paleomagnetism of coastal california and baja california alternatives to large scale northward transport paleomagnetic data from the santa lucia orocopia sloa and baja borderland bba allochthons of coastal california and baja california have been interpreted to indicate up to 2500 km of post mid cretaceous northward transport of these regions with respect to interior north america however with neogene strike slip offsets taken into account geological interpretations correlate basement rocks of the coastal allochthons with continental basement rocks directly across the san andreas and related fault systems we have examined paleomagnetic data from sloa and bba and conclude that apparent discordances can be explained without large scale pre neogene tectonic transport three major observations are fundamental to this analysis 1 paleolatitudes derived from volcanic rocks of the jurassic eugenia formation of bba and coast range ophiolite of sloa are concordant when compared to revised jurassic reference paleomagnetic poles from interior north america 2 isotopic and paleobarometric data from the peninsula ranges batholith in southern california indicate that the batholith has been tilted northeast side up by an amount that can account for discordant paleomagnetic directions observed in plutonic rocks of the batholith without large scale northward transport 3 literal interpretation of the paleolatitudes determined from paleomagnetic directions in upper cretaceous and paleogene marine sedimentary rocks of sloa and bba requires north then south then north transport and a complex motion history between the two allochthons however concordant paleolatitudes are indicated by some sedimentary rocks while coeval or younger sedimentary rocks of the same allochthon have discordant paleolatitudes coupled with recent documentations of compaction shallowing of paleomagnetic inclination in other marine sedimentary rocks these inconsistencies suggest that paleolatitudes derived from most of the marine sedimentary rocks of sloa and bba are biased towards low paleolatitudes by compaction shallowing

variations of biogenic particle flux in the southern atlantic section of the subantarctic zone during the late quaternary evidence from sedimentary and variations of intensity and composition of biogenic particle flux at the northern boundary of the present polarfrontal zone in the atlantic sector of the southern ocean are indicators of major changes of paleoenvironmentalconditions on glacial interglacial time scales during the late quaternary in order to estimate those pastchanges sediment accumulation patterns of two piston cores one from just north and one just south of thepresent day position of the subantarctic front were reconstructed using the 230thex method large contributionsof laterally supplied material were quantified and used to correct sediment accumulation rates during the lastglacial focussing of biogenic opal dominated material exceeded the original contribution from the surfacewater above by a maximum factor of 8 7 the initial activity ratio of 231paex 230thex was used as tracer forbiogenic particle flux and composition and indicates that during the glacial stages 2 and 4 the area of high opalproductivity was situated above the location of the southern core whereas the northern core has not beenreached by this northward shift during the last 130 kyr as shown by the pattern of focussing corrected bulkaccumulation rates if the position of the antarctic polar front has remained at the northern boundary of thehigh opal productivity area during the last 130 kyr the results suggest that was located exactly between thetwo core sites during glacial stages 2 and 4 a two box modeling approach involving particle flux and boundaryscavenging intensity of 231pa was applied to estimate the possible range of the 231paex 230thex ratio recordedin southern ocean sediments previous estimates on the export of 231pa from the atlantic into the southernocean are corroborated but the model suggests a low sensitivity of the 231paex 230thex ratio in southern oceansediments to variations of the residence time of north atlantic deep water in the atlantic ocean

26al 10be systematics in deep sea sediments we report the development of a naoh leaching technique to extract the authigenic al and be in marine sediments which should allow the sedimentary signals of cosmogenic 26al and 10be to be more effectively studied as geochemical geophysical tracers the technique has been applied to the study of 26al and 10be in opal rich sediments from the north pacific the 26al 27al and 10be 9be ratios of 3 10 14 and 1 10 7 leached from the sediments are higher than those in the total sediments by factors of 3 10 and 2 3 respectively the authigenic 10be 9be ratios are similar to those in deep waters at the study site pointing to the potential usefulness of the ratios in paleoceanographic studies the fractions of total be and al in the sediment studied that are of authigenic origin average about 40 and 17 respectively estimated 26al 27a1 ratios in detrital sediments are 10 15 low enough to indicate that the source of 26al in the ocean mainly comes from atmospheric production in the study area the deposition flux of 26al is comparable to its atmospheric supply however the deposition flux of 10be is about threefold higher than the atmospheric input signifying lateral transport of 10be from the open ocean to this area of relatively high particle flux the 26al 10be ratio being insensitive to the oceanic influx of lithogenic particles may serve as a valuable proxy for paleoproductivity both the authigenic and total sediment 26al 27al and 10be 9be ratios decreased significantly at 6 ka which could reflect an enhanced input of windblown lithogenic particles to the north pacific while the enhanced dust input did not significantly alter the deep water 9be concentration it contributed to the observed increase of authigenic 9be flux to the sediment

10be and9be in south atlantic dsdp site 519 relation to geomagnetic reversals and to sediment composition a high resolution10be profile has been measured on dsdp site 519 central south atlantic in order to search for changes in the flux of10be into a pelagic sediment during geomagnetic reversals as compared with times of constant magnetic polarity the decay corrected10be concentrations range from 1 to 9 108 at g the average10be flux rate is 5 108 at cm 2 kyr 1 9be and caco3 were measured on the same samples the10be vs depth curve is overall similar to the9be vs depth curve while the caco3 vs depth curve anticorrelates the beryllium isotope curves closely implying that be is carried mainly by the non caco3 phases of the sediment the positive correlation between10be and9be along with the fact that the average 10be 9be ratio of 5 5 10 8 is within the range of 10be 9be ratios reported for deep ocean water leads us to conclude 1 that the beryllium isotopes come close to an equilibrium in the open ocean and 2 that the 10be 9be in deep sea sediments with a low detrital component monitors the 10be 9be of deep ocean water through time relative increases of the 10be 9be ratio are observed in the vicinity of the geomagnetic reversals but the relationship between reversals and higher 10be 9be remains doubtful other mechanisms which could alter the 10be 9be ratio are discussed input of10be by melting of glacial ice changing input of9be due to changes in continental erosion changing deep ocean circulation changing scavenging activity at ocean margins but as yet no conclusive explanation for the observed behavior of the beryllium isotopes can be given

particulate removal of230th and231pa in the biologically productive northern north pacific settling particles were collected by sediment traps at four stations in the high latitudes of the north pacific and analyzed for234th 232th 230th 228th and231pa in the northern north pacific including the bering sea the average activity ratio of unsupported230th to231pa in settling particles was 5 5 whereas that in the gulf of alaska in the eastern north pacific was about 14 the northern north pacific may be an efficient sink for231pa relative to230th because the average ratio in the world ocean is equal to the production ratio of 10 8 in seawater the activity ratios of230th 231pa of the settling particles agree well with those of the surface sediments at the respective stations this indicates that both nuclides in the surface sediments originated from settling particles and their dissolution or uptake during early diagenesis are not effective the ratio of the particulate nuclide flux f to the overlying water column production rate p did not correlate well with the total mass flux for230th however that for231pa increased almost linearly with increase in total mass flux and reached unity when the total mass flux was about 110 mg m2 d this suggests that231pa transported from oligotrophic regions is being actively removed in the biologically productive northern north pacific

measurement of adsorbed and total 232th 230th ratios from marine sediments the predictable in situ production of 230th from the decay of uranium in seawater and its subsequent removal by scavenging onto falling particles provides a valuable tool for normalizing fluxes to the seafloor we describe a new application determination of the 232th that dissolves in the water column and is removed to the seafloor 232th is supplied to the ocean in continental minerals dissolution of which leads to a measurable standing stock in the water column sedimentary adsorbed 232th 230th ratios have the potential to provide a proxy for estimating the amount of dissolved material that enters the ocean both today and in the past ten core top samples were treated with up to eight different leaching techniques in order to determine the best method for the separating adsorbed from lattice bound thorium in addition separate components of the sediments were analyzed to test whether clay dissolution was an important contribution to the final measurement there was no systematic correlation between the strength of acid used in the leach and the measured 232th 230th ratios in all cases clean foraminifera produced the same ratio as leaches on bulk sediment in three out of five samples leaches performed on non carbonate detritus in the 63 mu m size fraction were also identical without additional water column data it is not yet clear whether there is a simple one to one correlation between the expected deep water 232th 230th and that produced by leaching especially in carbonate rich sediments however higher ratios and associated high 232th adsorbed fluxes were observed in areas with high expected detrital inputs the adsorbed fraction was 35 50 of the total 232th in seven out of ten samples our 230th normalized 232th fluxes are reasonable by comparison to global estimates of detrital inputs to the ocean in nine cases out of ten the total 230th normalized 232th flux is greater than predicted from the annual dust fall at each specific location but lower than the average global detrital input from all sources

application of paleomagnetism to accretionary tectonics and structural geology the use of paleomagnetism to determine translations and rotations of geologic terranes has contributed to a better understanding of deformation within accretionary complexes shear zones and rifts in this report to the i u g g we review the progress resulting from paleomagnetic studies during the last four years in the cordillera of north america the appalachian orogen and the circum pacific region

a primary magnetization fingerprint from the cretaceous laytonville limestone further evidence for rapid oceanic plate velocities paleomagnetic data from the cretaceous 101 88 ma laytonville limestone of northern california are of geodynamic interest because they suggest a rate of absolute plate motion 15 cm yr that exceeds those of all present day plates such findings assume that a primary magnetization is preserved in these accreted pelagic limestone outcrops this assumption is supported by a trend in the paleomagnetic inclination data that matches in magnitude and sign the expected sense of motion predicted by comparing the mean paleolatitude value with the north american apparent polar wander path the pervasiveness of remagnetizations seen in shallow water carbonates of north america and elsewhere however raises questions as to whether the laytonville limestone is remagnetized regardless of tests indicating a primary magnetization the remagnetized carbonates have a distinctive wasp waisted magnetic hysteresis signature thought to reflect a bimodal distribution of magnetite grain sizes this signature can be quantified by the relationship between saturation remanence mr saturation magnetization ms coercivity hc and the coercivity of remanence hcr mr ms 0 89 hcr hc 06 this power law is compared with reference data from pacific deep sea carbonates deep sea drilling project sites 167 317 and 463 ocean drilling program site 806 and tethyan pelagic carbonates valle del mis section southern alps which together define a different curve mr ms 0 53 hcr hc 1 0 the laytonville limestone falls in two categories on the basis of unblocking temperature spectra resistance to alternating field demagnetization and behavior during the acquisition of isothermal remanent magnetization red laytonville limestone is thought to contain pigmentary hematite in addition to magnetite hysteresis curves from red laytonville limestone are wasp waisted but because such curves also typify magnetite hematite mixtures these data do not provide an unambiguous test for remagnetization some white laytonville limestone however appears to contain negligible amounts of hematite and can be directly compared with the remagnetized carbonates hysteresis parameters derived from white samples are indistinguishable from those of the reference pelagic limestones such samples have a stratigraphic significance occurring where paleolatitude data indicate an equatorial crossing these samples may have depleted pigmentary hematite due to increased magnetic dissolution as the limestone entered the equatorial belt of high productivity the lack of a remagnetization fingerprint in these white samples together with paleomagnetic lithologic and paleontologic data form a consistent data set supporting the primary nature of the laytonville limestone magnetization and rapid oceanic plate velocities a small plate size coupled with the unusually vigorous mantle plume volcanism of the cretaceous pacific basin could have combined to reduce the effectiveness of asthenospheric drag accounting for the rapid motion

large scale right slip displacement on the east san francisco bay region fault system california implications for location of late miocene to pliocene pacific plate boundary a belt of northwardly younging neogene and quaternary volcanic rocks and hydrothermal vein systems together with a distinctive cretaceous terrane of the franciscan complex the permanente terrane exhibits about 160 to 170 km of cumulative dextral offset across faults of the east san francisco bay region esfbr fault system the offset hydrothermal veins and volcanic rocks range in age from 01 ma at the northwest end to about 17 6 ma at the southeast end in the fault block between the san andreas and esfbr fault systems where volcanic rocks are scarce hydrothermal vein system ages clearly indicate that the northward younging thermal overprint affected these rocks beginning about 18 ma the age progression of these volcanic rocks and hydrothermal vein systems is consistent with previously proposed models that relate northward propagation of the san andreas transform to the opening of an asthenospheric window beneath the north american plate margin in the wake of subducting lithosphere the similarity in the amount of offset of the permanente terrane across the esfbr fault system to that derived by restoring continuity in the northward younging age progression of volcanic rocks and hydrothermal veins suggests a model in which 80 110 km of offset are taken up 8 to 6 ma on a fault aligned with the bloomfield tolay franklin concord sunol calaveras faults an additional 50 70 km of cumulative slip are taken up 6 ma by the rogers creek hayward and concord franklin sunol calaveras faults an alternative model in which the permanente terrane is offset about 80 km by pre miocene faults does not adequately restore the distribution of 8 12 ma volcanic rocks and hydrothermal veins to a single northwardly younging age trend if 80 110 km of slip was taken up by the esfbr fault system between 8 and 6 ma dextral slip rates were 40 55 mm yr such high rates might occur if the esfbr fault system rather than the san andreas fault acted as the transform margin at this time major transpression across the boundary between the pacific and north american plates at about 3 to 5 ma would have resulted in the transfer of significant slip back to the san francisco peninsula segment of the san andreas fault since that time the esfbr fault system has continued to slip at rates of 11 14 mm yr if this interpretation is valid the esfbr fault system was the pacific north american plate boundary between 8 and 6 ma and this boundary has migrated both eastward and westward with time in response to changing plate margin geometry and plate motions

lithic volcanic sandstones derived from oceanic crust in the franciscan complex of california sedimental memories of source rock geochemistry the permanente terrane part of the franciscan accretionary complex of california contains an unusual fault bounded packet bearing lithic volcanic sandstones and conglomerates based on petrographical sedimentological stratigraphical and geochemical studies it is concluded that these rocks were deposited on the flank of an oceanic rise or plateau by sediment gravity flows probably below the carbonate compensation depth the bulk geochemistry of the sandstones is similar to the chemistry of greenstones in the permanente terrane suggesting that the greenstones or rocks similar to them represent the source of the lithic volcanic sandstones and that the sandstones geochemically remember the chemistry of their source rocks this sedimental memory is impressive geochemical variation in the sandstones is co linear with presumable magmatic variation trends in the greenstones sandstone geochemistry plotted on zr y vs y and v vs ti diagrams shows that compositions occupy similar fields as greenstones in the permanente terrane and oceanic crustal compositions in general because oceanic crustal sequences can become accreted to continental margins oceanic crust should be considered a potential source of sediment especially in continental margin settings however differentiating sandstones derived from oceanic arcs and from oceanic crust is extremely difficult unless discriminating geochemical criteria are used

on the importance of opal carbonate and lithogenic clays in scavenging and fractionating 230th 231pa and 10be in the ocean abstract the influence of particle composition on the scavenging of 230 th 231 pa and 10 be in the ocean is critically re examined based on the particle solution distribution coefficient k d data reported by chase et al earth planet sci lett 204 2002 215 229 our re examination shows that the k d s for these radionuclides are strongly influenced by the amount of lithogenic material lithogenics in particulates as reported previously by us and that a strong correlation between the lithogenic and carbonate contents in open ocean particulates results in an apparent non linear correlation between caco 3 and k d for each of the three radionuclides using a three end member model we estimate that the respective k d s g g of 230 th 231 pa and 10 be in the open ocean are 2 3 10 8 1 2 10 7 and 3 8 10 6 for lithogenics 1 0 10 6 1 0 10 5 and 3 0 10 4 for carbonate and 2 5 10 5 1 2 10 6 and 7 5 10 5 for opal suggesting that lithogenics have a much stronger affinity for any of the three nuclides than does carbonate or opal lithogenics and carbonate preferentially scavenge 230 th over 231 pa and 10 be whereas opal slightly favors 231 pa and 10 be over 230 th relative to lithogenics carbonate plays a very limited role in fractionating 230 th 231 pa and 10 be due to its orders of magnitude smaller k d values for the three nuclides our results indicate that fractionations between pa and th and between be and th through particle scavenging are mainly determined by the opal to lithogenic ratio in particulates rather than the opal to carbonate ratio suggested by chase et al

links between iron supply marine productivity sea surface temperature and co2 over the last 1 1 ma received 3 july 2008 revised 9 october 2008 accepted 27 october 2008 published 14 february 2009 1 paleoclimatic reconstructions have provided a unique data set to test the sensitivity of climate system to changes in atmospheric co2 concentrations however the mechanisms behind glacial interglacial g ig variations in atmospheric co2 concentrations observed in the antarctic ice cores are still not fully understood here we present a new multiproxy data set of sea surface temperatures sst dust and iron supply and marine export productivity from the marine sediment core ps2489 2 odp site 1090 located in the subantarctic atlantic that allow us to evaluate various hypotheses on the role of the southern ocean so in modulating atmospheric co2 concentrations back to 1 1 ma we show that antarctic atmospheric temperatures are closely linked to changes in so surface temperatures over the last 800 ka and use this to synchronize the timescales of our marine and the european project for ice coring in antarctica epica dome c edc records the close correlation observed between iron inputs and marine export production over the entire interval implies that the process of iron fertilization of marine biota has been a recurrent process operating in the subantarctic region over the g ig cycles of the last 1 1 ma however our data suggest that marine productivity can only explain a fraction of atmospheric co2 changes up to around 40 50 ppmv occurring at glacial maxima in each glacial stage in this sense the good correlation of our sst record to the edc temperature reconstruction suggests that the initial glacial co2 decrease as well as the change in the amplitude of the co2 cycles observed around 400 ka was most likely driven by physical processes possibly related to changes in antarctic sea ice extent surface water stratification and westerly winds position

reconstruction of global 10be production over the past 250ka from highly accumulating atlantic drift sediments in this study we present a reconstruction of the global 10be production rate over the past 250 000 years from three marine sediment cores located in high accumulation environments in the north northwest and south atlantic ocean odp sites 983 1063 and 1089 the 10be records are corrected for oceanic transport processes and principal component analysis pca is used to extract the common signal from the three records which we interpreted as variations of the global 10be production rate the reconstruction presented here may serve as i a record of past flux of galactic cosmic rays gcr ii a proxy for past geomagnetic dipole strength and iii as a global matching tool to synchronize marine archives with ice cores and terrestrial records

boundary scavenging in the pacific ocean a comparison of 10be and 231pa concentrations of u th 231pa and 10be were measured in holocene sediments from two cores collected off the west coast of south america two cores from the east pacific rise two from the equatorial pacific and one from the south pacific central gyre our results together with data from 5 cores reported in the literature show that boundary scavenging plays a major role in the removal of 10be from the pacific ocean deposition rates of 10be at three margin sites are more than an order of magnitude greater than at sites of red clay accumulation in the deep central pacific deposition of 231pa is 4 to 5 fold greater at the margin sites the residence time of 10be with respect to chemical scavenging defined as its inventory in the water column divided by its rate of removal to the sediments varies regionally from 1000 years at the red clay sites in the deep central pacific to 100 years at the margin sites different factors control boundary scavenging of pa and be for example scavenging of 231pa is enhanced by metal oxide coatings of particles whereas this seems to have little influence on the scavenging of 10be 1990

the influence of particle composition and particle flux on scavenging of th pa and be in the ocean we have examined the relative affinity of th pa and be for sorption from seawater onto particles of variable composition opal carbonate lithogenic particles and organic carbon nuclide concentrations in particles collected from time series sediment traps were normalized by the dissolved nuclide concentration in the overlying water column in order to compute partition coefficients under conditions spanning a wide range of particle flux and particle composition our results suggest that the affinity of particles for pa and be increases with their increasing opal content and decreasing carbonate content while the affinity of particles for th increases with increasing carbonate content and decreases with increasing opal content we find no correlation between the aluminosilicate content of particles and their affinity for scavenging of any of these elements extrapolating to a pure caco3 end member the partition coefficient for th 9 0 106 g g 1 is 40 times greater than for pa and roughly 100 times greater than for be whereas for a pure opal end member the partition coefficient for th 3 9 105 g g 1 is slightly less than that for pa and be partition coefficients decrease with increasing particle flux in open ocean settings but not in an ocean margin region this kinetic effect reflects the increasing contribution of unaltered surface material reaching the sediment traps as particle flux increases the degree of fractionation between pa and th and between be and th depends on the opal carbonate rain ratio these results challenge the use of sedimentary 231pa 230th and 10be 230th ratios as simple proxies of particle flux however the strong dependence of nuclide scavenging on the opal carbonate rain ratio may provide a needed tool for reconstructing past changes in planktonic community composition

highly resolved beryllium 10 record from odp site 1089 a global signal abstract in this study a highly resolved beryllium 10 record from a rapidly accumulating sediment core located in the southern cape basin odp leg 177 site 1089 is presented to extract the global 10 be production signal from the sedimentary record a dedicated correction procedure is applied first sediment redistribution is quantified by applying thorium 230 normalization then lateral transport of 10 be and 230 th is assessed using simple box model calculations the model results indicate that only minor transport corrections have to be applied thus site 1089 combines the advantage of good time resolution with nearly negligible oceanic transport of 10 be leading to a favored site for the reconstruction of global 10 be production changes from marine sediments our results suggest that the transport corrected 10 be record at site 1089 reflects long term variations of the global 10 be production rate over the past 300 kyr the absolute values of the youngest holocene samples are in good agreement with the estimated recent long term averaged global 10 be production rate deduced from observations the variability of the 10 be flux over the past 300 kyr corresponds well to the expected range deduced from model calculations the comparison with other reconstructions of geomagnetic paleointensity and with records of cosmogenic nuclides further emphasizes the global character of this 10 be record therefore our results show that it is possible to quantitatively extract the global 10 be production rate from a single marine record if transport processes are corrected for since the error of a single reconstruction is large a combination of several highly resolved and transport corrected 10 be records may lead to a significantly improved reconstruction of geomagnetic variability and of global cosmic ray flux and over the past 300 kyr

similar rates of modern and last glacial ocean thermohaline circulation inferred from radiochemical data today the ocean thermohaline circulation transports half of the 231pa produced by radioactive decay in the atlantic ocean water column to the southern ocean this export respectively imparts low and high 231pa 230th ratios to the surface sediments of these oceans ocean sediments from the last glacial maximum bear a similar isotopic fingerprint implying that advection of north atlantic deep intermediate water into the circumpolar deep water of the southern ocean occurred at a similar or slightly higher rate during the last glacial period

characterization of a gold tailings with hypersaline pore fluid a series of samples obtained from adjacent to piezocone penetration test cptu locations within a gold tailings storage facility with hypersaline pore fluid was tested to compare the inferred stat

trapping efficiencies of sediment traps from the deep eastern north atlantic the 230th calibration bottom tethered sediment traps deployed in the deep eastern north atlantic between 54 n 20 w and 33 n 20 w l1 l2 l3 at the european continental margin at 49 n omex and off the canary islands estoc were investigated for the determination of 230th trapping efficiencies the ratios of 230th flux measured in the traps fa to the expected 230th flux from the production rate of 230th in the overlying water column fp ranged between 0 09 and 1 26 for the traps with deployment periods 300 days the interannual variation of fa fp ratios different years but same location and water depth were up to 10 suggesting that the average 230th flux to the sediment traps did not vary significantly the influence of lateral advection on the 230th flux was taken into account either by applying a mass balance of 230th and 231pa or by assuming a constant removal rate of 230th from the water column an assumption based on similar 230th concentration depth profiles observed at most locations investigated 230th trapping efficiencies were between 9 and 143 showing a trend of increasing efficiencies with increasing water depth no relation was found between current velocities and 230th trapping efficiencies our investigations suggest that the observation of constant or even increasing particle flux rates with increasing water depths in several sediment trap arrays investigated may be a result of sediment trap biases the correction for the trapping biases is important for the understanding of the regional differences in the particle flux in the eastern north atlantic

plate tectonics and orogenic research after 25 years a tethyan perspective abstract orogeny the process by which the earth s prominent mountain ranges are constructed has been a central topic of interest in the earth sciences since at least the end of the 18th century the recognition that strains and displacements of very considerable magnitude occur along all of the three dimensions within an orogenic belt during its evolution has grown gradually during the last two centuries emphasis on primary vertical movements dominated the ideas on the nature of orogeny during the first half of the 19th century whereas compression and consequent uplift across mountain belts were believed to be the main cause for their origin during the subsequent one hundred years or so that were spent under the dominance of the fixist contraction theory mobilist tectonicians realised that continental drift in places also required motion along the trend of orogenic belts but this view did not gain general acceptance recognition of significant strike slip motion parallel or subparallel with mountain ranges evolved independently and mostly within the fixist camp by the 1960 s presence of important motions both along and across mountain belts had become common knowledge but no theoretical basis existed to account for them all

mid cretaceous oceanic anoxic events in the pacific ocean revealed by carbon isotope stratigraphy of the calera limestone california usa the paleoceanographic history of the pacific ocean during the mid cretaceous is poorly constrained due to the loss of much of the contemporaneous pacific seafloor to subduction and difficulties in recovering chert rich sediments by ocean drilling pelagic sediments that were originally deposited in the pacific ocean but that have been subsequently accreted during subduction potentially provide an alternative paleoceanographic archive this study presents micropaleontological and carbon isotope data from the calera limestone part of the classic franciscan complex exposed in permanente quarry central california usa in the three stratigraphic sections studied pelagic limestones with low organic carbon contents are the dominant lithology however two stratigraphic intervals are recognized that contain organic carbon and these date to the early aptian and late albian early cenomanian these time intervals correspond to two mid cretaceous oceanic anoxic events oaes early aptian oae1a equivalent to the selli level and late albian oae1d equivalent to the breistroffer event it is well established that both of these events were associated with significant carbon isotope excursions which are also shown to exist in the calera limestone the record of oae1a from the calera limestone complements ocean drilling records by providing further evidence for variability in the sedimentary and stratigraphic record of this event the carbon isotope data from the late albian early cenomanian provide the first detailed chemobiostratigraphic record of this period for the pacific ocean confirming that environmental change occurred at this time in the pacific possibly related to oae1d

deglacial diatom productivity and surface ocean properties over the bermuda rise northeast sargasso sea 1 diatom assemblages document surface hydrographic changes over the bermuda rise between 19 2 and 14 5 ka subtropical diatom species and chaetoceros resting spores dominate the flora as in north atlantic productive regions today from 16 9 to 14 6 ka brackish and fresh water diatoms are common and their contribution is generally coupled with total diatom abundance this same interval also contains rare grains of ice rafted debris coupling between those proxies suggests that successive discharge of icebergs might have stimulated productivity during heinrich event 1 h1 iceberg migration to the subtropics likely created an isolated environment involving turbulent mixing upwelled water and nutrient rich meltwater supporting diatom productivity in an otherwise oligotrophic setting in addition the occurrence of mode water eddies likely brought silica rich waters of southern ocean origin to the euphotic zone the persistence of lower salinity surface water beyond the last ice rafting suggests continued injection of fresh water by cold core rings and advection around the subtropical gyre these results indicate that opal productivity may have biased estimates of meridional overturning based on 231pa 230th ratios in bermuda rise sediments during h1

mesozoic evolution of exotic terranes and marginal seas western north america abstract regional terrane analysis has been combined with a global evaluation of plate kinematics to produce a new tectonic model for the mesozoic evolution of western north america and its associated marginal seas the model employs a two tiered data reliability ranking system to resolve conflicts within data sets the lower tier of the ranking system involves the assignment of a numerical rank to paleomagnetic and or paleobiogeographic data based on each data set s reliability the upper tier of the ranking system places the paleomagnetic and paleobiogeographic data in perspective by assigning a relative order of importance to different types of data the most reliable data are considered to be departure rift and arrival collision times that are tightly constrained by independent data sets evidence of subduction and or strike slip motion also ranks high in the master ranking system paleomagnetic and vertebrate paleobiogeographic data come next in the hierarchy followed by invertebrate and floral paleobiogeographic data application of this approach to a case study the baja british columbia controversy has resulted in a coherent model for the entire region results derived from the application of this modelling approach to the problem of the mesozoic assembly of western north america suggest that its evolution may be modeled using a minimum of 57 large terranes oblique convergence may have been the dominant tectonic process along the western north american margin during the mesozoic causing large scale latitudinal transport of many exotic terranes the motions of the terranes produced a number of marginal seas yukonia etc that were short lived but important components of western margin tectonics a combination of collision events side swiping episodes and changes in plate kinematics led to the initiation of several regional tectonic upheavals including the nevadan and sevier orogenies

the global average production rate of10be precipitation collected in continuously open containers for about a year at seven sites around the united states was analyzed for10be 90sr 210pb and238u based on these data and long term precipitation 90sr and210pb delivery patterns the stratospheric tropospheric and recycled10be components in the collections were estimated and the global10be production rate was assessed single station production rate estimates range from 0 52 106 atoms cm 2 yr 1 to 2 64 106 atoms cm 2 yr 1 the mean value is 1 21 106 atoms cm 2 yr 1 with a standard error of 0 26 106 atoms cm 2 yr 1

cyclic loading response of loose air pluviated fraser river sand for validation of numerical models simulating centrifuge tests cyclic loading response of loose fraser river sand was investigated as input to numerical simulation of centrifuge physical models using constant volume direct simple shear tests conducted with a

k o ocr relationships in soil the relationships between k o and ocr are investigated for primary loading unloading reloading conditions the study reviews laboratory data from over 170 different soils and presents an approach common to clays silts and sands simple empirical methods for predicting k o for normally consolidated and overconsolidated soils are evaluated the validity of the methods is supported by statistical analyses on the basis of the findings only the effective stress friction angle o and prior stress history ocr and ocrmax are needed to predict approximate values of k o

removal of230th and231pa from the open ocean concentrations of230th and231pa were measured in particulate matter collected by sediment traps deployed in the sargasso sea site s2 the north equatorial atlantic site e and the north equatorial pacific site p as well as in particles collected by in situ filtration at site e concentrations of dissolved th and pa were determined by extraction onto manganese dioxide adsorbers at site p and at a second site in the sargasso sea site d dissolved230th 231pa activity ratios were 3 6 at sites p and d in contrast for all sediment trap samples from greater than 2000 m unsupported230th 231pa ratios were 22 35 average 29 7 ratios were lower in particulate matter sampled at shallower depths particles filtered at 3600 m and 5000 m at site e had ratios of 50 and 40 results show that suspended particulate matter in the open ocean preferentially scavenges th relative to pa most of the230th produced by decay of234u in the open ocean is removed by adsorption to settling particulate matter in contrast less than 50 of the231pa produced by decay of235u is removed from the water column by this mechanism mixing processes transport the remainder to other sinks

230th normalization an essential tool for interpreting sedimentary fluxes during the late quaternary there is increasing evidence indicating that syndepositional redistribution of sediment on the seafloor by bottom currents is common and can significantly affect sediment mass accumulation rates notwithstanding its common incidence this process generally referred to as sediment focusing is often difficult to recognize if redistribution is near synchronous to deposition the stratigraphy of the sediment is not disturbed and sediment focusing can easily be overlooked ignoring it however can lead to serious misinterpretations of sedimentary fluxes particularly when past changes in export flux from the overlying water are inferred in many instances this problem can be resolved at least for sediments deposited during the late quaternary by normalizing to the flux of 230th scavenged from seawater which is nearly constant and equivalent to the known rate of production of 230th from the decay of dissolved 234u we review the principle advantages and limitations of this method notwithstanding its limitations it is clear that 230th normalization does provide a means of achieving more accurate interpretations of sedimentary fluxes and eliminates the risk of serious misinterpretations of sediment mass accumulation rates

effect of particle fabric on the coefficient of lateral earth pressure observed during one dimensional compression of sand the effect of initial particle fabric on the one dimensional compression response of fraser river sand was investigated one dimensional compression with lateral stress measurement was carried out

fast instantaneous oceanic plate velocities recorded by the cretaceous laytonville limestone paleomagnetic analysis and kinematic implications new paleomagnetic results from 101 89 ma laytonville limestone of the franciscan central belt melange of northern california confirm a southern hemisphere origin as first proposed by alvarez et al 1980 discovery and study of new laytonville limestone outcrops extend the paleomagnetic record and provide a definitive determination of age stratigraphic polarity and hemisphere of deposition paleontological determinations show that five sections are presently overturned and four are presently right side up as expected from a random distribution of nine blocks in a melange the exact accretion time is unknown but geologically reasonable estimates range between 70 and 50 ma leading to averaged estimates of poleward velocity between 30 and 14 cm yr the averaged values are obtained by dividing the total paleolatitude shift by the difference between magnetization and estimated accretion ages they reflect net poleward transport over a long time interval and are minimum estimates because they record only the poleward component of motion an instantaneous poleward velocity is recorded by the systematic inclination decrease of 160 paleomagnetic samples with respect to decreasing age over the 12 m y section conservative estimates place this minimum velocity at 15 cm yr the consistency between the values predicted by the average velocity calculations and those measured within the outcrops serves as an important check on the primary nature of the magnetization this minimum velocity is much higher than any present day plate velocity the subduction of old oceanic crust at the boundary of a relatively small plate is hypothesised as a driving mechanism to explain the measured velocities coupled with the minimum instantaneous poleward velocities this hypothesis suggests that the velocities of subducting plates may vary up to a factor of 5 similar plate geometries and resultant velocities have probably existed at other times in the past but their discovery may have been hindered by low preservation potential

magnetostratigraphy of the kavur tepe section southwestern turkey a magnetic polarity time scale for the norian we present the magnetostratigraphy of the late triassic pelagic kavur tepe section from the taurides southwestern turkey the section investigated is about 30 m thick and consists of fine grained whitish limestones the biostratigraphy based on the conodont zonation gives an age from the lacian 2 zone lower norian to the sevatian 2 zone upper norian the paleomagnetic analyses indicate very favourable behaviour with two magnetic components which can be isolated both by thermal and af demagnetization the magnetization is carried by magnetite and goethite which are clearly evident in irm experiments the first component of normal magnetic polarity has roughly the direction of the present day field the high unblocking temperature component shows directions of both polarities in total fifteen magnetic polarity intervals are observed within the kavur tepe section the characteristic calculated fisherian mean direction is particularly tightly grouped d 220 2 and i 32 1 with k 40 9 95 1 7 and nsamp 179 after bedding correction polarity correlations with two other sections in turkey and in austria northern calcareous alps show that the kavur tepe sediments were deposited in the southern hemisphere by combining the magnetostratigraphic results from the bolucektasi tepe 1 and the kavur tepe sections an almost complete norian magnetic polarity sequence is established showing 30 magnetic intervals that are well calibrated with the conodont and ammonoid zonations a magnetic reversal frequency close to about 2 7 reversals myr is derived for the norian this medium frequency is in agreement with the hypothesis of a long time constant 150 200 myr in the changes of the magnetic reversal frequency since the kiaman reversed superchron

beryllium geochemistry in soils evaluation of 10be 9be ratios in authigenic minerals as a basis for age models soils contain a diverse and complex set of chemicals and minerals being an open system both in the chemical and nuclear sense soils have defied quantitative nuclear dating however based on the published studies of the cosmogenic atmospheric 10be in soils its relatively long half life 1 5 ma and the fact that 10be gets quickly incorporated in most soil minerals this radionuclide appears to be potentially the most useful for soil dating we therefore studied the natural variations in the specific activities of 10be with respect to the isotope 9be in mineral phases in eight profiles of diverse soils from temperate to tropical climatic regimes and evaluated the implications of the data for determining the time of formation of soil minerals following an earlier suggestion lal et al 1991 development of cosmogenic nuclear methods for the study of soil erosion and formation rates current sci 61 636 639 we find that the 10be 9be ratios in both bulk soils and in the authigenic mineral phases are confined within a narrower range than in 10be concentrations also the highest 10be 9be ratios in authigenic minerals are observed at the soil rock interface as predicted by the model we present model 10be 9be ages of the b horizon and the corresponding soil formation rates for several soil profiles the present study demonstrates that the 10be 9be ratios in the authigenic phases e g clay and fe hydroxides can indeed be used for obtaining useful model ages for soils younger than 10 15 ma however the present work has to be pushed considerably further to take into account more realistic age models in which for instance downward transport 10be and clays and in situ dissolution of clay minerals at depths altering the 10be 9be ratios of the acidic solutions are included we show that in the case of younger soils 1 ma studied here their 10be inventories and 10be 9be ratios have been significantly disturbed possibly by mixing with transported soils

influence of generalized initial state and principal stress rotation on the undrained response of sands the dependence of the undrained behaviour of sand on the initial stress state and the orientation of principal stresses with respect to the bedding planes is assessed under generalized loading path

grain size effects on th 230 xs inventories in opal rich and carbonate rich marine sediments abstract excess thorium 230 230thxs as a constant flux tracer is an essential tool for paleoceanographic studies but its limitations for flux normalization are still a matter of debate in regions of rapid sediment accumulation it has been an open question if 230thxs normalized fluxes are biased by particle sorting effects during sediment redistribution in order to study the sorting effect of sediment transport on 230thxs we analyzed the specific activity of 230thxs in different particle size classes of carbonate rich sediments from the south east atlantic and of opal rich sediments from the atlantic sector of the southern ocean at both sites we compare the 230thxs distribution in neighboring high vs low accumulation settings two grain size fractionation methods are explored we find that the 230thxs distribution is strongly grain size dependent and 50 90 of the total 230thxs inventory is concentrated in fine material smaller than 10 m which is preferentially deposited at the high accumulation sites this leads to an overestimation of the focusing factor and consequently to an underestimation of the vertical flux rate at such sites the distribution of authigenic uranium indicates that fine organic rich material has also been re deposited from lateral sources if the particle sorting effect is considered in the flux calculations it reduces the estimated extent of sediment focusing in order to assess the maximum effect of particle sorting on we present an extreme scenario in which we assume a lateral sediment supply of only fine material comparing 230thxs normalized mass fluxes biased by sorting effects with uncorrected mass fluxes we suggest that 230thxs normalization is still a valid tool to correct for lateral sediment redistribution however differences in focusing factors between core locations have to be evaluated carefully taking the grain size distributions into consideration

constraints on deep water formation from the oceanic distributions of 10be 1 an analysis of the oceanic distribution of cosmogenic 10be shows that deep waters are formed by descending of cold dense surface waters at a rate of 18 sv 106 m3 s 1 in the northern north atlantic and 21 sv of which 17 sv enters the pacific in the antarctic over the last mixing cycle of 800 years lending support to the estimates based on radiocarbon and nutrient distributions it also indicates that deep water production in the northern north atlantic is 50 higher averaging over the recent 100 years than over the last mixing cycle suggesting a possible increase in the thermohaline ventilation of the north atlantic during the past century

distribution of10be and9be in the pacific ocean abstract the vertical distributions of10be and9be at three locations in the pacific 25 n 170 e 17 n 118 w 3 s 117 w are presented the results show that both isotopes exhibit nutrient like profiles from the surface to the bottom the increase for10be is two to threefold and that for9be is about fivefold while the inter station variations in surface water concentrations may reach a factor of two deep water values tend to be much more uniform averaging about 2000 atoms g for10be and 30 pm for9be a similar situation applies to the10be 9be ratio it varies approximately from 1 to 3 10 7 atom atom at shallow depths but tends toward a value close to 1 1 10 7 in the deep ocean the variation of10be 9be can be viewed as resulting from the fact that10be in a given parcel of water consists of two components recycled and primary the recycled component is that part of10be which has reached tracer equilibrium with9be as opposed to the primary component which upon entering the sea from the atmosphere has yet to equilibrate with9be through particle cycling and mixing processes it is estimated that 70 to nearly 100 of10be at the three stations are being recycled and the recycled beryllium bears an atomic ratio of10be 9be close to 1 10 7 the oceanic residence time of be is of the order of 1000 4000 years comparable to or slightly longer than the ocean mixing time

remagnetization and northward coastwise transport of franciscan complex rocks northern california a reinterpretation of the paleomagnetic data previous paleomagnetic studies of accreted oceanic rocks within the franciscan complex of northern california have concluded that these rocks originated far to the south of their present positions with respect to the north american continent based on positive fold tests the characteristic remanent magnetizations were inferred to predate accretion related deformation and metamorphism and to have been acquired during or soon after deposition of these rocks thus the paleomagnetic data were thought to provide direct information on ancient oceanic plate motions however the plate motions implied by some of these paleomagnetic data are problematic e g exceptional plate velocities and uniform polarity magnetizations in almost all of these rocks indicate the possibility of remagnetization recent work on oceanic rocks in similar subduction complexes of japan and mexico have shown that they were most likely chemically remagnetized during accretion prior to disruption of the original stratigraphic sequences modern analogs indicate that the oceanic rocks in mexico were probably remagnetized while still part of a shallow dipping subducting slab 10 at the base of an accretionary prism assuming these rocks were near horizontal at the time of remagnetization paleolatitudes at which these rocks were subducted and subsequent arc parallel displacements along the western margin of north america can be inferred in this paper franciscan rocks in northern california are reinterpreted as also having been remagnetized prior to accretion related deformation this scenario satisfies both geologic and paleomagnetic constraints for these rocks and resolves conflicts between data indicating both remagnetization and tectonic displacement transport of the laytonville limestone from the southern hemisphere is not required paleolatitudes of subduction and remagnetization in the northern hemisphere 12 to 33 appear to be inversely proportional to age of accretion middle cretaceous to oligocene for the franciscan rocks subsequent northward diplacements 800 to 3700 km and clockwise rotations 56 and 154 of these rocks inferred from the paleomagnetic data are consistent with potential displacements along the western margin of north america during late mesozoic and cenozoic time calculated using examples of modern subduction zones and current plate reconstruction models

paleomagnetic evidence for motions of parts of the canadian cordillera abstract paleomagnetic evidence from major terranes of the western cordillera in canada referred to collectively as baja british columbia indicates that they have moved as a whole about 2300 km from the south and rotated 60 clockwise relative to north america in the late cretaceous and earliest tertiary 85 50 ma sometime between the early jurassic and the mid cretaceous 190 100 ma these same terranes moved south over 1000 km and underwent irregular but where well constrained counter clockwise rotations the terranes amongst themselves seem to have shared much the same paleolatitude during and since the late triassic although they may have undergone relative rotations in the later jurassic and early cretaceous these motions are now known to be broadly consistent with the motions of oceanic plates to the west as calculated by independent procedures and indicate that the terranes of the western cordillera were for part of their existence coupled to oceanic plates first to the farallon plate during the late jurassic and early cretaceous and then to the kula plate during the late cretaceous and early tertiary it was this change of allegiance from farallon to kula that caused first the southerly and then the northerly motion the paleomagnetic evidence despite claims to the contrary is consistent with geologically inferred displacements along major faults in the canadian cordillera when due account is taken of the age constraints on those motions

does sedimentary 231pa 230th from the bermuda rise monitor past atlantic meridional overturning circulation 1 ocean circulation may have undergone reductions and reinvigorations in the past closely tied to regional climate changes measurements of 231pa 230th ratios in a sediment core from the bermuda rise have been interpreted as evidence that the atlantic meridional overturning circulation amoc was weakened or completely eliminated during a period of catastrophic iceberg discharges heinrich event 1 h1 here we present new data from the bermuda rise that show further 231pa 230th peaks during heinrich 2 h2 and heinrich 3 h3 additionally a tight correlation between diatom abundances biogenic silica and 231pa 230th is discovered in this core our results redirect the interpretation of 231pa 230th from the bermuda rise as a proxy for ocean circulation towards a proxy that reacts highly sensitive to changes of particle composition and water mass properties

glacial interglacial circulation changes inferred from 231pa 230th sedimentary record in the north atlantic region 1 studies from the subtropical western and eastern atlantic ocean using the 231pa 230th ratio as a kinematic proxy for deep water circulation provided compelling evidence for a strong link between climate and the rate of meridional overturning circulation moc over the last deglaciation in this study we present a compilation of existing and new sedimentary 231pa 230th records from north atlantic cores between 1710 and 4550 m water depth comparing sedimentary 231pa 230th from different depths provides new insights into the evolution of the geometry and rate of deep water formation in the north atlantic during the last 20 000 years the 231pa 230th ratio measured in upper holocene sediments indicates slow water renewal above 2500 m and rapid flushing below consistent with our understanding of modern circulation in contrast during the last glacial maximum lgm glacial north atlantic intermediate water gnaiw drove a rapid overturning circulation to a depth of at least 3000 m depth below 4000 m water renewal was much slower than today at the onset of heinrich event 1 transport by the overturning circulation declined at all depths gnaiw shoaled above 3000 m and significantly weakened but did not totally shut down during the bolling allerod ba that followed water renewal rates further decreased above 2000 m but increased below our results suggest for the first time that ocean circulation during that period was quite distinct from the modern circulation mode with a comparatively higher renewal rate above 3000 m and a lower renewal rate below in a pattern similar to the lgm but less accentuated moc during the younger dryas appears very similar to ba down to 2000 m and slightly slower below

reversed flow of atlantic deep water during the last glacial maximum the meridional overturning circulation moc of the atlantic ocean is considered to be one of the most important components of the climate system this is because its warm surface currents such as the gulf stream redistribute huge amounts of energy from tropical to high latitudes and influence regional weather and climate patterns whereas its lower limb ventilates the deep ocean and affects the storage of carbon in the abyss away from the atmosphere despite its significance for future climate the operation of the moc under contrasting climates of the past remains controversial nutrient based proxies1 2 and recent model simulations3 indicate that during the last glacial maximum the convective activity in the north atlantic ocean was much weaker than at present in contrast rate sensitive radiogenic 231pa 230th isotope ratios from the north atlantic have been interpreted to indicate only minor changes in moc strength4 5 6 here we show that the basin scale abyssal circulation of the atlantic ocean was probably reversed during the last glacial maximum and was dominated by northward water flow from the southern ocean these conclusions are based on new high resolution data from the south atlantic ocean that establish the basin scale north to south gradient in 231pa 230th and thus the direction of the deep ocean circulation our findings are consistent with nutrient based proxies and argue that further analysis of 231pa 230th outside the north atlantic basin will enhance our understanding of past ocean circulation provided that spatial gradients are carefully considered this broader perspective suggests that the modern pattern of the atlantic moc with a prominent southerly flow of deep waters originating in the north atlantic arose only during the holocene epoch

the influence of particle composition on thorium scavenging in the ne atlantic ocean pomme experiment abstract 230th 232th and 234th were analyzed in sinking particles collected by moored and drifting sediment traps in the ne atlantic ocean pomme experiment in order to constrain the phase s carrying th isotopes in the water column it reveals a contrasted behaviour between 234th and 230th 234th is correlated to the particulate organic carbon suggesting that it is primarily scavenged by organic compounds in the surface waters 230thxs is correlated with mn ba and the lithogenic fraction that are enriched in small suspended particles and incorporated in the sinking particulate flux throughout the water column the lack of correlation between 230thxs and caco3 or biogenic silica bsi indicates that caco3 and bsi are not responsible for 230th scavenging in the deep waters of this oceanic region 230th is generally correlated with the lithogenic content of the trapped material but this correlation disappears in winter during strong atmospheric dust inputs suggesting that lithogenic matter is not directly responsible for 230th scavenging in the deep waters or that sufficient time is required to achieve particle solution equilibration mno2 could be the prevalent 230thxs bearing phase the narrow range of kd mno2th obtained for very contrasted oceanic environments supports a global control of 230thxs scavenging by mno2 and raises the possibility that the 230th 231pa fractionation is controlled by the amount of colloidal mno2 in seawater

lower export production during glacial periods in the equatorial pacific derived from 231pa 230th xs 0 measurements in deep sea sediments 1 the 231pa 230th xs 0 records obtained from two cores from the western md97 2138 1 25 s 146 24 e 1900 m and eastern ocean drilling program leg 138 site 849 0 11 59 n 110 31 18 w 3851 m equatorial pacific display similar variability over the last 85 000 years i e from isotopic stages 1 to 5a with systematically higher values during the holocene isotopic stage 3 and isotopic stage 5a and lower values approaching the production rate ratio of the two isotopes 0 093 during the colder periods corresponding to isotopic stages 2 and 4 we have also measured the 230th normalized biogenic preserved and terrigenous fluxes as well as major and trace elements concentrations in both cores the 231pa 230th xs 0 results combined with the changes in preserved carbonate and opal fluxes at the eastern site indicate lower productivity in the eastern equatorial pacific during glacial periods the 231pa 230th xs 0 variations in the western equatorial pacific also seem to be controlled by productivity carbonate and or opal the generally high 231pa 230th xs 0 ratios 0 093 of the profile could be due to opal and or mno2 in the sinking particles the profiles of 231pa 230th xs 0 and 230th normalized fluxes indicate a decrease in exported carbonate and possibly opal during isotopic stages 2 and 4 in md97 2138 using 230th normalized flux we also show that sediments from the two cores were strongly affected by sediment redistribution by bottom currents suggesting a control of mass accumulation rates by sediment focusing variability

scavenging of 230th 231pa and 10be in the southern ocean sw pacific sector the importance of particle flux particle composition and advection abstract the scavenging of 230 th 231 pa and 10 be was studied in the pacific sector of the southern ocean along 170 w using measurements from surface sediments time series sediment traps and the water column all sediment traps collected an annual flux of 231 pa greater than the integrated rate of production by 235 u decay up to 5 5 times greater and a flux of 10 be greater than the global average deposition rate of 10 be up to 3 4 times greater fluxes of 230 th were on average close to the production rate in the overlying water column these large fluxes of 231 pa and 10 be and high unsupported 231 pa 231 th and 10 be 230 th ratios in the sediments are not associated with depletion of nuclides in the water column and therefore are not the result of the classical boundary scavenging mechanism we estimate that of the 231 pa and 230 th advected into the southern ocean as part of the large scale overturning circulation only those nuclides associated with the upper limb of this circulation i e those that pass through the surface as part of the wind driven ekman flow are scavenged efficiently the majority of the nuclides advected into the southern ocean and associated with the bottom water limb are not scavenged to the sediments of the southern ocean but are returned northward throughout the year the unsupported 231 pa 230 th and 10 be 230 th ratios of material reaching sediment traps at 1000 m at a given site increase with increasing particle flux this behavior is explained by a conceptual model in which th pa and be are scavenged reversibly by fine grained suspended particles at all depths while pa and be are in addition scavenged strongly by diatom rich aggregates in surface waters spatial variability in the annually averaged unsupported 231 pa 230 th and 10 be 230 th ratios of sinking particulate matter reflects primarily the variability in particle composition and in the ratio and quantity of nuclides upwelled to the mixed layer rather than variability in particle flux

10be and 9be in marine sediments and their potential for dating using sequential leaching experiments we have measured the fraction of the cosmogenic isotope 10be half life 1 5 my and its stable isotope 9be co extracted with the following phases in marine sediments exchangeable calcium carbonate fe and mn oxyhydroxides organic opal and detrital the extraction of the authigenic phases typically release 70 of the 10be but only 40 of the 9be in order to test its potential for dating marine sediments we have measured the authigeniccally associated 10be 9be in 17 surface sediment samples from different ocean basins the observed spatial variability which appears to be influenced by proximity to continental input of 9be precludes the general and precise applications of leached 10be 9be for dating however the relatively constant value observed in surface sediments over large areas of the pacific indian and southern atlantic oceans shows considerable promise for approximate dating of open oceans sediments in order to test temporal variability a profile of the authigenically associated 10be 9be ratio has been measured in the independently dated central pacific core rc12 65 the observed variation in 10be 9be over the past nine my is approximately twice that expected on the basis of 10be decay alone several possible explanations for such behavior and their potential consequences for the use of leached 10be 9be for dating are discussed

removal of 230th and 231pa at ocean margins abstract uranium thorium and protactinium isotopes were measured in particulate matter collected by sediment traps deployed in the panama basin and by in situ filtration of large volumes of seawater in the panama and guatemala basins concentrations of dissolved th and pa isotopes were determined by extraction onto mno 2 adsorbers placed in line behind the filters in the in situ pumping systems concentrations of dissolved 230 th and 231 pa in the panama and guatemala basins are lower than in the open ocean whereas dissolved 230 th 231 pa ratios are equal to or slightly greater than ratios in the open ocean particulate 230 th 231 pa ratios in the sediment trap samples ranged from 4 to 8 in contrast to ratios of 30 or more at the open ocean sites previously studied particles collected by filtration in the panama basin and nearest to the continental margin in the guatemala basin contained 230 th 231 pa ratios similar to the ratios in the sediment trap samples the ratios increased with distance away from the continent suspended particles near the margin show no preference for adsorption of th or pa and therefore must be chemically different from particles in the open ocean which show a strong preference for adsorption of th ocean margins as typified by the panama and guatemala basins are preferential sinks for 231 pa relative to 230 th furthermore the margins are sinks for 230 th and to a greater extent 231 pa transported by horizontal mixing from the open ocean

age and origin of cretaceous planktonic foraminifers from limestone of the franciscan complex near laytonville california detailed planktonic foraminiferal biostratigraphy from eight measured sections of cretaceous limestone near laytonville california indicates a composite sequence that extends in age from late albian to early turonian the sequence contains seven biozones and two subzones based on the first and last appearance datums of planktonic foraminifers examined in thin section unequivocal biostratigraphic facing directions show four sections are right side up and four are reversed and confirm the stratigraphic polarity employed in the paleomagnetic studies of alvarez et al 1980 and tarduno et al 1986 temporal changes in the microfauna deviate from the global trend early albian through early cenomanian planktonic foraminiferal assemblages dominated by opportunistic eurytopic species of hedbergella and globigerinelloides give way in the late cenomanian to assemblages containing more abundant larger heavily ornamented stenotopic species of rotalipora and praeglobotruncana typical of stratified tethyan oceans radiolarian replacement chert increases slightly in the late albian to early cenomanian part of the laytonville sequence and then decreases in the late cenomanian and early turonian benthic foraminifers show a similar decrease in abundance and diversity we propose that this complex of biogenic and lithogenic patterns records transit via oceanic plate motion from a depositional site in the southern part of the paleoequatorial zone of high productivity characterized by pronounced upwelling and habitat destabilization perhaps augmented by topographic upwelling to the central part of the equatorial zone dominated by biogenic calcite deposition our model of northward transit from below the equator supports the paleomagnetic determinations of alvarez et al 1980 and tarduno et al 1986 arrival at the paleoequator coincided with the onset of stratification in the world ocean during the middle cenomanian indicated by the diversification of the more complex rotaliporids and the subsequent intensification of oxygen depleted intermediate waters in the latest cenomanian to early turonian two pulses in heterohelicid abundance signify the onset or intensification of an oxygen minimum layer if cretaceous heterohelicids occupied habitats analagous to tertiary biserial heterohelicids the first pulse beginning in the middle cenomanian rotalipora reicheli zone may indicate a minor expansion of the oxygen minimum zone or regional upwelling due to transit of the site beneath the equatorial divergence the second pulse in the late cenomanian dicarinella algeriana subzone signals the onset of upwelling of deeper oceanic water masses that characterized the succeeding whiteinella archaeocretacea zone organic rich black shales typical of the whiteinella archaeocretacea zone are missing at laytonville although samples do contain the low diversity partially dissolved planktonic assemblages that characterize this zone the lack of black shales suggests that deposition occurred at depths greater than the oxygen depleted intermediate water depths or alternately indicates paleoceanographic conditions unique to the pacific

radionuclide fluxes in the arabian sea the role of particle composition we investigated the influence of the composition of the vertical particle flux on the removal of particle reactive natural radionuclides th 230 and pa 231 from the water column to the sediments radionuclide concentrations determined in sediment traps moored in the western central and eastern arabian sea were related to the major components carbonate particulate organic matter poc opal lithogenic material of the particle flux these data were combined with sediment trap data previously published from the southern ocean equatorial pacific and north atlantic z chase r f anderson m q fleisher p w kubik the influence of particle composition and particle flux on scavenging of th pa and be in the ocean earth planet sci lett 204 2002 215 229 j c scholten f fietzke s vogler m rutgers van der loeff a mangini w koeve j waniek p stoffers a antia j kass trapping efficiencies of sediment traps from the deep eastern north atlantic the th 230 calibration deep sea research 1148 2001 2383 2408 the correlations observed between the particle dissolved distribution coefficients k d of th 230 and pa 231 and the concentrations of the particle types depend on the sediment trap data set used this result suggests that scavenging affinities of the nuclides differ between oceanic regions several factors k d values reactive surface areas of particles inter correlations in closed data set can however influence the observed relationships and thus hamper the interpretation of these correlation coefficients as a measure of relative scavenging affinities of the nuclides to the particle types investigated the mean fractionation factor f pa th k d pa k d th from the equatorial pacific f 0 11 0 03 is similar to that from the north atlantic f pa th 0 077 0 026 and both are lower than the factors from the arabian sea f pa th 0 35 0 12 and from the southern ocean f pa th 0 87 0 4 for opal concentrations exceeding similar to60 an increase in the fractionation factors is observed causing a higher mean fractionation factor for the southern ocean trap data set for the other areas investigated differences in the mean fractionation factors cannot be related to the particles types considered in the arabian sea seasonally variable pa 231 ex th 230 ex ratios observed in the sediment traps as well as differences of the ratios between recently deposited phytodetritus fluff and normal surface sediments indicate seasonal changes in scavenging processes which the generally accepted reversible scavenging models do not envisage we assume that variable sinking rates of particles and or particles not considered in this study e g colloids manganese oxides transparent exopolymer particles may play an important but as yet unexplored role in deep water scavenging processes c 2004 elsevier b v all rights reserved

southern hemisphere origin of the cretaceous laytonville limestone of california new paleomagnetic paleontologic and stratigraphic data from outcrops of the laytonville limestone 101 to 88 million years old support a southern hemisphere origin a paleomagnetic megaconglomerate test is statistically significant and suggests magnetization at 14 5 south predating late cretaceous to eocene 70 to 50 million years ago accretion rapid kula plate movement or the existence and demise of a now vanished oceanic plate or both are required to accommodate the greater than 50 of poleward displacement implied by the paleomagnetic data this rapid motion brings into question the validity of a speed limit for absolute plate velocity based on present day plate motions

fractionation of 230th 231pa and 10be induced by particle size and composition within an opal rich sediment of the atlantic southern ocean this study centers on the question how sensitive are 231pa 230th and 10be 230th to sediment composition and redistribution the natural radionuclides 231pa 230th and 10be recorded in deep sea sediments are tracers for water mass advection and particle fluxes we investigate the influence of oceanic particle composition on the element adsorption in order to improve our understanding of sedimentary isotope records we present new data on particle size specific 231pa and 10be concentrations an additional separation step based on settling velocities led to the isolation of a very opal rich phase we find that opal rich particles contain the highest 231pa and 10be concentrations and higher 231pa 230th and 10be 230th isotope ratios than opal poor particles the fractionation relative to 230th induced by the adsorption to opal rich particles is more pronounced for 231pa than for 10be we conclude that bulk 231pa 230th in southern ocean sediments is most suitable as a proxy for past opal fluxes the comparison between two neighboring cores with rapid and slow accumulation rates reveals that these isotope ratios are not influenced significantly by the intensity of sediment focusing at these two study sites however a simulation shows that particle sorting by selective removal of sediment winnowing could change the isotope ratios consequently 231pa 230th should not be used as paleocirculation proxy in cases where a strong loss of opal rich material due to bottom currents occurred

concordant paleolatitudes from ophiolite sequences in the northern california coast ranges u s a abstract paleomagnetic data have been obtained from two ophiolite sequences in the northern california coast ranges from mount diablo in the san francisco bay area and from potter valley north of clear lake the ophiolite exposed at mount diablo is part of the late middle to late jurassic coast range ophiolite and that exposed near potter valley is late jurassic to perhaps early cretaceous in age and occurs within the franciscan assemblage data from the sheeted dike complex at mount diablo show these rocks to be strongly overprinted probably following uplift and erosion of the ophiolite samples whose primary remanent magnetization seems to be recovered yield a mean paleomagnetic pole at 30 7 n 159 5 e with 95 5 6 a comparison of this pole with the jurassic apparent polar wander path for north america indicates that the ophiolite has rotated 45 7 counterclockwise relative to the craton and has not been latitudinally displaced the diabase and pillow basalt in potter valley have not been strongly overprinted and data from those rocks yield a paleomagnetic pole at 79 0 n 61 5 e with 95 6 4 this result indicates that the ophiolite at potter valley has rotated approximately 29 8 clockwise and has undergone little or no latitudinal displacement because of the predominantly northeastward transport of oceanic plates converging with the western margin of north america since middle mesozoic time the absence of appreciable northward displacement of either ophiolite fragment indicates that both formed close to the continental margin

reply to comment on on the importance of opal carbonate and lithogenic clays in scavenging and fractionating 230th 231pa and 10be in the ocean we extend our analysis of the chase et al data earth and planetary science letters 204 2002 215 229 to those other than from the equatorial pacific and the southern ocean the analysis offers support to our previous conclusion that kd th for carbonate is on the order of 1 0 106 g g or about two orders of magnitude smaller than that for open ocean lithogenics there is a lowering of kd th of lithogenics at high lithogenic sites attributable to factors including the sediment remobilization from ocean margin deposits but the lowered kd th of lithogenics is still about one order of magnitude greater than that of carbonate at those high lithogenic sites using an independent method we estimate that kd l th is 2 2 0 9 108 g g at stations adjacent to our eqpac sites reinforcing our conclusion that the major scavenger for 230th is lithogenic not carbonate particles even in the low lithogenic open ocean

glacial interglacial changes in sediment rain rate in the sw indian sector of subantarctic waters as recorded by 230th 231pa u and δ15n high resolution records of opal carbonate and terrigenous fluxes have been obtained from a high sedimentation rate core md84 527 43 50 s 51 19 e 3269 m by normalization to 230th this method estimates paleofluxes to the seafloor on a point by point basis and distinguishes changes in sediment accumulation due to variations in vertical rain rates from those due to changes in syndepositional sediment redistribution by bottom currents we also measured sediment 15n to evaluate the changes in nitrate utilization in the overlying surface waters associated with paleoflux variations our results show that opal accumulation rates on the seafloor during the holocene and stage 3 based on 14c dating were respectively tenfold and fivefold higher than the vertical rain rates at this particular location changes in opal accumulation on the seafloor appear to be mainly controlled by sediment redistribution by bottom currents rather than variations in opal fluxes from the overlying water column correction for syndepositional sediment redistribution and the improved time resolution that can be achieved by normalization to 230th disclose important variations in opal rain rates we found relatively high but variable opal paleoflux during stage 3 with two maxima centered at 36 and 30 kyr b p low opal paleoflux during stage 2 and deglaciation and a pronounced maximum during the early holocene we interpret this record as reflecting variations in opal production rates associated with climate induced latitudinal migration of the southern ocean frontal system sediments deposited during periods of high opal paleoflux also have high authigenic u concentrations suggesting more reducing conditions in the sediment and high pa 231 th 230 ratios suggesting increased scavenging from the water column sediment 15n is circa 1 5 per mil higher during isotopic stage 2 and deglaciation the low opal rain rates recorded during that period appear to have been associated with increased nitrate depletion this suggests that opal paleofluxes do not simply reflect latitudinal migration of the frontal system but also changes in the structure of the upper water column increased stratification during isotopic stage 2 and deglaciation could have been produced by a meltwater lid leading to lower nitrate supply rates to surface waters

collapse of dry sand loose cohesionless saturated materials have proved responsible for a number of serious or catastrophic flow slides liquefaction failures with no obvious triggering mechanism have also been recorded this phenomenon of sudden liquefaction without a presence of cyclic shear stresses is often referred to as spontaneous or static liquefaction results from previously published studies suggest that liquefaction is triggered not by the undrained loading and generation of pore pressures but by the collapse of the metastable sand structure which in turn generates the driving pore pressures in a saturated material hence the collapse is a characteristic response of a material to certain stress states rather than a result of some enforced undrained loading this theory is evaluated on very loose dry ottawa sand it is shown that the very loose dry sand when subjected to a constant deviatoric stress path significantly changes its behavior at a certain discreet stress state increases compressibility and becomes

franciscan complex limestone deposited at 24 n limestone and diabase from 11 sites in the permanente quarry the largest outcrop of calera limestone in the franciscan terranes have been studied by paleomagnetic and biostratigraphic methods observation of the upper albian uppennost albian boundary at one outcrop provides age and polarity control we propose a primary origin for a magnetic component identified in this unit another unit has been remagnetized by the diabase sill however predeformational inclinations are in agreement suggesting that remagnetization occurred shortly after deposition inclinations from these sites and another farther north at royce quarry successfully pass a megaconglomerate test and suggest a depositional paleolatitude of 24 n 4 this agrees with a plate model in which the calera limestone was deposited on the farallon plate at about 100 ma and was accreted to north america at about 70 ma

subduction and accretion of the permanente terrane near san francisco california previous studies of the calera limestone permanente terrane franciscan complex of california have shown that deposition occurred at approximately 25 n paleolatitude atop an oceanic plateau or rise and that it was subsequently transported northeast and accreted to the north american continental margin in the early tertiary the permanente terrane in the study area along the pacific coast south of san francisco contains a suite of rock types present in north dipping imbricate thrust slices possibly related to the subduction and accretion of an oceanic crustal sequence geochemical studies of greenstones thought to represent fragments of the dismembered oceanic crust indicate affinities with mid ocean ridge basalts and within plate basalt these greenstones may represent fragments of the rise upon which the calera limestone was deposited metamorphic minerals in the greenstones indicate both sea floor metamorphism and locally high pressure low temperature metamorphism it is concluded tentatively that the entire permanente terrane in the study area underwent high pressure low temperature metamorphism but that temporal or geologic conditions prevented widespread recrystallization or development of blueschist facies minerals structures in the deformed rocks can be related to underthrusting beneath the continental margin and attachment to the overriding plate studies of veins indicate several stages of dewatering it is likely that dewatering was a major process in the attachment event as shown by veins associated with this phase of deformation structurally interleaved melanges and broken formation contain sedimentary rock clearly derived from a continental margin these rocks probably represent trench and trench slope facies that were underthrust with the accreting oceanic crustal sequence

the distribution of 230th and 231pa in the deep sea surface sediments of the pacific ocean in order to determine the areal extent and distribution of 231pa sinks in the pacific ocean we have analyzed 34 deep sea surface sediment samples from widely distributed locations for their pa th and u isotopes while the 230thxs content varies by more than a factor often the 231paxs content is confined in a relatively narrow range with a mean value of 2 8 1 4 dpm g there is a positive correlation between 230thxs and 231paxs and using the regression line it is possible to calculate the 230thxs231paxs activity ratios in samples for which only 230th data are available we then constructed a map of 230thxs231paxs distribution using 230paxs231paxs 11 the production ratio in the water column as a criterion for identifying preferential 231pa sinks we have identified an area covering 30 40 of the pacific ocean this area includes most of the pacific margins the northwest pacific the antarctic ocean and perhaps the mid ocean ridge regions and is nearly coincident with that of high sediment accumulation rates this suggests that the paniculate flux is important for the removal of 231pa from the ocean two models for the removal of 231pa produced in the open ocean are 1 1 lateral transport into the vertical flux in regions of high particulate flux damaster 1979 andersonet al 1983a b or 2 2 uptake at the sediment water boundary the second model is more likely to be correct to distinguish unequivocally between the two proposed models we would need sediment trap data for the western north pacific

enhanced scavenging of 231pa relative to 230th in the south atlantic south of the polar front implications for the use of the 231pa 230th ratio as a paleoproductivity proxy abstract the fractionation of 230th and 231pa was investigated throughout the atlantic sector of the southern ocean published scavenging models generally assume that the 231pa 230t ratio of surface sediments is primarily determined by the mass flux of particles this relationship holds north of the polar front where low primary productivity coincides with ratios of unsupported 231pa 230th xs 231pa 230th in surface sediments below the production ratio of both radionuclides in the water column however we observed high xs231pa 230th ratios conventionally interpreted as a high productivity signal in surface sediments south of the polar front especially throughout the weddell sea in contradiction with the low particle flux of this region measurements of both dissolved and particulate fractions of 231pa and 230th in the water column revealed a strong n s decrease in the th pa fractionation factor from typical open ocean values around 10 north of the polar front to values between 1 and 2 south of 60 s this observation clearly indicates that the high xs231pa 230th ratios in surface sediments south of the antarctic circumpolar current are produced by a n s increase in the relative scavenging efficiency of 231pa relative to 230th most probably due to a change in the chemical composition of particulate matter and not by a high mass flux it is speculated that biogenic opal suggested not to significantly fractionate231pa and 230th may explain the enhanced scavenging of 231pa to the south this assumption is further supported by extremely high 231pa 230th ratios up to 0 34 in material collected with sediment traps south of the polar front where fluxes are primarily determined by biogenic opal based on these results we conclude that in regions where the sedimenting flux is dominated by biogenic opal the 231pa 230th ratio is not a reliable indicator for the mass flux of particles thus limiting its use as a paleoproductivity proxy in the southern ocean

opal burial in the equatorial atlantic ocean over the last 30 ka implications for glacial interglacial changes in the ocean silicon cycle 1 the silicic acid leakage hypothesis salh suggests that during glacial periods excess silicic acid was transported from the southern ocean to lower latitudes which favored diatom production over coccolithophorid production and caused a drawdown of atmospheric co2 downcore records of 230th normalized opal fluxes and 231pa 230th ratios from seven equatorial atlantic cores were used to reconstruct diatom productivity over the past 30 ka where a is years and to test the salh downcore records of 231pa 230th ratios and opal fluxes are highly correlated suggesting that they constitute a production based record of opal flux opal flux records support the salh in that glacial opal burial exceeded holocene burial by 1 8 gt opal ka in the area 0 40 w and 5 n 5 s earlier results from the eastern equatorial pacific ocean showed the opposite trend with greater holocene than glacial opal burial but approximately the same magnitude of difference between glacial and interglacial opal burial we suggest four nonexclusive scenarios to explain the data from both basins 1 increased upwelling in the equatorial atlantic and el nino like conditions suppressing upwelling in the eastern equatorial pacific altered the overall nutrient supply to both basins 2 si leaked from the southern ocean because of fe fertilization but was prevented from upwelling in the equatorial pacific because of el nino like conditions during the lgm 3 si leaked from the southern ocean because diatom productivity was limited by increased sea ice extent and was again prevented from upwelling in the equatorial pacific or 4 changes in ocean circulation related to the decreased input of agulhas water to the glacial south atlantic provided excess dissolved si to the equatorial atlantic ocean a deglacial opal pulse is seen in both the atlantic and pacific oceans all four scenarios and the presence of the common deglacial opal pulse suggest a common driver in the southern ocean

late slowdown of the atlantic meridional overturning circulation during the last glacial inception new constraints from sedimentary 231 pa 230 th our study gives new constraints on the response of atlantic meridional overturning circulation amoc export to various forcings during the last glacial inception the decay corrected excess sedimentary 231 pa 230 th activity ratio hereafter referred to as pa th has been measured over that period in two deep cores from the western su90 11 44 degrees 04 n 40 degrees 01 w 3645 m and eastern md01 2446 39 degrees 03 n 12 degrees 37 w 3547 m basins of the north atlantic both records display significant changes despite the relatively short half life of 231 pa similar to 32 kyr compared to the period we investigate the pa th variability does not correlate to changes in local opal flux normalized to 230 th moreover the pa th profiles display a high degree of coherency with indirect proxies of amoc activity such as the benthic foraminifera delta 13 c and the mid latitude summer sea surface temperature in nearby reference cores these additional pieces of evidence support our interpretation of the pa th as reflecting amoc export the pa th repeatedly underwent rapid changes during the last glacial inception associated with the extension of ice rafted detritus in the north atlantic highlighting the control of ice sheet dynamics through freshwater forcing on amoc export amoc export remains large during periods of ice sheet growth and its decreases lag the northern hemisphere summer insolation forcing amoc modulation appears driven by ice sheet dynamics itself driven by the seasonal insolation gradient between low and high northern hemisphere latitudes and the associated intensity of the meridional oceanic and atmospheric circulation c 2009 elsevier b v all rights reserved

particulate fluxes of 230th 231pa and 10be in the northeastern pacific ocean abstract measurements of 230th 231pa and 10be in sediment trap samples and holocene sediments collected along a transect in the northeastern pacific indicate that the removal of these nuclides from the ocean is greatly influenced by boundary scavenging more than 35 of the 230th at least 70 of the 231pa and as much as 85 of the 10be fluxes collected by sediment traps at a nearshore site located 120 km off shore are supplied by lateral transport of the dissolved nuclides from the open ocean these findings are consistent with the hypothesis that boundary scavenging is proportional to the oceanic residence times of the nuclides 10 40 y for 230th 100 y for 231 pa and 1000 y for 10be results of this study indicate that particle flux is a principal factor influencing scavenging of 230th 231pa and 10be from the water column the marine geochemistry of 10be in ocean margins is fundamentally different from that in the open ocean scavenging of 10be occurs throughout the water column at the margin area in this study in contrast to the pattern of 10be being removed only in the surface waters and then remineralized at depth in the open ocean aluminosilicate may be a major phase removing 10be from the water column in the open ocean but not at ocean margins nuclide accumulation rates in the underlying holocene sediments are all higher than the corresponding fluxes collected by sediment traps several possibilities that could account for this observation include downslope sediment transport deployment of the traps during a period when the particle flux was not representative of long term average conditions and scavenging of the nuclides from near bottom waters the high accumulation rate of authigenic mn in some holocene sediments which can be attributed to redox cycling of mn may have caused near bottom scavenging of 230th and 231pa as well as certain other trace elements such as ba cu and zn

franciscan complex calera limestones accreted remnants of farallon plate oceanic plateaus the calera limestone part of the franciscan complex of northern california may have formed in a palaeoenvironment similar to hess and shatsky rises of the present north west pacific1 we report here new palaeomagnetic results palaeontological data and recent plate motion models that reinforce this assertion the calera limestone may have formed on farallon plate plateaus north of the pacific farallon spreading centre as a counterpart to hess or shatsky rises in one model2 the plateaus were formed by hotspots close to the farallon pacific ridge axis on accretion to north america plateau dissection in the late cretaceous to eocene 50 70 myr could explain the occurrence of large volumes of pillow basalt and exotic blocks of limestone in the franciscan complex partial subduction of the plateaus could have contributed to laramide 70 40 myr compressional events3

quantifying the opal belt in the atlantic and southeast pacific sector of the southern ocean by means of 230th normalization 1 a set of 114 samples from the sediment surface of the atlantic eastern pacific and western indian sectors of the southern ocean has been analyzed for 230th and biogenic silica maps of opal content th normalized mass flux and th normalized biogenic opal flux into the sediment have been derived significant differences in sedimentation patterns between the regions can be detected the mean bulk vertical fluxes integrated into the sediment in the open southern ocean are found in a narrow range from 2 9 g m 2 yr 1 eastern weddell gyre to 15 8 g m 2 yr 1 indian sector setting upper and lower limits to the vertically received fraction of open ocean sediments the silica flux to sediments of the atlantic sector of the southern ocean is found to be 4 2 1 4 1011 mol yr 1 just one half of the last estimate this adjustment represents 6 of the output term in the global marine silica budget

organic matter in the franciscan and cedros subduction complexes the problems of instantaneous maturation and missing petroleum in accretionary prisms abstract most accretionary complexes are submarine mountain belts consisting predominantly of sedimentary rock past studies of accretionary complexes have concluded that they have minimal petroleum potential although they do contain potential source rocks owing to their great bulk of sedimentary rock large amounts of petroleum must be generated in accretionary prisms and these hydrocarbons must be trapped in the complexes or vented into the ocean or on land to understand the nature and abundance of organic material in accretionary complexes organic matter in the shales limestones and melange matrix of the franciscan and cedros subduction complexes was studied mostly using rock eval pyrolysis the largest amounts of total organic carbon toc were found in the calera limestone from the san francisco area 1 6 toc terrigenous sedimentary rocks of probable trench or trench slope origin contain from

thorium adsorption in the ocean reversibility and distribution amongst particle sizes abstract experiments have been carried out to determine whether the adsorption of th by marine suspended particles is a reversible process the results indicate reversibility on a time scale of hours the distribution of th between the dissolved state bacon and anderson 1982 and on the settling model of tsunogai and minagawa 1978 are discussed

paleo ocean chemistry records in marine opal implications for fluxes of trace elements cosmogenic nuclides 10be and 26al and biological productivity abstract here we provide evidence suggesting that marine diatom opal contains not only a high fidelity record of dissolved oceanic concentrations of cosmic ray produced radionuclides 10 be and 26 al but also a record of temporal variations in a large number of trace elements such as ti fe zn and mn this finding is derived from measurements in purified biogenic opal that can be separated from detrital materials using a newly developed technique based on surface charge characteristics initial results from a sediment core taken near the present day position of the antarctic polar front odp site 1093 show dramatic changes in the intrinsic concentrations of be al ti fe mn and zn in the opal assemblages during the past 140 kyr bp the results imply appreciable climatically controlled fluctuations in the level of bioreactive trace elements the time series of total be al ti fe and 10 be in the sediment core are all well correlated with each other and with dust records in the polar ice cores the observations suggest that a significant flux of these trace metals to oceans is contributed by the aeolian dust in this case presumably from the patagonia this observation also allows determination of fluxes of dust contributed 10 be to the antarctica ice sheets however our data show that the relationships among the various metals are not perfectly linear during periods of higher dissolved concentrations of trace elements indicated by fe and ti the relative concentrations of bioreactive elements be al mn and zn are decreased by contrast the fe zn and fe mn ratios decrease significantly during each transition from cold to warm periods the relative behavior could be consistent with any of the following processes i enhanced biological productivity due to greater supply of the bioreactive elements e g zn during cold periods ii increased biological and inorganic scavenging of particle active elements e g be and al during early interglacial periods iii differential uptake removal of the metals by the various diatom taxa whose relative productivity or growth rate changes with large scale climate in any case with one sedimentary phase and in single sedimentary sections we now have the potential to compare directly a proxy for aeolian input of micronutrients e g fe or ti with a proxy for production e g 26 al al ratios we expect that studies of the temporal records of trace elements and cosmogenic nuclides in contrasting regions of upwelling and productivity which exhibit different sensitivities to global climate fluctuations and micronutrient inputs would lead to a direct and comprehensive test of ideas such as the hypothesis of iron control of atmospheric carbon dioxide martin j h 1990 glacial interglacial co 2 change the iron hypothesis paleoceanography 5 1 13 our present data from a single site do not show that increases in dissolved fe concentrations per se were responsible for increased biological productivity however a much clearer picture of the effect of increased dust fluxes should emerge when we have data for trace elements and the cosmogenic nuclides 10 be and 26 al from various oceanic provinces

sortable silt and fine sediment size composition slicing parameters for palaeocurrent speed and palaeoceanography fine sediment size 63 ixm is best measured by a sedimentation technique which records the whole size distribution repeated size measurement with intermediate steps of removal of components by dissolution allows inference of the size distribution of the removed component as well as the residue in this way the size of the biogenic and lithogenic noncarbonate fractions can be determined observations of many size distributions suggest a minimum in grain size frequency curves at 8 to 10 ixm the dynamics of sediment erosion deposition and aggregate breakup suggest that fine sediment behavior is dominantly cohesive below 10 1xm grain size and noncohesive above that size thus silt coarser than 10 ixm displays size sorting in response to hydrodynamlc processes and its properties may be used to infer current speed silt that is f mer than 10 ixm behaves in the same way as clay 2 xm useful parameters of the distribution are the 10 63 ixm mean size and the percentage 10 63 ixm in the fine fraction we cannot use size distributions to distinguish the nature of the currents therefore to infer water mass advection speeds i e the mean kinetic energy of the flow ku regions of high eddy kinetic energy ke must be avoided at the present such abyssal regions lie under the high surface k e of major current systems gulf stream kuroshio agulhas antarctic circmpolar current and brazil falldand currents in the argenthe basin this is probably a satisfactory guide for the pleistocene with regard to the carbonate subfraction of the size spectrum size modes due to both cocco iths and foramlnlferal fragments can be recognized and analyzed with the boundary between them again at about 10 lm the flux of less than 10 lm carbonate at pelagic sites above the lysocline is another candidate for a productivity indicator

comment on on the importance of opal carbonate and lithogenic clays in scavenging and fractionating 230th 231pa and 10be in the ocean by s luo and t l ku luo and ku have reanalyzed part of the data set we published in 2002 to address the question of the differential scavenging of thorium protactinium and beryllium by different particulate phases organic carbon lithogenic material opal and calcium carbonate they conclude upon reanalysis that the data are consistent with their earlier proposal based on sediment separation experiments that lithogenic material possesses an affinity for th some 500 times greater than do biogenic phases while we welcome new analyses and fresh interpretations of our data set we have to disagree with their conclusion that the partition coefficient kd for adsorption of th onto lithogenic particles kd th l is on the order of 2 3 108 and far greater than the kd for adsorption of th onto calcium carbonate kd th c here we show that such a high value for kd th l is inconsistent with a large body of observations these observations suggest kd th l is closer to 1 107 consistent with our previous study

the coefficient of earth pressure at rest laboratory experiments on undisturbed specimens of a large number of soft clay deposits as well as previous measurements on clays and granular soils were used to examine and explain the magnitude and behavior of the coefficient of earth pressure at rest k0 i after sedimentation primary consolidation ii during secondary compression aging iii after active or passive preshearing away from the laterally constrained condition iv during a decrease in effective vertical stress and v during an increase in effective vertical stress in the recompression or compression range in terms of the slope of the effective horizontal versus effective vertical stress path the behavior of k0 is explained using the concept of mobilized angle of friction in laterally constrained deformation condition the jaky equation provides in terms of the angle of internal friction a good estimate of k0 of sedimented normally consolidated young clays and granular soils as well as of of presheared clays and sands

similar glacial and interglacial export bioproductivity in the atlantic sector of the southern ocean multiproxy evidence and implications for glacial atmospheric co2 we present time series of export productivity proxy data including 230thex normalized deposition rates rain rates of 10be dissolution corrected biogenic ba and biogenic opal as well as authigenic u concentrations which are complemented by rain rates of total detrital fe and sea ice indicating diatom abundances from five sediment cores across the atlantic sector of the southern ocean covering the past 150 000 years the results suggest that 10be rain rates and authigenic u concentration cannot serve as quantitative paleoproductivity proxies because they have also been influenced by detrital particle fluxes in the case of 10be and bulk sedimentation rates sediment focussing and deep water oxygenation in the case of u the combined results of the remaining productivity proxies of this study rain rates of biogenic opal and biogenic ba in those sections without authigenic u and other previously published proxy data from the southern ocean 231pa 230th and nitrogen isotopes suggest that a combination of sea ice cover shallow remineralization depth and stratification of the glacial water column south of the present position of the antarctic polar front and possibly fe fertilization north of it have been the main controlling factors of export paleoproductivity in the southern ocean over the last 150 000 years an overall glacial increase of export paleoproductivity is not supported by the data implying that bioproductivity variations in the southern ocean are unlikely to have contributed to the major glacial atmospheric co2 drawdown observed in ice cores

the influence of particle composition on thorium scavenging in the mediterranean sea abstract sediment trap data are crucial for the study of marine biochemical cycles but they need careful validation by thorium th isotopes in the present study 230th 232th uranium u aluminum al barium ba and manganese mn were analyzed in sinking particles collected by moored sediment traps in the ligurian sea dyfamed site in order to determine the collection efficiency of the traps and to constrain which particulate phase s carries th isotopes in a region with strong lithogenic inputs the 230thxs evaluation was based on the u content of each sample rather than on the 232th content of each sample and the average 238u 232th ratio of the continental crust because the latter method introduced too much uncertainty in the calculation high trapping efficiencies 187 85 at 200 m and 87 11 at 1000 m indicated no evidence of particle under collection by the traps the lack of correlation between 230thxs and the carbonate or the organic matter fraction suggests that these phases are not major 230thxs carrying phases in the deep ocean for most samples of the time series the 230thxs concentration is correlated with the lithogenic fraction and the mn concentration but pulses of particles with high lithogenic and mn content and low 230thxs concentration occur in winter assuming that 230thxs is only carried by lithogenic particles we estimate kd lithoth ranges from 0 42 0 04 107 ml g to 0 8 0 2 107 ml g assuming that 230thxs is only carried by authigenic mn oxide precipitates mno2 we estimate that kd mno2th ranges from 0 6 0 1 1010 ml g to 1 1 0 4 1010 ml g the relative variation of kd mno2th a factor 7 between different oceanic sites is significantly lower than the relative variation of kd lithoth a factor 50 suggesting that 230thxs has a tighter link with mno2 rather than with lithogenic particles and hence that 230thxs may be more likely scavenged by mno2 than by lithogenic particles the unambiguous determination of the particles carrying 230thxs remains to be done