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 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

late cretaceous and early paleogene nutrient and paleoproductivity records from blake nose western north atlantic ocean 1 we evaluate phosphorus p and biogenic barium bio ba as nutrient burial and export productivity indicators for the late cretaceous and early paleogene combining these with calcium carbonate caco3 organic carbon c and bulk caco3 c isotopes 13c sample ages span 36 71 ma 1 sample 0 5 m y for a depth transect of sites in the western north atlantic blake nose ocean drilling program leg 171b sites 1052 1051 and 1050 we use a multitracer approach including redox conditions to investigate export productivity surrounding the global paleocene 13c maximum 57 ma reducing conditions render most of the bio ba record not useful for export productivity interpretations p and organic c records indicate that regional nutrient and organic c burial were high at 61 and 69 ma and low during the paleocene 13c maximum a time of proposed global high relative organic c burial observed organic c burial changes at blake nose cannot explain this c isotope excursion

sediment geochemical evidence for an early middle gilbert early pliocene productivity peak in the north pacific red clay province abstract current attempts to understand climatic variability during the early to middle pliocene require paleoceanographic information from the pacific and indian oceans that may serve to test and or constrain future circulation models ocean drilling program odp sites 885 886 are located in the central subarctic north pacific at water depths exceeding 5700 m recent studies of rock magnetic properties suggest that the fine grained fe oxide component in sediment at sites 885 886 experienced reductive dissolution during the early middle gilbert because such an interval in the north pacific red clay province suggests a maximum in the sedimentary flux of organic carbon and or a minimum in bottom water dissolved o 2 concentrations and hence a peak change in north pacific oceanographic conditions a geochemical investigation was conducted to test the hypothesis quaternary sediment at hole 886b was subjected to an oxyhydroxide removal procedure and chemical analyses indicate that bulk sediment concentrations of fe and the fe sc ratio decrease significantly upon reductive dissolution downcore chemical analyses of untreated sediment at hole 886b demonstrate that similar depletions also occur across the proposed interval of reduced sediment downcore chemical analyses also indicate that a pronounced increase in the ba sc ratio occurs across the interval these results are consistent with an interpretation that abyssal sediment of the north pacific experienced a decrease in redox conditions during the early middle gilbert and that this change in oxidation state was related to a peak in paleoproductivity if the zenith of late miocene to middle pliocene enhanced productivity observed at other indo pacific divergence regions similarly can be constrained to the early middle gilbert there exists an oceanographic boundary condition in which to test future models concerning pliocene warmth

modeling ash fall distribution from a yellowstone supereruption we used the volcanic ash transport and dispersion model ash3d to estimate the distribution of ashfall that would result from a modern day plinian supereruption at yellowstone volcano the simulations required modifying ash3d to consider growth of a continent scale umbrella cloud and its interaction with ambient wind fields we simulated eruptions lasting 3 days 1 week and 1 month each producing 330 km3 of volcanic ash dense rock equivalent dre results demonstrate that radial expansion of the umbrella cloud is capable of driving ash upwind westward and crosswind n s in excess of 1500 km producing more or less radially symmetric isopachs that are only secondarily modified by ambient wind deposit thicknesses are decimeters to meters in the northern rocky mountains centimeters to decimeters in the northern midwest and millimeters to centimeters on the east west and gulf coasts umbrella cloud growth may explain the extremely widespread dispersal of the 640 ka and 2 1 ma yellowstone tephra deposits in the eastern pacific northeastern california southern california and south texas

evolution of pangea paleomagnetic constraints from the southern alps italy abstract a new early late triassic paleopole for adria has been obtained from the val sabbia sandstone in the southern alps as early permian and jurassic cretaceous paleomagnetic data from para autochthonous regions of adria such as the southern alps are consistent with african apwps 1 2 paleomagnetic data from this region can be used to bolster the west gondwana apwp in the poorly known late permian triassic time interval the southern alpine paleopoles are integrated with the west gondwana and laurussia apwps of van der voo 1 and used to generate a tectonic model for the evolution of pangea the early permian overall mean paleopole for west gondwana and adria in conjunction with the coeval laurussia paleopole support pangea b of morel and irving 3 the late permian early triassic and the middle late triassic paleopoles from adria and laurussia support pangea a 2 of van der voo and french 4 the phase of transcurrent motion between laurasia and gondwana 5 that caused the pangea b to a 2 transition occurred essentially in the permian at the end of variscan orogeny with an average relative velocity of approximately 10 cm yr finally the late triassic early jurassic paleopoles from west gondwana and laurussia agree with pangea a 1 of bullard et al 6 the widely accepted pangea configuration at the time of the jurassic breakup

the record of sea water 187os 186os variation through the cenozoic the variation of sea water 187os 186os during the cenozoic has been determined by analyzing the hydrogenous os released by acidic hydrogen peroxide leaching of layers in an abyssal north pacific pelagic clay core overall sea water 187os 186os has increased from 3 2 at 58 ma to the present day value of 8 6 this pattern is similar to the well known 87sr 86sr evolution of sea water the increase in the proportion of continental os 187os 186os 10 could be due to enhanced weathering rates of black shales associated with the uplift of the himalayas other elements associated with black shale weathering such as u and p should show effects in the sedimentary record

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

similar phosphorus fluxes in ancient phosphorite deposits and a modern phosphogenic environment phosphogenesis is major sink for phosphorus p in the modern ocean and the deposition of ancient phosphorites appears to have been an important sink for p in past oceans to evaluate the importance of p burial we combined published estimates along with our data for one section of the monterey formation california of p inventories areal extents and time intervals of deposition for three well studied major phosphorite deposits to calculate p accumulation and burial rates phosphorus accumulation and burial rates of major phosphorite deposits are comparable to those of the modern peru margin though phosphorite deposition probably requires favorable sedimentological tectonic and or oceanographic conditions it does not appear to be a geochemically anomalous phenomenon when compared to modern oceanic conditions

a comparison of early paleogene export productivity and organic carbon burial flux for maud rise weddell sea and kerguelen plateau south indian ocean 1 marine biological productivity has been invoked as a possible climate driver during the early paleogene through its potential influence on atmospheric carbon dioxide concentrations however the relationship of export productivity the flux of organic carbon c from the surface ocean to the deep ocean to organic c burial flux the flux of organic c from the deep ocean that is buried in marine sediments is not well understood we examine the various components involved with atmosphere to ocean c transfer by reconstructing early paleogene carbonate and silica production using carbonate and silica mass accumulation rates mars export productivity using biogenic barium bio ba mars organic c burial flux using reactive phosphorus p mars redox conditions using uranium and manganese contents and the fraction of organic c buried relative to export productivity using reactive p to bio ba ratios our investigations concentrate on paleocene eocene sections of sites 689 690 from maud rise and site 738 from kerguelen plateau in both regions export productivity organic c burial flux and the fraction of organic c buried relative to export productivity decreased from the paleocene early eocene to the middle eocene a shift is indicated from an early paleogene two gyre circulation in which nutrients were not efficiently recycled to the surface via upwelling in these regions to a circulation more like the present day with efficient recycling of nutrients to the surface ocean export productivity was enhanced for kerguelen plateau relative to maud rise throughout the early paleogene possibly due to internal waves generated by the plateau regardless of gyre circulation

influence of late cenozoic mountain building on ocean geochemical cycles in a steady state ocean input fluxes of dissolved salts to the sea must be balanced in mass and isotopic value by output fluxes for the elements strontium calcium and carbon rivers provide the primary input whereas marine biogenic sedimentation dominates removal dissolved fluxes in rivers are related to rates of continental weathering which in turn are strongly dependent on rates of uplift the largest dissolved fluxes today arise in the himalayan and andean mountain ranges and the tibetan plateau during the past 5 m y uplift rates in these areas have increased significantly this suggests that weathering rates and river fluxes may have increased also the oceanic records of carbonate sedimentation level of the calcite compensation depth and delta sup 13 c and delta sup 87 sr in biogenic sediments are consistent with a global increase in river fluxes since the late miocene the cooling of global climate over the past few million years may be linked to a decrease in atmospheric co sub 2 driven by enhanced continental weathering in these tectonically active regions

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

volcanic plume electrification experimental investigation of a fracture charging mechanism although ashfall from particulate volcanic plumes is known to be highly electrically charged little is known about the charging mechanism we describe experiments designed to investigate the particle charges generated from the fracture of pumice small silicate particles were produced in the laboratory during collisions between two samples cut from pumice clasts the net charge magnitudes detected on these particles are similar to those previously measured on ashfall from volcanic plumes 10 5 to 10 6 c kg 1 this net charge is also shown to be the result of a small imbalance between the sums of individual particle charges of both polarities which are up to several orders of magnitude larger than the net charge the magnitude of both the net and single polarity specific charges were only weakly affected by changes of relative humidity but single polarity charges increased steadily with increasing sample impact velocities the dominant charging process during the experiments was that of material fracture the charging mechanism is thus interpreted to be fractoemission the release of nuclear particles from fresh crack surfaces occurring during the production of the silicate particles this implies that the electrification of volcanic plumes could be the result of brittle fragmentation of magma or pumice clasts within the upper regions of the conduit and in the jet region of the plume

tectonics of the umbria marche romagna arc central northern apennines italy new paleomagnetic constraints we present the results of a paleomagnetic study carried out on 32 sites from mainly messinian clayey sediments distributed throughout the external umbria marche romagna arc umra these data together with published results from coeval sediments demonstrate that this arc is an orocline in its central northern sector bending not well constrained in time was due to about 15 clockwise rotations of the central part of this arc and to counterclockwise rotations farther north in this latter area post messinian counterclockwise rotations are of the same amplitude as those calculated for some classic mesozoic paleomagnetic sections in northern umbria suggesting a plio pleistocene age for the rotations reported from the older sequences

paleomagnetic data from umbria italy implications for the rotation of adria and mesozoic apparent polar wander paths abstract sixteen new jurassic and cretaceous paleomagnetic sampling sites are located in northern umbria along three river valleys bosso burano sentino the late jurassic and early cretaceous data are consistent in declination but not inclination with previously published data from these valleys early jurassic data from eight sites give site mean declinations which are significantly different from the two site mean declinations of this age which were previously available comparison of the data with cretaceous and jurassic mean directions from the southern alps indicate 20 anticlockwise rotation relative to the southern alps of this part of northern umbria during neogene deformation of the umbrian fold and thrust belt if the umbrian mean directions are rotated to compensate for the tectonic rotation the early jurassic and cretaceous umbrian and southern alpine pole positions coincide closely with a recently derived african apparent polar path apwp implying that adria moved with africa since at least early jurassic times the late jurassic umbrian and southern alpine poles however are not consistent with current apwps and imply rapid apparent polar wander in both african and north american coordinates from high latitude to lower latitude between bathonian and oxfordian times

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

sr isotope evolution of seawater the role of tectonics we use a high resolution seawater sr isotopic evolution curve for the last 100 m y in conjunction with modern riverine sr flux measurements and also geologic tectonic and geochronological data to make the case for a close relationship between seawater sr isotopic composition and the india asia continental collision using a simple seawater sr budget model we begin by showing that the sr flux associated with alteration of seafloor basalts is too small and does not have the right time evolution to account for much of the seawater sr isotopic curve of the last 100 m y the flux of dissolved sr carried by rivers originating in the himalaya tibet region on the other hand is presently a significant fraction of the global sr budget we calculate how this riverine flux would have had to change with time in order to match the observed seawater sr isotopic curve and find that the riverine flux remains relatively constant prior to the collision of india with asia but then increases very significantly after collision we note that the period of most rapid change in seawater sr isotopic ratio from 20 ma to 15 ma is also a period of exceptionally high erosion in parts of the himalayas and the tibetan plateau as further evidence that sr derived from the collision of india with asia plays a major role in the sr isotopic evolution of seawater we show that the total amount erosion of the himalaya tibetan plateau since collision which we calculate separately represents a total amount of sr that is very nearly the same as the cumulative amount required by the sr isotopic change of seawater since collision the relationship between erosion and riverine sr flux allows us to use the sr isotopic evolution of seawater to reconstruct a history of erosion since collision and we find that the erosion rate accelerates with time since collision with the present having the largest rate when we apply the sr budget model to the entire phanerozoic using a new compilation of deformed continental area versus time we find that we can account for the large scale structure of the seawater sr isotopic curve but fail to reproduce several local maxima and minima especially in the period 100 300 ma the present high s7sr s6sr of seawater and similar highs in the devonian and cambrian do correlate with extensive deformation on the continents

disseminated phosphorus in oceanic sediments a review abstract the content of disseminated phosphorus in sediments of the world oceans fluctuates between 0 01 and 4 36 terrigenous and hemipelagic sediments contain on average about 0 07 phosphorus higher concentrations are characteristic of sediments enriched in iron and manganese hydroxides or bone detritus and phosphoritic material the general features of the phosphorus distribution in surface sediments depend on the ratio of continental runoff area to basin area which diminishes from the atlantic to the indian and pacific areas the relative extent of the nearshore phosphorus rich zone contracts whereas that of the pelagic phosphorus rich zone widens in the transition from the atlantic through the indian to the pacific areas the distribution of phosphorus in vertical sections of sediments gives some evidence of the diagenetic mobilisation of phosphorus and its partial loss to bottom water the rate of phosphorus accumulation in oceanic sediments is evaluated as between 10 g cm 2 k y 1 the bulk mass of phosphorus is accumulated in marginal zones of the oceans

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

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

opal sedimentation shifts in the world ocean over the last 15 myr biogenic silica opal accumulation records were used to trace mechanisms consequence and geographic pattern of shifts in the main locus of opal deposition of the world ocean over the last 15 myr over this time interval the main opal sink seems to have moved from the north atlantic to the pacific equatorial pacific eastern equatorial pacific eastern boundary current upwelling systems california namibia peru and finally to the southern ocean the interplay between opal deposition and a series of climatic tectonic oceanographic and biologic events has been analyzed and discussed these events include the cenozoic global cooling trend intensified glaciation in antarctica late miocene early pliocene biogenic bloom development of northern hemisphere glaciation nhg closing of the panama seaway transition of the climate system from a monopolarto a bipolar glaciated world mid pleistocene revolution mpr nutrient availability evolution of diatoms and c4 plants and changes in continental weathering rates while the observed shifts are mostly traceable to oceanic reorganizations and global climatic evolution conditions favorable to opal deposition involve the above mentioned complex mix of processes for this reason the interpretation of opal deposition records might not always be straightforward we however believe that it can still provide clear indications of large scale oceanographic reorganizations in the geological past d 2004 elsevier b v all rights reserved

in search of the late miocene early pliocene biogenic bloom in the atlantic ocean ocean drilling program sites 982 925 and 1088 1 we reconstruct paleoproductivity at three sites in the atlantic ocean ocean drilling program sites 982 925 and 1088 to investigate the presence and extent of the late miocene to early pliocene biogenic bloom from 9 to 3 ma our approach involves construction of multiple records including benthic foraminiferal and caco3 accumulation rates uvigerina counts dissolution proxies and geochemical tracers for biogenic and detrital fluxes this time interval also contains the so called late miocene carbon isotope shift a well known decrease in benthic foraminiferal 13c values we find that the timing of paleoproductivity maxima differs among the three sites at site 982 north atlantic benthic foraminifera and caco3 accumulation were both at a maximum at 5 ma with smaller peaks at 6 ma the paleoproductivity maximum was centered earlier 6 6 6 0 ma in the tropical atlantic site 925 in the south atlantic site 1088 paleoproductivity increased even earlier between 8 2 ma and 6 2 ma and remained relatively high until 5 4 ma we note that there is some overlap between the interval of maximum productivity between sites 925 and 1088 as well as the minor productivity increase at site 982 we conclude that the paleoproductivity results support hypotheses aiming to place the biogenic bloom into a global context of enhanced productivity in addition we find that at all three sites the 13c shift is accompanied by carbonate dissolution this observation is consistent with published studies that have sought a relationship between the late miocene carbon isotope shift and carbonate preservation

paleoceanography and the diachrony of radiolarian events in the eastern equatorial pacific the development of an orbitally tuned time scale for the odp leg 138 sites provides biostratigraphers a very high resolution chronostratigraphic framework with this framework we are better able to define which of the first and last appearances of species appear to be synchronous in addition the geographic distribution of sites provides the means with which the detailed spatial patterns of invasion of new species and the extinction of older species can be mapped these maps not only provide information on the process of evolution migration and extinction they can also be related to water mass distributions and near surface circulation of the ocean of 39 radiolarian events studied at 11 sites in the eastern equatorial pacific 28 were found to have a minimum range in their estimated age that exceeded 0 15 m y the temporal pattern of first and last appearances of these diachronous events have coherent spatial patterns that indicate shifts in the areas of high oceanographic gradients over the past 10 ma these changes in the locations of high gradient regions suggest that the south equatorial current sec was north of its present position prior to approximately 7 ma there was a southward shift in the northern boundary of this current between approximately 6 and 7 ma and the development of a relatively strong gradient between the northeastern and northwestern sites between approximately 3 7 and 3 4 ma there was a very slight northward shift in the northern boundary of the sec and the steep gradients between the northeastern and northwestern sites may have disappeared this change is thought to be associated with the closing of the isthmus of panama the temporal spatial patterns of diachronous events younger than 3 4 ma are consistent with patterns of circulation in the modern ocean

a new geomagnetic polarity time scale for the late cretaceous and cenozoic we have constructed a magnetic polarity time scale for the late cretaceous and cenozoic based on an analysis of marine magnetic profiles from the world s ocean basins this is the first time since heirtzler et al 1968 published their time scale that the relative widths of the magnetic polarity intervals for the entire late cretaceous and cenozoic have been systematically determined from magnetic profiles a composite geomagnetic polarity sequence was derived based primarily on data from the south atlantic anomaly spacings in the south atlantic were constrained by a combination of finite rotation poles and averages of stacked profiles fine scale information was derived from magnetic profiles on faster spreading ridges in the pacific and indian oceans and inserted into the south ariantic sequence based on the assumption that spreading rates in the south atlantic were smoothly varying but not necessarily constant a time scale was generated by using a spline function to fit a set of nine age calibration points

the latest miocene early pliocene biogenic bloom a revised indian ocean perspective abstract numerous investigations of neogene sediment sequences from the indian and pacific oceans have led to a paleoceanographic hypothesis that recently has been coined the biogenic bloom this hypothesis suggests that primary productivity increased substantially at indo pacific upwelling zones during the latest miocene early pliocene although it is clear that recognition of a widespread biogenic bloom provides a fundamental framework for understanding late neogene global change it also is apparent that investigations of this phenomena require syntheses of a variety of information from time correlated sediment sequences that span large oceanic regions late neogene polarity chron boundaries and nannofossil events are placed on a common and current time scale for 12 ocean drilling program odp sediment sequences in order to construct a coherent description of the biogenic bloom in the indian ocean carbonate mass accumulation rates mars were significantly higher than present day in the north and west indian ocean between 9 0 and 3 5 ma sediment deposited during this time interval also is dominated by planktic faunal assemblages that are indicative of high productivity and redox conditions that are explained by an increase in the supply of organic carbon further sediment of this age contains benthic faunal assemblages and chemical characteristics that are consistent with low dissolved o 2 in intermediate waters these observations collectively suggest that between 9 0 and 3 5 ma productivity in the north and west indian ocean was significantly higher than present day and the intermediate water oxygen minimum zone omz was more extensive than present day this paleoceanographic condition was most intense between 6 0 and 5 0 ma in the indian ocean comparison of the indian ocean sites with two locations in the pacific ocean suggests that the biogenic bloom was time coincident in the indian and pacific oceans the biogenic bloom therefore implies an important change in global nutrient cycling occurred during the latest miocene early pliocene although a satisfactory explanation for the change remains elusive

rare earth elements in foraminifera tests abstract the concentrations of nine rare earth elements ree la ce nd sm eu gd dy er and yb have been determined in mixed species assemblages of foraminifera tests taken from atlantic ocean sediment core tops reductive cleaning techniques have revealed that ree are present in three phases in foraminifera tests collected from sea floor sediments ree included in the foraminiferal calcite matrix termed lattice ree ree associated with an authigenic femn rich phase adsorbed onto the surface of the test following the death of the organism termed coating ree and ree associated with alumino silicate detritus termed detrital ree which commonly infills the test chambers after burial in the sediment the concentrations of ree in the nondetrital lattice plus coating and lattice phases have been measured in this study approximately 90 of the ree measured in the non detrital phase reside in the coating phase the remainder being present in the lattice phase these data have been used to investigate the relationship between the distribution of dissolved ree in the ocean and in the coating and lattice phases in addition to the ree the concentrations of mn fe cu al and po4 have been measured as an aid to characterisation of the various phases

terrestrial paleorecords of ge si cycling derived from lake diatoms abstract modern river studies support the generalization that surface waters in regions undergoing extensive chemical weathering have elevated dissolved germanium silicon ge si ratios compared to regions with less extensive chemical weathering thought to be the result of ge fractionation in 2 1 clays temporal variations in ge si observed in marine diatoms have thus been linked to past global trends in terrestrial weathering however this relationship has not been adequately ground truthed by a terrestrial based paleoclimate study utilizing ge si ratios in lake diatoms to this end a sediment core was extracted from dry lake el 2763 m in the headwaters of the santa ana river of southern california in july 1996 the dry lake drainage basin is comprised of biotite muscovite gneiss and granite with sparse pine forests and relatively high relief the core had a basal ams 14c age of 8 350 60 ybp we successfully separated diatom samples large enough for cleaning dissolution and chemical analysis without contamination by detrital materials confirmed by trace metal analyses two dissolved opal samples were analyzed for ge and si concentrations along with modern water samples collected from waters within the drainage basin diatoms obtained from 8000 year old sediments near the bottom of the core had an opal ge si of 0 79 10 6 mol mol a composite sample of diatoms deposited within the past 100 years yielded a significantly lower ge si of 0 34 10 6 analysis of ge si was also performed from a variety of other materials in the dry lake basin including stream and lake water unweathered bedrock soils and mineral separates together with sedimentologic records from the lake sediments and ge si recorded in other basin materials it appears that the high ge si values recorded in the 8000 year opal sample were the result of preferential early weathering of high ge si biotite and muscovite minerals from the slopes thus the detailed examination of ge si cycling in this isolated basin indicates that factors other than clay mineral transformations may drive ge si paleorecords in some settings

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

coupled productivity and carbon isotope records in the southwest pacific ocean during the late miocene early pliocene biogenic bloom biogenic components of sediment accumulated at high rates beneath frontal zones of the indian and pacific oceans during the late miocene and early pliocene the 13c of bulk and foraminiferal carbonate also decreased during this time interval although the two observations may be causally linked and signify a major perturbation in global biogeochemical cycling no site beneath a frontal zone has independent records of export production and 13c on multiple carbonate phases across the critical interval of interest deep sea drilling project dsdp site 590 lies beneath the tasman front tf an eddy generating jetstream in the southwest pacific ocean to complement previous 13c records of planktic and benthic foraminifera at this location late neogene records of caco3 mass accumulation rate mar ca ti ba ti al ti and of bulk carbonate and foraminiferal 13c were constructed at site 590 the 13c records include bulk sediment bulk sediment fractions 63 m and 5 25 m and the planktic foraminifera globigerina bulloides globigerinoides sacculifer with and without sac and orbulina universa using current time scales caco3 mars ca ti al ti and ba ti ratios are two to three times higher in upper miocene and lower pliocene sediment relative to overlying and underlying units a significant decrease also occurs in all 13c records all evidence indicates that enhanced export production the biogenic bloom extended to the southwest pacific ocean between ca 9 and 3 8 ma and this phenomenon is coupled with changes in 13c the chron c3ar carbon shift however caco3 mars peak ca 5 ma whereas elemental ratios are highest ca 6 5 ma foraminiferal 13c starts to decrease ca 8 ma whereas bulk carbonate 13c begins to drop ca 5 6 ma temporal discrepancies between the records can be explained by changes in the upwelling regime at the tf perhaps signifying a link between changes in ocean atmosphere circulation change and widespread primary productivity

the effect of hydrothermal processes on midwater phosphorus distributions in the northeast pacific abstract the distributions of dissolved particulate and sedimentary phosphorus were measured in the region of the juan de fuca ridge to determine the impacts of hydrothermal processes on the phosphorus cycle in the oceans significant negative dissolved phosphate anomalies ranging from 0 to 60 nmol l were observed in the water column at depths between 1900 and 2300 db the largest anomalies

the himalayas organic carbon burial and climate in the miocene cooling ages of rock in the himalayas imply that rapid exhumation between the main central thrust system and the south tibetan detachment system occurred between 21 and 17 ma the generation of relief and enhanced weathering which followed this event may have resulted in a pronounced increase in the delivery of dissolved strontium carbon phosphorus and other chemical weathering products to the ocean richter et al 1992 the increased supply of nutrients stimulated productivity in oceanic upwelling zones and expansion of the oxygen minimum zone leading to enhanced burial and preservation of organic matter in the monterey formation and other deposits from this interval a downdraw of atmospheric co2 associated with enhanced chemical weathering rates and organic matter burial may have led to global cooling and the expansion of the antarctic ice sheet by 15 ma the above scenario differs from the monterey hypothesis of vincent and berger in that co2 downdraw is primarily via silicate weathering rather than organic carbon burial and that organic carbon burial is driven by increased delivery of nutrients to the ocean rather than by stronger upwelling a carbon mass balance calculation which assumes that river fluxes have been increasing over the last 40 ma predicts that absolute organic carbon burial increased over this interval while at the same time the fraction of carbon buried as organic matter versus carbonate decreased this implies that the organic carbon cycle has acted as a net source of co2 to the atmosphere over the late cenozoic

pore water fluoride in peru continental margin sediments uptake from seawater abstract fluoride analyses display downward decreasing pore water gradients in peru shelf phosphatic muds that require diffusion from the overlying seawater into the sediment column and removal by reaction within the upper few tens of centimeters presumably by incorporation into carbonate fluorapatite the profiles can be modeled as first order f removal with rate constants of 3 yr 1 and asymptotic f concentrations deep in the cores of 35 45 m almost one half the seawater value the integrated flux of fluoride from seawater into organic rich shelf sediments in coastal upwelling zones phosphatic muds yields a contemporaneous global f burial of 0 54 10 10 mol f yr 1 about one fifth the burial in other sinks mostly carbonates and opal the associated burial flux of phosphorus in shelf phosphorites is about 1 6 10 10 mol p yr 1 comparable to p burial in the deep sea with organic matter 1 4 10 10 mol yr 1 and biogenic carbonates 1 4 10 10 mol yr 1 thus phosphorite formation on the peru shelf is a significant contemporaneous process

himalayan tectonics weathering processes and the strontium isotope record in marine limestones the time evolution of the isotopic composition of seawater strontium the ratio of strontium 87 to strontium 86 over the last 500 million years has the form of an asymmetric trough the values are highest in the cambrian and recent 0 7091 and lowest in the jurassic 0 7067 superimposed on this trend are a number of smaller oscillations consideration of the geochemical cycle of strontium and the dynamics of weathering shows that only himalayan style continental collisions can influence the isotope ratio on the scale observed the contemporary himalayan orogeny is by far the largest since the late precambrian pan african event that produced the high in the cambrian

geochemistry and isotopic study of southern bay of bengal sediments implications for provenance and paleoenvironment during the middle miocene abstract the bay of bengal bob the largest bay in the world is known to receive large amounts of fresh water and suspended particulate matter from different sources the sediments deposited in the bay serve as a repository for paleoenviromental reconstruction studies the miocene epoch is an important interval in geologic time as it is marked by major climatic events that controlled ocean productivity redox conditions and provenance of sediments however limited work has been carried out to establish paleoenviromental changes and provenance of sediments during the miocene here we present detailed geochemical and radiogenic sr nd isotopic results from predominantly middle miocene sediments of ocean drilling program odp site 758a located in the southern bob lat 5 23 n long 90 21 e water depth 2925 m to understand paleoredox conditions paleoproductivity and provenance the results suggest that these sediments are strongly linked to climatically modulated surface processes that affected the region the distribution of redox sensitive element proxies u v cr at interval 17 8 ma points to an oxic depositional environment the major trace and rare earth elements distribution supports prevalence of the indian summer monsoon ism at 12 10 ma productivity proxies babio porg show a decreasing trend during colder events east antarctic ice sheet expansion eais and advent of late miocene cooling lmc events the trace and rare earth element concentrations are generally low except at intervals where glass shards were found the 87sr 86sr and end 0 values indicate that the sediments belong to the high himalayan sedimentary series hhss throughout the middle miocene however prior to initiation of the ism these sediments underwent meteoric alteration in the lowlands before deposition in the bob our records suggest that sediments at odp site 758a may have been introduced into the bob through the irrawaddy yarlung tsangpo drainage system during the entire period of this study the irrawaddy yarlung tsangpo system drained the indus tsangpo suture zone southern tibet the eastern himalayas and the arakan coast before debouching in the bob

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

revised and synthetic apparent polar wander paths of the african eurasian north american and indian plates and true polar wander since 200 ma we have reviewed paleomagnetic data available for the eurasian african north american and indian plates over the last 200 ma selection criteria are those generally accepted with an emphasis on evidence for lack of remagnetization accurate dating and proper structural analysis this results in 23 35 51 and 2 poles for eurasia africa north america and india respectively we believe that this limited set of higher quality data is more likely to reveal key features of apparent polar wander apw paths than averaging of larger data sets involving less stringent selection criteria we propose and describe revised apw paths but more importantly we next use relative motion models to transfer all data in a common reference frame we find good agreement between transferred data when they are averaged separately for each plate in independent 20 ma windows this is a check on consistency of paleomagnetic data kinematic models and of the geocentric dipole hypothesis transferred data from all plates are averaged in 20 ma windows to generate synthetic apw paths for all plates studied these synthetic paths are in agreement with the original revised apw paths that use only data from a single plate moreover both geographic and time resolution are improved spatial confidence intervals are of the order of 5 the synthetic paths display interesting features such as a previously ill recognized apw loop for eurasia paleomagnetic and hotspot apw are next compared and a determination of true polar wander tpw is derived we find significant tpw amounting to over 20 in the last 200 ma tpw appears to be episodic with a standstill between 180 and 110 ma there is general agreement with a previous study of livermore et al 1984 the tpw standstill appears to correlate with a time of decreasing reversal frequency ending with the cretaceous long normal superchron other periods of fast tpw would seem to correspond to increasing reversal frequency however it is suggested that the major tpw hairpin at 50 ma might correspond to the collision of india with eurasia tentative correlations with core or mantle indicators can be understood as a result of couplings between the core mantle and lithosphere we believe primarily related to episodic evolution of the d layer

a new model for atmospheric oxygen over phanerozoic time a mathematical model has been constructed that enables calculation of the level of atmospheric o2 over the past 570 my from rates of burial and weathering of organic carbon c and pyrite sulfur s burial rates as a function of time are calculated from an assumed constant worldwide clastic sedimentation rate and the relative abundance and c and s contents of the three rock types marine sandstones and shales coal basin sediments and other non marine clastics red beds arkoses by our model values of o2 versus time using a constant total sedimentation rate agree with those for variable sedimentation derived from present day rock abundances and estimates of erosional losses since deposition this agreement is the result of our reliance on the idea that any increase in total worldwide sediment burial with consequently faster burial of c and s and greater o2 production must be accompanied by a corresponding increase in erosion and increased exposure of c and s on the continents to o2 consumption via weathering it is the redistribution of sediment between the three different rock types and not total sedimentation rate that is important in o2 control to add stability to the system negative feedback against excessive o2 fluctuation was provided in the modeling by the geologically reasonable assignment of higher weathering rates to younger rocks resulting in rapid recycling of c and s we did not use direct o2 negative feedback on either weathering of c and s or burial of c because weathering rates are assumed to be limited by uplift and erosion and the burial rate of c limited by the rate of sediment deposition the latter assumption is the result of modern sediment studies which show that marine organic matter burial occurs mainly in oxygenated shallow water and is limited by the rate of supply of nutrients to the oceans by rivers results of the modeling indicate that atmospheric o2 probably has varied appreciably over phanerozoic time during the late carboniferous and permian periods o2 was higher than previously because of the rise of vascular land plants and the widespread burial of organic matter in vast coal swamps a large decrease in o2 during the late permian was due probably to the drying up of the coal swamps and deposition of a large proportion of total sediment in c and s free continental red beds sensitivity study shows that major parameters affecting results are the mean c concentration in coal basins and the relative sizes of the reservoirs of young rapidly recycled versus old rocks less sensitivity was found for changes over time in total land area undergoing weathering and the use of direct o2 negative feedback on marine carbon burial good agreement for rates of c burial calculated via our model and via independent models which are based on the use of stable carbon isotopes indicates that the dominant factor that has brought about changes in atmospheric o2 level and the isotopic composition of dissolved inorganic carbon in seawater over phanerozoic time is sedimentation and not weathering or higher temperature phenomena such as basalt seawater reaction

miocene phosphate accumulation in the cuyama basin southern california abstract middle and upper miocene phosphatic strata in the cuyama basin of southern california contain approximately 6 4 10 9 metric tons 2 1 10 14 mol of phosphorus p that accumulated in slope and shelf strata at rates between 0 9 and 3 8 mol p cm 2 year 1 from 15 5 to 10 8 ma an estimated 63 of all phosphorus lies in a single third order sequence deposited between 14 8 and 13 ma the main impetus for this brief phosphogenic event was a 200 m relative sea level rise that resulted from strike slip faulting immediately east of the basin minor element and petrologic analyses suggest the overall increase in phosphorus accumulation correlates with less reducing conditions in the shallowly buried marine sediments on the slope and the expansion of phosphogenesis to the outer shelf both events were probably related to landward shifts of the pacific oxygen minimum zone and coastal upwelling centers during the relative sea level rise whereas these tectonic events were apparently local the phosphatic deposits of the cuyama basin clearly demonstrate that tectonism can strongly influence phosphate accumulation rates in marginal marine environments

neogene growth of the sedimentary organic carbon reservoir we develop a recycling model using 13c 12c mass balance for net growth loss of the sedimentary organic carbon corg reservoir and apply it to the neogene bulk marine carbonate 13c record the model allows for variations in photosynthetic fractionation factors carbon cycling rates and the isotopic composition of riverine carbon inputs to the oceans the sign of the net flux term is controlled by the difference between fractional corg burial and fractional corg weathering independent of any variations in carbon cycling rate these terms are in turn estimated from the carbon isotope mass balance of newly deposited and weathered sediments respectively the magnitude of the net flux is sensitive to the global carbon cycling erosion deposition rate which may be estimated by the use of the records of radiogenic isotopic variations nd sr in paleoseawater a key observation and input to the model is that photosynthetic carbon isotope fractionation by both marine algae and terrestrial plants has decreased during the cenozoic incorporating time dependent carbon isotope fractionation into the model shows that the sedimentary corg reservoir has grown throughout most of the neogene even as marine 13c values fell after 14 ma a similar result is obtained if the variation in the marine 13c record is largely caused by changes in the carbon isotopic composition of river fluxes to the oceans rather than changes in the organic inorganic ratio of output to the burial sink the growth of the sedimentary organic carbon reservoir requires that the neogene sedimentary carbon cycle was a net source of o2 and a net sink of co2 to the atmosphere at least until the plio pleistocene as a consequence neogene co2 consumption by silicate weathering cannot be balanced by oxidation of sedimentary corg placing a significant constraint on global carbon balance models a related prediction of our model is that atmospheric o2 levels rose during the neogene

two major cenozoic episodes of phosphogenesis recorded in equatorial pacific seamount deposits seamount phosphorites have been recognized since the 1950s but this is the first study to provide an in depth exploration of the origin and history of these widespread deposits representative samples from equatorial pacific cretaceous seamounts were analyzed for chemical mineralogical and stable isotope compositions the phosphorites occur in a wide variety of forms but most commonly carbonate fluorapatite cfa replaced middle eocene and older carbonate sediment in a deep water environment 1000 m element ratios distinguish seamount phosphorites from continental margin plateau and insular phosphorites uranium and thorium contents are low and total rare earth element ree contents are generally high ree ratios and shale normalized patterns demonstrate that the rees and host cfa were derived from seawater strontium isotopic compositions compared with inferred cenozoic seawater curves define two major episodes of cenozoic phosphatization late eocene early oligocene 39 34 ma and late oligocene early miocene 27 21 ma three minor events are also indicated the major episodes occurred at times of climate transition the first from a nonglacial to glacial earth and the second from a predominantly glacial to warm earth the paleoceanographic conditions that existed at those times initiated and sustained development of phosphorite by accumulation of dissolved phosphorus in the deep sea during relatively stable climatic conditions when oceanic circulation was sluggish fluctuations in climate sealevel and upwelling that accompanied the climate transitions may have driven cycles of enrichment and depletion of the deep sea phosphorus reservoir as temperature gradients in the oceans increased antarctic glaciation expanded and oceanic circulation and upwelling intensified expansion and intensification of the oxygen minimum zone may have increased the capacity for midwater storage of phosphorus supplied by dynamic upwelling around seamounts however the bottom waters never became anoxic during the phosphogenic episodes fluctuations in the ccd and lysocline co2 fluxes and changes in bottom water circulation and temperatures may have bathed the seamount carbonates in more corrosive waters which coupled with increased supplies of dissolved phosphorus promoted replacement processes the late eocene early oligocene phosphogenic episode recorded in seamount deposits is not matched by large phosphorite deposits in the geologic record whereas the late oligocene early miocene episode and middle miocene event are matched by large deposits distributed globally the seamount phosphorites are exposed at the surface of the seamounts and have been for most of the neogene and oligocene the phosphorites do not show signs of etching that would indicate substantial undersaturation of seawater phosphate with respect to cfa mass balance calculations indicate that about 5 4 19 1012 g of p2o5 are locked up in equatorial pacific seamount phosphorites that amount is equivalent to about 2 7 years of the present annual input from rivers

volcanic plume monitoring using atmospheric electric potential gradients by monitoring perturbations of the natural atmospheric electric potential gradient it is possible to detect and track particle laden volcanic plumes the perturbations are produced by electrical charge that resides on the solid particles and liquid droplets of the plume and the ions within it a network of potential gradient monitoring stations around a volcano can provide data on eruption time magnitude plume dispersion direction and areas of ashfall our laboratory experiments have produced electrically charged ash by fragmenting pumice these results support the theory that charging is due to the magma fragmentation process and should therefore be ubiquitous in all particulate volcanic plumes

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

a model for atmospheric co 2 over phanerozoic time a new model has been constructed for calculating the level of atmospheric co sub 2 over phanerozoic time which is much simpler mathematically than the blag model but more complex geologically and biologically results suggest that there has been a notable pattern of varying atmospheric co sub 2 level over the past 570 my with high levels during the mesozoic and early paleozoic and low levels during the permo carboniferous and late cenozoic sensitivity analysis shows that within reasonable limits of the principal governing parameters this qualitative trend of varying co sub 2 is relatively insensitive to the actual values chosen for these parameters causes of the co sub 2 variation are multiple and no single geological or biological process can be called upon to explain all co sub 2 variation for all time the calculated trend of co sub 2 over time agrees well with independent estimations of paleoclimates thus the greenhouse theory of paleoclimate on a long geological time scale is supported by the results of the present study

satellite observations and interpretation of the 1991 mount pinatubo eruption plumes we demonstrate the use of hourly geostationary meteorological satellite gms and noaa polar orbiting advanced very high resolution radiometer avhrr satellite images of the june 1991 mount pinatubo volcanic eruption plumes in providing details of the timing changing eruptive style and umbrella plume movement and dynamics a chronology of explosive events which culminated in a 9 hour long climactic phase on june 15 has been determined from satellite data and favorably compared to ground based and other ancillary information maximum eruption column altitudes of 40 km and column top undercooling in excess of 55 c below the ambient atmosphere occurred during the climactic phase phases dominated by plinian versus coignimbrite eruptive plumes can be distinguished on the images analysis of the spreading umbrella plume during the climactic phase suggests that over the first 4 5 hours the plume spread laterally as a gravitational intrusion before becoming advected in the ambient winds we compare the rate of plume growth to a model of a radially symmetric continuously fed intrusion to describe the motion the rate of plume growth shows good agreement with this simple model for the first 4 5 hours from column top heights we determine eruption rates and obtain an independent estimate of the total volume of magma erupted from june 12 16 of 5 5 km3 dense rock equivalent dre in good agreement with an independent estimate of the total eruptive volume made from deposits on land and submarine ash fall of up to 5 3 km3 dre we also show that secondary explosions in the pinatubo ignimbrite deposits produced ash plumes reaching altitudes as high as 19 km in september 1991 this study indicates that realistic interpretation and monitoring of major eruption plumes can be accomplished by analysis of high temporal resolution satellite data

late miocene carbon isotope records and marine biological productivity was there a dusty link 1 we examine whether or not a relationship exists between the late miocene carbon isotope shift 7 6 6 6 ma and marine productivity at four sites from the indian and pacific oceans ocean drilling program sites 721 1146 1172 and 846 we use a multiproxy approach based on benthic foraminiferal accumulation rates elemental ratios and dissolution indices and we compare these data to benthic foraminiferal 13c values measured on the same samples although some of these sites have been targeted previously in studies of either the late miocene early pliocene biogenic bloom sites 721 and 846 or the late miocene carbon isotope shift site 1172 our records are the first to establish paired proxy records of carbon isotopes and paleoproductivity allowing a direct assessment of a potential link our results indicate that at all sites productivity increased sometime during the 13c shift at three sites 721 1146 and 846 productivity increased at the beginning of the shift the correlation coefficients derived from linear regression between micropaleontologically derived productivity and foraminiferal 13c values are relatively high during the time interval containing the late miocene 13c shift and statistically significant at three of the sites carbon flux and isotope mass balance considerations illustrate that transfer of organic matter between the terrestrial and marine reservoirs together with enhanced oceanic upwelling best approximates observed changes in carbon isotope records and paleoproductivity we note that long term trend in the site 846 paleoproductivity record can be correlated to the long term trend in the site 848 eolian flux reconstructions of hovan 1995 hinting at a link between strengthened wind regime and productivity during the late miocene

the global water cycle and continental erosion during phanerozoic time 570 my asensitivity study is conducted to determine what effect two mechanisms namely continental size and latitudinal location might have on the global wtaer cycle the global water cycle over phanerozoic time 570 my is established first by analyzing the distribution of rainfall p evaporation e and runoff d by bands of 10 of latitude on the present day earth and then applying these values to the ancient phanerozoic world in this backward projection the global cosmic climatic and orographic conditions prevailing today are supposed constant through time while the only variable parameter controlling the system are the latitudinal positions of the continents and the relative area of continents and oceans the calculated phanerozoic global runoff clearly shows that the humid periods are the cretaceous 100 my the devonian silurian 400 my and the cambrian 500 my while the dry periods are close to the present day 0 my and the permo triassic 200 my the continal global runoff together with the survival rate of the volcanics are used to predict the fluctuations of the isotopic ratio 87sr 86sr in marine sediments predicted and measured values appear to be in good agreement except for the present which somewhat validate the calculations the continental runoff is also related to the sedimentation rate and used to estimate the specific erosion rate of the continents through the phanerozoic thus the sedimemtation rate variations are understood as a consequence of the continental runoff fluctuations through time

a rapidly deposited pennate diatom ooze in upper miocene lower pliocene sediment beneath the north pacific polar front abstract rapidly deposited thalassionema thalassiothrix pennate diatom oozes previously have been described in upper miocene lower pliocene sediment beneath the frontal boundary of the eastern equatorial pacific here we document a new occurrence of thalassionema thalassiothrix ooze in upper miocene lower pliocene sediment beneath the frontal boundary of the subarctic north pacific the ooze is a 6 m interval of siliceous sediment at ocean drilling program odp sites 885 886 that was rapidly deposited between approximately 5 0 and 5 9 ma bulk sediment in this interval may contain greater than 85 pennate diatom tests there are also abundant laminae and pockets that are composed entirely of thalassionema and thalassiothrix diatoms the presence of a rapidly deposited ooze dominated by pennate diatoms indicates unusual past conditions in the overlying surface waters time coincident deposition of such oozes at two distinct frontal boundary locations of the pacific suggests that the unusual surface water conditions were causally linked to large scale oceanographic change this same oceanographic change most likely involved 1 addition of nutrients to the ocean or 2 redistribution of nutrients within the ocean the occurrence and origin of pennate diatom oozes may be a key component to an integrative understanding of late neogene paleoceanography and biogeochemical cycling

tertiary paleoceanic chemical variability unintended consequences of simple geochemical models five lines of concrete quantitative evidence about oceanic chemical composition during the past 65 m y can provide insights into the controlling processes and their temporal variations but the system constraints are not yet fully understood the calcium carbonate compensation depth mean carbon isotopic ratio and strontium isotopic ratio have all changed significantly during this time while changes in lithium to calcium and strontium to calcium ratios have been much smaller when these tracers are considered separately simple scenarios of changes in geochemical and geological factors can be used to explain the historical records these factors include 1 increases in continental chemical weathering rates and net continental fluxes to the oceans 2 changes in the isotopic composition of material weathered from continents to the oceans 3 decreases in the proportion of calcium carbonate deposited on continental shelves 4 changes in the deposition or weathering rates of certain types of sediments and 5 changes in hydrothermal circulation because these geochemical cycles are linked to each other and to others such as nutrients and global atmospheric carbon dioxide an explanation invoked for one tracer must satisfy the direction magnitude and timing of the patterns for all the tracers several simple scenarios for geochemical variations have been evaluated for their consequences both intended and unintended and compared to the historical records despite the attractiveness and possible justifications of some simple hypotheses for example decreases in organic carbon burial rates increases in carbonate weathering rates on the continents or increases in all continental weathering rates no one simple scenario appears to be consistent with both the timing and magnitude of the changes observed during the past 65 m y for all tracers considered the contradictions uncovered can be useful in defining what knowledge is crucial to further understanding of oceanic chemical history better knowledge is needed of absolute deep ocean sediment accumulation rates and their temporal variability of the extent and time scale of variability in the net carbon isotope input to the ocean from continental weathering of steady state fluxes for oceanic mass balances and the extent to which these mass balances approach steady state behavior and of the links and interactions between the geochemical cycles of various elements

geochemical consequences of increased late cenozoic weathering rates and the global co2 balance since 100 ma large imbalances in the relative net co2 flux over the last 100 m y are obtained from independently derived estimates of co2 uptake by weathering and organic carbon burial and of co2 outgassing assumed proportional to the mean mid ocean ridge mor spreading and mantle plume production mpp rates increasing the river flux of ca mg p and c by 50 since 30 ma to parallel the proposed increase in the sr river flux needed to explain the sr isotopic evolution of seawater richter et al 1992 has a large impact on the global carbon cycle by reducing the excess net co2 imbalance in the late cenozoic co2 uptake is calculated by assuming that 19 of the ca river flux and 60 of the mg river flux are derived from weathering silicates and that mg is removed in the oceans by 1 1 molar exchange reactions with calcsilicates an increase in the mg river flux combined with an overall decrease in the mor spreading rate predicts as much as a factor of 2 increase in the seawater mg concentration since 100 ma the net organic carbon burial flux burial minus weathering largely reflects changes in the bulk carbonate 13c record and to a lesser extent variations in the net carbonate burial flux and mean 13c value of the carbonate weathering flux organic carbon burial efficiency is markedly less than that of p from the middle middle miocene to the present because of early diagenetic transfer of organic p to francolite and oxidation of organic carbon during reworking of margin sediments by sea level fluctuations the large co2 imbalance of the late cretaceous requires significantly less carbonate subduction or greater weathering rates a co2 balance can be achieved in the miocene by decreasing the proposed increase in river fluxes by up to half or by variably increasing the amount of carbonate subducted variations in shallow water carbonate burial and hence the global carbonate record are currently too poorly known to differentiate between the above possibilities the decrease in the excess co2 flux generally parallels the trend to cooler climate inferred from the 18o record but periods of large co2 imbalance generally precede 18o shifts by several million years

paleoproductivity nutrient burial climate change and the carbon cycle in the western equatorial atlantic across the eocene oligocene boundary paleoproductivity nutrient burial and carbon cycling were investigated across the eocene oligocene e o boundary begin to end 36 9 32 7 ma at 40 kyr resolution timescale of shackleton et al 1999 at ocean drilling program site 925 on the ceara rise in the western equatorial atlantic 3040 m present water depth 748 26 850 70 mbsf downcore bulk sediment records of biogenic barium total reactive phosphorus biogenic silica and calcium carbonate are interpreted to represent export production net nutrient burial biogenic opal production and inorganic carbon burial respectively the global positive excursion in 13c subsequent to the e o boundary is recorded at site 925 export production appears to have been externally forced by orbital parameters at eccentricity frequencies during the study interval based on spectral analysis of the biogenic barium and reactive phosphorus records biogenic silica production or preservation increased after the eocene oligocene boundary to a higher baseline although overall productivity and nutrient burial did not increase based on barium and reactive phosphorus records thus although absolute production did not increase at this site a shift in relative abundance of siliceous versus carbonate productivity may have resulted in a change in relative organic carbon burial this may have contributed to the positive excursion in global oceanic 13c subsequent to the eocene oligocene boundary although the silica maximum persists after the carbon isotope excursion ends

river fluxes of dissolved silica to the ocean were higher during glacials ge si in diatoms rivers and oceans two centric marine diatom species thalassiosira oceanica and thalassiosira antarctica were grown in batch cultures to determine the incorporation of germanium ge and silicon si into siliceous shells opal the results were modeled as ge si isotope fractionation during exponential growth diatoms take up and incorporate ge si from solution without major discrimination against ge during stationary phase growth near silica limitation the antarctic species t antarctica discriminates slightly against ge but integrated ge si opal produced over the latter portion of the growth cycle is indistinguishable from the initial solution ratio these results confirm experiments using radioactive 68ge that showed absence of fractionation during diatom silica uptake azam and volcani 1981 in contrast to two box ocean models that invoke 50 ge discrimination by diatoms to explain the observed excess surface ocean germanium concentration murnane and stallard 1988 froelich et al 1989 and late pleistocene ocean sediment ge si opal records mortlock et al 1991 runs of a 10 box ocean ge and si model pandora with 50 discrimination reproduce the excess surface ocean ge but introduces curvature into the deep ocean ge versus si relationship that is not observed in the oceans thus 50 fractionation is not supported by either cultures or models if diatoms do not fractionate ge si then late pleistocene ge si opal variations in piston cores are caused not by changes in local biosiliceous production and silica utilization mortlock et al 1991 but rather by whole ocean changes in ge si seawater the marine ge si opal record of the last 450 kyr can be modeled as transient oceanic responses to instantaneous continental climate transitions consistent with the chemical weathering model of murnane and stallard 1990 glacial periods are characterized by lower continental weathering intensity lower ge si riv and two fold higher dissolved silica river fluxes marine ge si opal records thus contain a history of ocean silica chemistry that reflect rapid global changes in continental weathering

mechanisms of thrust faulting in the gran sasso chain central apennines italy abstract the gran sasso chain in central italy is made up of an imbricate stack of eight thrust sheets which were emplaced over the upper miocene lower pliocene laga flysch the thrust sheets are numbered from 1 to 8 in order of their decreasing elevation in the tectonic stack and their basal thrusts are numbered from t 1 to t 8 accordingly on the basis of their different deformation features the major thrust faults fall into three groups 1 thrust faults marked by thick belts of incoherent gouges and breccia zones t 1 t 2 t 3 2 thrust faults characterized by a sharp plane which truncates folds that had developed in the footwall rocks t 5 t 6 and 3 thrust faults truncating folds developed in both the hangingwall and footwall units and bordered by foliated fault rocks t 7 the deformation features observed for the different faults seem to vary because of two combined factors 1 lithologic changes in the footwall and hangingwall units separated by the thrust faults and 2 increasing amounts of deformation in the deepest portions of the imbricate stack the upper thrust sheets from 1 to 6 are characterized by massive calcareous and dolomitic rocks they maintain a homoclinal setting and are truncated up section by the cataclastic thrust faults the lowermost thrust sheets 7 and 8 are characterized by a multilayer with competence contrasts which undergoes shear induced folding prior to the final emplacement of the thrust sheets bedding and axial planes of folds rotate progressively towards the t 5 t 6 t 7 and t 8 thrust boundaries and are subsequently truncated by propagation of the brittle thrust faults the maximum deformation is observed along the t 7 thrust fault consistent with horizontal displacement that increases progressively from the uppermost to the lowermost thrust sheet in the tectonic stack the axial planes of the folds developed in the hangingwall and footwall units are parallel to the t 7 thrust fault and foliated fault rocks have developed field data and petrographic analysis indicate that cleavage fabrics in the fault rocks form by a combination of cataclasis cataclastic flow and pressure solution slip associated with pervasive shearing along subtly distributed slip zones parallel to the t 7 thrust fault the development of such fabrics at upper crustal levels creates easy slip conditions in progressively thinner domains which are regions of localized flow during the thrust sheet emplacement

evolution of tethyan phosphogenesis along the northern edges of the arabian african shield during the cretaceous eocene as deduced from temporal variations of ca and nd isotopes and rates of p accumulation abstract the evolution of tethyan phosphogenesis during the cretaceous eocene is examined to try to explain fluctuations of phosphogenesis through time and whether or not they reflect long term changes in ocean circulation or in continental weathering twenty seven time stratigraphic phosphate levels in various tethyan sites covering a time span of about 90 myr from the hauterivian to the eocene were analyzed for 44 ca 42 ca and 143 nd 144 nd in their carbonate fluorapatite cfa fraction p and ca accumulation rates and bulk sedimentation rates were quantified throughout the cretaceous eocene negev sequence to examine how changes in 44 ca 42 ca and 143 nd 144 nd are reflected in the intensity of phosphogenesis a clear cut change occurs in e nd t and 44 ca and in the rates of p and ca accumulation and bulk sedimentation through the time analyzed e nd t is much lower in the hauterivian lower cenomanian 12 8 to 10 9 than in the upper cenomanian eocene 7 8 to 5 9 much lower 44 ca values occur in the hauterivian turonian 0 22 to 0 02 than in the coniacian eocene 0 23 to 0 40 p accumulation rates in the negev steeply increase from 2 k yr 1 in the albian coniacian to 1500 mol cm 2 k yr 1 in the campanian whereas a strong decrease is concomitantly recorded in the rates of ca accumulation and bulk sedimentation in addition distinct e nd t values are shown by the phosphorites of the negev 6 7 to 6 4 and egypt 9 1 to 7 6 during the campanian and by those of the negev 7 8 to 6 3 and north africa 10 1 to 8 9 during the maastrichtian eocene the culmination of p accumulation rates in the negev during the campanian occurring with a high in e nd t and 44 ca and a low in sedimentation rates indicates that paleoceanographic and paleogeographical factors mostly governed phosphorite accumulation in this area the abrupt e nd t rise after the cenomanian is attributed to increased incursion of pacific radiogenic water masses into the tethys driven by the late cretaceous global sea level rise the connection between north and south atlantic the global post santonian cooling and the progressive widening of the caribbean threshold all acting in combination to significantly intensify the tethyan circumglobal current tcc it also reflects a weakening of the continental nd signal due to a reduction of exposed landmasses caused by increased flooding of continental shelves high 44 ca values at those times also point to a decrease in weathering ca 2 fluxes and expansion of carbonate sedimentation in shelves both enriching seawater with isotopically heavy ca 2 deep ocean circulation intensified by the post santonian cooling of high latitudes increased p inventory in the tethys basin whereas the strengthened tcc and the folded shelf likely resulted in coastal and topographically induced upwelling supplying p rich intermediate waters to southeastern tethys shelves only in the paleocene eocene following major changes in global circulation produced by narrowing of tethys and widening of the atlantic did phosphogenesis shifts its locus of high intensity to the western atlantic tethys and west african atlantic coasts this change in paleocirculation is expressed by distinctly differing e nd t in the middle east and the north and west african phosphorites suggesting different oceanic p sources and current systems for these two major groups of phosphorites our nd isotope results further suggest a weaker tcc during the mid cretaceous becoming more intense in late cretaceous times they also point to the north pacific ocean as major source of deep water formation for the intermediate deep waters in the tethys basin during the late cretaceous

electric potential gradient changes during explosive activity at sakurajima volcano japan we report electric potential gradient measurements carried out at sakurajima volcano in japan during 1 explosions which generated ash plumes 2 steam explosions which produced plumes of condensing gases and 3 periods of ashfall and plume induced acid rainfall sequential positive and negative deviations occurred during explosions which generated ash plumes however no deflections from background were found during steam explosions during periods of ashfall negative electric potential gradients were observed while positive potential gradients occurred during fallout of plume induced acid rain from the same eruption these results suggest that a dipole arrangement of charge develops within plumes such that positive charges dominate in the volcanic gas rich top and negative charges in the following ash rich part of the plume the charge polarity may be reversed for other volcanoes hatakeyama and uchikawa 1952 we suggest that charge is generated by fracto emission donaldson et al 1988 processes probably during magma fragmentation within the vent rather than by frictional effects within the plume

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

origin and age of phosphorite from the south central florida platform relation of phosphogenesis to sea level fluctuations and δ13c excursions abstract francolite carbonate fluorapatite from predominantly peloidal phosphorite grains in the miocene hawthorn group from the babcock deep core southwestern florida is highly substituted with an average composition of ca4 61na0 22mg0 14k0 05sr0 02 po4 2 23 co3 0 62 so4 0 12 f 1 04 13c values of 1 0 7 8 pdb of the francolite co3 indicate a substantial contribution of c from an organic source the sulfur isotopic composition of francolite so4 is depleted to slightly enriched relative to miocene seawater and suggests that phosphogenesis occurred during early burial diagenesis in organicrich sediments above or in the zone of sulfate reduction the uniformly high sr na mg so4 and co3 contents of the francolite the 18o values of the francolite co3 0 2 4 2 pdb and the inclusion of pyrite and organic matter in phosphorite grains suggest that the francolite has had minimal chemical alteration since its formation phosphorite from the babcock deep core has sr 87 86 ratios that range from 0 708148 0 708880 and sr derived ages that range from late oligocene 25 6 0 7 ma to early late miocene 9 2 1 4 ma the sr derived ages of relatively fragile calcareous benthic foraminifers are consistently younger than associated hard tightly cemented phosphorite and support textural evidence of extensive reworking the age of the host sediment ranges from early miocene to pliocene and its depositional history is related to sea level fluctuations approximately three quarters of the total phosphorite in the babcock deep core formed during or within 2 my before the major early to mid miocene positive 13cshift as recorded at dsdp site 588 southwest pacific one third of the total phosphorite formed just prior to the carbon shift in the short interval between 21 9 and 20 4 ma these results indicate that reworked phosphorite deposits may provide a proxy of organic carbon cycling on continental shelves that correspond to sealevel fluctuations and to variations in the 13crecord

phosphorus accumulation rates in a miocene low oxygen basin the monterey formation pismo basin california abstract phosphorus p limits oceanic productivity on long time scales and therefore determining changes in oceanic p accumulation through time is important for modeling oceanic paleoproductivity we determined p concentrations and accumulation rates at shell beach california a section of phosphatic rich marine sedimentary rocks which includes the widespread phosphatic and siliceous facies of the monterey formation phosphorus concentrations had wide ranges in the major lithologies found in these facies with values in phosphatic shales ranging from 0 36 to 3 9 wt compared to 0 02 to 0 42 wt in dolomitic and siliceous strata phosphorus accumulation rates in mol p cm 2 yr 1 for all values reported here showed significant variability with both sample lithology and position in the section phosphorus accumulation rates were much higher in phosphatic shale strata 1 5 29 than in dolomitic and siliceous strata 0 1 3 1 in both facies furthermore p accumulation rates were generally higher in phosphatic shale strata of the upper siliceous facies 3 1 29 compared to the lower phosphatic facies 1 5 14 mean p accumulation rates calculated using linear sedimentation rate models for each facies and observations of the relative amount of phosphatic shale dolomite and siliceous strata are comparable between the portions of phosphatic and siliceous facies studied this indicates that the two facies with their faunal and sedimentological characteristics considered to reflect major oceanic and climatic changes during the middle miocene are similar in terms of p burial total p accumulation rates are also comparable to other phosphogenic miocene and modern environments we modeled variable sedimentation rates to examine the sensitivity of mean p accumulation rates to the linear sedimentation rate assumption increasing shale sedimentation rates to values above those estimated by linear models yields higher mean p accumulation rates in both facies though they remain comparable in terms of net p burial modeling also revealed that for increased shale sedimentation rates in each facies siliceous sedimentation must be about three times faster than dolomitic strata sedimentation

productivity and continental denudation history from the south china sea since the late miocene late miocene recent micropaleontological and geochemical records from ocean drilling program odp site 1143 in the southern south china sea scs indicate that increase and decrease in abundance of siliceous plankton may be controlled mainly by the input of nutrients derived from land and provided by upwelling a high export production event a biogenic bloom event occurred in the southern scs between 12 and 6 ma during this period high ratios of smectite illite chlorite smectite quartz and al k indicate a high weathering intensity of the asian continent possibly due to the intensification of the east asian summer monsoon easm which may have increased the net flux of nutrients to the ocean both directly through terrestrial input and indirectly through upwelling activity a drop in ba ti al ti and ca ti values around 6 ma may indicate a lowering of productivity possibly due to the large consumption of sea surface nutrients by the biogenic bloom alternatively it may indicate a shift in terrigenous input source area at about 5 4 ma a decrease in weathering intensity as indicated by a sudden decrease in the values of smectite illite chlorite smectite quartz and al k might have led to a sudden decrease of terrestrial nutrient input to the scs we suggest that the biogenic bloom ended when nutrients in surface waters were exhausted because of a decrease in supply as well as a decrease in upwelling intensity due to weakening of the easm as a result radiolarians were absent in the studied area between similar to 6 and 3 2 ma at similar to 3 2 ma radiolarians began to recover possibly because the start of northern hemispheric glaciation and the rapid uplift of the tibet plateau led to intensification of the east asian monsoon after the mid pleistocene climate transition at 0 9 ma the abundance and mass accumulation rates of radiolarians increased probably as a result of increased upwelling activity driven by the increasing intensity of the summer monsoon crown copyright c 2009 published by elsevier b v all rights reserved

paleomagnetically determined rotations in the western sicilian fold and thrust belt new paleomagnetic data from the west sicilian fold and thrust belt indicate large scale clockwise rotations during tectonic transport for the platform and seamount paleogeographic units of the fold and thrust belt panormide and trapanese units there is a general consistency in the magnitude of rotation along strike suggesting the existence of large coherent structural units for the panormide platform clockwise rotations in the range of 90 to 140 relative to the underlying iblean parautochthon are recorded along 125 km of outcrop strike in the case of the trapanese unit clockwise rotations in the range of 47 to 70 relative to iblei are recorded along about 90 km of outcrop strike intervening basinal paleogeographic units imerese and sicanian units show clockwise rotations of similar magnitude although few reliable data are available from these units palinspastic reconstruction of the thrust belt incorporating the rotations and arguments for the present orientation of the margins of the paleogeographic units implies that the panormide platform and trapanese seamounts were originally elongated more or less north south relative to the present orientation of iblei the two units apparently coalesced to the south and were discontinuous to the north they and their intervening basins were part of a passive continental margin which occupied a large part of the area that was subsequently rifted to form the tyrrhenian sea

a comparison of spatially resolved and global mean reconstructions of continental denudation under ice free and present conditions we assess the impact of continental scale processes on global denudation through the use of spatially resolved information for both an ice free paleoclimate and the present climate runoff from general circulation modeling cases representing the early eocene is superimposed upon an eocene paleogeologic reconstruction and this information is combined with chemical denudation rates for silica dissolved moles si and bicarbonate dissolved moles hco3 global fluxes of silica and bicarbonate to the global ocean are then calculated a parallel procedure is carried out with present day distributions of lithology and model derived runoff this work demonstrates that fluxes produced by a simple model such as the one used here are significantly different when calculated with spatially uniform runoff values versus those calculated with a spatially varying runoff distribution having the same global mean value use of a uniform runoff distribution produces denudation rates that are significantly higher than the global results derived from a spatially varying runoff distribution we show that present day fluxes of silica calculated by our model containing spatially varying runoff and lithology are similar to observations of current fluxes suggesting that our model captures the first order relationship accurately however the bicarbonate value compares less well to observations comparison of eocene and present day flux results shows that present day fluxes of si are greater than eocene values while calculated present day hco3 fluxes are greater than or equal to eocene values this result occurs despite the existence of greater global mean annual runoff for the eocene cases and despite the existence of ice covered areas by definition not contributing to chemical weathering in our model in the present case the increase in si global denudation fluxes from the eocene to the present are caused primarily by the large increase in exposed granitic basaltic and shale lithologies and a decrease in exposed sandstone areas between the eocene and present

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

late cenozoic ge si record of marine biogenic opal implications for variations of riverine fluxes to the ocean we have determined germanium silicon ratios in purified diatoms and radiolarians from siliceous sediments in holocene core tops one late pleistocene piston core and four high latitude southern ocean deep sea drilling project dsdp sites ranging in age from holocene to oligocene high latitude holocene diatoms in the 10 to 38 m size fraction ge si opal 0 693 0 039 10 6 faithfully record the present oceanic ratio ge si seawater 0 699 0 004 10 6 this confirms that diatoms from siliceous oozes are monitors of seawater ge si and may record past changes in rates of delivery of weathering products to the sea from continental and seafloor weathering large diatoms and radiolarians display ratios much lower than ge si seawater suggesting that ge si opal to some extent displays the effects of biological fractionation from 0 to 2 5 m y b p ge si opal in diatoms from dsdp sites ranges from about 0 54 to 0 70 10 6 similar to the range observed in one late pleistocene piston core over the last 25 kyr from 2 5 to 6 m y b p the ratio is more variable while prior to 10 m y b p ratios are clearly higher averaging about 0 9 10 6 in the early to middle miocene low values of the ratio are consistent with global weathering regimes dominated by river silica input to the sea while higher ratios suggest periods of enhanced hydrothermal input or reduced fluvial contribution nevertheless an oceanic one box model with variable river and hydrothermal inputs and biogenic opal output cannot adequately account for the magnitude or the timing of changes observed in the record suggesting the existence of other sources sinks for inorganic germanium and or silicon to or from the sea

genesis and evolution of a curved mountain front paleomagnetic and geological evidence from the gran sasso range central apennines italy abstract the gran sasso range is a striking salient formed by two roughly rectilinear e w and n s limbs in the past 90 counterclockwise ccw rotations from the eastern gran sasso were reported tectonophysics 215 1992 335 suggesting west east increase of rotation related northward shortening along the e w limb in this paper we report on paleomagnetic data from meso cenozoic sedimentary dykes and strata cropping out at corno grande central part of the e w gran sasso limb the highest summit of the apennine belt predominant northwestward paleomagnetic declinations in the normal polarity state from both sedimentary dykes and strata are observed when compared to the expected declination values for the adriatic foreland our data document no thrusting related rotation at corno grande the overall paleomagnetic data set coupled with the available geological information shows that the gran sasso arc is in fact a composite structure formed by an unrotated low shortening western e w trending limb and a strongly ccw rotated eastern salient late messinian and post early pliocene shortening episodes documented along the gran sasso front indicate that belt building and arc formation occurred during two distinct episodes we suggest that the southern part of a late messinian n s front was reactivated during early middle pliocene time forming a tight range salient due to ccw rotations and differential along front shortening rates the formation of a northward displacing bulge in an overall nw se chain is likely a consequence of the collision between the latium abruzzi and apulian carbonate platforms during northeastward propagation of the apennine wedge inducing lateral northward extrusion of latium abruzzi carbonates towards ductile basinal sediment areas

pacific pelagic phosphorus accumulation during the last 10 m y as a limiting nutrient to marine life phosphorus p is an effective tracer of today s marine productivity the distribution of p in marine sediments likewise tracks the history of marine productivity because of its relative insolubility in seawater caco3 biogenic opal terrigenous sediment and total p have been measured in cores from nine pacific sites deep sea drilling project dsdp 65 66 310 77 62 572 463 586 and gpc 3 and one subantarctic dsdp 266 site these sites were specifically chosen to provide information on biota burial flux changes with time for sedimentary sinks that represent key oceanographic variables i e rate of upwelling water depth and carbonate dissolution gradient the accumulation rates of these components for the last 10 ma were then calculated from determined core age versus depth plots core bulk density and porosity data the accumulation of p weakly correlates with that of caco3 moderately with that of total sediment and very strongly with carbonate free accumulation two prominent peaks for all components occur at 2 3 ma and 5 6 ma and record the chemical loading of dissolved caco3 sio2 and p from glacially emergent continental shelves these results indicate that continental shelf phosphorites form during interglacially high sea levels and correspond to low deep sea p accumulation rates whereas glacially lowered sea levels allow for shelf bypassing and greater deep sea p accumulation rates

discrepancies in the oceanic carbon isotope record for the last fifteen million years abstract the s hackleton and h hall 1984 record of carbon isotope ratios for bulk caco3 from dsdp sites 525 to 528 in the south atlantic has been widely used as an indicator of how the 13 c 12 c for caco3 leaving the ocean has changed over the last 68 million years of particular interest is the approximately 2 decrease which occurred during the last 15 million years for it suggests a change in the o2 content of the atmosphere s hackleton 1987 as a check on the assumption that this record serves as a global indicator we have compiled measurements on planktonic foraminifera from a number of tropical cores we find that this data set suggests a much smaller 13 c 12 c decrease over the same time interval we can find no satisfactory explanation for this difference and hence can conclude only that more measurements and thought will be required before the time trend in carbon isotope composition can be established

early diagenesis of organic matter in peru continental margin sediments phosphorite precipitation abstract pore water chemistry total dissolved co 2 nh 4 no 3 no 2 po 4 si oh 4 ca mg fe mn so 4 h 2 s and f and titration alkalinity solid phase chemistry c org p org c tot n tot f si opal and s ii and sediment characteristics porosity dry bulk density and formation factors were determined on a centimeter scale spacing in the upper 20 40 cm of sediments under intense upwelling areas on the peru continental shelf these data demonstrate that carbonate fluorapatite cfa is precipitating from pore waters in the upper few centimeters of a gelatinous mud with high organic carbon content up to 20 c org very high porosity 0 96 ml cm 3 and very low dry bulk density 3 dissolved phosphate concentrations at the sediment water interface range from 20 to 100 m orders of magnitude higher than bottom water concentrations and much higher than predicted from regeneration of organic matter the mechanism of this interfacial phosphate release is unclear but is apparently uncoupled from carbon and nitrogen metabolism and thus may be linked either to dissolution of fish debris or to the presence of a microbial mat in surficial sediments fluoride is incorporated into cfa by diffusion from the overlying seawater and carbonate ions are provided from pore water alkalinity magnesium concentrations in this reaction zone are not significantly different from those of seawater suggesting that magnesium depletion is not a necessary prerequisite for cfa precipitation the environment of precipitation is interface linked rather than driven by organic diagenesis of phosphorus deeper in the sediment most of the cores display a wide range of diagenetic characteristics below the immediate interfacial region but almost all show the precipitation signature near the interface this interface linked early diagenetic porewater environment for the precipitation of cfa explains many of the geochemical characteristics of phosphorites and provides a testable model to compare the modern phosphogenic analog with ancient phosphorite deposits two of the cores display very high solid phase phosphorus and fluoride contents reflecting the presence of apparently modern pelletal apatites

carbon and oxygen isotopes of bulk carbonate in sediment deposited beneath the eastern equatorial pacific over the last 8 million years to improve the understanding and utility of bulk carbonate stable carbon and oxygen isotope measurements we examine sediment from cores in the eastern equatorial pacific that span the last 8ma we measured c 13 and o 18 in 791 samples from integrated ocean drilling program site u1338 and deep sea drilling project site 573 both located close to the pacific equator in 100 samples we measured c 13 and o 18 on isolated 63 mu m and 38 mu m fractions which concentrates calcareous nannofossil carbonate and progressively excludes foraminiferal carbonate bulk carbonate c 13 and o 18 records are similar to published records from other sites drilled near the equator and seem to reflect mixed layer conditions albeit with some important caveats involving the precipitation of calcite by coccolithophores the comparatively lower c 13 and o 18 of the 63 mu m and 38 mu m fractions in sediments younger than 4 4ma is attributed to an increase in deep dwelling planktic foraminifera material in bulk carbonate shifting the bulk isotopic signals toward higher values bulk carbonate c 13 is similar over 2500km along the pacific equator suggesting covarying concentrations and c 13 of dissolved inorganic carbon within surface waters since 8ma greater bulk sediment c 13 and o 18 higher sedimentation rates and low content of coarse material suggest intensified wind driven upwelling and enhanced primary productivity along the pacific equator between 8 0 and 4 4ma although a full understanding of bulk carbonate records will require extensive future work