dinoflagellate cyst assemblages as tracers of sea surface conditions in the northern north atlantic arctic and sub arctic seas the new n 677 data base and its application for quantitative palaeoceanographic reconstruction the distribution of dinoflagellate cyst dinocyst assemblages in surface sediment samples from 677 sites of the northern north atlantic arctic and sub arctic seas is discussed with emphasis on the relationships with sea surface parameters including sea ice cover salinity and temperature of the coldest and warmest months difficulties in developing a circum arctic data base include the morphological variation within taxa e g operculodinium centrocarpum islandinium cezare and polykrikos sp which probably relate to phenotypic adaptations to cold and or low salinity environments sparse hydrographical data together with large interannual variations of temperature and salinity in surface waters of arctic seas constitute additional limitations nevertheless the use of the best analogue technique with this new dinocyst data base including 677 samples permits quantitative reconstruction of sea surface conditions at the scale of the northern north atlantic and the arctic domain the error of prediction calculated from modern assemblages is 1 3 ca nd 1 8 c for the temperature of february and august respectively 1 8 for the salinity and 1 5 months yr 1 for the sea ice cover application to late quaternary sequences from the western and eastern subpolar north atlantic labrador sea and barents sea provide reconstructions compatible with those obtained using the previous dinocyst data base n 371 which mainly included modern data from the northern north atlantic copyright 2001 john wiley sons ltd journal of quaternary science

long chain alkenone patterns in the baltic sea an ocean freshwater transition two different patterns of long chain alkenones are found in surficial sediments of the baltic sea which is the largest brackish water body on earth one pattern occurs in surficial sediments from the western baltic sea where surface water salinitiy is in excess of 7 7 psu it corresponds to the pattern produced by the marine coccolithophorid emiliania huxleyi with a suite of c37 di to tetra unsaturated methyl ketones and c38 di and tri unsaturated methyl and ethyl ketones a second pattern resembling that found in lake sediments in lacking c38 methyl ketones and having distinctly higher c37 4 methyl ketone concentrations dominates in surficial sediments of the eastern and northern baltic sea where salinities are lower than 7 7 psu correspondence of sea surface temperature sst estimates from the u37 and u379 indices using marine calibrations with mean sst in the euphotic zone from july august the main haptophyte growth season is poor thus these indices are not applicable as sedimentary thermometers in surficial sediments of the baltic sea the different patterns may either reflect the salinity dependent occurrence of specific alkenone producers or changes in the alkenone biosynthesis due to physiological stress caused by salinity variations furthermore advection of saline and oxygenated north sea water may transport marine algal material characterized by a marine e huxleyi like alkenone pattern into the western baltic sea thus covering the signature of the local alkenone producers with a baltic sea pattern copyright 2000 elsevier science ltd

constraints on the correlation of p and s wave velocity heterogeneity in the mantle from p pp ppp and pkpab traveltimes we investigate the correlation of large scale p and s velocity heterogeneity in the mantle by determining how well 106 000 compressional p pp ppp and pkpab traveltimes can be explained by s wave velocity model s20rts scaled using a depth dependent factor and by a model in which the lateral p velocity variations are different we first assess the assumption that p wave traveltimes can be explained by a model in which lateral p velocity variations p are identical to s velocity variations s in model s20rts for a given depth we project s from s20rts into model s2p using a depth dependent scaling factor r defined as s r z x p we find by grid search that the highest reduction of data variance is obtained when r increases linearly from 1 25 at the surface to 3 0 at the core mantle boundary a comparison of s wave ss and p wave pp traveltimes for identical source receiver pairs also indicates that r increases with depth significantly higher variance reduction is not obtained when r is parametrized with an additional degree of freedom therefore the precise shape of r cannot be constrained by our data p and pp wave traveltime anomalies with respect to the scaled model s2p yield coherent geographic variations this indicates that there are large scale lateral p velocity variations in the mantle that are different from those in model s2p we estimate these variations by inverting p wave traveltime anomalies with respect to model s2p for a degree 12 model of p velocity heterogeneity this model p 12 s 2 p indicates where in the well sampled mantle regions we need to modify model s2p to further improve the fit to the traveltime data anomalies in p12 s 2 p exist throughout the mantle it is therefore not obvious that compositional heterogeneity is prominent in the lower 1000 km of the mantle only as suggested previously low p wave velocities in the upper mantle beneath oceans are the strongest anomalies in p12 s 2 p and explain better the delayed traveltimes of pp wave phases with oceanic surface refection points lower mantle anomalies include high and low p velocity structures beneath eastern asia and north america respectively the high p velocity anomaly in the lower mantle beneath the central pacific is consistent with the assertion made by other researchers that large scale lower mantle upwellings are not purely thermal in origin

albian to santonian carbon isotope excursions and faunal extinctions in the canadian western interior sea recognition of eustatic sea level controls on a forebulge setting abstract the forebulge region of the cretaceous canadian western interior sea cwis was susceptible to subaerial exposure and marine erosion during sea level lowstands the middle albian to santonian record as cored at cold lake east central alberta canada documents numerous disconformities that are expressed in bioclastic concentration horizons and faunal extinctions and turnovers detailed comparison between a newly established 13 c org record measured on bulk sediment at cold lake and a combined 13 c carb reference curve based on the cretaceous english chalk and se france hemipelagic marlstones highlights missing positive and negative 13 c excursions at the cwis forebulge and thus missing sections that precisely corroborate with sequence boundaries disconformable boundaries correlate closely with global sea level lowstands as established for the cretaceous north atlantic suggesting a pronounced eustatic influence on the cwis forebulge setting sequence boundaries occur in the uppermost middle albian lowermost upper albian albian cenomanian boundary cenomanian turonian boundary middle turonian to lower coniacian and uppermost middle santonian each followed by a positive 13 c excursion oceanic anoxic events 1d 2 and 3 are recognized and linked to major faunal and floral assemblage changes of these the albian cenomanian biotic turnover is the most severe in the cwis marked by the total loss of albian benthic foraminifera species causes of this benthic extinction might be linked to a period of anoxia oae 1d during the latest albian followed by sea level controlled basin restriction

sharpness of upper mantle discontinuities determined from high frequency reflections an understanding of the nature of seismic discontinuities in the earth s upper mantle is important for understanding mantle processes in particular the amplitude and sharpness of these discontinuities are critical for assessing models of upper mantle phase changes and chemical layering so far seismic studies aimed at determining the thickness and lateral variability of upper mantle discontinuities have yielded equivocal results particularly for the discontinuity at 410km depth1 2 here we present short period 0 8 2 0 s recordings of upper mantle precursors to the seismic phase p p pkppkp from two south american earthquakes recorded by the 700 station short period array in california our results show that the 410 and 660 km discontinuities beneath the indian ocean are locally simple and sharp corresponding to transi tion zones of 4 km or less these observations pose problems for mineral physics models3 5 which predict a transitional thickness greater than 6 km for the peridotite to spinel phase transition in contrast to the results of long period studies6 7 we observe no short period arrivals from near 520 km depth

size distribution of holocene planktic foraminifer assemblages biogeography ecology and adaptation the size of any organism is influenced by the surrounding ecological conditions in this study we investigate the effects of such factors on the size spectra of planktic foraminiferal assemblages from holocene surface sediments we analyzed assemblages from 69 holocene samples which cover the major physical and chemical gradients of the oceans on a global scale the range of sizes in assemblages triples from the poles to the tropics this general temperature related size increase is interrupted by smaller sizes at temperatures characteristic of the polar and subtropical fronts at 2 c and 17 c respectively as well as in upwelling areas on a regional scale surface water stratification seasonality and primary productivity are highly correlated with the size patterns such environmentally controlled size changes are not only characteristic for entire assemblage but also for the dominant single species

morphological variation of emiliania huxleyi and sea surface salinity morphometric analysis of coccoliths of various coccolithophore species from core top and culture samples has revealed that the morphology of single placoliths can be affected by environmental parameters such as temperature salinity and productivity in this study we have tested the morphological variations of placoliths of emiliania huxleyi the most common coccolithophore species in the modern ocean with respect to environmental gradients we have investigated especially the potential effect of salinity on the morphology as it is known from culture studies that the growth of e huxleyi placoliths is strongly influenced by varying salinities morphometric analysis of about 2150 placoliths from 37 globally distributed core top and plankton samples revealed that the morphology of e huxleyi varies significantly along a sea surface salinity gradient from 33 to 38 morphological parameters such as the mean size of placoliths are used as explaining variables in multiple regression analysis to reconstruct sea surface salinities sss the best model for mean sss yields an r 2 of 0 88 with a standard error of 0 49 whereas statistical models describing surface water temperature or productivity are less reliable and accurate application of the best model to plankton samples allows the prediction of in situsalinitieswithingivenerrorestimates theapplicationofthebestmodeltofossilassemblagesfromthelgm however ismore puzzling paleosalinity reconstructions in the south atlantic the caribbean sea and the subtropical atlantic are in good agreement with the published values 2007 elsevier b v all rights reserved

error analysis of paleosalinity calculations a detailed error analysis is performed for the calculation of open ocean salinity changes from carbonate oxygen 18 proxy data measurement errors are generally negligible however errors due to the goodness of fit of various regressions used in the calculation are significant depending on the method used and on the proxies available error bars 1 for the salinity range from 0 6 to 1 8 in particular expected errors for the midlatitude and tropical salinity differences at the last glacial maximum are around 1 1 to 2 5 the largest errors occur because of the differences between temporal and spatial seawater oxygen 18 salinity relationships and through the use of nonconcurrent temperature measurements methods of improving paleosalinity estimates should focus on eliminating these large sources of uncertainty

paleosalinity confidence limits and future applications error propagation is investigated through the only commonly applied technique for reconstruction of paleosalinity based on oxygen isotope residuals although this technique is known to be fairly inaccurate there remained a need for thorough assessment of confidence limits in a variety of global settings here it is found that a theoretical minimum error bar of between 0 3 and 0 7 applies to paleosalinity estimates and that real life practical limits are rarely better than 0 6 best results are expected in the latitudinal ranges 50 n and 70 s taking care to avoid the sea ice margin confidence intervals at low and mid latitudes including marginal seas are very wide at least 1 8 for the mediterranean and 2 2 for the equatorial atlantic it appears that oxygen isotope distributions are best used in their own right to investigate circulation and advective processes in coupled ocean atmosphere cryosphere models instead of calibrating them to paleosalinity to define restoring boundary conditions however isotope residual based paleosalinity maps from large numbers of regionally averaged studies in the above mentioned latitudinal bands may help in defining initial conditions and first order validation arguments for models

evidence for a sharp 670 km discontinuity as inferred from p to s converted waves the fine structure of the upper mantle discontinuities is investigated using observations of converted waves on short period and broadband seismograms using a stacking technique to analyze the p wave coda of teleseismic records evidence is found for coherent near receiver p to s converted phases generated by the 400 and 670 km discontinuity beneath a number of the stations used in this study variations in travel time slowness and amplitude of these phases as observed among the stacks for stations of the regional seismic test network in the united states and of the network of autonomously recording seismographs in western europe are very likely the expression of upper mantle heterogeneity observations of coherent converted phases from the 400 km discontinuity are fewer in number than of phases converted at the 670 km discontinuity suggesting that the latter is more pronounced some of the seismograms especially of station rscp show extremely high amplitude p to s converted phases from the 670 km discontinuity these seismograms allow a detailed waveform comparison of the converted phase with the direct p phase and present evidence for a sharp 670 km discontinuity

a n s receiver function profile across the variscides and caledonides in sw ireland summary teleseismic receiver functions have been calculated from data of a temporary seismological network of broad band three component stations to investigate the lithospheric and asthenospheric structure across the late caledonian iapetus suture zone isz in southern ireland the stations were deployed during the irish seismological lithospheric experiment isle 2002 3 and straddle the killarney mallow fault zone a remnant of the variscan orogeny and the isz the inferred boundary between the laurentia and eastern avalonia plates fused together during the caledonian orogeny receiver functions from the western part of the network were projected onto the n s varnet 1996 seismic refraction profile extending from the old head of kinsale to galway bay in sw ireland laterally continuous p to s conversions from the moho at delay times of about 3 8 4 1 s are clearly observed and correspond to moho depths of about 29 32 km the moho has a transitional character to the south of the isz synthetic receiver functions calculated from a 2 d velocity model of the previous varnet experiment show moho conversions and multiple crustal phases compatible to those observed in the isle data furthermore p to s conversions from the 660 km discontinuity 66 68 s delay time are well determined at the stations in comparison the conversion from the 410 km discontinuity at about 43 45 s delay time is considerably weaker delay times of stacked receiver functions from the mantle transition zone are in agreement with the standard iasp91 earth model and thus no structural changes are observed across the isz at this depth interval

seismic evidence for accumulated oceanic crust above the 660 km discontinuity beneath southern africa 1 high pressure assemblages of subducted oceanic crust are denser than the normal upper mantle but less dense than the uppermost lower mantle thus subducted oceanic crust may accumulate at the base of the upper mantle direct observational evidence for this hypothesis however remains elusive we present an analysis of a negative polarity shear wave converted from compressional wave at a seismic discontinuity near 570 600 km depth beneath southern africa the negative polarity of the converted phase indicates a 2 2 0 2 s velocity decrease with depth at the seismic discontinuity this velocity reduction is associated however with a low velocity contrast at the 660 km discontinuity the exsolution of ca perovskite in former oceanic crust at depth greater than 600 km and the associated small volume fraction of ringwoodite are plausible explanations for the apparent paradox between the negative velocity discontinuity and the low velocity contrast at the 660 km discontinuity

relationship of the tetra unsaturated c37 alkenone to salinity and temperature implications for paleoproxy applications 1 this study assesses the relationship to salinity and temperature of the levels of the tetra unsaturated 37 carbon methyl alkenone c37 4 in the surface ocean uk 37 a measure of the relative abundances of the c37 2 and the c37 3 alkenones has a well constrained linear relationship to temperature in the open ocean prahl and wakeham 1987 and is a well established technique for estimating past sea surface temperatures in the sediments e g muller et al 1998 unlike the di and tri unsaturated c37 alkenones the temperature response of the tetra unsaturated c37 alkenone is less certain sikes et al 1997 and recent work has suggested a relationship to salinity instead rosell mele 1998 schulz et al 2000 our study examined 106 surface water and sediment trap samples from the atlantic pacific and southern oceans to assess the relationship of the relative abundance of c37 4 to temperature and salinity we also examined the relative unsaturation of c37 2 and c37 3 the parameter uk 37 to the same parameters to place the c37 4 results in context uk 37 has a strong correlation to salinity in the atlantic but the relationship does not hold worldwide whereas uk 37 shows a strong linear relationship to temperatures in all ocean basins as shown in previous calibrations the salinity response in the atlantic does not confirm cause and effect and interpretation of the broader data set suggests any correlation is an artifact of the strong correlation of salinity to temperature in this basin implying salinity has no effect on the unsaturation of the c37 2 or c37 3 alkenones the c37 4 alkenone shows no discernable relationship to temperature or salinity across the several basins even when correlations are restricted to cooler temperatures where the tetra unsaturated alkenone would be expected to be present these results indicate that c37 4 alkenone levels in the open ocean do not reflect either salinity levels or temperature but respond most strongly to some other environmental variable perhaps changes in growth rate light or nutrient supply as suggested by culture studies

crustal thickness estimation beneath the southern central andes at 30 s and 36 s from s wave receiver function analysis summary we have used the s wave receiver function srf technique to investigate the crustal thickness beneath two seismic profiles from the charge project in the southern central andes a previous study employing the p wave receiver function method has observed the moho interface beneath much of the profiles they found however that the amplitude of the p to s conversion was diminished in the western part of the profiles and have attributed it to a reduction of the impedance contrast at the moho due to lower crustal ecologitization with srf we have successfully detected s to p converted waves from the moho as well as possible conversions from other lithospheric boundaries the continental south american crust reaches its maximum thickness of 70 km along 30 s between 70 w and 68 5 w beneath the principal cordillera and the famatina system and becomes thinner towards the sierras pampeanas with a thickness of 40 km negative phases possibly related to the base of the continental and oceanic lithosphere can be recognized in the summation traces at different depths by comparing our results with data obtained from previous investigations we are able to further constrain the thickness of the crust and lithosphere beneath the central andes

anisotropic shear wave velocity structure of the earth s mantle a global model 1 we combine a new large data set of surface wave phase anomalies long period waveforms and body wave travel times to construct a three dimensional model of the anisotropic shear wave velocity in the earth s mantle our modeling approach is improved and more comprehensive compared to our earlier studies and involves the development and implementation of a new spherically symmetric reference model simultaneous inversion for velocity and anisotropy as well as discontinuity topographies and implementation of nonlinear crustal corrections for waveforms a comparison of our new three dimensional model s362ani with two other models derived from comparable data sets but using different techniques reveals persistent features 1 strong 200 km thick high velocity anomalies beneath cratons likely representing the continental lithosphere underlain by weaker fast anomalies extending below 250 km which may represent continental roots 2 weak velocity heterogeneity between 250 and 400 km depths 3 fast anomalies extending horizontally up to 2000 3000 km in the mantle transition zone beneath subduction zones 4 lack of strong long wavelength heterogeneity below 650 km suggesting inhibiting character of the upper mantle lower mantle boundary and 5 slow velocity superplumes beneath the pacific and africa the shear wave radial anisotropy is strongest at 120 km depth in particular beneath the central pacific lateral anisotropic variations appreciably improve the fit to data that are predominantly sensitive to the uppermost and lowermost mantle but not to the waveforms that control the transition zone and midmantle depths tradeoffs between lateral variations in velocity and anisotropy are negligible in the uppermost mantle but noticeable at the bottom of the mantle

reconstructing sea surface temperature and salinity using δ 18 o and alkenone records the oxygen isotope 18o composition of foraminiferal tests from deep sea sediments is widely used as a palaeoclimate proxy but it includes contributions from sea surface temperature global ice volume and local salinity which are difficult to separate recently a new technique for deriving palaeotemperatures has been developed which is based on the abundance ratios of unsaturated alkenones in phytoplankton algae1 2 here we use a combination of oxygen isotope and alkenone records in a deep sea core from the juncture of the arabian sea and the bay of bengal to extract the salinity signal from the former record variations in salinity are related to the balance between evaporation and precipitation3 and are thus a sensitive indicator of climate change our 170 kyr salinity record enables us to reconstruct changes in the indian monsoon over this period considerably extending earlier studies which reached back to 18 kyr ago 4 8 like these previous studies we find that large variations in the monsoon occurred during the transition from the last glacial period to the present interglacial but our results also provide a view of the monsoon throughout the last glacial and demonstrate the potential of this approach for reconstructing palaeosalinity

multiproxy approach for the reconstruction of the glacial ocean surface margo michal kucera antoni rosell mele ralph schneider claire waelbroeck mara weinelt department of geology royal holloway university of london egham tw20 0ex uk icrea and institute of environmental science and technology universitat autonoma de barcelona 08193 bellaterra catalonia spain departement de geologie et oceanographie umr5805 epoc cnrs universite de bordeaux1 33405 talence cedex france laboratoire des sciences du climat et de l environnement laboratoire mixte cnrs cea f 91198 gif sur yvette france institute for geosciences university of kiel olshausen strasse 40 d 24098 kiel germany

alkenones and multiproxy strategies in paleoceanographic studies 1 we assess multiproxy strategies involving alkenone based and other paleoceanographic indicators in an effort to define uncertainties and to advance understanding of past oceanic and climatic changes looking to the future we recommend a parallel strategy of applying proxies to the geologic record while continuously seeking refinements in methods and understanding of mechanisms that control each proxy a multiproxy strategy increases confidence in results and provides oceanographic context for more effective interpretation of processes a combination of proxies allows derivation of additional properties such as upper ocean paleosalinity or paleo pco2 for a more complete view of the oceanographic and climate mechanisms involved in changing earth s environment

frequency dependence of the visibility and depths of mantle seismic discontinuities the visibility and apparent position of a seismic gradient zone depends on the seismic wave frequency at which it is observed which we illustrate by showing how the visibility and depth of the olivine phase transformation 410 km discontinuity change as temperature varies temperature variations change bottomside reflection coefficients by factors of 2 4 in the 0 5 1 0 hz frequency band which can explain spatial variability in short period p 410p observations and the small apparent variability in observed 410 km discontinuity depths discontinuity depths inferred from the time lags of these reflections are also frequency dependent leading to a frequency dependence of estimates of mantle lateral thermal variability based on discontinuity displacements the frequency dependent seismic clapeyron slopes for the olivine phase change we compute are 2 04 mpa k 1 at 0 2 hz and 2 12 mpa k 1 at 0 05 hz and differ significantly from thermodynamic slope for the mg2sio4 end member

secular environmental precursors to early toarcian jurassic extreme climate changes the early toarcian oceanic anoxic event t oae about 183 myr ago was a global event of environmental and carbon cycle perturbations which deeply affected both marine biota and carbonate production nevertheless the long term environmental conditions prevailing prior to the main phase of marine extinction and carbonate production crisis remain poorly understood here we present a similar to 8 myr long record of early pliensbachian middle toarcian environmental changes from the lusitanian basin portugal in order to address the long term paleoclimatic evolution that ultimately led to carbonate production and biotic crises during the t oae paleotemperature estimates derived from the oxygen isotope compositions of well reserved brachiopod shells from two different sections reveal a pronounced similar to 5 degrees c cooling in the late pliensbachian margaritatus spinatum ammonite zones boundary this cooling event is followed by a marked similar to 7 10 degrees c seawater warming in the early toarcian that after a second cooling event in the mid polymorphum zone culminates during the t oae calcium carbonate caco3 contents the amount of nannofossil calcite and the mean size of the major pelagic carbonate producer schizosphaerella all largely covary with paleotemperatures indicating a coupling between climatic conditions and both pelagic and neritic caco3 production furthermore the cooling and warming episodes coincided with major marine regressions and transgressions respectively suggesting that the growth and decay of ice caps may have exerted a strong control on sea level fluctuations throughout the studied time interval this revised chronology of environmental changes shows important similarities with neogene and paleozoic episodes of deglacial black shale formation and thus prompts the reevaluation of ice sheet dynamics as a possible agent of mesozoic events of extinction and organic rich sedimentation c 2010 elsevier b v all rights reserved

discorhabdus as a key coccolith genus for paleoenvironmental reconstructions middle jurassic lusitanian basin biometry and taxonomic status abstract biometric analyses of discorhabdus coccoliths were performed on a set of 29 samples taken from the marl limestone couplets of the reference section of cabo mondego lusitanian basin west portugal late aalenian to early bajocian in age mixture analysis performed on the whole dataset revealed a bimodal length size distribution for the discorhabus pool composed of d striatus and d ignotus the size limit at 5 m proposed here can be reliably used to distinguish both populations but optical characteristics namely birefringence form an additional criterion essential to discriminate the two species an increase in discorhabdus size occurred from the late aalenian to the early bajocian due to a raise in size of the whole discorhabdus pool and in the abundance of d striatus we propose that an increase in discorhabdus size upward in the section is associated with a positive trend in paleoproductivity as supported by the increase of nannofossil accumulation rates as well as the 13 c values of bulk carbonates sampled in the cabo mondego section however the discorhabdus size pattern may also represent a response to sea surface temperature salinity or an evolutionary trend a relative supra regional warming of sea surface water masses is suggested by 18 o values of biogenic carbonates and apatites that were sampled in several mediterranean tethyan settings rise of sea surface temperature may have triggered an increase in the abundances of d striatus as well as of the size of the discorhabdus pool a hypothetical influence of changing sea surface salinity on discorhabdus size or species specific discorhabdus abundances is not supported by our micropaleontological data or by available geochemical data our results also reveal that the increase in discorhabdus size matches the history of calcareous nannofossil turnover radiation diversity and increasing abundances during the middle jurassic

the thermal influence of the subducting slab beneath south america from 410 and 660 km discontinuity observations summary regional seismic network data from deep south american earthquakes to western united states and western european seismic arrays is slant stacked to detect weak near source interactions with upper mantle discontinuities these observations are complemented by an analysis of earlier work by sacks snoke 1977 who observed s to p conversions from deep events to stations in south america and similar observations from 1994 95 events using the banjo and seda networks observations of the depth of the 410 km discontinuity are made beneath central south america in the vicinity of the aseismic region of the subducting nazca plate these results image the 410 km discontinuity over a lateral extent of up to 850 km perpendicular to the slab and over a distance of 2700 km along the length of the slab away from the subducting slab the discontinuity is mainly seen near its global average depth whilst inside the slab there is evidence for its elevation by up to around 60 km but with significant scatter in the data these results are consistent with the presence of a continuous slab through the aseismic region with a thermal anomaly of 900 uc at 350 km depth this value is in good agreement with simple thermal models though our data are too sparse to accurately constrain them sparse observations of the 660 km discontinuity agree with tomographic models suggesting penetration of the lower mantle by the slab in the north but stagnation at the base of the transition zone in the south the geographical distribution of the data however does not allow us to rule out the possibility of slab stagnation at the base of the transition zone in the north these observations together with the presence of deep earthquakes require more complicated thermal models than previously used to explain them possibly including changes in slab dip and age with depth

ocean surface water response to short term climate changes revealed by coccolithophores from the gulf of cadiz ne atlantic and alboran sea w mediterranean the response of coccolithophore assemblages to short term millennial and centennial climatic changes over the last 50 kyr is studied in core m39029 7 from the gulf of cadiz atlantic ocean and core md95 2043 from the alboran sea western mediterranean sea the nannoplankton data are compared with oxygen isotopes u37k sst and other biogeochemical and sedimentological proxies to obtain a new perspective of the paleoceanography and paleoecology of the area during these short term climatic changes coccolithophores indicate that heinrich events he were characterised by the presence of cold low salinity and turbid water masses on both sides of the strait of gibraltar high abundances of the lower photic zone lpz species florisphaera profunda in the gulf of cadiz synchronous with he are interpreted as being an evidence of upper water column stratification on the atlantic side these episodes coincided with input of terrigenous material especially during h2 surface waters during dansgaard oeschger do stadials were also cold and turbid while most of do interstadials were characterised by warm water flora the increase in small placoliths small gephyrocapsa and emiliania huxleyi 4 m which is considered here as a cold water indicator the sharp decrease in large specimens of e huxleyi related to the warming trend in the last deglaciation can be used as a biostratigraphic reference level that marks at least approximately the deglaciation and the beginning of the holocene peaks of f profunda are observed during termination 1 t1 in the alboran sea they are isochronous with the organic rich layer 1 recognised in the western mediterranean in this interval the water column of the region was stratified as a consequence of the global increase in the sea level following the deglaciation quantitative analyses of the coccolithophore assemblage allow us to interpret that coccolithophore production has been higher in the alboran sea than in the gulf of cadiz during the holocene

the 1991 coccolithophore bloom in the central north atlantic 1 optical properties and factors affecting their distribution optical scattering and absorption were measured in the central north atlantic ocean during a mesoscale bloom of the coccolithophorid emiliania huxleyi the chlorophyll specific absorption was similar to previously measured levels for this species in laboratory cultures suspended coccoliths were responsible for 80 of the total backscattering in the center of the bloom and the greatest calcite dependent backscattering was observed just below the base of the mixed layer areal maps of calcite dependent backscattering and reflectance were similar because of the dominance of backscattering over absorption calculated reflectance at 440 and 550 nm reached 24 which is slightly less than what has been observed previously in gulf of maine blooms total scattering b was also calculated as the difference between beam attenuation and absorption the ratio b backscattering divided by total scattering was 0 01 0 02 at 440 and 550 nm at the most turbid parts of the coccolithophore bloom b l 3 m l as total scattering decreased below 1 m l bb increased the behavior of b was compared for coccolith dominated vs chlorophyll dominated waters vertical profiles of calcite dependent scattering combined with satellite remote sensing data were used to assess the factors responsible for vertical transport of calcite the subsurface peak in calcite dependent scattering did not result from detached coccoliths sinking but resulted either from plated coccolithophores sinking and then detaching their plates or from deep coccolithophores producing and detaching their plates in situ

paleo sea surface salinities in the low latitude atlantic the δ18o record of globigerinoides ruber white on the basis of the comparison of 18o values of globigerinoides ruber white 18og ruber from modern sediments and measured sea surface temperatures sst and salinity sss 18og ruber values most clearly record summer sst and sss of the uppermost 50 m of water in the low latitude atlantic a new transfer equation is presented for estimating local summer paleo sss at 0 50 m depth using 18og ruber paleo sst and the global 18o ice effect of sea water with the standard error reaching 0 72 0 77 sss the equation was applied to a 35 kyr long 18og ruber record and paleo sst estimates based on planktonic foraminiferal assemblages to reconstruct the paleo sss changes along the east atlantic margin off the northwest sahara the resulting local sss show a general increase by 0 3 1 4 during the last glacial maximum lgm and large parts of glacial termination i suggesting a general increase in the upwelling of the highly saline north atlantic central water and or a reduced lateral advection of less saline canary current water two short salinity lows up to 0 35 less than today during and after the lgm are coeval with the heinrich meltwater events 1 and 2 in the north atlantic indicating the breakdown of coastal upwelling and meltwater advection from the north both events are followed by an extreme sss maximum 38 15 along with the restoration of the salinity conveyor belt at 9 0 5 5 ka the salinity minimum up to 0 65 less than today reflects the continental runoff linked to the phase of strong north saharan humidity during the early holocene climatic optimum

analysis of nonlinear internal waves observed by landsat thematic mapper in this work we test the compatibility between the theoretical parameters of a nonlinear wave model and the quantitative information that one can deduce from satellite derive0 data the theoretical parameters are obtained by applying an inverse problem to the solution of the cauchy problem for the korteweg de vries equation our results are applied to the case of internal wave patterns elaborated from two different satellite sensors at the south of messina the thematic mapper and at the north of messina the synthetic aperture radar

circumpolar transport of a volcanic cloud from hekla iceland 1 hekla volcano iceland erupted on 17 august 1980 and emplaced a sulfur dioxide so2 cloud into the north polar stratosphere at a maximum altitude of 15 km the so2 is tracked using satellite data from the ultraviolet uv nimbus 7 total ozone mapping spectrometer n7 toms and the infrared ir high resolution infrared radiation sounder hirs 2 on the noaa tiros operational vertical sounder tovs platform the eruption emitted 0 5 0 7 tg of so2 which later split into three distinct clouds one of which circled the north pole at the perimeter of an atypically persistent arctic cyclone for six days impacting airspace on three continents separate clouds drifted across eastern russia alaska and canada maximum so2 columns derived from toms and hirs 2 accurately define the volcanic cloud s path and fit trajectories produced by the noaa hybrid single particle lagrangian integrated trajectory hysplit model providing confidence in the model when combined with the so2 measurements trajectory altitudes derived from hysplit provide robust estimates of the altitudes of the so2 clouds 8 15 km which would be elusive using either the satellite data or the trajectory model in isolation near coincident spectrally discrete uv and ir retrievals are compared in the volcanic cloud and indicate good agreement between toms and hirs 2 so2 columns for pixels with similar viewing geometry hekla eruptions which follow a pattern of early explosive venting of volcanic gases with significant stratospheric injection could play a role in promoting arctic ozone loss depending on the phase of the north atlantic oscillation during the eruption

the structure and sharpness of mg fe 2sio4 phase transformations in the transition zone abstract to calculate accurately the pressure interval and mineral proportions i e yields across the olivine to wadsleyite and wadsleyite to ringwoodite transformations requires a detailed knowledge of the non ideality of fe mg mixing in these mg fe 2 sio 4 solid solutions in order to constrain the activity composition relations that describe non ideal mixing fe mg partitioning experiments have been conducted between magnesiowustite and mg fe 2 sio 4 olivine wadsleyite and ringwoodite as a function of pressure at 1400 c using known activity composition relations for magnesiowustite the corresponding relations for the three polymorphs were determined from the partitioning data in all experiments the presence of metallic iron ensured redox conditions compatible with the earth s transition zone the non ideality of the mg fe 2 sio 4 solid solutions was found to decrease in the order w wadsleyite femg w ringwoodite femg w olivine femg these partitioning data were used along with published phase equilibria measurements for the mg 2 sio 4 and fe 2 sio 4 end member transformations to produce an internally consistent thermodynamic model for the mg 2 sio 4 fe 2 sio 4 system at 1400 c using this model the pressure interval of the olivine to wadsleyite transformation is calculated to be significantly smaller than previous determinations by combining these results with fe mg partitioning data for garnet the widths of transition zone phase transformations in a peridotite composition were calculated the olivine to wadsleyite transformation at 1400 c in dry peridotite was found to occur over a pressure interval equivalent to approximately 6 km depth and the mineral yields were found to vary almost linearly with depth across the transformation this transformation is likely to be even sharper at higher temperatures or could be significantly broader in wet mantle or in regions with a significant vertical component of mantle flow the entire range of estimated widths for the 410 km discontinuity 4 35 km could therefore be explained by the olivine to wadsleyite transformation in a peridotite composition over a range of quite plausible mantle temperatures and h 2 o contents the wadsleyite to ringwoodite transformation in peridotite mantle was calculated to take place over an interval of 20 km at 1400 c this transformation yield was also found to be near linear

palaeoceanographic differences of early late aptian black shale events in the vocontian basin se france abstract a high resolution study focussing on the distribution of calcareous nannofossils and carbon isotopes was carried out to improve the understanding of mid cretaceous black shale formation the studied interval of the early late aptian is characterized by two major black shale couplets the niveau noire 4 nn4 and niveau noire calcaire 2 nnc2 of the serre chaitieu section in the vocontian basin se france breheret 1997 this interval occurs within a long term negative carbon isotope excursion of 1 5 following the early aptian oceanic anoxic event 1a oae1a in contrast to the local nn4 black shales the black shales of nnc2 are of regional significance and occur at the end of the major negative carbon isotope excursion of the early late aptian time equivalent black shales are suggested to be coeval with black shales found in the western tethys and atlantic ocean herrle et al 2004 calcareous nannofossil analyses and carbon isotopes indicate higher surface water productivity mesotrophic warmer surface water and higher sea level during the formation of the nn4 black shales in contrast the formation of the nnc2 black shales took place during a cooler phase lower surface water productivity and lower sea level a sea level fall may cause a restriction of water mass exchange between the open marine western tethys and the vocontian basin this resulted in a longer residence time of the bottom water decreased ventilation and less mixing of surface waters and thus enhanced preservation of organic matter at the sea floor our results indicate that the black shale formation of nn4 and nnc2 was caused by different processes such as increased surface water productivity and enhanced preservation of organic matter at the sea floor thus we emphasize the role of different forcing factors which control the formation of local and regional black shales the most important factors are sea level fluctuations increasing productivity and changes in precipitation and evaporation rates

global calibration of gephyrocapsa coccolith abundance in holocene sediments for paleotemperature assessment 1 a global sea surface temperature calibration based on the relative abundance of different morphotypes within the coccolithophore genus gephyrocapsa in holocene deep sea sediments is presented there is evidence suggesting that absolute sea surface temperature for a given location can be calculated from the relative abundance of gephyrocapsa morphotypes in sediment samples with a standard error comparable to temperature estimates derived from other temperature proxies such as planktic foraminifera transfer functions a total of 110 holocene sediment samples were selected from the pacific indian and atlantic oceans covering a mean sea surface temperature gradient from 13 6 to 29 3 c standard multiple linear regression analyses were applied to this data set linking the relative abundance of gephyrocapsa morphotypes to sea surface temperature the best model revealed an r2 of 0 83 with a standard residual error of 1 78 c for the estimation of mean sea surface temperature this new proxy provides a unique opportunity for the reconstruction of paleotemperatures with a very small amount of sample material due to the minute size of coccoliths permitting examination of thinly laminated sediments e g a pinhead of material from laminated sediments for the reconstruction of annual sea surface temperature variations such fine scale resolution is currently not possible with any other proxy application of this new paleotemperature proxy may allow new paleoenvironmental interpretations in the late quaternary period and discrepancies between the different currently used paleotemperature proxies might be resolved

modeling water isotopologues during the last glacial implications for quantitative paleosalinity reconstruction quantitative paleosalinity reconstructions with reasonable uncertainties remain a challenge in paleoceanography in this study we focus on stable isotope based methods 18o and 2h to derive paleosalinity we use the water isotopes enabled fully coupled atmosphere ocean vegetation land surface three dimensional model of intermediate complexity iloveclim to simulate the climate and water isotopes during the last glacial maximum lgm and heinrich event 1 we investigate how the isotopes in water can be used as reliable proxies to quantitatively reconstruct past changes in seawater salinity our results demonstrate that a quantitative salinity reconstruction during glacial conditions based on present day regional 18o salinity relationships can lead to considerable errors up to 25 g kg in certain regions however we show that these eventual uncertainties on paleosalinity reconstruction can be reduced by allowing for model derived regional 18o salinity relationships to vary through time our results indicate a rather stable dependence between 2h and 18o in surface seawater during the lgm this suggest that quantitative reconstruction of salinity based on the 2h measurement of alkenones 2ha might be possible if the slope and the intercept of the regression between the fractionation factor 2ha 2hsw and salinity can be sufficiently tightly constrained in open ocean conditions we confirm that pairing water isotopologues has a strong potential to reduce uncertainties on quantitative paleosalinity reconstructions also under glacial boundary conditions

biometry of emiliania huxleyi and its biostratigraphic significance in the eastern north atlantic ocean and western mediterranean sea in the last 20 000 years abstract a detailed biometric study of coccoliths of emiliania huxleyi has been performed on 34 samples from three sediment cores of the north atlantic ocean and the western mediterranean sea su90 08 m39029 7 and md95 2043 all three cores contain the last glacial interglacial transition marine isotopic stages 1 2 enabling us to study in detail the morphology of this taxon during this period of change one hundred coccoliths of e huxleyi were randomly chosen in each sample distal shield length and width measurements were performed on each of the individuals selected the data show that e huxleyi specimens larger than 4 m are frequent in glacial samples and that these larger forms decreased sharply in abundance during the deglaciation and holocene smaller forms are more abundant in this latter group of samples the decrease in larger forms seems to be time transgressive since it is recorded between 12 and 11 kyr cal bp in southern locations alboran sea and gulf of cadiz and around 8 4 kyr cal bp in the central north atlantic scanning electron microscope analyses indicated that the two forms have the same degree of calcification and hence this parameter should not be used in taxonomic classifications we suggest that the larger coccoliths belong to a cold water variety of e huxleyi which can be distinguished from the small coccolith variety in light microscope analyses by its distal shield length the decrease in the abundance of this larger variety during the deglaciation period could be used as a biostratigraphic event in the north atlantic and mediterranean areas

calcareous plankton response to orbital and millennial scale climate changes across the middle pleistocene in the western mediterranean abstract the paleoenvironmental conditions through mis 15 9 at the mediterranean ocean drilling program odp site 975 were interpreted by high resolution study of calcareous plankton assemblages compared with available 18o and 13c records and high resolution paleoclimate proxies from the atlantic ocean sea surface temperatures ssts have been estimated from planktonic foraminiferal assemblages using the artificial neural networks method calcareous plankton varied dominantly on a glacial interglacial scale as testified by the sst record foraminiferal diversity total coccolith abundance and changes in warm water calcareous nannofossil taxa a general increase in foraminiferal diversity and of total coccolith abundance is observed during interglacials warmest ssts are reached during mis 11 while mis 12 and mis 10 represent the coldest intervals of the studied record during mis 12 one of the most extreme glacials of the last million years occurrence of globorotalia inflata and of neogloboquadrinids indicates a shoaling of the interface between atlantic inflowing and mediterranean outflowing waters among calcareous nannofossils the distribution of gephyrocapsa margereli gephyrocapsa muellerae 4 m also supports a reduced atlantic mediterranean exchange during mis 12 superimposed on glacial interglacial variability six short term coolings are recognized during mis 12 and 10 which appear comparable in their distribution and amplitude to the heinrich type events documented in the atlantic ocean in the same interval during these h type events neogloboquadrina pachyderma s and g margereli g muellerae 4 m increase as a response to the enhanced inflow of cold atlantic water into the mediterranean via the strait of gibraltar mediterranean surface water hydrography appears to have been most severely affected at termination v during the h type event ht4 possibly as a response to a large volume of atlantic meltwater inflow via the strait of gibraltar and or to freshwater terrigenous input deriving from local mountain glaciers three additional sst coolings are recorded through mis 14 16 but these are not well correlated with heinrich type events documented in the atlantic ocean in the same interval during these cooling episodes only the subpolar turborotalita quinqueloba increases these results highlight the sensitive response of the mediterranean basin to millennial scale climate variations related to northern hemisphere ice sheet instability and support the hypothesis that the tight connection between high latitude climate dynamics and mediterranean sea surface water features can be traced through the middle pleistocene

seismic waves converted from velocity gradient anomalies in the earth s upper mantle summary modelling of elastic wave propagation in 1 d structures is frequently performed using reflectivity techniques in which the earth s velocity profile is approximated by stacks of homogeneous layers the complete reflection transmission r t response of a zone with arbitrary 1 d depth variation including both gradients and discontinuities in material properties can however be calculated using invariant embedding techniques results from earlier studies are here extended to derive exact expressions for r t matrices in arbitrary 1 d anisotropic media using a form of born approxi mation valid for thin scatterers and which does not assume small perturbations in material properties the r t matrices are solutions to a system of non linear ordinary differential equations of ricatti type and may be manipulated using standard r t matrix algebra in an equivalent description the wavefield within the heterogeneous zone is considered in terms of depth dependent contributions from up and downgoing waves propagating within the embedding reference medium this leads to efficient calculation of the internal wavefield using r t matrices of the heterogeneous stratification and portions thereof at minor additional expense mode conversion of teleseismic p and s phases from velocity gradients is examined by way of examples and comparison with three component data from broad band stations of the yellowknife seismic array the frequency dependence of such wave interactions depends on the differences in vertical slowness between incident and scattered modes it is shown that significant energy is converted from transition zones with extent l p 2 a broader interval than will generally produce intramode reflections a layer structure identified from ps conversions near 75 km depth below the slave craton is shown to be compatible with a 10 km thick gradient zone in which anisotropy increases from ambient levels to vp 5 per cent vs 2 5 per cent at a discontinuous upper boundary this characterization supports a previous interpretation as the upper strata of a former oceanic plate juxtaposed against overriding lithosphere during an ancient episode of shallow subduction

the 410 km depth discontinuity a sharpness estimate from near critical reflections the abrupt increase in seismic velocity and density about 410 km below the surface of the earth occurs at the depth where a phase change in olivine is expected akaogi et al 1989 katsura and ito 1989 ringwood 1969 we have assembled recordings from 22 short period seismometers in washington and british columbia of 35 nuclear explosions in nevada these data reveal relatively noise free reflections from the 410 discontinuity most of the transition is completed within a depth interval of less than 10 km under the western united states this result adds to the accumulating seismic evidence of a fairly sharp 410 transition

environmental processes of the ice age land oceans glaciers epilog knowledge of the state of the earth at the last glacial maximum lgm an interval around 21 000 years ago is an important benchmark for understanding the sensitivity of global environmental systems to change much progress in understanding climates of the lgm has occurred in the 20 years since the end of the climap project of the 1970s climate long range investigation mapping and prediction here we review this progress based on presentations and discussion at a rst open science meeting of the epilog project environmental processes of the ice age land oceans glaciers held in delmenhorst germany may 1999 we outline key controversies and document protocols for epilog contributions so that a new synthesis of the lgm earth can emerge as an open project of the world s community of scientists 2001 elsevier science ltd all rights reserved

the effect of sea water salinity on the morphology of emiliania huxleyi in plankton and sediment samples abstract we analysed the morphology of emiliania huxleyi from globally distributed plankton samples and demonstrate that the size of e huxleyi placoliths is highly correlated to in situ sea surface water salinity we used multiple linear regression analysis to link morphological parameters of e huxleyi to in situ salinity and in situ temperature the best multiple regression model yielded an r 2 0 84 with a standard residual error of 0 65 for in situ salinity over a gradient from 32 6 to 38 8 no significant correlation existed with temperature our results suggest that the morphology of e huxleyi placoliths of recent and ancient sediments may provide a robust method to reconstruct sea surface salinities one caveat is that the plankton derived multiple regression model for in situ salinities is different from that reported from previous work on holocene sediments this discrepancy is most likely caused by taphonomic processes or from the biogeographically biased data sets which were used open ocean versus near shore the cause of the tight relation between salinity and morphological response is not well understood but may be related to cell turgor regulation that affects the size of the cell and thus the size of a single coccolith

multiple transition zone seismic discontinuities and low velocity layers below western united states with p to s converted waves recorded at seismic stations of the us transportable array we image the fine structure of upper mantle and transition zone tz beneath the western us we map the topographies of seismic discontinuities by stacking data by common conversion points along profiles systematic depth and amplitude measurements are performed not only for the well known 410 and 660 interfaces but also for minor seismic discontinuities identified around 350 590 and 630 km depths the amplitude of conversion suggests shear wave velocity vs increase by 4 at the 410 and the 660 the observed 660 velocity contrast is smaller than expected from the 6 in iasp91 but consistent with a pyrolitic model of mantle composition the gorda plate subducted under northern california is tracked to the tz where it seems to flatten and induce uplift of the 410 under northern nevada maps of 410 660 amplitude topography reveal that the tz is anomalous beneath the geographical borders of washington oregon and idaho with i a thickened tz ii a sharp change in depth of the 660 iii a reduced 410 conversion amplitude in the north and iv a positive 630 discontinuity such anomalous structure might be inherited from the past history of plate subduction accretion a thinned tz under the yellowstone suggests higher than average temperatures perhaps due to a deep thermal plume both the 350 and the 590 negative discontinuities extend over very large areas they might be related either to an increased water content in the tz a significant amount of oceanic material accumulated through the past 100 my or both

response of planktic foraminiferal size to late quaternary climate change 1 geographical size distribution within entire holocene foraminiferal assemblages is related to global environmental gradients such as temperature primary productivity and environmental variability this study demonstrates that these correlations are also recognizable in late quaternary assemblages from three locations in the south atlantic on temporal and latitudinal scales the size response to temporal paleoenvironmental changes during glacial interglacial cycles mimics the geographic holocene size variability the amplitude of size variability is directly related to the amplitude of the climatic fluctuations as shown by the stable size temperature relationship over time the documented changes in the assemblage size are caused by species replacement and intraspecific size variability the relative importance of these processes depends on the environmental setting species have been shown to reach their maximum size and abundance under certain optimum conditions and decrease in size if environmental conditions differ from these optima we confirm that late quaternary species sizes were largest at paleotemperatures identical to holocene ones

global coccolith size variability in holocene deep sea sediments abstract we report on the size variability of coccoliths calcite platelets produced by planktic marine haptophyte algae in globally distributed holocene surface sediments the sizes of 400 600 coccoliths in 51 holocene deep sea carbonate ooze samples were measured using automated scanning electron microscopy and image analysis processes the resulting coccolith size histograms are highly variable but the largest 10 in each sample showed a size increase from the tropics to subpolar regions this is the opposite trend from the one observed in planktic foraminifera which have their largest tests in tropical regions in a subset of 13 samples which cover the major environmental gradients of today s surface waters coccolith sizes of the nine most common genera were analyzed these show that the observed macroecological size variability which is related to a complex mixture of environmental parameters is mostly the result of changing species occurrence and abundance biogeography rather than size changes within genera and species this holocene calibration will help to test evolutionary hypotheses of environmental selection in marine phytoplankton and can serve as a useful benchmark for analyses of coccolith size variability in older deep sea sediments

controls on shell mg ca and sr ca in cultured planktonic foraminiferan globigerinoides ruber white mg ca and sr ca ratios were determined on a single species of planktonic foraminiferan globigerinoides ruber white collected from the gulf of eilat and cultured in seawater at five different salinities 32 to 44 five temperatures 18 to 30 c and four ph values 7 9 to 8 4 the mg ca temperature calibration of cultured g ruber with an exponential slope of 8 3 c agrees well with previously published calibrations from core tops and sediment traps however the dependence of mg ca on salinity with an exponential slope of 5 3 psu is also significant and should be included in the calibration equation with this purpose we calculated a calibration equation for g ruber dependent on both temperature and salinity within the 95 confidence limits mg ca mmol mol exp 0 06 0 02 s psu 0 08 0 02 t c 2 8 1 0 r2 0 95 the influence of ph on mg ca ratios is negligible at ambient seawater ph 8 1 to 8 3 however we observe a dominating ph control on shell mg ca when the ph of seawater is lower than 8 0 sr ca in g ruber shows a significant positive correlation with average growth rate presumably part of the variability in shell sr ca in the geological record is linked to changes in growth rates of foraminifera as a response to changing environmental conditions

the s receiver functions synthetics and data example summary recently the s receiver function method has been successfully developed to identify upper mantle interfaces s receiver functions have the advantage of being free of s wave multiple reflections and can be more suitable than p receiver functions for studying mantle lithosphere however because of specific ray geometry and interference of diverse phases the s receiver function method has some technical difficulties and limitations we use synthetic seismograms to demonstrate the feasibility and limitations of s receiver functions for studying mantle structures full wavefield seismograms were calculated using the reflectivity method and processed to generate synthetic s receiver functions for s sks and scs waves results show that s receiver functions can be obtained from waveforms of s sks and scs waves the synthetic s receiver functions for these incident waves show s to p converted phases at all discontinuities in the crust and upper mantle useful ranges of epicentral distances for calculation of s receiver functions are 55 85 for s 85 for sks and 50 75 for scs waves we apply both the s and p receiver function methods to data recorded at broadband station ykw3 in northwest canada the study shows that there is significant agreement among different receiver function methods and demonstrates the usefulness of s receiver functions for imaging the mantle lithosphere

mantle anomalies beneath southern africa evidence from seismic s and p receiver functions summary to understand deep structure and processes beneath southern africa we apply the doublestacking version of the s receiver function srf technique to the recordings of the south african seismic experiment in this technique the wavefields of s and sks are separated by space time filtration and the receiver functions are constructed separately for the s and sks seismic phases the results are consistent with those obtained from the srfs of the permanent stations bosa and lbtb evidence for a reduced s velocity atop the 410 km discontinuity is present in both srfs and p receiver functions the s velocity contrast at the 410 km discontinuity is 40 per cent larger than the norm and there are observations of s350p and p350s seismic phases from the negative 350 km discontinuity beneath the kaapvaal craton the s350p and p350s phases display a dependence on the azimuth which can be caused by anisotropy in the layer atop the 350 km discontinuity this dependence is consistent with observations of shear wave splitting in sks there are observations of the s450p phase from the 450 km negative discontinuity in the transition zone the most anomalous transition zone is found close to the region where the kalahari craton was located in the mesozoic lateral variations of the s velocity are found beneath the 660 km discontinuity teleseismic s and p traveltime residuals with respect to iasp91 model are evaluated from the traveltimes of the p410s and pp410s seismic phases in the uppermost mantle these residuals as well as s410p traveltimes require a reduced vp vs ratio around 1 75 0 01 versus 1 8 in iasp91 an effect of the depletion of the mantle lithosphere in basaltic material in the models obtained by a joint inversion of the receiver functions and the teleseismic traveltime residuals the low velocity zone lvz with the onset of low velocity at a depth of 140 20 km is present at most locations the minimum s velocity in the lvz is 4 5 km s 1 the lvz in our models is consistent with the s velocity vp vs velocity ratio and depth range of high temperature lerzholites in the mantle xenoliths from southern africa our most intriguing finding is a very low quality factor qs on the order of a few tens in the upper mantle we interpret high attenuation the lvz and the low s velocity atop the 410 km discontinuity as the effects of plume like phenomena in the upper mantle

high pressure single crystal elasticity of wadsleyite and the seismic signature of water in the shallow transition zone abstract earth s transition zone at depths between 410 km and 660 km plays a key role in earth s deep water cycle since large amounts of hydrogen can be stored in the nominally anhydrous minerals wadsleyite and ringwoodite mg fe 2 sio 4 previous mineral physics experiments on iron free wadsleyite proposed low seismic velocities as an indicative feature for hydration in the transition zone here we report simultaneous sound wave velocity and density measurements on iron bearing wadsleyite single crystals with 0 24 wt h 2 o by comparison with earlier studies we show that pressure suppresses the velocity reduction caused by higher degrees of hydration in iron bearing wadsleyite ultimately leading to a velocity cross over for both p waves and s waves modeling based on our experimental results shows that wave speed variations within the transition zone as well as velocity jumps at the 410 km seismic discontinuity both of which have been used in previous work to detect mantle hydration are poor water sensors instead the impedance contrast across the 410 km seismic discontinuity that is reduced in the presence of water can serve as a more robust indicator for hydrated parts of the transition zone

upper mantle seismic discontinuities and the thermal structure of subduction zones the precise depths at which seismic velocities change abruptly in the upper mantle are revealed by the analysis of data from hundreds of seismometers across the western united states the boundary near 410km depth is locally elevated that near 660 km depressed the depths of these boundaries which mark phase transitions provide an in situ thermometer in subduction zones the observed temperature contrasts require at least moderate thickening of the subducting slab near 660 km depth in addition a reflector near 210 km depth may mark the bottom of the aesthenosphere

lithospheric and upper mantle structure of central chile and argentina summary the tectonics of central chile and argentina have been greatly affected by the shallow dips of the subducting nazca plate which controlled patterns of magmatism and deformation nearly 1000 km away from the plate boundary we calculate receiver functions from data recorded by the charge array which transected the andes and sierras pampeanas in central chile and argentina to better constrain the crustal structure of this region beneath the northern transect of the charge array where the nazca slab flattens near 100 km we find the crust is over 60 km thick beneath the andes and thin to the east the thick crust however extends 200 km to the east of the high elevations estimates of vp vs obtained from receiver functions vary along ancient terrane boundaries exhibiting higher values to the west interestingly we observe that the amplitude of the phase corresponding to the moho on receiver functions diminishes to the west complicating our images of crustal structure we proposed that the observations presented here of thickened crust within a region of low elevations diminished receiver function arrivals and reports of high shear wave speeds atop of the mantle wedge overlying the shallowly subducted nazca slab can be explained by partial eclogitization of the lower crust the moho appears simpler across the southern transect where it can be identified near 50 km depth at its deepest point beneath the andes and shallows eastwards volcanism remains active near the latitudes of our southern transect and we observe multiple crustal lowvelocity zones indicative of regions of partial melt near the centres of volcanism signals related to the nazca slab remain more elusive suggestive of a small impedance contrast between the slab and overlying mantle

astronomically paced coccolith size variations during the early pliensbachian early jurassic though climate and environmental changes are known to influence diversity and assemblages of coccolithophorids unicellular photoautotroph algae the relationships between the size fluctuations of coccoliths the small calcite plates covering the coccolithophorid cell and environmental parameters remain unclear to understand possible interactions between coccolith size and environmental changes a high resolution every 5 cm biometric study of crepidolithus crassus coccoliths was performed in the lower pliensbachian lower jurassic similar to 188 myr hemipelagic deposits of peniche portugal the six measured parameters show covariant patterns related to size variations rather than morphological changes the size variations are cyclic and they occur in opposite phase to changes in the sedimentary calcium carbonate content spectral analyses performed on the size measurements of the c crassus coccoliths and the calcium carbonate contents show that changes in both parameters are paced by the earth s eccentricity and precession orbital cycles as revealed by mixture analyses the observed size variations result from changes in the relative abundance of two distinct biometric groups that are statistically stable through the analysed time interval these two groups are classified as small crassus with a major axis mean size of 6 5 0 75 mu m and large crassus which averages at 8 5 0 75 mu m and dominates the assemblages in the studied interval crepidolithus crassus has been recently interpreted as a deep dweller living in the lower photic zone and its development may have been greatly dependent on light availability and nutrient concentration accordingly the two size groups likely developed at different water depths due to differential coccolith and cell masses and buoyancies consequently we propose that changes in the transparency of the water column may have been an important factor controlling the replacement between the two groups and hence the resulting coccolith mean size fluctuations ultimately both water transparency and nutrient recycling within the photic zone were mainly influenced by the frequency and intensity of storms that occurred under orbital control

receiver function imaging of upper mantle complexity beneath the pacific northwest united states abstract small scale topographic variations on the upper mantle seismic discontinuities provide important constraints on the thermal influences of upwellings and downwellings in geodynamically complex regions subduction of the juan de fuca plate and other tectonic processes dominating the pacific northwest united states in the cenozoic involve massive thermal flux that likely result in an upper mantle that has strong 3 d temperature variations we address the interaction of such processes in the region using receiver functions to image the upper mantle seismic discontinuities at 410 and 660 km we utilized over 15 000 high quality receiver functions gathered from 294 teleseismic earthquakes recorded at 277 regional broadband seismic stations primarily those of the earthscope usarray transportable array we find the average depths of the discontinuities to be 412 km and 658 km respectively with no obvious 520 km discontinuity detected the peak to peak range is greater on the 410 than the 660 suggesting the possibility of more significant regional dynamic processes at upper mantle depths our results are not consistent with a mantle plume below central oregon in the high lava plains region our observation of a thinner transition zone beneath the western snake river plain region however is consistent with a regional increase in mantle temperatures perhaps due to either asthenospheric flow from beneath and around the southern edge of the juan de fuca plate or to vertical flow in the form of regional mantle upwelling related to the snake river plain yellowstone hotspot track further our results are not consistent with a simple subducting juan de fuca slab morphology but rather suggest similar levels of significant complexity in slab structure found by recent regional tomographic studies we find evidence for a thickened and therefore cooler mantle transition zone beneath the wallowa idaho batholith region consistent with tomographic models which suggest broad scale increased seismic velocities to transition zone depths we speculate that this region may be the location of mantle downwelling at larger scales than previously proposed

high frequency climate fluctuations over the last deglaciation in the alboran sea western mediterranean evidence from calcareous plankton assemblages abstract a high resolution study with a centennial scale resolution has been performed on the calcareous plankton assemblage coccolithophores and planktonic foraminifera at ocean drilling program site 976 alboran sea western mediterranean focusing on the interval between 20 and 9 ka in order to reconstruct changes in surface and subsurface water dynamics and productivity the biotic surface water proxies integrate the extremely detailed multi decadal scale geochemical data set and the pollen record already available at the core thus providing a complete paleoenvironmental paleoceanographic reconstruction the results highlight the sensitivity of the calcareous plankton in recording stadial interstadial phases and higher frequency climatic events that produced changes in sea water features wind induced upwelling and river discharge during the last glacial period favored nutrient availability and moderate productivity during heinrich stadial 1 hs1 the arrival of cold and fresher waters from iceberg melting in the north atlantic significantly hampered productivity at its lowest values of the whole investigated interval calcareous plankton behavior supports the hypothesis that hs1 is a composite event marked by three phases hs1a characterized by the coldest sst polar atlantic water inflow into the basin and a first step toward a dry climate on the continent hs1b recording enhanced freshwater inflow and drought on land and hs1c indicating reduced polar water influx the bolling allerod ba interstadial sees the highest rate of productivity in the entire interval and accompanies the deposition of organic rich layer 1 during the ba coccolithophore assemblage also marks higher frequency changes in hydrographic conditions apparently in relation with greenland interstadial i gi i high variability the younger dryas stadial yd is characterized by refunding cold and dry conditions although not as severe as during hs1 and by enhanced detrital input in surface water during drier conditions on land the holocene onset records climate amelioration both in the marine and continental environment although coccolithophore productivity is not as high as during the ba the rapid shifts in climate sensitive taxa support the hypothesis that each of the climate phases subphases is characterized by a complex pattern forced by strong interaction between ice sheet instability meltwater discharge entering the gibraltar strait north atlantic westerlies and moisture availability clearly impacting over surface water temperature productivity and land masses

topography of the transition zone seismic discontinuities phase transformations in mantle mineralogies probably cause the transition zone seismic discontinuities nominally at 410 520 and 660 km depth thermodynamic principles govern phase transformations making them sensitive to changes in the mantle s ambient conditions through the thermodynamic response changes in temperature or composition shift the transformation to a different pressure creating topography on a level discontinuity with this use as an exploratory tool for the mantle in mind we review the basic seismological and phase equilibrium concepts underlying the detection and interpretation of the seismic wave arrivals associated with the transition zone discontinuities reviewing the evidence for and against the phase transition model we conclude that it is viable and describe how discontinuities have been and can be used to probe the physical and chemical state of the transition zone

one dimensional physical reference models for the upper mantle and transition zone combining seismic and mineral physics constraints one dimensional seismic reference models are known to be a nonunique solution to global seismic data hampering an interpretation in terms of physical structure here we test the compatibility of the simplest hypothesis of a mantle convecting as a whole with a constant pyrolitic composition with phase transitions directly against the kind of seismic data that went into global seismic reference models focusing on upper mantle structure down to 800 km depth by randomly varying the elastic and anelastic parameters of the main mantle minerals within their uncertainty bounds we generate a set of 100 000 adiabatic pyrolitic models a small number of these models 0 1 give a fit to far regional p and s travel times reprocessed isc catalog u 18 5d 26d and fundamental spheroidal and toroidal modes reference earth model web page 1 60 that is as satisfactory as the fit of preliminary reference earth model prem or ak135 f although the accepted models have widely different combinations of the mineral parameters there is a preference for a relatively high olivine shear modulus and its pressure and temperature derivatives relatively low wadsleyite bulk and shear parameters and relatively high ringwoodite bulk modulus derivatives the resulting seismic profiles are very similar and compared to prem or ak135 have lower velocities above 400 km larger jumps near 410 lower transition zone gradients lower jumps around 660 and stronger gradients directly below such physical models that fit seismic data well enough to be useful as a seismic reference model can significantly facilitate physical interpretation of seismic structures

slab1 0 a three dimensional model of global subduction zone geometries 1 we describe and present a new model of global subduction zone geometries called slab1 0 an extension of previous efforts to constrain the two dimensional non planar geometry of subduction zones around the focus of large earthquakes slab1 0 describes the detailed non planar three dimensional geometry of approximately 85 of subduction zones worldwide while the model focuses on the detailed form of each slab from their trenches through the seismogenic zone where it combines data sets from active source and passive seismology it also continues to the limits of their seismic extent in the upper mid mantle providing a uniform approach to the definition of the entire seismically active slab geometry examples are shown for two well constrained global locations models for many other regions are available and can be freely downloaded in several formats from our new slab1 0 website http on doi gov d9arbs we describe improvements in our two dimensional geometry constraint inversion including the use of average active source seismic data profiles in the shallow trench regions where data are otherwise lacking derived from the interpolation between other active source seismic data along strike in the same subduction zone we include several analyses of the uncertainty and robustness of our three dimensional interpolation methods in addition we use the filtered subduction related earthquake data sets compiled to build slab1 0 in a reassessment of previous analyses of the deep limit of the thrust interface seismogenic zone for all subduction zones included in our global model thus far concluding that the width of these seismogenic zones is on average 30 larger than previous studies have suggested

the upper mantle transition zone beneath the ibero maghrebian region as seen by teleseismic pds phases abstract we investigate the upper mantle transition zone thickness beneath the ibero maghrebian region using teleseismic events recorded at 258 seismic stations from the iberarray of the spanish topoiberia project for this purpose the 410 km and 660 km depth discontinuities are mapped through the detection of p to s conversions in order to add consistency and robustness to the detections the final results are based on a joint analysis of receiver functions and two different cross correlation functionals discontinuity depths are determined using time corrections obtained from a 3 d velocity model this study presents the first high resolution topography maps for the 410 and 660 discontinuities which show lateral variations in the transition zone thickness beneath the study area the results are discussed to add new constraints on temperature and composition to seismic velocity anomalies observed in the transition zone beneath the controversial ibero maghrebian region we obtained a thickened transition zone beneath the alboran sea and the north balearic sea suggesting low transition zone temperatures and coinciding with the position of the high velocity anomalies in the tomographic images related to the betic alboran slab and the alpine tethys remnant slab respectively a dominantly thinned transition zone beneath the gulf of cadiz and its surroundings suggest high mantle temperatures we also found evidences of the presence of a low velocity layer atop the 410 discontinuity beneath the study area

mantle transition zone shear velocity gradients beneath usarray broadband p to s scattering isolated by teleseismic receiver function analysis is used to investigate shear velocity v s gradients in the mantle transition zone beneath usarray receiver functions from 2244 stations were filtered in multiple frequency bands and migrated to depth through p and s tomography models the depth migrated receiver functions were stacked along their local 410 and 660 km discontinuity depths to reduce stack incoherence and more accurately recover the frequency dependent amplitudes of p410s and p660s the stacked waveforms were inverted for one dimensional v s between 320 and 840 km depth first a gradient based inversion was used to find a least squares solution and a subsequent monte carlo search about that solution constrained the range of v s profiles that provide an acceptable fit to the receiver function stacks relative to standard references models all the acceptable models have diminished v s gradients surrounding the 410 a local v s gradient maximum at 490 500 km depth and an enhanced v s gradient above the 660 the total 410 v s increase of 6 3 is greater than in reference models and it occurs over a thickness of 20 km however 60 of this v s increase occurs over only 6 km the 20 km total thickness of the 410 and diminished v s gradients surrounding the 410 are potential indications of high water content in the regional transition zone an enhanced v s gradient overlying the 660 likely results from remnants of subduction lingering at the base of the transition zone cool temperatures from slabs subducted since the late cretaceous and longer term accumulation of former ocean crust both may contribute to the high gradient above the 660 the shallow depth of the 520 km discontinuity 490 500 km implies that the regional mean temperature in the transition zone is 110 160 k cooler than the global mean a concentrated v s gradient maximum centered near 660 km depth and a low v s gradient below 675 km confirms that the ringwoodite to perovskite magnesiowustite reaction is the dominant cause of the 660 in the region

the gephyrocapsa sea surface palaeothermometer put to the test comparison with alkenone and foraminifera proxies off nw africa abstract recently a new palaeotemperature proxy was developed based on the morphology of the coccolithophore genus gephyrocapsa here we apply and validate this new methodology by comparing gephyrocapsa derived palaeotemperature estimates with temperature estimates obtained from alkenone ratios mg ca ratios in foraminiferal calcite and planktic foraminifera assemblages we investigated a downcore record off cape blanc geob 1048 20 55 n 19 43 w spanning the last 28 000 years in the vicinity of bofs core 31k 19 00 n 20 10 w for which a detailed multiproxy palaeotemperature record has already been established our data show an especially good correspondence between the gephyrocapsa and alkenone derived palaeotemperatures and thus validate the great potential of the new gephyrocapsa proxy to reconstruct sea surface water temperatures ssts both indicate a glacial drop in sst of 3 c compared to holocene values similar to the mg ca palaeotemperature record although the latter is consistently 2 5 c cooler largest discrepancies both in terms of downcore amplitude changes and same age sample estimates are found with available planktic foraminifera transfer function data this can be due to fundamental differences in the season of production ecologic preferences and habitats and or preservation on the other hand it may be a result of differences inherent to the transfer functions used and their original calibration i e regional vs global approach or different temperature ranges covered in addition to the downcore record off cape blanc sediment samples corresponding to the last glacial maximum lgm were selected from a dispersed set of eighteen well dated gravity cores in order to derive palaeo sst maps off northwest africa during this time slice by applying a regional gephyrocapsa transfer function for the first time we show that mean ssts in the canary islands region during the lgm were 4 6 c colder than today we found lowest glacial temperatures 14 15 5 c offshore morocco and south of the volcanic canary islands likely due to intensified upwelling related to stronger trade winds consistent with estimates from climap and other palaeotemperature reconstructions for the same region in contrast for offshore cape blanc today s centre of perennial upwelling our temperature estimates for the lgm are significantly warmer t today lgm 2 5 4 c than proposed by climap t today lgm 6 10 c however our results consistently support temperature reconstructions based on alkenones that also indicate rather small temperature changes t today lgm 2 4 c in this area we show that gephyrocapsa morphotypes may also provide useful qualitative information about relative changes in primary productivity although no linear relationship is apparent in summary our palaeotemperature and palaeoproductivity data support the observation that enhanced glacial productivity appears geographically limited to the northernmost latitudes of the nw african upwelling system whilst upwelling intensity off cape blanc was reduced despite overall enhanced trade wind intensity

mantle flow through a tear in the nazca slab inferred from shear wave splitting nsf ear 0738935 ear 0739001 ear 1565475 colorado college patricia buster scholarship fund national science foundation through the seismological facilities for the advancement of geoscience and earthscope sage proposal of the national science foundation ear 1261681

interannual changes of austral summer coccolithophore assemblages and southward expanse in the southern indian ocean abstract coccolithophore ecology and biogeography in the southern indian ocean was studied during the austral summer of 2009 soe09 late austral summer 2010 soe10 mid austral summer and 2012 isea12 early austral summer during the soe09 and soe10 surface water samples 55 and 54 water samples respectively were collected from two different transects between mauritius and antarctica 48 e 57 3 e whereas during the isea12 22 sea surface water samples were collected between cape town and prydz bay highest coccolithophore diversity was during soe10 36 taxa followed by soe09 and isea12 12 and 7 taxa respectively whereas highest coccolithophore abundance was reported during the isea12 up to 2203 103 coccospheres l followed by soe10 up to 742 103 coccospheres l and soe09 up to 217 103 coccospheres l during each expedition elevated coccolithophore diversity was documented at the subtropical zone whereas the highest abundance was recorded at the subantarctic zone which was dominated by emiliania huxleyi differences in the occurrence and southward expanse of coccolithophores were documented during each expedition i e maximum southward expanse during the soe10 and lowest during the isea12 we show that biogeographic boundaries of coccolithophores are highly variable in the southern indian ocean which is controlled by environmental factors in the early and mid austral summer and grazing pressure in the late austral summer in addition the physical forcing also may play a key role in transport of coccoliths and coccospheres in the high latitudes we indicate that southward expanse of coccolithophores is significant and may occur for short periods during austral summer

magnetic anomaly interpretation across the southern central andes 32 34 s the role of the juan fernandez ridge in the late tertiary evolution of the margin marine and terrestrial magnetic surveys have been integrated to study the tectonic structure of the convergent margin of chile between 32 34 s three magnetic domains have been identified oceanic continental margin and subaerial the oceanic domain has seafloor spreading anomalies 16 37 ma to 18 39 5 ma disturbed by anomalies of the juan fernandez hot spot chain in the continental margin the most prominent fabric are e w anomalies in the upper slope corresponding to onshore e w anomalies of large intrusive bodies onshore a n s lineament of short wavelength anomalies defines the roots of a cretaceous volcanic arc a resembling lineament offshore indicates a submerged older volcanic arc and that continental basement extends to 50 km landward of the trench absolute cenozoic plate motion for nazca and south american plates and dating of the juan fernandez chain provide a kinematic model of ridge continent collision the reconstruction indicates rapid southward migration of the collision point along 1400 km of the margin from 20 to 11 ma 20 cm yr 1 from 11 ma to present the collison point has migrated at a slower rate along 375 km of the margin 3 5 cm yr 1 the predicted location of the subducted portion of the juan fernandez chain coincides with the south edge of the southward migrating flat slab segment of the subducted lithosphere and with a cluster of deep earthquakes indicating a causal relationship in the last 10 myr the ridge has separated a sediment starved trench to the north where subduction erosion may dominate from a sediment filled trench to the south where recent sediment accretion dominates these observations indicate that subduction of the juan fernandez chain plays a major role in arc forearc tectonics

seismic evidence for water deep in earth s upper mantle water in the deep upper mantle can influence the properties of seismic discontinuities in the mantle transition zone observations of converted seismic waves provide evidence of a 20 to 35 kilometer thick discontinuity near a depth of 410 kilometers most likely explained by as much as 700 parts per million of water by weight

reconstruction of sea surface temperatures from assemblages of planktonic foraminifera multi technique approach based on geographically constrained calibration data sets and its application to glacial atlantic and pacific oceans abstract we present a conceptual framework for a new approach to environmental calibration of planktonic foraminifer census counts this approach is based on simultaneous application of a variety of transfer function techniques which are trained on geographically constrained calibration data sets it serves to minimise bias associated with the presence of cryptic species of planktonic foraminifera and provides an objective tool for assessing reliability of environmental estimates in fossil samples allowing identification of adverse effects of no analog faunas and technique specific bias we have compiled new calibration data sets for the north n 862 and south n 321 atlantic and the pacific ocean n 1111 we show evidence that these data sets offer adequate coverage of the sea surface temperature sst and faunal variation range and that they are not affected by the presence of pre holocene samples and or calcite dissolution we have applied four transfer function techniques including artificial neural networks revised analog method and simmax with and without distance weighting on faunal counts in a last glacial maximum lgm data set for the atlantic ocean 748 samples in 167 cores based on the glamap 2000 compilation and a new data set for the pacific ocean 265 samples in 82 cores and show that three of these techniques provide adequate degree of independence for the advantage of a multi technique approach to be realised the application of our new approach to the glacial pacific lends support to the contraction and perhaps even a cooling of the western pacific warm pool and a substantial 3 c cooling of the eastern equatorial pacific and the eastern boundary currents our results do not provide conclusive evidence for lgm warming anywhere in the pacific the atlantic reconstruction shows a number of robust patterns including substantial cooling of eastern boundary currents with considerable advection of subpolar waters into the benguela current a cooling of the equatorial atlantic by 5 c and steep sst gradients in the mid latitude north atlantic the transfer function techniques generally agree that subtropical gyre areas in both hemispheres did not change significantly since the lgm although the ann technique produced glacial sst in the southern gyre 1 2 c warmer than today we have revisited the issue of sea ice occurrence in the nordic seas and using the distribution of subpolar species of planktonic foraminifera in glacial samples we conclude that the norwegian sea must have been ice free during the summer

constraining velocity and density contrasts across the crust mantle boundary with receiver function amplitudes summary this paper investigates the ability of p wave receiver functions to constrain both the velocity and density contrasts across the moho expressions for receiver function amplitudes corresponding to a layer over a half space are extended to media with depth dependent properties by explicitly accounting for free surface reflection coefficients forward numerical computations show that receiver function amplitudes become frequency dependent for depth dependent structures and that for a given frequency wavelengths associated to ps converted phases are larger than wavelengths associated to multiply reverberated phases when consistent measurements of the amplitudes of ps phase and multiples can be obtained the extended expressions suffice to account for the observed amplitudes receiver function amplitudes are sensitive to both velocity and density contrasts across the moho and a two step grid search procedure is proposed to recover the contrasts from their measurement the near surface velocity is recovered in the first step from the amplitude of the direct p wave and then used in the second step to work out the relative density and s wave velocity contrast from the amplitude of the secondary phases examples from central spain pab and the indian shield hyb are discussed and demonstrate that receiver function amplitudes can constrain contrasts across the moho accurately enough to be utilized in geological interpretation

climate and paleoceanography controlled size variations of calcareous nannofossils during the valanginian weissert event early cretaceous abstract strata of valanginian age early cretaceous 139 8 132 9 ma record a 1 5 positive carbon isotope excursion cie the weissert event it coincides with volcanic activity of the parana etendeka large igneous province unlike the mesozoic oceanic anoxic events oaes no organic rich deposits documenting widespread perturbation of the marine carbon cycle are associated with the weissert event to study the impact of paleoceanographic changes in the valanginian on calcareous nannofossils this study analyzes coccolith size data of three species biscutum constans watznaueria barnesiae zeugrhabdotus erectus from northern germany and the western north atlantic further it presents a new valanginian carbon isotope record of organic material 13corg from northern germany the dataset records the weissert event cie in the late valanginian at both locations biometric analyses reveal size decreases of b constans coccoliths during the weissert event a size reduction of 1 m has been observed for northern germany 37 n and of 0 4 m for the north atlantic 23 n the different magnitudes of size decrease possibly reflect the different paleogeographic positions of the sites and the paleoceanographic response to the late valanginian climate variations proxy data support a link between a humid climate with increased weathering and the observed coccolith size variations this impacted nannoplankton communities either through the availability of light or by eutrophication and possibly nutrient limitation in addition to increased terrigenous input emissions of the parana etendeka volcanism possibly acted fertilizing furthermore widely dispersed volcanic emissions possibly caused increased concentrations of toxic trace metals in the surface ocean which affected marine primary producers

rapid warming and salinity changes of cretaceous surface waters in the subtropical north atlantic paleomarine carbon isotopic records reveal occasional and rapid release of greenhouse gases into the atmosphere the regional consequences on surface ocean properties and time relationships between the atmosphere and the ocean however are still far from understood we observe a sudden 1 5 shift in leaf wax n alkane 13c values at the onset of oceanic anoxic event oae 1b from early albian sediments off northwest africa deep sea drilling project site 545 that is best explained by the rapid release of isotopically light carbon into the cretaceous atmosphere this 1 5 shift in the n alkanes precedes a negative isotope excursion of similar magnitude observed in marine carbonate organic matter and algal steranes a tex86 based record of sea surface temperature sst confirms almost instantaneous warming by 3 5 c along with the marine isotope shifts at site 545 paralleled by an 2 c tex86 sst increase and a freshening of surface water salinity from 43 to 41 at blake nose ocean drilling program site 1049 multiproxy evidence indicates that once established these warm ssts prevailed and were stable during oae 1b suggesting that the emission of 13c depleted carbon started abruptly but then continued over tens of thousands of years the sst cooled by 1 2 c at the end of the event not reaching pre excursion levels the new records provide evidence for a time lag best estimate 1 3 k y between atmospheric and oceanic processes that we interpret as a direct response to changes in the atmospheric greenhouse gas concentrations followed by propagation into the ocean and subsequent heating of surface waters

paleosalinity and δ18o a critical assessment in paleoceanography a traditional application of oxygen isotope ratios in fossil carbonate from deep sea cores concerns the reconstruction of paleotemperatures recently isotopic data have been increasingly employed in the reconstruction of paleosalinities as well this application involves a number of basic assumptions a critical review of which is presented here as the calculation of paleosalinity from 18o residuals assumes constant and linear surface water salinity s 18o relationships we investigate this basic assumption for areas with important and variable freshwater budget and or sea ice influences we show that it is particularly unwarranted to assume such temporally invariant linearity in temperate and subpolar seas because of the effects of freezing and melting more critically we argue that the determinant of many regions s 18o is advection not the local water balance so that the basic 18o of seawater in many regions of the world ocean would likely have changed in a manner somewhat different from that expected from the ice volume record although the differences may not be significant for the gross reconstruction of such features as past sea level we believe they do potentially bias paleosalinity reconstructions mostly toward high salinities to fully exploit the potential of oxygen isotope records as quantitative paleosalinity indicators both the spatial and temporal variabilities need to be constrained hence we recommend that 1 for any time slice of specific interest to paleoceanographic and paleoclimatological studies a coupled ocean atmosphere isotope model or at least an ocean isotope model driven by a paleoclimate isotope model should be used to define the distribution of the base mixing end member 18o of sea water 2 much further regional scale research is needed on flux rates and isotopic compositions of the various terms in the freshwater budget as well as on the variability in the various advective terms the latter variability may be assessed from reconstructions of past seaice distributions and of volume fluxes isotopic compositions of outflow from marginal seas and through sea straits passages

elemental and isotopic proxies of paleotemperature and paleosalinity climate reconstruction of the marginal northeast pacific ca 80 ka isotope 18 o and minor element mg ca sr ca analyses of a fossil shell of the marine mussel mytilus trossulus gould from the whisky run terrace at coquille point bandon oregon enable reconstruction of a paleoclimatic profile for the temperate northeastern pacific ca 80 85 ka the whisky run terrace is correlative with marine oxygen isotope 18 o substage 5a the final sea level highstand of the last interglacial complex herein we provide sea surface temperature estimates and report on a new technique that allows estimates to be made of 18 o of seawater and riverine discharge from the skeletal chemistry of a single mussel shell estimates of mean annual temperature from mg ca ratios are lower than those suggested by the accompanying fossil fauna and significantly lower than present day conditions the data also suggest a decrease in the range of seasonal temperature extremes at 80 ka compared to today estimates of the fresh water and seawater 18 o end members 4 5 and 0 5 respectively are slightly greater than modern values

crustal thickness beneath the andes and sierras pampeanas at 30 s inferred from pn apparent phase velocities 1 we obtained a 2d crustal model beneath central chile and western argentina using apparent pn phase velocities recorded along an ew trending transect at 30 s this model is characterized by a thick 65 km crustal root beneath the high cordillera a 60 km thick crust beneath the precordillera and a gradual shallowing of moho depths beneath the sierras pampeanas from 55 km in the west to 40 km in the east beneath the sierras pampeanas where very little crustal shortening is observed the thick crust must be explained by means other than simple tectonic shortening isostatically balanced crustal thickness is consistently shallower than our model shows suggesting the existence of dynamic forces possibly linked to the flat slab

finite frequency whole mantle p wave tomography improvement of subducted slab images received 23 july 2013 revised 14 october 2013 accepted 17 october 2013 1 we present a new whole mantle p wave tomographic model gap p4 we used two data groups short period data of more than 10 million picked up onset times and long period data of more than 20 thousand differential travel times measured by waveform cross correlation finite frequency kernels were calculated at the corresponding frequency bands for both long and short period data with respect to an earlier model gap p2 we find important improvements especially in the transition zone and uppermost lower mantle beneath the south china sea and the southern philippine sea owing to broadband ocean bottom seismometers bbobss deployed in the western pacific ocean where station coverage is poor this new model is different from a model in which the full data set is interpreted with classical ray theory bbobs observations should be more useful to sharpen images of subducted slabs than expected from simple raypath coverage arguments citation obayashi m j yoshimitsu g nolet y fukao h shiobara h sugioka h miyamachi and y gao 2013 finite frequency whole mantle p wave tomography improvement of subducted slab images geophys res lett 40 doi 10 1002 2013gl057401

pervasive seismic low velocity zones within stagnant plates in the mantle transition zone thermal or compositional origin abstract we exploit conversions between p and s waves for large scale high resolution imaging of the mantle transition zone beneath northwest pacific and the margin of eastern asia we find pervasive reflectivity concentrated in two bands with apparent wave speed reduction of 2 to 4 about 50 km thick at the top of the transition zone and 100 km thick at the bottom this negative reflectivity associated with the scattered waves at depth is interpreted jointly with larger scale mantle tomographic images and is shown to delineate the stagnant portions of the subducted pacific plate in the transition zone with largely positive shear wave velocity contrasts the upper reflectivity zone connects to broad low velocity regions below major intra plate volcanoes whereas the lower zone coincides locally with the occurrence of deep focus earthquakes along the east asia margin similar reflectivity is found in pacific northwest of the usa we demonstrate that the thermal signature of plates alone is not sufficient to explain such features alternative explanations for these reflective zones include kinetic effects on olivine phase transitions meta stability compositional heterogeneities within and above stagnant plates complex wave propagation effects in the heterogeneous slab structure or a combination of such factors we speculate that part of the negative reflectivity is the signature of compositional heterogeneities as revealed by numerous other studies of seismic scattering throughout the mantle and that such features could be widespread across the globe

upper mantle stratification by p and s receiver functions summary seismic stratification of the upper mantle is investigated by applying two complementary techniques to the records of the graefenberg array in southern germany the anisotropic p receiver function technique kosarev et al 1984 vinnik montagner 1996 is modified by using summary seismic events instead of individual events and different weighting functions instead of the same function for the harmonic angular analysis of the sv and t components of the pds phases the summary events provide better separation of the second azimuthal harmonic than the individual events the parameters of the second harmonics of sv and t thus evaluated should be similar if they reflect the effects of azimuthal anisotropy this can be used as a criterion to identify the anisotropy to detect the sdp phases and their azimuthal variations caused by azimuthal anisotropy we have developed a stacking technique which can be termed the s receiver function technique it includes axis rotation to separate interfering p and s arrivals determination of the principal m component of the s wave motion deconvolution of the p components of many recordings by their respective m components and stacking of the deconvolved p components with weights depending on the level of noise and the angle between the m direction and the backazimuth of the event both techniques yield consistent results for the graefenberg array as indicated by the p receiver functions the upper layer of the mantle between the moho and 80 km depth is anisotropic with dvs vs around 0 03 and the fast direction close to 20 clockwise from north the fast direction of anisotropy below this layer is around 110 the boundary between the upper and the lower anisotropic layers is manifested by the detectable pds and sdp converted phases shear wave splitting in sks is strongly dominated by azimuthal anisotropy in the lower layer asthenosphere

continental and oceanic crustal structure of the pampean flat slab region western argentina using receiver function analysis new high resolution results summary the pampean flat slab of central chile and argentina 30 32 s has strongly influenced cenozoic tectonics in western argentina which contains both the thick skinned basement cored uplifts of the sierras pampeanas and the thin skinned andean precordillera fold and thrust belt in this region of south america the nazca plate is subducting nearly horizontally beneath the south american plate at 100 km depth to gain a better understanding of the deeper structure of this region including the transition from flat to normal subduction to the south three iris passcal arrays of broad band seismic stations have been deployed in central argentina using the dense siembra array combined with the broader charge and esp arrays the flat slab is imaged for the first time in 3 d detail using receiver function rf analysis a distinct pair of rf arrivals consisting of a negative pulse that marks the top of the oceanic crust followed by a positive pulse which indicates the base of the oceanic crust can be used to map the slab s structure depths to moho and oceanic crustal thicknesses estimated from rf results provide new more detailed regional maps an improved depth to continental moho map shows depths of more than 70 km in the main cordillera and 50 km in the western sierras pampeanas that shallow to 35 km in the eastern sierras pampeanas depth to moho contours roughly follow terrane boundaries offshore the hotspot seamount chain of the juan fernandez ridge jfr is thought to create overthickened oceanic crust providing a mechanism for flat slab subduction by comparing synthetic rfs based on various structures to the observed rf signal we determine that the thickness of the oceanic crust at the top of the slab averages at least 13 19 km supporting the idea of a moderately overthickened crust to provide the additional buoyancy for the slab to remain flat the overthickened region is broader than the area directly aligned with the path of the jfr however and indicates along with the slab earthquake locations that the flat slab area is wider than the jfr volcanic chain observed in the offshore bathymetry further rfs indicate that the subducted oceanic crust in the region directly along the path of the subducted ridge is broken by trench parallel faults one explanation for these faults is that they are older structures within the oceanic crust that were created when the slab subducted alternatively it is possible that faults formed recently from tectonic underplating caused by increased interplate coupling in the flat slab region

interhemispheric appraisal of the value of alkenone indices as temperature and salinity proxies in high latitude locations alkenone sediment data from the nordic seas and north atlantic are compared to those from sikes et al 1997 for the southern ocean to evaluate further uk37 and uk37 as proxies to estimate cold temperatures 10 c and the effect of salinity and temperature in the relative abundance of 37 4 to the total abundance of c37 alkenones 37 4 uk37 and uk37 are found to be equally viable as proxies but there are significant regional differences in their cold temperature dependence the measurement of 37 4 in cores from the north atlantic region can be used to identify situations when uk37 is not a reliable paleothermometer variations in salinity are probably responsible for changes in the sedimentary record of 37 4 and a preliminary calibration has been obtained for 37 4 f salinity this new relationship should be further confirmed through field or laboratory experiments but it paves the way to derive a molecular proxy to reconstruct paleosalinity in surface waters