oxygen and carbon isotope record of east pacific core v19 30 implications for the formation of deep water in the late pleistocene north atlantic abstract a detailed oxygen and carbon isotope record has been obtained from benthic foraminifera in core v19 30 from the carnegie ridge on the south side of the panama basin expressing these records and the oxygen and carbon isotope records previously published for atlantic core m 12392 on a common timescale it is apparent that the oxygen isotope records are very similar but that the carbon isotope records are quite different by obtaining the carbon isotope gradient between the two sites as a function of time we show that the production of north atlantic deep water has varied over a wide range during the late pleistocene and that the pattern of variation is not simply related to the well known oxygen isotope record although the two oxygen isotope records are very similar changes in the interoceanic gradient are detectable and support the hypothesis that in the glacial mode the north atlantic was colder and less oxygenated than it is today shackleton s 1 1977 interpretation whereby the carbon isotope record from the atlantic core reflects changes in the terrestrial biomass is an over simplification however the record from the pacific core v19 30 probably can be explained in these terms since it probably approximates the carbon isotope record of global mean oceanic dissolved co 2

return of the coral reef hypothesis basin to shelf partitioning of caco3 and its effect on atmospheric co2 differences in the rate of coral reef carbonate deposition from the pleistocene to the holocene may account for the quaternary variation of atmospheric co sub 2 volumes of carbonate associated with holocene reefs require an average deposition rate of 2 0 times 10 sup 13 mol yr for the past 5 ka in light of combined riverine mid ocean ridge and ground water fluxes of calcium to the oceans of 2 3 times 10 sub 13 mol yr the current flux of calcium carbonate to pelagic sediments must be far below the pleistocene average of 1 2 times 10 sub 13 mol yr the authors suggest that sea level change shifts the locus of carbonate deposition from the deep sea to the shelves as the normal glacial interglacial pattern of deposition of quaternary global carbonates to assess the impact of these changes on atmospheric co sub 2 a simple numerical simulation of the global carbon cycle was developed atmospheric co sub 2 as well as calcite saturation depth and sediment responses to these carbonate deposition changes are examined atmospheric co sub 2 changes close to those observed in the vostok ice core approximately 80 ppm co sub 2 for the quaternary are observed as well as the approximate depth changes in percent carbonate of sediments measured in themore pacific ocean over the same time interval less

increased productivity in the eastern equatorial pacific during the last glacial maximum 19 000 to 14 000 yr b p a widespread pronounced enrichment in the organic carbon content occurs at shallow depths in eastern equatorial pacific sediments the c org peak is shown by radiocarbon dating to be temporally coincident with the last stage 2 or wisconsin glacial maximum in contrast caco 3 profiles show less overall variation which appears to be partly a function of the location of the sediments relative to the lysocline consideration of the iodine c org ratio in the sediments rules out enhanced preservation as a cause of the stage 2 organic carbon enrichment the peak instead must have resulted from a significant increase in productivity during the glacial maximum

changes in the c n p burial rates in some baltic sea sediments over the last 150 years relevance to p regeneration rates and the phosphorus cycle three major depositional basins the gdansk bornholm and eastern gotland basins of the baltic proper which together account for 50 of the depositional areas in the entire baltic sea have accumulated increased amounts of sediment and organic carbon during the last 50 years as is shown in 210 pb dated sediment cores the shallow arkona basin has had constant accumulation rates and rate increases of bulk sediment organic carbon and aluminium in the bornholm basin are parallel and are interpreted to reflect increased material input from land or from erosion of shallow water areas in the gdansk and eastern gotland basins the accumulation rates of mineral matter have risen at lower rates than those of organic carbon and point to preferential enrichment of organic matter at increasing rates of burial the material in the gdansk and eastern gotland basins appears to have been depleted in phosphorus relative to nitrogen and organic carbon using c n p ratios from a sediment trap mooring in the gotland basin and from fluffy layer material in the pomeranian bight as characteristic ratios for sedimenting material we find evidence for significant increases in the ratios of c to p in sediments younger than 15 25 years in cores from the eastern gotland basin coincident with h2s build up in deep waters paired oxygen and phosphorus concentration data from the sub halocline water column of the gotland basin covering the time since 1970 suggest that the phosphate reflux is fed from two sources at the transition from oxic to anoxic conditions iron bound phosphate is suddenly liberated at the sediment water interface and results in a concentration jump of approximately 2 mmol dm 23 phosphate in deep water during anoxic periods with h2s in bottom waters phosphate diffuses out of the sediment and adds to the dissolved phosphate pool our data imply that the sediment contributed approximately 14 000 t a 21 of phosphorus to the water column of the deep gotland basin since the early 1970s compared to total p input to the baltic sea 1993 39 000 t the reflux of p from anoxic sediments in the gotland basin thus is a major source of p for the baltic sea on time scales of years and decades the reflux of phosphorus from the sediments may be the reason for discrepancies between the ratios of nitrogen and phosphorus in the baltic sea and for a lack of effects of declining phosphate discharge into this large ecosystem q 2000 elsevier science b v all rights reserved

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

carbon to phosphorus ratios in sediments implications for nutrient cycling defining the transformations of phosphorus p in sediments is critical to assessing the geochemical behavior of sedimentary p and the behavior of reactive p preactive poxide associated pauthigenic porganic relative to organic carbon corganic this study includes the determination of p components and corganic concentrations on samples from sites in the california current region ocean drilling program odp leg 167 sites 1010 1011 1012 1014 1016 and 1021 in the benguela current region odp leg 175 sites 1082 1084 and 1085 and on blake nose in the western atlantic odp leg 17 1b sites 1050 and 1052 sample depths range up to 650 m and ages range up to 65 ma our data demonstrate the transformation of labile forms of p porganic and poxide associated to pauthigenic throughout the sediment column in all redox states and at all sedimentation rates investigated until a substantial portion of reactive p is in the authigenic form 80 c p organic ratios are always greater than or equal to the redfield ratio in all of the sediments we studied sediments with corganic concentrations 2 wt have corganic preactive ratios less than the redfield ratio and corganic preactive ratios increase linearly with corganic consistent with degradation of corganic with age in general corganic preactive ratios for sediments with corganic concentrations 2 wt from a variety of redox states and sedimentation rates center around the redfield ratio although some ratios are as high as 3 times the redfield ratio however corganic preactive ratios up to 400 do not approach the high ratios observed for c p organic ratios up to 4500 because of the efficient transfer of labile forms of p to pauthigenic corganic preactive ratios better describe the geochemical behavior of sedimentary p

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

carbon cycle in the coastal zone effects of global perturbations and change in the past three centuries abstract the coastal zone consisting of the continental shelves to 200 m including bays lagoons estuaries and near shore banks is an environment that is strongly affected by two much bigger environmental reservoirs adjacent to it the land and open ocean in the coastal zone as elsewhere in the earth system the biogeochemical cycle of carbon is coupled to and driven by the cycles of nitrogen and phosphorus through biological transfer processes human activities in the past 300 years have become an increasingly important geological factor with respect to the coastal zone through four major environmental perturbations 1 c n and s emissions from fossil fuel burning 2 changes in land use activities resulting in gaseous c emissions increased dissolved and particulate loads organic matter transport and feedbacks to biological production 3 application of inorganic nitrogen and phosphorus containing fertilizers and 4 discharges of sewage containing reactive organic c n and p in addition the mean global surface temperature of the planet has increased over this period of time by approximately 1 c perhaps also because of human activities starting with the year 1700 as a base for the industrial age perturbations on land we analyzed the consequences of these five perturbations to the carbon cycle in the coastal zone using the thirteen reservoir process driven model totem for the coupled c n p s biogeochemical cycles an indicator of the reliability of the model is the good agreement of its results showing the time course of increasing atmospheric co 2 concentrations since the year 1700 with the observational results reported in the literature during the past three centuries there has been a significant increase in the amount of organic carbon transported from land and stored in coastal zone sediments of the total transported about 65 was stored in sediments and the remaining 35 primarily recycled through exchange with the atmosphere and open ocean the imbalance between the amounts of organic carbon produced by gross photosynthesis and remineralized has apparently increased slightly in favor of remineralization corresponding to an increase in the degree of heterotrophy of the global coastal zone this process along with the release of co 2 from the formation of caco 3 counteracts the invasion of co 2 from the atmosphere to coastal waters that is driven by the rise in atmospheric co 2 concentrations an analysis of a possible reduction or full collapse of the oceanic thermohaline circulation as believed to have occurred in the past and a possibility for future centuries indicates that the co 2 transfer from the atmosphere to coastal waters would increase while that from the atmosphere to open ocean surface waters would decrease if such an event took place this is attributable to a reduced supply to the coastal zone of dissolved inorganic carbon by coastal upwelling from the deeper ocean a process linked to the global conveyor belt of the thermohaline circulation to date fossil fuel co 2 emissions to the atmosphere changes in land use practices and sewage discharges have been the three main factors affecting the carbon cycle in the global coastal zone the latter inputs from land have apparently produced a slight increase in the heterotrophy of the global coastal zone however increases in the inputs of nutrient nitrogen and phosphorus from land to the coastal zone in the future may drive its trophic state toward net production and storage autotrophy thereby also increasing its potential role as a sink for atmospheric co 2 the direction of future change in net ecosystem production in the coastal zone strongly depends on changes in the relative magnitudes of organic carbon and nutrient n and p fluxes to the coastal zone via rivers provided the upwelling fluxes remain constant

what do we learn from peaks of uranium and of manganese in deep sea sediments abstract uranium and manganese are two redox sensitive trace elements with complementary behavior under anoxic conditions u is immobile while reduced mn is dissolved in pore water of sediments uranium diffuses from sea water into reducing sediments and is enriched there the depth of the reducing layers and the sediment accumulation rate determine the enrichment of authigenic uranium on the contrary mn is dissolved in the reducing sediment sections diffuses in pore water and forms peaks of mn oxide as soon as oxygen is available thus the profiles of both mn and authigenic u record the depth of the redoxcline during periods of oxygen limitation in the sediments estimates of the depth of incorporation of uranium during the last glacial were derived for several cores at localities in the atlantic numerical modeling of the redoxcline as a function of the oxygen content of the water column and of the flux of organic matter to the sediments constrains these values during periods of extreme shallow redoxcline depths burn down of organic matter and deepening of the redoxcline during the holocene may have significantly altered the organic matter and uranium signals of glacial sediments at present day conditions sediments accumulating at rates smaller than 2 cm ky 1 may have lost the u signals peaks of manganese are then the only reliable record for a less ventilated sediment column in the past

dysaerobic conditions during heinrich events 4 and 5 evidence from phosphorus distribution in a north atlantic deep sea core abstract reactive phosphorus undergoes diagenetic transformation once transferred into marine sediments the degree of regeneration and redistribution of phosphorus depends on early diagenetic and environmental conditions which may be linked to larger scale phenomena such as bottom water circulation water column ventilation and organic carbon flux phosphorus phases of the

biological productivity during sapropel s5 formation in the eastern mediterranean sea evidence from stable isotopes of nitrogen and carbon we determined 15n 14n ratios in modern surface and sapropel s5 sediments of the mediterranean sea to clarify differences in the nutrient regime associated with sapropel formation in the modern situation high 15n of unused nitrate 15 20 remaining in the surface waters during the winter phytoplankton bloom evidences p limitation of biological production in winter 15n of surface sediments decrease towards the east of the basin 5 to 2 5 this is a consequence of either eastward increasing nitrogen fixation during the summer months or of particulate matter being supplied predominantly by the p limited winter bloom very low 1 1 15n values in sapropel s 5 from four locations require a very light source of nutrient n assimilated at a minimum of ten times the modern export flux because the isochronous records show no spatial gradient in 15n we exclude both ekman type upwelling and direct riverine discharge as likely sources of nutrients our data are consistent with an anti estuarine thermohaline circulation in the upper 500m during s5 time allowing for the trapping of nutrients in the eastern basin the most likely scenario for s5 is that phosphorus release from a relatively shallow redox boundary resulted in an imbalanced supply of n p 16 1 to the photic zone the result was a slow assimilation of carbon during summer stratification and extensive n2 fixation providing the majority of the export flux from a n limited system

glacial interglacial co2 change the iron hypothesis several explanations for the 200 to 280 ppm glacial interglacial change in atmospheric co2 concentrations deal with variations in southern ocean phytoplankton productivity and the related use or nonuse of major plant nutrients an hypothesis is presented herein in which arguments are made that new productivity in today s southern ocean 7 4 1013g yr 1 is limited by iron deficiency and hence the phytoplankton are unable to take advantage of the excess surface nitrate phosphate that if used could result in total southern ocean new production of 2 3 1015 g c yr 1 as a consequence of fe limited new productivity holocene interglacial co2 levels preindustrial are as high as they were during the last interglacial 280 ppm in contrast atmospheric dust fe supplies were 50 times higher during the last glacial maximum lgm because of this fe enrichment phytoplankton growth may have been greatly enhanced larger amounts of upwelled nutrients may have been used and the resulting stimulation of new productivity may have contributed to the lgm drawdown of atmospheric co2 to levels of less than 200 ppm background information and arguments in support of this hypothesis are presented

glacial enrichments of authigenic cd and u in subantarctic sediments a climatic control on the elements oceanic budget we examine the possibility that glacial increase in the areal extent of reducing sediments might have changed the oceanic cd inventory thereby decoupling cd from po4 we suggest that the precipitation of cd sulfide in suboxic sediments is the single largest sink in the oceanic cd budget and that the accumulation of authigenic cd and u is tightly coupled to the organic carbon flux into the seafloor sediments from the subantarctic ocean and the cape basin south atlantic where oxic conditions currently prevail show high accumulation rates of authigenic cd and u during glacial intervals associated with increased accumulation of organic carbon these elemental enrichments attest to more reducing conditions in glacial sediments in response to an increased flux of organic carbon a third core overlain by circumpolar deep water cpdw as are the other two cores but located south of the antarctic polar front shows an approximately inverse pattern to the subantarctic record the contrasting patterns to the north and south of the antarctic polar front suggest that higher accumulation rates of cd and u in subantarctic sediments were driven primarily by increased productivity this proposal is consistent with the hypothesis of glacial stage northward migration of the antarctic polar front and its associated belt of high siliceous productivity however the increase in authigenic cd and u glacial accumulation rates is higher than expected simply from a northward shift of the polar fronts suggesting greater partitioning of organic carbon into the sediments during glacial intervals lower oxygen content of cpdw and higher organic carbon to biogenic silica rain rate ratio during glacial stages are possible causes higher glacial productivity in the cape basin record very likely reflects enhanced coastal up welling in response to increased wind speeds we suggest that higher productivity might have doubled the areal extent of suboxic sediments during the last glacial maximum however our calculations suggest low sensitivity of seawater cd concentrations to glacial doubling of the extent of reducing sediments the model suggests that during the last 250 kyr seawater cd concentrations fluctuated only slightly between high levels about 0 66 nmol kg 1 on glacial initiations and reaching lowest values about 0 57 nmol kg 1 during glacial maxima the estimated 5 lower cd content at the last glacial maximum relative to modern levels 0 60 nmol kg 1 cannot explain the discordance between cd and 13c such as observed in the southern ocean this low sensitivity is consistent with foraminiferal data suggesting minimal change in the glacial cd mean oceanic content

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

active diagenetic formation of metal rich layers in n e atlantic sediments sediment cores from the porcupine abyssal plain exhibit an indurated layer 0 5 3 cm thick at depths of approximately 50 cm this is some 15 20 cm below the glacial holocene transition as interpreted by radiocarbon dating and the palaeontological criteria of ruddiman and mcintyre 1981 the layer is forming currently at the oxic post oxic boundary in the sediments as revealed by pore water data o2 and no 3 are present in solution above the layer while fe2 mn2 po3 4 and nh 4 are present in solution below and all these species show concentration gradients indicating fluxes into the layer these data are consistent with the hypothesis for the initiation and sustained formation of such layers proposed by wilsonet al 1986a b the elements mn ni co fe p v cu zn and u are all enriched to varying degrees in the vicinity of the layer some differential stratification of these elements in the vertical consistent with a redox control is observed at one site with a 0 5 cm layer with mn ni and co above fe p v and cu in the layer and u below at another site the metal rich layer has higher fe and p concentrations and is more indurated here all enrichments except co are contained within a single layer sample 3 cm thick

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

non steady state diagenetic record in eastern equatorial atlantic sediments abstract the radiocarbon age profile of a sediment core from the eastern equatorial atlantic shows a marked decrease in both clay and carbonate accumulation rates at the end of the last glacial period with overall rates of 3 2 and 8 1 cm kyr for the holocene and late glacial respectively the transition from glacial to postglacial conditions recorded in the sediments at 39 cm is above the visual fe ii fe iii redox boundary at 48 cm which has been used in the past to identify the glacial section and even further above the increase in preserved organic carbon content at 55 cm it is concluded from the present organic carbon profile and recent observations in this area and elsewhere that organic diagenesis in these sediments is not steady state instead it is suggested that the uppermost glacial sediments lost carbon through oxic remineralisation at the change to postglacial conditions and that this process is now continued with nitrate as the electron acceptor these observations suggest that the double mno x solid phase peak which occurs in these and similar sediments is a direct consequence of an adjustment of the oxic layer depth following the decrease in carbon flux at the onset of the holocene

a prominent colour front in false bay south africa cross frontal structure composition and origin abstract colour fronts are a frequent occurrence in false bay south africa and their occurrence has been the subject of previous study and anecdotal conjecture the opportunity arose to make a cross frontal study of this feature in november 2005 photographs were taken and subsequently satellite imagery was obtained measurements were made of temperature salinity turbidity dissolved oxygen suspended solids plant nutrients and chlorophyll a cross frontal comparisons were also made on particulate material using a scanning electron microscope sem and elemental dispersive x ray edx analysis frontal waters were milky white green in colour in stark contrast to the adjacent clearer green blue waters the milky white green water mw gw was found to be warmer apparently less saline more turbid richer in nitrate and silicate and had a higher chlorophyll a concentration the dissolved oxygen signal was less pronounced both water types being supersaturated paradoxically in spite of the higher turbidity in the mw gw both water types had similar weights of suspended solids although the mw gw material was found to be more abundant and fragmentary when compared with its green blue water g bw counterpart the mw gw was rich in calcium whereas the g bw was silicon enriched the central findings of this study are that the strong southerly onshore wind conditions prior to mw gw formation introduced calcium rich fine particulates into the waters of the surf zone the sources of these particulates are thought to be the sea bed sediments and the sea land interface the particulates are close to neutral buoyancy enabling the mw gw to persist over the time scale of days a mechanism reinforced by the warming of this water in the nearshore zone the water was then advected by wind forcing and subsequently its own inertia around the north west corner of false bay at which stage it was easily observed and sampled it is suggested that the eventual collapse of the front was due to the slowing down of inertial movement in combination with the passive sinking of fine particulates and evaporative cooling resulting in downward convection

porewater ph and authigenic phases formed in the uppermost sediments of the santa barbara basin abstract in this paper porewater and solid phase analyses are used in combination with in situ o 2 and ph microelectrode measurements to characterize early diagenetic processes in the uppermost sediments of the santa barbara basin california rapid reduction of dissolved oxygen nitrate solid phase manganese and iron and dissolved sulfate is observed between sediment depths of 0 and 2 cm reductive solubilization of ferric iron phases releases fe 2 adsorbed phosphate and fluoride to the porewaters and contributes to a sharp increase in porewater ph between 2 and 4 cm sulfate reduction rates peak ph levels off and acid volatile sulfides and pyrite become the dominant forms of solid phase iron saturation state calculations which depend largely on ph indicate that the porewaters of the santa barbara basin become saturated with respect to carbonate fluorapatite and calcite within the first 0 25 mm of the sediment and are highly supersaturated by and below 2 cm in spite of this result porewater evidence of phosphate and fluoride removal into a solid phase is observed only in the first 5 cm of some cores whereas dissolved ca profiles suggest dispersed calcite precipitation throughout the sediment column this finding is interpreted as an indication of the nonsteady state nature of the surface reactions that may given sufficient nucleation sites and time lead to carbonate fluorapatite genesis in anoxic sediments finally microelectrode ph profiles from two other basins in the california borderlands are presented these demonstrate that the porewaters of the santa barbara basin are more alkaline than those of other basins this outcome is attributed to the lack of particle mixing and a unique interplay between fe liberation and fes precipitation reactions in the santa barbara basin

enhanced chemical weathering of rocks during the last glacial maximum a sink for atmospheric co2 abstract it has been proposed that increased rates of chemical weathering and the related drawdown of atmospheric co2 on the continents may have at least partly contributed to the low co2 concentrations during the last glacial maximum lgm variations in continental erosion could thus be one of the driving forces for the glacial interglacial climate cycles during quaternary times to test such an hypothesis a global carbon erosion model has been applied to a lgm scenario in order to determine the amount of co2 consumed by chemical rock weathering during that time in this model both the part of atmospheric co2 coming from silicate weathering and the part coming from carbonate weathering are distinguished the climatic conditions during lgm were reconstructed on the basis of the output files from a computer simulation with a general circulation model only the predicted changes in precipitation and temperature have been used whereas the changes in continental runoff were determined with an empirical method it is found that during the lgm the overall atmospheric co2 consumption may have been greater than today by about 20 mainly because of greater carbonate outcrop area related to the lower sea level on the shelves this does not however affect the atmospheric co2 consumption by silicate weathering which alone has the potential to alter atmospheric co2 on the long term silicate weathering and the concomitant atmospheric co2 consumption decreased together with a global decrease of continental runoff compared to present day both by about 10 nevertheless some uncertainty remains because the individual lithologies of the continental shelves as well as their behavior with respect to chemical weathering are probably not well enough known the values we present refer to the ice free continental area only but we tested also whether chemical weathering under the huge ice sheets could have been important for the global budget although glacial runoff was considerably increased during lgm weathering under the ice sheets seems to be of minor importance

production and accumulation of calcium carbonate in the ocean budget of a nonsteady state present day production of caco3 in tne world ocean is calculated to be about 5 billion tons bt per year of which about 3 bt accumulate in sediments the other 40 is dissolved nearly half of the carbonate sediment accumulates on reefs banks and tropical shelves and consists largely of metastable aragonite and magnesian calcite deep sea carbonates predominantly calcitic coccoliths and planktonic foraminifera have orders of magnitude lower productivity and accumulation rates than shallow water carbonates but they cover orders of magnitude larger basin area twice as much calcium is removed from the oceans by present day carbonate accumulation as is estimated to be brought in by rivers and hydrothermal activity 1 6 bt suggesting that outputs have been overestimated or inputs underestimated that one or more other inputs have not been identified and or that the oceans are not presently in steady state one missing calcium source might be groundwater although its present day input is probably much smaller than that of rivers if as seems likely caco3 accumulation presently exceeds terrestial and hydrothermal input this imbalance presumably is offset by decreased accumulation and increased input during lowered sea level shallow water accumulation decreases by an order of magnitude with a 100 m drop in sea level while groundwater influx increases because of heightened piezometric head and the diagenesis of metastable aragonite and magnesian calcite from subaerially exposed shallow water carbonates

thorium and uranium isotopes in a manganese nodule from the peru basin determined by alpha spectrometry and thermal ionization mass spectrometry tims are manganese supply and growth related to climate thorium and uranium isotopes were measured in a diagenetic manganese nodule from the peru basin applying alpha and thermal ionization mass spectrometry tims alpha counting of 62 samples was carried out with a depth resolution of 0 4 mm to gain a high resolution230thexcess profile in addition 17 samples were measured with tims to obtain precise isotope concentrations and isotope ratios we got values of 0 06 0 59 ppb 230th 0 43 1 40 ppm 232th 0 09 0 49 ppb 234u and 1 66 8 24 ppm 238u the uranium activity ratio in the uppermost samples 1 6 mm and in two further sections in the nodule at 12 5 1 0 mm and 27 3 33 5 mm comes close to the present ocean water value of 1 144 0 004 in two other sections of the nodule this ratio is significantly higher probably reflecting incorporation of diagenetic uranium the upper 25 mm section of the mn nodule shows a relatively smooth exponential decrease in the230thexcess concentration tims the slope of the best fit yields a growth rate of 110 mm ma up to 24 5 mm depth the section from 25 to 30 3 mm depth shows constant230thexcess concentrations probably due to growth rates even faster than those in the top section of the nodule from 33 to 50 mm depth the growth rate is approximately 60 mm ma two layers in the nodule with distinct laminations 11 15 and 28 33 mm depth probably formed during the transition from isotopic stage 8 to 7 and in stage 5e respectively the mn fe ratio shows higher values during interglacials 5 and 7 and lower ones during glacials 4 and 6 a comparison of our data with data from adjacent sediment cores suggests a a variable supply of hydrothermal mn to sediments and mn nodules of the peru basin or b suboxic conditions at the water sediment interface during periods with lower mn fe ratios

enhanced regeneration of phosphorus during formation of the most recent eastern mediterranean sapropel s1 phosphorus regeneration and burial fluxes during and after formation of the most recent sapropel s1 were determined for two deep basin low sedimentation sites in the eastern mediterranean sea organic c p ratios and burial fluxes indicate enhanced regeneration of p relative to c during deposition of sapropel s1 this is largely due to the enhanced release of p from organic matter during sulfate reduction release of p from fe bound p also increased but this was only a relatively minor source of dissolved p pore water hpo4 concentrations remained too low for carbonate fluorapatite formation an increased burial of biogenic ca p i e fish debris was observed for one site estimated benthic fluxes of p during sapropel formation were elevated relative to the present day 900 to 2800 vs 70 to 120 mol m 2 yr 1 the present day sedimentary p cycle in the deep basin sediments is characterized by two major zones of reaction 1 the zone near the sediment water interface where substantial release of hpo4 from organic matter takes place and 2 the oxidation front at the top of the s1 where upward diffusing hpo4 from below the sapropel is sorbed to fe oxides the efficiency of aerobic organisms in retaining p is reflected in the low organic c p ratios in the oxidized part of the sapropel burial efficiencies for reactive p were significantly lower during s1 times compared with the present day 7 to 15 vs 64 to 77 budget calculations for the eastern mediterranean sea demonstrate that the weakening of the antiestuarine circulation and the enhanced regeneration of p both contributed to a significant increase in deep water hpo 4 concentrations during sapropel s1 times provided that sufficient vertical mixing occurred enhanced regeneration of p at the seafloor may have played a key role in maintaining increased productivity during sapropel s1 formation copyright 2002 elsevier science ltd

the sequence of events surrounding termination ii and their implications for the cause of glacial interglacial co2 changes events surrounding termination ii as preserved in the vostok ice core provide a number of clues about the mechanisms controlling glacial to interglacial climate change antarctic temperature and the atmosphere s co2 content increased together over a period of 8000 years this increase is bounded by a drop in dust flux at its onset and by a drop in the 18o of trapped air at its finish a similar lag between dust flux and foraminiferal 18o is seen in a southern ocean marine record suggesting that the 18o in air trapped in vostok ice is a valid proxy for ice volume the synchronous change of atmospheric co2 and southern hemisphere temperature thus preceded the melting of the northern hemisphere ice sheets this observation coupled with the fact that nutrient reorganization in the north atlantic occurs with or after the sea level rise eliminates many scenarios proposed to explain the co2 rise including those which rely on sea level change conveyor related nutrient redistribution or north atlantic cooling southern ocean scenarios become the front runners but the most popular mechanism iron fertilization has two problems in explaining the co2 rise before termination ii first much of the dust demise occurs prior to the change in co2 so if iron is the villain a threshold value of its supply must be called upon above which productivity does not continue to increase second the co2 rise continues for some 4 5 kyr after the dust flux has fallen to close to zero these problems may be solved if the increased iron supply in dust caused higher rates of nitrogen fixation during the glacial periods in this case the residence time of oceanic nitrate of a few thousand years would enable decreasing productivity to be a global rather than a local phenomenon and would explain the slow rampup of atmospheric co2

quantification of diffusive benthic fluxes of nitrate phosphate and silicate in the southern atlantic ocean pore water data from surface sediments and bottom water data at 180 locations were used to create distribution maps of diffusive benthic release rates of nitrate phosphate and silicate in the southern atlantic ocean for water depths 1000 m geostatistical methods of variogram analysis and kriging were used for data interpolation since benthic fluxes are controlled by organic matter degradation and dissolution processes and therefore by the supply of organic matter to the sediment surface the distribution pattern of all investigated constituents should reflect a general coupling to surface water productivity this seems to be true for the most part of the oligotrophic central south atlantic and the upwelling area off southwest africa striking regional differences in this regard however exist for the eastern equatorial region where unexpectedly low fluxes were calculated and the argentine basin where benthic fluxes are very high the argentine basin obviously receives a higher input of degradable dissolvable material whereas in the eastern equatorial region the low benthic fluxes are possibly due to intense nutrient recycling within the water column estimated fluxes vary considerably over the entire region no3 10 180 mmol m 2 yr 1 po4 2 11 mmol m 2 yr 1 and si 0 0 65 mol m 2 yr 1 areas of highest release rates are the continental margins off southwest africa and off argentina the investigated area comprises a total of approximately 32 106 km2 between 8 n and 40 50 s our estimations reveal benthic release rates of 1 55 l012 mol no3 yr 1 3 5 l010 mol po4 yr 1 and 2 1 1012 mol si yr 1 open ocean areas with middle to low fluxes contribute about 70 80 of the total estimated fluxes the release of phosphate is probably underestimated because of core recovery artifacts and is therefore based on the assumption that fluxes are not lower than 0 25 mmol m 2 yr 1 at any location of the studied area the investigated area represents about one tenth of the world deep ocean without the arctic ocean assuming the south atlantic to be representative we calculate annual global release rates of 15 l012 mol no3 32 l010 mol po4 and 20 1012 mol si if our estimates are correct about 4 6 of silicate 3 4 of nitrate and 1 of phosphate annually produced in the surface waters are remineralized in surface sediments from water depths 1000 m

dust sources and deposition during the last glacial maximum and current climate a comparison of model results with paleodata from ice cores and marine sediments mineral dust aerosols in the atmosphere have the potential to affect the global climate by influencing the radiative balance of the atmosphere and the supply of micronutrients to the ocean ice and marine sediment cores indicate that dust deposition from the atmosphere was at some locations 2 20 times greater during glacial periods raising the possibility that mineral aerosols might have contributed to climate change on glacial interglacial time scales to address this question we have used linked terrestrial biosphere dust source and atmospheric transport models to simulate the dust cycle in the atmosphere for current and last glacial maximum lgm climates we obtain a 2 5 fold higher dust loading in the entire atmosphere and a twenty fold higher loading in high latitudes in lgm relative to present comparisons to a compilation of atmospheric dust deposition flux estimates for lgm and present in marine sediment and ice cores show that the simulated flux ratios are broadly in agreement with observations differences suggest where further improvements in the simple dust model could be made the simulated increase in high latitude dustiness depends on the expansion of unvegetated areas especially in the high latitudes and in central asia caused by a combination of increased aridity and low atmospheric co2 the existence of these dust source areas at the lgm is supported by pollen data and loess distribution in the northern continents these results point to a role for vegetation feedbacks including climate effects and physiological effects of low co2 in modulating the atmospheric distribution of dust

relation between sedimentation rate and burial of organic phosphorus and organic carbon in marine sediments organic carbon and organic phosphorus concentrations in marine sediment cores with known sedimentation rates were determined and collected from the literature with the exception of organic rich sediments from upwelling areas organic phosphorus concentrations in marine sediments do not correlate linearly with organic carbon concentrations the c p ratios of organic matter buried in marine sediments vary systematically with sedimentation rate over the range studied 0 0001 to 2 5 cm y low c p ratios 200 atomic occur in sediments with sedimentation rates both less than 0 002 cm y and greater than 1 cm y higher c p ratios up to 600 are found at intermediate sedimentation rates a simple steady state model is developed for the early diagenesis of organic carbon and organic phosphorus in marine sediments the processes included are sediment burial pore water diffusion and bacterial decomposition of organic matter by oxic respiration and sulfate reduction preferential regeneration of phosphorus relative to carbon is assumed to take place during oxic respiration the modeling shows that both organic matter preservation and the degree of elemental fractionation between phosphorus and carbon depend strongly on the overall sedimentation rate very high sedimentation rates coastal deltaic environment result in a good preservation of deposited organic matter with an initial c p ratio close to the redfield value at very slow sedimentation rates pelagic environment the oxidation of the sedimentary organic matter is nearly complete and produces a low c p residual organic material this residual organic matter may represent either refractory detrital organic compounds enriched in phosphorus or in situ synthesized low c p bacterial remains the high c p ratios at intermediate sedimentation rates slope and shelf environment reflect the preferential regeneration of phosphorus during the incomplete decomposition of the metabolizable organic matter

geochemical evidence for anoxic deep water in the arabian sea during the last glaciation various paleoceanographic studies have indicated that the deep ocean was probably depleted in dissolved oxygen during the last glacial period approximately 18 kyr b p delta sup 18 o stage 2 compared to present time however direct evidence of low oxygen content in the deep waters has been lacking here the authors report geochemical evidence of near anoxic conditions in the deep arabian sea during the entire last glacial cycle delta sup 18 o stages 2 3 and 4 anoxia is inferred from the concomitant enrichment of organic carbon and authigenic uranium in the glacial sections of a core from the deep eastern arabian sea the anoxic conditions during the last glacial period probably caused by a change in deep water circulation evidently enhanced preservation of organic matter and simultaneous removal of uranium from seawater 57 refs 3 figs 2 tabs

glacial interglacial variations in production and nitrogen fixation in the cariaco basin during the last 580 kyr the effect of sea level change on nutrient supply to the anoxic cariaco demonstrates the fundamental importance of nitrogen n2 fixation and phosphate to oceanic production as n2 fixation produces biomass of low 15n and has been reported to be an important component of the nitrogen cycle in the modern cariaco basin we propose that it contributes to the light interglacial 15n 2 3 values observed in the ocean drilling program odp site 1002 sediment record during the glacials the sediments are bioturbated oxic conditions with low total organic carbon toc contents and sedimentary 15n values of 5 suggesting that nitrogen n2 fixation contributed little to the n nutrition of cariaco surface waters the most plausible explanation for the inferred glacial interglacial changes in n2 fixation in the cariaco is that they have occurred in response to variations in the n p ratio of the nutrient supply driven by changes in denitrification

authigenic apatite formation and burial in sediments from non upwelling continental margin environments abstract evidence for precipitation of authigenic carbonate fluorapatite cfa in long island sound and mississippi delta sediments suggests that formation of cfa is not restricted to environments of active coastal upwelling we present porewater data suggestive of cfa formation in both these areas application of a sequential leaching procedure designed specifically to separate authigenic carbonate fluorapatite from other phosphorus containing phases including detrital apatite of igneous or metamorphic origin provides strong supporting evidence for authigenic apatite formation in these sediments the size of the authigenic apatite reservoir increases with depth indicating continued formation of cfa during early diagenesis this depth increase is mirrored by a decrease in solid phase organic p at both sites suggesting that cfa is forming at the expense of organic p mass balance considerations application of diagenetic models to interstitial water nutrient data and the saturation state of the interstitial water are consistent with this interpretation diagenetic redistribution of phosphorus among the different solid phase reservoirs is observed at both sites and results in near perfect retention of p by these sediments over the depth intervals sampled formation of cfa in continental margins which do not conform to the classically defined regions of phosphorite formation renders cfa a quantitatively more important sink than has previously been recognized including this reservoir as a newly identified sink for reactive p in the ocean the residence time of p in the modern ocean must be revised downward the implication for ancient oceans of cfa formation in continental margin sediments other than phosphorites is that phosphorite formation may be less a representation of episodicity in removal of reactive p from the oceans than of localized concentration of cfa in phosphatic sediments by secondary physical processes

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

geochemical cycles in an ocean general circulation model preindustrial tracer distributions a state of the art report is given of the hamburg model of the oceanic carbon cycle the model advects geochemical tracers important to the carbon cycle by the currents of a general circulation model the geochemical cycling is driven by a michaelis menten type production kinetics the model is an extension of the bacastow and maier reimer 1990 model it is based on a more realistic current field and includes a mechanism of lysocline sediment interaction principal variables are co2 alkalinity phosphate oxygen and silicate the carbon variables are defined for 12c 13c and 14c separately in addition to these carbon isotopes 39a and 18o of dissolved oxygen are predicted the model predicts realistic global patterns of tracer distribution in the equatorial eastern pacific however the structures are exaggerated due to a strong upwelling which is a common feature of coarse resolution models of the general circulation of the ocean

phosphorus accumulation in marine sediments and the oceanic phosphorus cycle ideas about key factors in the oceanic mass balance of dissolved reactive phosphate have changed substantially i present an integrated overview of these here with an emphasis on evaluating the burial sinks for p and defining areas needing further research the major source of reactive p to the ocean is river input reactive p is delivered to the oceanic sediment water interface primarily in particulate organic matter p scavenged by hydrothermal iron rich oxyhydroxide particles with uptake in proportion to deep water phosphate concentrations represents a substantially smaller flux to the sediment water interface diagenetic transformations are important influences on the form of reactive p burial in marine sediments p burial occurs with organic carbon burial and as p associated with iron rich oxyhydroxide particles and coatings formation of authigenic p rich phases presumably apatite at the expense of organic p and oxide associated p is significant in open ocean marine sediments the authigenic p sink may represent a substantially larger portion of the sedimentary burial than indicated by previous estimates focused on p burial in organic rich continental margin sediments

accumulation of organic carbon rich sediments in the late jurassic and cretaceous atlantic ocean a synthesis abstract organic carbon rich sediments black shales were deposited at some 40 deep sea drilling project dsdp sites in the atlantic ocean during late jurassic and cretaceous times in order to reconstruct the depositional environments of black shale formation we have studied in detail changes in the occurrence of black shales as well as the type and amount of organic matter in relation to changes in paleogeography paleooceanic circulation and paleoclimate we have calculated accumulation rates of marine and terrigenous organic carbon and combined these with organic carbon content sedimentation rate relationships to obtain information about paleoenvironments main factors causing the preservation and accumulation of organic carbon are 1 the supply of terrestrial organic matter 2 the supply of marine organic matter 3 the oxygenation of the deep water and 4 the bulk sedimentation rate changes in the importance of these different factors and changes in the interrelationships among them determine the complex system of black shale formation and their cyclic variations increased supply of terrestrial organic matter due to increased river discharge and humid climate in northeast america southwest europe and south africa were important in the hauterivian albian northwest and northern northeast atlantic and in the late jurassic aptian south atlantic in the latter anoxic deep water conditions due to restricted circulation in the nascent largely isolated basin as well as higher oceanic productivity may have reinforced the high preservation rates of marine organic matter during that time off northwest africa higher flux rates of marine organic matter were recorded in areas of higher productivity which may have been caused by fluvial nutrient supply during the hauterivian and by intensified upwelling during albian turonian times in general the depositional environment was oxygenated and the content of marine organic matter was a function of the sedimentation rate furthermore at some places redeposition by turbidity currents or slumps may have been important for the accumulation of organic matter in the deep sea basins the only episode of widespread anoxia in the western and eastern basins of the north atlantic may have occurred in the cenomanian turonian when high amounts of marine organic matter were also preserved in areas of low productivity and low sedimentation rates

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

benthic phosphorus regeneration net primary production and ocean anoxia a model of the coupled marine biogeochemical cycles of carbon and phosphorus we examine the relationships between ocean ventilation primary production water column anoxia and benthic regeneration of phosphorus using a mass balance model of the coupled marine biogeochemical cycles of carbon c and phosphorus p the elemental cycles are coupled via the redfield c p ratio of marine phytoplankton and the c p ratio of organic matter preserved in marine sediments the model assumes that on geologic timescales net primary production in the oceans is limited by the upwelling of dissolved phosphorus to the photic zone the model incorporates the dependence on bottom water oxygenation of the regeneration of nutrient phosphorus from particulate matter deposited at the water sediment interface evidence from marine and lacustrine settings modern and ancient demonstrates that sedimentary burial of phosphorus associated with organic matter and ferric oxyhydroxides decreases when bottom water anoxia dysoxia expands steady state simulations show that a reduction in the rate of thermohaline circulation or a decrease of the oxygen content of downwelling water masses intensifies water column anoxia dysoxia and at the same time increases surface water productivity the first effect reflects the declining supply of oxygen to the deeper parts of the ocean the second effect is caused by the enhanced benthic regeneration of phosphorus from organic matter and ferric oxyhydroxides sedimentary burial of organic carbon and authigenic calcium phosphate mineral francolite on the other hand is promoted by reduced ocean ventilation according to the model global scale anoxia dysoxia leads to a more efficient recycling of reactive phosphorus within the ocean system consequently higher rates of primary production and organic carbon burial can be achieved even when the continental supply of reactive phosphorus to the oceans remains unchanged

feedbacks between oceanic redox states and marine productivity a model perspective focused on benthic phosphorus cycling a new model for the marine cycles of particulate organic carbon poc oxygen nitrate and phosphorus has been developed and applied to explore the controls and constraints on marine productivity and nutrient inventories the coupled benthic pelagic model uses a new approach for the simulation of the reactive phosphorus turnover preac corresponding to the sum of organic p authigenic p and adsorbed phosphate in marine sediments the simulated poc preac burial ratio in shelf slope and rise and deep sea sediments increases under strongly reducing conditions in agreement with field observation the model runs revealed that the spread of anoxia in bottom waters may enhance the productivity of the global ocean by one order of magnitude if sufficient nitrate is provided by n2 fixation thus anoxic bottom waters promote eutrophic conditions and vice versa additional model runs showed that the productivity and nutrient inventory of the glacial ocean were probably enhanced due to the falling sea level marine regression induced a narrowing of the depositional areas on the continental shelves and thereby an increase in the fraction of poc exported to the deep ocean the accelerated poc delivery in turn decreased the oxygen contents of the deep water and thus favored the release of phosphate from deep sea and rise sediments enhanced recycling of phosphate at the seafloor promoted further poc export in a positive feedback loop

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

influence of water column anoxia on the burial and preservation of carbon and phosphorus in marine shales abstract organic p and organic c concentrations were measured in several well characterized phanerozoic marine shale sequences with the primary focus being the camp run member of the devonian mississippian new albany shale sequences were selected with close spatial association of bioturbated and laminated sediments which reflect deposition from oxic and anoxic waters respectively average organic c p mole ratios calculated from the data are 150 for bioturbated shales and 3900 for the laminated shales of the new albany differences in the extent and mechanisms of early diagenesis related to the oxygenation of waters at the sediment water interface can account for the c p ratios of buried organic matter low c p ratios of bioturbated sediments are attributed to 1 1 the increased ability of bacteria to store p in well oxygenated environments which leads to the production of low c p ratio bacterial biomass and 2 2 the extensive oxidation of sedimentary organic matter resulting in the formation of residual organic phases with low c p ratios high organic c p ratios of laminated sediments are explained by a combination of 1 1 the limited ability of bacteria to store p under anoxic conditions 2 2 extensive p regeneration from sedimentary organic matter 3 3 enhanced c preservation relative to the bioturbated shales it is also shown that relative to organic c laminated shales are not as effective a p sink as are bioturbated shales this provides a mechanism in anoxic environments for burying large quantities of organic matter without simultaneously sequestering the p needed to sustain further productivity

influence of water column anoxia on the elemental fractionation of carbon and phosphorus during sediment diagenesis abstract organic carbon oxidation and benthic total phosphorus flux measurements from sites covering a range of bottom water oxygen concentrations have been compiled the data show that p regeneration relative to carbon oxidation is much more extensive in sediments overlain by oxygen depleted waters these results are consistent with studies showing that low oxygen bottom water concentrations correlate with reduced total phosphorus burial efficiencies and enhanced organic carbon burial efficiencies based on these observations a positive feedback is proposed between water column anoxia enhanced benthic phosphorus regeneration and marine productivity this feedback may help explain the widespread accumulation of organic rich marine sediments from anoxic waters observed in the geologic record

evidence for enhanced phosphorus regeneration from marine sediments overlain by oxygen depleted waters phosphorus regeneration and burial fluxes determined from in situ benthic flux chamber and solid phase measurements at sites on the californian continental margin peruvian continental slope north carolina continental slope and from the santa monica basin california are reported comparison of these sites indicates that o2 depleted bottomwaters enhance p regeneration from sediments diminishing overall phosphorus burial efficiency based on these observations a positive feedback linking ocean anoxia enhanced benthic phosphorus regeneration and marine productivity is proposed on shorter timescales these results also suggest that o2 depletion in coastal regions caused by eutrophication may enhance p regeneration from sediments thereby providing additional p necessary for increased biological productivity