experimental study of boron geochemistry implications for fluid processes in subduction zones a comprehensive experimental study utilizing an autoclave hydrothermal apparatus with a 10b isotopic tracer has been conducted to monitor the geochemical behavior of sediment b during early subduction zone processes the partition coefficient of exchangeable b kd was determined over a temperature range of 25 350 c at 800 bars and a water rock ratio of 3 1 5 w w these kd are shown to be a complex function of temperature ph and possibly mineralogy at low temperatures kd is significantly high at 4 in contrast to the value of essentially zero at temperatures higher than 100 c a kd of zero represents no b adsorption implying efficient mobilization of exchangeable b at shallow depths during sediment subduction our experimental results demonstrate high mobilization of bulk b in sediments both exchangeable and lattice bound at elevated temperatures 200 350 c in good agreement with previous observations of b in metasediments indicating progressive depletion during metamorphism in addition this study emphasizes the importance of a possible water rock ratio dependence of b mobilization in other words the degree of sedimentary b mobilization in subduction zones strongly depends on the local thermal structure and porosity distribution in low geothermal gradient areas large amounts of porewater are expelled before significant b mobilization has occurred so that some sedimentary b will survive and get into the deeper parts of the subduction zone our results imply that efficient mobilization of b from the subducted slab must occur and that arc magmatism recycles most of the remaining subducted b back to surface reservoirs a reconsideration of the b budget in subduction zones provides critical information with respect to b sources and sinks in the ocean

fluid flow in and around a mud volcano field seaward of the barbados accretionary wedge results from manon cruise a field of mud diapirs and mud volcanoes situated in the barbados trench at 13 50 n and extending along an old oceanic fracture zone mercurus was investigated during the manon cruise using both surface ship and nautile submersible sampling and measurements the entire zone from 13 50 n up to 14 20 n has an anomalously high heat flow which implies that fluids are drained into it from a segment of the accretionary wedge a few hundred kilometers wide two structures interpreted as diatremes atalante and cyclops expell large amounts of water and methane we propose that they were formed from the release of a light fluid when gas hydrates were dissociated in the sediment as the result of the circulation of warm fluid in the area however they expell only a small fraction of the incoming fluid implying that disperse flow is the dominant mode of expulsion in this area the chemoautotrophic communities on the surface of the structures rely mostly on sulfides submersible observations temperature measurements in the sediment and the chemistry of the pore fluid indicate that convection of seawater occurs within the first few meters of sediment through high permeability channels such as cemented carbonate conduits we propose that this convection is driven by the density difference between the pore fluid and seawater but fresh water released by the dissolution of shallow hydrates may also contribute this shallow convection may be a frequent process in cold seep environments

pore water anomalies of submarine gas hydrate zones as tool to assess hydrate abundance and distribution in the subsurface what have we learned in the past decade abstract the most significant new contributions to the study of natural gas hydrates in the past decade have come from findings of the ocean drilling program odp notably legs 112 141 146 and 164 and to a lesser extent legs 131 160 170 and 186 leg 164 in particular was dedicated to gas hydrate drilling in the blake ridge gas hydrate field in the west atlantic in an unprecedented multidisciplinary research effort paull et al 1996 proc ocean drill program initial rep 164 623 pp paull c k matsumoto r wallace p j dillon w p eds 2000a proc ocean drill program sci results 164 ocean drilling program college station tx 459 pp most important for the progress of hydrochemical studies related to gas hydrates has been the growing awareness of the significance of diffusion modulated advective processes shaping the chemical and isotopic pore water profiles in hydrate zones this started with qualitative evidence for advective flow from drilling the hydrate bearing peru and hydrate free barbados active margins continued with the nankai trough accretionary prism the japan trench slope and the cascadia and costa rica active margins and culminated in the quantitative advection diffusion model of egeberg and dickens chem geol 153 1999 53 for the passive margin setting of the blake ridge advective flow regimes are different at active and passive margins as there is a tendency for the flow at active margins to be focussed along landward dipping thrust planes and faults in the wedge of imbricated thrust sheets that finds expression in a step pattern of the pore water profiles for passive margins but also for some active margin sites advection is from sources below the drilled section either through subvertical faults passive margins or from the decollement zone active margins we have learned that the well known coupled pore water anomalies that are ascribed to hydrate dissociation downward chlorinity decrease combined with 18 o increase hesse and harrison 1981 earth planet sci lett 55 1981 453 need not occur together in the presence of hydrates because the isotope effect may be overprinted by the effects of other reactions such as volcanic ash alteration or by the advection of low 18 o fluids however if the anomalies show up hydrates are present almost invariably with the exception of advected low cl high 18 o waters coming to terms with the effects of advection and diffusion has allowed successful modeling of the simpler hydrate affected pore water profiles at passive margins instrumental for modeling are chlorine isotopes which provide an effective tool to assess advection rates the egeberg and dickens model allows estimation of hydrate concentration and distribution in the subsurface because it separates the effects of advection diffusion and hydrate dissociation but critically depends on samples taken under in situ pressure and temperature conditions modeling the more complex pore water profiles of active margins is a challenge for the future compared to geophysical methods to estimate hydrate concentration the geochemical method gives minimum amounts

the composition and diagenesis of interstitial solutions ii fluxes and diagenesis at the water sediment interface in the high latitude north and south atlantic studies of the major element composition of in situ sampled pore waters are reported for the north atlantic and southern ocean between africa and antarctica the pattern of diagenetic modification of pore water composition is similar throughout the entire atlantic enrichment of na ca2 and alkalinity and depletion of mg2 and k are nearly universal only siliceous oozes consistently provide very limited evidence of cation diagenesis the changes observed and the calculated fluxes across the seawater sediment interface are much the same as those reported previously for other areas of the atlantic and caribbean fluxes of the major cations across the interface continue to be indicated as a major factor in the geochemical cycling of these elements particularly na mg2 and k diagenetic modelling indicates that aerobic oxidation of organic matter and consequent dissolution of caco3 is a dominant reaction throughout the north atlantic the data indicate that o2 oxidation to at least 30 cm is prevalent at nearly all stations dissolution of caco3 in response to the introduction of metabolic co2 can lead to significant post depositional modification of the sediments the modelling also indicates a 1 1 stoichiometric relationship between na release and mg2 uptake by sedimentary components although dissolved silica concentrations in biogenic siliceous sediments are among the highest yet reported 700 m calculations demonstrate that solubility control cannot be through equilibria with the mineral sepiolite further the influence of cation silicate surface phases generally upon solubility is contraindicated by si oh 4 mg2 h relationships evaluation of the influence of fluid advection on pore water profiles indicates that at the stations studied in the north atlantic it is small a more general consideration of the potential contribution of fluid advection to shaping interstitial water profiles demonstrates that advection can be a dominant factor in such circumstances serious misinterpretation of the nature of diagenetic reactions may result from a lack of knowledge and consideration of fluid advection

fluid flow methane fluxes carbonate precipitation and biogeochemical turnover in gas hydrate bearing sediments at hydrate ridge cascadia margin numerical modeling and mass balances a numerical model was applied to investigate and to quantify biogeochemical processes and methane turnover in gas hydrate bearing surface sediments from a cold vent site situated at hydrate ridge an accretionary structure located in the cascadia margin subduction zone steady state simulations were carried out to obtain a comprehensive overview on the activity in these sediments which are covered with bacterial mats and are affected by strong fluid flow from below the model results underline the dominance of advective fluid flow that forces a large inflow of methane from below 869 mumol cm 2 a 1 inducing high oxidation rates in the surface layers anaerobic methane oxidation is the major process proceeding at a depth integrated rate of 870 mumol cm 2 a 1 a significant fraction 14 of bicarbonate produced by anaerobic methane oxidation is removed from the fluids by precipitation of authigenic aragonite and calcite the total rate of carbonate precipitation 120 mumol cm 2 a 1 allows for the build up of a massive carbonate layer with a thickness of i m over a period of 20 000 years aragonite is the major carbonate mineral formed by anaerobic methane oxidation if the flow velocity of methane charge fluids is high enough greater than or equal to10 cm a 1 to maintain super saturation with respect to this highly soluble carbonate phase it precipitates much faster within the studied surface sediments than previously observed in abiotic laboratory experiments suggesting microbial catalysis the investigated station is characterized by high carbon and oxygen turnover rates approximate to1000 mumol cm 2 a 1 that are well beyond the rates observed at other continental slope sites not affected by fluid venting this underlines the strong impact of fluid venting on the benthic system even though the flow velocity of 10 cm a 1 derived by the model is relative low compared to fluid flow rates found at other cold vent sites non steady state simulations using measured fluid flow velocities as forcing demonstrate a rapid respond of the sediments within a few days to changes in advective flow moreover they reveal that efficient methane oxidation in these sediments prevents methane outflow into the bottom water over a wide range of fluid flow velocities 80 cm a 1 only at flow rates exceeding approximately 100 cm a 1 does dissolved methane break through the sediment surface to induce large fluxes of up to 5000 mumol ch4 cm 2 a 1 into the overlying bottom water

sources of fluids and gases expelled at cold seeps offshore georgia eastern black sea four seep sites located within an 20 km2 area offshore georgia batumi seep area pechori mound iberia mound and colkheti seep show characteristic differences with respect to element concentrations and oxygen hydrogen strontium and chlorine isotope signatures in pore waters as well as impregnation of sediments with petroleum and hydrocarbon potential all seep sites have active gas seepage near surface authigenic carbonates and gas hydrates cokheti seep iberia mound and pechori mound are characterized by oil stained sediments and gas seepage decoupled from deep fluid advection and bottom water intrusion induced by gas bubble release pechori mound is further characterized by deep fluid advection of lower salinity pore fluids the pechori mound pore fluids are altered by mineral water reactions at elevated temperatures between 60 and 110 c indicated by heavier oxygen and lighter chlorine isotope values distinct li and b enrichment and k depletion strontium isotope ratios indicate that fluids originate from late oligocene strata this finding is supported by the occurrence of hydrocarbon impregnations within the sediments furthermore light hydrocarbons and high molecular weight impregnates indicate a predominant thermogenic origin for the gas and oil at pechori mound iberia mound and colkheti seep c15 hydrocarbons at the oil seeps are allochtonous whereas those at the batumi seep area are autochthonous the presence of oleanane an angiosperm biomarker suggests that the hydrocarbon source rocks belong to the maikopian formation in summary all investigated seep sites show a high hydrocarbon potential and hydrocarbons of iberia mound colkheti seep and pechori mound are predominantly of thermogenic origin however only at the latter seep site advection of deep pore fluids is indicated

multi instrument observations of sed during 24 25 october 2011 storm implications for sed formation processes 1 we present multiple instrument observations of a storm enhanced density sed during the 24 25 october 2011 intense geomagnetic storm formation and the subsequent evolution of the sed and the midlatitude trough are revealed by global gps vertical total electron content maps in addition we present high time resolution poker flat incoherent scatter radar pfisr observations of ionospheric profiles within the sed we divided the sed observed by pfisr into two parts both parts are characterized by elevated ionospheric peak height hmf2 and total electron content compared to quiet time values however the two parts of the sed have different characteristics in the electron temperature te the f region peak density nmf2 and convection flows the first part of the sed is associated with enhanced te in the lower f region and reduced te in the upper f region and is collocated with northward convection flows the nmf2 was lower than quiet time values the second part of the sed is associated with significantly increased nmf2 elevated te at all altitudes and is located near the equatorward boundary of large northwestward flows based on these observations we suggest that the mechanisms responsible for the formation of the two parts of the sed may be different the first part is due to equatorward expansion of the convection pattern and the projection of northward convection flows in the vertical direction which lifts the ionospheric plasma to higher altitudes and thus reduces the loss rate of plasma recombination the second part is more complicated besides equatorward expansion of the convection pattern and large upward flows evidences of other mechanisms including horizontal advection due to fast flows energetic particle precipitation and enhanced thermospheric wind in the topside ionosphere are also present estimates show that contribution from precipitating energetic protons is at most 10 of the total f region density the thermospheric wind also plays a minor role in this case

provenance sea level and monsoon climate controls on silicate weathering of yellow river sediment in the northern okinawa trough during late last glaciation abstract high resolution multi proxy records including geochemical and grain size data from detrital sediments of iodp site u1429 in the northern okinawa trough provide reliable evidence for constraining sediment source and transport processes they also allow silicate weathering and erosion controlled by sea level change and east asian summer monsoon evolution since 34 ka to be reconstructed provenance proxies indicated that sediments in the northern okinawa trough were mainly supplied by the yellow river middle reach at 34 8 ka the low sea level and proximity of paleo yellow river mouth to the northern okinawa trough were the causes of the dominant yellow river input after 8 ka a retreated yellow river mouth coupled with the blocking effect of the kuroshio current and its branches together with strong east asian summer monsoon precipitation resulted in relatively strong sediment input from kyushu to the northern okinawa trough meanwhile yellow river upper reach supplied more sediments to the study site than that during the 34 8 ka on glacial interglacial scale silicate weathering proxies indicate that the core sediment was more weathered during the last glacial and deglacial than that in the modern yellow river we attribute this to the increased upper reach sediment input which supplied more weak weathered sediment to the study site during the holocene besides composite effect of weathering during glacial and deglacial sediment production and additional weathering upon subaerial exposure of shelf deposits during low sea level stage as well as older weathered sediments reworking during sea level rise could also account for this weathering regime on multi millennial scale from 34 to 18 5 ka silicate weathering was mainly controlled by the east asian summer monsoon with a cooling and drying climate associated with weakened summer monsoon activity this is consistent with the reduced alteration of sediments eroded from the yellow river basin from 18 5 to 8 ka strong reworking of older weathered sediments overwhelmed the east asian summer monsoon in controlling silicate weathering which induced a continuous increase in chemical alteration of the sediments during this period

instantaneous mapping of high latitude convection with coherent hf radars coherent hf radars at goose bay labrador and schefferville quebec are used to study plasma convection in the high latitude ionosphere maps of the two dimensional flow pattern are obtained by merging simultaneous sets of radial velocity data each with a time resolution of a few minutes from a time sequence of such maps we have separated the changes in flow due to magnetic local time mlt variations over the region of observation from those due to ut time variations we study in detail the convection in the early morning sector observed on october 15 1989 when the interplanetary magnetic field imf reversed from southward to northward this imf reversal was not associated with a clear response in the nightside convection but rather with several sudden changes some of which anticipated the bz reversal we suggest that these changes are associated with delayed and superposed ionospheric responses to previous imf perturbations or to local effects after the imf reversal from south to north our observations of westward and southwestward velocities in the 71 77 invariant latitude range are consistent with the earlier simulations for bz 0 and by 0 during the period of steady northward imf after the reversal the convection pattern was observed to reconfigure slowly a region of large westward velocities progressively moved poleward while convection in the low latitude part of the field of view faded away the time constant of this slow reconfiguration was about 1 hour and varied with mlt such that it was larger closer to midnight these data combined with particle data from successive passes of the dmsp satellites provide information on the contraction of the polar cap after the imf bz reversal and on the mlt dependency of the velocity at which this contraction occurs they show that the polar cap contracts more rapidly in the daytime than in the nightime and more rapidly in the postmidnight sector than in the premidnight sector

a statistical study of the subauroral polarization stream over north american sector using the millstone hill incoherent scatter radar 1979 2019 measurements this work conducts a statistical study of the subauroral polarization stream saps feature in the north american sector using millstone hill incoherent scatter radar measurements from 1979 to 2019

first observations of the temporal spatial variation of the sub auroral polarization stream from the superdarn wallops hf radar 1 in this letter we present the first two dimensional observations of sub auroral ion drift said variability within the sub auroral polarization stream saps using a new mid latitude superdarn radar located at wallops island va the radar data are complemented with observations from the dmsp f15 timed and noaa 18 spacecraft to confirm that a backscatter feature observed at the equatorward edge of the auroral oval is a manifestation of saps said during a several hour long period on august 6 2005 the velocity data indicate that significant changes in the saps flow occurred on time scales of a few minutes the wallops hf radar observations demonstrate that the saps phenomenon is a source of small scale irregularities extending over many hours of mlt and that the electric fields associated with said in particular are highly variable

unusual composition of pore waters found in the izu bonin fore arc sedimentary basin extensively altered brines with a composition different from that of any previously reported natural water have been recovered by deep coring of sediments in the izu bonin fore arc sedimentary basin samples from successive depths document the chemical evolution of these unusual pore waters from sea water to highly enriched cacl2 brines the origin of these pore waters seems to be related to the special environment of a fore arc sedimentary basin where accumulation rates of volcanogenic sediment are extremely high and the sediments are susceptible to alteration

identification of the temperature gradient instability as the source of decameter scale ionospheric irregularities on plasmapause field lines 1 recent observations with the new mid latitude superdarn hf radar located at wallops island virginia have identified a class of ionospheric irregularities that is prevalent in the nightside sub auroral ionosphere under low to moderate kp conditions these irregularities can be observed for many hours and generally exhibit very low doppler velocities a recent collaborative experiment using the wallops radar and the millstone hill incoherent scatter radar has determined that these irregularities are located at the ionospheric footprint of the plasmapause and in a region of opposed electron density and electron temperature gradients we conclude that the irregularities are produced by the temperature gradient instability tgi or by turbulent cascade from primary irregularity structures produced from this instability this is the first experimental confirmation that the tgi is effective in producing decameter scale ionospheric irregularities

organic matter production and preservation and evolution of anoxia in the holocene black sea dating of sediments collected in gravity cores during leg 1 of the 1988 r v knorr expedition to the black sea suggests that the onset of water column anoxia at 7 5 ka was virtually synchronous across the basin over a depth range of 200 2250 m a finely laminated organic carbon oc rich sapropel unit ii was produced as a result of this anoxia the trigger for increased oc production and development of anoxia was the spillover of saline waters through the bosporus that probably began at 9 0 ka and peaked between 7 0 and 5 5 ka this spillover enhanced vertical mixing and nutrient cycling and caused a short term 2 3 kyr burst in surface water productivity during the early part of unit ii deposition continued incursion of saline waters enhanced vertical stability and inhibited mixing of nutrients into surface waters thus limiting primary production and decreasing the oc flux to sediments beginning 5 5 ka concentration accumulation rate and degree of preservation of organic matter all decreased in the upper part of unit ii as a result of decreasing productivity but anoxia persisted throughout most of the water column the end of unit ii sapropel deposition was synchronous across the black sea as the result of the first blooms of the coccolith emiliania huxleyi which presumably marked an increase in surface water salinity above 11 and the beginning of unit i deposition the high coccolith carbonate fluxes that occurred during deposition of unit i diluted the oc concentration in the sediments but oc accumulation rates are about the same as those in upper part of unit ii

a lithium isotope study of hot springs and metabasalts from mid ocean ridge hydrothermal systems the li isotopic compositions of seawater and of fresh and altered basalts are distinct and therefore applicable to the study of the hydrothermal processes in the oceanic crust and the li balance in the ocean high temperature fluids from seven vents on the east pacific rise epr at 21 n and 11 13 n have 6li values ranging between 6 and 11 i e 3 7 heavier than fresh basalt values the intervent variations in li concentration and isotopic composition correlate well with water rock ratios no temporal change in the isotopic value was observed between 1981 and 1985 metabasalts show both li depletion and enrichment relative to fresh basalt they display light li isotopic values which reflect incorporation of li mobilized from fresh basalt from these observations we conclude that the li isotopic composition of submarine hot springs is controlled by a path dependent process involving dissolution of primary minerals and precipitation of li with alteration phases 6li values of fluids from the mid atlantic ridge 6 to 8 fall in the range of the epr indicating similar reaction controls at the two ridge systems the lack of 7li enrichment in the fluids from slower spreading ridges indicates that li is not recycled from older weathered crust thus the difference between the 3he and 87sr 86sr based hydrothermal flux and the crustal transfer rate of li cannot be reconciled by the inclusion of secondary li from older crust

modeling subauroral polarization streams during the 17 march 2013 storm the subauroral polarization streams saps are one of the most important features in representing magnetosphere ionosphere coupling processes in this study we use a state of the art modeling framework that couples an inner magnetospheric ring current model ram scb with a global mhd model block adaptive tree solar wind roe upwind scheme bats r us and an ionospheric potential solver to study the saps that occurred during the 17 march 2013 storm event as well as to assess the modeling capability both ionospheric and magnetospheric signatures associated with saps are analyzed to understand the spatial and temporal evolution of the electrodynamics in the midlatitude regions results show that the model captures the saps at subauroral latitudes where region 2 field aligned currents facs flow down to the ionosphere and the conductance is lower than in the higher latitude auroral zone comparisons to observations such as facs observed by active magnetosphere and planetary electrodynamics response experiment ampere cross track ion drift from defense meteorological satellite program dmsp and in situ electric field observations from the van allen probes indicate that the model generally reproduces the global dynamics of the region 2 facs the position of saps along the dmsp and the location of the saps electric field around l of 3 0 in the inner magnetosphere near the equator the model also demonstrates double westward flow channels in the dusk sector the higher latitude auroral convection and the subauroral saps and captures the mechanism of the saps however the comparison with ion drifts along dmsp trajectories shows an underestimate of the magnitude of the saps and the sensitivity to the specific location and time the comparison of the saps electric field with that measured from the van allen probes shows that the simulated saps electric field penetrates deeper than in reality implying that the shielding from the region 2 facs in the model is not well represented possible solutions in future studies to improve the modeling capability include implementing a self consistent ionospheric conductivity module from inner magnetosphere particle precipitation coupling with the thermosphere ionosphere chemical processes and connecting the ionosphere with the inner magnetosphere by the stronger region 2 facs calculated in the inner magnetosphere model

lithium sources in pore fluids of peru slope sediments and implications for oceanic fluxes high li concentrations up to a maximum of 1155 m are observed in the pore fluids of the peru convergent margin slope sediments at ocean drilling program sites 683 and 685 9 s the li concentration depth gradients are twice as steep as at site 682 and 688 11 s within the sediments the most important li sources are from aluminosilicate minerals biogenic opal a contains little li and thus dilutes the li concentration of the bulk sediments the sediment compositions and the thermal regimes are similar at 9 and 11 s suggesting there is an additional non sedimentary source for the observed high li concentrations in the northern pore fluids at 9 s the 87sr 86sr ratios reach a maximum value of 0 709958 the observed radiogenic 87sr 86sr values in the pore fluids support the suggestion that the additional li may derive from exchange reactions with underlying continental crust the high concentrations of li at 11 s may derive from basalt alteration at moderate to high temperatures as suggested by the non radiogenic 87sr 86sr ratios in these pore fluids which reach a minimum value of 0 707218 based on 1 li concentrations in the pore fluids in slope sediments from peru and several other margins and 2 an approximate estimate of fluid flux from continental margins into the ocean continental margins provide an estimated 1 to 3 1010 moles li yr to the ocean this source of oceanic li which has not been considered previously is of the same order of magnitude as some estimates of hydrothermal and river li fluxes and may have important consequences for the oceanic li isotope budget the sink is unknown for this newly discovered and possibly large li source but it may be more pervasive low temperature alteration of oceanic basement than previously estimated or burial of mineral phases such as authigenic clay minerals or metal oxyhydroxides which may be li rich

the oxygen geochemical cycle dynamics and stability abstract the first and possibly only major rise of atmospheric oxygen from p o 2 0 1 pal the present atmospheric level to p o 2 10 pal appears to have occurred sometime before 2 ga ago although the exact time of and the cause s for the rise have been hotly debated equally important questions on the atmospheric oxygen concern its stability especially the mechanisms regulating the atmospheric p o 2 level and the causes and magnitude of p o 2 variations since the first major rise of atmospheric oxygen previous efforts to model the p o 2 variation during the phanerozoic time have typically relied on secondary information such as the carbon and sulfur isotopic records of sedimentary rocks and on simple dynamics of the geochemical cycles of o c s and p based on box type models as a result many kinetic questions about the variation and stability of atmospheric oxygen could not have been answered here we quantitatively evaluate the dynamics and stability of atmospheric o 2 and co 2 using recent experimental data field observations and a new model for the c o coupled geochemical cycles we examine the change with time in the fluxes of various compounds o 2 co 2 phosphate organic c carbonate c c bearing reduced volcanic gases and c free reduced volcanic gases among the various reservoirs atmosphere soil surface ocean deep ocean the lower crust and mantle and upper crust under a variety of scenarios our model does not assume steady state fluxes for any of the reservoirs rather the model incorporates the kinetic experimental data on oxidation of coal a proxy for kerogen the dynamics of soil formation and erosion the kinetics of decomposition of organic matter in the oceans by aerobic and anaerobic bacteria the equilibrium ocean atmosphere carbonate model the observed relationships among the organic burial flux dissolved o 2 content of deep ocean and sedimentation rates and the three box model ocean the important parameters that strongly influence the dynamics of atmospheric o 2 are found to be a the total area of soil formation on earth b the average soil depth c the average rate of physical erosion of soils which is linked to the average rate of accumulation of clastic sediments in the oceans d the composition and flux of volcanic gas and e the level of atmospheric co 2 we develop kinetic equations linking these parameters to the production and consumption fluxes of atmospheric oxygen and also to stable p o 2 values considering the likely ranges of variations in these parameters in geologic history we suggest that the atmospheric p o 2 level is likely to have stayed within a very narrow range of 0 6 2 pal and that the entire ocean except for local euxinic basins is likely to have been basically oxygenated since the first major rise of atmospheric oxygen more than 2 ga ago

alteration of volcanic matter in deep sea sediments evidence from the chemical composition of interstitial waters from deep sea drilling cores six deep sea drilling project dsdp sites 252 285 315 317 336 386 were examined for the chemical composition of the dissolved salts in interstitial waters the oxygen isotopic composition of the interstitial waters and the major ion composition of the bulk solid sediments an examination of the concentration depth profiles of dissolved calcium magnesium potassium and h218o in conjunction with oxygen isotope mass balance calculations confirms the hypothesis that in dsdp pelagic drill sites concentration gradients in ca mg k and h218o are largely due to alteration reactions occurring in the basalts of layer 2 and to alteration reactions involving volcanic matter dispersed in the sediment column oxygen isotope mass balance calculations require substantial alteration of layer 2 up to 25 of the upper 1000 m but only minor exchange of ca mg and k occurs with the overlying ocean this implies that alteration reactions in layer 2 are almost isochemical

traveling ionospheric disturbances in the weddell sea anomaly associated with geomagnetic activity we present observations from the falkland islands super dual auroral radar network radar of the propagation of hf radio waves via the weddell sea ionospheric anomaly wsa a region of enhanced austral summer nighttime ionospheric electron densities covering the southern pacific and south americas region this anomaly is thought to be produced by uplift of the ionosphere by prevailing equatorward thermospheric winds of particular interest are perturbations of the wsa supported propagation which suggest that during periods of geomagnetic disturbance the ionospheric layer can be lowered by several tens of kilometers and subsequently recover over a period of 1 to 2 h perturbations can appear singly or as a train of two to three events we discuss possible causes of the perturbations and conclude that they are associated with equatorward propagating large scale atmospheric waves produced by magnetospheric energy deposition in the auroral or subauroral ionosphere changes in high middle latitude electrodynamics during geomagnetic storms may also account for the perturbations but further modeling is required to fully understand their cause

empirical partition coefficients for sr and ca in marine barite implications for reconstructing seawater sr and ca concentrations 1 a robust record of fluctuations in seawater sr and ca concentrations is critical for understanding the long term global carbon cycle as it is influenced by the history and location of carbonate precipitation chemical weathering and hydrothermal activity such a record is also necessary for interpretation of paleoceanographic records temperature productivity derived from carbonate sources e g sr ca mg ca li ca marine barite an inorganic phase preserved in oxic deep sea sediments may record seawater sr and ca concentrations using core top barite samples we have derived the partition coefficients for sr dsr 2 9 10 5 ca dca 1 9 10 8 and sr ca dsr ca 1 6 103 in barite the natural variability of core top marine barite sr ca sr ba and ca ba ratios selected from different ocean basins is 10 1 15 0 and 16 3 respectively since estimates of cenozoic fluctuations in seawater sr ca ratios are large possibly greater than 80 relative to the variability recorded in core tops marine barite may be used to reconstruct seawater sr ca ratios and sr and ca concentrations using empirically derived partition coefficients

strong b enrichment and anomalous δ11b in pore fluids from the japan trench forearc abstract interstitial pore waters from ocean drilling program odp sites 1150 and 1151 both penetrating 1200 m of sub seafloor sediment from the upper japan trench forearc were analyzed for b concentrations and 11 b isotopes b concentrations cover a wide range from 329 to 3920 m 0 8 9 3 seawater and vary isotopically from 20 to 46 relative to srm 951 in general b concentrations increase more or less steadily with depth at both sites the b enrichment and isotopic changes seem to be related to a deep fluid influence possibly coupled with alteration of volcanic products silica diagenesis does not affect the b geochemistry of the waters as is evident from intact diatom tests and high opal a contents throughout the holes the b enrichment is more pronounced at site 1150 in the seismic portion of the forearc here a large positive anomaly in 11 b values is observed which corresponds with abundant fracturing and two prominent shear zones at about the same depth range at site 1151 the 11 b values show a negative shift attesting to an enrichment in 10 b in the fluid as a result of b desorption from clay due to burial and tectonic stress we conclude that b release from clay minerals is the major contributor to pore fluid anomalies and that fluid flow through permeable out of sequence thrust like the shear zones at site 1150 may be an efficient mechanism for b backflux from the forearc into the hydrosphere

submarine weathering of silicate minerals and the extent of pore water freshening at active continental margins in order to investigate how submarine weathering processes may affect the water balance of sediments at convergent plate margins six sediment cores were retrieved off central chile at water depth between 800 and 4000 m the sediment solid phase was analyzed for its major element composition and the pore fluids were analyzed for dissolved sulfate sulfide total alkalinity major cations chloride bromide iodide hydrocarbons as well as the carbon isotopic composition of methane because of negligible weathering on land surface sediments off central chile are rich in reactive silicate minerals and have a bulk composition similar to volcanic rocks in the adjacent andes deep sourced fluxes of alkalinity cations and chloride indicate that silicate minerals are subject to weathering in the forearc during burial comparison of deep sourced signals with data from nearby ocean drilling program sites reveals two different types of weathering processes in shallow tens of meters methanic sediments of slope basins with high organic carbon burial rates reactive silicate minerals undergo incongruent dissolution through reaction with co2 from methanogenesis at greater burial depth hundreds of meters silicate weathering is dominated by authigenic smectite formation this process is accompanied by uptake of water into the clay interlayers thus leading to elevated salinities in the surrounding pore water deep seated smectite formation is more widespread than shallow silicate dissolution as it is independent from the availability of co2 from methanogenesis although solute transport is not focused enough to form cold seeps in the proper sense tectonically induced diffuse fluid flow transfers the deep seated signal of smectite formation into the shallow sediments the temperature controlled conversion of smectite to illite is considered the most important dehydration process in marine forearc environments depth of kilometers however in agreement with other studies at active margins e g aleutians cascadia nankai trough and despite ubiquitous evidence for smectite formation little evidence for seafloor seepage of dehydration fluids could be found off central chile we argue that the circular process of pore water uptake during smectite formation and release upon illitization implies a balanced freshwater budget and therefore a rather limited potential for net pore water freshening on a margin wide scale according to this rationale pore water freshening at seafloor seeps preferentially occurs at lower latitudes central america barbados mediterranean ridge where terrestrial weathering is more intense thus leading to external i e detrital smectite and thus freshwater inputs to the subduction system

direct observations of the role of convection electric field in the formation of a polar tongue of ionization from storm enhanced density 1 we examine the relationship of convection electric fields to the formation of a polar cap tongue of ionization toi from midlatitude plumes of storm enhanced density sed observations from the geomagnetic storm on 26 27 september 2011 are presented for two distinct sed events during an hour long period of geomagnetic activity driven by a coronal mass ejection a channel of high density f region plasma was transported from the dayside subauroral ionosphere and into the polar cap by enhanced convection electric fields extending to middle latitudes this toi feature was associated with enhanced hf backscatter indicating that it was the seat of active formation of small scale irregularities after the solar wind interplanetary magnetic field conditions quieted and the dayside convection electric fields retreated to higher latitudes an sed plume was observed extending to but not entering the dayside cusp region this prominent feature in the distribution of total electron content tec persisted for several hours and elongated in magnetic local time with the rotation of the earth no ionospheric scatter from superdarn radars was observed within this sed region the source mechanism enhanced electric fields previously drawing the plasma from midlatitudes and into the polar cap as a toi was no longer active resulting in a fossil feature we thus demonstrate the controlling role exercised by the convection electric field in generating a toi from midlatitude sed

coprecipitation and isotopic fractionation of boron in modern biogenic carbonates abstract the abundances and isotopic composition of boron in modern biogenic calcareous skeletons from the gulf of elat israel the great barrier reef australia and in deep sea sediments have been examined by negative thermal ionization mass spectrometry the selected species foraminifera pteropoda corals gastropoda and pelecypoda yield large variations in boron concentration that range from 1 ppm in gastropod shells to 80 ppm in corals the boron content of the biogenic skeletons is independent of mineralogical composition and is probably related to biological vital effects the 11 b values of the carbonates range from 14 2 to 32 2 relative to nbs srm 951 and overlap with the 11 b values of modern deep sea carbonate sediments 11 b 8 9 to 26 2 the variations of 11 b may be controlled by isotopic exchange of boron species in which 10 b is preferentially partitioned into the tetrahedral species and coprecipitation of different proportions of trigonal and tetrahedral species in the calcium carbonates carbonates with low 11 b values 15 may indicate preferential incorporation of tetrahedral species whereas the higher 11 b values 30 may indicate 1 1 uptake of both boron species assuming equilibrium with seawater 2 2 preferential incorporation of b oh 4 from in situ high ph internal fluids of organisms that are isolated from seawater the b content and 11 b values of deep sea sediments foraminifera tests and corals are used to estimate the global oceanic sink of elemental boron by calcium carbonate deposition as a result of enrichment of b in corals a substantially higher biogenic sink of 6 4 0 9 10 10 g yr is calculated for carbonates this is only slightly lower than the sink for desorbable b in marine sediments 10 10 10 g yr and approximately half that of altered oceanic crust 14 10 10 g yr thus carbonates are an important sink for b in the oceans being 20 of the total sinks the preferential incorporation of 10 b into calcium carbonate results in oceanic 11 b enrichment estimated as 1 2 0 3 10 12 per mil g yr the boron isotope composition of authigenic well preserved carbonate skeletons may provide a useful tool to record secular boron isotope variations in seawater at various times in the geological record the potential use of boron isotope geochemistry in skeletons as a tracer for palaeoenvironments is demonstrated in ostracoda and foraminifera from the gulf of carpentaria australia the 11 b values of glacial age buried skeletons 4 0 and 4 9 respectively are lower than that of their modern equivalents 17 6 and 13 3 respectively this may reflect a terrestrial boron isotope signature of the water in the gulf during the late quaternary when it was isolated from the ocean

influence of auroral streamers on rapid evolution of ionospheric saps flows subauroral polarization streams saps often show large rapid enhancements above their slowly varying component we present simultaneous observations from ground based all sky imagers and flows from the super dual auroral radar network radars to investigate the relationship between auroral phenomena and flow enhancement we first identified auroral streamers approaching the equatorward boundary of the auroral oval to examine how often the subauroral flow increased we also performed the reverse query starting with subauroral flow enhancements and then evaluated the auroral conditions in the forward study 98 of the streamers approaching the equatorward boundary were associated with saps flow enhancements reaching 700 m s and typically hundreds of m s above background speeds the reverse study reveals that flow enhancements associated with streamers 60 and enhanced larger scale convection 37 contribute to saps flow enhancements the strong correlation of auroral streamers with rapid evolution approximately minutes of saps flows suggests that transient fast earthward plasma sheet flows can often lead to westward saps flow enhancements in the subauroral region and that such enhancements are far more common than only during substorms because of the much more frequent occurrences of streamers under various geomagnetic conditions we also found a strong correlation between flow duration and streamer duration and a weak correlation between saps flow velocity and streamer intensity this result suggests that intense flow bursts in the plasma sheet which correlate with intense streamers are associated with intense saps ionospheric flows perhaps by enhancing the ring current pressure and localized pressure gradients when they are able to penetrate close enough to earth

bromine and iodine in peru margin sediments and pore fluids implications for fluid origins at the peruvian convergent margin two distinct pore fluid regimes are recognized from differences in their cl concentrations the slope pore fluids are characterized by low cl concentrations but elevated br and i concentrations due to biogenic production the shelf pore fluids exhibit elevated cl and br concentrations due to diffusive mixing with an evaporitic brine in the slope pore fluids the br i and nh4 concentrations are elevated following bacterial decomposition of organic matter but the i concentrations are in excess of those expected based on mass balance calculations using nh4 and br concentrations the slope sediment organic matter which is enriched in iodine from oxidationreduction processes at the oxygenated sediment water interface is responsible for this enrichment the increases in dissolved i and the i enrichments relative to nh4 and br correlate well with sedimentation rates because of differential trapping following regeneration the pore fluid i br ratios suggest that membrane ion fiitration is not a major cause of the decreases in cl concentrations other possible sources for low cl water including meteoric water clathrate dissociation and or mineral dehydration reactions imply that the diluting component of the slope low cl fluids has flowed at least 1 km through the sediment the low bottom water oxygenation in the shelf is responsible for the low if any enrichment of iodine in the shelf sediments fluctuations in bottom water oxygen concentrations in the past however may be responsible for the observed variations in the sediment ibr ratios comparison of na cl and br cl molar ratios in the pore fluids shows that the shelf high cl fluid formed from mixing with a brine that formed from seawater concentrated by twelve to nineteen times and probably was modified by halite dissolution this dense brine located below the sediment sections drilled appears to have flowed a distance 500 km through the sediment

hydrochemistry and isotope geochemistry of the upper danube river abstract the upper danube river and 19 of its major tributaries were monitored for 1046 km downriver and seasonally for ca mg sr na k hco3 co2 cl po4 sio2 no3 no2 nh4 so4 13cdic 18oh2o dh2o 34sso4 18oso4 and 87sr 86sr hydrological considerations and 18o d data show that the water balance in the river particularly after its confluence with the inn is controlled by the southern tributaries draining the mesozoic carbonate complexes of the alps as a result chemical balance at bratislava is mostly a conservative product of its tributaries the concentrations of ca mg and sr in the danube are 6 to 9 times higher than in pristine rivers although all these cations are derived from dissolution of mesozoic carbonates the ultimate cause is likely the enhanced generation of soil co2 due to agricultural and forestry practices dissolution of triassic sulfates is an additional factor for ca enrichment in the headwater section of the river dissolved sulfate with a comparable enrichment factor to that of alkaline earths appears to be derived mostly from atmospheric deposition a proposition based on consideration of its sulfur and oxygen isotopic compositions na k and cl are enriched by a factor of 2 5 to 4 times mostly as a result of industrial and municipal pollution sources in contrast to the above components which behave mostly conservatively during the downriver flow of the danube biogenic elements such as nutrients and si are influenced by in river processes the photosynthesis respiration balance that impacts the carbon cycle and the oxygen balance has been discussed elsewhere pawellek and veizer 1994 no3 no2 and nh4 are enriched by a factor of 10 to 16 times from point and diffuse sources along the watercourses generating at times downflow nitrification plumes from nh4 to no3 po4 varies seasonally chiefly as a result of biologic demand during the warm periods for sio2 the biological uptake mostly for secretion of diatom frustules combined with the deficiency of this compound that results from the predominantly carbonate lithology of the catchment results in concentrations that are below those of pristine rivers overall the present day salted characteristics of the river are chiefly a consequence of the long habitation history of the upper danube watershed

a simple evolutionary model for water and salt in the black sea this paper presents a time dependent variable size box model for the total fluid and salinity balances of the black sea in addition to the advective flows due to riverine and mediterranean inputs of water the model accounts for entrainment flows which are parameterized using the theory of ellison and turner 1959 and employs a modified version of the gargett 1984 formulation for eddy diffusivity in describing cross pycnocline mixing flows the variable volume of the boxes permits explicit simulation of the replacement of the preexisting late pleistocene lake water by the inflow of denser mediterranean water our results indicate that the time needed to displace the old deep water with new saltier water is 2000 years or less because of the effects of mixing the salinity of both the surface and deep waters requires a greater time interval to obtain present day values i e 4000 years if the inflow of mediterranean water is constant in time at its present value and 6000 years if this input changes with time in approximation to the rate of sea level rise the occurrence of the marine coccolithophorid emiliania huxleyi in the holocene sapropel layer requires a minimum surface salinity of 11 which takes some 1600 to 3100 years to develop this range is a result of the uncertainty in the history of the mediterranean water input the model is also employed to investigate the freshening of the black sea after cutoff of mediterranean input the salinity of both surface and deep waters is found to fall below 11 in less than 3000 years and the freshening process is complete in 9000 years

average characteristics and activity dependence of the subauroral polarization stream 1 data from the millstone hill incoherent scatter radar taken over two solar cycles 1979 2000 are examined to determine the average characteristics of the disturbance convection electric field in the midlatitude ionosphere radar azimuth scans provide a regular database of ionospheric plasma convection observations spanning auroral and subauroral latitudes and these scans have been examined for all local times and activity conditions we examine the occurrence and characteristics of a persistent secondary westward convection peak which lies equatorward of the auroral two cell convection individual scans and average patterns of plasma flow identify and characterize this latitudinally broad and persistent subauroral polarization stream saps which spans the nightside from dusk to the early morning sector for all kp greater than 4 premidnight the saps westward convection lies equatorward of l 4 60 invariant latitude spans 3 5 of latitude and has an average peak amplitude of 900 m s in the predawn sector saps is seen as a region of antisunward convection equatorward of l 3 55 spanning 3 of latitude with an average peak amplitude of 400 m s

on the spatial distribution of decameter scale subauroral ionospheric irregularities observed by superdarn radars 1 the midlatitude super dual auroral radar network superdarn radars regularly observe nighttime low velocity sub auroral ionospheric scatter sais from decameter scale ionospheric density irregularities during quiet geomagnetic conditions to establish the origin of the density irregularities responsible for low velocity sais it is necessary to distinguish between the effects of high frequency hf propagation and irregularity occurrence itself on the observed backscatter distribution we compare range azimuth and elevation data from the blackstone superdarn radar with modeling results from ray tracing coupled with the international reference ionosphere assuming a uniform irregularity distribution the observed and modeled distributions are shown to be very similar the spatial distribution of backscattering is consistent with the requirement that hf rays propagate nearly perpendicular to the geomagnetic field lines aspect angle 1 for the first time the irregularities responsible for low velocity sais are determined to extend between 200 and 300 km altitude validating previous assumptions that low velocity sais is an f region phenomenon we find that the limited spatial extent of this category of ionospheric backscatter within superdarn radars fields of view is a consequence of hf propagation effects and the finite vertical extent of the scattering irregularities we conclude that the density irregularities responsible for low velocity sais are widely distributed horizontally within the midlatitude ionosphere but are confined to the bottom side f region

ground based gps observation of sed associated irregularities over conus 1 it has been known that steep total electron content tec gradients observed at the boundary between the storm enhanced plasma density sed and the low tec region at subauroral and midlatitude regions are associated with ionospheric irregularities that impact communication and navigation systems however the relationship between the sed associated irregularities and tec gradients is still not well understood partly because of the difficulties of resolving small scale tec gradients from sparsely distributed tec observations in this study we examine the relationship between the sed associated irregularities and tec gradients during the intense geomagnetic storms of 31 march 2001 and 30 october 2003 to explore this relationship tec maps over the continental united states conus were constructed from ground based gps tec observations using kalman filter update formulae with a recently developed nonstationary wavelet based covariance model that enables resolution of tec structures on both large and finer scales our results show that intense tec gradients and ion drifts are thought to be required conditions for the formation of irregularities on the northeast side of the sed additionally our methodology identified the narrow east west stretch of tec enhancement within the midlatitude low tec region on 30 october 2003 and this tec enhancement is most likely to be caused by auroral precipitation

the boron isotopic composition of altered oceanic crust samples of drilled oceanic crust from dsdp holes 417a 417d and 418a and odp hole 735b and oceanic crust from the oman and cyprus ophiolites were analyzed for b contents and 11b composite samples from dsdp holes 417a 417d and 418a were used to represent the upper 550 m of altered oceanic crustal layer 2a whole rock samples from the troodos ophiolite cyprus and the oman ophiolite wer selected to represent crustal layer 2b dikes composite samples from odp hole 735b were used to represent crustal layer 3 the b content of the dsdp composites ranges from 7 2 ppm to 104 ppm and correlates with both 18o and k showing that it is a good indicator of the extent of low temperature alteration the 11b of the dsdp composites varies between 2 5 and 5 4 the b content of the samples from the troodos ophiolite ranges from 2 4 ppm to 8 1 ppm 11b varies from 0 9 to 7 8 the b content of the oman ophiolite samples ranges from 5 0 ppm to 11 1 ppm 11b varies from 1 6 to 16 9 the b content of the samples from odp hole 735b ranges from 1 1 ppm to 7 1 ppm 11b varies from 4 3 to 24 9 the general pattern displayed by these samples is one of greatest and most variable b enrichment at the top of the crust and least enrichment at the bottom of the section all of these samples are enriched compared to unaltered morb which is believed to have a b content of approximately 0 5 ppm the 11b values of deeper samples from layers 2b and 3 are more variable and generally higher than those from layer 2a boron contents and 11b are not correlated the data from the dsdp site 417418 composites indicate that the 11b of fluid circulating in the upper crust changes only slightly during alteration increasing by an average of 5 1 with an accompanying decrease in b concentration of 7 low temperature alteration appears to be a water dominated process resulting in minor modification of circulating seawater a minimum water rock ratio of 400 is calculated for these samples implying a minimum low temperature seawater flux through the upper oceanic crust of 3 4 1014 l y the average b content of altered oceanic crust as represented by these samples is 5 2 1 7 ppm and the average 11b is 3 4 1 1 this average isotopic composition is measurably different from the apparent average of oceanic sediments supporting the idea that 11b could be useful for identifying the source s of b in island arcs

boron isotope systematics of marine sediments abstract boron contents and boron isotopic compositions were determined for modern and ancient permian to miocene marine sediments including pelagic clay calcareous ooze siliceous ooze and neritic clay sediments 11b values of modern marine sediments range from 6 6 to 4 8 isotopic variation is controlled by the simple mixing of four major constituents detritus of continental origin marine smectite biogenic carbonates and biogenic silica detritus of continental origin with an average 11b value of 13 to 8 is the low 11b end member constituent of marine sediments and its boron is largely controlled by the concentration of illite which originates from wind or fluvial transport marine smectite biogenic carbonate and biogenic silica on the other hand represent the high 11b end members with 11b values of 2 3 to 9 2 8 0 to 26 2 and 2 1 to 4 5 respectively these high 11b values are the result of the equilibrium uptake of boron from seawater spatial variations in boron isotopes in the pacific sediments are essentially due to the distribution of the above four constituents although ancient argillaceous sediments shale and slate have boron contents that are identical with those of modern equivalents boron contents of limestone and chert are distinctly lower than those of modern calcareous and siliceous oozes ancient marine sediments have systematically lower 11b values 17 0 to 5 6 than those of the modern sediments the lower 11b values can be caused by diagenesis which induces 1 preferential removal of high 11b boron in calcium carbonate and silica during recrystallization and 2 boron isotopic exchange in the course of the smectite illite transition the observed boron isotopic compositions of ancient argillaceous sediments are distinctly different from those of fresh and altered morb therefore boron isotope systematics will be useful in identifying components from the descending oceanic slab involved in the formation of island arc magma and in investigating mantle crust recycling through subduction processes

carbon accumulation rates and the origin of the holocene sapropel in the black sea a detailed radiocarbon chronology obtained by accelerator mass spectrometry together with organic carbon and carbonate measurements on two black sea cores has been used to compare and contrast the burial fluxes of organic carbon in the holocene sapropel and the modern sediment at both deep water and eastern slope sites the sapropel is separated from the modern facies by a variable thickness of compositionally homogeneous sediment with low levels of organic carbon and anomalously old radiocarbon ages this homogeneous unit probably represents deposition by slumping or mudflow the age limits of the sapropel are 1600 6600 b p at the deep water site and 4000 6000 b p radiocarbon years before 1950 a d at the shallow water site the carbon accumulation rate in the deep water sapropel is higher than that in the modern deep water facies by a factor of 2 and is approximately the same as that in the modern sediment in shallow water the revised chronology of sapropel formation and the differences in the carbon accumulation rates probably indicate that the sapropel was formed by increased production during the transition from the premodern lake to the modern marine phases of the black sea this conclusion is consistent with the clear marine carbon isotope signal in the organic mattermore in the sapropel in both cores results to be reported elsewhere in contrast to the mixed source of carbon in the other facies less

large scale observations of a subauroral polarization stream by midlatitude superdarn radars instantaneous longitudinal velocity variations 1 we present simultaneous measurements of flow velocities inside a subauroral polarization stream saps made by six midlatitude high frequency superdarn radars the instantaneous observations cover three hours of universal time and six hours of magnetic local time mlt from velocity variations across the field of view of the radars we infer the local 2d flow direction at three different longitudes we find that the local flow direction inside the saps channel is remarkably constant over the course of the event the flow speed however shows significant temporal and spatial variations after correcting for the radar look direction we are able to accurately determine the dependence of the saps velocity on magnetic local time we find that the saps velocity variation with magnetic local time is best described by an exponential function the average velocity at 00 mlt was 1 2 km s and it decreased with a spatial e folding scale of two hours of mlt toward the dawn sector we speculate that the longitudinal distribution of pressure gradients in the ring current is responsible for this dependence and find these observations in good agreement with results from ring current models using tec measurements we find that the high westward velocities of the saps are as expected located in a region of low tec values indicating low ionospheric conductivities

boron isotope systematics in large rivers implications for the marine boron budget and paleo ph reconstruction over the cenozoic abstract the chemical composition of the oceans and long term climate changes are believed to be linked reconstruction of seawater ph evolution is desirable as ph may be related to atmospheric pco2 and hence to climate evolution boron isotopes in oceanic carbonates have been suggested to be a proxy for oceanic paleo ph reconstruction nevertheless the calculation of paleo ph values over geological periods requires a precise knowledge of the boron isotopic composition of the oceans when calcite precipitated we present the systematics of boron isotopic composition of the world s main rivers we deduce a continental boron flux to the oceans of 38 1010 gb year with a mean isotopic composition of 10 these results lead to a balanced boron budget in the oceans and allow the development of a model for the marine boron secular evolution over the past 100 myr it is shown that the oceanic boron cycle is mainly controlled by the boron continental discharge and the boron uptake from the oceans during low temperature alteration of oceanic crust however the recent important increase of the clastic sediment supply linked to the himalayan erosion impacts the oceanic boron budget by enhancing significantly the boron uptake by adsorption on sediments we predict a boron isotopic composition in the oceans lower during the cenozoic and slightly higher during the cretaceous than today the modelled values for the marine boron isotopes follow the variations of boron isotopes in carbonates over the cenozoic era provided by previous studies suggesting that the variations of the seawater ph may not have been important on this time scale if this is the case it involves that buffering mechanisms occur in the oceans to maintain seawater ph at a roughly constant value against past atmospheric pco2 variations

oceanography of the black sea a review of some recent results abstract a new synthesis of the black sea oceanography is presented primarily based on studies carried out in the southern black sea as well as on some recent work covering the entire basin obtained in a new era of increasing cooperation between the riparian countries a review of the physical environment is given seasonal and interannual climatic variability of the system are discussed in relation to its hydrology water mass variability and formation are studied with emphasis on the inflow of mediterranean waters pycnocline variability shelf and internal mixing and double diffusive convection the general circulation of the basin and the roles of stratification topography and coastline variations in determining the behaviour of the rapid unstable boundary currents and upwelling along the coast are discussed based on hydrographic data and satellite observations impacts of the physical processes on the ecosystem are discussed

chemical and isotopic evidence for sources of fluids in a mud volcano field seaward of the barbados accretionary wedge chemical isotopic and heat budgets are controlled by fluid flow and venting at convergent margins fluids vent from accretionary complex sediments via numerous pathways including mud volcanoes which are common at the barbados convergent margin chemical and isotopic compositions of fluids collected from four mud volcanoes located east of the barbados deformation front at 13 50 n indicate venting is sufficiently rapid to prevent diffusion from seawater in sediments surrounding the mud volcanoes the rate of nonfocused fluid flow is 0 26 cm yr although this rate is 3 orders of magnitude slower than the flow from the mud volcanoes significantly more fluid vents from the sediments surrounding the mud volcanoes than from the restricted areas of rapid flow from the volcanoes chloride concentrations are depleted to a minimum of 211 mm 45 of seawater value primarily by mixing diagenetically altered pore fluids with an 18o enriched fresh water released from the dissociation of methane hydrate this reaction is accompanied by the release of sufficient methane to form a free gas phase and initiate eruption of the mud volcanoes the geochemical compositions of the diagenetically altered pore fluids reflect the interplay between five major reactions 1 clay mineral dehydration which releases h2o and influences a range of chemical and isotopic compositions 2 organic matter regeneration which increases alkalinity nh4 and br and decreases so42 concentrations 3 cation exchange with clay minerals which increases na and decreases nh4 concentrations 4 carbonate recrystallization and precipitation which decrease ca2 but increase sr2 concentrations and 5 conversion of volcanic ash to clay minerals which utilizes h2o and decreases mg2 concentrations the geochemistry of the pore fluids suggests that these reactions occurred at temperatures ranging from 75 to 115 c thus at the regional geothermal gradients of 27 to 40 c km these temperatures indicate that the source regions are at 2 to 4 5 km depth

lithium and its isotopes in major world rivers implications for weathering and the oceanic budget abstract the outstanding problem in the lithium geochemical cycle is the lack of an isotopic mass balance in the ocean the 6li compositions of fresh basalts 4 the hydrothermal fluids derived from them average 9 and seawater significantly heavier at 32 are well understood but only very sparse river input data are available for li mass balance calculations in an attempt to rectify the situation we have measured the lithium concentrations and isotopic compositions of major world rivers draining representative geological terrains this helps both to constrain the river endmember and to understand the behavior of lithium isotopes in the continental weathering environment fluvial isotopic compositions display a very large range 6 0 to 32 2 there is no definitive relationship between 6li and lithology but in general rivers draining marine evaporites are 20 to 22 carbonates 26 to 32 black shales 26 shields 6 6 to 19 and mixed siliceous terrains 6 to 28 the flow weighted mean concentration of the measured rivers is 215 nm at 23 this updated riverine 6li value responsible for 30 of the global riverine discharge does not solve the isotopic imbalance if the measured li concentrations and isotopic compositions are representative of all rivers the presence of a yet unidentified sink with a higher fractionation factor 1 023 than determined for low temperature basalt alteration 1 019 is required for an isotopic steady state of li in the ocean authigenic clays are a possible candidate as clays are known to be enriched in both lithium and in the light isotope preferentially alternatively the hydrothermal flux must be much less than half of that estimated by the 3he inventory and the oceanic budgets for 87sr 86sr and mg the relationship of 6li to the major ions and 87sr 86sr suggests that the important processes affecting river dissolved lithium isotopic compositions are fractionation between solution and secondary minerals and thus the intensity of weathering

super dual auroral radar network observations of meteor echoes radar echoes from ranges less than 500 km are routinely observed by the super dual auroral radar network superdarn on most days many of these echoes have properties which are markedly different from what one would expect from e or f region irregularities we show that these unusual short range hf echoes are due to scattering off meteor trails this explains why among other things the doppler shift from the short range echoes taken from the superdarn saskatoon antenna are consistent with the mesospheric winds observed by the saskatoon mf radar this means that the superdarn radars can be used to study neutral winds at meteor heights a result which is especially interesting since it opens up the capability for a global coverage of mesospheric winds using the worldwide distribution of superdarn radars

the sedimentary cycle of the boron isotopes abstract marine sediments contain two isotopically distinct components a non desorbable fraction with 11b between 4 3 and 2 8 per mil n 10 and a desorbable component with 11b between 13 9 and 15 8 per mil n 6 the adsorption coefficient k for the uptake of b from seawater by fluvial suspended material mississippi has an experimentally determined value of 1 54 0 05 the associated isotope fractionation factor is 0 974 0 003 empirical values for k determined from the analysis of marine sediments n 6 were between 3 and 4 the amount of b adsorbed onto fluvial suspended material during estuarine mixing is about 9 109 moles yr based on pore water data adsorption experiments and comparative size fraction analyses suspended sediments from the mississippi river vs bottom deposits from the delta there is no evidence for the incorporation of b into detrital sediments at low temperature however the high b content of bauer deep metalliferous sediments must be due to incorporation of seawater b during formation of authigenic silicates the 11b of these minerals is 2 3 per mil hydrothermally altered sediments from dsdp hole 477 guaymas basin gulf of california have variable b contents from 33 ppm similar to the unaltered detritus to 1 2 ppm in the recrystallized material the latter has 11b as low as 9 0 per mil substantially lower than the unaltered material hydrothermal solutions collected from vents adjacent to the hole have boron contents elevated by about a factor of 4 relative to seawater and 11b between 16 5 and 23 2 per mil the b mobilized from the sediments is isotopically fractionated with the fluids being preferentially enriched in the heavy isotope analysis of an oxisol profile developed over granite in the guyana shield showed that boron is partially mobilized during weathering with an isotopic offset of 2 5 per mil between bedrock and soil the observed enrichment of b in shales relative to igneous rocks does not occur during weathering or during exposure to seawater at low temperature incorporation occurs only during burial diagenesis at temperatures greater than about 60 c however the enrichments cannot be attained during a single cycle of primary weathering and burial but must be cumulative over many cycles

evidence for the submarine weathering of silicate minerals in black sea sediments possible implications for the marine li and b cycles 1 the role of sediment diagenesis in the marine cycles of li and b is poorly understood because li and b are easily mobilized during burial and are consumed in authigenic clay mineral formation their abundance in marine pore waters varies considerably exchange with the overlying ocean through diffusive fluxes should thus be common nevertheless only a minor li sink associated with the low temperature alteration of volcanic ash has been observed we describe a low temperature diagenetic environment in the black sea dominated by the alteration of detrital plagioclase feldspars fluids expelled from the odessa mud volcano in the sorokin trough originate from shallow 100 400 m deep sediments which are poor in volcanic materials but rich in anorthite these fluids are depleted in na k li b and 18o and enriched in ca2 and sr2 indicating that anorthite is dissolving and authigenic clays are forming using a simple chemical model we calculate the ph and the partial pressure of co2 pco2 in fluids associated with this alteration process our results show that the ph of these fluids is up to 1 5 ph units lower than in most deep marine sediments and that pco2 levels are up to several hundred times higher than in the atmosphere these conditions are similar to those which favor the weathering of silicate minerals in subaerial soil environments we propose that in black sea sediments enhanced organic matter preservation favors co2 production through methanogenesis and results in a low pore water ph compared to most deep sea sediments as a result silicate mineral weathering which is a sluggish process in most marine diagenetic environments proceeds rapidly in black sea sediments there is a potential for organic matter rich continental shelf environments to host this type of diagenesis should such environments be widespread this new li and b sink could help balance the marine li and li isotope budgets but would imply an apparent imbalance in the b cycle

statistical patterns of high latitude convection obtained from goose bay hf radar observations we have derived patterns that describe the statistical interplanetary magnetic field imf dependencies of ionospheric convection in the high latitude region of the northern hemisphere the observations of plasma motion were made with the hf coherent backscatter radar located at goose bay labrador over the period september 1987 to june 1993 the area covered by the measurements extended poleward of 65 to a working limit of about 85 distributions of electrostatic potential have been derived and expressed as series expansions in spherical harmonics the patterns are the first derived from direct ground based observations of ionospheric convection that approach in completeness and level of detail the patterns derived in recent satellite studies rich and hairston 1994 weimer 1995 we show the dependence of the convection on imf angle in the gsm y z plane for three intervals of imf magnitude in this plane except for predominantly northward imf the convection is primarily two cell the dusk cell is larger in terms of both spatial extent and potential variation the effect of imf by is apparent in the global shaping of the cells and the orientation of the overall pattern in mlt for by by the dusk dawn cell is more round crescent shaped and the pattern more rotated toward earlier mlts the by effect on the nightside convection is pronounced and is hemispherically antisymmetric like the well known day side by effect for imf increasingly northward the convection trajectories on the dayside become increasingly distorted evolving through a three cell to a four cell circulation the additional cells appear on either side of the noon meridian and result in sunward flow the overall agreement with the results of the satellite studies is good and extends to quite fine detail in the case of the comparison with weimer 1995 there are significant differences with the statistical patterns derived from magnetometer measurements which tend to show domination by the dawn rather than the dusk cell

lithium isotopic composition of submarine basalts implications for the lithium cycle in the oceans abstract we have measured the li isotope composition of young pristine basalts from active ocean ridge crests of progressively older basalts along a dredging transect and a limited number of hydrothermally altered basalts the data significantly extend our limited knowledge of the isotopic abundance ratio of li in geological material fresh mid ocean ridge basalts have 6li values of between 3 4 and 4 7 relative to isotope standard l svec during low temperature weathering on the seafloor the isotopic composition of the rock becomes increasingly heavier due to addition of seawater li 6li 32 3 the oldest 46 m y and most altered rock studied has an isotopic composition of 14 a linear relationship exists between 6li and the inverse of li concentration suggesting that li in weathered basalts can be regarded as a two component mixture of basaltic li and seawater derived li that has been incorporated in alteration minerals most likely secondary clays such as smectite and phillipsite the inferred li isotopic composition of the alteration endmember indicates an apparent isotopic fractionation factor of 1 019 relative to the seawater source thus li uptake by secondary minerals from the low temperature weathering process and by analogy incorporation in similar authigenic minerals in marine sediments provides a mechanism for preferential removal of the lighter li isotope from ocean water however isotopic fractionation due to authigenic clay formation alone cannot account for the isotopic difference between seawater and its principal sources unless the hydrothermal flux is comparable to the river flux alternatively more important sinks of6li must exist if the steady state isotopic composition of li in ocean water is to be maintained

postglacial faulting in eastern canada nature origin and seismic hazard implications abstract at more than 70 locations in southeastern canada and the adjacent united states tiny bedrock faults displace glacial striations that are about 10 000 years old these reverse faults mostly of small displacement occur in a broad arc from western ontario to newfoundland the faults lie near the margin of the laurentian ice sheet strike generally tangential to it and imply compression nearly normal to the ene directed contemporary regional stress these observations and some age relationships suggest that the faults formed very soon after deglaciation perhaps in the first few thousand years after ice melting in each place and probably represent the release of stresses caused by flexural deformation of the upper crust although the individual offsets are small the faults are believed to be pervasive and individual outcrops reflect amounts of stress relief consistent with stresses implied by the postglacial tilt of nearby lake shorelines

complex flow patterns through hydrate ridge and their impact on seep biota our recent measurements of long term fluid flux rates and output fluid chemistry at seep sites on hydrate ridge cascadia suggest that the mechanisms driving fluid flow in gas hydrate bearing forearc settings may be significantly more complex than previously thought temporal changes in the polarity and magnitude of flow and in seep fluid chemistry were observed the nature of flow appears to generate a strong response in the chemosynthetic seep community ecology we document here 1 the frequency and range of temporal variability in flow rates 2 the relatively rapid changes in outflow composition 3 strong outflow of seawater like fluids 4 the association of calyptogena sp clams with oscillatory and inflow settings and 5 microbial mat communities associated with strong advection of altered fluids these results suggest that a reappraisal may be required of the nature of the hydrologic system and its effect on related processes such as benthic seep community ecology and biogeochemical cycles

lithium isotope geochemistry of sediments and hydrothermal fluids of the guaymas basin gulf of california abstract lithium isotopic compositions of hydrothermally altered sediments of deep sea drilling project dsdp site 477 477a as well as high temperature vent fluids of the guaymas basin have been determined to gain an understanding of lithium exchange during fluid sediment interaction at this sediment covered spreading center unaltered turbidite of the basin has a 6 li value of 10 5 7 heavier than fresh oceanic basalts contact metamorphism induced by a shallow sill intrusion results in a decrease of the lithium content of the adjacent sediments and a lighter isotopic value 8 below the sill sediments altered by a deep seated hydrothermal system show strong depletions in lithium while lithium isotopic compositions vary greatly ranging from 11 to 1 the shift to lighter composition is the result of preferential retention of the lighter isotope in recrystallized phases after destruction of the primary minerals the complexity of the isotope profile is attributed to inhomogeneity in mineral composition the tortuous pathway of fluids and the temperature effect on isotopic fractionation the range of lithium concentration and 6 li values for the vent fluids sampled in 1982 and 1985 overlaps with that of the sediment free mid ocean ridge systems the lack of a distinct expression of sediment input is explained in terms of a flow through system with continuous water recharge the observations on the natural system agree well with the results of laboratory hydrothermal experiments the experimental study demonstrates the importance of temperature pressure water rock ratio substrate composition and reaction time on the lithium isotopic composition of the reacted fluid high temperature authigenic phases do not seem to constitute an important sink for lithium and sediments of a hydrothermal system such as guaymas are a source of lithium to the ocean the ready mobility of lithium in the sediment under elevated temperature and pressure conditions also has important implications for lithium cycling in subduction zones

numerical modeling of benthic processes in the deep arabian sea abstract aerobic and anaerobic degradation of particulate organic carbon poc and carbonate equilibria in deep sea surface sediments were studied at five stations located in the western wast northern nast eastern east central cast and southern sast arabian sea in situ oxygen fluxes porewater profiles of dissolved oxygen nitrate and mn ph profiles and solid phase profiles of particulate organic carbon mn and fe were measured at each station an early diagenesis model was applied to simulate the degradation and dissolution processes and to determine the benthic fluxes of poc oxygen nitrate phosphate co2 hco3 and co32 the benthic data sets were evaluated to constrain the poc input and the kinetics of organic matter degradation used in the model the modeling showed that the poc rain rate to the seafloor is high at the western and northern stations and decreases towards the southeast at stations located in the vicinity of continental margins wast nast east 5 7 of the primary production sinks to the deep sea floor this unusually high poc rain is either caused by dust particles that accelerate and amplify the particle export from the euphotic zone or by rapid lateral transport processes at the more remote stations cast sast that receive lower dust inputs the rain efficiency decreases to 1 4 in the model organic matter was separated into three fractions 3 g model that differ considerably in reactivity at stations wast nast east and cast the bulk of organic matter is composed of extremely labile organic matter with a first order degradation constant k of 15 30 yr 1 the moderately labile fraction with a kinetic constant of 0 2 0 6 yr 1 dominates the poc input at the oligotrophic station in the southern arabian sea sast the third fraction that has a very low reactivity k 2 5 10 4 yr 1 is only a minor component of the poc rain at all investigated stations more than 95 of the organic matter is consumed in aerobic degradation processes denitrification and metal oxide reduction only contribute 1 2 to the total poc degradation at the western station wast a non negligible portion 2 of organic matter is consumed via sulfate reduction the modeling demonstrates that carbonate dissolution is a major process in the deep arabian sea 52 83 of the carbonate rain to the seafloor is dissolved within the surface sediments in the western arabian sea the monsoon systems produce a strong seasonality in the primary production non steady state modeling indicates that the benthic oxygen nutrient and inorganic carbon fluxes closely follow the seasonal dynamics in primary and export production this very close benthic pelagic coupling is established by the extremely labile organic matter fraction that dominates the poc rain to the seafloor the metabolically released co2 induces a seasonal change in carbonate dissolution and carbonate alkalinity fluxes

alteration of the oceanic crust implications for geochemical cycles of lithium and boron abstract fresh tholeiitic basalt glass has been reacted with seawater at 150 c water rock mass ratio of 10 and fresh diabase has been reacted with a na k ca cl fluid at 375 c water rock mass ratios of 1 2 and 5 to understand better the role of temperature basalt composition and water rock mass ratio on the direction and magnitude of b and li exchange during basalt alteration at 150 c slight but nevertheless significant amounts of b and li were removed from seawater and incorporated into a dominantly smectite alteration phase at 375 c however b and li were leached from basalt b behaved as a soluble element and attained concentrations in solution limited only by the b concentration in basalt and the water rock mass ratio li however was less mobile for example at water rock mass ratios of 1 2 and 5 the percent of li leached from basalt was 58 70 and 92 respectively this suggests some mineralogic control on li mobility during hydrothermal alteration of basalt especially at low water rock mass ratios in general these results as well as those for b are consistent with the temperature dependent chemistry of altered seafloor basalt and the chemistry of ridge crest hydrothermal fluids based on the distribution and chemistry of products of seafloor weathering low 150 c and high temperature hydrothermal alteration of basalt and the chemistry of ridge crest hydrothermal fluids it was estimated that alteration of the oceanic crust is a li source for seawater this is not true for b however since the hot spring flux estimated for b is balanced by low temperature basalt alteration these data coupled with b and li flux estimates for other processes e g continental weathering clay mineral adsorption authigenic silicate formation and formation of siliceous skeletal material yield new insight into the b and li geochemical cycles calculations performed here indicate relatively good agreement between the magnitude of b and li sources and sinks the geochemical cycle of b however may be affected by serpentinization of mantle derived peridotite in oceanic fracture zones serpentinites are conspicuously enriched in b and if the b source for these rocks is seawater then an additional b sink exists which must be integrated into the b geochemical cycle however until more data are available in terms of areal extent of serpentinization serpentite chemistry and isotopic composition the importance of b in these rocks with respect to the b geochemical cycle remains speculative at best

time evolution of the subauroral electric fields a case study during a sequence of two substorms 1 the temporal evolution of the subauroral polarization stream saps is investigated using the doppler velocity observations by the unwin hf radar in conjunction with the simultaneously observed auroral luminosity and plasma convection reversal regions the event under study of 14 december 2004 1000 1600 ut occurred during geomagnetically quiet conditions when a sequence of two substorms separated by 2 hours was observed by the image satellite it is shown that the saps appeared shortly after the first substorm onset and continued to dominate the westward plasma convection at subauroral magnetic latitudes 59 63 s for 6 hours an unexpected exception occurred near the second substorm onset time when a narrow channel of weaker saps westward convection became embedded in the slow eastward drifting plasma for a short 25 min period which was attributed to the equatorward expansion of the dawn convection cell during the growth and expansion phases of the second substorm another remarkable plasma convection feature was observed in the same 25 min period 5 poleward of saps this was a narrow mirror channel of the eastward drifting plasma parallel to the main saps channel it is argued that the latter feature may also be caused by the equatorward expanding dawn convection cell whose streamlines become compressed by and aligned with the saps poleward edge a possible relationship between the saps intensity and its position relative to the auroral oval is also investigated the results suggest that the magnetosphere ionosphere feedback processes within saps become more effective as the equatorward edge of the eastward convection region retreats poleward with the saps position much less affected by the auroral dynamics

modeling of subsurface calcite dissolution including the respiration and reoxidation processes of marine sediments in the region of equatorial upwelling off gabon abstract mineralization of organic matter and the subsequent dissolution of calcite were simulated for surface sediments of the upper continental slope off gabon by using microsensors to measure o2 ph pco2 and ca2 in situ pore water concentration profiles of no3 nh4 fe2 and mn2 and so42 ex situ as well as sulfate reduction rates derived from incubation experiments the transport and reaction model cotrem was used to simulate the degradation of organic matter by o2 no3 fe oh 3 and so42 reoxidation reactions involving fe2 and mn2 and precipitation of fes model application revealed an overall rate of organic matter mineralization amounting to 50 mol c cm 2 yr 1 of which 77 were due to o2 17 to no3 and 3 to fe oh 3 and 3 to so42 the best fit for the ph profile was achieved by adapting three different dissolution rate constants of calcite ranging between 0 01 and 0 5 d 1 and accounting for different calcite phases in the sediment a reaction order of 4 5 was assumed in the kinetic rate law a caco3 flux to the sediment was estimated to occur at a rate of 42 g m 2 yr 1 in the area of equatorial upwelling the model predicts a redissolution flux of calcite amounting to 36 g m 2 yr 1 thus indicating that 90 of the calcite flux to the sediment is redissolved

quantifying fluid flow solute mixing and biogeochemical turnover at cold vents of the eastern aleutian subduction zone in situ oxygen fluxes were measured at vent sites in the aleutian trench at a water depth of almost 5000 m using a tv guided benthic flux chamber the flux was 2 orders of magnitude greater than benthic oxygen fluxes in areas unaffected by venting on the continental margin off alaska porewater profiles taken from the surface sediment below a vent site showed high concentrations of sulfide methane and ammonia the reduced carbon and nitrogen compounds are transported to the vent site by fluids expelled from deeper anoxic sediment layers by the forces of plate convergence the tectonically driven fluid flow was determined from the biochemical turnover in vent communities and was found to be 3 4 0 5 m yr 1 a model was used to quantify the transport of silica ca2 and sulfate via diffusion advection and bioirrigation through the surface sediments of a vent site a nonlocal mixing coefficient of 20 30 yr 1 was determined by fitting the model curves to the measured porewater profiles showing that the transport of solutes within the near surface sediments and across the sediment water interface is dominated by the activity of the vent fauna sulfate containing oceanic bottom water and methane rich vent fluids were mixed below the clam colony to produce sulfide and a caco3 precipitate the vent biota shape their immediate environment and control the sediment water exchange and the benthic fluxes at vent sites the oxygen consumption at vent sites is a major sink for oxygen at the study area

the oxygen and carbon isotope distribution in the mediterranean water masses abstract the oxygen and carbon stable isotope compositions of the present day mediterranean waters have been measured in order to evaluate their variability which is related to the specific climatic and hydrological conditions within the basin the experimental equation between the 18 o value and the salinity of water based on 300 measurements on surface intermediate and deep waters sampled during the vicomed 2 and 3 cruises in the western central and eastern mediterranean has a slope of 0 27 a value which is significantly lower than the slope of 0 45 as defined in the northeast atlantic ocean this difference in the 18 o salinity relationship which occurs immediately in the alboran basin is basically a characteristic of the climatic regime of the mediterranean i e of an excess evaporation over fresh water input the largest variations of these two parameters 18 o of water and 13 c of co 2 are observed in the surface waters mostly in the western mediterranean this evolution mirrors the progressive eastward restriction which separates the less evaporated and more productive western basins from the more evaporated and less productive eastern basins the intermediate waters constitute a homogeneous layer however their 18 o values decrease eastward by 0 35 at maximum due to progressive dilution by mixing with overlying and underlying water masses their 13 c values decrease also eastward by 0 35 at maximum due to an increasing input of nutrients issued from the regeneration of sinking organic particles the deep waters have similar 18 o values but slightly higher 13 c values often by less than 0 1 than the overlying intermediate waters indicating generally well ventilated conditions due to active winter convection

lithium isotope geochemistry of pore waters from ocean drilling program sites 918 and 919 irminger basin the distribution of li isotopes in pore waters to a depth of 1157 m below seafloor is presented for odp sites 918 and 919 in the irminger basin offshore greenland lithium isotope data are accompanied by strontium isotope ratios to decipher diagenetic reactions in the sediments which are characterized by the pervasive presence of volcanic material as well as by very high accumulation rates in the upper section the lowering of the 87sr 86sr ratio below contemporaneous seawater values indicates several zones of volcanic material alteration the li isotope profiles are complex suggesting a variety of exchange reactions with the solid phases these include cation exchange with nh4 and mobilization from sediments at depth in addition to the alteration of volcanic matter lithium isotopes are therefore a sensitive indicator of sediment water interaction 6li values of pore waters at these two sites vary between 42 and 25 at shallow depths 100 mbsf rapid decreases in the li concentration accompanied by a shift to heavier isotopic compositions indicate uptake of li into alteration products a positive anomaly of 6li observed at both sites is coincident with the nh4 maximum produced by organic matter decomposition and may be related to ion exchange of li from the sediments by nh4 in the lower sediment column at site 918 dissolved li increases with depth and is characterized by enrichment of 6li the li isotopic compositions of both the waters and the solid phase suggest that the enrichment of li in deep interstitial waters is a result of release from pelagic sediments the significance of sediment diagenesis and adsorption as sinks of oceanic li is evaluated the maximum diffusive flux into the sediment due to volcanic matter alteration can be no more than 5 of the combined inputs from rivers and submarine hydrothermal solutions adsorption on to sediments can only account for 5 10 of the total inputs from rivers and submarine hot springs