mno 2 precipitation is caused by oxidation of dissolved mn 2 ions which are supplied from the oxygen minimum zone a model reaction by combining the two half reactions is formulated assuming a coprecipitation of pt with mno 2 an alternative mechanism to explain pt enrichment in ferromanganese crusts might be surface adsorption of anionic pt tetrachloro complexes onto positively charged amorphous iron hydroxide particles cosmic spherules were discovered in samples of the older ferromanaganese crust generation the spherules are mostly concentrated in the upper part of this crust layer iron meteorites often have pt concentrations up to 20 ppm the relative quantity recovered in the grain size class 0 1 0 4 mm only amounts to 2 10 4 which is significantly too low to explain the pt content of the crust samples however smaller cosmic particles may exist and also contribute to the pt enrichment suggesting that rough crust surfaces are excellent collectors of denser detrital material the maximum pt values observed in the youngest part of the older crust generation may be explained by physical incorporation of cosmic particles

distribution patterns of the elements in the ocean a synthesis the observed partition patterns of elements between a marine solid phase e g pelagic clays deep sea manganese nodules seamount manganese crusts and plankton and seawater can be to the first approximation explained by the james and healy adsorption model except for ce co mn pb and tl which are concentrated in the solid phase through oxidative uptake processes in other words the composition of seawater is mainly controlled by the compositions of source materials i e the crustal igneous rocks and primary magmatic volatiles and the physicochemical principles regulating the adsorption processes of various chemical species in seawater onto oceanic pelagic clays

paleoceanographic implications of rare earth element variability within a femn crust from the central pacific ocean abstract results of detailed geochemical analyses of thick fe mn oxide crust accumulations from the central pacific ocean lead to the suggestion that variations in their chemical composition and microstructure reflect the influence of prevailing environmental conditions at the time of formation of the deposit these findings imply that well preserved fe mn crusts represent a geologic record that may extend back to the onset of fe mn oxide precipitation on the subsrtate material current crust growth rate estimates of 1 3 mm m y imply that 6 10 cm thick fe mn oxide accumulations represent a growth record of 20 to a maximum of 100 m y detailed chemical and mineralogical analyses were performed on successive hand picked layers of a 95 mm thick fe mn crust recovered from schumann seamount in the hawaiian archipelago the analyses reveal significant variations in the elemental distribution and abundance of major constituents and rees as a function of depth within the crust the trivalent rees generally exhibit sympathetic concentration changes in pure fe mn oxides but the fractionation observed between the light and heavy rees differs in layers enriched in phosphatic matter the compositional variability and the extent of ree fractionation can be explained in large part by mineralogical control but can also be inferred to reflect differing depositional conditions in the seawater from which the deposits formed variations in the ce anomaly and ree fractionation patterns within the individual layers of the crust are related to their major element composition and mineralogy and to the anomalies observed by other workers these are used to attempt to reconstruct the growth history of the crust

nickeliferous opaque minerals associated with chromite alteration in the sakhakot qila complex pakistan and their compositional variation chemical compositions of the awaruite heazlewoodite pentlandite assemblage from the sakhakot qila ultramafic complex pakistan indicate its genesis in highly reducing conditions with f o 2 and f s 2 much below those yielding nickel sulphide ores the compositions from various parts of the complex exhibit larger variations than those reported so far from a single complex and include unusually high ni contents awaruite compositions extend beyond the previously known limit of ni content and are unique in containing cu and not co as the third constituent after ni and fe with sympathetic relation between cu and ni previous reports indicate genesis of such minerals by serpeatinization only but the present example links them to chloritization and the formation of ferritchromit as well their petrographic distribution is related to that of chromite grains and segregations and not to that of serpentine

60 myr records of major elements and pb nd isotopes from hydrogenous ferromanganese crusts reconstruction of seawater paleochemistry we compare the time series of major element geochemical and pb and nd isotopic composition obtained for seven hydrogenous ferromanganese crusts from the atlantic indian and pacific oceans which cover the last 60 myr average crust growth rates and age depth relationships were determined directly for the last about 10 myr using be 10 be 9 profiles in the absence of other information these were extrapolated to the base of the crusts assuming constant growth rates and constant initial be 10 be 9 ratios due to the lack of additional information co contents have also been used previously to estimate growth rates in co rich pacific and atlantic seamount crusts puteanus and halbach 1988 a comparison of be 10 be 9 and co based dating of three co rich crusts supports the validity of this approach and confirms the earlier chronologies derived from extrapolated be 10 be 9 based growth rates back to 60 ma our data show that the flux of co into co poor crusts has been considerably lower the relationship between growth rate and co content for the co poor crusts developed from these data is in good agreement with a previous study of a wider range of marine deposits manheim 1986 the results suggest that the co content provides detailed information on the growth history of ferromanganese crusts particularly prior to 10 12 ma where the be 10 based method is not applicable the distributions of pb and nd isotopes in the deep oceans over the last 60 myr are expected to be controlled by two main factors a variations of oceanic mixing patterns and flow paths of water masses with distinct isotopic signatures related to major paleogeographic changes and b variability of supply rates or provenance of detrital material delivered to the ocean linked to climate change glaciations or major tectonic uplift the major element profiles of crusts in this study show neither systematic features which are common to crusts with similar isotope records nor do they generally show coherent relationships to the isotope records within a single crust consequently any interpretation of time series of major element concentrations of a single crust in terms of paleoceanograghic variations must be considered with caution this is because local processes appear to have dominated over more basin wide paleoceanographic effects in this study co is the only element which shows a relationship to pb and nd isotopes in pacific crusts a possible link to changes of pacific deep water properties associated with an enhanced northward advection of antarctic bottom water from about 14 ma is consistent with the pb but not with the nd isotopic results the self consistent profiles of the pb and nd isotopes suggest that postdepositional diagenetic processes in hydrogenous crusts including phosphatization events have been insignificant for particle reactive elements such as pb be and nd isotope time series of pb and nd show no systematic relationships with major element contents of the crusts which supports their use as tracers of paleo seawater isotopic composition

geological and mineralogical study of co rich ferromanganese crusts from a submerged atoll in the tuamotu archipelago french polynesia the tuamotu archipelago in french polynesia is a co rich ferromanganese crust province the nodco i survey 1986 provided detailed data on co rich crusts in this environment through the exploration of a restricted zone in the vicinity of niau island on the southern flank of the archipelago this flat zone is a fossil atoll which under the action of subsidence and tectonic movements has collapsed to a water depth of 1000 m the plateau is partially filled with coralline sediments outcrops of ferromanganese crusts associated with rare nodules and slabs are located on the inner side of the coral reef which bounds the ancient lagoon the successive episodes of plateau history have been recorded in the different growth periods of the ferromanganese crusts the crusts nodules and slabs belong to the same morphological mineralogical and geochemical family cobalt contents vary from 0 7 to 1 3 the highest values belong to the thinnest ferromanganese crusts which are located on the flanks of the plateau average ni contents are about 0 5 and cu contents about 0 1 pt contents vary from 0 2 to 1 3 ppm platinum and co are enriched in the outermost oxide zone of the crusts poorly crystallized mno2 is the dominant mineralogical phase cobalt enrichment seems to be related to mno2 particle size the greatest contents are located in the finest material where the particle size is less than 0 1 m cobalt rich crusts of the niau zone have the same characteristics as the co rich crusts from the equatorial north pacific they differ in original setting the reefal environment in the niau zone is superficial overlying a volcanic substrate

continuous growth of hydrogenetic ferromanganese crusts since 17 myr ago on takuyo daigo seamount nw pacific at water depths of 800 5500 m ferromanganese crusts cover all outcrops on takuyo daigo seamount traversed during remotely operated underwater vehicle rov dives except in places covered by foraminifera sand takuyo daigo is a cretaceous seamount located in the northwest pacific ocean geological and bathymetric mapping provide the framework for this study chemical and mineralogical analyses of the hydrogenetic ferromanganese crusts show temporal and spatial variations typical of those found in previous studies outcrops from 800 to 5500 m water depths are covered with ferromanganese crusts up to 105 mm thick beryllium isotope dating shows that the crusts have apparently been growing continuously at all water depths even through the modern oxygen minimum zone omz contrary to some earlier models for deposition growth rates vary from 2 3 to 3 5 mm myr with fe or mn fluxes of 0 07 0 11 g cm2 myr since the early middle miocene co mn ratios decrease with water depth while fe mn and other metallic elements increase or show no change based on the analysis of the uppermost crust surface this is probably because co is the most abundant redox sensitive element derived from seawater that occurs in crusts

enhancement and hf doppler observations of sporadic e during the solar eclipse of 22 july 2009 1 the sporadic e es frequently emerging in midlatitude during summer is a very special layer in the ionosphere and its formation mechanism is different to from that of other layers the total solar eclipse of 22 july 2009 provided a very unique opportunity to study the relationship of es and solar radiation during the solar eclipse day and the days before and after the vertical incidence ionosonde was located in wuhan to record the ionograms for this event two oblique incidence high frequency radio systems were used to record the waves from wuhan to suzhou and from wuhan to huaian the enhancement of es during the eclipse period was observed in the vertical and oblique incidence ionograms the quasi periodic fluctuations in the critical frequency and doppler frequency shift curves indicated the possible existence of the gravity waves which may be responsible for the es enhancement however we find that the enhancement occurred earlier than the appearance of gravity waves and consider that there may be other mechanisms which contribute to the observed enhancement in the ionosphere a hypothesis is put forward that the cooling effect of the lunar shadow induced powerful airflow from the northern and southern limits of the shadow toward its center which accelerated the irregularities in es to produce the large scale doppler shift in the reflected waves and form the meridional windshear both the windshear and the gravity waves may affect the es layer and increase the electron concentration many observed phenomena are in accordance with this

the hf isotope composition of global seawater and the evolution of hf isotopes in the deep pacific ocean from fe mn crusts this paper presents a revised chemical purification method of hf for the measurement of hf isotope ratios of fe mn crusts on a new generation of double focusing multiple collector plasma source mass spectrometer mc icp ms by measuring surface scrapings of hydrogenetic fe mn crusts distributed over the three major ocean basins the present day hf isotope distribution of oceanic deep water is assessed in detail the results show an ehf provinciality correlated with those of other radiogenic isotope tracers such as nd and pb in agreement with previous studies this supports the use of hf isotopes as tracer of element source provenance and water masses fe mn crusts display the same present day hf nd isotope array as given before for mn nodules the smaller isotopic variability of hf compared with nd may either be caused by a more efficient mixing of hf than nd in the ocean due to a longer residence time or may be a consequence of a systematically more radiogenic hf than nd isotope signature delivered to the oceans by weathering of continental crust a hf isotope time series was measured on crust va13 2 to assess the hf isotope compositions of the central pacific deep water over the past 26 ma no consistency is observed between the hf and pb isotope time series in contrast hf and nd isotope time series display similar patterns which are however apparently offset by 2 ma prior to 14 ma differential diffusion of hf and nd does not explain this offset the smaller amplitude in the hf isotope variations compared with the nd isotopes rather argues for more efficient mixing of hf in the ocean we suggest that both isotope systems have responded in a similar way to the processes affecting the dissolved radiogenic isotope composition of pacific deep water during this time interval the parallel increase in ehf and end observed between 14 and 3 ma may probably be attributed to the increased inputs of hf and nd into the central pacific ocean derived from the weathering of the pacific islands arcs over the past 3 ma an increased aeolian continental input derived from asia most likely caused negative shifts in end and ehf recorded by va13 2 the fact that hf and nd isotope compositions plot along the present day array for fe mn crusts and mn nodules over the entire past 26 ma suggests that aeolian supply of hf to the pacific ocean has been a long term important feature

nighttime ionospheric enhancements induced by the occurrence of an evening solar eclipse 1 the solar eclipse on 15 january 2010 traversed asia and completed its travel on the shandong peninsula in china at sunset two vertical incidence ionosondes at wuhan and beijing and the oblique incidence ionosonde network in north china were implemented to record the ionospheric response to the solar eclipse following the initial electron density decrease caused by the eclipse the ionosphere was characterized by a strong premidnight enhancement and a subsequent ionospheric decay and a 10 h later postmidnight enhancement neither geomagnetic disturbance occurred during the eclipse day nor did obvious nighttime peak appear for the 10 day mean of the f2 layer critical frequency fof2 the electron density profilogram of the beijing ionosonde indicates that the two enhancements were the result of the plasma flux downward from the top ionosphere possibly due to the steep decrease of the ionospheric electron density and plasma temperature during the solar eclipse the two dimensional differential fof2 maps present the regional variations of the nighttime electron density peaks and decay both the pre and postmidnight enhancements initially appeared in a belt almost in parallel with the eclipse track and then drifted southward the different magnitudes of greatest eclipse in the umbra and outside tend to account for the different occurrence times of the plasma flux the ionospheric decay following the premidnight enhancement is also considered as a consequence of the eclipse shade

interelement relationship in abyssal pacific ferromanganese nodules and associated pelagic sediments abstract by r mode factor analysis and enrichment factor calculations most of the elements in abyssal ferromanganese nodules and associated pelagic sediments excluding common authigenic minerals like apatite barite opal and carbonates are found to be preferentially concentrated in one of the following three major phases aluminosilicates e g al si sc ga cr be na k rb and cs fe oxides e g fe p s v se te as b sn u hg pb ti ge y zr nb pd in rare earths hf th pa pu am ru and bi and mn oxides e g mn tl ag cd mg ca ba ra co ni cu zn mo sb and probably w the specific association of elements with these three phases can be explained by the difference in chemical forms of elements in seawater and by fundamental differences in physicochemical properties e g the ph of zero point of charge and dieletric constant of these three phases

formation of ferromanganese crusts on northwest intertropical pacific seamounts electron photomicrography and microprobe chemistry abstract seven ferromanganese crusts from the northwest intertropical pacific seamounts were analyzed for photomicroscopic growth structures microprobe chemistry and ages based on co chronometer growth rate the crusts on the marshall islands seamounts are thick and are divided into phosphatized lower older and nonphosphatized upper younger growth generations the older crust consists of compact laminations and columns impregnated with carbonate fluoapatite cfa whereas the younger crust is characterized by porous botryoids and columns of mno2 and fe oxyhydroxide the crusts on the federated states of micronesia fsm and palau islands seamounts are thin and are often incorporated with inorganic opal a in the uppermost part comprising the younger generation some crusts show scours and fractures although the growth of crusts has been often interrupted by mass failure of slope sediments the crusts on the marshall islands seamounts are estimated to have grown at rate of about 3 mm ma since the middle eocene and to have been phosphatized in the late oligocene during the host seamounts were located beneath the equatorial zone of high productivity prolonged infiltration of the oxygen minimum zone omz water into shallower water older crusts redistributed crust composition by precipitating cfa enriching subsequent amounts of mn and ni and removing some co the younger crust has formed at slower rate about 2 mm ma under the stronger influence of bottom water circulation in the north of the equatorial zone concentrating abundant co in the uppermost part of some crusts siliceous skeletons transform with burial to inorganic opal a and si rich fe oxyhydroxide suggesting that biosilica diagenesis can enhance crust growth

cenozoic accumulation history of a pacific ferromanganese crust to investigate the growth rates and absolute time stratigraphy of marine hydrogenetic ferromanganese encrustations we performed 10be profiling and co chronometry of crustal layers as well as 87sr86sr and 18o analysis of phosphatised limestone francolite within a 9 5 cm thick ferromanganese crust from schumann seamount in the hawaiian archipelago together with microfossil stratigraphy our results indicate that some seamount crusts greatly exceed the commonly accepted miocene maximum age in this case probably approaching the cretaceous age of the seamount in addition to the unconformity at the crust substrate boundary at least eight major disconformities are indicated in the schumann seamount crust which probably represent depositional hiatuses or episodes of crust erosion three of the six upper disconformities can be placed at the plio pleistocene middle miocene and paleocene eocene based on 10be microfossil and co chronometer evidence 87sr86sr and 18o values of purified francolite from an inclusion rich layer between the depths of 44 and 49 mm suggest apparent ages that approach those of eocene late paleocene microfossils reported in overlying layers whereas francolite vein infillings in the lower part of the crust and in the basaltic substrate yield values that if interpreted as ages of phosphatization suggest a minimum oligocene age paleotracking suggests the phosphogenesis observed here and on other central pacific seamounts could not have resulted from upwelling enhanced productivity associated with equatorial divergence if the oligocene and middle miocene isotopic ages reported here and elsewhere are correct however a maximum late paleocene age for the phosphogenesis consistent with the stratigraphy would place these seamounts within 10 n of the equator paleotracking also suggests northeast tradewind transport of aluminosilicates in the cenozoic in agreement with other evidence for the antiquity of this ferromanganese crust

origin of negative ce anomalies in mixed hydrothermal hydrogenetic fe mn crusts from the central indian ridge abstract layered fe mn crusts from the off axis region of the first segment of the central indian ridge north of the rodrigues triple junction were studied geochemically and mineralogically vernadite mno2 is the main mineral oxide phase 230thxs and co concentrations suggest high growth rates of up to 29 mm myr and a maximum age of the basal crust layer of 1 ma whereas most of the major and minor elements show concentrations which are typical of hydrogenetic formation co pb ni and ti concentrations are strikingly lower concentrations and distribution of the strictly trivalent rare earths and yttrium rey are typical of hydrogenetic ferromanganese oxide precipitates but in marked contrast the crusts are characterized by negative cesn shale normalized anomalies and ce pr sn ratios less than unity profiles through the crusts reveal only minor variations of the rey distribution and ce pr sn ratios range from 0 45 to 0 68 compared to ratios of up to 2 for typical hydrogenetic crusts from the central indian basin the apparent bulk partition coefficients between the crusts and seawater suggest that for the strictly trivalent rey the adsorption desorption equilibrium has been reached positive ce anomalies in the partition coefficient patterns reveal preferential uptake of ce but to a lesser extent than in normal hydrogenetic crusts a new parameter excess ce cexs to quantify the degree of decoupling of ce from rey iii is established on the basis of partition coefficients cexs cebulk ratios suggest that the cir crusts formed by precipitation of fe mn oxides from a hydrothermal plume and that in hydrothermal plumes and normal seawater the enrichment of ce results from the same oxidative sorption process the growth rates calculated with 230thxs data as well as with the co formula are inversely related to cexs

the midlatitude f2 layer during solar eclipses observations and modeling national natural science foundation of china 40725014 40674090 40636032 national important basic research project 2006cb806306

revised global model of thermosphere winds using satellite and ground based observations thermospheric wind data obtained from the atmosphere explorer e and dynamics explorer 2 satellites have been combined with wind data for the lower and upper thermosphere from ground based incoherent scatter radar and fabry perot optical interferometers to generate a revision hwm90 of the hwm87 empirical model and extend its applicability to 100 km comparison of the various data sets with the aid of the model shows in general remarkable agreement particularly at mid and low latitudes the ground based data allow modeling of seasonal diurnal variations which are most distinct at mid latitudes while solar activity variations are now included they are found to be small and not always very clearly delineated by the current data they are most obvious at the higher latitudes the model describes the transition from predominately diurnal variations in the upper thermosphere to semidiurnal variations in the lower thermosphere and a transition from summer to winter flow above 140 km to winter to summer flow below significant altitude gradients in the wind are found to extend to 300 km at some local times and pose complications for interpretation of fabry perot observations

uranium isotope systematics of ferromanganese crusts in the pacific ocean implications for the marine 238u 235u isotope system abstract variations of 238u 235u ratio 238u in sedimentary rocks have been proposed as a possible proxy for the paleo oceanic redox conditions although the marine 238u system is not fully understood here we investigate the spatial variation of 238u in modern ferromanganese fe mn crusts by analyzing u isotopes in the surface 0 3 mm depth layer of 19 fe mn crusts collected from 6 seamounts in the pacific ocean 238u values in the surface layers show little variation and range from 0 59 to 0 69 the uniformity of 238u values is consistent with the long residence time of u in modern seawater although the 238u values are lighter than that of present day seawater by 0 24 the light 238u values are consistent with the isotope offset observed in previously reported adsorption experiment of u to mn oxide these results indicate that removal of u from seawater to mn oxide is responsible for the second largest u isotope fractionation in the modern marine system and could contribute to isotopically heavy u to seawater depth profiles of u isotopes 234u and 238u in two fe mn crusts mr12 03 d06 r01 and mc10 cb07 b dated by os isotope stratigraphy were investigated to reconstruct the evolution of the oceanic redox state during the cenozoic the 238u depth profiles show very limited ranges 0 57 to 0 67 for mr12 03 d06 r01 and 0 56 to 0 69 for mc10 cb07 b and have values that are similar to those of the surface layers of fe mn crusts the absence of any resolvable variation in the 238u depth profiles may suggest that the relative amounts of oxic and reducing u sinks have not varied significantly over the past 45 myr however the 234u depth profiles of the same samples show evidence for the possible redistribution of 234u after deposition therefore the depth profile of 238u in fe mn crusts may have been also overprinted by later chemical exchange with pore water or seawater and may not reflect the paleo oceanic environmental changes to assess the potential role of u removal by mn oxides on seawater 238u we calculated seawater 238u with different u sink fluxes into mn oxides using a simple mass balance model the results of these calculations suggest that seawater 238u could have varied significantly throughout earth s history due to changes in the accumulation rate of mn oxides

composition of water and suspended sediment in streams of urbanized subtropical watersheds in hawaii abstract urbanization on the small subtropical island of oahu hawaii provides an opportunity to examine how anthropogenic activity affects the composition of material transferred from land to ocean by streams this paper investigates the variability in concentrations of trace elements pb zn cu ba co as ni v and cr in streams of watersheds on oahu hawaii the focus is on water and suspended particulate matter collected from the ala wai canal watershed in honolulu and also the kaneohe stream watershed as predicted suspended particulate matter controls most trace element transport elements such as pb zn cu ba and co exhibit increased concentrations within urbanized portions of the watersheds particulate concentrations of these elements vary temporally during storms owing to input of road runoff containing elevated concentrations of elements associated with vehicular traffic and other anthropogenic activities enrichments of as in samples from predominantly conservation areas are interpreted as reflecting agricultural use of fertilizers at the boundaries of urban and conservation lands particulate ni v and cr exhibit distributions during storm events that suggest a mineralogical control principal component analysis of particulate trace element concentrations establishes eigenvalues that account for nearly 80 of the total variance and separates trace elements into 3 factors factor 1 includes pb zn cu ba and co interpreted to represent metals with an urban anthropogenic enrichment factor 2 includes ni v and cr elements whose concentrations do not appear to derive from anthropogenic activity and is interpreted to reflect mineralogical control another albeit less significant anthropogenic factor includes as cd and u and is thought to represent agricultural inputs samples collected during a storm derived from an offshore low pressure system suggest that downstream transport of upper watershed material during tradewind derived rains results in a 2 3 fold dilution of the particulate concentrations of pb zn and cu in the ala wai canal watershed

southward shift of the intertropical convergence zone in the western pacific during the late tertiary evidence from ferromanganese crusts on seamounts west of the marshall islands 1 hydrogenetic ferromanganese crusts were dredged from four seamounts in the western pacific osm7 osm2 lomilik and lemkein aligned in a nw se direction parallel to pacific plate movement the crusts consist of four well defined layers with distinct textural and geochemical properties the topmost layer 1 is relatively enriched in mn co ni and mo compared to the underlying layer 2 which is relatively enriched in al ti k and rb and cu zn and excess ba textural and geochemical properties of layer 2 suggest growth conditions under high biogenic and detrital flux such conditions are met in the equatorial pacific i e between the intertropical convergence zone itcz and equatorial high productivity zone layer 2 likely formed when each seamount was beneath the equatorial pacific along its back track path on the other hand layer 1 probably started to grow after seamounts moved northwest from the itcz this interpretation is consistent with the thickness of layer 1 across the four crusts which increases to the northwest ages of the layer 1 layer 2 boundary in each crust a potential proxy for northern margin of the itcz also increase to the northwest at 17 11 8 and 5 ma for osm7 osm2 lomilik and lemkein respectively assuming pacific plate motion of 0 3 myr the seamounts were located at 12 n 11 n 9 n and 8 n at the time of boundary formation this result suggests that the north edge of the itcz has shifted south since the middle miocene in the western pacific which agrees with information from the eastern pacific

ionospheric and thermospheric response over millstone hill to the may 30 1984 annular solar eclipse the national center for atmospheric research ncar thermospheric general circulation model tgcm is used to calculate the time dependent thermospheric response to the may 30 1984 annular solar eclipse the path of maximum obscurity begins at sunrise in the pacific ocean near 2 n and 135 w it moves northeastward passing across central mexico the eastern united states and then the atlantic before ending near 28 n and 4 e in algeria the area of the partial shadow is relatively large and the total solar flux incident on the dayside of the earth is decreased by about 6 during the eclipse the tgcm calculates the time dependent response of the winds temperature and the mass mixing ratios of the major constituents throughout the thermosphere perturbations follow the path of the annular eclipse with maximum deviations occurring near 1700 ut at about 300 km for the temperature and at higher altitudes for the winds and composition the perturbation winds converge from all directions toward the shadow at speeds reaching 75 m s 1 in the upper thermosphere the maximum temperature anomaly 55 k and vertical wind anomaly 7 m s 1 occur near the center of the shadow at a constant altitude of 300 km both the n2 density and the o density decrease by about 10 and 6 respectively the path of maximum obscuration passes within 3 of latitude of the incoherent scatter radar at millstone hill massachusetts 42 6 n 71 5 w the station experiences a maximum solar obscuration of 86 at 1700 ut 1200 lt a time dependent one dimensional numerical model of the ionosphere that uses the tgcm calculated winds temperature and composition at millstone hill is used to calculate the electron and ion densities and temperatures and the densities of the odd nitrogen species no n 4s and n d during the eclipse the calculated electron density decreases by about factors of 2 in the f region 4 in the f1 region and 3 in the e region compared to a similar control run without an eclipse the f1 region emerges during the eclipse with an increase in the no o ratio the calculated electron temperature decreases by 460 k during the eclipse but then increases 200 k following the eclipse because of the intense solar heating in a region of reduced electron densities the calculated ion temperature generally follows the changes in neutral temperature the calculated thermospheric and ionospheric responses agree well with measurements made by the millstone hill incoherent scatter radar

determination of the mg mn ratio in foraminiferal coatings an approach to correct mg ca temperatures for mn rich contaminant phases the occurrence of manganese rich coatings on foraminifera can have a significant effect on their bulk mg ca ratios thereby biasing seawater temperature reconstructions the removal of this mn phase requires a reductive cleaning step but this has been suggested to preferentially dissolve mg rich biogenic carbonate potentially introducing an analytical bias in paleotemperature estimates in this study the geochemical composition of foraminifera tests from mn rich sediments from the antarctic southern ocean odp site 1094 was investigated using solution based and laser ablation icp ms in order to determine the amount of mg incorporated into the coatings the analysis of planktonic and benthic foraminifera revealed a nearly constant mg mn ratio in the mn coating of 0 2 mol mol consequently the coating mg mn ratio can be used to correct for the mg incorporated into the mn phase by using the down core mn ca values of samples that have not been reductively cleaned the consistency of the coating mg mn ratio obtained in this study as well as that found in samples from the panama basin suggests that spatial variation of mg mn in foraminiferal mn overgrowths may be smaller than expected from mn nodules and mn ca carbonates however a site specific assessment of the mg mn ratio in foraminiferal coatings is recommended to improve the accuracy of the correction