development of a modified sedex phosphorus speciation method for ancient rocks and modern iron rich sediments abstract we report the development of a modified method for evaluating different reservoirs of sedimentary phosphorus p in ancient marine sedimentary rocks and in modern fe rich sediments utilising the existing sedex scheme for p partitioning in modern sediments we initially demonstrate limitations in the application of the original scheme to sediments and rocks containing crystalline hematite and magnetite we tested additional extractions for these crystalline fe phases using both synthetic minerals and modern and ancient sediments the addition of 6 h oxalate and 6 h citrate dithionate acetate extractions considerably enhanced the total recovery of synthetic magnetite and hematite to 88 7 1 1 and 76 9 3 8 respectively in addition application of the 6 h oxalate extraction to synthetic p containing magnetite recovered 93 9 1 7 of the fe present and 88 2 12 8 of the co precipitated p based upon these results we developed a modified sedex extraction scheme the modified scheme was applied to modern fe rich sediments from golfo dulce costa rica which resulted in 16 higher fe bound p recovery application of the scheme to a variety of ancient marine rocks increased the recovery of fe bound p by up to 22 we also highlight the potential for authigenic carbonate fluorapatite to convert to more crystalline apatite in ancient rocks during deep burial and metamorphism we suggest that in such systems minimum and maximum estimates of the total reactive p pool may be calculated with and without the inclusion of crystalline p it is noted that the application of the revised method may have important implications for understanding the cycling of p in ancient marine environments

particulate organic carbon fluxes to the ocean interior and factors controlling the biological pump a synthesis of global sediment trap programs since 1983 particulate organic carbon poc is vertically transported to the oceanic interior by aggregates and their ballasts mainly caco3 and biogenic opal with a smaller role for lithogenic aerosols through the mesopelagic zone diel migrating zooplankton communities effect vertical transport and remineralization of poc in the upper layers of the ocean below 1 5 km the presence of zooplankton is reduced and thus the aggregates travel mainly by gravitational transport we normalized the fluxes of poc caco3 and biogenic opal from data published on samples collected at 134 globally distributed bottom tethered time series sediment trap ts trap stations to annual mole fluxes at the mesopelagic bathypelagic boundary m b at 2 km and defined them as fm bcorg fm bcinorg and fm bsibio using this global data set we investigated 1 the geographic contrasts of poc export at m b and 2 the supply rate of co2 to the world mesopelagic water column fm bcorg varies from 25 pacific warm pool to 605 divergent arabian sea mmolc m 2 yr 1 fm bcinorg varies from 8 high latitude polar oceans or 15 pacific warm pool to 459 divergent arabian sea mmolc m 2 yr 1 and fm bsibio the most spatially temporally variable flux ranges from 6 north atlantic drift to 1118 pacific subarctic gyre mmolsi m 2 yr 1 the oceanic region exhibiting the highest poc flux over a significantly large region is the area of the north pacific boreal gyres where the average fm bcorg 213 fm bcinorg 126 and fm bsibio 578 mmol m 2 yr 1 fm bcorg and fm bcinorg are particularly high in large upwelling margins including the divergent arabian sea and off cape verde one of the data sets showing the lowest flux over a significant region basin is fm bcorg 39 fm bcinorg 69 and fm bsibio 22 mmol m 2 yr 1 in the north pacific subtropical tropical gyres pan atlantic average fluxes are similar except fm bsibio fluxes are even lower where corg cinorg and sibio cinorg are 1 defines the carbonate ocean and where these ratios are 1 defines the silica ocean the carbonate ocean occupies about 80 of the present world pelagic ocean between the two major oceanographic fronts the north pacific polar front and the antarctic polar front and the silica ocean is found on the polar sides of these fronts the total global annual fluxes of fm bcorg fm bcinorg and fm bsibio at m b calculated by parameterizations of the export flux data from 134 stations are surprisingly similar 36 2 33 8 and 34 6 teramol yr 1 120 112 and 114 mmol m 2 yr 1 respectively resulting in a near uniform binary ratio between the above three elements of about one the global ternary ratios estimated from 152 ts trap samples of the three elements are 35 32 33 from our global fm bcorg and a published model estimate of the global export production we estimate the regeneration rate of co2 through the mesopelagic zone by the biological pump is 441 teramolc yr 1 based on our global fm bcinorg and recently estimated global primary production of pic 36 86 teramolc yr 1 of pic is assumed to be dissolved within the upper 2 km of the water column

the influence of pore water advection benthic photosynthesis and respiration on calcium carbonate dynamics in reef sands to investigate diel calcium carbonate caco3 dynamics in permeable coral reef sands we measured porewater profiles and fluxes of oxygen o2 nutrients ph calcium ca2 and alkalinity ta across the sediment water interface in sands of different permeability at heron reef australia background flushing rates were high most likely as a result of infaunal burrow irrigation but flux chamber stirring enhanced pore water exchange light and pore water advection fueled high rates of benthic primary production and calcification in sunlit surface sediments in the light benthic photosynthesis and calcification induced surface minima in ca2 and ta and peaks in ph and o2 oxygen penetration depth in coarse sands decreased from 1 2 cm during the day to 0 6 cm at night total oxygen uptake tou in dark chambers was three to fourteen times greater than diffusive uptake and showed a direct effect of pore water advection greater sediment oxygen consumption rates were observed in higher permeability sands in the dark ta release was not stimulated by increasing tou because of a damping effect of pore water advection on metabolic caco3 dissolution efficiency on a daily basis caco3 undergoes net dissolution in heron reef sands however pore water advection can reverse the caco3 budget and promote caco3 preservation under the most energetic conditions

release of dissolved organic carbon doc from sediments of the n w european continental margin goban spur and its significance for benthic carbon cycling abstract pore water samples from n w european continental margin sediments 49 48 n 16 10 w were analyzed for dissolved organic carbon doc using a high temperature combustion method two transects across the margin were investigated a gentle undisturbed slope goban spur 670 4800 m and the centre of a nearby precipitous canyon whittard canyon 180 3680 m concentrations of pore water doc were typically an order of magnitude greater than those from the overlying water therefore the sediments appear to act as a doc source to the bottom water conservative estimates ignoring possible bioirrigation of the doc fluxes from the sediments gave daily fluxes of 0 09 0 15 mmol m 2 d 1 for the goban spur sediments and 0 05 0 16 mmol m 2 d 1 at the canyon transect these relatively low variations in doc concentrations and fluxes under widely differing environmental conditions suggest that production and consumption of labile doc components proceed at similar rates irrespective of what the overall benthic activity is to the total benthic degradation rate of organic carbon the doc fluxes contribute 2 32 median 11 a part that is missing when the carbon degradation rate is solely based on determinations of the oxygen consumption rate or on pore water modeling of the reaction thus doc effluxes are a significant component of benthic carbon budgets in continental margin sediments

recent increase in pacific caco3 dissolution a mechanism for generating old 14c ages abstract western equatorial pacific box cores taken from water depths greater than 4 km show increased dissolution and anomalously old 14c ages in the upper 8 cm the temporal response of the vertical distribution of sediment carbonate fraction and 14c age to a decrease in the dissolved carbonate ion concentration of the deep sea is examined with a diffusion advection dissolution model the nature of this response is highly sensitive to both the magnitude of the dissolved carbonate ion decrease and the rate of mixing of the upper few centimeters of sediment if the sediment is initially calcareous and the increase in undersaturation is sufficient to eventually dissolve away most of the solid carbonate the system relaxes on a very long time scale greater than 10 000 years the dissolution flux in such a case temporally is greater than the total sedimentation input and chemical erosion occurs the cumulative erosion is about 4 times greater for strong sediment mixing d 200 cm 2 ka 1 than for weak mixing d 2 cm2 ka 1 the chemical erosion causes old carbonate to be transferred into the sediment mixed layer as the interface moves downwards thus the 14 c 12 c ratio initially decreases when erosion decreases because the surface carbonate content is diminished the 14c age of the sediment continues to become older in the case of weak mixing but reverses itself and becomes younger in the presence of moderate or strong mixing an attempt to predict the observed caco3 and 14 c 12 c in west equatorial pacific sediment suggests that beginning a few thousand years ago the deep pacific was 20 more undersaturated than today for about 1500 yrs this could possibly have been caused by late holocene growth of coral reefs following after the deglaciation

the variability of benthic fluxes and sedimentary remineralization rates in response to seasonally variable organic carbon rain rates in the deep sea a modeling study

the influence of organic matter diagenesis on caco3 dissolution at the deep sea floor abstract in situ benthic flux chamber measurements were performed at seafloor locations in the atlantic and pacific oceans where the bottomwaters were supersaturated approximately saturated and undersaturated with respect to calcite there was no evidence of significant dissolution at or above the saturation horizon below the saturation horizon however significant benthic fluxes of titration alkalinity and calcium out of the sediments were observed indicating appreciable dissolution where observed the rate of dissolution is consistent with a rate expression of reaction order 4 5 and a rate constant in the range of 0 05 to 0 5 per day a numerical simulation was constructed to represent organic matter and caco3 diagenesis at the seafloor at the supersaturated and near saturation sites the model over predicts the influence of metabolically produced co2 on the extent of caco3 dissolution it is possible that these results can be reconciled by a better understanding and parameterization of organic matter mineralization and porewater transport processes in surface sediments the primary factors to be considered include 1 the oxidation state of the carbon being oxidized 2 the vertical distribution of oxidation rates including the role of doc in sediment remineralization 3 the influence of nondiffusive transport of near surface porewaters and 4 the influence of episodic depositional events on organic and inorganic carbon cycling

benthic recycling of biogenic debris in the eastern tropical atlantic ocean abstract distributions of pore water o2 no 2 no 3 nh 4 si oh 4 po3 4 mn2 f and t a were determined at 15 stations in the eastern equatorial atlantic while overall profile characteristics are consistent with previous models of organic matter diagenesis profile shapes suggest that a deep reaction layer rich in organic c is also present at many sites while it is unlikely that the oxidation of organic c in this layer has had a major effect on the ocean c cycle pore water profile shapes are significantly altered despite exposure to seawater so2 4 concentrations for 1000 years decomposition of the organic matter in the layer appears to be restricted to oxic and suboxic processes these results suggest major differences in organic carbon decomposition and preservation under oxic suboxic and anoxic conditions present day benthic fluxes are largest adjacent to the eastern boundary coastal upwelling region and similar in magnitude to values reported for the eastern pacific preliminary estimates suggest that the benthic respiration in the eastern 1 3 of the north atlantic south of 20 n may alone account for 20 of the total deep north atlantic respiration combining these results with estimates of organic c burial and deep water column decomposition suggests that this region is a major location of organic c input into the deep sea

dissolved organic matter in abyssal sediments core recovery artifacts we report measurements of pore water dissolved organic carbon doc dissolved organic nitrogen total dissolved carbohydrates dissolved free monosaccharides and ammonium in recovered deep sea sediments from the porcupine abyssal plain pap northeast atlantic there were distinct maxima close to the sediment water interface of these constituents at all times of the year the very high diffusive effluxes calculated from these porewater distributions were not compatible with simultaneous sediment trap measurements of particulate organic carbon nitrogen and carbohydrate fluxes toward the seafloor effluxes calculated from pore water doc distributions in recovered cores from another atlantic deep sea site showing almost identical maxima as those at pap were more than an order of magnitude greater than simultaneous in situ chamber doc flux measurements we suggest that the dissolved organic matter maxima are predominantly artifacts induced by lysis of or leakage from mainly bacterial biomass resulting from decompression and or warming during recovery of the sediment cores from the abyssal seafloor temperature elevation during core recovery from the abyss gives a n2 saturation of about 150 and the combined effect of warming and decompression results in a co2 saturation of about 135 which together plausibly are associated with bubble formation creating cell bursting previous estimates of microbial biomass in abyssal sediments may be underestimates because of the difficulty of counting lysed bacterial cells since exoenzymes are inducible previous measurements of their activities in recovered abyssal sediments may be overestimates

the global ocean flux of particulate organic carbon areal distribution and magnitude the magnitude and distribution of the particulate organic carbon poc rain rate to the seafloor in the atlantic pacific and indian ocean basins between 61 n and 61 s has been estimated from benthic oxygen flux estimates for water depths 1000 m only the calculation utilizes the extensive data sets of sedimentary organic carbon caco3 and accumulation rate to extrapolate between individual benthic flux measurement sites using an empirically derived correlation between the seafloor oxygen flux and these parameters the poc flux through the 1000 m depth horizon was then estimated from published correlations between sediment trap determined fluxes and water depth total oxygen utilization in the deep ocean is estimated to be 1 2 1014 mol o2 yr 1 a value that agrees well with previous estimates which were based on surface water primary productivity sediment trap and depth relationships and with deep water respiration rates estimated from apparant oxygen utilization aou 14c relationships on the basis of the derived global ocean flux distribution it is concluded that 1 dissolved organic carbon doc inputs are not required to account for estimated deep water respiration rates 2 the majority of the poc input to the deep ocean occurs within 30 of the equator 3 the proportion of primary production that reaches the deep sea does not vary greatly with latitude 4 gyre and continental margin regions contribute roughly equally to the deep poc flux with a relatively minor contribution from the equatorial divergence region 5 of the estimated 7 2 1013 mol c yr 1 of poc that sinks below the 1000 m depth horizon 45 3 3 1013 mol c yr 1 reaches the seafloor where it is oxidized 6 when normalized to basin area average deep flux rates in the atlantic and pacific are similar while highest rates are observed in the indian ocean and 7 the results can be fully reconciled only if the benthic flux of doc is significantly less than the benthic o2 flux

dissolution of calcite in deep sea sediments ph and o2 microelectrode results abstract we present microelectrode profiles of oxygen ph and porosity measured at in situ depth across the sediment water interface from stations above and below the calcite saturation horizon in the equatorial atlantic resistivity electrode data indicate that the diffusion coefficient for solutes is attenuated by nearly a factor of two within the top centimeter of the sediment lattice oxygen and porosity data are used to estimate that the organic carbon respiration rate of the sediment is 10 15 mol cm 2 yr 1 in these locations comparison of the ph data with numerical model results reveals that sedimentary calcite dissolves in response to respiration in the top few centimeters of sediment even above the saturation horizon we calculate that the effective in situ dissolution rate constant for calcite required to explain these data is the neighborhood of 10 100 d 1 although more data are needed to confirm this result it appears to be at least an order of magnitude less than the rate observed in laboratory stirred reactor experiments

triggering of tremor and inferred slow slip by small earthquakes at the nankai subduction zone in southwest japan the correlation of earthquakes with tremor and slow slip has not been clearly quantified we investigate 12 year earthquake and tremor catalogs for southwest japan and find that nearby small intraslab earthquakes are weakly correlated with tremor in particular the intraslab earthquakes with magnitudes 2 7 tend to be followed by tremor more often than expected at random by a factor of 2 to 6 the excess number of tremor before earthquakes is not as significant although marginally more than expected the underlying physical mechanism of the observed triggering of tremor and inferred slow slip by earthquakes is most likely to be the dynamic stress changes several to several tens of kilopascals rather than the much smaller static stress changes the rate of triggering of tremor by earthquakes is similar to although somewhat lower than rates observed for similar amplitude stress changes due to the lower frequency teleseismic surface waves and tidal stressing

presence of oxygen and aerobic communities from sea floor to basement in deep sea sediments the depth of oxygen penetration and microbial activity in marine sediments varies by region sediment cores from the south pacific gyre host oxygen and aerobic microbial communities to at least 75 metres below the sea floor

the influence of the sw monsoon on the deep sea organic carbon cycle in the holocene abstract results from long term sediment trap experiments carried out since 1986 in the western central and eastern arabian sea are combined with satellite derived wind fields and paleoceanographic information to link the intensity of the sw monsoon to organic carbon fluxes and its preservation in sediments the sw monsoon is characterized by the low level jet findlater jet that crosses the arabian sea almost parallel to the arabian coast the intensity of the findlater jet mainly controls the velocities of upwelling that occurs to the northeast of the jet since up welling in turn mainly governs the organic carbon fluxes in the western arabian sea variation in the strength of the findlater jet is the dominant factor determining the organic carbon fluxes on seasonal time scales changes in the subsurface nutrient concentrations due to variations in the surface ocean current systems seem to be another factor influencing the organic carbon fluxes mostly on interannual time scales the translation of sedimentary organic carbon burial rates into organic carbon fluxes according to jahnke 1996 global biogeochemical cycles 10 71 88 allows us to extend our reflections also to a millennium time scale this indicates that changes in the sw monsoon intensity as observed during the last decade could almost account for the range of organic carbon fluxes deciphered from the holocene record

sedimentation and formation of secondary minerals in the hypersaline discovery basin eastern mediterranean two cores recovered from the discovery basin and one reference core from a location outside the basin were investigated in detail in order to decipher the influence of hypersaline brines on sediment geochemistry the cores contain a tephra layer presumable y 5 and carbonate microfossils which permit a tentative chrono and lithostratigraphic correlation a layer containing up to 60 wt biogenic opal and 6 6 wt organic carbon was identified in one basin core which probably represents the best preserved example of eastern mediterranean sapropel s 1 the basin is filled with a concentrated solution of mgcl2 which is enriched in dissolved sulfate and has the highest salinity ever encountered in the marine environment pore water profiles demonstrate that this brine dissolves sedimentary calcite to form secondary carbonate and sulfate bearing minerals of these dolomite magnesite and gypsum were identified by x ray diffractometry thermodynamic calculations show that these phases form in equilibrium with the anomalous brine composition

bioturbation and holocene sediment accumulation fluxes in the north east atlantic ocean benthic boundary layer experiment sites bioturbation and holocene sediment accumulation are quantified in the three experimental areas of the benthic boundary layer benbo programme by means of the natural radionuclides 14c and 210pb and the artificial radionuclides 137cs and 241am the holocene accumulation rates determined by the radiocarbon method are 4 4 and 6 5 cm kyr 1 at sites b rockall plateau 1100 m water depth and c feni drift 1925 m water depth respectively accumulation at site a situated between feni drift and porcupine bank at 3570 m water depth was interrupted by an erosional event in the mid holocene which removed 0 25 m or more of the uppermost sediment present at that time the estimated accumulation rate since that event is 2 1 cm kyr 1 different estimates of surficial bioturbation mixing depths at site b are returned by the 210pbexcess and 14c methods with the former indicating 10 cm and the latter unusually deep at 17 cm at site c 210pbexcess and the fallout radionuclides 137cs and 241am are present in two distinctly separated depth zones with the deepest mixing down to 15 cm similar to the 14c mixed layer depth this is ascribed to deep burrowing by sipunculid or echiuran worms at site c and similar deep mixing is inferred to be necessary at site b to produce the differences in mixed layer depths derived from the longer and shorter lived radionuclide profiles although the deep burrowing episodes must be rare 1 event per 102 yr the greater accumulation rate at site c compared with site b is produced by an enhanced flux of current driven clay and silt sized material this fine material both dilutes the caco3 content of the site c sediment and is responsible for the higher corg content observed at site c compared with site b unlike the site b and c sediments which are fine grained the coarse 63 125 m size fraction is the most abundant size class in the late holocene sediments at site a suggesting that the sediments at this location are winnowed

factors controlling the flux of organic carbon to the bathypelagic zone of the ocean 1 particle fluxes measured with time series sediment traps deployed below 2000 m at 68 sites in the world ocean are combined with satellite derived estimates of export production from the overlying water to assess the factors affecting the transfer of particulate organic matter from surface to deep water multiple linear regression is used to derive an algorithm suggesting that the transfer efficiency of organic carbon defined as the settling flux of organic carbon normalized to export production increases with the flux of carbonate and decreases with water depth and seasonality the algorithm predicts 80 of the organic carbon transfer efficiency variability in diverse oceanic regions the influence of the carbonate flux suggests that the ballasting effect of this biogenic mineral may be an important factor promoting export of organic carbon to the deep sea by increasing the density of settling particles however the lack of a similar effect for biogenic opal suggests that factors other than particle density also play a role the adverse effect of increasing seasonality on the transfer efficiency of carbon to the deep sea is tentatively attributed to greater biodegradability of organic matter exported during bloom events in high latitude opal dominated regions with high f ratios and seasonality while a higher fraction of net production is exported a higher fraction of the exported organic matter is remineralized before reaching bathypelagic depths on the other hand in warm low latitude carbonate dominated regions with low f ratios and seasonality a higher fraction of the exported organic matter sinks to the deep sea

shallow remineralization in the weddell gyre 1 the region influenced by the polar front in the southern ocean is characterized by relatively high productivity which is mirrored in strong depletions of 234th in the surface water a good tracer of export production and by high accumulation rates on the underlying seabed farther south the weddell sea is generally considered a low productivity region with very low export fluxes this finding is based on satellite observations sediment accumulation rates trap deployments and phytoplankton distribution if this would be true 234th should be close to equilibrium with its parent however in a series of high resolution transects of 234th 238u across the antarctic circumpolar current acc 234th was found to be depleted by 10 15 throughout the clear weddell gyre only to reach equilibrium in sea ice covered regions of the coastal zone vertical profiles showed that the depletion was limited to the upper mixed layer and was balanced by an enrichment of similar magnitude at 100 250m depth this implies that the export of particles below 250 m is negligible such shallow remineralization is in line with the discrepancies between biogenic silica production rates and sediment trap data observed in the weddell and ross seas these observations in the weddell sea are fully consistent with our inverse modeling results for both organic carbon and opal and they are not inconsistent with tco2 and oxygen sections that show a tco2 enriched oxygen reduced shallow subsurface layer this blue ocean characterized by upwelling of co2 enriched deep waters supports sufficient productivity to be a net sink for co2 to abyssal depths hoppema et al 1999 no record of this productivity and export is stored in the underlying sediment which has important palaeoceanographic consequences

downhole magnetostratigraphy in sediments comparison with the paleomagnetism of a core the magnetostratigraphy of weakly magnetized sediments is determined for the first time from direct downhole measurements experimental results were obtained in both scientific and oil exploration drillholes penetrating jurassic sediments of the paris basin france the magnetic polarity of the remanence is deduced from the total magnetic induction combined with the magnetic susceptibility the magnetic induction is measured in depth by a proton precession magnetometer with overhauser effect designed by the laboratoire d electonique de technologie et instrumentation commissariat a i energie atomique this method gives a continuous record with an accuracy of 0 1 nt and an excellent stability in order to cancel out the transient component of the earth s magnetic field the magnetic induction is computed as the difference between the induction measured in the borehole and that obtained at a surface reference point located near the drillhole the dipole dipole susceptibility probe gives a continuous record with an accuracy of a few 10 6 the four total magnetic induction logs recorded in oil exploration holes show a tight correlation although distant from up to 80 km this technique is therefore excellent for precise stratigraphic correlation data processing allows us to isolate the component of induction due to remanent magnetization and to find the magnetic polarity a sequence of magnetic polarity is proposed for kimmeridgian and oxfordian stages the variation of the sedimentation rate is analyzed with a very high resolution in time and compared with the mean sedimentation rate deduced from a lithologic log cores were collected in the lowermost part of two holes the correlation between the magnetostratigraphy deduced from paleomagnetic measurements performed on 240 standard plugs and that obtained by logging is good a study of the components of magnetization found in the core has shown that the remagnetization occurred mainly during the coring operation itself or during the storage of the core consequently downhole magnetostratigraphy proves to be reliable besides providing the advantage of a continuous investigation performed over a large volume of rock scrutinized in situ

benthic fluxes and pore water studies from sediments of the central equatorial north pacific nutrient diagenesis benthic exchange rates of radon 222 oxygen nitrate ammonia and silica were determined using an in situ benthic flux chamber and by modeling pore water profiles at three sites in the central equatorial north pacific a comparison of these results reveals several artifacts of pore water collection and processing whole core squeezer wcs silica profiles are influenced by adsorption during squeezing and yield calculated fluxes that are too large pore water ammonia profiles show near surface maxima that appear to be an artifact of core recovery near surface nitrate measurements may also be suspect due to oxidation of the ammonia released causing anomalously large nitrate gradients that yield overestimates of benthic exchange rates fluxes of radon oxygen and nitrate calculated from wcs profiles agree with chamber fluxes to better than 40 at all sites fluxes of silica and nitrate calculated from pore water data collected at coarser scales 1 cm intervals agree within 50 with chamber measurements previous flux estimates from pore water and solid phase models established at two of these sites using data collected 6 years prior to this work differ from these chamber measurements in some cases by up to a factor of 5 due to modeling uncertainties and temporal variabilities in the delivery of organic matter to a site the benthic oxygen consumption rates measured at these sites are similar they average 0 36 0 03 mmol m 2 day 1 and are consistent with a trend of oxygen uptake vs water depth previously established by others on a transect through the oligotrophic north pacific gyre

isotopic fractionation of oxygen and nitrogen in coastal marine sediments abstract the bulk and isotopic exchanges of o2 n2 no3 and nh4 between sediments and the overlying water benthic flux were measured at three shallow locations in puget sound using a benthic tripod oxygen consumption by the sediments averaged 4 4 mmol m 2 d 1 while n2 gas fluxes averaged 1 1 mmol m 2 d 1 the nitrogen gas flux out of the sediments was always greater than the corresponding no3 flux into the sediments indicating a large nitrification contribution to the n2 flux isotopic changes in overlying water 18o of o2 were small with an average apparent sediment respiration fractionation factor e of 3 this fractionation factor is much smaller than that measured in either the open ocean or in the laboratory the low degree of fractionation is hypothesized to occur because of the interaction of diffusive layers around reactive microsites within these sediments there was no apparent isotopic fractionation of downward diffusing no3 e 0 while the ammonium that diffused out of the sediments averaged 4 5 o heavier than both source organic matter within the sediments and overlying water no3 the large discrepancy in isotopic composition between the source organic material and nh4 can be attributed to significant isotopic fractionation of ammonium during nitrification in the oxic zone finally the 15n of n2 did not change significantly over the course of the incubations in agreement with the nitrogen isotopic budget for these sediments

widespread influence of resuspended sediments on oceanic particulate organic carbon insights from radiocarbon and aluminum contents in sinking particles globally widespread also a strong correlation is found to exist between d 14 c values of organic carbon and aluminum content in sinking particles that is consistent over a range of oceanic settings together these findings imply that aged organic carbon associated with lithogenic material from sediment resuspension is responsible for the observed low d 14 c values as opposed to other processes such as incorporation of dissolved inorganic carbon or dissolvedorganiccarbonintopocatdepth anestimatebasedonpocflux weightedd 14 c values shows that about 35 of sinking poc at the locations studied is derived from resuspended sediment our results suggest that resuspension of sediment and its subsequent lateral transport is an important component of the oceanic carbon cycle and should be considered in models of oceanic carbon export and burial

the influence of caco3 dissolution on core top radiocarbon ages for deep sea sediments radiocarbon ages on caco3 from deep sea cores offer constraints on the nature of the caco3 dissolution process the idea is that the toll taken by dissolution on grains within the core top bioturbation zone should be in proportion to their time of residence in this zone if so dissolution would shift the mass distribution in favor of younger grains thereby reducing the mean radiocarbon age for the grain ensemble we have searched in vain for evidence supporting the existence of such an age reduction instead we find that for water depths of more than 4 km in the tropical pacific the radiocarbon age increases with the extent of dissolution we can find no satisfactory steady state explanation and are forced to conclude that this increase must be the result of chemical erosion the idea is that during the holocene the rate of dissolution of caco3 has exceeded the rain rate of caco3 in this circumstance bioturbation exhumes caco3 from the underlying glacial sediment and mixes it with caco3 raining from the sea surface