the rates of plate creation and consumption summary an alternative vector derivation of the expression for the rates of plate creation and consumption is given from which it can be seen that the rates are proportional to the scalar product of the edges of the geohedron and plate polyhedron corresponding to the same boundary the plate polyhedron is defined by the set of triple junction vectors this is used together with a recent determination of the angular velocity vectors and a number of auxiliary plate boundary vectors to revise the rates of plate creation and consumption along sections of plate boundaries all plates which have a substantial proportion of their boundary connected to a downgoing slab are found to be decreasing in area the total rate of plate generation is used in estimates of the area of the ocean floor and the total heat loss from the oceans the rate of consumption within a relatively small area around new guinea implies a large mass flux away from this region knowledge of the rates of plate creation and consumption is used in a number of different areas calculating the contribution of plate creation to the total heat loss of the earth calculating geochemical fluxes out of the mantle such as for the rare gases and other volatiles and return fluxes back into the mantle resulting from reactions between sea water and the ocean crust during hydrothermal circulation calculating the area of the ocean floor as a function of age mass fluxes related to the distribution of the rates of creation and destruction along the plate boundaries are important boundary conditions on the flow pattern in the mantle previous estimates of these rates deffeyes 1970 chase 1972 garfunkel 1975 have applied a simple expression derived for spreading ridges deffeyes 1970 using angular distances from the poles of rotation measured graphically on a globe an alternative derivation of the expression for rates of plate creation and consumption which is independent of assumptions about the nature of the boundary is given below in terms of the framework used to describe plate motions by mckenzie parker 1967 1974 this derivation emphasizes that the rates depend on two sets of vectors one the instantaneous rotation vectors defining the relative plate motions the other a set of triple junction and auxiliary vectors defining the plate boundaries

controls on phosphorus concentration and accumulation in oceanic sediments understanding phosphorus p sedimentation in the ocean is important both for quantifying outputs in the marine phosphorus cycle and for determining the controls on phosphogenesis the authigenic formation of carbonate fluorapatite and phosphorite deposition large accumulations of p rich sediments on continental margins in this study i have compiled literature data on sedimentary p concentrations and sedimentation rates from continental margins phosphogenic continental margins and open ocean environments i have also calculated p accumulation rates the product of p concentration sediment density and sedimentation rate in these settings sedimentary p concentrations exhibit a similar range in a wide variety of oceanic environments and sedimentation rate conditions for example p concentrations in continental margin sediments range from 8 to 108 mol p g 1 with sedimentation rates from 80 to 8 000 m my 1 in open ocean sediments the p concentration range is similar 7 307 mol p g 1 even though sedimentation rates are generally about 100 times lower 2 50 m my 1 the exception to this are phosphogenic environments where p concentrations are exceptionally high 580 3 700 mol p g 1 while sedimentation rates are relatively low 20 310 m my 1 phosphorus accumulation rates appear to be controlled by sedimentation rate in ocean sediments although p concentrations generally exhibit similar ranges the large difference in sedimentation rates between various environments results in p accumulation rates that are several orders of magnitude higher in continental margins 90 8 000 mol p cm 2 kyr 1 compared to open ocean sediments 2 75 mol p cm 2 kyr 1 in the case of phosphogenic environments low sedimentation rates result in p accumulation rates 80 6 300 mol p cm 2 kyr 1 that are surprisingly similar to those of non phosphogenic continental margin sediments

a view of the lower crustal component of hydrothermal systems at the mid atlantic ridge an extensive suite of hydrothermally altered gabbros was recovered by alvin and dredging from the mid atlantic ridge in the vicinity of the eastern ridge transform intersection rti of the kane fracture zone mark where tectonic extension has provided a window into the lower crustal component of hydrothermal cells four alteration types are distinguished on the basis of metamorphic assemblage mineral composition and deformation textures a conceptual model is presented that places temperature fluid rock ratio relationships in conjunction with styles of deformation into a spatial and temporal framework exsolution of late stage magmatic fluids in the vicinity of the magma hydrothermal interface at temperatures 700 c marks the onset of fluid rock interaction in the mark gabbros kelley et al this issue with subsequent alteration involving seawater derived fluids being strongly influenced by deformation mechanisms in zones of ductile shear hydration was initiated at temperatures between 550 and 700 c and moderate fluid rock ratios elsewhere in the lower crust the onset of seawater penetration occurred at temperatures of 400 550 c and was facilitated by brittle fracturing early vein networks indicate very low initial fluid rock ratios and are interpreted as being related to the solidification of plutons later fractures indicate higher water rock ratios and may be related to the downward propagation of shallow fault systems throughout the crust fluid rock interaction ceased at temperatures 180 300 c subsequent cataclastic deformation associated with the unroofing and emplacement of crustal blocks in the rti massif produced moderate fluid rock ratios within localized zones hydrothermal alteration in the crustal section exposed at mark was initiated at lower temperatures and water rock interaction proceeded to lower temperatures than many other plutonic suites these differences must reflect the temporal and spatial evolution of magmatic and tectonic extension that is particular to each section of sampled crust

early archean serpentine mud volcanoes at isua greenland as a niche for early life the isua supracrustal belt greenland of early archean age 3 81 3 70 ga represents the oldest crustal segment on earth its complex lithology comprises an ophiolite like unit and volcanic rocks reminiscent of boninites which tie isua supracrustals to an island arc environment we here present zinc zn isotope compositions measured on serpentinites and other rocks from the isua supracrustal sequence and on serpentinites from modern ophiolites midocean ridges and the mariana forearc in stark contrast to modern midocean ridge and ophiolite serpentinites zn in isua and mariana serpentinites is markedly depleted in heavy isotopes with respect to the igneous average based on recent results of zn isotope fractionation between coexisting species in solution the isua serpentinites were permeated by carbonate rich high ph hydrothermal solutions at medium temperature 100 300 c zinc isotopes therefore stand out as a ph meter for fossil hydrothermal solutions the geochemical features of the isua fluids resemble the interstitial fluids sampled in the mud volcano serpentinites of the mariana forearc the reduced character and the high ph inferred for these fluids make archean serpentine mud volcanoes a particularly favorable setting for the early stabilization of amino acids

high temperature alteration of oceanic gabbros by seawater hess deep ocean drilling program leg 147 evidence from oxygen isotopes and elemental fluxes two major stages of high temperature water rock interactions have been identified in gabbros of oceanic layer 3 exposed in the hess deep rift valley at the east pacific rise 2 n 101 w the 154 m of plutonic rocks cored at site 894g show mineralogies and textures that suggest that they represent the roof of an approximate 1 myr magma chamber a late stage of hydrothermal alteration produced mineral assemblages typical of lower amphibolite upper greenschist facies conditions the hydration of the gabbros occurred locally through the development of well crystallized green amphiboles significant chemical fluxes were associated with the fluid flow and precipitation dissolution mechanisms oxygen isotope data suggest an earlier cryptic stage of hydrothermal alteration of the hess deep gabbros at temperatures above 500 c hydration was limited with only minute amphibole lamellae in pyroxenes that trapped cl na and minor k from seawater ca plagioclases remained stable and preserved their magmatic cationic compositions and zoning patterns we propose that this high temperature event lowered the 18o of the gabbros by isotopic exchange with a hydrothermal fluid through solid state oxygen diffusion although it is unclear whether the 18o depletion of hole 894g gabbros is representative of the entire lower oceanic crust it is nevertheless thought to contribute to the oxygen isotope buffering of the oceans during this stage water rock ratios calculated using sr isotopes are underestimated 0 1 0 5 because of insignificant diffusion of this cation in plagioclases better estimates of water rock ratios are provided by oxygen isotopes 0 2 1 which are important in unraveling the cooling history of the oceanic crust

the relationship between near axis hydrothermal cooling and the spreading rate of mid ocean ridges recent seismic observations and new crustal thermal models suggest that near axis 1 km from the spreading axis hydrothermal cooling increases linearly with increasing spreading rate we present here the first corroborating evidence from near axis hydrothermal plume observations comprehensive surveys of plume distributions have now been conducted on multi segment portions of ridge crest with full spreading rates from 20 to 150 km myr these surveys find thatph the fraction of ridge crest length overlain by hydrothermal plumes and full spreading rate us are related byph us where 0 004 myr km we recast this large scale spatial variability into long term temporal variability by postulating that any vent field site is hydrothermally active for an us fraction of geologic time we then use this relationship and the mean of eight studies that have determined instantaneous heat flux ha at vent field scales 75 45 mw km to estimate the time averaged heat flux ha asha us applying these scaled values ofha to the distribution of mid ocean ridge spreading rates yields a global near axis heat flux ha of 8 8 1011 w this value is 10 of the total oceanic hydrothermal heat flux and agrees with a crustal cooling model derived value of ha of 9 1011 w our estimate of ha implies a mean global3he heat ratio of 2 4 8 3 10 13 cm3 j stp and high temperature hydrothermal fluid flow of 1 8 1013 kg yr

oceanic phosphorus imbalance magnitude of the mid ocean ridge flank hydrothermal sink 10 10 mol p yr 1 this value is larger 130 than the riverine dissolvedfluxofinorganicphosphateandisasmuchas35 of the sedimentary p sink the concordant seawater flux 2 1 10 16 kg yr 1 is 65 of the riverine fluid flux and circulates a fluidvolumeequivalenttotheentireoceaninabout70 000yr additional sampling of seafloor springs is required to further constrain the range of calculated phosphate fluxes nevertheless the modern phosphorus budget is clearly unbalanced with total sinks outpacing sources index terms 1045 geochemistry low temperature geochemistry 1050 geochemistry marine geochemistry 4835 4850 3015 marine geology and geophysics heat flow benthic and hydrothermal processes 4805 oceanography biological and chemical biogeochemical cycles 1615 4845 oceanography biological and chemical nutrients and nutrient cycling keywords ridge flank hydrothermal phosphate ocean drilling program geochemical cycles citation wheat c g j mcmanus m j mottl and e giambalvo oceanic phosphorus imbalance magnitude of the mid ocean ridge flank hydrothermal sink geophys res lett 30 17 1895 doi 10 1029 2003gl017318 2003

the marine phosphorus cycle phosphorus introduced to the ocean must ultimately be removed if a steady state is to be maintained over geologic time aeolian input is insignificant and there is evidently no hydrothermal contribution rivers dominate p input to the ocean the fluvial p flux is poorly quantified due to the interactions of two factors 1 man s influence on river nutrient fluxes and 2 inherent complexities in understanding the biological and inorganic associations of p in estuarine and coastal waters our best estimate of the natural or pre man p input flux is about 10 x 10 sup 9 moles p cm sup 2 ocean surface year of the identified flux of phosphorus to the sediments about 90 percent is in the form of biogenic debris or its regeneration products the burial of phosphatic fish debris is negligible p removal by direct reaction of phosphate in seawater with sea floor basalts during mid ocean ridge hydrothermal circulation is insignificant p removal by processes such as sorption on clay surfaces or formation of authigenic fe and al phosphate phases is presently unquantified and remains a serious uncertainty in the phosphorus cycle the identified sources and sinks approximately balance yielding a residence time for p in the oceans of about 10 sup 5 yrs

digital isochrons of the world s ocean floor we have created a digital age grid of the ocean floor with a grid node interval of 6 arc min using a self consistent set of global isochrons and associated plate reconstruction poles the age at each grid node was determined by linear interpolation between adjacent isochrons in the direction of spreading ages for ocean floor between the oldest identified magnetic anomalies and continental crust were interpolated by estimating the ages of passive continental margin segments from geological data and published plate models we have constructed an age grid with error estimates for each grid cell as a function of 1 the error of ocean floor ages identified from magnetic anomalies along ship tracks and the age of the corresponding grid cells in our age grid 2 the distance of a given grid cell to the nearest magnetic anomaly identification and 3 the gradient of the age grid i e larger errors are associated with high age gradients at fracture zones or other age discontinuities future applications of this digital grid include studies of the thermal and elastic structure of the lithosphere the heat loss of the earth ridge push forces through time asymmetry of spreading and providing constraints for seismic tomography and mantle convection models

diffusive cation fluxes in deep sea sediments and insight into the global geochemical cycles of calcium magnesium sodium and potassium the biogeochemical cycles of the ocean s major cations calcium magnesium sodium and potassium are linked to the ocean s alkalinity budget through terrestrial weathering and the subsequent formation and burial of calcium carbonate in the ocean chemical reactions within ocean sediments play a critical role in the biogeochemical cycles of the major cations as indicated by geochemical gradients both positive and negative in the concentrations of these cations within the pore fluid system i e fluid trapped between sediment particles here we review the biogeochemical cycles of calcium magnesium and sodium and provide new estimates of the diffusive fluxes of these cations within marine sediments to explore the importance of these sedimentary processes we quantify these fluxes by compiling a global database of pore fluids from the various ocean drilling programs deep sea drilling program dsdp ocean drilling program odp international ocean drilling program iodp comprising nearly 700 locations which allows a wider geographic coverage and therefore better integrated flux estimates than previous work has allowed the myriad of subseafloor chemical reactions that may influence the concentrations of the major cations in pore fluids include authigenic carbonate precipitation carbonate dissolution clay mineral formation and ion exchange as previous work has shown we confirm that these integrated fluxes are globally significant because the dsdp odp iodp cores begin sampling one meter below the sediment water interface additional studies of the processes within the top meter are needed to accurately calculate total cation fluxes across the sediment water interface delineating the various processes that control the major cation chemistry of seawater over geologic time scales remains critical for understanding the operation of the co2 silicate weathering thermostat on geologic timescales

cool seafloor hydrothermal springs reveal global geochemical fluxes abstract we present geochemical data from the first samples of spring fluids from dorado outcrop a basaltic edifice on 23 m y old seafloor of the cocos plate eastern pacific ocean these samples were collected from the discharge of a cool hydrothermal system chs on a ridge flank where typical reaction temperatures in the volcanic crust are low 2 20 c and fluid residence times are short ridge flank hydrothermal systems extract 25 of earth s lithospheric heat with a global discharge rate equivalent to that of earth s river discharge to the ocean chss comprise a significant fraction of this global flow upper crustal temperatures around dorado outcrop are 15 c the calculated residence time is 80 within the upper basaltic crust by biotic and or abiotic consumption this calculation demonstrates that permeable pathways within the upper crust can support oxic water rock interactions for millions of years

controls on the solute geochemistry of subglacial discharge from the russell glacier greenland ice sheet determined by radiogenic and stable sr isotope ratios abstract we used radiogenic and stable sr isotope ratios 87sr 86sr and 88 86sr to examine controls on solute acquisition in subglacial discharge from the russell glacier a land terminating lobe of the greenland ice sheet gris located in western greenland the study focused on two melt seasons in 2014 and 2015 subglacial discharge 87sr 86sr ratios are 13 000 ppm higher than those measured for bedload and suspended sediment digests and are more similar to those of bedload sediment leachates these results point to the preferential dissolution of minerals with high 87sr 86sr ratios analyses of mineral separates from bulk rocks demonstrate that biotite chlorite hornblende and k feldspar have relatively high 87sr 86sr ratios subglacial discharge 88 86sr values are 0 10 higher than those for bedload and suspended sediment digests isotope fractionation during secondary mineral formation and or adsorption cannot account for the difference between subglacial discharge and bedrock 88 86sr values as suspended and bedload sediment leachates and digests produced similar 88 86sr values and are within the range for bulk silicate earth consistent with the interpretation of 87sr 86sr ratios we attribute the difference to the preferential dissolution of minerals with high 88 86sr values mineral separates display a wide range of 88 86sr values 0 40 those having high 88 86sr values include hornblende and k feldspar as well as apatite and titanite taken together the preferential weathering of predominately silicate minerals explains the sr isotope geochemistry of subglacial discharge subglacial discharge from the russell glacier feeds the proglacial akuliarusiarsuup kuua river akr along a 32 km transect of the akr from the gris margin toward the coast riverine 87sr 86sr ratios increase from 0 722 to 0 747 in an approximately step wise pattern that corresponds to point source inputs of additional subglacial discharge major cation concentrations and 87sr 86sr ratios minimally vary along lengths of the transect with no hydrological inputs this suggests that proglacial chemical weathering is negligible and likely does not contribute significantly to gris solute fluxes in general this study supports the recent contention that silicate mineral weathering dominates the solute geochemistry of gris subglacial discharge in contrast to valley glaciers which typically show substantial contributions from carbonate and sulfide weathering regardless of primary bedrock composition ice sheet subglacial chemical weathering may therefore have a greater impact on long term atmospheric co2 drawdown than previously realized

dissolved amino acids in oceanic basaltic basement fluids the oceanic basaltic basement contains the largest aquifer on earth and potentially plays an important role in the global carbon cycle as a net sink for dissolved organic carbon doc however few details of the organic matter cycling in the subsurface are known because great water depths and thick sediments typically hinder direct access to this environment in an effort to examine the role of water rock microorganism interaction on organic matter cycling in the oceanic basaltic crust basement fluid samples collected from three borehole observatories installed on the eastern flank of the juan de fuca ridge were analyzed for dissolved amino acids our data show that dissolved free amino acids 1 13 nm and dissolved hydrolyzable amino acids 43 89 nm are present in the basement the amino acid concentrations in the ridge flank basement fluids are at the low end of all submarine hydrothermal fluids reported in the literature and are similar to those in deep seawater amino acids in recharging deep seawater in situ amino acid production and diffusional input from overlying sediments are potential sources of amino acids in the basement fluids thermodynamic modeling shows that amino acid synthesis in the basement can be sustained by energy supplied from inorganic substrates via chemolithotrophic metabolisms furthermore an analysis of amino acid concentrations and compositions in basement fluids support the notion that heterotrophic activity is ongoing similarly the enrichment of acidic amino acids and depletion of hydrophobic ones relative to sedimentary particulate organic matter suggests that surface sorption and desorption also alters amino acids in the basaltic basement in summary although the oceanic basement aquifer is a net sink for deep seawater doc similar amino acid concentrations in basement aquifer and deep seawater suggest that doc is preferentially removed in the basement over dissolved amino acids our data also suggest that organic carbon cycling occurs in the oceanic basaltic basement where an active subsurface biosphere is likely responsible for amino acid synthesis and degradation

habitability of the marine serpentinite subsurface a case study of the lost city hydrothermal field the lost city hydrothermal field is a dramatic example of the biological potential of serpentinization microbial life is prevalent throughout the lost city chimneys powered by the hydrogen gas an

forest soil mineral weathering rates use of multiple approaches knowledge of rates of release of base cations from mineral dissolution weathering is essential to understand ecosystem elemental cycling although much studied rates remain enigmatic we compared the results of four methods to determine cation ca mg k release rates at five forested soils sites in the northcentral u s a our premise was that multiple approaches each with their own specific strengths and weaknesses would yield a best overall estimate we used 1 a cation input output budget on a pedon scale 2 trends in elemental and mineral depletion in silt size particles 3 a laboratory batch dissolution technique with the results adjusted for field conditions and 4 a steady state soil chemistry model profile the soils included a loamy sand typic udipsamment a sandy loam spodic udipsamment a fine sandy loam typic dystrochrept a very fine sandy loam glossic eutroboralf and a clayey glossic eutroboralf weathering rates varied among both soils and methods and neither methods nor soils could easily be grouped the data spanned a continuum with overlapping ranges of least significant differences although the assumptions necessary for some methods were better suited to specific soils we rejected only one method soil combination as being inappropriate input output budget for the clay mean release rates for the sum of cations ranged from 470 eq ha 1 yr 1 for the clayey soil to 460 for the fine sandy loam soil to 430 for the very fine sandy loam soil to 375 for the sandy loam soil to 195 for the loamy sand soil these rates are lower than those reported for similar soils in the literature because most reported rates are based on watershed studies our low rates of cation release within soil pedons the ultimate source of nutrient ions for plant growth has implications for estimated nutrient budgets and long term soil sustainability

heat of fusion of basaltic magma abstract the heat of fusion of haplobasaltic liquids in the systems forsterite diopside sio2 and basaltic liquids in natural peridotite has been determined by high temperature solution calorimetry for liquids in the systems diopside anorthite and forsterite diopside anorthite the heat of fusion was calculated from literature data the heats of fusion for eutectic liquids in the system anorthite diopside and forsterite diopside anorthite for haplobasaltic liquid in equilibrium with olivine and two pyroxenes in the system forsterite diopside sio2 and for basaltic melts from natural peridotite parent are 130 6 121 1 157 4 and 161 5 cal g respectively the heat of mixing in the liquids contributes up to about 5 of this value the magnitude of this contribution increases when the structure of the endmember minerals is significantly different e g forsterite and anorthite or quartz the pressure effect on the heat of fusion results in a 10 20 increase in the pressure range 10 30 kbar compared with the 1 atm values this increase results from the larger compressibility of silicate liquids compared with that of the coexisting minerals in both model and natural compositions

dynamics of oceanic iron prior to the great oxygenation event abstract we report fe isotope compositions in banded iron formations bif from three cores from the pre goe transvaal supergroup south africa and one core from the pre goe joffre member of the hamersley group australia the low abundances of detrital elements such as al ti sc and v suggest that these bif were deposited in distal positions with respect to precambrian continents while the very low p abundances are incompatible with strong biological productivity at these localities a combination of u pb chronology and cobalt accumulation rates is used to establish a high resolution time scale and deduce chemical fluxes the e folding time of 56 fe variations up stratigraphy is used to determine fe oceanic residence times and fe concentrations as well as the dissolved carbonate content of early proterozoic seas iron oceanic residence times increased from 0 2 to 2 3 ma during the time interval between 2521 and 2394 ma covered by the present cores translating into ocean fe concentrations increasing from 6 4 to 37 mmol kg 1 massive bif precipitation was triggered by release of co2 into the atmosphere and subsequent surges of alkalinity into the ocean due to the weathering of large subaerial volcanic systems we argue that a suitable electron acceptor for fe2 oxidation to magnetite is the inorganic conversion of co2 or dissolved inorganic carbon to ch4 in the process h is produced which is reinjected into oceanic hydrothermal systems liberating fe2 the couple fe2 magnetite may in the archean have played the same buffering role as the couple ca2 calcite plays today massive injection of methane into the atmosphere would accompany bif deposition and make the early earth similar to modern titan therefore although biological processes may have assisted iron oxidation and precipitation they are not a prerequisite for bif deposition

identification of organic compounds in ocean basement fluids abstract we have analyzed the dissolved organic carbon oc in ocean basement fluids using fourier transform ion cyclotron resonance mass spectrometry ft icr ms the compounds identified at the two sites near the juan de fuca and mid atlantic ridges north pond differ substantially from each other and from seawater compared to juan de fuca north pond organics had a lower average molecular weight 349 vs 372 g mol 50 more identifiable compounds 2181 vs 1482 and demonstrably lower average nominal oxidation state of carbon 0 70 vs 0 56 the north pond fluids were also found to have many more n and s bearing compounds based on our data the marine subsurface can alter the types of dissolved oc doc compounds in seawater

phosphorus in sediments of the amazon river and estuary implications for the global flux of phosphorus to the sea abstract the distribution of various forms of p in suspended and depositional bank sediments of the amazon river and bottom sediments of the mixing and freshwater portions of the amazon estuary and shelf have been determined using a modified sequential extraction method forms of p distinguished are p associated with ferric oxides hydroxides fe p organic p org p p extracted with acetate buffer at ph 4 acet p and detrital apatite detr p results indicate that there is a distinct drop in fe p org p and total p after deposition of suspended sediment on the banks of the river similar results are found for sediment deposited on the freshwater portion river channel bottom of the continental shelf sediment deposited on estuarine portions of the shelf also shows a significant drop in total p due mostly to a drop in org p no appreciable change in acet p was found between river suspended sediments and those of either the river banks or of the estuarine shelf an inverse correlation is found for all sediments between concentrations of fe p and detr p because of the association of detrital apatite with the coarser fractions of the sediments and fe p with the finer fractions these results suggest that considerable amounts of p are added to the oceans by the bacterial decomposition of river transported organic matter and by the desorption of p from iron oxides hydroxides some desorption from al silicates may also occur the organic p is released to interstitial solution during early diagenesis and this p may be adsorbed by fe oxides in the sediment during frequent resuspension events the fe oxides are carried to the overlying water where the p is desorbed and thereby released to solution based on our amazon results the total global p flux to the oceans by rivers may be more than three times that carried only in solution by the rivers further work is needed on other river systems to check these preliminary results

tracing low temperature fluid flow on ridge flanks with sedimentary uranium distribution the uranium content of sediments and pore fluids along a ridge axis to ridge flank transect perpendicular to the southern east pacific rise is used to assess the impact of low temperature fluid flow on u distribution two distinct regions are identified 1 a young crustal site 0 36 ma crust where significant solid phase u enrichments occur and 2 the ridge flank 1 9 4 6 ma crust with uniform u association with hydrothermal fe oxide phases in the solid phases upward advection and diffusion of cool u depleted basement fluids occurs at many coring sites at the 0 36 ma site the oxic basal fluids strip the plume derived sediment of the excess u effectively migrating the u upwards through the sediment into the overlying water column at the ridge flank sites the pore fluid advection rates are highest at bathymetric basement highs and advection velocities of up to 7 5 mm yr 1 are inferred from the pore fluid profiles these estimates are consistent with previous calculations based on fluoride pore fluid distributions the basal fluid u depletions are in the range 10 70 relative to seawater depending on temperature and redox state low temperature uptake of u during basalt alteration is a significant sink from seawater in the global seawater u budget 6 7 29 mmol yr 1 pore fluid u content is a sensitive tracer of extremely low temperature advection through ridge flank systems and the basal sediment u fe ratio is potentially a useful proxy for basement alteration history where low ratios indicate extensive oxic alteration of basal sediments during fluid flow

inorganic chemistry gas compositions and dissolved organic carbon in fluids from sedimented young basaltic crust on the juan de fuca ridge flanks abstract the permeable upper oceanic basement serves as a plausible habitat for a variety of microbial communities there is growing evidence suggesting a substantial subseafloor biosphere here new time series data are presented on key inorganic species methane hydrogen and dissolved organic carbon doc in ridge flank fluids obtained from subseafloor observatory corks circulation obviation retrofit kits at integrated ocean drilling program iodp boreholes 1301a and 1026b these data show that the new sampling methods cowen et al 2012 employed at 1301a result in lower contamination than earlier studies furthermore sample collection methods permitted most chemical analyses to be performed from aliquots of single large volume samples thereby allowing more direct comparison of the data the low phosphate concentrations 0 06 0 2 m suggest that relative to carbon and nitrogen phosphorus could be a limiting nutrient in the basement biosphere coexisting sulfate 17 18 mm hydrogen sulfide 0 1 m hydrogen 0 3 0 7 m and methane 1 5 2 m indicates that the basement aquifer at 1301a either draws fluids from multiple flow paths with different redox histories or is a complex environment that is not thermodynamically controlled and may allow co occurring metabolic pathways including sulfate reduction and methanogenesis the low doc concentrations 11 18 m confirm that ridge flank basement is a net doc sink and ultimately a net carbon sink based on the net amounts of doc oxygen nitrate and sulfate removed 30 m 80 m 40 m and 10 mm respectively from entrained bottom seawater organic carbon may be aerobically or anaerobically oxidized in biotic and or abiotic processes

mapping the fluid flow of the mariana mounds ridge flank hydrothermal system pore water chemical tracers we present a conceptual model of fluid circulation in a ridge flank hydrothermal system the mariana mounds the model is based on chemical data from pore waters extracted from piston cores and from push cores collected by deep sea research vessel alvin in small meter sized mounds situated on a local topographic high these mounds are located within a region of heat flow exceeding that calculated from a conductive model and are zones of strong pore water upflow we have interpreted the chemical data with time dependent transport reaction models to estimate pore water velocities in the mounds themselves pore water velocities reach several meters per year to kilometers per year within about 100 m from these zones of focused upflow velocities decrease to several centimeters per year up to tens of centimeters per year a larger area of low heat flow surrounds these heat flow and topographic highs with upwelling pore water velocities less than 2 cm yr in some nearby cores downwelling of bottom seawater is evident but at speeds less than 2 cm yr downwelling through the sediments appears to be a minor source of seawater recharge to the basaltic basement we conclude that the principal source of seawater recharge to basement is where basement outcrops exist most likely a scarp about 2 4 km to the east and southeast of the study area

reassessment of the oceanic residence time of phosphorus phosphorus p is an essential nutrient for the growth of all organisms and is believed to limit marine productivity especially on geologic time scales holland 1984 smith 1984 howarth 1988 codispoti 1989 as a result of the link between marine photosynthetic productivity and atmospheric co2 phosphorus along with other nutrients present in short supply in the euphoric zone have been cited as potential players in the ocean s role in climate change this link has been referred to as the nutrient co2 connection broecker 1982 model simulations which aim to quantify the role of oceanic nutrient inventories in promoting or enhancing climate change rely on the most currently formulated element budgets for the ocean in this paper significant modifications to the currently accepted marine phosphorus budget are proposed the modified p budget presented here requires a reassessment of phosphorus residence time in the ocean and a concomitant review of the role of p as a potential player in climate change over glacialinterglacial time scales element budgets constructed for the oceans consist of a mass balance between inputs and outputs for which the simplifying assumption is generally made that the ocean is in steady state with the specific element in question the fluvial p flux constitutes the bulk of the input term for the marine phosphorus budget atmospheric input is 10 of the fluvial input froelich et al 1982 burial with sediments is the mechanism for ultimate removal of p from the oceans for a system at steady state the input flux equals the output flux in the present paper we focus on the output flux burial with sediments for two reasons first the chemistry of phosphorus buried in sediment cores from which p burial fluxes are calculated has not been affected to the same degree as rivers by anthropogenic perturbation it is therefore simpler to quantify the output term of the p budget which can be extrapolated to pre anthropogenic times second detailed p speciation data permit us to quantify the burial flux of reactive p as contrasted with refractory p in sediments this distinction is significant because burial of reactive p constitutes removal of potentially bio available p from the oceans two types of modification to the marine phosphorus budget are proposed here first the locus of p burial is addressed specifically the importance of p burial in the deep sea is contrasted with p burial in continental margins second the burial flux is characterized in terms of reactive potentially bio available p vs refractory p this distinction is made possible by obtaining detailed p speciation data from application of the sedex method ruttenberg 1992 a selective leaching procedure which separates solid phase p into five reservoirs on the basis of chemical reactivity loosely sorbed p ferric iron bound p authigenic apatite biogenic apatite c a c o 3 bound p detrital apatite p and organic p detailed p spe

hydrothermal circulation through mid ocean ridge flanks fluxes of heat and magnesium thermally driven convection of seawater occurs through oceanic crust of all ages at the seafloor spreading axis on mid ocean ridge flanks and in the ocean basins at the ridge axis and on the flanks circulating seawater produces a major chemical exchange between the oceans and the crust based on heat budget constraints and the composition of hot springs between 10 and 40 of the river flux of mg can be taken up during high temperature alteration of the basaltic crust along the ridge axis most of the hydrothermal heat loss however occurs on the mid ocean ridge flanks where the temperatures are lower and the seawater flux correspondingly larger the estimated heat loss on the flanks is so large that upwelling must occur over a large fraction 5 30 of the seafloor less than 65 ma in age if temperatures are 20 c and seepage velocities are on the order of 10 to 100 cm y the circulating seawater needs to lose on average less than 1 2 of its mg content in order to solve the mg mass balance for the oceans chemical fluxes through mid ocean ridge flanks are poorly known because of the wide range of crustal conditions that prevail there and the paucity of study to date the most critical parameter for characterizing crustal conditions is temperature in basement which is a function of crustal age basement topography and sediment thickness and permeability basement temperature which can usually be inferred from heat flow and seismic reflection surveys largely determines the change in the composition of seawater circulating through basement this change can be inferred in turn from profiles of sediment porewater chemistry all sites studied to date with temperatures at the sediment basement interface 25 c have a large component of advective heat loss and show only a small 80 mg loss both types of sites may be important for chemical fluxes whether the cooler sites are important depends on how much the seawater changes in composition as it circulates through the crust only small changes are needed whether the warmer sites are important depends on how much heat is lost by advection in this type of setting the warmer sites could produce significant chemical fluxes even if they are scarce they could account for the entire river input of mg to the oceans even if they represent only 8 20 of the total advective heat loss on ridge flanks

phosphorus imbalance in the global ocean the phosphorus budget of the pre human modern ocean is constrained applying the most recent estimates of the natural riverine eolian and ice rafted input fluxes the phosphorus burial in marine sediments and the hydrothermal removal of dissolved phosphate from the deep ocean this review of current flux estimates indicates that the phosphorus budget of the ocean is unbalanced since the accumulation of phosphorus in marine sediments and altered oceanic crust exceeds the continental input of particulate and dissolved phosphorus the phosphorus mass balance is further tested considering the dissolved phosphate distribution in the deep water column the marine export production of particulate organic matter rain rates of phosphorus to the seafloor benthic dissolved phosphate fluxes and the organic carbon to phosphorus ratios in marine particles these independent data confirm that the phosphate and phosphorus budgets were not at steadystate in the pre human global ocean the ocean is losing dissolved phosphate at a rate of 11 6 x 1010 mol yr 1 corresponding to a decline in the phosphate inventory of 4 5 kyr 1 benthic data show that phosphate is preferentially retained in pelagic deep sea sediments where extended oxygen exposure times favor the degradation of particulate organic matter and the up take of phosphate in manganese and iron oxides and hydroxides enhanced c p regeneration ratios observed in the deep water column 400 m water depth probably reflect the preferential burial of phosphorus in pelagic sediments excess phosphate is released from continental margin sediments deposited in low oxygen environments the dissolved oxygen threshold value for the enhanced release of dissolved phosphate is 20 m benthic phosphate fluxes increase drastically when oxygen concentrations fall below this value

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