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

paired dissolved and particulate phase cu isotope distributions in the south atlantic abstract copper cu is both an essential micronutrient and toxic to photosynthesizing microorganisms at low concentrations its dissolved vertical distribution in the oceans is unusual being neither a nutrient type nor scavenged type element this distribution is attributed to biological uptake in the surface ocean with remineralisation at depth combined with strong organic complexation by dissolved ligands scavenging onto particles and benthic sedimentary input we present coupled dissolved and particulate phase cu isotope data along the uk geotraces south atlantic section alongside higher resolution dissolved and particulate phase cu concentration measurements our dissolved phase isotope data contribute to an emerging picture of homogeneous deep ocean 65cu at about 0 65 relative to nist srm 976 we identify two pools of cu in the particulate phase a refractory lithogenic pool at about 0 and a labile pool accessed via a weak acidic leach at about 0 4 these two pools are comparable to those previously observed in sediments we observe deviations towards lighter 65cu values in the dissolved phase associated with local enrichments in particulate cu concentrations along the continental slopes and in the surface ocean copper isotopes are thus a sensitive indicator of localised particle associated benthic or estuarine cu inputs the measurement of cu isotopes in seawater is analytically challenging and we call for an intercalibration exercise to better evaluate the potential impacts of uv irradiation storage time and different analytical procedures

a sea floor spreading event captured by seismometers two thirds of earth s surface is formed at mid ocean ridges yet sea floor spreading events are poorly understood because they occur far beneath the ocean surface at 9 50 n on the east pacific rise ocean bottom seismometers recently recorded the microearthquake character of a mid ocean ridge eruption including precursory activity a gradual ramp up in activity rates since seismic monitoring began at this site in october 2003 suggests that eruptions may be forecast in the fast spreading environment the pattern culminates in an intense but brief 6 hour inferred diking event on 22 january 2006 followed by rapid tapering to markedly decreased levels of seismicity

isotope variations of dissolved zn in the rio grande watershed usa the role of adsorption on zn isotope composition abstract in order to better understand the factors influencing zinc zn isotope composition in hydrological systems we analyzed the 66 zn of dissolved zn in the streams and groundwater of the upper and middle rio grande watershed in colorado and new mexico united states the stream water samples have a wider variation of 66 zn 0 57 to 0 41 relative to the jmc 3 0749 lyon standard than groundwater samples 0 13 to 0 12 and than samples from streams that are in close proximity to abandoned mining sites 0 24 to 0 40 regional changes of bedrock geology from primarily igneous rocks to primarily sedimentary rocks have no resolvable effect on the 66 zn of aqueous samples instead an increase in water ph from 7 5 to 8 5 corresponds to a considerable decrease in the 66 zn of dissolved zn r 2 0 37 p 0 003 n 22 consequently we link the observed zn isotope variations to the process of adsorption of zn onto suspended sediment and bedrock minerals average 66 zn adsorbed dissolved 0 31 our results are in good agreement with previous experimental and empirical studies suggesting that zn adsorption leads to a residual dissolved pool enriched in light zn isotopes given that anthropogenic zn sources can also be responsible for lowering of 66 zn and may overlap with the ph adsorption effect on 66 zn the latter needs to be carefully considered in future studies to differentiate between natural and anthropogenic factors influencing zn isotopes in this and other aquatic systems

molybdenum behavior during early diagenesis insights from mo isotopes 1 we present molybdenum isotope and concentration data from 14 sites in the eastern pacific from the central california to the peru margin the environments studied have been chosen to represent a broad range in oxidation reduction redox potential which provide a framework for the behavior of this redox sensitive element manganese rich hemipelagic sediments from the eastern tropical pacific have a mean characteristic mo isotope signature 98 95mo 0 49 0 04 two times the standard deviation of the mean 2 sdom with n 14 that reflects fractionation between ocean water and authigenic mo associated with mn oxides authigenic fe mo s deposits from reducing continental margin settings also have a characteristic mo isotopic signature 98 95mo 1 64 0 04 2 sdom with n 136 both of these values are in contrast to highly sulfidic 11 m h2saq restricted basin environments which contain mo isotope values analytically indistinguishable from seawater in terms of the mo isotope composition the modern oceanic mo sink is dominated by continental margin type environments where 98 95mo 1 6 and mn rich sediments where 98 95mo approximately 0 5 with a minor contribution from euxinic settings where h2saq 11 m

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

hydroacoustic monitoring of seismicity at the slow spreading mid atlantic ridge 1 in february 1999 long term hydroacoustic monitoring of the northern mid atlantic ridge mar was initiated six autonomous hydrophones were moored between 15 n and 35 n on the flanks of the mar results from the first year of data reveal that there is significant variability in along axis event rate groups of neighboring segments behave similarly producing an along axis pattern with high and low levels of seismic activity at a wavelength of 500 km this broad scale pattern is likely influenced by the axial thermal regime several earthquake sequences with variable temporal characteristics were detected suggesting fundamental differences in the cause of their seismicity off axis most seismic faulting occurs within a zone 15 km from the axis center

depth of the 660 km discontinuity near the mariana slab from an array of ocean bottom seismographs 1 high frequency records of deep mariana earthquakes from a dense array of ocean bottom seismographs deployed in the mariana arc and back arc regions are stacked and searched for the phases p660p and s660p to constrain the depth of the 660 km discontinuity near the mariana slab results of the high resolution study suggest that around 18 n the 660 km discontinuity lies at about 710 730 km 14 km depth within or in the vicinity of the slab core in the region seismicity ceases at 620 km depth this implies that although tomographic images show the mariana slab penetrating into the lower mantle deep seismicity in the region terminates 100 km above the base of the transition zone these findings and similar observations in tonga argue that factors other than the phase transition at the base of the upper mantle may control the maximum down dip extent of the deep seismogenic region in the slab

molybdenum and uranium geochemistry in continental margin sediments paleoproxy potential abstract we measured solid phase mo and u concentrations in marine sediments from the california mexico peru and chile margins to ascertain the behavior of mo and u during early diagenesis in continental margin settings at sites along the california mexico and peru margins where there are estimates of mass accumulation rates authigenic u accumulation rates range from 0 50 nmol m 2 day 1 at the california and mexico margin sites mo accumulation rates range from 0 to 134 nmol m 2 day 1 whereas at the peru margin site rates may be as high as 550 nmol m 2 day 1 we observe relationships between metal accumulation rates and the delivery and burial rates of organic carbon corg in the case of mo there appears to be at least two relationships between metal accumulation rate and organic carbon burial for most of the data presented in this manuscript continental margin sediments have a mo corg accumulation rate ratio of 20 mol mol 1 this value is significantly lower however than those reported for anoxic basins 100 mol mol 1 but is consistent with reported mo corg rain ratios from mexico margin sediment traps in contrast to mo there appears to be a single u corg burial ratio of 5 mol mol 1 which includes a range of environments from anoxic basins and open ocean sites we interpret the relationships between metal accumulation and organic carbon to indicate that the reactions that govern authigenic metal accumulation are primarily sensitive to the delivery and burial of organic carbon in these particular settings however we note that any relationship between metal accumulation and organic carbon could be indirect in the particular case of mo based on what is known about mo geochemistry from the literature it is possible that mo authigenesis is coupled to sulfur cycling in many of the environments covered by this study and that the observed association between mo and organic carbon burial is a consequence of the coupling between carbon and sulfur burial using the observed relationships between mo and corg burial as well as constraints from the mo isotope budget we estimate that continental margin sediments are an important sink for mo the magnitude of this sink 0 4 108 mol y 1 or larger may be as much as one quarter of the oceanic removal term and is likely to be larger than the modern anoxic basin sink

copper and zinc isotope systematics of altered oceanic crust at iodp site 1256 in the eastern equatorial pacific this paper presents the first combined cu and zn isotopic study of altered oceanic crust aoc at iodp hole 1256d that penetrates a volcanic section a lava dyke transition zone a sheeted dyke complex and a plutonic complex in the volcanic section all but one rocks have cu and zn isotopic compositions similar to fresh mid ocean ridge basalt morb reflecting restricted seawater circulation and low oxygen fugacity rocks in the transition zone have morb like 65cu and 66zn indicating the dominant influence of basalt derived cu and zn during alteration rocks in the dyke complex have more variable 65cu 0 50 0 90 and 66zn 0 19 0 55 and those in the plutonic complex have 65cu of 0 43 to 0 20 and 66zn of 0 21 to 0 41 the rocks with heavier 66zn and heavier or lighter 65cu relative to morb are characterized by cu zn depletions low li yb 1 0 and low 18o 5 suggesting that hydrothermal extraction during high temperature alteration of oceanic crust can result in significant cu and zn isotope fractionation such large cu and zn isotopic variations are the results of redox transformation of cu as well as cu and zn isotope fractionation between altered basaltic rocks and dissolved cu and zn species in hydrothermal fluids e g cucl3 1 zn hs 42 this work is the first to define the distribution of cu and zn isotopes in an intact oceanic crust with concentration weighted averages of 65cu 0 05 0 03 and 66zn 0 27 0 01 the potential implications of these new observations are discussed

estimation of the rupture length and velocity of the great sumatra earthquake of dec 26 2004 using hydroacoustic signals 1 unprecedented hydroacoustic observations of the megathrust earthquake of 26 dec 2004 were afforded by a network of 5 small hydroacoustic arrays located in the indian ocean at distances of 2800 to 7000 km from the epicenter each array recorded acoustic waves called t waves generated by this event analysis of a series of short time windows within the t wave coda shows that the receiver to source azimuth varies smoothly as a function of time indicating that the apparent t wave source is not stationary the apparent t wave source moves northward along the sunda trench at an average velocity of 2 km s closely tracking event rupture the hydroacoustic data suggest that the rupture proceeded in two distinct phases initially it progressed northwest along the sunda trench with a velocity of approximately 2 4 km s at 600 km from the epicenter the rupture slowed to approximately 1 5 km s as it continued to propagate to the northwest

p and t wave detection thresholds pn velocity estimate and detection of lower mantle and core p waves on ocean sound channel hydrophones at the mid atlantic ridge since 1999 six sound fixing and ranging sofar hydrophones have been moored along the mid atlantic ridge mar 15 35 n these hydrophones 8 bit data resolution are designed for long term monitoring of mar seismicity using the acoustic t waves of seafloor earthquakes the completeness level of the mar t wave earthquake catalog estimated from size frequency constraints is mb 3 0 a significant improvement in detection compared to the mb 4 6 completeness level estimated from national earthquake information center magnitude frequency data the hydrophones also detect the acoustic phase of converted upper mantle p arrivals from regional earthquakes at epicentral distances of 374 1771 km and from events as small as mb 3 6 these regional p waves are used to estimate a pn velocity of 8 0 0 1 km sec 1 along the east and west mar flanks an unexpected result was the identification of p arrivals from earthquakes outside the atlantic ocean basin the hydrophones detected p waves from global earthquakes with magnitudes of 5 8 8 3 at epicentral distances ranging from 29 6 to 167 2 examination of travel times suggests these teleseismic p waves constitute the suite of body wave arrivals from direct mantle p to outer and inner core reflected refracted phases the amplitudes of the teleseismic p waves also exhibit the typical solid earth wave field phenomena of a p shadow zone and caustic at d 144 these instruments offer a long term relatively low cost alternative to ocean bottom seismometers that allows for obser vation of pn velocities and mantle core phases arriving at normally inaccessible deep sea locations

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

using seismic waves to image earth s internal structure seismic waves generated in earth s interior provide images that help us to better understand the pattern of mantle convection that drives plate motions

manganese nodules and other ferromanganese oxide deposits from the indian ocean ferromanganese oxide concretions from the indian ocean exhibit considerable mineralogical and chemical variation often differentiated on a regional basis nodules richest in mn ni cu and zn are found in sub equatorial basin areas but enrichments of some of these metals also occur in nodules elsewhere particularly where there is evidence of major biogenic contributions to their underlying sediments fe co and pb are most enriched in concretions from sea mounts and the mid ocean ridge system but also attain high values in some basin areas local variations in concretion composition have been found off southern africa and are due to both biological and continental influences there are several major controls on the compositions of the concretions source variations influence composition in that mn ni and cu show evidence of diagenetic enrichment in deposits after being cycled through the biogenic component of sediments whereas fe co and pb appear to be supplied mainly by normal seawater environmental influences including bottom water characteristics affect the degree of dissolution of biogenic remains and this affects the sediment type and the supply of metals to the deposits and also their mineralogy which in turn affects trace metal uptake in the central indian basin source and environmental influences combine to produce ore grade nodules

molecular controls on cu and zn isotopic fractionation in fe mn crusts abstract the isotopic systems of the transition metals are increasingly being developed as oceanic tracers due to their tendency to be fractionated by biological and or redox related processes however for many of these promising isotope systems the molecular level controls on their isotopic fractionations are only just beginning to be explored here we investigate the relative roles of abiotic and biotic fractionation processes in controlling modern seawater cu and zn isotopic compositions scavenging to fe mn oxides represents the principal output for cu and zn to sediments deposited under normal marine oxic conditions using fe mn crusts as an analogue for these dispersed phases we investigate the phase association and crystal chemistry of cu and zn in such sediments we present the results of an exafs study that demonstrate unequivocally that cu and zn are predominantly associated with the birnessite mno2 phase in fe mn crusts as previously predicted from sequential leaching experiments e g koschinsky and hein 2003 the crystal chemistry of cu and zn in the crusts implies a reduction in coordination number in the sorbed phase relative to the free metal ion in seawater thus theory would predict equilibrium fractionations that enrich the heavy isotope in the sorbed phase e g schauble 2004 in natural samples fe mn crusts and nodules are indeed isotopically heavy in zn isotopes at 1 compared to deep seawater at 0 5 consistent with the predicted direction of equilibrium isotopic fractionation based on our observations of the coordination environment of sorbed zn further 50 of inorganic zn is chloro complexed the other 50 is present as the free zn2 ion and complexation by cl is also predicted to favour equilibrium partitioning of light zn isotopes into the dissolved phase the heavy zn isotopic composition of fe mn crusts and nodules relative to seawater can therefore be explained by an inorganic fractionation during uptake however cu in fe mn crusts is isotopically light at 0 3 to 0 5 compared to the dissolved phase in seawater at 0 9 we suggest that this is because dissolved cu in the oceans is overwhelmingly complexed to strong organic ligands which are better competitors for the heavy isotope

natural mass dependent variations in the isotopic composition of molybdenum we present the first observations of natural mass dependent fractionation of the isotopic composition of molybdenum mo using multi collector inductively coupled plasma mass spectrometry variations in the isotopic composition of mo are reported as 97 95mo 97mo 95mo sample 97mo 95mo standard 1 1000 external analytical precision of 97 95mo is 1 between sediments deposited under anoxic conditions 97 95mo 1 02 to 1 52 relative to our in house standard and ferromanganese nodules 97 95mo 0 63 to 0 42 97 95mo of pacific ocean seawater 97 95mo 1 48 lies within the range of values for anoxic sediments closest to modern black sea anoxic sediments molybdenites from continental ore deposits have intermediate 97 95mo ranging from 0 26 to 0 09 variations in the abundances of 92mo 95mo 96mo 97mo and 98mo are consistent with mass dependent fractionation a sporadic unidentified interference occurs at mass 94 and 100mo is not measured we hypothesize that the 97 95mo offset between anoxic sediments and ferromanganese nodules results from mo isotope fractionation during inefficient scavenging of mo from seawater by mn oxides under oxic conditions the similarity in 97 95mo of anoxic sediments and seawater is consistent with the very efficient removal of mo from seawater under anoxic conditions in the presence of h2s the data can be interpreted in terms of a steady state mass balance between the mo flux into the oceans from the continents and the mo flux out of the oceans into oxic and anoxic sediments such an interpretation is quantitatively consistent with existing estimates of the removal fluxes of mo to anoxic and oxic sediments these findings suggest that 97 95mo in seawater may co vary with changes in the relative proportions of anoxic and oxic sedimentation in the oceans and that this variation may be recorded in 97 95mo of anoxic sediments hence the mo isotope system may be useful in paleoredox investigations

crystal chemistry of ni in marine ferromanganese crusts and nodules marine ferromanganese crusts and nodules are highly enriched in transition metals such as ni and co yet the crystal chemistry and mode of incorporation of these metals is poorly known we characterized the crystal chemistry of ni in two hydrogenetic pacific ocean ferromanganese crust samples and a hydrogenetic nodule from the madeira abyssal plain energy dispersive spectrometry shows that ni is associated with the manganese oxide phases in agreement with previous work x ray diffraction patterns show that the dominant mn3 4 oxide is a phyllomanganate similar to hexagonal birnessite or mno2 extended x ray absorption fine structure spectroscopy shows that the coordination environment of ni results from structural incorporation into the phyllomanganate phase by replacement of mn3 4 in contrast ni initially sorbs to freshly prepared synthetic birnessite by surface complexation over vacancy sites in the mno2 layer we propose that the transformation of ni sorption from surface complexation to structural incorporation provides a potentially irreversible sink for ni in seawater

geochemical fates and unusual distribution of arsenic in natural ferromanganese duricrust abstract preferential enrichment of arsenic in iron oxides relative to manganese oxides has been well documented in this study however a distinct arsenic enrichment is revealed in natural ferromanganese duricrusts which are commonly found in natural weathering profiles of manganese bearing carbonate rocks in the studied ferromanganese duricrust covering carboniferous carbonates at qixia mountain in eastern china stromotalite like structures composed by hematite goethite pyrolusite and hetaerolite have been observed electron microprobe analysis empa mapping and synchrotron based micro scanning x ray fluorescence xrf analyses reveal that the arsenic content in manganese oxides is elevated with respect to iron oxide phases for example the arsenic content of pyrolusite is approximately 5 times as much as that of hematite or hetaerolite however the highest arsenic content 0 58 wt as 2 o 5 occurs in 2 75 0 96 m micro bands of hematite fe x mn iii 1 x 2 o 3 0 75 fe and as mn bond distances of 3 24 a and 3 23 a respectively in addition it is found that zinc is also more enriched in mn oxides besides hetaerolite than in fe oxides the fine hematite crust with low contents of heavy metals could act as a protective seal to separate mn oxides core with high zn and as from environmental fluids this separation could reduce the interaction between them and decrease the release of zn and as from this ferromanganese duricrusts which ensures long term sequestration of heavy metals the unique structural and mineralogical constraints on the distribution of heavy metals can provide insights into novel strategies for environmental remediation of heavy metals contaminations

the copper isotope geochemistry of rivers and the oceans abstract we present the first extensive dataset for copper cu isotopes in rivers as well as preliminary data for estuaries and seawater rivers exhibit a range in dissolved 65 cu relative to nist srm 976 of 0 02 to 1 45 per mil the discharge weighted average dissolved 65 cu and cu concentration for the studied rivers representing around 25 of the global riverine water discharge are 0 68 and 18 8 nmol kg 1 respectively isotopic data for the dissolved phase in two small estuaries in se england exhibit relatively minor variation through the salinity gradient 0 42 to 0 94 and are close to both the data for the rivers upstream from the estuaries and a measurement of the coastal sea at their mouths analyses of the particulate phase in the estuaries reveal a complementary light pool 0 24 to 1 02 the isotopic composition of the total cu inventory is however close to that of the crustal source these data along with published constraints suggest that the isotopically heavy dissolved phase of all the rivers originates in an isotopic partitioning of the weathered pool of cu between a light fraction adsorbed to particulates and a heavy dissolved fraction dominated by cu bound to strong organic complexes open ocean seawater samples generally exhibit even heavier dissolved cu isotopic compositions than the riverine input 65 cu 0 9 to 1 5 the heavy isotopic composition of seawater is inferred to originate from intra oceanic processes the small dataset presented here is most consistent with further isotopic partitioning between an isotopically light pool adsorbed to particulates and a heavy dissolved pool strongly bound to organic ligands scavenging appears to have greatest impact in the surface ocean and least in both the oxygen minimum zone and the ocean bottom perhaps reflecting the relative importance of scavenging and thus the sequestration of light cu to particulate material at different depths

towards balancing the oceanic ni budget abstract nickel isotopes are a novel and promising tracer of the chemistry of past ocean environments but realisation of this tracer s potential requires a comprehensive understanding of the controls on ni burial in the marine sedimentary archive an outstanding puzzle in the marine budget of ni first recognised in the 1970s is a major imbalance in the known inputs and outputs to and from the ocean the sedimentary outputs of ni are much larger than the inputs rivers dust much more recently it has also been recognised that the outputs are also considerably isotopically heavier than the inputs in this study we find light ni isotope compositions 60 ninist srm986 0 2 to 0 8 for mn rich sediments from the eastern pacific compared to fe mn crusts at about 1 6 these data suggest that diagenetic remobilisation of isotopically heavy ni leads to a significant benthic ni flux estimated at 0 6 2 3 10 8 mol yr similar in magnitude to the riverine flux to the ocean diagenetic remobilisation of ni may occur either via cycles of mn oxide dissolution and precipitation with associated ni sorption and release or during mineralogical transformation of birnessite to todorokite a minor role for retention of isotopically light ni by fe oxides or fe rich authigenic clays is also proposed overall a benthic flux of isotopically heavy ni at about 3 can balance the marine ni budget pinpointing diagenesis as a key missing piece of the ni puzzle

wavelet analysis for geophysical applications wavelet transforms originated in geophysics in the early 1980s for the analysis of seismic signals since then significant mathematical advances in wavelet theory have enabled a suite of applications in diverse fields in geophysics the power of wavelets for analysis of nonstationary processes that contain multiscale features detection of singularities analysis of transient phenom ena fractal and multifractal processes and signal com pression is now being exploited for the study of several processes including space time precipitation remotely sensed hydrologic fluxes atmospheric turbulence can opy cover land surface topography seafloor bathymetry and ocean wind waves it is anticipated that in the near future significant further advances in understanding and modeling geophysical processes will result from the use of wavelet analysis in this paper we review the basic properties of wavelets that make them such an attractive and powerful tool for geophysical applications we dis cuss continuous discrete orthogonal wavelets and wavelet packets and present applications to geophysical processes

magnitude determination using initial p waves a single station approach 1 prompted by recent success in the research and application of earthquake early warning systems we conducted an investigation into the relationship between the magnitudes of earthquakes and the properties of the first three seconds of the p waves at a single station using waveforms at station nacb of the broadband array in taiwan for seismology from 46 earthquakes within 100 km epicentral distance we found a linear correlation between the magnitudes and the logarithmic characteristic periods of the initial p waves for earthquakes up to magnitude 6 5 we also detected a deterministic relationship between the magnitudes and the peak amplitudes of the initial p waves for earthquakes of magnitude m 6 5 while further study needs to be done on the behavior of the initial p wave peak amplitudes from larger earthquakes we propose here that the characteristic periods and peak amplitudes of the first three seconds of the p waves be used jointly in onsite single station earthquake early warning operations

normal mode and free air gravity constraints on lateral variations in velocity and density of earth s mantle with the use of a large collection of free oscillation data and additional constraints imposed by the free air gravity anomaly lateral variations in shear velocity compressional velocity and density within the mantle dynamic topography on the free surface and topography on the 660 km discontinuity and the core mantle boundary were determined the velocity models are consistent with existing models based on travel time and waveform inversions in the lowermost mantle near the core mantle boundary denser than average material is found beneath regions of upwellings centered on the pacific ocean and africa that are characterized by slow shear velocities these anomalies suggest the existence of compositional heterogeneity near the core mantle boundary

a complex pattern of mantle flow in the lau backarc shear wave splitting analysis of local events recorded on land and on the ocean floor in the tonga arc and lau backarc indicate a complex pattern of azimuthal anisotropy that cannot be explained by mantle flow coupled to the downgoing plate these observations suggest that the direction of mantle flow rotates from convergence parallel in the fiji plateau to north south beneath the lau basin and arc parallel beneath the tonga arc these results correlate with helium isotopes that map mantle flow of the samoan plume into the lau basin through an opening tear in the pacific plate

sorption of ni by birnessite equilibrium controls on ni in seawater abstract synthetic hexagonal birnessite hx birnessite is a close analogue to natural poorly crystalline phyllomanganate phases found in soils and marine ferromanganese deposits these phases are often highly enriched in trace metals such as ni and co we measured the sorption of ni ii onto synthetic hexagonal birnessite hx birnessite from ph 1 to 7 exafs spectra show that at ph 3 7 ni is adsorbed to the hx birnessite surface above vacancy sites on 001 as a tridentate corner sharing complex we developed a surface complexation model for ni adsorption based on the equilibria 3 mn 2 o 2 3 ni 2 mn 2 o 3 ni 0 3 mn 2 o 2 3 ni 2 h 2 o mn 2 o 3 ni oh h using this surface complexation model we predict the concentration of ni in seawater in equilibrium with ni bearing birnessite found in hydrogenetic femn crusts and nodules our predicted results are in good agreement with observed ni concentrations in seawater and suggest that the concentration of dissolved ni in seawater is buffered by sorption to birnessite or a related mno 2 phase however in addition to the surface complex ni also sorbs by structural incorporation into the vacancy site in our synthetic samples at ph 7 exafs shows 10 of ni is structurally incorporated into hx birnessite in natural birnessites found in marine ferromanganese crusts and nodules exafs shows that all of the sorbed ni is structurally incorporated structural incorporation suggests that ni sorption may be irreversible

monitoring pacific ocean seismicity from an autonomous hydrophone array since may 1996 an array of autonomous hydrophone moorings has been continuously deployed in the eastern equatorial pacific to provide long term monitoring of seismic activity including low level volcanic signals along the east pacific rise between 20 n and 20 s and the galapagos ridge the instruments and moorings were designed to continuously record low frequency acoustic energy in the sofar channel for extended periods and produce results comparable to those previously derived by using the u s navy sound surveillance system sosus in the northeast pacific the technology and methodology developed for this experiment including instrument design mooring configuration analysis software location algorithms with an analysis of errors and a predicted error field are described in detail volcanic activity is observed throughout the pacific along with seismicity along transform faults subduction zones and intraplate regions comparison data sets indicate detection thresholds and accuracy better than the land networks for open ocean areas and results comparable to or better than sosus volcanic seismicity along the fast spreading east pacific rise appears similar to documented examples in the northeast pacific but with much shorter durations one example from the intermediate spreading galapagos ridge is comparable to northeast pacific examples and several episodes of activity were observed in the wilkes transform fault zone a site of continuing off axis seismicity is located near 18 s and 116 w isolated intraplate earthquakes are observed throughout the study area earthquake information from this experiment and future observations will be provided through the world wide web and earthquake data centers

uranium isotope fractionation during coprecipitation with aragonite and calcite abstract natural variations in 238u 235u of marine calcium carbonates might provide a useful way of constraining redox conditions of ancient environments in order to evaluate the reliability of this proxy we conducted aragonite and calcite coprecipitation experiments at ph 7 5 and 8 5 to study possible u isotope fractionation during incorporation into these minerals small but significant u isotope fractionation was observed in aragonite experiments at ph 8 5 with heavier u isotopes preferentially enriched in the solid phase 238u 235u of dissolved u in these experiments can be fit by rayleigh fractionation curves with fractionation factors of 1 00007 0 00002 0 00003 1 00005 0 00001 and 1 00003 0 00001 in contrast no resolvable u isotope fractionation was observed in an aragonite experiment at ph 7 5 or in calcite experiments at either ph equilibrium isotope fractionation among different aqueous u species is the most likely explanation for these findings certain charged u species are preferentially incorporated into calcium carbonate relative to the uncharged u species ca2uo2 co3 3 aq which we hypothesize has a lighter equilibrium u isotope composition than most of the charged species according to this hypothesis the magnitude of u isotope fractionation should scale with the fraction of dissolved u that is present as ca2uo2 co3 3 aq this expectation is confirmed by equilibrium speciation modeling of our experiments theoretical calculation of the u isotope fractionation factors between different u species could further test this hypothesis and our proposed fractionation mechanism these findings suggest that u isotope variations in ancient carbonates could be controlled by changes in the aqueous speciation of seawater u particularly changes in seawater ph p co 2 ca2 or mg2 concentrations in general these effects are likely to be small

combining altimeter and subsurface float data to estimate the time averaged circulation in the upper ocean 1 a new technique is presented for estimating time averaged upper ocean geostrophic velocity from a combination of altimeter data and subsurface float data the technique makes uses of the strong relationship between sea surface height anomaly and anomalous velocity at depth to reduce mesoscale eddy variability in subsurface float displacements the technique is demonstrated on a region in the north atlantic that was well sampled by argo floats the 2004 through 2006 time averaged density field was estimated from the surface to 2000 db by combining altimeter and hydrographic data from the floats in addition a reference velocity field was estimated at 1000 db based on a combination of altimeter data and subsurface float displacements the reference velocity field was combined with geostrophic shear based on the density field to produce a three dimensional estimate of geostrophic velocity from the surface to 2000 db the gulf stream transport in the upper 2000 db is estimated to be 76 sv at 73 w in addition an estimate of the 3 year average dynamic height at the surface was computed by combining the 1000 db reference dynamic height and the time averaged density field

abundance of zinc isotopes as a marine biogeochemical tracer 1 the zn isotopic compositions of ferromanganese nodules sediment trap samples sediments and organic reference samples have been analyzed by multiple collector inductively coupled plasma mass spectrometry icp ms the range of isotopic variations 1 for 66zn 64zn is significant with respect to the analytical precision 0 04 at the 95 confidence level marine argillaceous sediments show rather constant values consistent with those of continental shales and loess and with the value of a basalt from reunion island we infer that the depletion of the light zn isotopes in marine particles and in ferromanganese nodules presumably equilibrated with seawater results from biological activity in the upper water column the 66zn values of sediment trap samples collected near the upwelling off the coast of mauritania central atlantic show a seasonal isotopic fluctuation consistent with biological pumping during the high productivity period higher values of 66zn in nodules appear to be associated with the amplitude of seasonal variations rather than with the mean values of the biological productivity

the oceanic mass balance of copper and zinc isotopes investigated by analysis of their inputs and outputs to ferromanganese oxide sediments abstract the oceanic biogeochemical cycles of the transition metals have been eliciting considerable attention for some time many of them have isotope systems that are fractionated by key biological and chemical processes so that significant information about such processes may be gleaned from them however for many of these nascent isotopic systems we currently know too little of their modern oceanic mass balance making the application of such systems to the past speculative at best here we investigate the biogeochemical cycling of copper cu and zinc zn isotopes in the ocean we present estimates for the isotopic composition of cu and zn inputs to the oceans based on new data presented here and published data the bulk isotopic composition of dissolved cu and zn in the oceans 65cu 0 9 66zn 0 5 is in both cases heavier than their respective inputs at around 65cu 0 6 and 66zn 0 3 respectively implying a marine process that fractionates them and a resulting isotopically light sedimentary output for the better known molybdenum isotope system this is achieved by sorption to fe mn oxides and this light isotopic composition is recorded in fe mn crusts hence we present isotopic data for cu and zn in three fe mn crusts from the major ocean basins which yield 65cu 0 44 0 23 mean and 2sd and 66zn 1 04 0 21 thus for cu isotopes output to particulate fe mn oxides can explain the heavy isotopic composition of the oceans while for zn it cannot the heavy zn in fe mn crusts and in all other authigenic marine sediments measured so far implies that a missing light sink is still to be located these observations are some of the first to place constraints on the modern oceanic mass balance of cu and zn isotopes

seismic tomography of the earth s mantle the analysis of information contained in seismograms is the most promis ing tool for retrieving the three dimensional structure of the earth s mantle and thereby improving our understanding of its dynamics the procedure through which three dimensional images of different parts of the earth s interior arc obtained by inversion of a set of observables measured on the surface of the earth is commonly termed tomography by analogy with the medical procedure with which it shares many aspects of methodology but with much less favorable experimental conditions ideally one would like to be able to model entire seismograms over a wide frequency band for a large number of uniformly distributed sources and stations in order to obtain an optimal illumination of the inhomogeneities appropriate for tomographic inversion in practice a number of difficulties and limitations arise onc is the nonuniform distribution of sources and receivers seis micity is concentrated at plate boundaries and the distribution of con tinental and island areas leaves large portions of the oceans unin strumented another difficulty is our limited ability to accurately forward model the effects of wave propagation in a realistic earth which presents departures from a spherically symmetric referencc model of both elastic anc1astic and isotropic anisotropic nature this is why until now the simplest kind of tomography travel time tomography has prevailed relying on simplifying assumptions concerning the interaction of asphericity with propagating seismic waves ray theory and the laws of geometrical optics in their

aftershock sequences in the mid ocean ridge environment an analysis using hydroacoustic data abstract hydroacoustic data from autonomous arrays and the u s navy s sound surveillance system sosus provide an opportunity to examine the temporal and spatial properties of seismicity along portions of the slow spreading mid atlantic ridge mar intermediate spreading juan de fuca ridge jdfr and fast spreading east pacific rise epr aftershock and foreshock events are selected from the hydroacoustic earthquake catalog using single link cluster slc analysis with a combined space time metric in the regions examined hydroacoustic data improve the completeness level of the earthquake catalog by 1 5 2 0 orders of magnitude allowing the decay constant p of the modified omori law mol to be determined for individual sequences a non parametric goodness of fit test indicates six of the seven sequences examined are described well by a mol model the p values obtained for individual ridge and transform sequences using hydroacoustic data are larger than that previously estimated from the analysis of a stacked sequence generated from teleseismic data for three sequences along the siqueiros discovery and western blanco transforms p values are estimated to be 0 94 1 29 the spatial distribution of aftershocks suggests that the mainshock rupture is constrained by intra transform spreading centers at these locations an aftershock sequence following a 7 1 m s thrust event near the northern edge of the easter microplate exhibits p 1 02 0 11 within the sequence aftershocks are located to the north of a large topographic ridge which may represent the surface expression of the shallow dipping fault that ruptured during the mainshock two aftershock sequences near 24 25 n and 16 35 n on the mar exhibit higher p values 1 74 0 23 and 2 37 1 65 although the latter estimate is not well constrained because of the small number of aftershocks larger p values along the ridge crest might reflect a hotter thermal regime in this setting additional monitoring however will be needed to determine if p value differences between the ridge and transform sequences are robust a 1999 sequence on the endeavour segment of the jdfr which has been correlated with changes in the hydrothermal system is described poorly by the mol model the failure of the mol model the anomalously large number of earthquakes within the sequence and absence of a clearly dominant mainshock are inconsistent with aftershock activity and the simple tectonic origin that has been proposed previously for this sequence

isotopic disequilibrium of cu in marine ferromanganese crusts evidence from ab initio predictions of cu isotope fractionation on sorption to birnessite abstract in the oceans cu is strongly scavenged by ferromanganese fe mn crusts the isotopic fractionation of cu between seawater and crusts provides insight into the mechanisms of trace metal cycling in the oceans dissolved cu in seawater is isotopically heavy 0 66 0 19 relative to cu in crusts 0 31 0 24 the primary mineral phase sorbing divalent trace metals in fe mn crusts is birnessite recent laboratory measurements show that isotopically light cu is preferentially sorbed on birnessite with a fractionation factor of 0 45 0 18 here we use first principles quantum mechanical calculations to predict the isotopic fractionation between aqueous cu2 complexes and cu as a surface complex on birnessite we find that isotopic fractionation between the cu h2o 5 complex and sorbed cu should be 0 49 at 25 c in close agreement with experiments confirming that these experimental results reflects equilibrium fractionation we then predict the isotopic fractionation between dissolved inorganic cu in seawater and birnessite given the thermodynamic speciation of dissolved cu at ph 8 we find dissolved inorganic cu should be 0 94 at 5 c heavier than cu sorbed to birnessite this value is substantially greater than the observed fractionation between seawater and fe mn crusts sw fmc 0 35 moreover it is well established that dissolved cu in seawater is strongly complexed by organic ligands based on model cu complexes and published experimental data we estimate that fractionation of cu by organic ligands should increase the equilibrium fractionation between seawater and fe mn crusts by 0 2 to 1 5 to yield sw fmc 1 1 to 2 4 we conclude that cu in marine fe mn crusts in not in isotopic equilibrium with dissolved cu in seawater and consider the possible explanations of this surprising finding

copper isotope signatures in modern marine sediments abstract the development of metal stable isotopes as tools in paleoceanography requires a thorough understanding of their modern marine cycling to date no cu isotope data has been published for modern sediments deposited under low oxygen conditions we present data encompassing a broad spectrum of hydrographic and redox regimes including continental margin and euxinic sulphide containing settings taken together with previously published data from oxic settings these data indicate that the modern oceanic sink for cu has a surprisingly homogeneous isotopic composition of about 0 3 65cu relative to nist srm976 we suggest that this signature reflects one of two specific water column processes 1 an equilibrium isotope fractionation between soluble isotopically heavy cu complexed to strong organic ligands and an isotopically light pool sorbed to particles that deliver cu to the sediment or 2 an equilibrium isotope fractionation between the same isotopically heavy ligand bound pool and the particle reactive free cu2 species with the latter being scavenged by particulates and thereby delivered to the sediment an output flux of about 0 3 into sediments is isotopically light relative to the known inputs to the ocean at around 0 6 and the seawater value of 0 6 to 0 9 suggesting the presence of an as yet unidentified isotopically light source of cu to the oceans we hypothesize that this source may be hydrothermal or may result from the partial dissolution of continentally derived particles

coupled seismoacoustic modes on the seafloor 1 wave to wave coupling arises when an acoustic pulse selects a rayleigh mode of the same speed and both travel together swapping energy across an interface ewing et al 1957 a distinctive signal is observed at the hawaii 2 observatory for purely oceanic paths from earthquakes on the blanco and mendocino fracture zones off the coast of north america the signal appears to be a composite of undispersed higher rayleigh modes propagating along the ocean floor both in the sediments and in the water the new coupled modes are identified by their frequency composition and their phase and group velocities seismoacoustic coupling at the seafloor is conditioned on a the presence of a low velocity interface at the ocean floor and b the wavelength of the rayleigh component being shorter than the depth of the water layer

molybdenum isotope fractionation during adsorption by manganese oxides the isotopic composition of mo 97 95mo in seawater is 2 heavier than mo in marine ferromanganese crusts and nodules barling et al earth planet sci lett 193 2001 447 457 siebert et al earth planet sci lett 211 2003 159 171 to explore this phenomenon we have conducted an experimental investigation into the mass dependent fractionation of mo isotopes during adsorption onto mn oxyhydroxide two series of experiments were carried out a time series in which adsorption proceeded for 2 96 h and a ph series in which ph varied from 6 5 to 8 5 the extent of mo adsorption by mn oxyhydroxides decreases with increasing ph a trend typical of anion adsorption and takes 48 h to reach steady state lighter mo isotopes are preferentially adsorbed experimentally determined fractionation factors soln mnox exhibit no systematic variation with either time or experimental ph the mean soln mnox for all experiments is 1 0018 0 0005 2 s d comparison of the mo isotopic data for experimental solutions and mo adsorbed to mn oxyhydroxide with predictions for closed system equilibrium and rayleigh fractionation models indicates that isotope fractionation occurs as a result of closed system equilibrium exchange between dissolved and adsorbed mo the isotopic offset between dissolved and adsorbed mo is comparable to that observed between mo in seawater and mo in ferromanganese nodules and crusts it is therefore likely that adsorption of mo to mn oxyhydroxides is a significant factor in the fractionation of mo isotopes in the oceans

evolution of nd and pb isotopes in central pacific seawater from ferromanganese crusts abstract hydrogenetic ferromanganese crusts incorporate elements from ambient seawater during their growth on seamounts by analysing nd pb and be isotope profiles within crusts it is possible to reconstruct seawater tracer histories depth profiles of 10be 9be ratios in three pacific ferromanganese crusts have been used to obtain growth rates which are between 1 4 and 3 8 mm ma nd and pb isotopes provide intact records of isotopic variations in pacific seawater over the last 20 ma or more there were only small changes in pb isotope composition in the last 20 ma this indicates a constant pb composition for the erosional sources and suggests further that erosional nd inputs may have been uniform too end values vary considerably with time and most probably reflect changes in ocean circulation the end values of the crusts not only vary as a function of age but also as a function of water depth from 25 to 0 ma crust va13 2 from 4 8 km water depth has a similar pattern of end variation to the two shallower crusts from 1 8 and 2 3 km but about 1 0 to 1 5 units more negative this suggests that end stratification in pacific seawater as demonstrated for the present day has been maintained for at least 20 ma each crust shows a decrease in end from 3 5 ma to the present which is interpreted in terms of an increase in the nadw component present in the pacific from 10 to 3 5 ma ago the crusts show an increase in end this suggests a decreasing role for a deep water source with end less than circum pacific sources in this regard the panamanian gateway restriction from 10 ma with final closure at 3 5 ma may have played an important role in reducing access of atlantic derived nd to the pacific

intermediate level circulation of the southwestern part of the east japan sea estimated from autonomous isobaric profiling floats 1 with trajectory data from autonomous isobaric profiling floats palace apex and provor we obtained a detailed intermediate level circulation pattern over the southwestern part of the east japan sea the circulation pattern which is consistent with moored current meter data obtained at a few locations is largely controlled by the bottom topography the main features we have found are as follows 1 a cyclonic circulation along the korean coast and the continental break around the ulleung basin and the western side of oki spur to the yamato rise and 2 a cold current from the japan basin to the ulleung basin through the ulleung interplain gap which is a part of the anticyclonic flow over the korea plateau a taylor column

elliptical boundary of an intraplate volcanic field auckland new zealand abstract the outer vents in the auckland volcanic field lie within 19 to 559 m mean 224 75 m of a best fit ellipse with a 28 9 km long major axis trending almost north south and a minor axis 16 5 km long the ellipse has formed the outer boundary of the field since the inception of volcanism 140 000 years ago we present the following testable hypotheses as an explanation of this pattern the boundary is the expression of a corresponding elliptical source area at depth in the lithospheric mantle possibly asthenosphere material trapped at this level the ellipse may represent a depth contour on a very small upper mantle dome or of a lens intruding into a neck of an extensional structure alternatively it could be the boundary of a flat elliptical area where tensional stresses allow decompressional melting the elliptical tensional region may either have developed in a releasing bend during strike slip faulting along a fundamental lithosphere structure inherited from mesozoic tectonics associated with the nnw trending dun mountain ophiolite belt or may represent the tip of a fracture along which the auckland volcanic province is propagating northward

biogeochemical cycling of zinc and its isotopes in the southern ocean abstract we report zn concentration and isotope data for seawater samples from the atlantic sector of the southern ocean collected during the ipy geotraces ant xxiv iii cruise along the greenwich zero meridian data are reported for the full depth range of the water column at three stations as well as a transect of surface samples using a new analytical approach that is presented in detail here zn concentrations increase with depth though due to proximity to upwelling sites surface concentrations are not as low as in some parts of the ocean such as further northward into the sub antarctic zone for two depth profiles south of the polar front zone the physical stratification of the upper water column is reflected in sudden near surface changes in zn concentration with depth in contrast beneath 100 300 m zn concentrations barely change with depth zn isotopic data beneath 1000 m for the southern ocean data presented here as well as published data from the north atlantic and north pacific are strikingly homogeneous with an average 66zn 0 53 0 14 2sd 2se 0 03 n 21 the surface southern ocean is more variable with 66zn ranging from 0 07 to 0 80 between the two is a thin horizon at 40 80 m which in the southern ocean as well as the north atlantic and north pacific is characterised by distinctly light isotopic signatures with 66zn about 0 3 lower than surface waters strong correlations between si and zn concentrations seen here and elsewhere coupled to the lack of any systematic relationship between si and zn isotopes in the southern ocean suggest that the removal of zn associated with diatom opal involves little or no isotopic fractionation regeneration of this zn also explains the homogeneous zn isotopic composition of the global deep ocean so far sampled however the low zn content of opal requires that deep ocean zn does not directly come from the opal phase itself but rather from associated organic material external to the diatom frustule during growth experimental data are consistent with little or no fractionation during incorporation of zn into this material on the other hand the light zinc at 40 80 m is most consistent with the regeneration of an intra cellular pool that both culturing experiments and field data suggest will be isotopically light the data thus imply two processes by which zn is taken up in the surface ocean that these pools have very different regeneration lengthscales and that physical mixing of the oceans cannot eradicate their isotopic signatures finally the deep 66zn ocean value is significantly higher than the current best estimate of the input to the oceans the most obvious candidate for the required light sink is the survival of some of the cellular zn to be buried in sediment

the behaviour of cu and zn isotopes during soil development controls on the dissolved load of rivers abstract the stable isotopes of copper cu and zinc zn are finding increasing applications in surface earth geochemistry an important early observation is that aqueous pools of cu rivers and oceans are isotopically heavier than rocks of the continental crust for zn the global average 66 zn for rivers is identical to estimates of the upper continental crust but the oceans are slightly heavier here we study cu and zn abundances and isotopes in soils to assess how processes in the weathering environment control isotopic values of rivers and ultimately the oceans we investigated a range of soils developed on granitoid scotland and basaltic hawaiian islands rock substrates representing soil development times from 0 1 to 400 kyr mean annual temperatures of 6 16 c and mean annual precipitation map of 1060 5050 mm soils developed on the island of maui over 400 kyr and under high rainfall show the clearest chemical weathering signatures here in oxic soils cu and zn are both depleted by 50 90 with preferential loss of heavy cu 65 cu up to 1 2 lower than parent material and small shifts in 66 zn we attribute this to equilibrium fractionation between aqueous organic species that are removed from the soil versus sorption to residual fe oxyhydroxides in soils that are 0 1 150 kyr old in scotland and hawaii this same pattern is overprinted by biological cycling and the addition of mineral aerosol cu and zn with heavier isotope compositions in reducing soils on maui developed under the highest rainfall cu and zn are almost completely stripped from the soil leaving a very small residual pool with 65 cu and 66 zn values that range from those for the oxic soils back to and beyond parent material this removal of the light sorbed cu seen in oxic soils is attributed to the dissolution of fe oxides under anaerobic conditions perhaps microbially mediated leaving a very small residual isotopically heavier pool overall these data suggest that processes in soils create significant variability in cu isotopes with the heavy isotope exported from oxic soils in contrast small isotope fractionations of zn are generated in the soil environment these observations are consistent with those made previously for cu and zn isotopes in rivers but the maximum amount of cu and zn stored by world soils equates to only 30 130 years of the dissolved riverine flux soils cannot be the ultimate repository of the residual cu and zn required balancing the riverine flux and this must ultimately reside in the erosive products of soil formation in continental and ocean margin sediments

p wave detection thresholds pn velocity estimates and t wave location uncertainty from oceanic hydrophones p wave arrivals recorded by the u s navy s sound surveillance system sosus hydrophone arrays were used to estimate earthquake detection thresholds and pn velocities in the northeast pacific ocean the navy hydrophones have been used successfully to detect and locate oceanic earthquakes using their waterborne acoustic tertiary t waves however use of these hydrophones for seismic body wave detection allows regional seismic analyses to be extended to the oceanic environment the p wave detection threshold of the sosus hydrophones was quantified using the epicentral distance and magnitude of 250 northeast pacific ocean earthquakes earthquakes with body wave magnitudes as low as 2 have detectable p wave arrivals at epicentral distances of 500 km earthquakes with mb between 3 5 and 5 were detected 50 of the time at distances of 100 1500 km while events with mb 5 were all detected even out to distances of 1000 1500 km both p and t wave hydrophone arrival times were used to estimate the epicenters of 100 earthquakes the peak amplitude of the t wave coda and the onset of the p wave were used as the earthquake arrival times to estimate event locations t wave arrival time residuals have a gaussian distribution with zero mean which implies that using t wave peak amplitude is consistent with using the p wave onset as the arrival time there are typically 6 stations used to derive a t wave based location hence location error ellipses are not well constrained a monte carlo technique was employed to estimate t wave event location uncertainty t wave locations have error bars of 1 km in latitude and longitude when 3 hydrophones are used for a location estimate the detected p wave arrivals and earthquake locations were used to measure pn velocities pn velocity values of 7 9 0 1 and 8 0 0 1 km s were found for the pacific and juan de fuca plates respectively a pn velocity of 7 5 0 1 km s was measured for rays traveling northward from the mendocino triple junction along the cascadia subduction zone a pn velocity of 7 7 0 3 km s was estimated for ray paths originating onshore western north america and traveling to the offshore hydrophones

the geochemistry of redox sensitive trace metals in sediments abstract we analyzed the redox sensitive elements v mo u re and cd in surface sediments from the northwest african margin the u s northwest margin and the arabian sea to determine their response under a range of redox conditions where oxygen penetrates 1 cm or less into the sediments mo and v diffuse to the overlying water as mn is reduced and remobilized authigenic enrichments of u re and cd are evident under these redox conditions with the onset of sulfate reduction all of the metals accumulate authigenically with re being by far the most enriched general trends in authigenic metal accumulation are described by calculating authigenic fluxes for the 3 main redox regimes oxic reducing where oxygen penetrates 1 cm and anoxic conditions using a simple diagenesis model and global estimates of organic carbon rain rate and bottom water oxygen concentrations we calculate the area of sediments below 1000 m water depth in which oxygen penetration is 1 cm to be 4 of the ocean floor we conclude that sediments where oxygen penetrates 1 cm release mn v and mo to seawater at rates of 140 260 60 150 and 5 10 of their respective riverine fluxes using the authigenic metal concentrations and accumulation rates from this work and other literature these sediments are sinks for re cd and u with burial fluxes of 70 140 30 80 and 20 40 respectively of their dissolved riverine inputs we modeled the sensitivity of the response of seawater re cd and v concentrations to changes in the area of reducing sediments where oxygen penetrates 1 cm our analysis suggests a negligible change in seawater re concentration whereas seawater concentrations of cd and v could have decreased and increased respectively by 5 10 over 20 kyr if the area of reducing sediments increased by a factor of 2 and by 10 20 if the area increased by a factor of 3 the concentration variations for a factor of 2 increase in the area of reducing sediments are at about the level of uncertainty of cd ca and v ca ratios observed in foraminifera shells over the last 40 kyr this implies that the area of reducing sediments in the ocean deeper than 1000 m 4 has not been greater than twice the present value in the recent past

comparative geochemistry of four ferromanganese crusts from the pacific ocean and significance for the use of ni isotopes as paleoceanographic tracers abstract ferromanganese fe mn crusts are potential archive of the ni isotope composition of seawater through time in this study we aim at 1 understanding ni isotope fractionation mechanisms and metal enrichment processes in fe mn deposits 2 addressing global vs local control of ni isotope composition of these deposits two fe mn crusts from the north pacific ocean apuupuu seamount hawaii and two fe mn crusts from the south pacific ocean near rurutu island austral archipelago of french polynesia were characterized for their elemental geochemistry and ni isotope composition geochemical analyses were performed at millimeter intervals in order to provide time resolved record of ni isotopes chronology and growth rates were determined using cosmogenic 10be isotope abundances the results show that despite different growth rates textures and geochemical patterns fe mn crusts from both north and south pacific oceans have fairly homogenous ni isotope compositions over the last 17 ma yielding average 60 58ni values of 1 79 0 21 2sd n 31 and 1 73 0 21 2sd n 21 respectively in one crust sample however layers directly in contact with the altered substrate show anomalously light 60 58ni values down to 0 25 0 05 2se together with rejuvenated 10be 9be ratios correlating with elevated ni mn ratios such patterns are best explained by protracted fluid rock interactions leading to alteration of mn phases after crust formation isotopically light ni would be the result of ni isotope fractionation during adsorption rather than the contribution of external ni sources e g hydrothermal sources having light ni isotope compositions the combination of our results with previously published data on fe mn crusts indicates that the average ni isotope composition in deep waters has not changed through the cenozoic 70 ma we propose that ni isotope variations in fe mn crusts may not only record variations of ni sources to the oceans but also post depositional processes depending on the growth history and geological settings of fe mn crusts

on the potential of recording earthquakes for global seismic tomography by low cost autonomous instruments in the oceans 1 we describe the development and testing of an autonomous device designed to revolutionize earth structure determination via global seismic tomography by detecting earthquakes at teleseismic distances in the oceans one prototype mermaid short for mobile earthquake recording in marine areas by independent divers was constructed and tested at sea the instrument combines two readily available relatively low cost but state of the art components a sounding oceanographic lagrangian observer or solo float and an off the shelf hydrophone with custom built data logging hardware we report on the development of efficient wavelet based algorithms for the detection and discrimination of seismic events and analyze three time series of acoustic pressure collected at a depth of 700 m in pilot experiments conducted offshore san diego ca in these tests over 120 hours of data were gathered and five earthquakes of which one was teleseismic were recorded and identified quantitative estimates based on these results suggest that instruments of the mermaid type may collect up to a hundred tomographically useful teleseismic events per year the final design will also incorporate a global positioning system receiver onboard signal processing software optimized for low power chips and high throughput satellite communication equipment for telemetered data transfer with these improvements we hope to realize our vision of a global array of autonomous floating sensors for whole earth seismic tomography

fractionation of zn isotopes in terrestrial ferromanganese crusts and implications for tracing isotopically heterogeneous metal sources abstract zinc liberated from geological sources during surface weathering is the main source of zn to the surface environment and is ultimately sequestered by sinks such as mn oxides and oxyhydroxides this behaviour has been applied to geochemical mineral exploration studies and terrestrial ferromanganese crusts have been shown to have anomalously high zn mn ratios around known zn pb ore deposits this poses the question if zn isotopic compositions of these fe mn crusts can also discriminate the underlying anomalous metal sources from the surrounding non mineralized lithologies isotopic fractionation during fractionation onto mn oxides in well studied marine fe mn crusts has shown that isotopically heavy zn is preferentially adsorbed in that environment which has a comparatively isotopically homogeneous zn reservoir however isotopic fractionation behaviour in terrestrial fe mn crusts that may have more heterogeneous zn sources is unknown here we present the first zn and pb isotope study of terrestrial fe mn crusts to test if zn isotopic compositions can be used to delineate isotopically different lithological metal sources our data from fe mn crusts that formed overlying isotopically variable lithologies hydrothermal polymetallic zn pb deposits and non mineralized archean rocks show that while adsorption of zn onto mn oxyhydroxides in terrestrial fe mn crusts generally favours isotopically heavy zn the magnitudes of isotopic fractionation varies in fe mn crusts overlying mineralized and non mineralized areas fractionation factors 66 64zncrust source up to 0 54 in crusts overlying non mineralized lithological sources with a 66zn value of 0 30 are comparable with the predicted equilibrium fractionation onto birnessite conversely magnitudes of 66 64zncrust source up to 0 37 in crusts overlying isotopically light zn pb mineralization that has a mean 66zn value of 0 15 are much lighter than non mineralized counterparts with similar zn mn ratios this difference may be explained by changes in hydrogeochemical complexation of zn with localized chloro complexes that carry isotopically light zn from the isotopically light mineralization these findings demonstrate that different lithological zn sources that are isotopically variable give rise to isotopic heterogeneity in the surface zn reservoir this can be reflected by differing fractionation patterns following adsorption onto mn oxyhydroxides in terrestrial fe mn crusts that overly different zn sources furthermore pb isotope compositions of the fe mn crusts also closely reflect that of the underlying geology this highlights that the use of zn isotopes may be a valuable means of vectoring towards anomalous metal sources such as ore deposits

cu isotopes in marine black shales record the great oxidation event the oxygenation of the atmosphere 2 45 2 32 billion years ago ga is one of the most significant geological events to have affected earth s redox history our understanding of the timing and processes surrounding this key transition is largely dependent on the development of redox sensitive proxies many of which remain unexplored here we report a shift from negative to positive copper isotopic compositions 65 cuerm ae633 in organic carbon rich shales spanning the period 2 66 2 08 ga we suggest that before 2 3 ga a muted oxidative supply of weathering derived copper enriched in 65 cu along with the preferential removal of 65 cu by iron oxides left seawater and marine biomass depleted in 65 cu but enriched in 63 cu as banded iron formation deposition waned and continentally sourced cu became more important biomass sampled a dissolved cu reservoir that was progressively less fractionated relative to the continental pool this evolution toward heavy 65 cu values coincides with a shift to negative sedimentary 56 fe values and increased marine sulfate after the great oxidation event goe and is traceable through phanerozoic shales to modern marine settings where marine dissolved and sedimentary 65 cu values are universally positive our finding of an important shift in sedimentary cu isotope compositions across the goe provides new insights into the precambrian marine cycling of this critical micronutrient and demonstrates the proxy potential for sedimentary cu isotope compositions in the study of biogeochemical cycles and oceanic redox balance in the past

depth extent of the lau back arc spreading center and its relation to subduction processes seismic tomography and wave form inversion revealed that very slow velocity anomalies 5 to 7 percent beneath the active lau spreading center extend to 100 kilometer depth and are connected to moderately slow anomalies 2 to 4 percent in the mantle wedge to 400 kilometer depth these results indicate that geodynamic systems associated with back arc spreading are related to deep processes such as the convective circulation in the mantle wedge and deep dehydration reactions in the subducting slab the slow regions associated with the tonga arc and the lau back arc are separated at shallow levels but merge at depths greater than 100 kilometers suggesting that slab components of back arc magmas occur through mixing at these depths

a critical evaluation of copper isotopes in precambrian iron formations as a paleoceanographic proxy abstract trace metals in iron formations if have been widely used as proxies for oceanic redox processes and oxygen evolution leading to the great oxidation event goe copper has hitherto received comparatively little attention with a single study reporting variation in 65cu between pre and post goe black shales this is attributed to postulated isotope fractionation effects in the pre goe ocean during widespread iron oxide deposition in if here we focus on the application of cu isotopes in two classic if containing sequences of the neoarchean paleoproterozoic namely the hamersley australia and transvaal south africa supergroups we specifically targeted the oxide rich joffre and kuruman if the carbonate rich griquatown if and the mn rich hotazel if which collectively record over 100 ma of sustained if deposition in the pre goe ocean the aim was to assess the utility of cu isotopes in if as a paleoceanographic proxy in view of existing oxygen evolution models iron formation cu concentrations are low compared to average crust and modern oceanic fe mn oxide deposits with average values between 1 and 5 ppm for all four if data sets copper concentrations show no systematic variability with mineralogy no statistical correlation with bulk fe and mn contents good correlations with ti rcu ti 0 73 for the joffre data set and with cr ni and v for the south african data sets and shale like cu ti ratios isotopic results show statistically invariant average 65cu values very close to 0 for all but the joffre if which has a marginally negative average 65cu value 0 24 0 22 combined with other trace transition metal systematics the cu isotope data point to a cu source that was controlled largely by inputs of fine volcanic derived particles ash thus placing limitations on its utility as a paleoceanographic redox proxy during if genesis