oxygenation episodes on the continental shelf of central peru remote forcing and benthic ecosystem response abstract the interplay between the oxygen minimum zone and remotely forced oxygenation episodes determines the fate of the benthic subsystem off the central peruvian coast we analyzed a 12 year monthly time series of oceanographic and benthic parameters at 94 m depth off callao central peru 12 s to analyze i near bottom oxygen level on the continental shelf in relation to dynamic height on the equator 095 w and ii benthic ecosystem responses to oxygen change macrobiotic infauna meiofauna and sulphide oxidizing bacteria thioploca spp shelf oxygenation episodes occurred after equatorial dynamic height increases one month before consistent with the propagation of coastal trapped waves several but not all of these episodes occurred during el ninos the benthic biota responded to oxygenation episodes by undergoing succession through three major ecological states under strong oxygen deficiency or anoxia the sediments were nearly defaunated of macro invertebrates and thioploca was scarce such that nematode biomass dominated the macro and meiobiotas when frequency of oxygenation events reduced the periods of anoxia but the prevailing oxygen range was 10 20 mol l 1 mats of thioploca formed and dominated the biomass finally with frequent and intense 40 mol l 1 oxygenation the sediments were colonized by macrofauna which then dominated biomass the thioploca state evolved during the 2002 2003 weak en while the macrofauna state was developed during the onset of the strong1997 1998 en repeated episodes of strong oxygen deficiency during the summer of 2004 in parallel with the occurrence of red tides in surface waters resulted in the collapse of thioploca mats and development of the nematode state ecological interactions may affect persistence or the transition between benthic ecosystem states

surface and subsurface data integration and geological modelling from the little ice age to the present in the ravenna coastal plain northwest adriatic sea emilia romagna italy abstract new geological analysis of the ravenna coastal plain has allowed a major update of the geological coastal model with anthropogenic overprints removed from an area heavily affected by human actions in the last four centuries a period in which the little ice age lia has had a large influence on the coastal dynamics the geological build up of the coastal plain is a natural occurrence that is important for understanding the present day coastal buildup however coastal zone anthropization has defined the actual coastal morphology canceling out most of surface expression needed to create an accurate coastal evolution model as the beach ridges morphology in the study area as the lack of surface expression due to the anthropogenic actions has changed the coastal zone under study it is not possible to only use geomorphological analysis to construct a local coastal evolution model because of this building a new model and understanding how coastal evolution would proceed without human influence would allow us to understand the interaction between natural forces and anthropogenic influence which has acted to shape the actual morphology of the study area from the lia period to the present days we therefore propose an integration of data using the following actual data from the surface such as the high resolution digital surface model dsm and the digital terrain model dtm the actual database from the emilia romagna region geological survey including the shapefile with the regional soil chart and the geological elements present in the study area knowledge from previous work carried out in the area and the subsurface data from ground penetrating radar gpr which would make the study the first to use a gpr survey of the coastal plain of the northwest adriatic in addition the work will follows a successful case study done in the southern brazilian coastal plain that integrated previous works done in the coastal plain with new methods such as gpr data acquisition the gpr data allows for corroboration of the interpretation of the coastal model constructed using the surface data finally the surface geological model proposed in this work may aid by providing the following i a new means for local coastal geology research ii a methodology to apply to other barrier lagoon systems around the world in order to update our knowledge about these systems and iii powerful information to support coastal managers and decision makers in constructing a long term master plan for effective integrated coastal zone management

sedimentary architecture and depositional controls of a pliocene river dominated delta in the semi isolated dacian basin black sea abstract sedimentological facies models for semi isolated basins are less well developed than those for marine environments but are critical for our understanding of both present day and ancient deltaic sediment records in restricted depositional environments this study considers an 835 m thick sedimentary succession of mid pliocene age which accumulated in the dacian basin a former embayment of the black sea detailed sedimentological and palaeontological analyses reveal a regression from distal prodelta deposits with brackish water faunas to delta top deposits with freshwater faunas sediments contain frequent hyperpycnal plumes and an enrichment in terrestrial organic material ichnofossils and in situ brackish and freshwater faunas deltaic progradation created thin sharply based sand bodies formed by multiple terminal distributary channels covering a wide depositional area the system experienced frequent delta lobe switching resulting in numerous thin parasequences parasequences are overlain by erosive reddish oxidized sand beds enriched in broken abraded brackish and freshwater shells these beds were formed after sediment starvation on top of abandoned delta lobes during each flooding event a robust magnetostratigraphic time frame allowed for comparison between the observed sedimentary cyclicity and the amplitude and frequency of astronomical forcing cycles our results indicate that parasequence frequencies are significantly higher than the number of time equivalent astronomical cycles this suggests that delta lobe switching was due to autogenic processes we consider the observed facies architecture typical for a delta prograding on a low gradient slope into a shallow brackish protected semi isolated basin furthermore in the absence of significant wave and tidal influence sediment progradation in such a protected depositional setting shaped a delta strongly river dominated

de glauconiarum origine the glauconitic facies is widespread on present day continental shelves from 50 s to 65 n and at water depths between 50 and 500 m and is in particularly great abundance on the upper slope and outer shelf between 200 and 300 m it is also common in many ancient rocks of post late precambrian age it occurs as sand to pebble sized essentially green particles granular facies but also as a surface coating on particles and hardgrounds and as a diffuse impregnation film and diffuse facies we suggest the replacement of the term glauconite which has been interchangeably used to designate a morphological form and a specific mineral by glaucony facies and glauconitic smectite and glauconitic mica as end members of the glauconitic mineral family the widely accepted model of burst and hower for glauconitization requires a degraded micaceous 2 1 layer lattice structure parent clay mineral however detailed analysis of numerous samples of recent glaucony reveals that such a parent substrate is exceptional the model therefore requires modification generally the parent material is carbonate particles argillaceous kaolinitic faecal pellets infillings of foraminiferal tests various mineral grains and rock fragments that pass gradually into the commonly occurring green grains we show that the process of glauconitization is achieved by de novo authigenic growth of automorphous crystallites in the pores of the substrate accompanied by progressive alteration and replacement of the substrate it is this two fold evolution that causes the verdissement of granular substrates macrofossils and hardgrounds the authigenic mineral is an iron rich and potassium poor glauconitic smectite while new smectites are growing into the remaining pore space the earlier smectites are modified by incorporation of potassium producing decreasingly expandable minerals with a non expandable glauconitic mica as the end member this mineralogical diversity of the glauconitic mineral family explains the highly variable physical and chemical properties of glaucony four categories nascent little evolved evolved and highly evolved glaucony are distinguished glauconitization appears to be controlled by a delicate balance between degree of physical confinement of a particle and the amount of ionic exchange between the micro environment and ambient open marine sea water the optimum conditions for glauconitization are those of semi confinement as a result the interior of a grain is more glauconitized than its less confined periphery similarly for identical substrate types large grains 500 m provide more favourable substrates for glauconitization than lesser confined small grains on a larger scale the formation of glaucony is governed by the availability of iron and potassium and the balance between detrital influx and winnowing low accumulation rates expose grains to the open marine environment for sufficiently long times 105 106 years for highly evolved glaucony

elasticity and pressure induced structural changes in vitreous mgsio3 enstatite to lower mantle pressures abstract knowledge of the pressure density relations and elastic properties of silicate melts at high pressure and temperature conditions is fundamental for a better understanding of the dynamics and properties of the earth s interior here we report the sound velocities and elastic properties of vitreous mgsio 3 enstatite a simple analog for melts in the earth s mantle determined up to 33 4 1 2 gpa in a diamond anvil cell by brillouin scattering spectroscopy the adiabatic bulk and shear moduli of mgsio 3 glass at ambient conditions are k s0 78 4 6 gpa and 0 41 1 3 gpa corresponding to compressional and shear wave velocities of v p 6 969 30 km s and v s 3 868 20 km s on compression both longitudinal v p and transverse v s modes exhibit anomalous change in slope at 8 gpa and between 15 0 1 and 17 9 2 gpa that are associated with polyamorphic phase transitions in the glass the acoustic data were used to determine the density and compressibility of mgsio 3 glass at high pressure in both compression and decompression experiments in contrast to velocities and elastic moduli the density increases smoothly without singularities upon compression over the investigated pressure range densities of recovered glasses at room pressure are 1 5 to 2 4 higher than uncompressed glasses indicating pressure induced irreversible densification the anomalous changes in velocities and compressibility with pressure are consistent with structural modifications that have been identified as the main densification mechanisms of the glass by in situ spectroscopic studies and molecular dynamic calculations the results suggest that the residual densification of recovered glasses is associated with irreversible structural changes in the intermediate range order i e ring statistics rather than with changes in the coordination number of si upon pressurization if the changes in compressibility of mgsio 3 glasses identified in the present brillouin study also occurs in the analog melts they may have important implications for the present day dynamics of the mantle and early evolution of the earth during a magma ocean phase

glaucony and sequence stratigraphy a conceptual framework of distribution in siliciclastic sequences abstract detailed analysis of recent literature on glaucony and selected case studies eocene isle of wight miocene northern apennines shows that the presence of glaucony alone is not diagnostic of a specific systems tract of a depositional sequence a reliable sequence stratigraphic interpretation of glaucony bearing units requires additional information on glaucony including 1 spatial distribution 2 maturity distinction between nascent slightly evolved evolved and highly evolved glaucony and 3 genetic attributes differentiation of autochtonous from allochthonous and intrasequential from extrasequential glaucony autochthonous glaucony is common at various stratigraphic levels in the transgressive systems tract tst and the lower highstand systems tract hst showing an upward increase tst and then decrease hst in abundance and maturity the condensed section can be distinguished from the overlying and underlying deposits by the higher concentration and maturity of glaucony allochthonous intrasequential parautochthonous glaucony can be present in the entire tst hst and lowstand systems tract lst generally showing lower concentration and maturity than its autochthonous counterpart allochthonous extrasequential detrital glaucony is present mainly in the lst its concentration and composition depending on the characteristics of the source horizon the associa ion between autochthonous and allochthonous intrasequential and extrasequential glaucony commonly exists in the lst and in the lower tst

spin states and hyperfine interactions of iron in mg fe sio3 perovskite under pressure abstract with the guidance of first principles phonon calculations we have searched and found several metastable equilibrium sites for substitutional ferrous iron in mgsio 3 perovskite in the relevant energy range there are two distinct sites for high spin one for low spin and one for intermediate spin iron because of variable d orbital occupancy across these sites the two competing high spin sites have different iron quadrupole splittings qs at low pressure the high spin iron with qs of 2 3 2 5 mm s is more stable while the high spin iron with qs of 3 3 3 6 mm s is more favorable at higher pressure the crossover occurs between 4 and 24 gpa depending on the choice of exchange correlation functional and the inclusion of on site coulomb interaction hubbard u our calculation supports the notion that the transition observed in recent mossbauer spectra corresponds to an atomic site change rather than a spin state crossover our result also helps to explain the lack of anomaly in the compression curve of iron bearing silicate perovskite in the presence of a large change of quadrupole splitting and provides important guidance for future studies of thermodynamic properties of this phase

1997 1998 el nino off peru a numerical study an eddy resolving numerical simulation for the peru chile system between 1993 and 2000 is analyzed mainly for the 1997 1998 el nino atmospheric and lateral oceanic forcings are realistic and contain a wide range of scales from days to interannual the solution is validated against altimetric observations and the few in situ observations available the simulated 1997 1998 el nino closely resembles the real 1997 1998 el nino in its time sequence of events the two well marked sea level peaks in may june and november december 1997 are reproduced with amplitudes close to those observed other sub periods of the el nino seem to be captured adequately simple dynamical analyses are performed to explain the 1997 1998 evolution of the upwelling in the model the intensity of the upwelling appears to be determined by an interplay between alongshore poleward advection related to coastal trapped waves and wind intensity but also by the cross shore geostrophic flow and distribution of the water masses on a scale of 1000 km or more involving rossby waves westward propagation and advection from equatorial currents in particular the delay of upwelling recovery until fall 1998 i e well after the second el nino peak is partly due to the persistent advection of offshore stratified water toward the coast of peru altimetry data suggest that these interpretations of the numerical solution also apply to the real ocean

on enso coastal currents and sea levels abstract sea level measurements along the western coast of the americas have shown that there is a strong signal at enso frequencies approximately 2 2 yr 1 to 2 5 yr 1 that propagates poleward at about 40 to 90 cm s 1 this enso sea level signal must be associated with enso coastal currents but because adequate interannual current time series are unavailable the structure and strength of these currents are not known coastal enso currents must be fundamentally affected by bottom topography and bottom friction but previous theory has not taken these effects into account a near boundary numerical model with realistic bottom friction stratification and shelf and slope topography was therefore constructed to study enso coastal flow i at enso frequencies previous results for models with no bottom topography and no bottom friction suggest that sea level should not propagate poleward with realistic bottom friction and bottom topography coastal sea level propagates poleward at speeds similar to tho

circulation and low frequency variability near the chilean coast remotely forced fluctuations during the 1991 92 el nino results are reported from the first long recording current meter observations over the slope off chile these observations at 308s during the 1991 92 el nino event are analyzed together with observations of currents at a local deep sea site local wind and sea level sea level from the peru and chile coasts and wind temperature and currents from the equatorial pacific mean poleward flow of 12 cm s21 was observed within the peru chile undercurrent over the slope mean flow in the depth range of antarctic intermediate water was not distinguishable from zero in the presence of strong low frequency lf variability which dominated slope currents at all depths the strongest lf fluctuations had periods of about 50 days but periods of 10 and about 5 days were also observed significant local wind forcing of slope currents was only found in the period band 6 10 days and may be related to coastal trapped waves in the atmosphere our analysis shows that free coastal trapped waves in the ocean arriving from the north dominated the lf variability over the shelf and slope off northern and central chile during the 1991 92 el nino event strong 50 day period fluctuations there started their journey about two months earlier and 15 000 km farther up the coastal equatorial waveguide near the date line in the equatorial pacific as equatorial kelvin waves forced by westerly wind events of similar period upon reaching the south american coast these waves forced coastal trapped waves which propagated along the peru coast into the study region likewise a scenario of equatorial trapped waves forcing coastal trapped waves may explain 10 day as well as 6 day and 4 5 day period coastal trapped waves off chile stemming from mixed rossby gravity and inertia gravity waves trapped at the equator since the large 50 day period coastal trapped waves may strongly modify coastal upwelling source water such remotely forced waves may have a significant influence on the pelagic ecosystem off chile at least during el nino events

the frictional nearshore response to forcing by synoptic scale winds abstract an analytic barotropic model was used to study the nearshore frictional response to synoptic scale wind forcing the results depend only on the region where the surface and bottom ekman layers interact strongly and the water is consequently well mixed thus the conclusions apply even to shelves where baroclinic effects are not negligible father offshore the main findings are as follows i the blocking of the surface ekman flux which drives the shelf flow is a consequence of the interaction of ekwan layers in the nearshore region the interaction transfers progressively more of the surface stress directly to bottom stress as the depth decreases the consequent decrease in ekman flux toward the shore creates an ekman flux divergence which drives the interior flow ii the region over which the shelf is effectively forced is narrow it extends approximately from where the depth divided by the ekman layer e folding scale is 0 2 to where it is 2 5 iii simple equations for pressure and the

vertical structure variability in a seasonal simulation of a medium resolution regional model of the eastern south pacific a seasonal simulation from a medium resolution ocean general circulation mode ogcm is used to investigate the vertical structure variability of the southeast pacific sep the focus is on the extra tropical rossby wave etrw variability and associated forcing mechanism some aspects of the model mean state are validated from available observations which justifies a vertical mode decomposition of the model variability the analysis of the baroclinic mode contributions to sea level indicates that the gravest mode is dominant over most of the domain at all frequencies annual variability is on average twice as large as the semi annual variability which is confined near the coast for all the modes the first baroclinic mode contribution to the annual cycle exhibits a clear westward propagation north of the critical latitude the higher order modes only contribute near the coast where they are associated with vertically propagating energy the residual variability which is the energy at all timescales other than annual and semi annual periods peaks offshore between similar to 20 degrees s and similar to 30 degrees s for all baroclinic modes the third baroclinic mode also exhibits a relative maximum variability off the coast of peru south of the critical latitude of the annual cycle similar to 13 degrees s where the peru chile undercurrent is the most intense sensitivity experiments to the atmospheric and boundary forcing suggest that the residual variability results from the non linear interaction between annual rossby waves and the mean flow while the annual etrws in the model result from the summed contribution from both the local wind stress and remote equatorial forcing overall the study extends the classical analysis of sea level variability in the sep based on linear theory and suggests that the peculiarities of the baroclinic modes need to be taken into account for interpreting the sea level variability and understanding its connection with the equatorial variability c 2008 published by elsevier ltd

single crystal elasticity of mg0 9fe0 1 o to 81 gpa ferropericlase is the second most abundant mineral in earth s lower mantle and knowledge of its elastic properties at relevant conditions is needed to adequately interpret seismic observations in terms of the mineralogy and thermal state of the deep earth here we report the complete elastic tensor of mg sub 0 9 fe sub 0 1 o ferropericlase to 81 2 gpa at room temperature measured by brillouin spectroscopy and x ray diffraction in the diamond anvil cell our data indicate that the spin transition of iron between 45 and 63 gpa dramatically affects the longitudinal and off diagonal elements of the elastic stiffness tensor c sub 11 and c sub 12 whereas it leaves the shear constant c sub 44 almost unaffected based on our results the spin transition markedly changes the pressure and temperature dependence of the compressional and bulk sound velocities and must be taken into account in any attempt to match average radial seismic velocity profiles with mineral physics observations the different pressure dependence of compressional and bulk and shear sound velocities across the high spin to low spin hs ls transition implies that the spin transition might be best observed in the v sub p v sub s ratio and its pressure and temperature derivative we also point out the possibility that the spin transitionmore leads to an anti correlated temperature dependence of shear and compressional wave speeds in certain pressure temperature regimes in earth s lower mantle less

dynamics of seasonal and interannual variability of the peru chile undercurrent 1 coastal sea level current satellite altimeter data and an equatorial kelvin wave model are used to study the dynamics of seasonal and interannual fluctuations of the peru chile undercurrent satellite altimetry shows that low frequency sea level anomalies near 30 s propagate offshore as expected from rossby wave theory those anomalies are related to disturbances of equatorial origin observed near the coast of south america with a wind forced equatorial kelvin wave model and simple rossby wave dynamics we show that much of the sea level anomalies and more than 50 of the observed undercurrent variability near 30 s at seasonal and interannual periods can be explained by long rossby waves forced by the equatorial kelvin waves the amplitude of the equatorial kelvin wave can be used to estimate the amplitude of the rossby wave near the south american coast and thus to monitor low frequency changes in the peru chile undercurrent

seasonal variability of the permanent thermocline off northern chile 1 the seasonal cycle of the depth of several isotherms representative of the main thermocline near the western coast of south america shows important semiannual and annual components annual thermocline oscillations are mainly related to wind stress curl changes and secondarily to alongshore wind and the annual equatorial kelvin wave in contrast the important semiannual component observed in hydrographic data off peru and chile is mainly of equatorial origin based on satellite sea level anomalies and rossby wave theory we show that the coastal seasonal signal annual and semiannual propagates seaward near 21s in the form of long rossby waves which may modulate the thermocline depth several hundreds of kilometers offshore citation ramos m o pizarro l bravo and b dewitte 2006 seasonal variability of the permanent thermocline off northern chile geophys res lett 33 l09608 doi 10 1029 2006gl025882

precise determination of phase relations in pyrolite across the 660 km seismic discontinuity by in situ x ray diffraction and quench experiments abstract mineral assemblage changes in a pyrolite composition with increasing pressure were observed by in situ x ray diffraction and quench experiments at pressures near that of the 660 km seismic discontinuity and at a fixed temperature of 1600 c according to results obtained by in situ x ray diffraction experiments ringwoodite rw was observed with majorite garnet and casio 3 rich perovskite at pressures of about 20 22 gpa dissociation of ringwoodite to mgsio 3 rich perovskite and magnesiowustite mw was completed at 22 0 0 2 gpa according to matsui et al s periclase pressure scale and at 21 7 0 1 gpa according to shim et al s gold pressure scale majorite garnet persisted to about 24 gpa where pyrolite transformed to a lower mantle mineral assemblage i e mgsio 3 perovskite casio 3 rich perovskite and magnesiowustite thus majorite garnet coexists with the lower mantle assemblage at pressures of about 22 24 gpa in the quench experiments an assemblage of mgsio 3 perovskite magnesiowustite casio 3 rich perovskite and majorite garnet was synthesized at 22 5 gpa and 1600 c in which mg perovskite contained 2 8 wt al 2 o 3 and was significantly poorer in fe than coexisting magnesiowustite the fe mg partition coefficient between mg perovskite and magnesiowustite including ferric iron k app 0 27 0 06 is very close to that in the al free system which suggests that these p t conditions are in the vicinity of those of ringwoodite decomposition both the results of in situ x ray diffraction and quench experiments in the present study yield a convergent result that ringwoodite decomposes into mg perovskite and magnesiowustite before the garnet to perovskite transition at 1600 c in pyrolite the relation between the al content in mg perovskite and k app in pyrolite is non linear which is consistent with the fe mg partitioning between mg perovskite and magnesiowustite previously reported for a simpler mgo feo al 2 o 3 sio 2 system

equatorial forcing of interannual rossby waves in the eastern south pacific 1 long baroclinic rossby waves generated along the western coasts of continents play an important role in transferring coastal perturbations westwards into the ocean s interior to investigate interannual rossby waves in the eastern south pacific 10 s to 40 s combined topex poseidon and ers 1 2 satellite altimeter data were compared with model simulations of rossby waves for the 1992 2000 period the multimode linear model includes dissipation and was forced by observed wind stress curl from ers 1 2 and coastal pycnocline depth anomalies the latter were determined by a high resolution eastern boundary linear model initialized by observed sea level at the equator strong westward propagation of pycnocline anomalies originating at the coast can be observed at least as far south as 40 s the results suggest that an important part of the interannual mid latitude free baroclinic rossby waves originated at the coast were forced by pycnocline fluctuations originating from the equator in 1992 2000 a period which was dominated by the 1997 98 el nino event

spin state of ferric iron in mgsio3 perovskite and its effect on elastic properties abstract recent studies have indicated that a significant amount of iron in mgsio 3 perovskite pv is fe 3 fe 3 fe 10 60 due to crystal chemistry effects at high pressure p and that fe 3 is more likely than fe 2 to undergo a high spin hs to low spin ls transition in pv in the mantle we have measured synchrotron mossbauer spectroscopy sms x ray emission spectroscopy xes and x ray diffraction xrd of pv with all iron in fe 3 in the laser heated diamond anvil cell to over 100 gpa fe 3 increases the anisotropy of the pv unit cell whereas fe 2 decreases it in pv synthesized above 50 gpa fe 3 enters into both the dodecahedral a and octahedral b sites approximately equally suggesting charge coupled substitution combining sms and xes we found that the ls population in the b site gradually increases with pressure up to 50 60 gpa where all fe 3 in the b site becomes ls while fe 3 in the a site remains hs to at least 136 gpa fe 3 makes pv more compressible than mg endmember below 50 gpa because of the gradual spin transition in the b site together with lattice compression the completion of the spin transition at 50 60 gpa increases bulk modulus with no associated change in density this elasticity change can be a useful seismic probe for investigating compositional heterogeneities associated with fe 3

a numerical study of the upwelling circulation off central chile effects of remote oceanic forcing 1 a numerical ocean model is used to study the upwelling circulation off central chile in response to local winds and remote forcing in an idealized study of equatorial forced intraseasonal variability period of 50 days a first mode coastal trapped wave ctw paddle is applied to the northern boundary with coastal sea level amplitude of 12 cm without this ctw forcing the steady seasonal winds upwell undercurrent water from depths of 250 320 m to depths of 180 250 m the subsequent formation of mesoscale and headland eddies drive this water into the gulf of arauco and to depths of 50 120 m with the ctw paddle the circulation is strongly modified the mesoscale and headland eddies reform during the ctw upwelling phase during the ctw upwelling phase the upwelling over winds and eddies is enhanced by up to 40 m on the shelf model simulations are undertaken using realistic winds and a ctw paddle modulated by observed sea level without ctw forcing included in the model the agreement with data is poor in the gulf of arauco area the variability of alongshore currents below 130 m is dominated by ctw activity above 130 m wind driven current variability dominates in agreement with the idealized ctw analysis water is found to be upwelled from depths of 320 m to 100 m or less and 10 c undercurrent water is found at the surface and within the gulf

the response of stratified frictional flow of shelf and slope waters to fluctuating large scale low frequency wind forcing abstract numerical and analytical models are developed to discuss large scale low frequency wind driven fluctuations over the continental shelf and slope in the presence of realistic density stratification and bottom friction the models employ the long wave assumption that frequencies are small relative to the inertial frequency and that alongshore scales are large relative to cross cross shelf scales an attempt is made to make the effect of bottom friction on the flow as realistic as possible by taking into account the influence of surface gravity waves on bottom stress the results were obtained for sinusoidal wind forcing having frequency and alongshore wavenumber l and are described below a general criterion for barotropic shelf water response for wind forcing frequencies in the weather band 2 few weeks to 2 few days can be derived for the purpose of rapid calculation this criterion reduces approximately tohere ns2 is a shelf averaged value of the buoyancy frequency squared is

late quaternary temperature record from buried soils of the north american great plains we present the first comprehensive late quaternary record of north american great plains temperature by assessing the behavior of the stable isotopic composition 13 c of buried soils after examining the relationship between the 13 c of topsoil organic matter and july temperature from 61 native prairies within a latitudinal range of 46 38 n we applied the resulting regression equation to 64 published 13 c values from buried soils of the same region to construct a temperature curve for the past 12 k y estimated temperatures from 12 to 10 ka 1 k y 1000 14 c yr b p fluctuated with a periodicity of 1 k y with two cool excursions between 4 5 and 3 5 c and two warmer excursions between 1 and 0 c relative to modern early holocene temperatures from ca 10 7 5 ka were 1 0 to 2 0 c before rising to 1 0 c in the middle holocene between 6 0 and 4 5 ka after a cool interlude from 4 2 to 2 6 ka when temperatures dropped to slightly below modern another warm interval ensued from 2 6 to 1 ka as temperatures increased to 0 5 c a final decline in temperature to below modern occurred beginning ca 0 5 ka cooler than present temperatures in the great plains indicate telecommunications with cool water episodes in the gulf of mexico and north atlantic potentially governed by a combination of glacial meltwater pulses and low solar irradiance

stratigraphic unmixing reveals repeated hypoxia events over the past 500 yr in the northern adriatic sea in the northern adriatic sea and in most semi enclosed coastal regions worldwide hypoxia induced by eutrophication in the late 20 th century caused major die offs of coastal marine organisms however ecosystem responses to hypoxia over longer centennial scales are unclear because the duration of direct observations is limited to a few decades and or the temporal resolution of sedimentary archives is compromised by slow sedimentation and bioturbation to assess whether perturbations of ecosystems by hypoxia recurred over centuries in the northern adriatic sea we evaluate the timing and forcing of past hypoxia events based on the production history of the opportunistic hypoxia tolerant bivalve corbula gibba using 210 pb data radiocarbon dating amino acid racemization and distribution of foraminifers in sediment cores that capture the past 500 yr in the gulf of trieste unmixing the stratigraphic record on the basis of 311 shells of c gibba we show that the reconstructed fluctuations in abundance do not correlate with abundances in the raw stratigraphic record we find that production of c gibba has undergone major decadal scale fluctuations since the 18 th century with outbreaks corresponding to density of more than 1000 individuals per square meter these outbreaks represent long term phenomena in the northern adriatic ecosystem rather than novel states characteristic of the 20 th century eutrophication they positively correlate with centennial scale fluctuations in sea surface temperature indicating that the hypoxia events were coupled with water column stratification rather than with nutrient enrichment

high pressure phases in a shock induced melt vein of the tenham l6 chondrite constraints on shock pressure and duration abstract the microtexture and mineralogy of a 580 m wide melt vein in the tenham l6 chondrite were investigated using field emission scanning electron microscopy and transmission electron microscopy to better understand the shock conditions the melt vein consists of a matrix of silicate plus metal sulfide grains that crystallized from immiscible melts and sub rounded fragments of the host chondrite that have been entrained in the melt and transformed to polycrystalline high pressure silicates the melt vein matrix contains two distinct textures and mineral assemblages corresponding to the vein edge and interior the 30 m wide vein edge consists of vitrified silicate perovskite ringwoodite akimotoite majorite with minor metal sulfide the 520 m wide vein interior consists of majorite magnesiowustite with irregular metal sulfide blebs although these mineral assemblages are distinctly different the pressure stabilities of both assemblages are consistent with crystallization from similar pressure conditions the melt vein edge crystallized at about 23 25 gpa and the vein interior crystallized at about 21 25 gpa this relatively narrow pressure range suggests that the melt vein either crystallized at a constant equilibrium shock pressure of 25 gpa or during a relatively slow pressure release using a finite element heat transfer program to model the thermal history of this melt vein during shock we estimate that the time required to quench this 580 m wide vein was 40 ms because the entire vein contains high pressure minerals that crystallized from the melt the shock pressure duration was at least 40 ms using a synthetic hugoniot for tenham and assuming that the sample experienced a peak shock pressure of 25 gpa near the impact site we estimate that the tenham parent body experienced an impact with collision velocity 2 km s based on a one dimensional planar impact model we estimate that the projectile size was 150 m in thickness

upwelling response to atmospheric coastal jets off central chile a modeling study of the october 2000 event the spatial and temporal variability of nearshore winds in eastern boundary current systems affect the oceanic heat balance that drives sea surface temperature changes in this study regional atmospheric and oceanic simulations are used to document such processes during an atmospheric coastal jet event off central chile the event is well reproduced by the atmospheric model and is associated with the migration of an anomalous anticyclone in the southeastern pacific region during october 2000 a robust feature of the simulation is a sharp coastal wind dropoff which is insensitive to model resolution as expected the simulated oceanic response is a significant sea surface cooling a surface heat budget analysis shows that vertical mixing is a major contributor to the cooling tendency both in the jet core area and in the nearshore zone where the magnitude of this term is comparable to the magnitude of vertical advection sensitivity experiments show that the oceanic response in the coastal area is sensitive to wind dropoff representation this is because total upwelling i e the sum of coastal upwelling and ekman pumping depends on the scale of wind dropoff because the latter is much larger than the upwelling scale coastal wind dropoff has only a weak positive effect on vertical velocities driven by ekman pumping but has a strong negative effect on coastal upwelling interestingly though the weakening of coastal winds in the dropoff zone has a larger effect on vertical mixing than on vertical advection with both effects contributing to a reduction of cooling

taphonomic trade offs in tropical marine death assemblages differential time averaging shell loss and probable bias in siliciclastic vs carbonate facies radiocarbon calibrated amino acid racemization ages of individually dated bivalve mollusk shells from caribbean reef nonreefal carbonate and siliciclastic sediments in panama indicate that siliciclastic sands and muds contain significantly older shells median 375 yr range up to 5400 yr than nearby carbonate seafloors median 72 yr range up to 2900 yr maximum shell ages differ significantly at p 0 02 using extreme value statistics the implied difference in shell loss rates is contrary to physicochemical expectations but is consistent with observed differences in shell condition greater bioerosion and dissolution in carbonates higher rates of shell loss in carbonate sediments should lead to greater compositional bias in surviving skeletal material resulting in taphonomic trade offs less time averaging but probably higher taxonomic bias in pure carbonate sediments and lower bias but greater time averaging in siliciclastic sediments from humid weathered accretionary arc terrains which are a widespread setting of tropical sedimentation

phase relation and physical properties of an al depleted komatiite to 23 gpa abstract knowledge of the mineralogical constituents of the earth s mantle depends heavily on high p experiments of pyrolite composition in order to understand the planetary interior better phase relations and mineral physics properties of compositions other than pyrolite may also be important high p and high t experiments were conducted on an al depleted komatiite which can be regarded as a kind of piclogite composition fourteen experiments were carried out along a model geotherm between 5 and 23 gpa and 1100 and 1600 c with a multi anvil apparatus analyses of quenched run products showed that in the studied komatiite the fractions of olivine and its high p polymorphs wadsleyite and ringwoodite are 40 50 vol pyroxene garnet phase transition occurs at 13 17 gpa while the respective values for pyrolite are 60 vol and 12 15 gpa the density and seismic velocity profiles of komatiite mantle were calculated using thermoelastic parameters of related minerals and they showed quite good agreements with those of seismic observations around the transition zone as well as those for pyrolite

dynamics of remotely forced intraseasonal oscillations off the western coast of south america abstract six years of sea level observations at six locations along the south american coast from peru to chile were analyzed at intraseasonal frequencies periodicity 1 2 months a high resolution low frequency numerical coastal model having realistic shelf and slope topography and bottom friction and forced by an equatorial signal was used to analyze the intraseasonal coastal dynamics at these latitudes the following results were obtained lagged correlations between sea level stations imply a sea level poleward propagation of 250 km day 1 the frictionless vertical wall theory poleward phase speed was considerably less at 216 km day 1 model runs with realistic bottom friction and shelf and slope bottom topography gave poleward phase speeds much closer to that observed for typical parameters the phase speed was 253 km day 1 both bottom friction and topography significantly affect the propagation speed past work has shown that the sea level amplitude should grow alongshore like f f coriolis

effects of the fe3 spin transition on the properties of aluminous perovskite new insights for lower mantle seismic heterogeneities abstract we have measured the effects of the coupled substitution of fe3 and al on the density and compressibility of mantle silicate perovskite pv up to 95 gpa x ray emission spectroscopy and synchrotron mossbauer spectroscopy reveal a rapid increase in the population of low spin fe3 in fe3 al bearing pv over a narrow pressure range near 70 gpa which is in sharp contrast with al free fe3 bearing pv where fe3 undergoes a gradual spin transition and with al free fe2 bearing pv where fe2 does not become low spin at low pressure fe3 and al expand the perovskite lattice however near the pressure range of the abrupt increase in the low spin population the unit cell volume of fe3 al bearing pv becomes similar to that of mg endmember pv while those of al free fe3 bearing pv and al free fe2 bearing pv remain larger throughout the lower mantle consequently pv in al rich systems should have lower density in the shallow lower mantle but similar or greater density than pv in pyrolite in the deep lower mantle affecting the buoyancy and mechanical stability of heterogeneities although the fe3 spin transition in pv is unlikely to cause a seismic discontinuity at mantle temperatures it may result in a large change in bulk sound speed at 1200 1800 km depth such that a vertically extending structure with an elevated amount of fe3 would generate slower and faster anomalies above and below the depth of the spin transition respectively relative to the surrounding mantle this may have important implications for bulk sound speed anomalies observed at similar depths in seismic tomography studies

evolution of interannual warm and cold events in the southeast atlantic ocean extreme warm episodes in the southeast atlantic ocean known as benguela ninos have devastating envi ronmental impacts and have been shown to be remotely forced to place these extreme events into perspective the investigation is here extended to minor warm events as well as to cold episodes to this end different sets of observations have been combined with outputs from a numerical simulation of the tropical atlantic for the period 1982 99 it is shown that both warm and cold surface events develop regularly in the same specific region along the coast of angola and namibia some cold events compete in magnitude with major warm episodes local sea air heat flux exchanges do not seem to precondition the sea surface in the angola benguela region prior to the arrival of an event most warm and cold episodes are large scale events despite their limited surface signature they appear to be generated by wind anomalies in the western and central equatorial atlantic in the same way as benguela ninos seasonal fluctuations of the depth and shape of the tropical thermocline seem partly to control the way subsurface anomalies eventually impact the surface during austral summer surface anomalies create an identifiable pool centered near 158s whereas in winter they show an elongated pattern along the coast stretching toward the equator local upwelling or downwelling favorable wind regimes as well as local net heat fluxes may modulate the surface expression of events

exhumation of lower mantle inclusions in diamond atem investigation of retrograde phase transitions reactions and exsolution a multiphase inclusion kk 83 in a diamond from the kankan deposits in guinea resulting from complex reactions between primary lower mantle phases was examined in detail using analytical transmission electron microscopy the inclusion consists of a large 300 m diopside crystal with a small symplectitic intergrowth in one corner comprising olivine and tetragonal almandine pyrope phase tapp the olivine part of the symplectite contains small exsolutions of mg al chromite and rare ca carbonate a second inclusion of ferropericlase observed in the same diamond indicates a primary origin within the lower mantle the clinopyroxene formed through a series of reactions at the expense of touching inclusions of casi and mgsi perovskite during convective ascent of the diamond through the transition zone the proposed reaction sequence is mgsipvk casipvk mgsiilm casipvk ringwoodite stishovite casipvk clinopyroxene relict ringwoodite the high al content of the bulk symplectite indicates ringwoodite as precursor phase coexisting with clinopyroxene a slight deficiency of sio2 during the diopside forming reaction leads to a small amount of relict ringwoodite 0 1 vol of the total inclusion is occupied by ringwoodite coexisting with diopside the ringwoodite captures the observed high amount of al subsequent breakdown of ringwoodite to wadsleyite tapp produces the observed symplectitic intergrowth during the phase transformation of wadsleyite to olivine exsolution of mg al chromite occurs further decreasing the original solubility of al cr and ti in accordance with experimental data on the element partitioning between wadsleyite and olivine based on these observations tapp can form as a retrograde phase within the transition zone of the earth s mantle and is not restricted to the upper part of the lower mantle high fe3 contents may favour its formation

change in el nino flavours over 1958 2008 implications for the long term trend of the upwelling off peru abstract the tropical pacific variability has experienced changes in its characteristics over the last decades in particular there is some evidence of an increased occurrence of el nino events in the central pacific a k a central pacific el nino cp el nino or el nino modoki in contrast with the cold tongue or eastern pacific ep el nino which develops in the eastern pacific here we show that the different flavours of el nino imply a contrasted equatorial kelvin wave ekw characteristic and that their rectification on the mean upwelling condition off peru through oceanic teleconnection is changed when the cp el nino frequency of occurrence increases the simple ocean data assimilation soda reanalysis product is first used to document the seasonal evolution of the ekw during cp and ep el nino it is shown that the strong positive asymmetry of enso el nino southern oscillation is mostly reflected into the ekw activity of the ep el nino whereas during cp el nino the ekw is negatively skewed in the eastern pacific along with slightly cooler conditions off peru shallow thermocline during cp el nino this is favourable for the accumulation of cooler sst anomalies along the coast by the remotely forced coastal kelvin wave such a process is observed in a high resolution regional model of the humboldt current system using the soda outputs as boundary conditions in particular the model simulates a cooling trend of the sst off peru although the wind stress forcing has no trend the model is further used to document the vertical structure along the coast during the two types of el nino it is suggested that the increased occurrence of the cp el nino may also lead to a reduction of mesoscale activity off peru

global sea level control on local parasequence architecture from the holocene record of the po plain italy abstract holocene deposits exhibit distinct predictable and chronologically constrained facies patterns that are quite useful as appropriate modern analogs for interpreting the ancient record in this study we examined the sedimentary response of the po plain coastal system to short term millennial scale relative fluctuations of sea level through high resolution sequence stratigraphic analysis of the holocene succession meters thick parasequences form the building blocks of stratigraphic architecture above the younger dryas paleosol a prominent stratigraphic marker that demarcates the transgressive surface early holocene parasequences s 1 3 record alternating periods of rapid flooding and gradual shoaling and are stacked in a retrogradational pattern that mostly reflects stepped post glacial eustatic rise conversely middle to late holocene parasequences s 4 8 record a complex pattern of coastal progradation and delta upbuilding that took place following sea level stabilization at highstand starting at about 7 cal ky bp the prominent transgressive surface at the base of parasequence 1 correlates with the period of rapid global sea level rise at the onset of the holocene mwp 1b whereas flooding surfaces associated with parasequences 2 and 3 apparently reflect minor early holocene eustatic jumps reported in the literature changes in shoreline trajectory parasequence architecture and lithofacies distribution during the following eustatic highstand had instead an overwhelming autogenic component mostly driven by river avulsions delta lobe switching local subsidence and sediment compaction we document a 1000 year delayed response of the coastal depositional system to marine incursion farther inland from the maximum landward position of the shoreline a dramatic reduction in sediment flux due to fluvial avulsion resulted in marine inundation in back barrier position whereas coastal progradation was simultaneously taking place basinwards we demonstrate that the landward equivalents of marine flooding surfaces parasequence boundaries may be defined by brackish and freshwater fossil assemblages and traced for tens of kilometers into the non marine realm this makes millennial scale parasequences whether auto or allogenic in origin much more powerful than systems tracts for mapping detailed extents and volumes of sediment bodies the holocene parasequences of the po coastal plain with strong age control and a detailed understanding of sea level variation may provide insight into the driving mechanisms and predictability of successions characterized by similar depositional styles but with poor age constraint resulting in more robust interpretations of the ancient record

sedimentary response to late quaternary sea level changes in the romagna coastal plain northern italy data from 17 continuously cored boreholes 40 170 m deep reveal the subsurface stratigraphy of the romagna coastal plain sedimentological and microfaunal data allow the distinction of eight facies associations of late pleistocene holocene age including 18 lithofacies and 16 faunal associations ten 14c dates provide the basis to establish a sequence stratigraphic framework for the succession corresponding to the upper part 35 ky bp of the last glacio eustatic cycle the eight facies associations can be grouped into lowstand transgressive and highstand systems tracts the upper part of the lowstand systems tract consists of alluvial plain deposits these accumulated during the late pleistocene when the shoreline was 250 km south of its present day position a pronounced stratigraphic hiatus between 25 and 8 8 ky bp is invariably recorded at the upper boundary transgressive surface of these pleistocene indurated and locally pedogenized alluvial deposits the succeeding postglacial history is represented by a well developed transgressive regressive cycle transgressive deposits interpreted to reflect the rapid landward migration of a barrier lagoon system include two wedge shaped paralic and marine units these thicken in opposite directions and are separated by a ravinement surface above the transgressive deposits the maximum flooding surface mfs marks the change from a transgressive barrier lagoon complex to a prograding wave dominated delta system early po delta the mfs can be traced landwards where it constitutes the base of lagoonal deposits an aggradational to progradational stacking pattern of upper delta plain marsh lower delta plain lagoon bay and delta front beach ridge deposits reflects the progressive increase in the sediment supply accommodation ratio during the following highstand the alluvial deposits capping the sequence accumulated by the 13th century ad in response to an avulsion event that caused abandonment of the former po delta lobe and the northward migration of the po river towards its present position

amplitude frequency and drivers of caspian sea lake level variations during the early pleistocene and their impact on a protected wave dominated coastline the caspian sea the largest isolated lake in the world witnessed drastic lake level variations during the quaternary this restricted basin appears very sensitive to lake level variations due to important variations in regional evaporation precipitation and runoff the amplitude frequency and drivers of these lake level changes are still poorly documented and understood studying geological records of the caspian sea might be the key to better comprehend the complexity of these oscillations the hajigabul section documents sediment deposited on the northern margin of the kura basin a former embayment of the caspian sea the 2035 m thick well exposed section was previously dated by magneto biostratigraphic techniques and provides an excellent record of early pleistocene environmental lake level and climate changes within this succession the 1050 m thick apsheronian regional stage between ca 2 1 ma and 0 85 ma represents a particular time interval with 20 regressive sequences documented by sedimentary and palaeontological changes sequences are regressing from offshore to coastal lagoonal or terrestrial settings and are bounded by abrupt flooding events sediment reveals a low energy wave dominated reflective beach system wave baselines delimiting each facies association appear to be located at shallower bathymetries compared to the open ocean water depth estimations of the wave baselines allow reconstruction of a lake level curve recording oscillations of ca 40 m amplitude cyclostratigraphic analyses display lake level frequency close to 41 kyr pointing to allogenic forcing dominated by obliquity cycles and suggesting a direct or indirect link with high latitude climates and environments this study provides a detailed lake level curve for the early pleistocene caspian sea and constitutes a first step towards a better comprehension of the magnitude occurrence and forcing mechanisms of caspian sea lake level changes facies models developed in this study regarding sedimentary architectures of palaeocoastlines affected by repeated lake level fluctuations may form good analogues for other semi isolated basins worldwide

evidence of possible enhanced peat burning by deep origin methane in the po river delta plain italy abstract a burning peat site in the po valley italy has been investigated for the first time beyond the smoke from the smoldering combustion of peat there are carbonatic concretions and huge amounts of methane in the soil 60 by vol leading to fluxes to the atmosphere of the order of 102 103 mg m 2 d 1 a wide range of analyses gas composition stable isotopes of ch4 and caco3 methane radiocarbon were performed in order to understand whether methane is produced by peat layers or seeps from deeper natural gas reservoirs the quasi fossil character of ch4 methane derived carbonates methane stable isotopic compositions related to marine carbonates reduction the presence of helium and a fault corresponding to the burning site all converge to indicate that the major part of the methane ascends from deep horizons such methane seepage is likely to feed the peat combustion explaining the observed phenomena and the large outbursts of historical gas emission events

a potential global boundary stratotype section and point gssp for the tarentian stage upper pleistocene from the taranto area italy results and future perspectives abstract we present new data collected at the fronte composite section near taranto where the upper pleistocene marine sedimentary succession is continuously exposed above a fossiliferous calcarenite yielding the senegalese fauna and abundant cladocora the 230 th u age of which is consistent with marine isotope stage mis 5 a 6 25 m thick pelitic unit is characterized by lithologically homogeneous marine sediments in which stable oxygen isotope micropaleontological and palynological analyses suggest a long and undisturbed sedimentary interval across the marine isotope stage mis 5 5 peak plateau high sedimentation rates and a successful paleomagnetic pilot study indicate the probability of locating brief chronostratigraphic events useful for correlation with both continental and marine successions elsewhere these results show the composite section to be a very promising candidate in the search for the upper pleistocene global boundary stratotype section and point gssp

systematic vertical and lateral changes in quality and time resolution of the macrofossil record insights from holocene transgressive deposits po coastal plain italy abstract in siliciclastic marine settings skeletal concentrations are a characteristic feature of transgressive intervals that provide insights into biological and sequence stratigraphic processes to investigate taphonomic signatures of transgressive intervals we analysed three cores along a depositional profile from the high resolution chrono and stratigraphic framework of the holocene po coastal plain in northern italy coupled multivariate taphonomic and bathymetric trends delineated spatial and temporal gradients in sediment starvation bypassing suggesting that quality and resolution of the fossil record vary predictably along the studied depositional profile moreover integration of taphonomic bathymetric and fossil density trends across the study area reveals distinctive signatures useful in characterizing facies associations and determining surfaces and intervals of sequence stratigraphic significance within the southern po plain succession taphonomic degradation of macroskeletal remains increases from proximal nearshore to distal offshore locations this trend is discernible for both biologically driven bioerosion and physically driven e g dissolution abrasion shell alterations compared to the up dip most proximal core the down dip core is distinguished by shell rich lithosomes affected by ecological condensation co occurrence of environmentally non overlapping taxa and by higher taphonomic alteration the onshore offshore taphonomic trend likely reflects variation in sediment accumulation along the depositional profile of the holocene northern adriatic shelf with surface near surface residence time of macroskeletal remains increasing down dip due to lower accumulation rates these results indicate that during transgressive phases changes in sea level base level are likely to produce down dip taphonomic gradients across shelves where the quality and resolution of the fossil record both deteriorate distally radiocarbon calibrated amino acid racemisation dates on individual bivalve specimens and the chronostratigraphic framework for this profile suggest jointly that the high levels of taphonomic degradation observed distally developed over millennial time scales 8ky whereas in proximal setting overall low taphonomic degradation and geochronologic constrains point to centennial scale time averaging during the late transgression phase patterns documented in the holocene transgressive and lowermost regressive deposits of the southern po plain may be characteristic of siliciclastic dominated depositional systems that experience high frequency base level fluctuations

el nino sea level and currents along the south american coast comparison of observations with theory abstract interannual sea level fluctuations along the south american coast and 7 3 year long current records at 30 s off central chile were examined with a low frequency linear numerical model the model includes stratification and shelf and slope bottom topography which varies alongshore the coastal flow is driven by interannual alongshore wind stress and an interannual alongshore pressure gradient resulting from el nino la nina pressure fluctuations at the equator calculations suggest that along the south american coast the coastal interannual variability is primarily due to the remote equatorial forcing rather than interannual coastal alongshore wind stress past work using this model has shown that due to the scattering of lower vertical modes to higher ones by bottom friction the model predicts a low frequency jet trapped near the bottom along the continental slope until now adequate interannual current time series were unavailable to check this prediction analysis of the observations shows th

decadal variability in the large scale sea surface height field of the south pacific ocean observations and causes large scale sea surface height ssh changes in the extraequatorial south pacific ocean are investigated using satellite altimetry data of the past 12 yr the decadal ssh signals in the 1990s were dominated by an increasing trend in the 30 50 s band and a decreasing trend in the central south pacific ocean poleward of 50 s in recent years since 2002 there has been a reversal in both of these trends spatially varying low frequency ssh signals are also found in the tropical region of 10 25 s where the decadal ssh trend is negative in the eastern basin but positive in the western basin to clarify the causes for these observed spatially varying ssh signals a 11u2 layer reduced gravity model that includes the wind driven baroclinic rossby wave dynamics and the responses forced by ssh changes along the south american coast was adopted the model hindcasts the spatially varying decadal trends in the midlatitude and the eastern tropical regions well accumulation of the wind forced ssh anomalies along rossby wave characteristics is found to be important for both previously reported long term trends and their reversals in recent years the boundary forcing associated with the time varying ssh signals along the south american coast is crucial for understanding the observed ssh signals of all time scales in the eastern tropical south pacific basin but it has little impact upon the midlatitude interior ssh signals

in situ x ray diffraction study of the effect of water on the garnet perovskite transformation in morb and implications for the penetration of oceanic crust into the lower mantle abstract the phase boundary of the transformation of garnet to perovskite in hydrous mid ocean ridge basalt morb was determined by in situ high pressure and high temperature x ray diffraction xrd experiments the garnet bearing assemblage was formed in experiments at pressures below 21 gpa in contrast an assemblage of mg perovskite ca perovskite stishovite cf phase and or nal phase is stable at pressures above 21 gpa garnet and perovskite bearing assemblages were synthesized at a pressure range of 20 25 gpa and a temperature range of 1000 1600 c on the basis of our results we have located the garnet perovskite phase boundary and find that it can be described by the following equation p gpa 0 004t c 17 5 which positions it 2 gpa lower under dry conditions if the top 7 km of the slab is colder than 1200 c in the transition zone perovskite will appear at a depth shallower than that where ringwoodite decomposes this result indicates that the morb layer becomes denser than the peridotite portion of the slab throughout the transition zone and the lower mantle and thus no density crossover would exist between basalt and underlying peridotite along the cold subducting slab geotherm

discovery of bridgmanite the most abundant mineral in earth in a shocked meteorite meteorites exposed to high pressures and temperatures during impact induced shock often contain minerals whose occurrence and stability normally confine them to the deeper portions of earth s mantle one exception has been mgsio 3 in the perovskite structure which is the most abundant solid phase in earth here we report the discovery of this important phase as a mineral in the tenham l6 chondrite and approved by the international mineralogical association specimen ima 2014 017 mgsio 3 perovskite is now called bridgmanite the associated phase assemblage constrains peak shock conditions to 24 gigapascals and 2300 kelvin the discovery concludes a half century of efforts to find identify and characterize a natural specimen of this important mineral

equatorially forced intraseasonal propagations along the peru chile coast and their relation with the nearshore eddy activity in 1992 2000 a modeling study 1 a regional eddy resolving oceanic model spanning the 1992 2000 period is used to study the influence of 50 to 80 day intraseasonal equatorial kelvin waves iekw on mesoscale eddy activity off the west coast of peru and northern and central chile the model is shown to realistically simulate nearshore intraseasonal sea level variability poleward propagation of equatorially forced coastal trapped waves along the coastal waveguide and offshore variability related to mesoscale eddies and rossby waves rw in agreement with linear theory rw are confined equatorward of 12 s in the 50 80 days period range south of that critical latitude westward propagation is dominated by energetic mesoscale signals resulting mainly from coastal flow instability sensitivity experiments to the open boundary conditions are then used to estimate to what extent eddy activity is impacted by the remote equatorial forcing a coastal increase in eddy kinetic energy related to the energetic 60 day iekw activity present in the open boundary forcing is evidenced and is largest off northern peru whereas no major changes are observed offshore additional regional simulations with different open boundary conditions corroborate our findings and suggest that this limited effect of iekw on the offshore eddy kinetic energy may be a robust feature citation belmadani a v echevin b dewitte and f colas 2012 equatorially forced intraseasonal propagations along the peru chile coast and their relation with the nearshore eddy activity in 1992 2000 a modeling study j geophys res 117 c04025 doi 10 1029 2011jc007848

a review of the milankovitch climatic beat template for plio pleistocene sea level changes and sequence stratigraphy the milankovitch theory of climate change predicts that global ice volume and hence sea level changes were controlled by long term quasi periodic variations in the earth s orbital parameters obliquity precession and eccentricity d 18 o records from deep sea cores are a proxy for sea level changes and have an orbitally tuned chronology covering the last 5 ma the sea level signal in d 18 o data from east equatorial pacific core v19 30 is well calibrated with sea level data from coral terraces on huon peninsula new guinea over the last 140 ka and with less certainty back to 340 ka over the last 140 ka the sea level contribution to benthic glacial interglacial isotopic variation is about 1 2 1 3 or 0 011 m 1 and for core v19 30 the glacial age temperature contribution from deep ocean cooling of 1 7oc is 0 4 independent constraints on late pliocene sea level changes interpreted from shallow marine continental margin records indicate that the sea level d 18 o calibration may not have been the same over the last 2 6 ma and the temperature correction is unlikely to have been the same in all glacial periods and all ocean settings nevertheless the astronomically tuned isotopic records from deep sea cores provide an accurate chronology and approximate the magnitudes of sea level changes over the last 2 6 ma against which the facies architecture of stratigraphic sequences can be analysed and the concepts of sequence stratigraphy properly evaluated 1998 elsevier science b v all rights reserved

dynamics of the bottom boundary layer on the northern california shelf abstract time series measurements of velocity temperature and conductivity on the northern california shelf during two winter seasons permit an observational test in vertically integrated form of a simple set of subinertial momentum and heat balances for the bottom boundary layer which have resulted from recent theoretical work these are 1 an along isobath momentum equation that reduces to a classic ekman balance 2 a cross isobath momentum equation in which the ekman balance is modified by a buoyancy force caused by distortion of the isopycnal surfaces within the boundary layer and 3 a heat balance in which variability of temperature is produced by cross isobath advection the measurements confirm the importance of buoyancy in the cross isobath momentum equation and as has recently been predicted theoretically they indicate that buoyancy is a dominant effect when the boundary layer is thick which typically occurs during downwelling favorable flows an ekman balance describes subinertial flu

phase relation and mineral chemistry in pyrolite to 2200 c under the lower mantle pressures and implications for dynamics of mantle plumes 1 phase relations in pyrolite were studied at pressures of 24 and 30 gpa and temperatures up to 2200 c at 24 gpa and 1600 c an assemblage of mg perovskite magnesiowustite ca perovskite and garnet was observed with the proportion of garnet increasing continuously with temperature at 30 gpa only the two perovskites and magnesiowustite were observed and no significant changes in mineral proportions with temperature were observed iron was almost equally partitioned between mg perovskite and magnesiowustite at temperatures below about 1800 c at 24 and 30 gpa with increasing temperature however iron was concentrated more in magnesiowustite at both of these pressures the decrease of al content in mg perovskite with temperature which is caused by an increase in the proportion of garnet is likely to be responsible for the iron partitioning behavior at 24 gpa while the minor elements na al and cr in magnesiowustite may play an important role in fe partitioning at 30 gpa the density difference between ascending hot plumes t 200 and 400 c and the surrounding mantle was calculated using the present experimental data the density difference t 400 c at 30 gpa 806 km depth is 0 06 g cm3 but increases to 0 22 g cm3 at 24 gpa 670 km depth the large increase in the density difference that occurs in a hot plume at the uppermost part of the lower mantle originates from an increase of the proportion of garnet and may be a trigger for the plume s passage through the boundary between the lower mantle and the mantle transition zone

critical frequencies at ocean boundaries past theoretical work has shown that for low frequency flow at a given ocean boundary location a critical frequency c exists such that for c unforced motion is trapped to the coast while for c energy leaves the coast alternatively for motion of a given frequency on the boundary there exists a critical latitude such that the motion is trapped to the coast poleward of that latitude but equatorward it is not this theory is discussed physically for both meridional and nonmeridional boundaries the simple formula for critical frequency along a nonmeridional boundary is used to document critical periods for the eastern and western atlantic pacific and indian ocean boundaries the theory occasionally breaks down when boundary curvature is too large

interdecadal sea surface temperature sea level pressure coupled variability in the south pacific ocean 1 the main coupled sea surface temperature sst sea level pressure slp variability at interdecadal timescale in the south pacific is studied by means of correlation and combined complex empirical orthogonal function cceof analyses the sst slp coupled variability presents a bidecadal cycle from mid 1950s to 1970s and a decadal cycle from 1980s to early 1990s reproducing the enso like interdecadal oscillation particularly the first sst slp cceof mode describes the bidecadal cycle characterized by westward progression of sst and slp anomalies along the tropical pacific while the second sst slp cceof mode shows the decadal cycle with eastward development during both bidecadal and decadal cycles the sst fluctuations in the eastern equatorial pacific and along the western coast of south america are primarily forced by equatorial zonal wind variability specially during the bidecadal cycle the alongshore sst variability south of 30 s is maintained and reinforced by meridional coastal wind fluctuations associated with a stationary slp pattern off southern chile this stationary slp pattern appears connected to sst fluctuations in the central tropical pacific

low frequency reflection from a nonmeridional eastern ocean boundary and the use of coastal sea level to monitor eastern pacific equatorial kelvin waves abstract analytical theory and wind sea level and atmospheric pressure data were used to examine low frequency dynamics near the equatorial eastern pacific ocean boundary the analytical technique involves linking low frequency solutions near a nonmeridional boundary with the deep ocean equatorial kelvin wave for both unforced and wind forced flows using an equatorial wave orthogonality condition the following results were obtained mathematical and physical arguments show that nonmeridional boundaries should be less reflective than meridional ones and that the poleward coastal kelvin wave energy flux should be greater the more the boundary tilts from north to south the eastern pacific ocean boundary is more nonmeridional in the northern hemisphere and as a consequence calculations for the intraseasonal semiannual annual and interannual frequencies an indicated that poleward coastally trapped energy flux is greater in the northern hemisphere than in the southern hemisphere for most frequencies

hindcasts of sea level variations during the 1982 83 el nino abstract the sea level signature for the onset of the 1982 83 el nino is hindcasted using a linear wind driven model that consists of four vertical modes the hindcast solution is compared with sea level time series from 18 island and coastal stations throughout the tropical pacific the response of the first and second baroclinic modes when summed account for a significant portion of the phase and amplitude of the observed sea level the comparisons with observed sea level are best in the eastern tropical pacific along the equator and south american coast where the solutions are a function of integrals of the zonal wind field to the west the skill of the hindcast is notably less away from the equator

a low seasonality scenario in the mediterranean sea during the calabrian early pleistocene inferred from fossil arctica islandica shells understanding past seasonal temperature variability in the ocean is essential to evaluate the effects of future climate change on marine ecosystems here we estimate seasonal water temperature amplitudes from stable oxygen isotope 18oshell values of fossil shells of arctica islandica assuming 18owater 0 9 0 1 v smow specimens were collected from three pleistocene successions emilian and sicilian substages of the calabrian in central and southern italy i e rome lecce and sicily biostratigraphic analyses from rome quarry deposits indicate an age between 1 6 and 1 2 ma whereas sicily and lecce successions are slightly more recent between 1 1 and 0 62 ma prior to carbonate geochemical analysis we checked the shells for potential diagenetic alterations e g from aragonite to calcite using confocal raman microscopy 18oshell transects indicate an annual temperature amplitude of about 3 c during the early pleistocene this is in sharp contrast to reconstructions based on faunal assemblages according to which the simultaneous occurrence of boreal and warm water species in the calabrian mediterranean sea suggests a much higher seasonality ca 10 c the low seasonality and the relatively cold water 9 10 c indicate the outcrops represent colder climatic conditions compared to modern times and suggest the occurrence of a maximum glacial phase

planetary wave propagation off california and its effect on zooplankton abstract lagged correlation of dynamic height from the gappy california cooperative oceanic fisheries investigation calcofi with monthly san diego sea level for the period 1949 2001 shows that the dynamic height propagates westward at 4 10 cm s 1 about double the speed of the large scale low frequency rossby wave 2 2 cm s 1 ocean topography experiment topex poseidon jason 1 s along track sea level height estimates since january 1993 filtered interannually propagate westward at 4 3 cm s 1 verifying that observed westward propagation is about double that expected including the effect of the mean california current on the rossby wave propagation does not explain the discrepancy but rather slightly increases it if variations in the ocean depth in the calcofi region are also taken into account the westward propagation is still only about one half that observed standard theory therefore does not explain the observations because of the westward propagation interannual variations in alongshore ge

onshore to offshore anatomy of a late quaternary source to sink system po plain adriatic sea italy abstract in understanding the evolution of siliciclastic systems late quaternary analogs may enable reliable predictive models of facies tract architecture the po plain adriatic sea system where a wealth of research has been conducted during the last 20 years represents one of the most intensively investigated late quaternary successions with the aid of a chronologically well constrained stratigraphy paleoenvironmental evolution is tracked for the first time from fluvial to deep marine realms over 1000 km in length vertical stacking trends onshore and stratal terminations offshore are the key observations that allow identification of surfaces with sequence stratigraphic significance systems tract boundaries in the distinct segments of the system recurring motifs in stratigraphic architecture showing tight coupling of sedimentary responses among source area catchment basin and coastal and marine depocenters reveal a cyclicity driven by glacio eustatic fluctuations in the milankovitch band due to high rates of subsidence middle pleistocene forced regressive systems tracts are exceptionally expanded and the mis5e mis2 interval late pleistocene preserves a nearly continuous record of fourth order 100 kyr stepwise sea level fall the stratigraphic architecture of last glacial maximum deposits highlights the genetic relations between channel belt development pedogenesis and sediment delivery to the lowstand delta through narrow incised valley conduits the late glacial holocene succession records the last episode of sea level rise and stabilization through well developed patterns of shoreline transgression regression tst hst that can be readily traced updip from offshore to onshore locations architectural styles across the whole system reflect a dominance of allogenic forcing in the tst as opposed to a predominantly autogenic control on stratigraphic development in the hst external drivers of facies architecture were also effective on millennial timescales the younger dryas cold reversal which marks the transgressive surface on land records a short lived episode of subaqueous progradation that is correlative onshore with widespread immature paleosol development and small sized channel belt formation quantitative assessment of sediment budgets over different time intervals requires precise positioning of the key bounding surfaces based on this approach we outline for the first time over the entire po adriatic basin an estimate of the sediment volumes stored in each systems tract

early diagenesis of redox sensitive trace metals in the peru upwelling area response to enso related oxygen fluctuations in the water column pore water and solid phase data for redox sensitive metals mn fe v mo and u were collected on a transect across the peru upwelling area 11 s at water depths between 78 and 2025 m and bottom water oxygen concentrations ranging from 0 to 93 m by comparing authigenic mass accumulation rates and diffusive benthic fluxes we evaluate the respective mechanisms of trace metal accumulation retention and remobilization across the oxygen minimum zone omz and with respect to oxygen fluctuations in the water column related to the el nino southern oscillation enso sediments within the permanent omz are characterized by diffusive uptake and authigenic fixation of u v and mo as well as diffusive loss of mn and fe across the benthic boundary some of the dissolved mn and fe in the water column re precipitate at the oxycline and shuttle particle reactive trace metals to the sediment surface at the lower and upper boundary of the omz at the lower boundary pore waters are not sufficiently sulfidic as to enable an efficient authigenic v and mo fixation as a consequence sediments below the omz are preferentially enriched in u which is delivered via both in situ pre cipitation and lateral supply of u rich phosphorites from further upslope trace metal cycling on the peruvian shelf is strongly affected by enso related oxygen fluctuations in bottom water during periods of shelf oxygenation surface sediments receive particulate v and mo with metal oxyhydr oxides that derive from both terrigenous sources and precipitation at the retreating oxycline after the recurrence of anoxic conditions metal oxyhydr oxides are reductively dissolved and the hereby liberated v and mo are authigenically removed this alternation between supply of particle reactive trace metals during oxic periods and fixation during anoxic periods leads to a preferential accumulation of v and mo compared to u on the peruvian shelf the decoupling of v mo and u accumulation is further accentuated by the varying susceptibility to re oxidation of the different authigenic metal phases while authigenic u and v are readily re oxidized and recycled during periods of shelf oxygenation the sequestration of mo by authigenic pyrite is favored by the transient occurrence of oxidizing conditions our findings reveal that redox sensitive trace metals respond in specific manner to short term oxygen fluctuations in the water column the relative enrichment patterns identified might be useful for the reconstruction of past omz extension and large scale redox oscillations in the geological record

compression of a multiphase mantle assemblage effects of undesirable stress and stress annealing on the iron spin state crossover in ferropericlase

stratigraphic paleoecology bathymetric signatures and sequence overprint of mollusk associations from upper quaternary sequences of the po plain italy upper quaternary sequences of the po plain italy were used to assess the informative strength and sequence stratigraphic overprint of quantitative paleoecological patterns three densely sampled cores 89 samples 98 genera 23 280 specimens dominated by extant mollusk species with known environmental distributions were analyzed with detrended correspondence analysis dca the dca scores calibrated using extant genera provided outstanding estimates of bathymetry 3 m and related environmental parameters depth related successions of mollusk associations delineated by using dca were consistent with independent sequence stratigraphic interpretations and yielded insights inaccessible via routine techniques e g depth estimates for maximum flooding surfaces the dca ordination demonstrates the severity of the sequence stratigraphic overprint samples are highly uniform taxonomically during late transgressive systems tracts and highly variable during the following highstand systems tracts when analyzed across comparable systems tracts similar species associations repeat during the last and current interglacial cycles suggesting that po plain mollusk associations have remained remarkably stable over the past 125 k y the results are consistent with the bathymetric interpretation of the dc axis 1 postulated previously for the paleozoic fossil record demonstrate the sequence stratigraphic overprint of paleoecological patterns predicted by computer modeling and illustrate the utility of quantitative paleoecological patterns in augmenting sequence stratigraphic interpretations

stratigraphic paleoecology of the valle di manche section crotone basin italy a candidate gssp of the middle pleistocene abstract macro benthic assemblages from the lower to middle pleistocene of the valle di manche vdm section crotone basin southern italy were used to assess the value of merging paleoecological quantitative patterns into a sequence stratigraphic framework two way cluster and detrended correspondence dca analyses were applied to the macrofossil data matrix comprising 22 samples 157 species and 5761 specimens specifically two way cluster analysis allowed for the characterization of five shelf related biofacies and four sub biofacies along section biofacies change along the vdm generally supported previous sequence stratigraphic interpretations and suggests that faunal turnover is the result of habitat tracking dca stratigraphic curves dc1 sample scores calibrated to the depth preferences of extant species provided quantitative estimates of bathymetry and the assessment of related parameters e g grain size sedimentation turbidity when plotted stratigraphically calibrated dc1 scores highlight the magnitude of relative sea level fluctuations at the scale of the section as well as individual sequences and systems tracts additionally dca derived paleobathymetric trends track the oscillations of the 18 o record indicative of global sea level change based on this comparison it is held that macro benthic assemblages once supported by a robust statistical interpretation can be employed successfully as a proxy for 18 o depicting the variability in local water depths the potential of this approach is especially high for studies in shallow water depositional settings where dependable 18 o data are typically difficult to obtain

long term accumulation of carbonate shells reflects a 100 fold drop in loss rate shells in modern seabeds can be thousands of years old far older than would be extrapolated from the rapid rates of shell loss detected in short term experiments an extensive shelldating program on the southern california usa shelf permits rigorous modeling of the dynamics of shell loss in the mixed layer discriminating the key rates of carbonate disintegration and sequestration for the first time we find that bivalve shells experience an initially high disintegration rate l 1 decadal half lives but shift abruptly within the first 500 yr postmortem to a 100 fold lower disintegration rate l 2 millennial half lives at sequestration rate t burial and or diagenetic stabilization this drop permits accrual of a long tail of very old shells even when sequestration is very slow and allows only a minority 1 of all shells to survive the first phase these high rates of disintegration and low rates of sequestration are consistent with independent measures of high carbonate loss and slow sedimentation on this shelf our two phase model thus reveals significant spatial and temporal partitioning of car bonate loss rates within the mixed layer and shows how shell age frequency distributions can yield rigorous and realistic estimates of carbonate recycling on geological time scales

sequence stratigraphy and the resolution of the fossil record sequence stratigraphy a major theoretical achievement of earth sciences integrates facies associations and stratal architecture within a chronological framework of the geological record the sequence stratigraphic model implies that sediment supply to the basin preservation potential of individual horizons and the resolution of paleontological data co vary with base level fluctuations especially for siliciclastic depositional systems using holocene transgressive regressive successions of the po plain italy we assessed the model s hypotheses by analyzing 249 marine mollusk shells dated individually using 14 c calibrated amino acid racemization methods as postulated by the model the temporal resolution of the fossil record frequency of depositional events and net accumulation rates decreased upward concomitantly through the transgressive systems tract reaching minima in the condensed section maximum flooding zone the reverse trend with increasingly frequent thicker and less time averaged beds was observed throughout the overlying highstand systems tract the results quantify the postulated sequence stratigraphic asymmetry in temporal resolution of the fossil and sedimentary records

palaeoecology taphonomy and preservation of a lower pliocene shell bed coquina from a volcanic oceanic island santa maria island azores abstract massive fossil shell accumulations require particular conditions to be formed and may provide valuable insights into the sedimentary environments favouring such concentrations shallow water shell beds appear to be particularly rare on reefless volcanic oceanic islands on account of narrow steep and highly energetic insular shelves where the potential for preservation is limited the occurrence of an exceptional coquina pedra que pica within the miocene pliocene deposits of santa maria island azores therefore provides a rare opportunity to understand the conditions that led to the formation and preservation of a massive shell bed at mid ocean insular setting this study provides a detailed analysis regarding a 10 11 m thick bivalve dominated fossil assemblage exposed at pedra que pica on santa maria island in the azores integration of taphonomical palaeoecological and sedimentological observations are used to reconstruct the genesis of the coquina bed and related events and to discuss why such exceptional sedimentary bodies are so rare on shelves around reefless volcanic oceanic islands the sequence at pedra que pica demonstrates a complex succession of sedimentary environments in response to the drowning of an existing coastline during a period of rapid sea level rise the pedra que pica shell bed incorporates storm related materials and possible debris falls that originated nearby in a shallow and highly productive carbonate factory deposition took place below fair weather wave base at around 50 m depth as inferred from the overlying volcanic succession the preservation of this coquina was favoured by deposition on a platform laterally protected by a rocky spur combined with rapid burial by water settled volcanic tuffs and subsequent volcanic effusive sequences the recent exhumation of the deposit is the result of island uplift and subsequent erosion

where does the time go mixing and the depth dependent distribution of fossil ages knowing how time is distributed within a fossil record is fundamental to paleobiology many efforts to quantify temporal resolution have estimated rates of specimen decay from the frequency distribution of specimen ages in near surface assemblages the implicit assumption has been that the shape of these distributions is invariant with depth and thus decay rate estimates reflect the temporal resolution of a fossil record s deeper layers as well here we present a new model that predicts how age frequency distribution shape will change with depth due to the interplay of burial mixing and decay unlike previous models this model distinguishes the dimensions of time specimen age and depth and predicts a right to left shift in age frequency distribution skewness and a decrease in kurtosis with increasing stratigraphic depth we find support for these predictions with the accelerator mass spectrometry 14c dating of 80 small mammal specimens spanning the quaternary fossil record of homestead cave utah united states our study indicates 1 that previous models overestimate rates of specimen decay 2 that the acuity of ecological information captured in near surface assemblages is higher than previously inferred and 3 how time averaging can alter the apparent dynamics of biodiversity over time we thereby offer a new quantitative framework to account for time averaging to merge modern and paleontological archives and to place ecological systems within the context of their past dynamics

a decline in molluscan carbonate production driven by the loss of vegetated habitats encoded in the holocene sedimentary record of the gulf of trieste carbonate sediments in non vegetated habitats on the north east adriatic shelf are dominated by shells of molluscs however the rate of carbonate molluscan production prior to the 20th century eutrophication and overfishing on this and other shelves remains unknown because i monitoring of ecosystems prior to the 20th century was scarce and ii ecosystem history inferred from cores is masked by condensation and mixing here based on geochronological dating of four bivalve species carbonate production during the holocene is assessed in the gulf of trieste where algal and seagrass habitats underwent a major decline during the 20th century assemblages of sand dwelling gouldia minima and opportunistic corbula gibba are time averaged to 1000 years and corbula gibba shells are older by 2000 years than shells of co occurring gouldia minima this age difference is driven by temporally disjunct production of two species coupled with decimetre scale mixing stratigraphic unmixing shows that corbula gibba declined in abundance during the highstand phase and increased again during the 20th century in contrast one of the major contributors to carbonate sands gouldia minima increased in abundance during the highstand phase but declined to almost zero abundance over the past two centuries gouldia minima and herbivorous gastropods associated with macroalgae or seagrasses are abundant in the top core increments but are rarely alive although gouldia minima is not limited to vegetated habitats it is abundant in such habitats elsewhere in the mediterranean sea this live dead mismatch reflects the difference between highstand baseline communities with soft bottom vegetated zones and hard bottom arca beds and present day oligophotic communities with organic loving species therefore the decline in light penetration and the loss of vegetated habitats with high molluscan production traces back to the 19th century more than 50 of the shells on the sea floor in the gulf of trieste reflect inactive production that was sourced by heterozoan carbonate factory in algal or seagrass habitats

fluvial responses to climate and sea level change a review and look forward summary fluvial landforms and deposits provide one of the most readily studied quaternary continental records and alluvial strata represent an important component in most ancient continental interior and continental margin successions moreover studies of the long term dynamics of fluvial systems and their responses to external or allogenic controls can play important roles in research concerning both global change and sequence stratigraphy as well as in studies of the dynamic interactions between tectonic activity and surface processes these themes were energized in the final decades of the twentieth century and may become increasingly important in the first decades of this millennium this review paper provides a historical perspective on the development of ideas in the fields of geomorphology quaternary geology vs sedimentary geology and then summarizes key processes that operate to produce alluvial stratigraphic records over time scales of 103 106 years of particular interest are changes in discharge regimes sediment supply and sediment storage en route from source terrains to sedimentary basins as well as changes in sea level and the concept of accommodation late quaternary stratigraphic records from the loire france mississippi usa colorado texas usa and rhine meuse the netherlands rivers are used to illustrate the influences of climate change on continental interior rivers as well as the influence of interacting climate and sea level change on continental margin systems the paper concludes with a look forward to a bright future for studies of fluvial response to climate and sea level change at present empirical field based research on fluvial response to climate and sea level change lags behind a the global change community s understanding of the magnitude and frequency of climate and sea level change b the sequence stratigraphic community s desire to interpret climate and especially sea level change as forcing mechanisms and c the modelling community s ability to generate numerical and physical models of surface processes and their stratigraphic results a major challenge for the future is to catch up which will require the development of more detailed and sophisticated quaternary stratigraphic sedimentological and geochronological frameworks in a variety of continental interior and continental margin settings there is a particular need for studies that seek to document fluvial responses to allogenic forcing over both shorter 102 103 years and longer 104 106 years time scales than has commonly been the case to date as well as in larger river systems from source to sink studies of quaternary systems in depositional basin settings are especially critical because they can provide realistic analogues for interpretation of the pre quaternary rock record

quantitative bathymetric models for late quaternary transgressive regressive cycles of the po plain italy abstractin marine settings quantitative bathymetric models can be developed using various water depth proxies including epibiont distribution sedimentologic features and the distribution of benthic taxa in time and space here the late quaternary bathymetric history of the po coastal plain italy has been reconstructed using mollusk samples from a network of 16 cores multiple analytical approaches have been applied in a comparative fashion a direct ordination approach was used to estimate sample bathymetry using weighted averaging of genera with known preferred depth weighted averaging carries an advantage of analytical simplicity and produces direct ordination models expressed in environmentally meaningful units indirect ordination methods based on depth estimates developed using posteriori calibrated ordination strategies correspondence and detrended correspondence analysis calibrated against present day bathymetric data yielded results consistent with weighted averaging regardless of the

equations of state of the high pressure phases of a natural peridotite and implications for the earth s lower mantle abstract to help determine the chemical composition of the earth s mantle we characterised the high pressure mineral assemblage of an undepleted natural peridotite thought to be representative of the earth s upper mantle to 107 gpa using high resolution x ray diffraction at lower mantle conditions the peridotite transforms to the assemblage 76 2 mg0 88fe0 052 fe0 013 al0 12si0 94 o3 orthorhombic perovskite by volume at zero pressure 17 2 mg0 80fe0 20 o magnesiowustite and 7 1 casio3 perovskite the measured room temperature bulk properties of this high pressure assemblage together with a range of estimates of thermal properties of the constituent minerals appear to be inconsistent with seismological constraints on the density and bulk modulus of the lower mantle our results suggest that the lower mantle differs in bulk composition e g richer in iron mg 0 85 from current estimates for the upper mantle requiring some amount of segregation between the upper and lower mantle over geological history

a review of the shelf slope circulation along australia s southern shelves cape leeuwin to portland abstract a review is presented of the ocean circulation along australia s southern shelves and slope uniquely the long zonal shelf is subject to an equatorward sverdrup transport that gives rise to the flinders current a small sister to the world s major western boundary currents the flinders current is strongest near the 600 m isobath where the current speeds can reach 20 cm s and the bottom boundary layer is upwelling favourable it is larger in the west but likely intermittent in both space and time due to possibly opposing winds thermohaline circulation and mesoscale eddies the flinders current may be important to deep upwelling within the ubiquitous canyons of the region during winter the leeuwin current and local winds act to drive eastward currents that average up to 20 30 cm s the currents associated with the intense coastal trapped wave field 6 12 day band are of order 25 30 cm s and can peak at 80 90 cm s wintertime winds and cooling also lead to downwelling to depths of 200 m or more and the formation of dense coastal water within the great australian bight and the south australian sea within the great australian bight the thermohaline circulation associated with this dense water is unknown but may enhance the eastward shelf edge south australian current the dense salty water formed within spencer gulf is known to cascade as a gravity current to depths of 200 m off kangaroo island this dense water outflow and meanders in the shelf circulation also fix the locations of a sequence of quasi permanent mesoscale eddies between the eyre peninsula and portland during summer the average coastal winds reverse and surface heating leads to the formation of warm water in the western great australian bight and the south australian sea no significant exchange of shelf water and gulf water appears to occur due to the presence of a dense nutrient rich sub surface pool that is upwelled off kangaroo island the winds lead to weak average coastal currents increasing evidence suggests that el nino events 4 7 year period can have a major impact on the winter and summer circulation these events propagate from the pacific ocean and around the shelf slope wave guide of west australia and into the great australian bight during winter el nino events the average shelf currents may be largely shut down during summer the thermocline may be raised by up to 150 m the nature and role of tides and surface waves is also discussed along with uncertainties in the general circulation and future research

low frequency baroclinic waves off coastal boundaries abstract the behavior of low frequency baroclinic rossby wave motion in the vicinity of coastal boundaries is investigated using linearized modulated wave theory in a stratified constant depth equatorial plane ocean a primary objective is to obtain an equation that describes large scale low frequency pressure fluctuations along variable geometry ocean boundaries at all latitudes for use in the analysis of coastal sea level observations both eastern and western boundaries are considered and the effect of direct wind stress forcing at the coast is included but our major interest concerns the response along eastern ocean boundaries to incident baroclinic equatorial kelvin waves in that case for an incident wave at a fixed frequency a critical latitude with coriolis parameter f fc exists such that for f fc the waves are coastally trapped the magnitude of fc depends on and on the angle of the coastline

pre drill predictions versus post drill results use of sequence stratigraphic methods in reduction of exploration risk sarawak deep water blocks malaysia abstract limited well control great distances from age equivalent producing fields and a largely unknown stratigraphy necessitated use of sequence stratigraphic methods to assess exploration risk associated with reservoir source and seal distribution in the mobil operated deep water blocks of sarawak malaysia these methods allowed predictions to be made and reservoir risks to be halved in each of the locations drilled in 1995 predictions regarding reservoir and stratigraphy proved correct as the mulu 1 and bako 1 wells penetrated numerous high quality thick sandstone reservoirs in the middle to lower miocene section shallow marine sandstones dominate the vertical succession in both wells with characteristic aggradational upward coarsening log motifs cores display classic wave generated stratification and hummocky cross bedding evidence such as marginal marine to neritic microfauna in cuttings of both wells supports these interpretations lack of hydrocarbon charge in the two wells may be due to their position relative to coaly hydrocarbon source beds these prospects have high trap and seal integrity being well defined on seismics as high relief horst blocks covered by a very thick shale prone section the mulu 1 well for example is located at least 20 30 km down stratigraphic dip from mapped coeval lower coastal plain deposits amplitude anomalies on the flank of the mulu horst are probably derived from transported organics buried in deep plio pleistocene kitchens in the northwest portion of the mobil blocks remaining potential of mapped prospects is high and efforts continue at characterizing the petroleum system of the deep water blocks seismic attribute and interval velocity analyses provide new clues to the location of probable coaly source rocks especially when viewed in their regional and sequence stratigraphic context future work is planned and will serve to reduce risk to acceptable levels and support further drilling in this prospective hydrocarbon province

oxidation during metamorphism of the ordinary chondrites subtle but progressive changes in the compositions and relative abundances of olivine pyroxene and metal with increasing metamorphic grade in equilibrated types 4 6 ordinary chondrites indicate that these meteorites experienced oxidation of metallic fe during heating oxygen fugacities calculated from these mineral assemblages increase with petrologic type the hypothesis of oxidation during chondrite metamorphism differs from a commonly accepted idea that chondritic fe was reduced by graphite the mineralogies of unequilibrated type 3 chondrites do not conform to the progressions in equilibrated chondrites allowing the possibility that fe may first have been reduced through reaction with graphite at the onset of metamorphism although there are conflicting observations supporting both oxidation and reduction in these meteorites as temperatures increased to levels appropriate for types 4 6 chondrites the activity of graphite may have been lowered by its dissolution in taenite and in any case oxygen fugacities appear to have been well within the stability field of graphite precluding its reaction at these temperatures oxidation state was largely controlled by equilibrium between ferromagnesian silicates and metal oxygen fugacities calculated from chondrite mineral equilibria are 2 3 log units below previously reported intrinsic o2 measurements we propose that progressive oxidation during metamorphism was promoted by interaction with small amounts of an oxidizing vapor derived by heating ices originally accreted into the parent asteroids assuming that this vapor was pure h2o the watenrock weight ratio required to account for the observed oxidation of fe in h and l chondrites is very modest less than several per mil progressive oxidation in the metamorphic sequence resulted from different degrees of reaction with such a fluid possibly caused by temperature variations or evolution of the composition of the fluid as it permeated through the body the presence of even minor amounts of a vapor phase during metamorphism affects interpretations of the volatile trace element and oxygen isotopic fractionations observed in ordinary chondrites and inferred to have formed by nebular or parent body processes

scale and structure of time averaging age mixing in terrestrial gastropod assemblages from quaternary eolian deposits of the eastern canary islands abstract quantitative estimates of time averaging age mixing in gastropod shell accumulations from quaternary the late pleistocene and holocene eolian deposits of canary islands were obtained by direct dating of individual gastropods obtained from exceptionally well preserved dune and paleosol shell assemblages a total of 203 shells of the gastropods theba geminata and t arinagae representing 44 samples stratigraphic horizons from 14 sections were dated using amino acid isoleucine epimerization ratios calibrated with 12 radiocarbon dates most samples reveal a substantial variation in shell age that exceeds the error that could be generated by dating imprecision with the mean within sample shell age range of 6670 years and the mean standard deviation of 2920 years even the most conservative approach monte carlo simulations with a non sequential bonferroni correction indicates that at least 25 of samples must have undergone substantial time averaging e g age variations within those samples cannot be explained by dating imprecision alone samples vary in shell age structure including both left skewed 17 out of 44 and right skewed distributions 26 out of 44 as well as age distributions with a highly variable kurtosis dispersion and shape of age distributions of samples do not show any notable correlation with the stratigraphic age of samples suggesting that the structure and scale of temporal mixing is time invariant the statistically significant multi millennial time averaging observed here is consistent with previous studies of shell accumulations from various depositional settings and reinforces the importance of dating numerous specimens per horizon in geochronological studies unlike in the case of marine samples typified by right skewed age distributions attributed to an exponential like shell loss from older age classes many of the samples analyzed here displayed left skewed distributions suggestive of different dynamics of age mixing in marine versus terrestrial shell accumulations