late miocene early pliocene biogenic bloom evidence from low productivity regions of the indian and atlantic oceans studies of the late miocene early pliocene biogenic bloom typically have focused on high productivity areas in the indian and pacific oceans in order to achieve high resolution samples thus there is a paucity of information concerning whether the atlantic ocean in general or low productivity regions in all three basins experienced this bloom this study measured the phosphorus mass accumulation rate pmar in five cores from low productivity regions of the atlantic and indian oceans all cores exhibit a peak in productivity 4 5 5 ma coincident with the indo pacific bloom this suggests that nutrients were not shifted away from low productivity regions nor out of the atlantic ocean instead it appears that the bloom was caused by an overall increase in nutrient flux into the world oceans four of the cores record the bloom s pmar peak as bimodal indicating a pulsed increase in phosphorus to the oceans this suggests that there may have been multiple causes of the biogenic bloom

phosphorus cycling in marine sediments from the continental margin off namibia abstract in this study we investigate benthic phosphorus cycling in recent continental margin sediments at three sites off the namibian coastal upwelling area examination of the sediments reveals that organic and biogenic phosphorus are the major p containing phases preserved high corg porg ratios just at the sediment surface suggest that the preferential regeneration of phosphorus relative to that of organic carbon has either already occurred on the suspension load or that the organic matter deposited at these sites is already rather refractory release of phosphate in the course of benthic microbial organic matter degradation cannot be identified as the dominating process within the observed internal benthic phosphorus cycle dissolved phosphate and iron in the pore water are closely coupled showing high concentrations below the oxygenated surface layer of the sediments and low concentrations at the sediment water interface the abundant presence of fe iii bound phosphorus in the sediments document the co precipitation of both constituents as p containing iron oxyhydr oxides however highly dissolved phosphate concentrations in pore waters cannot be explained neither by simple mass balance calculations nor by the application of an established computer model under the assumption of steady state conditions phosphate release rates are too high as to be balanced with a solid phase reservoir this discrepancy points to an apparent lack of solid phase phosphorus at sediment depth were suboxic conditions prevail we assume that the known active fast and episodic particle mixing by burrowing macrobenthic organisms could repeatedly provide the microbially catalyzed processes of iron reduction with authigenic iron oxyhydro oxides from the oxic surface sediments accordingly a multiple internal cycling of phosphate and iron would result before both elements are buried below the iron reduction zone

simulated effect of soil depth and bedrock topography on near surface hydrologic response and slope stability this paper explores the effect of hillslope hydrological behavior on slope stability in the context of transient subsurface saturation development and landslide triggering we perform a series of virtual experiments to address how subsurface topography affects the location and spatial pattern of slip surface development and pore pressure dynamics we use a 3d darcy richards equation solver hydrus 3 d combined with a cellular automata slope stability model to simulate the spatial propagation of the destabilized area our results showed that the soil bedrock interface and in particular bedrock depressions played a key role in pore pressure dynamics acting as an impedance for the downslope drainage of perched water filling and spilling of depressions in the bedrock surface microtopography induced localized zones of increased pressure head such that the development of pore pressure fields not predictable by surface topography lead to rapid landslide propagation our work suggests that landslide models should consider the subsurface topography in order to include a connectivity component in the mathematical description of hydrological processes operating at the hillslope scale copyright 2012 john wiley sons ltd

apatite weathering and the phanerozoic phosphorus cycle despite widespread debate in the literature there is still considerable uncertainty concerning which nutrient ultimately controls marine net ecosystem production nep over geologic time geochemical arguments suggest that phosphorus is the culprit the weathering of apatite the primary phosphorus sink in earth s exosphere controls long term phosphorus availability if phosphorus is the ultimate controlling nutrient over geologic time scales then long term marine nep is coupled to the release of phosphorus from apatite weathering the most abundant apatite compositions found in nature are igneous fluorapatite and marine sedimentary carbonate fluorapatite sparse data exist on how these compositions dissolve under earth s surface conditions to demonstrate a need for these data and their application we present a kinetic treatment of existing data augmented by new results we then use these results in a weathering model designed to illustrate the control exerted by temperature via activation energy and surface area on the phosphorus flux from apatite dissolution during the phanerozoic our conclusion is that activation energy and hence temperature and apatite surface area are important parameters governing the phosphorus flux from apatite weathering and therefore marine nep during phanerozoic time

an apparent contradiction in the role of phosphorus in cenozoic chemical mass balances for the world ocean little is known about the fluxes to and from the ocean during the cenozoic of phosphorus p a limiting nutrient for oceanic primary productivity and organic carbon burial on geologic timescales previous studies have concluded that dissolved river fluxes increased worldwide during the cenozoic and that organic carbon burial decreased relative to calcium carbonate burial and perhaps in absolute terms as well to examine the apparent contradiction between increased river fluxes of p assuming p fluxes behave like the others expected to drive increased organic carbon burial and observations indicating decreased organic carbon burial we determined p accumulation rates for equatorial pacific sediments from ocean drilling program leg 138 sites in the eastern equatorial pacific and leg 130 sites on the ontong java plateau in the western equatorial pacific although there are site specific and depth dependent effects on p accumulation rates there are important features common to the records at all sites p accumulation rates declined from 50 to 20 ma showed some variability from 20 to 10 ma and had a substantial peak from 9 to 3 ma centered at 5 6 ma these changes in p accumulation rates for the equatorial pacific are equivalent to substantial changes in the p mass balance however the pattern resembles neither that of weathering flux indicators 87sr 86sr and ge si ratios nor that of the carbon isotope record reflecting changes in organic carbon burial rates although these p accumulation rate patterns need confirmation from other regions with sediment burial significant in global mass balances e g the north pacific and southern ocean it appears that p weathering inputs to the ocean are decoupled from those of other elements and that further exploration is needed of the relationship between p burial and net organic carbon burial

an intermediate complexity model for simulating marine biogeochemistry in deep time validation against the modern global ocean we present a new high resolution 1 d intermediate complexity box model icbm of ocean biogeochemical processes for paleoceanographic applications the model contains 79 reservoirs in three regions that should be generally applicable throughout much of earth history 1 a stratified gyre region 2 a high latitude convective region and 3 an upwelling region analogous to those found associated with eastern boundary currents transport processes are modeled as exchange fluxes between boxes and by eddy diffusion terms significant improvement in the representation of middepth oxygen budgets was achieved by implementing nonlocal mixing between the high latitude surface and gyre thermocline reservoirs the biogeochemical submodel simulates coupled c n p o and s systematics with explicit representation of microbial populations using a process based approach primary production follows redfield stoichiometry while water column remineralization is depth and redox couple dependent settling particulate organic matter is incorporated into a benthic submodel that accounts for burial and remineralization the c p ratio of burial depends on bottom water oxygen denitrification takes place both by classical and anammox pathways the icbm was tested against modern oceanographic observations from the global ocean data analysis project joint global ocean flux study and other databases comparisons of model output with circulation tracers including salinity cfc 12 and radiocarbon permit a test of the physical exchange scheme vertical profiles of biogeochemically reactive components in each of the three regions are in good agreement with observations under modern conditions the upwelling zone displays a pronounced oxygen minimum zone and water column denitrification while these are not present in the high latitude or gyre regions model generated global fluxes also compare well to independent estimates of primary production burial and phosphorous and nitrogen cycling the icbm appears to adequately simulate the long term kyr evolution of several biogeochemical cycles and improves on previous box models in several important ways in a companion paper the model s performance under euxinic conditions is tested against modern black sea data the simple and adaptable structure of the model should make it applicable to a wide range of paleoceanographic problems the model source code is available in matlabtm 7 m files provided as auxiliary material

the climatic significance of late ordovician early silurian black shales the ordovician silurian transition approximate to 455 430ma is characterized by repeated climatic perturbations concomitant with major changes in the global oceanic redox state best exemplified by the periodic deposition of black shales the relationship between the climatic evolution and the oceanic redox cycles however remains largely debated here using an ocean atmosphere general circulation model accounting for ocean biogeochemistry mitgcm we investigate the mechanisms responsible for the burial of organic carbon immediately before during and right after the latest ordovician hirnantian 445 444ma glacial peak our results are compared with recent sedimentological and geochemical data we show that the late katian time slice approximate to 445ma typified by the deposition of black shales at tropical latitudes represents an unperturbed oceanic state with regional organic carbon burial driven by the surface primary productivity during the hirnantian our experiments predict a global oxygenation event in agreement with the disappearance of the black shales in the sedimentary record this suggests that deep water burial of organic matter may not be a tenable triggering factor for the positive carbon excursion reported at that time our simulations indicate that the perturbation of the ocean circulation induced by the release of freshwater in the context of the post hirnantian deglaciation does not sustain over sufficiently long geological periods to cause the rhuddanian approximate to 444ma oceanic anoxic event input of nutrients to the ocean through increased continental weathering and the leaching of newly exposed glaciogenic sediments may instead constitute the dominant control on the spread of anoxia in the early silurian

cellular automata as analysis and synthesis engines at the geomorphology ecology interface abstract the linkages between ecology and geomorphology can be difficult to identify because of physical complexity and the limitations of the current theoretical representations in these two fields of study deep divisions between these disciplines are manifest in the methods used to simulate process such as rigidly physical deterministic methods for many aspects of geomorphology compared with purely stochastic simulations in many models of change in landcover practical and theoretical research into ecology geomorphology linkages cannot wait for a single simulation schema which may never come as a result studies of these linkages often appear disjointed and inconsistent the grid based simulation framework for cellular automata ca allows simultaneous use of competing schemas ca use in general geographic studies has been primarily limited to urban simulations models of change for land cover both highly stochastic and or expert rule based in the last decade however methods for describing physically deterministic systems in the ca framework have become much more accurate the possibility now exists to merge separate ca simulations of different environmental systems into unified multiautomata models because cas allow transition rules that are deterministic probabilistic or expert rule based they can immediately incorporate the existing knowledge rules in ecology and geomorphology the explicitly spatial nature of ca provides a map like framework that should allow a simple and deeply rooted connection with the mapping traditions of the geosciences and ecological sciences

application of a new cellular model for bedload transporting extreme events at steep slopes abstract a cellular model for bedload transport at steep channel gradients and alluvial fans has been developed to simulate lateral distribution of erosion and deposition on alluvial fans of mountain streams the cellular model named fluvised applies a quasi steady state routing of a flood hydrograph over a rectangular grid bedload transport is calculated and the morphological changes are updated after each time step fluvised is designed to complement existing one dimensional bedload transport simulation tools by using their outcome as an input for the simulation of inundated areas the model has been evaluated against tomsed a one dimensional bedload transport model further a back calculation of a laboratory bedload experiment and a real flood event from 2005 at schnannerbach in austria are provided to test the model s suitability for reproducing morphological changes caused by flood events at high channel gradients

modeling organic carbon burial during sea level rise with reference to the cretaceous after three decades of research on the correlation between sea level and various proxies there has been very little quantification of the first order influence of sea level change on nutrient inventory marine productivity and burial of organic carbon we present a model aimed at quantifying the burial of organic carbon as a function of sea level rise the biogeochemical model explicitly considers the mean surface area distribution of the earth as a function of elevation also included is dissolved inorganic phosphate dip liberated from coastal sediments during transgression we quantify how sea level rise of magnitudes inferred for the mid cretaceous influences the phosphorus cycle and burial of organic carbon the burial efficiency is greater on the shelf therefore in the model the larger shelf area under high sea level results in more efficient burial of marine organic carbon for a given dip concentration and associated new production of organic matter np with a late cretaceous model shelf area the residence time of dip decreases by 60 relative to the present day reference thus in the final steady state dip and np in the open ocean are reduced compared to today when the biologically reactive phosphorus preac fluxes to the ocean from land are held constant the lower new production reduces the oxygen demand for respiration and results in a significant oxygenation of the global ocean finally the global organic carbon burial decreases by 30 relative to today in the model this decrease results from feedbacks between the flux of organic carbon to the seafloor and the ratio of organic carbon to preac in buried sediments in contrast during sea level rise coastal erosion may increase the preac flux to the ocean by up to 20 relative to today and cause a temporary increase in dip concentration in the ocean the resulting increase in organic carbon burial is equivalent to a carbon isotope event of 0 5 to 1 larger carbon isotope events can be triggered by sea level rise only when the ocean is sufficiently close to anoxia in the oxygen minimum zone just prior to the sea level rise

quantifying the paleogeographic driver of cretaceous carbonate platform development using paleoecological niche modeling abstract platform carbonates are a major component of the earth system but their spatial extent through geological time is difficult to reconstruct due to the incompleteness of the geological record sampling heterogeneity and their intrinsic complexity here we use coupled ecological niche modeling and deep time general circulation models to predict the occurrence of platform carbonates at the global scale during the cretaceous specifically niche modeling uses fuzzy logic to predict probable occurrence of platform carbonates as a function of sea surface temperature sea surface salinity primary productivity and water depth the first three parameters derive from cretaceous global paleoclimatic simulations using a coupled ocean atmosphere general circulation model while bathymetry is based on paleogeographical reconstructions model predictions are validated with the well documented and abundant geological data from the aptian the methodologies developed for the aptian are subsequently extended to other cretaceous time intervals the results of the niche model accurately predict the geographic distribution of aptian carbonate platforms if a preference for low open marine productivity levels is assumed for the rudist dominated carbonate factories however if a preference for high productivity levels is assumed the modeling results do not match the reported global distribution of aptian carbonate platforms from the early cretaceous into the late cretaceous sea level rose and the continents on average moved into lower latitudes the model predicts a corresponding increase in the extent of the carbonate platforms mainly due to the increasing extent of shallow water environments available to carbonate development these results indicate that long term sea level rise may have been a major factor responsible for the increase in the area of platform carbonates during the cretaceous

contribution of dendrochronology to the determination of magnitude frequency relationships for landslides abstract the determination of magnitude frequency m f relationships is necessary for landslide hazard assessment ideally this is achieved by using inventories of past landslide events recorded by technical units or aerial photo interpretation however direct sources of landslide data are often unavailable dendrogeomorphological techniques allow us to determine the frequency of events but few attempts have been made to estimate landslide magnitude by analysing the spatial distribution of disturbed trees this paper addresses m f determination for rockfalls debris flows and complex slides obtained by dendrogeomorphology the cases presented require the appropriate understanding of both the geomorphological context and the disturbance caused by landslide motion on trees both small and large rockfalls can be identified and dated by reconstructing the trajectories in the forest stand the larger the rockfall size the longer the path the higher the number of affected trees and the greater the area of deposition of rock fragments the area of damaged trees is proposed as an indicator of the rockfall magnitude the frequency and extent of a series of debris flows were reconstructed by mapping their deposits using relative dating criteria and by dating damaged trees local and global mudslide reactivations were deduced by sampling various tree generations and by analysing the location of the disturbed trees in the landslide units magnitude cumulative frequency curves were determined for the three cases

redox controlled carbon and phosphorus burial a mechanism for enhanced organic carbon sequestration during the petm abstract geological records reveal a major perturbation in carbon cycling during the paleocene eocene thermal maximum petm 56 ma marked by global warming of more than 5 c and a prominent negative carbon isotope excursion of at least 2 5 within the marine realm the entire event lasted about 200 000 yr and was associated with a massive release of light carbon into the ocean atmosphere system over several thousands of years here we focus on the terminal stage of the petm during which the ocean atmosphere system rapidly recovered from the carbon cycle perturbation we employ a carbon cycle box model to examine the feedbacks between surface ocean biological production carbon oxygen phosphorus and carbonate chemistry during massive co 2 release events such as the petm the model results indicate that the redox controlled carbon phosphorus feedback is capable of producing enhanced organic carbon sequestration during large carbon emission events the locale of carbon oxidation ocean vs atmosphere does not affect the amount of carbon sequestered however even though the model produces trends consistent with oxygen excess accumulation rates of organic carbon 1700 pg c during the recovery stage export production and 13 c data it fails to reproduce the magnitude of change of sediment carbonate content and the ccd over deepening during the recovery stage the ccd and sediment carbonate content overshoot during the recovery stage is muted by a predicted increase in caco 3 rain nonetheless there are indications that the caco 3 export remained relatively constant during the petm if this was indeed true then an initial pulse of 3 000 pg c followed by an additional slow leak of 2 500 pg c could have triggered an accelerated nutrient supply to the surface ocean instigating enhanced organic carbon export consequently increasing organic carbon sequestration resulting in an accelerated restoration of ocean atmosphere biogeochemistry during the termination phase of the petm

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

glacial interglacial variations in marine phosphorus cycling implications for ocean productivity 1 using a box model of organic carbon c and phosphorus p cycling in the global ocean we assess the effects of changes in the continental supply of reactive p oceanic mixing and sea level on the marine p cycle on glacial interglacial timescales our model results suggest that mixing is a dominant forcing during early glaciation causing retention of p in the deep ocean thereby lowering primary production and associated organic c and p burial sea level fall is the dominant forcing during late glaciation when reduced coastal trapping of reactive p enhances its transfer to the open ocean restoring primary production and p burial during postglacial periods changes in circulation and weathering dominate open ocean processes and oceanic primary production peaks as primary production is reduced upon glaciation changes in the marine p cycle are unlikely to drive enhanced primary production and co2 drawdown during glaciation

periodic changes in the cretaceous ocean and climate caused by marine redox see saw periodic changes in sediment composition are usually ascribed to insolation forcing controlled by earth s orbital parameters during the cretaceous thermal maximum at 97 91 myr ago ma a 37 50 kyr long cycle that is generally believed to reflect obliquity forcing dominates the sediment record here we use a numerical ocean model to show that a cycle of this length can be generated by marine biogeochemical processes without applying orbital forcing according to our model the restricted proto north atlantic and tethys basins were poorly ventilated and oscillated between iron rich and sulfidic euxinic states the panthalassa basin was fertilized by dissolved iron originating from the proto north atlantic hence it was less oxygenated while the proto north atlantic was in an iron rich state and better oxygenated during euxinic periods in the proto north atlantic this redox see saw was strong enough to create significant changes in atmospheric p mathrm co 2 we conclude that most of the variability in the mid cretaceous ocean atmosphere system can be ascribed to the internal redox see saw and its response to external orbital forcing an internal redox see saw between the panthalassa basin and the proto north atlantic can explain cyclic changes in the sediment record throughout the cretaceous thermal maximum 97 to 91 million years ago according to simulations with a numerical ocean model

pyrite oxidation during sample storage determines phosphorus fractionation in carbonate poor anoxic sediments abstract we investigated the phosphorus p and iron fe fractionation in four cores with anoxic sediments deposited during the mid cretaceous oceanic anoxic event 2 94 ma and the paleocene eocene thermal maximum 55 ma that were exposed to oxygen after core recovery surprisingly p associated with iron oxyhydroxides fe bound p was a major p phase in these laminated sediments deposited under euxinic conditions a significant fraction of total fe was present as poorly crystalline ferric fe this fraction increased with increasing storage time of the investigated cores in carbonate poor samples fe bound p accounted for up to 99 of total p and its abundance correlated with pyrite contents in samples with higher caco3 contents 5 wt in the investigated samples p was mostly present in authigenic ca p minerals irrespective of pyrite contents we conclude that the p fractionation in anoxic carbonate poor sediments is strongly affected by pyrite oxidation that occurs when these sediments are exposed to oxygen pyrite oxidation produces sulfuric acid and iron oxyhydroxides the abundance of poorly crystalline fe oxyhydroxides provides further evidence that these were indeed formed through recent post recovery oxidation rather than in situ tens of millions of years ago the acid dissolves apatite and the released phosphate is subsequently bound in the freshly formed iron oxyhydroxides pyrite oxidation thus leads to a conversion of authigenic ca p to fe bound p in more calcareous samples caco3 can act as an effective buffer against acidic dissolution of ca p minerals the results indicate that shielding of sediments from atmospheric oxygen is vital to preserve the in situ p fractionation and to enable a valid reconstruction of marine phosphorus cycling based on sediment records

new possibilities in controlled source seismology with a magnetic levitation vibrator summary a new technology broad band seismic land source based on the principle of magnetic levitation is under development the new source is designed to overcome limitations experienced with controlled signal seismic sources at the present time and to create new possibilities in particular the new source extends the constant peak force frequency band down to 2 hz and is capable of at least several weeks continuous coherent transmission it will enable three dimensional long range 200 km controlled signal seismology with the potential for active earth tomography down into the mantle and systematic earthquake precursor measurement and should improve shallow and deep seismic profiling technology the optimum transmission frequencies depend on q transmission range and noise spectrum

phosphorus burial and diagenesis in the central bering sea bowers ridge iodp site u1341 perspectives on the marine p cycle abstract to reconstruct the cycling of reactive phosphorus p in the bering sea a p speciation record covering the last 4 ma was generated from sediments recovered during integrated ocean drilling program iodp expedition 323 at site u1341 bowers ridge a chemical extraction procedure distinguishing between different operationally defined p fractions provides new insight into reactive p input burial and diagenetic transformations reactive p mass accumulation rates mars are 20 110 mol cm2 ka which is comparable to other open ocean locations but orders of magnitude lower than most upwelling settings we find that authigenic carbonate fluorapatite cfa and opal bound p are the dominant p fractions at site u1341 an overall increasing contribution of cfa to total p with sediment depth is consistent with a gradual sink switching from more labile p fractions fish remains fe oxides organic matter to stable authigenic cfa however the positive correlation of cfa with al content implies that a significant portion of the supposedly reactive cfa is non reactive detrital contamination by eolian and or riverine cfa in contrast to cfa opal bound p has rarely been studied in marine sediments we find for the first time that opal bound p directly correlates with excess silica contents this p fraction was apparently available to biosiliceous phytoplankton at the time of sediment deposition and is a long term sink for reactive p in the ocean despite the likelihood for diagenetic re mobilisation of this p at depth indicated by increasing ratios of excess silica to opal bound p average reactive p mars at site u1341 increase by 25 if opal bound p is accounted for but decrease by 25 if 50 of the extracted cfa fraction based on the lowest cfa value at site u1341 is assumed to be detrital combining our results with literature data we present a qualitative perspective of terrestrial cfa and opal bound p deposition in the modern ocean riverine cfa input has mostly been reported from continental shelves and margins draining p rich lithologies while eolian cfa input is found across wide ocean regions underlying the northern hemispheric dust belt opal bound p burial is important in the southern ocean north pacific and likely in upwelling areas shifts in detrital cfa and opal bound p deposition across ocean basins likely occurred over time responding to changing weathering patterns sea level and biogenic opal deposition

conditions required for oceanic anoxia euxinia constraints from a one dimensional ocean biogeochemical cycle model article i nfo widespread black shale depositional intervals termed oceanic anoxic events oaes occurred repeatedly during the phanerozoic eon here we developed a new vertical one dimensional ocean biogeochemical cycle model that involves several chemical reactions in an oxic anoxic sulfidic water column to explore the theoretical constraints for global oceanic anoxia euxinia quantitatively and systematically we conducted sensitivity analyses of the proposed causal mechanisms including elevated rates of riverine phosphorus p input ocean stagnation and lowered oxygen solubility due to climate warming we gave special attention to the vertical chemical structure of the ocean and also to the characteristic behaviors of the marine p cycle under anoxic conditions because the relationship between the depth of anoxia and the benthic phosphorus flux could be important for the occurrence of oceanic anoxia euxinia steady state simulations indicated that 1 a decrease in ocean stagnation or oxygen solubility is not enough by itself to achieve widespread anoxia with the present reactive p river input rate and 2 shallow water anoxia followed by massive p liberation from surface sediments can lead to widespread eutrophication and anoxia euxinia we conclude that elevated riverine flux of reactive p is the most important factor for triggering global anoxic events via a positive feedback loop among ocean anoxia phosphorus regeneration and surface biological productivity

u th ages obtained by mass spectrometry in corals from barbados sea level during the past 130 000 years the study of the sea level record during the last glacial cycle has primarily proceeded indirectly by means of oxygen isotope measurements on foraminifera from deep sea sediments1 2 the direct approach of dating sea level indicators stagnated during the past decade mainly because the samples required to complete our knowledge of the past glaciations are below the present day sea level3 7 using the 14c ages of acropora palmata samples collected by drilling offshore the island of barbados fairbanks8 presented the first detailed chronology for the last deglaciation this radiocarbon chronology is limited to the past 30 kyr because of the short half life of 14c 5 730 yr we must therefore rely on other dating methods to obtain information for the whole last glacial cycle during the past four years 230th 234u dating of corals by thermal ionization mass spectrometry has been shown to be significantly more precise and accurate than the classical counting method9 14 we have used this technique to measure u th ages in coral samples from the barbados collection and from subaerially exposed outcrops see also ref 15 here we present results bearing on the sea level record for the past 130 000 years we conclude that the last deglaciation started 3 000 years earlier than previously thought and confirm that there were two surges in melt water8 at about 11 kyr and 14 kyr bp before present

predictive uncertainty of peak outflow relations for landslides dam breach risk assessment development considering the failure of landslide dams often requires the estimation of peak outflow through the breach the empirical equations based on data from case studies tend to be the first direct approach this paper conducted an uncertainty analysis when these empirical relations were utilized to predict the peak outflow of a breached landslide dam the results suggest that the relations derived from manmade dams or embankments typically overestimate the peak outflow about 1 5 to 3 4 of an order of magnitude and the relations derived from the database of landslide dams have much smaller mean prediction errors and also exhibit broad uncertainty bands application of the uncertainly analysis was illustrated by the tangjiashan landslide dammed lake formed during 2008 wenchuan earthquake in addition the predicted results from eq 1 deduced herein were considered to be the reliable estimate of peak outflow through the breach of landslide dam

paleoenvironmental changes during the valanginian new insights from variations in phosphorus contents and bulk and clay mineralogies in the western tethys paleoenvironmental and paleoclimatic changes during the valanginian carbon isotopic excursion cie have been investigated in the western tethys for this purpose bulk rock and clay mineralogies as well as phosphorus p contents were evaluated in a selection of five sections located in the vocontian basin angles se france alvier e switzerland malleval e france and the lombardian basin capriolo n italy breggia s switzerland within the cie interval bulk rock and clay mineralogies are inferred to reflect mostly climate change the onset of the cie busnardoites campylotoxus ammonite zone is characterized by higher detrital index di sum of the detrital minerals divided by calcite contents values and the presence of kaolinite in their clay mineral assemblages in the late valanginian from the saynoceras verrucosum zone up to the end of the valanginian the samples show relatively variable di and lower values or the absence of kaolinite the variation in the mineralogical composition is interpreted as reflecting a change from a climate characterized by optimal weathering conditions associated with an increase in terrigenous input on the southern european margin during the cie towards an overall unstable climate associated with drier conditions in the late valanginian this is contrasted by a dissymmetry proximal vs distal along the studied transect the northern tethyan margin being more sensitive to changes in continental input compared to the distal environments p accumulation rates par present similar features in the vocontian basin p content variations are associated with changes in terrigenous influx whereas in the lombardian basin i e capriolo and breggia par values are less well correlated this is mainly because the deeper part of the tethys was less sensitive to changes in continental inputs the onset of the cie top of the b campylotoxus zone records a general increase in par suggesting an increase in marine nutrient levels this is linked to higher continental weathering rates and the enhanced influx of nutrients into the ocean in the period corresponding to the shift itself p contents show a dissymmetry between the vocontian and lombardian basins proximal vs distal for the sections of malleval alvier and angles a decrease in p concentrations associated to a decrease in detrital input is observed in capriolo and breggia par show maximum values during the plateau indicating a more complex interaction between different p sources the time interval including the top of s verrucosum zone up to the end of the valanginian is characterized by variable par values suggesting variable nutrient influxes these changes are in agreement with an evolution towards seasonally contrasted conditions in the late valanginian

the oceanic phosphorus cycle and continental weathering during the neogene little is known about the history of dissolved phosphorus p input to the ocean during the cenozoic an important factor in reconstructing global change because of the role of p in controlling net oceanic productivity and organic carbon burial we present p accumulation rates from the eastern neogene and western cenozoic equatorial pacific a region chosen to reflect oceanic p input trends because of its importance in global models of new production and biogenic sedimentation p accumulation rates range from 5 to 60 mol p cm 2 kyr 1 and exhibit a positive correlation with mass sediment accumulation rates calcium carbonate being the major sediment component the influences of surface productivity patterns site migration through time relative to equatorial upwelling and water depth are observed in the p accumulation rate records these site specific effects are relatively minor however compared to synchronous significant trends in p accumulation rates in these equatorial pacific sites the most notable event occurred in the late miocene when mean p accumulation rates exhibited a strong peak at 5 6 ma to the highest mean value of the neogene 37 mol p cm 2 kyr 1 followed by a sharp decrease to 1 2 ma 14 mol p cm 2 kyr 1 after which values increased slightly to the present these changes in p accumulation rates in the equatorial pacific translate into substantial changes in p burial the decrease from 5 6 to 1 2 ma signified a 62 decrease in p burial in the equatorial pacific and the difference is equivalent to 14 of the estimated modern p input rate to the oceans some of the late neogene change in the equatorial pacific p accumulation rate record may have been due to redistribution of p burial to high latitude regions however on the basis of p mass balance considerations redistribution alone cannot account for the bulk of the change in p accumulation and burial in the equatorial pacific the p accumulation rate record is markedly different from the unidirectional increases in continental weathering rates over the last 40 m y interpreted from the sr isotope record suggesting a decoupling of nutrient input fluxes from input fluxes of other dissolved constituents

early diagenetic processes in recent sediments of the gulf of st lawrence phosphorus carbon and iron burial rates abstract selective extraction procedures were used to quantify different forms of solid phase phosphorus carbon and iron in marine sediments and to evaluate the impact of authigenic formation of mineral forms such as carbonate fluorapatite cfa calcium carbonate caco3 and pyrite fes2 on major elemental cycles during early diagenesis detrital p and fe phases were successfully used as indicators of the constancy or variability of detrital inputs to several sedimentary environments from the deep channels of the gulf of st lawrence in cores characterized by near steady state influx rates solid phase p c and fe data and sediment burial rates indicate that cfa caco3 and probably fes2 are currently forming in the sediments of the gulf however high concentrations and or formation of caco3 in marine sediments appear to inhibit the formation of authigenic cfa on the other hand the formation of fes2 does not influence authigenic cfa precipitation in the deep troughs of the gulf of st lawrence total p burial rates range from 50 to 500 mgp m2 yr truly authigenic precipitation of cfa when observed may represent up to 25 of the total burial rate of p bioturbation of sub surface sediments reduces the potential for authigenic precipitation of cfa and caco3 thus affecting immobilization reactions that have a strong impact on the global oceanic cycles of c and p the spatial heterogeneity of diagenetic reactions precludes the establishment of an accurate quantification of p removal on the scale of a continental shelf such as the gulf of st lawrence

a procedure for landslide susceptibility zonation by the conditional analysis method numerous methods have been proposed for landslide probability zonation of the landscape by means of a geographic information system gis among the multivariate methods i e those methods which simultaneously take into account all the factors contributing to instability the conditional analysis method applied to a subdivision of the territory into unique condition units is particularly straightforward from a conceptual point of view and particularly suited to the use of a gis in fact working on the principle that future landslides are more likely to occur under those conditions which led to past instability landslide susceptibility is defined by computing the landslide density in correspondence with different combinations of instability factors the conceptual simplicity of this method however does not necessarily imply that it is simple to implement especially as it requires rather complex operations and a high number of gis commands moreover there is the possibility that in order to achieve satisfactory results the procedure has to be repeated a few times changing the factors or modifying the class subdivision to solve this problem we created a shell program which by combining the shell commands the gis geographical research analysis support system grass commands and the gawk language commands carries out the whole procedure automatically this makes the construction of a landslide susceptibility map easy and fast for large areas too and even when a high spatial resolution is adopted as shown by application of the procedure to the parma river basin in the italian northern apennines

controls on phosphorus regeneration and burial during formation of eastern mediterranean sapropels the carbon c and phosphorus p geochemistry of sapropels from four sites in the eastern mediterranean sea was determined to obtain more insight into the role of differences in sediment accumulation rates and bottom water anoxia on p regeneration and burial in sediments sediment corg porg with org organic ratios above redfield indicate enhanced regeneration of p relative to c from organic matter during formation of the most recent sapropel s1 and a pliocene sapropel odp site 969e i 282c release of p from fe oxides was relatively unimportant increased burial of ca p authigenic carbonate fluorapatite and or biogenic hydroxyapatite occurred but was of minor importance compared to the enhanced p release from organic matter for sapropel s1 corg porg and corg preac with reac reactive defined as the sum of organic fe bound authigenic and biogenic ca p ratios decreased with increasing sedimentation rate and oxygen exposure and decreasing water depth whether the water column in the deep basin was dysoxic semi euxinic s1 or euxinic pliocene does not appear to affect the estimated burial efficiencies of porg and preac enhanced corg burial under the euxinic water column explains the much higher corg porg and corg preac ratios in the pliocene sapropel on average 2860 and 760 respectively compared to sapropel s1 on average 530 and 160 respectively

assessing mutuality of change in soil and vegetation patch pattern characteristics by means of cellular automata simulation mutual variations in soil and vegetation pattern characteristics have not received much attention despite their role in the evolution of eco geomorphic systems five landscape metrics were employed to characterize complementary soil and vegetation patterns of patches over a wide range of densities number density size heterogeneity shape and dominance these metrics were calculated for a large number of modeled patterns based on a cellular automata technique employing four separate vegetation spread strategies at different adhesive growth levels as indicated by the data mutual variations in the soil and vegetation metrics allow differentiation between the pattern evolution stages such as perforation dissection fragmentation shrinkage and attrition of one surface type due to the spread expansion and aggregation of a complementary surface type such information may be indicative of the hydro geomorphological processes taking place

travel time monitoring with vibroseis abstract the general failure of searches for precursory seismic travel time variations associated with strike slip earthquakes in california has led to this investigation into the feasibility of using a controlled source seismic method to improve significantly the precision of travel time measurements and to investigate the nature of any detected travel time changes travel times have been measured over a period of several years at sites south of hollister california along the seismically active creeping zone of the san andreas fault using a single channel vibroseis system with real time on site data processing at a site near bear valley 7 km from the fault no variations in the travel time of a deep crustal reflection were observed that could be associated with local earthquakes however significant variations 0 5 to 2 5 msec of first arrival travel times observed near the cienega winery may have been associated with a series of nearby earthquakes and with a creep event major sources of measurement error have been identified in source variations and in rainfall induced variations in near surface properties the former limits the precision of the deep reflection measurements to about 0 05 per cent of the travel time and the first arrival measurements to about 0 1 per cent of the travel time the second effect is apparent as seasonal oscillations in travel time of as much as 15 to 20 msec and also in wavelet amplitude and waveform giving an implied travel time accuracy of about 0 2 per cent for the deep reflection measurements and about 1 per cent for first arrivals while these noise levels are disappointing they can be reduced significantly by improved field procedures ongoing experiments are testing such procedures

seismic vibrator control and the downgoing p wave while the need for phase compensation is well established the best method to measure the seismic vibrator output is not phase control of the force exerted by a seismic vibrator upon the earth s surface ground force is shown to be useful in producing consistent downhole p wave signatures experimental results are presented which compare the downhole correlation wavelets produced by phase locking to ground force reaction mass acceleration and baseplate acceleration as changes in vibrator type sweep bandwidth drive level and coupling medium are made the empirical results support earlier theoretical work which predicts with suitable assumptions that ground force and far field particle displacement are in phase except for a time delay

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

modelling oceanic carbon and phosphorus fluxes implications for the cause of the late cenomanian oceanic anoxic event oae2 a two box ocean model with a coupled carbon and phosphorus cycle is used to test which processes can realistically generate a rapid positive 2 13c excursion in the global carbon reservoir internal oceanic processes enhanced preservation of organic matter under anoxic conditions enhanced upwelling cannot produce a substantial 13c excursion under the assumption that burial rates of c and p are coupled loss of nutrients to the sediment acts as a negative feedback mechanism that prevents a substantial perturbation of the carbon cycle a large and renewable source of nutrients is needed either from increased continental weathering or from enhanced regeneration of sedimentary organic phosphorus under anoxic conditions measurements of total phosphorus and organic carbon in sediments from the tarfaya basin morocco suggest that a large decrease in p burial occurred relative to organic carbon at the base of the cenomanian turonian oceanic anoxic event oae2 with the right magnitude to quantitatively explain a 2 shift in 13c it is concluded that the main underlying mechanism that allowed and sustained enhanced carbon burial during the mid cretaceous was a perturbation of the oceanic phosphorus cycle

phosphorus burial as a function of paleoproductivity and redox conditions in arabian sea sediments in this study the response of sedimentary phosphorus p burial to changes in primary productivity and bottom water oxygen concentrations during the late quaternary is investigated using two sediment cores from the arabian sea one recovered from the continental slope and the other from the deep basin the average solid phase p speciation in both cores is similar authigenic and biogenic fish debris apatite make up the bulk of the p inventory ca 70 whereas p adsorbed to iron oxides organic p and detrital apatite constitute minor fractions postdepositional redistribution has not significantly altered the downcore distribution of total solid phase p phosphorus burial efficiencies are generally lower during periods of increased paleoproductivity this is caused by a partial decoupling of the p export flux consisting primarily of particulate organic p and the p burial flux consisting primarily of biogenic and authigenic apatite and b the lack of increased rates of authigenic cfa formation during periods of higher p deposition in addition fluctuations in bottom water oxygen concentrations may have affected p burial in continental slope sediments the results of this study indicate that higher primary productivity induces more efficient p cycling on time scales exceeding the oceanic p residence time this process may induce higher surface water productivity thus creating a positive feedback loop in the arabian sea this feedback mechanism may have contributed to changes in sea surface productivity on sub milankovitch time scales because p regenerated on the continental slopes of the oman and somalian coastal upwelling zones is reintroduced into the photic zone relatively fast

co diagenesis of iron and phosphorus in hydrothermal sediments from the southern east pacific rise implications for the evaluation of paleoseawater phosphate concentrations abstract we present a detailed study of the co diagenesis of fe and p in hydrothermal plume fallout sediments from 19 s on the southern east pacific rise three distal sediment cores from 340 1130 km from the ridge crest collected during dsdp leg 92 were analysed for solid phase fe and p associations using sequential chemical extraction techniques the sediments at all sites are enriched in hydrothermal fe oxyhydr oxides but during diagenesis a large proportion of the primary ferrihydrite precipitates are transformed to the more stable mineral form of goethite and to a lesser extent to clay minerals resulting in the release to solution of scavenged p however a significant proportion of this p is retained within the sediment by incorporation into secondary goethite by precipitation as authigenic apatite and by readsorption to fe oxyhydr oxides molar p fe ratios for these sediments are significantly lower than those measured in plume particles from more northern localities along the southern east pacific rise and show a distinct downcore decrease to a depth of 12 m molar p fe ratios are then relatively constant to a depth of 35 m the fe and p speciation data indicate that diagenetic modification of the sediments is largely complete by a depth of 2 5 m and thus depth trends in molar p fe ratios can not solely be explained by losses of p from the sediment by diffusion to the overlying water column during early diagenesis instead these sediments are likely recording changes in dissolved p concentrations off the sepr possibly as a result of redistribution of nutrients in response to changes in oceanic circulation over the last 10 million years furthermore the relatively low molar p fe ratios observed throughout these sediments are not necessarily solely due to losses of scavenged p by diffusion to the overlying water column during diagenesis but may also reflect post depositional oxidation of pyrite originating from the volatile rich vents of the southern east pacific rise this study suggests that the molar p fe ratio of oxic fe rich sediments may serve as a proxy of relative changes in paleoseawater phosphate concentrations particularly if fe sulfide minerals are not an important component during transport and deposition

evolution of a landslide creating a temporary lake successful prediction the anzola landslide is a complex landslide that failed on the left side of the ceno valley northern apennines italy it was studied using a multidisciplinary approach in which geomorphology geology and engineering geology were combined to understand the kinematics evolution the main rock mass characteristics the behavior of the landslide and its morphologic evolution the anzola landslide in 1996 was probably a neo activation it was affected by at least three re activations recently always in connection with heavy rainfall which twice caused the blockage of the valley and formed a small lake the possibility of river blockage as a consequence of the re activation of the landslide was investigated using a grass gis based shell script that simulates the landslide material descent and computes the dam and lake sizes the simulations allowed assessment of the amount of the depleted material coupled with the morphological situation characterized by a very narrow riverbed that can lead easily to the formation of consistent damming and lakes this situation of course can represent a serious risk in case of a dam break and the ensuing flooding could affect downstream infrastructures and small villages

terrigenous input and paleoproductivity in the southern ocean the geochemistry of several sites along the polar front zone of the southern ocean revealed significant changes in terrigenous input and productivity on glacial timescales our records indicate concentrations and fluxes of terrigenous elements i e fe al and ti are low during interglacials and increase tenfold to twentyfold during glacials phosphorus accumulation reactive p concentrations and p ti ratios exhibit similar trends as the terrigenous components suggesting increased export production during glacials in all cores elemental ratios remain relatively constant indicating terrigenous sources at each site have not likely varied over the past 250 kyr iron accumulation rates for these sites are 10 times higher during glacials than interglacials and exceed the estimated regional eolian fluxes by 50 times the source of this terrigenous material is thus likely to be hemipelagic rather than direct eolian input or ice rafting and we speculate fe upwelled from this source may have stimulated glacial productivity in the southern ocean

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

experimental study of igneous and sedimentary apatite dissolution control of ph distance from equilibrium and temperature on dissolution rates apatite dissolution experiments were conducted using both a fluidized bed and stirred tank reactor over a range of ph temperature solution saturation state and on non carbonated and carbonated apatite compositions igneous fluorapatite fap and sedimentary carbonate fluorapatite cfa respectively from 2 8 5 were not possible due to detection limits of the analytical techniques used in this study and the high insolubility of fap for the cfa compositions studied the dissolution rate decreased with increasing ph from 4 ph 7 during early stages of the dissolution reaction for both fap and cfa mineral components were released in non stoichiometric ratios with reacted solution ratios of dissolved ca p and ca f being greater than mineral stoichiometric ratios suggesting that ca was preferentially released compared to p and f from the mineral structure during the early stages of dissolution an increase in reacted solution ph accompanies this early elevated release of ca as the dissolution reaction proceeded to steady state dissolution became congruent when normalized to bet measured surface area fap dissolved faster from 4 ph 7 compared to cfa the apparent arrhenius activation energy ea of fap dissolution over the temperature range of 25 55 c at ph 3 0 i 0 1 and pco2 0 is 8 3 0 2 kcal mol 1 both the apparent exchange of solution h for solid bound ca at low ph in the early stage of dissolution and the ea of dissolution suggest a surface and not a diffusion controlled dissolution reaction for fap and cfa the degree of undersaturation of the solution gr with respect to fap was important in determining the dissolution rate at ph 3 0 i 0 1 and pco2 0 the dissolution rate of fap was 5 greater in the far from equilibrium region compared to the near equilibrium slope region a simple apatite weathering model incorporating the experimental results from this study was constructed and numerical calculations suggest that during the phanerozoic both the surface area of igneous rock available for weathering and the average global temperature were important factors in determining the p weathering flux from apatite dissolution it is possible that elevated global temperatures coupled with relatively high surface area of igneous rock during the early to mid paleozoic resulted in elevated p weathering fluxes which along with climatic evolutionary pressures of the neoproterozoic facilitated the radiation of multicellular organisms large scale phosphorite deposition and abundance of calcium phosphate shelled organisms during the early cambrian

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

nutrients as the dominant control on the spread of anoxia and euxinia across the cenomanian turonian oceanic anoxic event oae2 model data comparison 1 the cenomanian turonian oceanic anoxic event oae2 is characterized by large perturbations in the oxygen and sulfur cycles of the ocean potentially resulting from changes in oxygen supply via oxygen solubility and ocean circulation and in marine productivity we assess the relative impact of these mechanisms comparing model experiments with a new compilation of observations for seafloor dysoxia anoxia and photic zone euxinia the model employed is an intermediate complexity earth system model which accounts for the main ocean dynamics and biogeochemistry of the cretaceous climate the impact of higher temperature and marine productivity is evaluated in the model as a result of higher atmospheric carbon dioxide and oceanic nutrient concentrations the model shows that temperature is not alone able to reproduce the observed patterns of oceanic redox changes associated with oae2 observations are reproduced in the model mainly via enhanced marine productivity due to higher nutrient content responsible for 85 of the change higher phosphate content could have been sustained by increased chemical weathering and phosphorus regeneration from anoxic sediments which in turn induced an enhanced nitrogen nutrient content of the ocean via nitrogen fixation the model also shows that the presence of seafloor anoxia as suggested by black shale deposition in the proto north atlantic ocean before the event might be the result of the silled shape and lack of deep water formation of this basin at the late cretaceous overall our model data comparison shows that oae2 anoxia was quasi global spreading from 5 of the ocean volume before the event to at least 50 during oae2

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

major risk from rapid large volume landslides in europe eu project runout abstract project runout has investigated methods for reducing the risk from large volume landslides in europe especially those involving rapid rates of emplacement using field data from five test sites bad goisern and kofels in austria tessina and vajont in italy and the barranco de tirajana in gran canaria spain the studies have developed 1 techniques for applying geomorphological investigations and optical remote sensing to map landslides and their evolution 2 analytical numerical and cellular automata models for the emplacement of sturzstroms and debris flows 3 a brittle failure model for forecasting catastrophic slope failure 4 new strategies for integrating large area global positioning system gps arrays with local geodetic monitoring networks 5 methods for raising public awareness of landslide hazards and 6 geographic information system gis based databases for the test areas the results highlight the importance of multidisciplinary studies of landslide hazards combining subjects as diverse as geology and geomorphology remote sensing geodesy fluid dynamics and social profiling they have also identified key goals for an improved understanding of the physical processes that govern landslide collapse and runout as well as for designing strategies for raising public awareness of landslide hazards and for implementing appropriate land management policies for reducing landslide risk

the formation and failure of natural dams of the numerous kinds of dams that form by natural processes dams formed from landslides glacial ice and late neoglacial moraines present the greatest threat to people and property landslide dams form in a wide range of physiographic settings the most common types of mass movements that form landslide dams are rock and debris avalanches rock and soil slumps and slides and mud debris and earth flows the most common initiation mechanisms for dam forming landslides are excessive rainfall and snowmelt and earthquakes landslide dams can be classified into six categories based on their relation with the valley floor type i dams 11 of 184 landslide dams from around the world that we were able to classify do not reach from one valley side to the other type ii dams 44 span the entire valley floor in some cases depositing material high on opposite valley sides type iii dams 41 move considerable distances both upstream and downstream from the landslide failure type iv dams 1 are rare and involve the contemporaneous failure of material from both sides of a valley type v dams 1 also are rare and are created when a single landslide sends multiple tongues of debris into a valley and forms two or more landslide dams in the same reach of river type vi dams 3 involve one or more failure surfaces that extend under the stream or valley and emerge on the opposite valley side many landslide dams fail shortly after formation in our sample of 73 documented landslide dam failures 27 of the landslide dams failed less than 1 day after formation and about 50 failed within 10 days over topping is by far the most common cause of failure the timing of failure and the magnitude of the resulting floods are controlled by dam size and geometry material characteristics of the blockage rate of inflow to the impoundment size and depth of the impoundment bedrock control of flow and engineering controls such as artificial spill ways diversions tunnels and planned breaching by blasting or conventional excavation glacial ice dams can produce at least nine kinds of ice dammed lakes the most dangerous are lakes formed in main valleys dammed by tributary glaciers failure can occur by erosion of a drainage tunnel under or through the ice dam or by a channel over the ice dam cold polar ice dams generally drain supraglacially or marginally by downmelting of an outlet channel warmer temperate ice dams tend to fail by sudden englacial or subglacial breaching and drainage late neoglacial moraine dammed lakes are located in steep mountain areas affected by the advances and retreats of valley glaciers in the last several centuries these late neoglacial dams pose hazards because 1 they are sufficiently young that vegetation has not stabilized their slopes 2 many dam faces are steeper than the angle of repose 3 these dams and lakes are immediately downslope from steep crevassed glaciers and near vertical rock slopes and 4 downstream from these dams are steep canyons with easily erodible materials that can be incorporated in the flow and increase flood peaks the most common reported failure mechanism is overtopping and breaching by a wave or series of waves in the lake generated by icefalls rockfalls or snow or rock avalanches melting of ice cores or frozen ground and piping and seepage are other possible failure mechanisms natural dams may cause upstream flooding as the lake rises and downstream flooding as a result of failure of the dam although data are few for the same potential energy at the dam site ownstream flood peaks from the failure of glacier ice dams are smaller than those from landslide moraine and structed earth fill and rock fill dam failures moraine dam failures appear to produce some of the largest downstream flood peaks for potential energy at the dam site greater than 1011 1012 joules differences in flood peaks natural dam failures appear to be controlled by dam characteristics and failure mechanisms

ocean chemistry during glacial time abstract measurements of co2 to air ratios in the gas trapped in bubbles in ice of glacial age suggest that the co2 content of the atmosphere was considerably lower during peak glacial time than during holocene time the purpose of this paper is to show that such a change must in all likelihood be the result of alterations in the nutrient element chemistry of sea water two possible scenarios are presented one involves alternate storage and erosion of phosphorous leaving residues from shelf sediments the other involves changes in the c p ratio in the organic debris falling to the deep sea means of verifying the nutrient cycle hypothesis are also given it is shown that the 13c record as we know it in planktonic and benthic foraminifera the oxygen record as inferred from benthic foraminifera species distributions and the early post glacial caco3 preservation event as recorded by aragonitic pteropods are consistent with both of the hypotheses presented only if an early post glacial spike in the 13c record for planktonic shells could be found would it be possible to eliminate one of these hypotheses i e that involving shelf storage the implications of these nutrient hypotheses to climate theory are as follows if shelf storage is responsible for the glacial to interglacial co2 increase then the co2 change must be considered an amplifier of some primary cause the reason is that sea level changes are needed to drive deposition on and erosion from the shelves on the other hand if changes in the c p ratio for falling debris are responsible then the co2 change could either be an amplifier or a primary cause for the major glacial to interglacial climatic cycle the latter is possible as self sustained oscillations in ocean chemistry might be driven by interactions between ocean ecology and ocean nutrient chemistry

carbon and phosphorus cycling in anoxic sediments of the saanich inlet british columbia abstract uncertainty currently exists about the removal of carbon c and phosphorus p from the oceanic reservoir especially in low oxygen settings in this paper the cycling of c and p is examined in sediments from the anoxic saanich inlet cored by ocean drilling program odp leg 169s in 1996 at two sites although c org p org ratios are high and increase with depth in the saanich inlet this effect is due largely to a remobilization of p from an organic matter sink to an authigenic sink reducible sedimentary components act as temporary shuttles in this process even in this anoxic setting with the ultimate burial sink for the remobilized p being carbonate fluorapatite the effective c org p reactive molar ratio appears to be about 150 200 indicating some preferential loss of p compared to c during organic matter degradation but not approaching previously reported values of over 3000 in black shales reactive p accumulation rates in this basin range from 10 000 60 000 mol cm 2 kyr greatly exceeding the range of 500 8000 mol cm 2 kyr found in most continental margin settings including regions of modern phosphogenesis the initiation of marine sedimentation in the saanich inlet occurred after deglaciation and the high rates of p burial seen here may provide an end member example of the effects of sea level and margin sedimentation on the distribution of p within the marine p cycle

iron and manganese shuttles control the formation of authigenic phosphorus minerals in the euxinic basins of the baltic sea microanalysis of epoxy resin embedded sediments is used to demonstrate the presence of authigenic iron fe ii phosphates and manganese mn calcium ca carbonate phosphates in the deep euxinic basins of the baltic sea these minerals constitute major burial phases of phosphorus p in this area elevating the total p burial rate above that expected for a euxinic depositional environment particle shuttles of fe and mn oxides into the deep euxinic basins act as drivers for p bearing mineral authigenesis while fe ii phosphates are formed continuously in the upper sediments following the sulfidization of fe oxyhydroxides and release of associated p mn ca carbonate phosphates are formed intermittently following inflow events of oxygenated north sea water into the deep basins the mechanism of fe ii phosphate formation differs from previously reported occurrences of vivianite formation in marine sediments by occurring within rather than below the sulfate methane transition zone the spatial distribution of both authigenic phases in baltic sediments varies in accordance with the periodic expansion of anoxia on centennial to millennial timescales the results highlight the potential importance of authigenic p bearing minerals other than carbonate fluorapatite for total p burial in euxinic basins

artificial neural networks applied to landslide susceptibility assessment abstract landslide hazard mapping is often performed through the identification and analysis of hillslope instability factors usually managed as thematic data within geographic information systems gis in heuristic approaches these factors are rated by the attribution of scores based on the assumed role played by each of them in controlling the development of a sliding process other more refined methods based on the principle that the present and the past are keys to the future have also been developed thus allowing less subjective analyses in which landslide susceptibility is assessed by statistical relationships between past landslide events and hillslope instability factors the objective of this research is to define a method with the ability to forecast landslide susceptibility through the application of artificial neural networks anns the riomaggiore catchment a subwatershed of the reno river basin located in the northern apennines italy was chosen as an ideal test site as it is representative of many of the geomorphological settings within this region in the present application two different anns used in classification problems were set up and applied one belonging to the category of multi layered perceptron mlp and the other to the probabilistic neural network pnn family the hillslope factors that have been taken into account in the analysis were the following a lithology b slope angle c profile curvature d land cover and e upslope contributing area these factors have been classified on nominal scales and their intersection allowed 3342 homogeneous domains unique condition unit ucu to be singled out which correspond to the terrain units utilized in this analysis the model vector used to train the anns is a subset of that derived from the production of unique condition units and consists of 3342 records organized in input and output variable vectors in particular the hillslope factors once classified on nominal scales as binary numbers represent the 19 input variables while the presence absence of a landslide in a given terrain unit is assumed to be the output variable the comparison between the most up to date landslide inventory of the riomaggiore catchment and the hazardous areas as predicted by the anns showed satisfactory results with a slight preference for the mlp for this reason this is an encouraging preliminary approach towards a systematic introduction of ann based statistical methods in landslide hazard assessment and mapping

simulation of event based landslides and debris flows at watershed level abstract a coupled model has been developed to simulate at watershed level landslides and debris flows induced by a severe typhoon tropical cyclone in taiwan the model comprises a landslide susceptibility model to predict landslide occurrence an empirical model to select debris flow initiation points and a debris flow model to simulate the transport and deposit of failed materials from the identified source areas in raster format with a 10 m spatial resolution the model output includes unstable cells debris flow initiation cells debris flow velocities runout paths and deposition zones the model was first tested and calibrated in a small area where the damage by landslides had been investigated and recorded it was then applied to a watershed and the simulation results were validated by comparing them with a landslide debris flow inventory map prepared from satellite images using a multiple change detection technique model test and validation results confirm the usefulness of the model in predicting the number and size of affected areas landslides and runouts combined runout path and volume of runout deposits it is a common practice in taiwan to separate landslide and debris flow inventories and to study debris flows only in select drainage basins this study suggests that landslide and debris flow should be modeled as a sequential process for efficient watershed management

geomorphic hazard assessment of landslide dams in south westland new zealand fundamental problems and approaches abstract quantitative assessments of landslide hazard usually employ empirical heuristic deterministic or statistical methods to derive estimates of magnitude frequency distributions of landsliding the formation and failure of landslide dams are common geomorphic processes in mountain regions throughout the world causing a series of consequential off site hazards such as catastrophic outburst floods debris flows backwater ponding up and downstream aggradation and channel instability conceptual and methodological problems of quantifying geomorphic hazard from landslide dams result from a aspects of defining landslide dam magnitude b scaling effects i e the geomorphic long range and long term implications of river blockage and c paucity of empirical data geomorphic hazard from a landslide dam break flood on the basis of conditional probabilities is being analysed for the alpine south westland region of new zealand where formation and failure of landslide dams is frequent quantification of the annual probability of landsliding and subsequent dam formation in the area is limited by historical and only partially representative empirical data on slope instability since landslide dam stability is a major control governing the potential of catastrophic outburst flooding the ensuing hazard is best assessed on a recurring basis gis based modelling of virtual landslide dams is a simple and cost effective approach to approximate site specific landslide dam and lake dimensions reservoir infill times and scaled magnitude of potential outburst floods although crude these order of magnitude results provide information critical to natural hazard planning mitigation or emergency management decisions

impact of glacial interglacial sea level change on the ocean nitrogen cycle the continental shelves are the most biologically dynamic regions of the ocean and they are extensive worldwide especially in the western north pacific their area has varied dramatically over the glacial interglacial cycles of the last million years but the effects of this variation on ocean biological and chemical processes remain poorly understood conversion of nitrate to n2 by denitrification in sediments accounts for half or more of the removal of biologically available nitrogen fixed n from the ocean the emergence of continental shelves during ice ages and their flooding during interglacials have been hypothesized to drive changes in sedimentary denitrification denitrification leads to the occurrence of phosphorus bearing n depleted surface waters which encourages n2 fixation the dominant n input to the ocean an 860 000 y record of foraminifera shell bound n isotopes from the south china sea indicates that n2 fixation covaried with sea level the n2 fixation changes are best explained as a response to changes in regional excess phosphorus supply due to sea level driven variations in shallow sediment denitrification associated with the cyclic drowning and emergence of the continental shelves this hypothesis is consistent with a glacial ocean that hosted globally lower rates of fixed n input and loss and a longer residence time for oceanic fixed n a sluggish ocean n budget during ice ages in addition this work provides a clear sign of sea level driven glacial interglacial oscillations in biogeochemical fluxes at and near the ocean margins with implications for coastal organisms and ecosystems

oxygen isotope fractionation between apatite and aqueous phase phosphate 20 45 c abstract replacement of biogenic caco3 by apatite is an important mode of authigenic apatite formation in marine sediments active along the peru margin today synthesis experiments mimicking this process were undertaken in abiotic inorganic systems in order to determine the oxygen o isotope fractionation between apatite and aqueous phase inorganic phosphate po4 aq caco3 solids were added to po43 solutions made with 18o labeled waters and o isotope fractionations between solid and aqueous phase po43 were determined in a series of experiments at 20 45 c results of 18o analyses of apatite synthesis systems indicate that o isotope fractionation between solid and aqueous phase po43 is 1 not affected by variations in water 18o values 2 initially non equilibrium and 3 relatively small 1 fractionations determined from long term up to 6 years room temperature experiments were 1 due to initial rapid precipitation short experimental run periods 1 week to 4 months resulted in fractionations between apatite and po4 aq that were initially reversed from those of long term experiments over time and with progressive recrystallization these fractionations evolved to reach values consistent with long term experiments

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

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

first simulations of the sarno debris flows through cellular automata modelling abstract cellular automata ca can be efficiently applied in the simulation of complex natural processes they represent an alternative approach to classical methods based on the resolution of differential equations in this paper the general frame and the latest developments of the cellular automata model sciddica simulation through computational innovative methods for the detection of debris flow path using interactive cellular automata for simulating debris flow phenomena are presented landslides characterised by a dominant flow type e g earth flows debris flows debris avalanches can be considered as dynamical systems subdivided into elementary parts that evolve exclusively as a consequence of local interactions in sciddica space and time are discrete in particular the space in which the phenomenon evolves is represented by square cells whose states describe the considered physical characteristics time is implicit in the steps of model computation the peculiarities of the structure permitted to extend sciddica first release in order to progressively account for more complex phenomenological aspects of the considered landslides in this paper examples of application of sciddica to three real landslide events are presented after briefly describing earlier simulations of the 1992 tessina italy earth flow and of the 1984 mt ontake japan debris avalanche first attempts at modelling a debris flow that occurred in 1998 at sarno italy are discussed the model has been validated through the reconstruction of the initial topographic and geomorphological conditions of a selected typical phenomenon which occurred at chiappe di sarno curti on may 1998 and by successively comparing the simulation results with the actually observed debris flow path even though improvements to the algorithms are still needed and further testing of parameters on a more representative sample of phenomena desirable first simulations of the curti landslide have demonstrated the reliability of sciddica in the assessment of debris flow susceptibility

barremian danian chemostratigraphic sequences of the cauvery basin india implications on scales of stratigraphic correlation abstract chemostratigraphic concepts postulate that distinct chemozones could be recognized from rock records to help correlate geographically separated strata many studies have upheld this view but were limited to classic boundaries such as cenomanian turonian or cretaceous tertiary only a few elements and isotopic compositions were made use in such studies an attempt to recognize chemozones of barremian danian strata of the cauvery basin south india through whole rock chemistry had revealed many complex signals and depositional events as expressed by bulk geochemical profiles the signals indicate major shift in sedimentation pattern from dynamic depocenter to stable depositional conditions during santonian varying sensitivities of different elements towards prevalent depositional conditions are also inferred trends of geochemical composition indicated domination of single depositional control all through the depositional history basinal configuration that limited terrestrial sediment source and episodic influx of detrital materials presence of distinct change in whole rock geochemistry across geochronological and lithostratigraphic boundaries is deciphered through a statistical tool anova these results demonstrate that visual delineation of chemozones in a long ranging rock record would be tenuous and has to be exercised with caution

modeling phosphorus cycling and carbon burial during cretaceous oceanic anoxic events article i nfo in the greenhouse world of the cretaceous there were episodes of oxygen depletion in the deep ocean associated with enhanced organic carbon burial in sediments black shale formation in this study we use a box model of the oceanic phosphorus p organic carbon orgc and oxygen cycles to explore the hypothesis that variations in marine p availability control deep ocean oxygen depletion anoxia and the formation of black shales under cretaceous ocean conditions we find that for the cretaceous ocean with large continental shelves slow oceanic overturning and high sea surface temperatures oceanic anoxic events oaes can be triggered by enhanced p supply from land and that the system is particularly sensitive to oceanic mixing in our baseline scenario the deep sea becomes completely anoxic while the shelves attain only partial anoxia sedimentary burial differs between the shelves and open ocean while organic carbon burial is enhanced in both regions deep sea reactive p burial decreases dramatically under anoxia but not on the shelves where oxygen depletion is not complete furthermore our model results imply that oaes can be sustained by p recycling from sediments under low oxygen conditions ultimately however the feedbacks which result in the accumulation of atmospheric oxygen terminate the anoxic event atmospheric oxygen is modulated by land processes such as forest fires and oxidative weathering which limit the rise of atmospheric o2 our model findings are corroborated by p burial data from the geological record for oae2 approximately 94 myr bp through a sensitivity analysis we identify two necessary criteria for oaes low mixing of surface and deep waters poor ocean ventilation and enhanced sedimentary p recycling under low oxygen conditions when these criteria are met ocean anoxia is a robust result to a mild increase of continental supply of phosphorus under a wide range of environmental conditions

climate driven changes in sedimentation rate influence phosphorus burial along continental margins of the northwestern mediterranean abstract the burial of phosphorus p in continental margin sediments is a critical component of the marine reactive p budget and thus an important factor in marine biological productivity we determined downcore records of p from a site drilled on the upper slope of the gulf of lions prgl 1 northwestern mediterranean sea changes in total p content were monitored from marine isotope stage mis 6 to mis 11 in addition in two selected intervals 248 277 ka and 306 342 ka the total p record was expanded by adding detailed geochemical analyses of the various p fractions including oxyhydroxide associated p authigenic p detrital p and organic p increased sedimentation rates during glacials owing to seaward migration of the rhone s mouth enhanced the burial of reactive p oxyhydroxide associated authigenic organic phases by decreasing its time at the reactive sediment water interface in turn resulting in increasing proportion of authigenic to detrital phosphorus the inverse was found for interglacial stages the effects of glacial interglacial variation in sedimentation rate over p geochemistry resulted in changes in sediment water interface oxygenation as well as in the efficiency of p burial as shown by c p org and corg preact proxies respectively two events of high p deposition associated with authigenic p formation at 335 ka paut1 and 275 ka paut2 were associated with periods of rapid disintegration of north atlantic ice sheets leading to ice rafted debris ird deposition these high p deposition events appear to be linked to short warm periods that followed cold episodes enhanced continental runoff owing to more humid conditions during short warm episodes could play a critical role for enhanced biogenic productivity and posterior authigenic p accumulation

phosphorus in foraminiferal sediments from north atlantic ridge cores and in pure limestones samples of foraminiferal ooze from two north atlantic cores were cleaned and progressively dissolved most of the p fe and mn was released during the first of two reductive cleaning steps most of the remainder of these elements and most of the ca were released during the final acid dissolution step the p in these samples is present largely in fe and mn rich coatings not as a constituent of the foraminiferal shells themselves our results are consistent with those of earlier studies the concentration of p in carbonate oozes in which it is clearly associated with coatings is similar to that of modern calcareous sediments in general and with that of reasonably pure limestones of all ages phosphorus is apparently associated with fe mn oxide coatings in many carbonate sediments the rate of removal of p from the oceans as a constituent of such sediments depends on the rate of formation of fe mn coatings not on the rate of incorporation of p into calcium carbonate

discriminant analysis of the geomorphic characteristics and stability of landslide dams article i nfo landslides can cause the formation of dams but these dams often fail soon after lake formation thus rapidly evaluating the stability of a landslide dam is crucial for effective hazard mitigation this study utilizes discriminant analysis based on a japanese dataset consisting of 43 well documented landslide dams to determine the significant variables including log transformed peak flow or catchment area and log transformed dam height width and length in hierarchical order which affect the stability of a landslide dam the high overall prediction power 88 4 of the 43 training cases are correctly classified and the high cross validation accuracy 86 demonstrate the robustness of the proposed discriminant models phwl with variables including log transformed peak flow and log transformed dam height width and length and ahwl with variables including log transformed catchment area and log transformed dam height width and length compared to a previously proposed dbi index based graphic approach the discriminant model ahv which uses the log transformed catchment area dam height and dam volume as relevant variables shows better ability to evaluate the stability of landslide dams although these discriminant models are established using a japanese dataset only the present multivariate statistical approach can be applied for an expanded dataset without any difficulty when more completely documented worldwide landslide dam data are available

carbon and phosphorus burial associated with modern phosphorite formation phosphorite formation plays a significant but poorly constrained role in the marine c and p cycles this report concerns a site of modern phosphorite formation on the upper continental slope off southern baja california mexico sta 6 380 m water depth 23 41 n 111 05 w at this site a series of six narrow 1 3 cm partially indurated phosphorite layers have formed authigenically during the last 15 000 years within a surficial section of slowly but steadily accumulating 3 8 10 3 cm year 1 organic rich mud a poorly oxygenated benthic environment has prevailed at the study site since approximately 8100 year b p probably helping to produce and preserve the pristine phosphorite layers the mean p burial flux 1 1 mol cm 2 year 1 recorded by these deposits agrees closely with the downward diffusive p flux 1 3 mol cm 2 year 1 attributed to active francolite growth such a coincidence implies that the phosphorite layers could have formed entirely under present conditions however a much larger upward diffusive p flux 4 2 mol cm 2 year 1 directed out of the sediment limits the efficiency of ongoing phosphorite formation and the most recently deposited sediment does not contain enough labile p to maintain the overall p regeneration rate indefinitely attendant burial fluxes of inorganic and especially organic c 7 7 and 6 6 mol cm 2 year 1 respectively do not accord with a depositional model of coastal upwelling suggesting that an alternative mechanism possibly fe redox cycling controls porewater p concentrations and hence phosphorite formation a comparison with previously published p burial fluxes for a wide variety of other modern marine settings reveals that phosphorite formation in general does not disproportionately affect the global p burial flux from these data we tentatively estimate a minimum global p burial flux of approximately 70 109 mol year 1 with almost 80 occurring on continental margins

the late hauterivian faraoni oceanic anoxic event in the western tethys evidence from phosphorus burial rates in the uppermost hauterivian sediments of the western tethys a short lived anoxic event faraoni event is documented both in the form of an interval enriched in organic matter pelagic realm and in a condensed interval enriched in glauconite and phosphate shelf realm this latter interval represents the onset of a drowning episode on the helvetic carbonate platform along the northern tethyan margin that lasted throughout the early barremian this drowning episode marks a turning point in the way the platform carbonate factory functioned during the hauterivian carbonate production was dominated by heterozoans whereas during the late barremian a photozoan assemblage developed that is preserved in the so called urgonian limestone the late hauterivian faraoni oceanic anoxic event is of particular interest because it is not accompanied by a major positive shift in y 13 c unlike other oceanic anoxic events during the cretaceous valanginian early aptian cenomanian turonian boundary we have analyzed four hemi pelagic sections with regards to their phosphorus content to better understand the palaeoceanographic conditions related to this anoxic event and the associated changes in the shallow water carbonate factory the sections are

gis based cell model for simulating debris flow runout on a fan summary a gis based cell model based on a kinematic approach is proposed to simulate debris flow routing on a fan the sediment water mixture is modeled as a monophasic continuum and the flow pattern is discretized by square cells 1 m in size that coincide with the dem cells flow occurs from cells with a higher mixture free surface to those with a lower mixture free surface a uniform flow law is used if the elevation of the former cell is higher than that of the latter otherwise the flow is simulated using the broad crested weir law erosion and deposition are simulated using an empirical law that is adjusted for a monophasic continuum the sediment concentration in the routing volume is computed at each time step and controls both erosion and deposition the cell model is used to simulate a debris flow that occurred on the rio lazer dolomites north eastern italian alps on november 4th 1966 furthermore the hydrologic and the hydraulic conditions for the initiation of debris flow are simulated providing the solid liquid hydrograph of the resulting debris flow a number of simulations has been carried out with physically reasonable parameters the results are compared with the extension of the debris flow deposition area and the map of observed depths of deposited sediments this comparison shows that the proposed model provides good performance the analysis of sensitivity carried out by systematically varying the model parameters shows that lower performances are associated with parameter values that are not physically reasonable the same event is also simulated using a cellular automata model and a finite volume two dimensional model the results show that the two models provide a sediment deposition pattern less accurate than that provided by the present cell model

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

geochemistry of modern carbonaceous sediments overlain by a water mass showing photic zone anoxia in the saline meromictic lake kai ike southwest japan i early diagenesis of organic carbon nitrogen and phosphorus abstract the early diagenetic effects of organic matter om decomposition in carbonaceous sediments overlain by an anoxic water body were investigated using a sediment core kai4 from the saline meromictic lake kai ike in southwest japan lake kai ike a current model for past anoxic ocean environments is characterized by development of photic zone anoxia and a bacterial plate which create permanent density stratification in the water over the last 40 years rapid decreases in organic carbon corg 55 nitrogen 60 and reactive phosphorus p 85 contents accompanied by 1 increase positive shift in the stable isotope compositions of corg 13corg which is attributed to a preferential loss of low 13corg components during early diagenesis are reflected with increasing depth of the sediments the molar corg p and n p ratios increase with depth from initial values that are very close to those of the redfield ratio during the early diagenesis of om degradation the decomposition rate of p is much faster than that of corg and n in contrast the molar corg n ratios are rather insensitive to various biogeochemical reactions confirming their utility as a proxy for source om although the stable isotope compositions of nitrogen 15n in sedimentary om are useful indicators of om sources correlations to the above mentioned parameters for the kai4 core remain unclear we emphasize that the om present in ancient carbonaceous sediments or sedimentary rocks was most likely subject to very rapid

authigenic p formation and reactive p burial in sediments of the nazare canyon on the iberian margin ne atlantic profiles of different forms of sedimentary phosphorus were measured at four sites at the iberian margin ne atlantic which were chosen on the basis of differences in depositional environment a shelf site 113 m a mid slope station 1387 m and two stations at the head 396 m and base 3097 m of the nazarecanyon the sediment was sequentially extracted for fe bound p carbonate fluorapatite cfa biogenic p caco3 bound p and detrital ca p and non sequentially for total p and inorganic p where the difference between total and inorganic p was assumed to be organic p measurements of organic carbon and nitrogen citrate dithionite bicarbonate and citrate ascorbate bicarbonate extractable fe carbon oxidation rates fe reduction rates phosphate effluxes and sedimentation rates were used to quantify the cycling and burial of phosphorus at each site cfa formation was observed only in sediments of the nazarecanyon where enhanced rates of organic matter decomposition and fe reduction provided the necessary conditions the concentrations of reactive p were similar at all sites but the sediment accumulation rates differed greatly the high bulk accumulation rate at the base of the canyon results in a reactive p burial rate exceeding those estimated for continental margins including the iberian margin by an order of magnitude the estimated p burial efficiency is smallest at the slope station 3 24 reasonably high 63 86 at the shelf and head of the canyon stations and extremely high s 97 at the base of the canyon we propose that local depositories such as those at the base of canyons may be key sites for reactive p burial 2002 elsevier science b all rights reserved

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

phosphorus cycling from the margin to abyssal depths in the proto atlantic during oceanic anoxic event 2 abstract phosphorus p burial during the cenomanian turonian oceanic anoxic event oae 2 93 55 ma was studied using sediment records from four sites in the proto atlantic ocean the sites represent a variety of depositional settings from the continental margin and slope to the abyssal plain strong links between changing marine conditions during oae 2 and p cycling were observed in black shale sections on the continental margin and slope sedimentary p contents and p mars increased around the onset of oae 2 which may reflect enhanced productivity and p burial partly in the form of biogenic apatite fish debris during the main stage of oae 2 phosphorus was efficiently regenerated from the sediment resulting in p depleted sediments and high organic c corg total p ratios the increased availability of dissolved p may have helped to sustain high productivity during oae 2 the termination of oae 2 was associated with a strong recovery of p burial efficiency in the sediment sedimentary records from the two deep sites do not reveal such close links between different stages of oae 2 and the characteristics of p cycling here oae 2 was a period with maximum deposition of relatively thin black shale intervals that alternate with more oxic deep sea sediments the black shale layers record enhanced p regeneration from organic matter and in some cases p enrichment relative to the oxic sediments detailed chemical p fractionation was performed on sediment from all sites but the results were found to mostly reflect diagenesis and sample handling artifacts in these ancient sediments total p concentrations and the corg total p ratio appear to be the most robust indicators of p cycling and regeneration

productivity records from the southern ocean and the equatorial pacific ocean testing the glacial shelf nutrient hypothesis abstract quantifying variations in oceanic nutrient mass balances is central to understanding the links between biological productivity carbon cycle variations and climate one challenge in mass balance determinations is in developing appropriate proxies and applying them in a number of oceanic settings on comparable time scales on glacial timescales it is important to separate nutrient variations driven by external processes e g continental weathering dust inputs from those driven by internal processes i e changing loci of upwelling changes in nutrient inventories here we compare several upwelling regions as a first order analysis of phosphorus p inventory variations in the ocean sea level variations should have a profound impact on the continental margin sink of this biolimiting nutrient on glacial timescales new estimates for a shorter response time of p in the ocean suggest that variations in the p cycle play a role on marine biological productivity and thus the carbon cycle during glacial interglacial intervals although this glacial transfer of nutrients from shelves to the deep sea was postulated over two decades ago few quantitative data have been produced to support or refute this hypothesis supported by a more thorough understanding of p sedimentary geochemistry we present here detailed records of variations in oceanic p cycling on glacial timescales showing that the redistribution of this nutrient from marginal to deep sea sinks during glacial lowstands has had an impact on the oceanic p cycle furthermore p based records of export production from the southern and equatorial pacific oceans indicate that this redistribution of p resulted in higher oceanic dissolved p concentrations and increased oceanic productivity toward the end of glacials and the beginning of subsequent interglacials a 10 20 kyr lag between p based export production records and sea level supports the newer estimates of the marine p response time and indicates that this nutrient lag may be a heretofore unrecognized driver of other biological paleoproductivity records

the phosphorus cycle phosphogenesis and marine phosphate rich deposits abstract phosphorus in the form of phosphate is an essential nutrient and energy carrier on many different levels of life and a key element in mediating between living and lifeless parts of the biosphere one of the most important aspects of the phosphorus cycle is its vital role in governing productivity thereby interacting with the exogenic part of the carbon cycle which in turn is important in regulating earth s climate phosphorus is a prime element to be traced in earth s history because it allows for the reconstruction of long term feedback mechanisms between climate environment and ecology and of global change as such marine sedimentary phosphate deposits are particularly suited to study aspects of the phosphorus cycle because in the case of ubiquity their origin may result from a general acceleration of the global phosphorus cycle sources of sedimentary phosphate are microbial breakdown of buried organic matter and redox driven phosphate desorption from iron and manganese oxyhydroxides dissolved sea water phosphate represents an additional source which may become important in the formation of phosphatic hardgrounds the main locus of phosphogenesis is near the sediment water interface but phosphogenesis also occurs at greater sediment depths current induced winnowing and transport processes along the sea floor concentrate phosphate precipitates into deposits which exhibit internal stratification patterns typical for the prevailing hydraulic energy regime in a sequence stratigraphic context phosphate deposits preferentially occur along marine or maximum flooding surfaces consequent sedimentary reworking may result in the transfer of phosphates to highstand or lowstand deposits bio chemical weathering on continents represents the most significant source of bioavailable phosphorus this implies that long term changes in marine phosphorus levels and with these changes in marine ecology productivity rates and ratios of exported carbonate carbon and organic carbon are a response to changes in continental weathering rates a compilation of marine sedimentary phosphorus burial rates for the last 160 myr suggests that natural variations have occurred that span one order of magnitude for the late jurassic cretaceous and most of the paleogene the phosphorus cycle appears to have been accelerated in times of climate warming which was most likely due to the spreading of zones of humid climate and more intense continental weathering in the neogene the phosphorus cycle appears to have responded to changes in glacially induced weathering this suggests that uniform interpretations with respect to the emplacement of major phosphorite deposits should be treated with caution integrated analyses of the sedimentary and biogeochemical context of phosphorite occurrences may help to identify paleoenvironmental conditions as well as to improve our understanding of periods of enhanced phosphate accumulation periods which were usually characterized by steep gradients in the development of climate and environment with regard to the complexity of feedback mechanisms between the phosphorus cycle and the biosphere the present day input rates of phosphate into the world s oceans should be of great concern they are more than doubled by anthropogenic means and affect ecological systems on a rapidly increasing scale

complex landslide terrain in the kamienne mountains middle sudetes sw poland dense forest hides a complex landslide terrain in the kamienne mountains a part of the sudetes range in central europe combined geomorphological geophysical and dendrochronological research was carried out in three representative localities in order to decipher patterns of landslide evolution to determine the extent of slope deformations and to assess the contemporary activity of landslide terrain field mapping revealed the very complex nature of slope failures both in space and time deep seated sliding was the principal type of movement and was followed by rock wall retreat by fall in the depletion zone and earthflows in the toe area electric resistivity survey proved useful in constraining geometry of landslide units and suggests an occurrence of underground voids in the lesista landslide area dendrochronological research focused on tree ring reduction reaction wood wound and scar analysis that helped to unravel the pattern of debris supply and movement subsequent to the main events which includes free fall talus creep and sliding over snow cover today landslide complexes are at different stages of evolution whereas in some places the activity has been largely completed in others we have found the evidence for failure surfaces ready to accommodate movement hence although some landslides may be relict it is unjustified to extend this notion to all signs of hillslope instability in the area

applying genetic algorithms for calibrating a hexagonal cellular automata model for the simulation of debris flows characterised by strong inertial effects abstract in modelling complex a centric phenomena which evolve through local interactions within a discrete time space cellular automata ca represent a valid alternative to standard solution methods based on differential equations flow type phenomena such as lava flows pyroclastic flows earth flows and debris flows can be viewed as a centric dynamical systems and they can therefore be properly investigated in ca terms sciddica s4a is the last release of a two dimensional hexagonal ca model for simulating debris flows characterised by strong inertial effects s4a has been obtained by progressively enriching an initial simplified model originally derived for simulating very simple cases of slow moving flow type landslides using an empirical strategy in s4a the inertial character of the flowing mass is translated into ca terms by means of local rules in particular in the transition function of the model the distribution of landslide debris among the cells is obtained through a double cycle of computation in the first phase the inertial character of the landslide debris is taken into account by considering indicators of momentum in the second phase any remaining debris in the central cell is distributed among the adjacent cells according to the principle of maximum possible equilibrium the complexities of the model and of the phenomena to be simulated suggested the need for an automated technique of evaluation for the determination of the best set of global parameters accordingly the model is calibrated using a genetic algorithm and by considering the may 1998 curti sarno southern italy debris flow the boundaries of the area affected by the debris flow are simulated well with the model errors computed by comparing the simulations with the mapped areal extent of the actual landslide are smaller than those previously obtained without genetic algorithms as the experiments have been realised in a sequential computing environment they could be improved by adopting a parallel environment which allows the performance of a great number of tests in reasonable times

a sediment nutrient oxygen feedback responsible for productivity variations in late miocene sapropel sequences of the western mediterranean abstract cyclic sediments observed throughout the mediterranean during the late miocene have been related to precessional forcing of ocean stratification individual couplets typically 2 m thick sequences of sapropels and diatom rich marls can be reliably traced from western spain to crete and were formed in restricted marginal basins micropaleontological evidence indicates paradoxically that the organic carbon rich sapropels were formed under low productivity conditions marked by surface water stratification and deep anoxia whereas the diatom rich marls were formed under high productivity conditions marked by upwelling here we present geochemical evidence mainly from detailed phosphorus determinations and paleo redox proxies indicating that a sediment nutrient oxygen feedback herein dubbed the sno effect is in part responsible for driving the observed productivity variations during stratification anoxic conditions in these basins cause the release of the limiting nutrient phosphorus from reducible oxide phases in the sediments basin stagnation causes the buildup of phosphorus below the photic zone subsequent overturn driven by precessionally driven winds injects phosphorus rich bottom waters into the photic zone the biotic response to this overturn is high productivity in marls directly overlying the sapropels culminating in diatom mat formation exhaustion of the stored excess phosphorus results in lower productivity marls which grade back into sapropels due to lower wind stresses and the return of stagnant basin conditions these findings indicate that the sno effect may in part be responsible for precessional scale productivity variations observed in parts of the mediterranean and perhaps present in other restricted ocean basins like the miocene monterey formation and the modern santa barbara basin

francolite authigenesis in california continental slope sediments and its implications for the marine p cycle abstract authigenesis of francolite carbonate fluorapatite in continental slope sediments may represent the most important oceanic sink for reactive p we infer from sedimentary p speciation and pore fluid fluoride concentrations that francolite currently forms in holocene sediments on the california continental slope authigenic p accumulation rates range from 0 006 to 0 089 mol cm 2 yr and dissolved fluoride uptake rates range from 0 004 to 0 039 mol cm 2 yr these two independent parameters correlate positively with each other among all sites r 2 0 77 and the slope of their linear relationship gives a p f molar ratio of 2 4 a typical value for authigenic francolite our results imply that active francolite authigenesis sequesters nearly 30 of the remobilized organic and fe bound p at shallow burial depths in california continental slope sediments assuming that similar processes occur globally we estimate that francolite authigenesis in near surface continental slope sediments may account for a burial flux of 1 4 1 0 10 10 mol p yr or 8 to 48 of the global input flux of reactive p to the ocean

implications for the history of cenozoic opal deposition from a quantitative model in addition to being a time of enhanced crustal activity and a warmer climate the eocene also saw prolonged periods of silica accumulation on the ocean floor the peak of this accumulation occurred at approximately 50 ma creating horizon ac a layer of silica rich sediments spanning approximately 4 my horizon ac is comparatively isolated in time from known silicic acid addition processes leading mcgowran 1989 mcgowran b 1989 silica burp in the eocene ocean geology 17 pp 857 860 to suggest a novel mechanism the silica burp hypothesis that centres on the temporal decoupling of silicic acid supply and burial by climatic variation here we examine this hypothesis using a quantitative biogeochemical model of the silicon cycle our results unequivocally show that mcgowran s hypothesis is unable to account for horizon ac the model s residence time and ocean capacity for silicic acid are insufficient to permit the degree of temporal decoupling proposed by mcgowran inverting the model s results suggests that instead the sediment record may be a useful proxy for silicic acid additions to the ocean

simulation of the parma river blockage by the corniglio landslide northern italy abstract near the village of corniglio in the northern apennines about 40 km sw of parma a big landslide was recently 1994 1996 subjected to reactivation damaging many buildings and partially obstructing the parma river in this work we have carried out a quantitative analysis of the recent evolution of the landslide with the help of a geographic information system gis in order to predict the most plausible future developments then various simulations of landslide descent were carried out and above all to evaluate the possibility of blockage formation to this purpose two computer programs that simulate the material descent through a cellular automata model and define blockage characteristics were written many different simulations were carried out 16 of which are presented here for each of them the computer output consists of a table defining the quantity of displaced material area and volume of the dam and lake and of a map showing the areas involved in the landslide movement and upstream flooding in order to assess the probability of blockage formation and dam stability we applied the simulation results to some empirical rules defined by preceding authors through statistical analysis carried out on a high number of analogous phenomena these rules suggest that it is very unlikely that blockage takes place as the result of very slow landslide velocity riverbed width and high erodibility of the material if it were to occur the size and shape of the dam seem sufficient to guarantee a considerable degree of stability making a sudden failure improbable

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

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

long term controls on ocean phosphorus and oxygen in a global biogeochemical model 1 in this study we use a biogeochemical ocean general circulation model hamocc originally developed for the carbon and silicon cycles and expand it with a description of the sedimentary phosphorus p cycle the model simulates the release of reactive p by aerobic and anaerobic degradation of organic matter in the sediment as well as formation and burial of fe oxide bound p and authigenic ca p minerals we also include pre anthropogenic inputs of p from atmospheric dust which is mostly in the form of detrital apatite model predicted total p concentrations and rates of reactive p burial for the deep sea agree reasonably well with observations in open ocean and near continental margin sediments as part of a sensitivity analysis we assess the long term response of ocean productivity and deep water oxygenation to increases in the riverine input of p and preferential release of p from sediments the simulations show that the feedback from preferential p regeneration accelerates the expansion of suboxia o2 2 5mm along continental margins and in the naturally suboxic areas in tropical subtropical regions on timescales of 10 100 ka for a case in which maximum p regeneration from sediments is enabled a large scale pattern of bottom water suboxia 30 of the total ocean area develops over the southeastern tropical and northern pacific ocean sectors

biogeochemical phosphorus mass balance for lake baikal southeastern siberia russia abstract extensive data for lake baikal have been synthesized into a geochemical mass balance for phosphorus p some of the p budget and internal cycling terms for baikal have been compared to similar terms for oligotrophic lake superior mesotrophic lake michigan and the baltic sea and the ocean lake baikal has a large external source of fluvial p compared to the laurentian upper great lakes and the ocean the major tributary to lake baikal has experienced substantial increases in organic p loading during the past 25 years this coupled with potential p inputs from possible phosphorite mining may threaten baikal s oligotrophic status in the future water column remineralization of particulate organic p is substantially greater in lake baikal than in the laurentian great lakes this is probably due to the great water depths of lake baikal there is a gradient in p burial efficiency with very high values 80 for lake baikal and lake superior lower values 50 for lake michigan and the baltic sea and a low value 13 for the ocean the accumulation rate of p in lake baikal sediments is somewhat greater than that in the laurentian upper great lakes and the baltic sea and much greater than in the ocean benthic regeneration rates are surprisingly similar for large lacustrine and marine environments and supply less than 10 of the p utilized for primary production in these aquatic environments