annual biogenic particle fluxes to the interior of the north atlantic ocean studied at 34 n 21 w and 48 n 21 w abstract in order to clarify the annual quality quantity and export processes of biogenic particles from the euphotic zone to the deep ocean interior an array of automated time series sediment traps were deployed for 1 year from 4 april 1989 to 17 april 1990 at 34 n 21 w and 48 n 21 w as part of the joint global ocean flux program jgofs north atlantic bloom experiment nabe three sediment traps with 13 time series sediment collectors were placed at both stations approximately 1 and 2 km below the surface and 0 7 km above the bottom they collected settling particles during 26 14 day intervals for 376 days with an 20 day hiatus in september october 1989 for changeover of the trap moorings the collection periods of the six traps were synchronized forming a spatio temporal matrix of 156 samples the annual mass flux at about 2 km deep during this experiment was 22 and 27 g m 2 y 1 at the 34 and 48 n stations consisting of biogenic particles with traceable quantities of lithogenic particle flux the spring particle bloom characterized by the sedimentation of particles relatively enriched by norg began in january at the 34 n station and in march at the 48 n station the bloom continued for 4 5 and 3 months and provided 62 and 50 of the annual biogenic particle mass flux at 2 km at the 34 and 48 n stations the surface bloom penetrated to the ocean interior within a few weeks with apparently accelerated settling speed at deeper layers the order of susceptibility of biogenic elements to mineralization while settling in the 0 7 1 km a b water column was from least to most resistant p norg corg si and ca the c n p ratio at 0 7 km a b was 154 18 1 at the 34 n station and 148 18 1 at the 48 n station

neritic and pelagic carbonate sedimentation in the marine environment ignorance is not bliss synthesis of available data allows us to define general patterns of late quaternary carbonate production and sedimentation in the global ocean during high stands of sea level the neritic and pelagic environments appear to sequester approximately similar amounts of carbonate whereas during low stands of sea level the decreased neritic zone produces and accumulates approximately an order of magnitude less carbonate assuming that global accumulation of deep sea carbonates remains more or less constant during glacially induced changes in sea level the ocean becomes depleted with respect to calcium carbonate during high stands and recharges during low stands before we can achieve a better understanding of the global carbonate system however we need a better understanding of key environments and processes a production and accumulation on continental shelves both as potential sinks accumulation and as sources export to the deep sea b a better measure of pelagic carbonate production and c late quaternary late pleistocene and holocene mass accumulation rates in the deep sea

late quaternary variations in water mass in the shatsky rise area northwest pacific ocean abstract oxygen isotope analysis of planktonic and benthic foraminifera in piston core s 2 collected from the shatsky rise 33 21 75n 159 07 70e water depth 3107 m provides a paleoceanographic record for the last 540 000 years in the northwestern pacific ocean although peaks in the abundance of sinistral neogloboquadrina pachyderma occur during marine isotope stage 2 and particularly 6 and 12 the southward shifting of the subarctic front did not reach the core site during these glacial periods however mass accumulation rates of total organic carbon biogenic opal and terrigenous matter contents indicate that surface productivity increased during cold periods in addition the c n ratio analyzed in organic matter reached values of up to 10 during glacial periods these results imply that delivery of eolian dust to this site was enhanced by strengthened westerly winds during glacial periods down core fluctuations in 13c values of globigerinoides ruber and globorotalia inflata nearly overlap particularly during the period from 540 to 260 ka this latter trend suggest that the subtropical surface water mass prevailed at the core site throughout that period based upon the very small vertical 13c gradient through water column in modern kuroshio current water

fluid flow and volume loss during mylonitization an origin for phyllonite in an overthrust setting north carolina u s a abstract in the western blue ridge province of the southern appalachians north carolina granite gneisses are converted to phyllitic mylonites phyllonites along the base of the rector branch thrust sheet the mylonites show evidence for fluid infiltration and large volume losses with decreasing distance from the thrust and local shear zones feldspars undergo grain size reduction by cracking followed by chemical breakdown to muscovite sericite and zoisite the following reaction was important during mylonitization 3 k feldspar 2 h muscovite 2 k 6 sio 2 quartz displays evidence for dynamic recrystallization whereas feldspar deforms brittely which together with the secondary mineral assemblages suggest that deformation occurred at temperatures of between 300 c and 500 c in the presence of a fluid the mylonites are enriched by a factor of at least 2 5 in elements such as tio 2 p 2 o 5 zr y v la ce and depleted in sio 2 in comparison to their protolith gneisses the immobile element enrichments are attributed to enrichment in residual phases such as ilmenite zircon apatite and epidote in the mylonites and are interpreted as due to minimum volume losses of 60 mass balance calculations based on major element chemistry indicate the mylonites lost large amounts of sio 2 and smaller amounts of alkalies and were infiltrated by fluid rock weight ratios of between 10 2 and 10 3 phyllonitization as a process involves several deformation mechanisms including cataclasis and solution of feldspar as well as dislocation creep of quartz and micas reaction enhanced softening was apparently important in strain localization

fluctuations of eolian flux and ocean productivity in the mid latitude north pacific during the last 200 kyr abstract in order to understand fluctuations in terrestrial and marine environments a sedimentary core h3571 was investigated from the hess rise located in the mid latitude north pacific under the north westerly wind system the 18 o grain size and grain shape of type 1 quartz suggest that this quartz is of aerosol origin good correlation between al and aerosol quartz in content and mass accumulation rate mar indicates that the alumino silicate minerals in the sediments are mainly transported by wind mar of mineral aerosol maraerosol varies from 156 to 732 mg cm 2 kyr 1 during the last 200 kyr the maraerosol maxima occur in oxygen isotope stage ois 4 to latest ois 5 middle ois 6 moderate maxima occur in early ois 1 2 late ois 3 and middle ois 3 these maxima are ascribed to reduced precipitation during the summer monsoon and to strengthened wind speed during the winter monsoon the mean organic carbon total nitrogen atomic ratio is 7 2 suggesting that the organic matter in the core h3571 is also mainly of marine origin the mar of organic carbon marorganic exhibits two prominent maxima in ois 2 and 4 and relatively high values in middle and late ois 6 enhanced primary productivity is most likely to be responsible for the high burial rate of organic carbon in the sediments carbonate and phosphorus inputs with aerosol into sea surface have played a minor role through dissolution in diminishing pco2 in surface water during glacial times on the other hand the aerosol silica supply to the ocean may have some potential to affect the burial of biogenic silica into sediments the effect of mineral aerosol on the ocean carbon cycle would be greater in the coastal and hemipelagic regions of the western pacific and equatorial atlantic as compared with that in the hess rise regime

heat balance and regime shifts of the mixed layer in the kuroshio extension abstract we investigated the seasonal variations of the mixed layer depth and temperature in the kuroshio extension region 145 180 e 30 36 n and studied the causes of the mixed layer depth and temperature regime shifts which occurred in the late 1980s using upper ocean thermal and heat flux datasets incorporated with a bulk mixed layer model the mixed layer from fall to winter is cooled by the net surface heat flux the ekman transport and the entrainment and warmed by the horizontal heat convergence resulting from the kuroshio heat advection the mixed layer depth is controlled by the entrainment and the horizontal transport divergence convergence which act to slow the mixed layer deepening from fall to early winter and then in winter deepen the mixed layer the entrainment velocity is significantly influenced by the temperature difference between the mixed layer and the layer below the mixed layer shift from its deep to shallow phase occurred in 1985 this shift is preceded the sst shift in 1988 by three years and was caused by the horizontal transport divergence anomaly the horizontal heat convergence of the kuroshio extension caused the sst shift in 1988 whereas its anomaly had been already positive since 1983 the delay from 1983 to 1987 can be attributed to the effects of the negative fall sst anomaly stronger surface heat flux and ekman cooling and the shoaling of the mixed layer depth it is suggested that the kuroshio current system plays a major role in forcing the sst shift and thus the subsequent climate regime shift

spatial variations of magnetic susceptibility of chinese loess for the last 600 kyr implications for monsoon evolution 1 we examine spatial variations in magnetic susceptibility ms over the loess plateau in china based on 50 sections in order to identify spatial changes in monsoon climate at key glacial interglacial and interstadial intervals for the last 600 kyr the results indicate strong coherence between ms variations during the interglacial periods and present day precipitation and temperature patterns this suggests that the strength of the summer monsoon had a dominant influence on the ms signals in soils through modulating pedogenic intensity the distribution of ms during glacial periods is characterized by weak s n gradients and rough w e zonal patterns indicating a negligible effect of the summer monsoon interstadial patterns are intermediate between the glacial and interglacial ones interglacial patterns for the last 600 kyr are essentially similar suggesting that the climate regime during these periods has not undergone significant changes and that the east asian summer monsoon has remained the main moisture carrier our estimates of the relative amplitudes of climate oscillations during these time slices are consistent with earlier paleoclimate studies these data associated with the available susceptibility based climofunctions may be used to estimate spatial changes of paleorainfall and paleotemperature for these key periods and hence to test climate models

an evaluation of criteria to deduce the sense of movement in sheared rocks some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking apparently conflicting evidence from rotated pressure shadow regions around porphyroclasts and porphyroblasts is clarified the use of quartz crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations

fluxes of planktic foraminifera in response to monsoonal upwelling on the somalia basin margin abstract sediment trap samples collected off somalia bi weekly from early june 1992 through mid february 1993 show large seasonal variations in the shell flux and species composition of planktic foraminifera these variations mirror the monsoon driven circulation which resulted in massive upwelling and offshore eddy transport in summer during the sw monsoon june september and accounted for nearly 90 of the estimated annual shell flux of planktic foraminifera g bulloides dominated the sw monsoon along with g glutinata t quinqueloba n dutertrei and t iota in a fauna rich species but with a low diversity and equitability during the autumn intermonsoon november december the ocean became stratified and the nutrient exhausted whereas during the ne monsoon january march a warm surface mixed layer developed with the nutrients entrained by deep wind mixing it was dominated by g ruber in association with g tenella g aequilateralis g trilobus g sacculifer and g menardii in a fauna poorer in species but with a higher diversity and equitability consequently the ratio in the abundance of g bulloides and g ruber follows the monsoonal cycle closely as both species persist throughout the year only the rare g theyeri seems to be restricted to the sw monsoon in october at the end of the sw monsoon the trap at 265 m above the bottom intercepted massive amounts of fine grained carbonate m resuspended from the shelf and upper slope it contained extreme fluxes of bioclastic fragments benthic foraminifera and benthic ostracods as well as enhanced fluxes of small sized planktic foraminifera m notably g rubescens integrated over the year the species composition intercepted by the trap shows a very good match with the shell fauna in a core top sediment from the same site apparently the year estimated monsoonal record of planktic foraminifera which is strongly dominated by the sw monsoon production survives burial intact consequently the species composition of planktic foraminifera and measures such as the bulloides ruber ratio can be applied as a proxy for past changes in the intensity of the sw monsoon off somalia compared to the modern condition

coccolithophore carbonate during the last 450 ka in the nw pacific ocean odp site 1209b shatsky rise this study focuses on pleistocene holocene sediments from the shatsky rise ocean drilling program site 1209b nw pacific ocean we quantify the contribution of calcite made by coccoliths in oceanic sediments investigating the role of calcareous nannoplankton during the last 450 ka coccolith carbonate constitutes 60 90 of bulk carbonate coccolith carbonate accumulation rates cars and caco3 fine fraction confirm that coccolithophores are major contributors to the carbonate export and accumulation primary productivity shows highest values from marine isotope stage mis 12 to 8 thereafter although coccolith calcite content remains high other sediment components such as as foraminifera and biogenic opal seem to be favored perhaps related to an increase in fertilization by eolian dust our results demonstrate the important role of coccolithophore production and sedimentation on the regulation of ocean carbonate chemistry on time scales 1000 100 000 years on glacial interglacial scales coccolithophore productivity could have affected deep water saturation by buffering deep sea co2 through increased carbonate dissolution episodes spectral and wavelet analyses are consistent with cars primarily driven by glacial interglacial variability and obliquity controlled changes coccolith based paleoceanographic reconstructions allow us to establish that during the last 450 ka the mid latitudes of the nw pacific are controlled by the dynamics of the el nino southern oscillation perturbations and boreal monsoon system

rotation of fabric elements in convergent shear zones with examples from the southern appalachians plane strain shear zones between rigid walls which do not rotate but which converge and move laterally relative to each other are here in referred to as convergent shear zones analysis of the deformation in convergent shear zones indicates the existence of two flow apophyses one parallel to the shear zone wall and the other inclined to the wall modeling of the development of fabrics in convergent shear zones indicates the occurrence of stable orientations in which s and c do not rotate and are oppositely inclined to the shear zone boundary the stable c orientation is parallel to the inclined flow apophysis and also is parallel to the approach velocity vector of the opposing walls of the shear zone if it can be demonstrated from field relationships that the walls of a shear zone were rigid and remained parallel then the occurrence of a flow apophysis inclined in the direction of shear is diagnostic of convergent shear s and c fabrics in the ridge road and gundy creek shear zones of the southern appalachian piedmont are interpreted to indicate a convergent shear regime with an approach velocity vector oriented 10 13 clockwise from the strike of the zones

seasonal variations in planktonic foraminifera at three sediment traps in the subarctic transition and subtropical zones of the central north pacific ocean the distribution and flux of planktonic foraminifera in the north pacific ocean were studied for a 1 year period beginning in july 1993 using time series samples collected in three sediment traps deployed in a north south transect along 175 e longitude sediment trap locations allowed monitoring of faunas within the subarctic transition and subtropical water masses in this region seasonally high foraminiferal flux rates were recorded at the subarctic site during periods of intense stratification of surface water accompanied by high fluxes of organic matter and biogenic opal contents faunal composition dominated by sinistral forms of neogloboquadrina pachyderma and globigerina umbilicata at the latter site characterized the subarctic water mass feature data collected at the transitional and subtropical sites illustrate differences in seasonal flux rates and in relation to those recorded at the subarctic site faunal composition at the transitional water mass site was dominated by dextral phenotypes of n pachyderma whereas this taxon was absent at the subtropical site also during the period of warmest surface temperature october globigerinoides ruber became dominant at the transitional water mass site in contrast to the subtropical water mass site where globigerinoides sacculifer became dominant while associated with common occurrences of globigerinoides tenellus and globorotalia tumida much lower fluxes of planktonic foraminifera organic matter and biogenic opal also marked subtropical water the distinctive differences in faunal composition and flux rates at the transitional and subtropical sites suggest that little if any exchange of surface water occurred between these two sites and in particular in the area representing the distal kuroshio extension

planktic foraminiferal sedimentation and the marine calcite budget 1 the vertical flux and sedimentation rate of planktic foraminiferal tests are quantified and a global planktic foraminiferal cac0 3 budget is presented test and calcite flux rates are calculated according to the distribution of species obtained from multinet and sediment trap samples modern planktic foraminiferal population dynamics are discussed as a prerequisite for the quantification of the calcite budget highlighting the importance of ecological autecological e g reproduction and biogeochemical conditions that determine the presence or absence of species to complete the open marine particulate caco 3 inventory the contribution of coccolithophores pteropods and calcareous dinophytes is discussed based on the studied regions the global planktic foraminiferal calcite flux rate at 100 m depth amounts to 1 3 3 2 gt yr 1 equivalent to 23 56 of the total open marine caco 3 flux the preservation of tests varies on a regional and temporal scale and is affected by local hydrography and dissolution during most of the year off peak periods many tests dissolve above 700 m water depth while settling through the water column with on average only 1 3 of the initially exported caco 3 reaching the deep seafloor pulsed flux events mass dumps of fast settling particles yield a major contribution of tests to the formation of deep sea sediments on average 25 of the initially produced planktic foraminiferal test cac0 3 settles on the seafloor the total planktic foraminiferal contribution of caco 3 to global surface sediments amounts to 0 36 0 88 gt yr 1 32 80 of the total deep marine calcite budget

late pleistocene continental climate and oceanic variability recorded in northwest pacific sediments core v21 146 provides a continuous record of northwest pacific pelagic sedimentation spanning the past 530 000 years downcore variations of 18o from benthic foraminiferal calcite were correlated to the specmap record to provide an age model for late pleistocene paleoclimatic and paleoceanographic variation fluxes of caco3 and eolian material have been determined by combining information about linear sedimentation rates bulk densities and component percentages the mass accumulation rate mar of caco3 varies from 58 to 1435 mg cm kyr 1 and exhibits the pacific ocean pattern of higher accumulation associated with glacial periods for the younger portion of the record however the pattern of caco3 accumulation appears to shift during the mid brunhes so that prior to 350 000 years ago it exhibits an opposite pattern of greater accumulation during interglacial periods the flux of eolian dust is a proxy measure of the source area aridity and correlates well to the loess soil stratigraphy in china dust fluxes range from 43 to 718 mg cm kyr 1 and are greater by a factor of about 4 during glacial times cross spectral analysis of the eolian flux and oxygen isotope records shows an inphase and coherent relationship at each of the major orbital periodicities of 100 41 and 19 kyr eolian grain sizes generally used as a proxy record of wind intensity range from 8 4 2 9 m to 6 2 13 6 m a change in grain size variability occurs near about 300 ka such that the older portion is characterized by lower frequency and higher amplitude fluctuations than the younger portion power spectra for the eolian grain size record show dominant peaks at 100 and 50 kyr and a broad 25 35 kyr peak but coherency to the oxygen isotope curve at only the 100 and 33 kyr periodicities the phase relationship for eccentricity between the eolian grain size and 18o records suggests that at the 100 kyr frequency the smallest grain sizes are associated with glacial conditions

comparison of pelagic and nepheloid layer marine snow implications for carbon cycling abstract marine snow from upper and mid water i e pelagic depths on the california margin is texturally and compositionally different from that traveling in the nepheloid layer transmission electron microscopy shows that pelagic marine snow consists primarily of bioclasts e g diatom frustules foram tests organic matter and microbes these components are entrained as discrete particles or small aggregates 10 m in diameter in a loose network of exocellular muco polysaccharide material clays are infrequent but when present are constituents of comparatively compact organic rich microaggregates microbes are abundant and appear to decrease in number with increasing water depth in contrast marine snow aggregates collected from just above the sea floor in the nepheloid layer are assemblages of clay particles clay flocs and relatively dense clay organic rich microaggregates in an exocellular organic matrix bioclasts and microorganisms occur only rarely the prevalence of clay organic rich aggregates in the nepheloid layer suggests that prior to final deposition and burial marine snow from the pelagic zone is subject to disaggregation and recombination with terrigenous detrital material near or at the sea floor results have significant implications for the accumulation and burial rates of organic carbon on continental margins and the aging and bioavailability of sedimentary organic matter samples examined were collected offshore of northern and central california

planktonic foraminifera of the northern indian ocean distribution and preservation in surface sediments in the northern indian ocean planktonic foraminiferal tests accumulate in a wide variety of surface water environments and depositional settings this variability enables us to isolate the effects that surface water ecology and differential dissolution have on the distribution of planktonic foraminifera from 251 geographically widespread surface sediment samples foraminiferal abundance varies from 0 to 104 whole foraminifera in the greater than 150 m fraction per gram dry sediment values 10 characterize the three deep basins of the equatorial indian ocean and the western bay of bengal foraminiferal tests are most abundant on carbonate covered ninety east and carlsberg ridges absolute abundance patterns are mainly controlled by non ecological processes variations in dissolution resistant species rsp with water depth reveal that the foraminiferal lysocline fl varies regionally the fl is deepest 3 800 m in the equatorial region rises abruptly to 3 300 m in the arabian sea and varies from 2 600 m to near 2 000 m moving northward in the bay of bengal deep samples with anomalously low rsp 30 suggest redeposition systematic geographic and depth related variation is observed for the 17 most abundant foraminiferal species dissolution resistant species g menardii g tumida g dutertrei p obliquiloculata generally exhibit a rapid and continuous increase in relative abundance at and below the fl susceptible species g ruber g bulloides g glutinata for example exhibit a rapid and continuous decrease in relative abundance at and below the fl moderately susceptible species g conglobatus g aequilateralis g conglomerata for example rapidly increase in abundance at the fl and systematically decrease with depth below the fl principal components analysis pca of faunal data from minimally dissolved 30 rsp samples reveals important ecologically related species intercorrelations the major biogeographic gradient is the negative covarying relationship between ag bulloides g glutinata species pair and a grouping ofg sacculifer g conglobatus g aequilateralis andg ruber pca of all samples demonstrates how differential dissolution alters this and other species relationships species groupings that incorporateg ruber g menardii andg dutertrei are particularly affected by dissolution comparison of average faunal data from minimally dissolved samples in the northern indian ocean with similar samples from other tropical regions suggests varying environmental factors produce distinct faunas within the tropical ocean for example g bulloides g falconensis andg hexagona are significantly more abundant in northern indian ocean surface sediments while such species asg ruber g sacculifer g dutertrei andp obliquiloculata dominate in other tropical regions

seasonal changes in species composition numbers mass size and isotopic composition of planktonic foraminifera settling into the deep sargasso sea abstract planktonic foraminifera recovered from six successive sediment trap samples collected over fourteen months at a depth of 3200 m near bermuda show varied responses to seasonal changes in the near surface hydrography these include changes in species composition and within species changes in number of individuals collected per unit time average size and weight of individuals and in oxygen and carbon isotopic composition a total of seventeen species were identified and eleven were sufficiently abundant for isotopic analysis in at least some of the samples the accumulations on the sea floor of some of these species can be expected to contain a strong seasonal component in their oxygen isotopic composition which may be utilized in paleoclimatic and paleo oceanographic reconstructions best suited to this purpose are those species which form their tests in isotopic equilibrium with surface water and whose abundance is confined to a portion of the year only the best examples are pulleniatina o bliguiloculata globigerinoides conglobatus and neogloboquadrina dutertrei globigerinoides ruber is a good estimator of the average surface water temperature because it occurs in rather even abundance throughout the year hastigerina pelagica though very abundant in surface water is practically eliminated even before arrival on the sea floor by partial resorption and structural weakening of the tests during gametogenesis orbulina universa globorotalia truncaltulinoides and globorotalia hirsuta show morphological and istopic evidence for contibnued calcification in deeper water after initial test formation near ther surface globigerina bulloides represents the most striking example of oxygen isotopic disequilibrium with sea water

a simple model for interannual sandbar behavior time and length scales of beach variability have been quantified using 16 years of beach surveys sampled at the army corps of engineers field research facility located on the u s atlantic coast between 50 and 90 of the bathymetric variability at this site was explained by alongshore uniform response over the approximately 1 km alongshore span of the surveys although the incident wave height variance was dominated by frequencies at or higher than 1 cycle yr more than 80 of the bathymetric variance at all cross shore locations was explained by frequencies 1 cycle yr interannual cycles consisting of sandbar formation migration and decay contributed to the low frequency variability the observed behavior can be explained by a simple heuristic model the model assumes that bars migrate toward a wave height dependent equilibrium position this position was shown to coincide with the wave breakpoint additionally the rate of bar response is taken to be variable and was empirically determined to be proportional to the wave height cubed the net effect of a variable response rate is to shift the expected long term mean sandbar position offshore toward the equilibrium position associated with the largest waves the model explained up to 80 of the observed bar position time series variance and up to 70 of the variance of bar crest velocity time series which were extracted from three different sandbars characteristic bar response times related to the inverse of the response rate were found to be long relative to the characteristic timescale of the forcing 1 year in our case as a result transient response i e bar position far from equilibrium tended to persist for many cycles of the forcing transient bar behavior appears in the observations when bars formed near the shoreline or when outer bars decayed and inner bars faced a changed wave climate while the present model is able to explain the evolution of these transients it does not contain a mechanism for their introduction

the eigenvalues of steady flow in mohr space abstract the eigenvalues of the velocity gradients tensor and of the position gradients tensor describing instantaneous flow or incremental deformations are easily determined in mohr space as the points of intersection between a mohr circle and the horizontal mohr axis intersections occur only if the tensor has real eigenvalues eigenvectors associated with the eigenvalues are directions of no rotation a line of material particles under an eigenvector does not rotate during steady flow although the line is instantaneously stretching at a rate equal to its corresponding eigenvalue for non spinning steady sub simple shearing there will always be two eigenvectors the angle between the eigenvectors is dependent on the ratio of pure to simple shearing rates this angle decreases as the pure shearing component decreases relative to the simple shearing component superimposed increments of pure shear and simple shear produce an equivalent set of non rotated material lines but the deformation histories of these lines are rotational the influence of eigendirections on geological structures is constrained by the rheology of a rock during deformation in homogenous steady flow no influence may be obvious spatially periodic material softening along eigenvectors during bulk hardening may result in a complex fabric of intersecting shear zones the geometry of the fabric elements provides important information on the bulk deformation of the rock particularly on the bulk shear sense

planktic foraminifers and hydrography of the eastern and northern caribbean sea the distribution of living planktic foraminifers and their relation to the hydrography of the caribbean sea was investigated in plankton net tows and surface sediment samples taken along the antilles island arc during april may 1996 the planktic foraminiferal community was strongly influenced by spatial variations in salinity that were largely due to the influx of orinoco river water into the southeastern caribbean sea and inflowing sargasso sea water in the north along the antilles island arc globigerinoides ruber was the dominant species in the surface waters throughout in the southeastern caribbean sea where orinoco river outflow influences the planktic community standing stocks of planktic foraminifers 100 m between 4 and 50 specimens m 3 were medium to low the southeastern faunas between tobago and guadeloupe were characterized by increased proportions of neogloboquadrina dutertrei highest standing stocks of 159 specimens m 3 in the upper 20 m of the water column were recorded in the northeastern caribbean sea and the assemblages were characterized by high proportions of globigerinita glutinata associated with cyclonic eddies in the anegada passage where sargasso sea water flows into the caribbean sea low standing stocks of 18 specimens m 3 indicate oligotrophic conditions together with the oligotrophic surface waters the subtropical underwater enters the caribbean sea through the anegada passage in water depths between 100 and 300 m these waters are characterized by higher concentrations of globorotalia truncatulinoides relative to the adjacent water masses comparison of the living planktic foraminiferal fauna with empty test assemblages from the water column and from surface sediments shows that differences in the faunal composition mostly correspond to the distribution of water masses and to the differential dissolution of species in the vicinity of islands globigerinoides ruber reaches higher relative frequencies than in the open ocean pointing towards a higher tolerance of this species towards neritic conditions than in other species

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

planktonic foraminifera in the western north pacific during the past 150 000 years comparison of modern and fossil assemblages abstract planktonic foraminiferal abundance variations in 186 deep sea piston core tops from the western north pacific were used to create a calibration set to characterize the present day kuroshio gyre system q mode factor analysis helped identify six faunal assemblages 93 variance related to modern water masses two tropical assemblages differing in relative dissolution three assemblages representing subtropical subpolar and transitional conditions and a gyre margin assemblage lying between the kuroshio current and the mainland of asia multivariate regression produced transfer functions relating observed summer august and winter february sea surface temperatures sst to the assemblages with standard errors of estimate of 1 5 c and 2 5 c respectively data from 24 piston cores was used to interpret variations of the kuroshio gyre system during the past 150 000 yr stratigraphic control is based on oxygen isotopic measurements the extinction of pink pigmented globigerinoides ruber at 120 000 b p coiling direction changes in neogloboquadrina pachyderma north of 30 n and dissolution variations between resistant and fragile taxa major dynamic changes in the circulation of the kuroshio gyre occurred during the last two glacial maxima at 15 20 000 b p isotopic stage 2 and at 140 150 000 b p isotopic stage 6 these intervals are characterized by 1 lowered sea levels which reduced flow into the sea of japan and sea of okh okhotsk 2 advance of the polar front from its modern position at about 42 n to 35 38 n 3 southward penetration of the oyashio current along the pacific coast of japan to tokyo 4 2 3 c lowered sst in tropical areas little or no change in subtropical areas and a 4 6 c decrease in transitional areas and 5 an overall decrease in carbonate dissolution relative to interglacial stages the maximum interglacial at 120 000 b p isotopic substage 5e shows a retreat of the polar front north of its modern position and an overall relative increase in interglacial carbonate dissolution that does not become severe until substage 5d

morphologic properties derived from a simple cross shore sediment transport model this paper builds on the now classical discussions by bowen 1980 and bailard 1981 on the applicability and implications of bagnold s 1963 sediment transport model to nearshore profile modeling we focus on the morphologic implications of both the strengths and weaknesses of bagnold s model isolating the transport terms that are well predicted i e mean flow terms from those that are not well predicted i e transport due to correlations between flow and sediment load we factor bagnold s model into a dimensional transport magnitude and a nondimensional term the nondimensional term describes the relative importance of transport due to undertow gravity and correlations between flow and sediment load the transport magnitude largely determines the response time of nearshore profiles for typical nearshore environments this response time was estimated to vary as a function of incident rms wave height hrms from 500 years hrms 0 5 m to 2 years hrms 3 m the relative importance of competing transport mechanisms is shown to depend strongly on the relative wave height defined as the ratio of the rms wave height to the local depth simplified nearshore transport parameterizations that are a function of this variable were derived and were interrogated for the existence and form of equilibrium profiles several differences from previously computed equilibrium profiles were noted first because the relative wave height saturates in natural surf zones equilibrium profiles converge to a relatively flat profile near the shoreline second under some situations a seaward sloping equilibrium profile may not exist third the long response times combined with unknown stability of an equilibrium profile make it difficult to assess the physical connection between theoretical equilibrium profiles and profiles observed in nature

shell size variation of the planktonic foraminifer neogloboquadrina pachyderma sin in the norwegian greenland sea during the last 1 3 myrs implications for paleoceanographic reconstructions we present measurements of the maximum diameter of the planktonic foraminifer neogloboquadrina pachyderma sin from six sediment cores ocean drilling program sites 643 644 907 909 985 and 987 from the norwegian greenland sea our data show a distinct net increase in mean shell size of n pachyderma sin at all sites during the last 1 3 ma with largest shell sizes reached after 0 4 ma external factors such as glacial interglacial variability and carbonate dissolution alone cannot account for the observed variation in mean shell size of n pachyderma sin we consider the observed shell size increase to mirror an evolutionary trend towards better adaptation of n pachyderma sin to the cold water environment after 1 1 1 0 ma probably the mid pleistocene climate shift and the associated change of amplitude and frequency of glacial interglacial fluctuations have triggered the evolution of this planktonic foraminifer oxygen and carbon stable isotope analyses of diverent shell size classes indicate that the observed shell size increase could not be explained by the functional concept that larger shells promote increasing sinking velocities during gametogenesis for paleoceanographic reconstructions the evolutionary adaptation of neogloboquadrina pachyderma sin to the cold water habitat has significant implications carbonate sedimentation in highest latitudes is highly dependent on the presence of this species in the norwegian greenland sea carbonate poor intervals before 1 1 ma are therefore not necessarily related to severe glacial conditions they are probably attributed to the absence of this not yet polar adapted species further transfer function and modern analog techniques used for the reconstruction of surface water conditions in high latitudes could therefore contain a large range of errors if they were applied to samples older than 1 1 1 0 myrs 2000 elsevier science b v all rights reserved

new field evidence for an exposure of the appalachian decollement at the east end of the pine mountain terrane georgia detailed field mapping at the east end of the pine mountain terrane in central georgia indicates that the box ankle fault is an 4 km thick ductile shear zone separating grenvillian basement of laurentian affinity in the footwall from allochthonous accreted terranes in the hanging wall fabric data from the box ankle fault indicate that it is a gently southeast dipping northwest vergent thrust fault recently discovered structural relations together with geochronological data indicate that the box ankle fault is of late paleozoic age we argue that the box ankle fault is a surface exposure of the appalachian decollement the east end of the pine mountain terrane may be the only place in the entire orogen where this fundamentally important structure is exposed for study

a review of calcareous nannofossil astrobiochronology encompassing the past 25 million years this paper presents a review of astrobiochronological calibration of recent to late oligocene calcareous nannofossil datum events biohorizons included in the paper are those of the widely used standard nannofossil zonations of martini e 1971 standard tertiary and quaternary calcareous nannoplankton zonation in farinacci a ed proceedings of the second international conference on planktonic microfossils roma rome ed tecnosci vol 2 pp 739 785 and okada h and bukry d 1980 supplementary modification and introduction of code numbers to the low latitude coccolith biostratigraphy zonation bukry 1973 1975 marine micropaleontology 51 321 325 as well as supplementary biohorizons proposed in the literature the biohorizons have been selected on the basis of the unambiguous taxonomy of the index taxa and their biostratigraphic usefulness we emphasise the application of rigorous methodology in nannofossil studies which permits an evaluation of biohorizons in terms of reliability and calibrates their potential correlatability astrochronological age estimates rely on the geologic timescale developed by the ics in 2004 with some new calibrations included we provide an overview of the relative position of biohorizons versus the astronomically calibrated ages of magnetic reversals and reference isotope stratigraphies surprisingly there are still few high resolution quantitative biostratigraphic studies of astrochronologically tuned sections in spite of the central role of such studies in addressing fundamental problems such as the tempo and mode of plankton evolution

coccolithophorids on the continental slope of the bay of biscay production transport and contribution to mass fluxes abstract coccoliths collected by sediment traps deployed on the slope of the bay of biscay northeastern atlantic from june 1990 to august 1991 were examined to determine their contribution to the transport of carbonate on a mid latitude continental margin they also were used as tracers of particle transfer processes on this slope two traps located at 1900 m respectively at 2300 mooring site 1 and 3000 m mooring site 2 water depths provided high resolution 4 7 days time series samples covering a 14 month period at ms2 and a 3 month period at ms1 coccoliths from 28 species were identified over the course of the experiment among which emiliania huxleyi was always dominant relative abundance range 59 93 total coccoliths number fluxes were high but variable ranging from 390 106 to 1610 106 coccoliths m 2 day 1 at ms1 and from 58 106 to 1500 106 coccoliths m 2 day 1 at ms2 the time weighted mean flux calculated for the whole experiment at ms2 was 499 106 coccoliths m 2 day 1 estimate of coccoliths minimal contribution to total carbonate flux at 1900 m depth averaged 12 which represented a weighted mean flux of 7 3 mg m 2 day 1 2 7 g m 2 yr 1 lateral transport of coccoliths resuspended from shelf and or upper slope sediments seems to be the dominant transfer process to depth on this northeastern atlantic slope nevertheless the clear seasonal succession observed in the species composition implies that the deposition resuspension transport sequence is rapid presumably less than a few months several short and unsmoothed signals directly issued from coccoliths bloom events also were recorded in our traps a result that indicates rapid settling rates the overall coccolith sedimentation processes appear as being quite diversified but quantitative and qualitative analyses of aggregates collected by the traps suggest that they are important carriers of coccoliths in this margin environment

quaternary fluctuations in the northern hemisphere trade winds and westerlies the mass accumulation rate and grain size of the total colian component isolated from pelagic sediment in two north pacific cores piston core kk75 02 under the prevailing westerlies and deep sea drilling project site 503 beneath the trade winds have been used to evaluate changes in the intensity of atmospheric circulation and source area aridity over the past 700 000 yr the eolian grain size a direct indicator of wind intensity fluctuates at periodicities similar to those calculated for the earth s orbital parameters of precession obliquity and eccentricity both sites display greater variability in wind intensity prior to 250 000 yr ago eolian accumulation rates an indicator of source area aridity fluctuate at periodicities similar to those of the glacial interglacial cycles lower eolian accumulation rates during colder glacial times most likely reflect increased glacial age humidity at central asian and central american source areas

precessional forcing of nutricline dynamics in the equatorial atlantic climate control of nutricline depth in the equatorial atlantic can be monitored by variations in the abundance of the phytoplankton species florisphaera profunda a conceptual model based on in situ evidence associates high abundances of f profunda with a deep nutricline and low abundances with a shallow nutricline a 200 000 year record of f profunda relative abundances obtained from a deep sea core sited beneath the region of maximum equatorial divergence at 10 w has 52 percent of its variance centered on the 23 000 year precessional band cross spectral analysis between the signals of f profunda and sea surface temperature independently derived from zooplankton species shows their 23 000 year cycles to be coherent and nearly in phase abundance minima of f profunda coincide with times of december perihelion whereas abundance maxima coincide with june perihelion these relations indicate that nutricline dynamics in the divergence region of the equatorial atlantic are controlled by variations in the tropical easterlies forced by the precessional component of orbital insolation on time scales greater than 10 000 years

a model for the development of crenulations in shear zones with applications from the southern appalachian piedmont abstract two sets of crenulations are associated with a major alleghanian dextral shear zone which deformed stratigraphic and structural boundaries in the eastern piedmont of south carolina both sets of crenulation planes are oblique to the boundaries of the shear zone the morphologies and orientations of the crenulation sets and their spatial distributions indicate that they are related to slip along foliation planes and that they serve to compensate for displacement components of foliation slip normal to the overall movement direction in the shear zone the crenulations act to maintain the initial thickness of the shear zone our evaluation of the recent literature on shear zones suggests that crenulations related to foliation slip are abundant and constitute a reliable sense of shear indicator

multi scale analysis of proterozoic shear zones an integrated structural and geophysical study abstract structural mapping of poorly exposed shear zone outcrops is integrated with the analysis of aeromagnetic and bouguer gravity data to develop a multi scale kinematic and relative overprinting chronology for the palaeoproterozoic tallacootra shear zone australia d 2 mylonitic fabrics at outcrop record kimban aged ca 1730 1690 ma n s shortening and correlate with sz 1 movements overprinting d 3 sinistral shear zones record the partitioning of near ideal simple shear and initiated riedel to regional scale sz 2 strike slip on the tallacootra shear zone sz 2 previously undocumented ne sw extension led to the emplacement of aplite dykes into the shear zone and can be correlated to the ca 1595 1575 ma hiltaba magmatic event d 4 dextral transpression during the ca 1470 1450 ma coorabie orogeny reactivated the tallacootra shear zone sz 2 r4 exhuming lower crust of the northwestern fowler domain within a positive flower structure this latest shear zone movement is related to a system of west dipping shear zones that penetrate the crust and sole into a lithospheric detachment indicating wholesale crustal shortening these methods demonstrate the value of integrating multi scale structural analyses for the study of shear zones with limited exposure

reconstruction of paleoceanographic conditions in the northwestern pacific ocean over the last 500kyr based on calcareous nannofossil and planktic foraminiferal assemblages calcareous nannofossil and planktic foraminiferal assemblages from odp hole 1210a in the northwestern pacific ocean were used to reconstruct surface water conditions for the past 500 kyr stratigraphic control was provided by calcareous nannofossil events that are thought to be synchronous over a broad range of latitudes calcareous nannofossil and planktic foraminiferal assemblages and abundance patterns indicate the unlikelihood of long term milankovitch scale latitudinal shifts of the kuroshio extension over the last 500 kyr and illustrate two successive surface water mass states one that prevailed prior to 300 ka and one that existed after 300 ka the relative abundance of very small placoliths and the absolute abundance of the upper photic zone upz coccolith species decrease abruptly at approximately 300 ka the relative abundance of the lower photic zone lpz species florisphaera profunda greatly increases at the same time although intervals during which the relative abundance of this taxon is very low or absent also occur prior to 300 ka the absolute abundance of planktic foraminifera gradually increased after the 300 ka boundary including peaks of globoconella inflata these assemblage and abundance changes suggest significant modifications to the surface water mass structure surface water was weakly stratified prior to 300 ka but alternated between intensely stratified and vertically mixed after 300 ka changes in the surface water mass structure suggest an intensification of the east asian summer and winter monsoon after 300 ka

the last 100 000 years in the western mediterranean sea surface water and frontal dynamics as revealed by coccolithophores a quantitative analysis was carried out on coccolith assemblages from two pleistocene cores k1 and k10 from the western mediterranean the distribution of selected coccolithophore species provides new paleoclimatic and paleoceano graphic data a continuous sequence from the top of isotope stage 5 to the holocene was recorded the reversal in dominance between gephyrocapsa muellerae and emiliania huxleyi was dated in both cores at ca 73 ka at about 47 ka e huxleyi shows a regular increase whereas g muellerae progressively decreases in abundance during interglacial periods high concentrations of coccoliths are observed whereas in glacial times coccoliths are more diluted and the percentage of reworked forms increases as a consequence of the higher terrigenous input after taking careful account of the dilution factor we conclude that the production of coccolithophores was higher during warm periods maxima in coccolith concentrations coincide with highstand episodes probably as a result of the intensification of the atlantic flux into the mediterranean across the gibraltar strait this intensification could have produced an increase in nutrient content in the surface mediterranean waters during cold periods the western mediterranean front underwent a reduction in activity probably due to an increase in the saline and or thermal gradients between the superficial waters and intermediate waters in the liguro provencal basin

puzzles and the maximum effective moment mem criterion in structural geology abstract the essential difference in the formation between conjugate brittle shear fractures and ductile shear zones is that the intersection angle of conjugate faults in the contractional quadrants in the former is acute usually 60 and obtuse usually 110 in the latter the mohr coulomb failure criterion is an experimentally validated empirical relationship which structural geologists use to interpret the stress directions based on the orientation of the brittle shear fractures however a simple application of this criterion assuming that the principal stresses are vertical or horizontal throughout the crust fails to explain crustal scale low angle normal faults high angle reverse faults and certain types of conjugate strike slip faults that have intersection angles in the compressional quadrants greater than 90 although the maximum effective moment mem criterion has been used to analyze structures in several natural cases and obtained some new evidence in nature and experiments it is not yet commonly used to interpret non mohr coulomb features widely distributed in the crust it is important to review the mem criterion and its implications for explaining the formation mechanism of naturally occurring faults and shear zones behavior of a rock depends on its mechanical properties the latter in turn depends on pressure and temperature conditions related to crustal depth and strain rates conjugate fractures with obtuse angles ca 110 in the contractional direction at different scales and at different crustal levels are consistent with the prediction of the mem criterion and suggest deformation at low strain rates thus strain rate clearly plays an important role in the style of crustal deformation and the many observed departures from the mohr coulomb failure criterion

do sample preparation techniques affect the relative abundance of florisphaera profunda abstract we investigated which method among smearing settling filtration and random settling is the most accurate for determining the relative abundance of florisphaera profunda this species is included in paleoproductivity indices because it is one of the most important deep water dwellers therefore an accurate assessment of its relative abundance is key to monitoring variations in thermocline and nutricline depths the low birefringence and flat polygonal shape of f profunda may lead to inaccurate estimates of its relative abundance as it is poorly visible under light microscopy lm and different sample preparation may affect the number of specimens on each slide we studied eight samples from the ocean drilling program odp site 1209b shatsky rise nw pacific from the last 450 kyr each sample was prepared five times using each technique for a total of 160 slides through a rigorous analytical and statistical approach we demonstrated the high reproducibility of each method and showed good agreement among techniques at low percentages of f profunda when the percentage of this species increases the random settling technique differs from the others filtration and random settling preparation techniques were calibrated by spiking samples with microbeads the ratio of microbeads observed in slides prepared using these two methods reflects bias due to loss of particles in the filtration technique in addition a hydrodynamic model for a fluttering and tumbling plate such as f profunda nannoliths is proposed here along with calculated sinking velocities these findings confirmed the efficiency of the long decantation time proposed for the random settling technique the analysis of replicates the validation with microbeads and the estimation of settling velocity of nannofossils in the tube convinced us that the higher relative abundance recorded by the random technique is not due to an imprecision of this method but on the contrary reflects the fact that it is more effective

s c mylonites two types of foliations are commonly developed in mylonites and mylonitic rocks a s surfaces related to the accumulation of finite strain and b c surfaces related to displacement discontinuities or zones of relatively high shear strain there are two types of s c mylonites type i s c mylonites described by berthe et al typically occur in deformed granitoids they involve narrow zones of intense shear strain which cut across mylonitic foliation type ii s c mylonites described here have widespread occurrence in quartz mica rocks involved in zones of intense non coaxial laminar flow the c surfaces are defined by trails of mica fish formed as the result of microscopic displacement discontinuities or zones of very high shear strain the s surfaces are defined by oblique foliations in the adjacent quartz aggregates formed as the result of dynamic recrystallization which periodically resets the finite strain clock these oblique foliations are characterized by grain elongations alignments of segments of the grain boundary enveloping surfaces and by trails of grains with similar c axis orientations examples of this aspect of foliation development in mylonitic rocks are so widespread that we suggest the creation of a broad class of s c tectonites and a deviation from the general tradition of purely geometric analysis of foliation and time relationships kinematic indicators such as those discussed here allow the recognition of kilometre scale zones of intense non coaxial laminar flow in crustal rocks and unambiguous determination of the sense of shear

north pacific seasonality and the glaciation of north america 2 7 million years ago in the context of gradual cenozoic cooling the timing of the onset of significant northern hemisphere glaciation 2 7 million years ago is consistent with milankovitch s orbital theory which posited that ice sheets grow when polar summertime insolation and temperature are low however the role of moisture supply in the initiation of large northern hemisphere ice sheets has remained unclear the subarctic pacific ocean represents a significant source of water vapour to boreal north america but it has been largely overlooked in efforts to explain northern hemisphere glaciation here we present alkenone unsaturation ratios and diatom oxygen isotope ratios from a sediment core in the western subarctic pacific ocean indicating that 2 7 million years ago late summer sea surface temperatures in this ocean region rose in response to an increase in stratification at the same time winter sea surface temperatures cooled winter floating ice became more abundant and global climate descended into glacial conditions we suggest that the observed summer warming extended into the autumn providing water vapour to northern north america where it precipitated and accumulated as snow and thus allowed the initiation of northern hemisphere glaciation

southern ocean pleistocene calcareous nannofossil events calibration with isotope and geomagnetic stratigraphies abstract several cores recovered from the northern belt of the southern ocean were analysed to study the pleistocene calcareous nannofossil records calcareous nannofossil events previously described in medium and low latitudes were identified and calibrated with the oxygen isotope and geomagnetic time scales although sedimentation rates hiatuses and degree of calcareous nannofossil preservation sometimes prevent the identification and or accurate calibration of some of these events a useful stratigraphic framework was obtained the possibility of using these calibrated events from high to low latitudes facilitates correlations and should facilitate isotope event identification in a region with low temperature where calcareous plankton stratigraphies are in general restricted in general pleistocene southern high latitude calcareous nannofossil events show synchronism with those observed in warm and temperate surficial waters small discrepancies in the assigned ages are sometimes related to low sampling resolution due to low sedimentation rates the first occurrence fo of emiliania huxleyi and the last occurrence lo of pseudoemiliania lacunosa are observed in marine isotope stages mis 8 and 12 respectively a reversal in abundance between gephyrocapsa muellerae and e huxleyi is observed close to the mis 4 5 boundary mis 6 is characterised by an increase in g muellerae and mis 7 features a dramatic decrease in the proportion of gephyrocapsa caribbeanica this latter species began to increase its proportions from the mis 13 14 boundary to mis13 showing diachronism between the different sites the lo of reticulofenestra asanoi is observed at mis 22 confirming this event as a global synchronous reference datum by contrast the fo of r asanoi occurs at mis 35 and is diachronous with the existing data from other oceanic regions a re entry of medium sized gephyrocapsa 3 5 m maximum diameters can be identified in some cores close to mis 25 although the low abundance of this taxon prevents an accurate calibration it may be concluded that this event is diachronous as compared with the existing low latitude data the lo of large morphotypes of gephyrocapsa is well correlated with mis 37 showing synchronism with other oceanic regions whereas the fo of this species is not well calibrated due to the absence of age control points

pleistocene fluctuations in the northern benguela current system as revealed by coccolith assemblages late pleistocene coccolith data of odp site 1082 from the eastern south atlantic off namibia were analysed to document spatial and temporal changes in surface ocean circulation upwelling intensity and associated productivity the studied site is located on the continental slope close to prominent oceanographic features such as the coastal upwelling mixing area the openoceanic realm and the warm water regime of the angola current highest numbers of total coccoliths up to 30 10 9 coccoliths g 1 sediment were observed during relatively warm periods characterised bydecreased upwellingintensity these elevatednumbers ofcoccoliths are due to highersurface water temperatures anddocumentadomainprobablyinfluencedbylowernutrientconcentrationsinanareawhereoceanicandfilamentouswatermix in contrast low numbers of coccoliths during glacial periods probably characterise time intervals of enhanced upwelling accompanied byabroad filamentous mixing area coccoliths of the genusgephyrocapsaarethe most abundant taxain samples of site 1082 their occurrences are characterised by abrupt changes in the investigated time interval in addition calcidiscus leptoporus pseudoemilinia lacunosa and reticulofenestra asanoi contribute a common part of the assemblage coccoliths accountformorethanhalfofthecarbonate withpeakcontributionofupto 80 intheinterval560to280kawhengephyrocapsa caribbeanica is the major caco3 producer increased carbonate accumulation during this time interval point to an overall weakening of the coastal upwelling intensity accompanied by a reduction of the mixing zone influencing the site location during this event d 2004 elsevier b v all rights reserved

late quaternary nannofossil indicators of climate change in two deep sea cores associated with the leeuwin current off western australia the stratigraphic variations in nannoflora observed in the two deep sea cores recovered from the offshore western australia revealed a sequence of paleoceanographic changes for the last 250 kyr the dominance of small placolith taxa in the upper photic flora indicates continuous mild upwelling for the isotope stages 7 5 in this region the most important controlling factor for the abundance variation of florisphaera profunda in this region is considered to be the lower photic temperature rather than the stability of water column or the water turbidity the significant reduction in the abundance of f profunda combined with the stable in the northern core rs96gc21 and reduced in the southern core rs9 150 abundance of the small taxa suggest an intensified upwelling for the penultimate glaciation the sharp increase in f profunda abundance indicates a weakening of upwelling at the last interglacial climax lic offshore western australia after isotope stage 5 the existence of upwelling is not clear except in stage 2 when it was not strong enough to produce blooms of emiliania huxleyi among the subordinate taxa calcidiscus leptoporus calciosolenia murrayi neosphaera coccolithomorpha and oolithotus fragilis provide meaningful paleoceanographic signals supporting the conclusions of previous studies a weakening or cessation of leeuwin current for the glacial periods the shift of dominance from small gephyrocapsa mostly g ericsonii to small reticulofenestra mostly r parvula can be an useful datum event offshore western australia the reduced diversity of nannoflora during the interglacial periods can be explained by a lessened competition within nannoplankton community caused by particularly favorable conditions for the opportunists such as e huxleyi f profunda and small placoliths the variations in nannofossil abundance suggests an increased aeolian flux at the stages 6 and 2 offshore north west cape as well as at stage 6 offshore southwestern australia

state of strain in mylonites from the western blue ridge province southern appalachians the role of volume loss abstract this study examines the state of finite strain in quartzo feldspathic mylonites from two localities in the western blue ridge province of the southern appalachians mineral shape fabric and whole rock chemical and modal data suggest that the mylonites deformed by inhomogeneous shortening normal to the foliation and progressive shear parallel to the foliation the deformation involved substantial bulk rock volume loss strain was partitioned between solution transfer processes in feldspar and dislocation creep processes in quartz and micas at temperatures of between 300 and 450 c initially feldspars underwent grain size reduction by cataclasis but at advanced stages of mylonitization alkali feldspar grains display subrounded oblate shapes 0 k k values 0 2 k 60 bulk volume loss density changes were minor on the basis of feldspar grain shapes and modal and whole rock chemical data volume loss was largely accommodated by fluid infiltration and incongruent dissolution of alkali feldspar producing muscovite and involved the loss of alkalis and silica to the fluid phase the mylonites may have nucleated as solution zones which subsequently underwent strain softening and displacement parallel to the zone boundaries

an atlas of the distribution of calcium carbonate in sediments of the deep sea historical observations of the concentration of calcium carbonate in global deep sea sediments are compiled and compared with a new gridded field of seawater co3 concentration to reveal regional variations in the calcite lysocline the most obvious mode of variability of the calcite lysocline is the thickness of the lysocline defined here as the difference in overlying water carbonate saturation co3 between high and low calcite sediments with a thicker lysocline in the atlantic than in the pacific i attribute this variation to differences in the delivery rate of terriginous material a recent model for the lower glacial atmospheric pco2 proposed to change the relationship between the depth of the lysocline and the co3 of the water column by changing the rain rate ratio of organic carbon to calcite production the rain ratio model archer and maier reimer 1994 i search the data set for analogs to the proposed glacial world by looking for a link between the regional climate at the sea surface and the depth of the lysocline below the co3 at the carbonate compensation depth ccd in the tropics appears to be 10 20 mol kg 1 co3 more undersaturated than in high latitudes but this is smaller than the 40 mol kg 1 shift required by the model in addition the general resemblance of the glacial lysocline to the present day requires that the proposed shift in co3 at the ccd be globally uniform rather than locally variable as climate forcing would probably generate i conclude that the rain ratio model would probably require some globally uniform perturbation during glacial time such as a change in ocean si content if it is to explain the entire pco2 decrease observed in the glacial atmosphere finally i grid the sedimentary data to estimate that the inventory caco3 which is available to neutralize fossil fuel co2 is approximately 1600 gt carbon a quantity which may be exceeded by fossil fuel release in the next several centuries

sense and non sense of shear in flanking structures abstract the deformation of marker horizons across slip surfaces can lead to the development of several types of flanking structures the development of such structures was investigated using a numerical model to simulate the flow around a slip surface in a viscous medium the modelled structures can be classified on the basis of three criteria 1 the extensional or contractional offset of markers 2 the co or counter shearing sense along the slip surfaces and 3 the normal or reverse drag of markers relative to the shear sense along the slip surfaces as a function of the kinematic vorticity of the flow and the initial orientation of the slip surface with respect to the shear zone boundaries three main types of structures can develop 1 shear bands developed along co shearing extensional slip surfaces 2 a type flanking folds developed along counter shearing slip surfaces and 3 s type flanking folds developed along co shearing contractional slip surfaces all these structures can occur with either normal or reverse drag effects shear bands and a type flanking folds recording opposite shear senses can be geometrically very similar and consequently lead to kinematic misinterpretations however correctly identified flanking structures can provide quantitative information about the kinematic vorticity of the flow

impact of the azores front on the distribution of planktic foraminifers shelled gastropods and coccolithophorids abstract the azores front current system south of the azores islands has been studied in order to reveal the direct impact of an open oceanic thermohaline front on the distribution of the calcareous plankton planktic foraminifers pteropods heteropods and coccolithophorids were sampled from the upper 2500 m of the water column during august 1997 and january 1999 in addition the hydrography was recorded across the frontal jet on combined ctd and xbt transects in august 1997 a strong seasonal thermocline capped the azores front af at about 60 90 m water depth below the thermocline a distinct hydrographic front was indicated by temperature and salinity gradients the central af was an area of low planktic foraminiferal gastropod and coccolithophorid production and was a faunal barrier for shallow and deep dwelling species highest numbers of planktic foraminifers gastropods and coccolithophores were recorded from above the thermocline north of the af the most frequent planktic foraminiferal and pteropod species were globigerinoides ruber white and limacina inflata respectively below 100 m planktic foraminifers were most frequent north of the af and gastropod shells were rare in particular the deep dwelling planktic foraminifer globorotalia scitula was frequent only at sampling sites north of the af in january 1999 the surface water temperature of the azores front current system was lower and the thermocline was deeper than in august 1997 the planktic foraminiferal standing stock was three times higher than in august 1997 and no water depth related faunal changes occurred the fauna was dominated by globorotalia truncatulinoides and turborotalita humilis was frequent during both january and august the fauna from south of the azores was different from that to the southeast recording the occurrence of two different water masses in this study we present a micropaleontological definition of the af in order to provide a paleoceanographic tool that may be used to decipher the late quaternary current system of the north atlantic ocean

distribution of biogenic silica and quartz in recent deep sea sediments all available quartz and biogenic silica concentrations from deep sea surface sediments were intercalibrated plotted and contoured on a calcium carbonate free basis the maps show highest concentrations of biogenic silica opal along the west african coast along equatorial divergences in all oceans and at the polar front in the southern indian ocean these are all areas where upwelling is strong and there is high biological productivity quartz in pelagic sediments deposited far from land is generally eolian in origin its distribution reflects dominant wind systems in the pacific but in much of the atlantic and indian oceans the distribution pattern is strongly modified by turbidite deposition and bottom current processes

character of the alleghanian orogeny in the southern appalachians part ii geochronological constraints on the tectonothermal evolution of the eastern piedmont in south carolina a nearly concordant u pb zircon age of 550 4 ma is interpreted to closely date crystallization of the epizonal little mountain metatonalite in the southeastern part of the charlotte belt in south carolina this confirms field studies which indicate that the charlotte belt contains a plutonic metaigneous complex that developed as a sub volcanic arc infrastructure contemporaneous with vulcanism manifested in the carolina slate belt both paleontological and geochronological controls indicate that the south carolina slate belt is mostly younger than 570 ma cambrian whereas the slate belt in north carolina and virginia is mostly of late proterozoic age a regionally significant mid paleozoic ca 340 360 ma thermal event is suggested by discordant 40ar 39ar whole rock age spectra of slate phyllite in the northwestern carolina slate belt and from hornblende in the southeastern charlotte belt it is uncertain if this event was associated with deformation in the eastern piedmont however mid paleozoic deformation has been previously documented elsewhere in the western piedmont a slightly disconcordant u pb zircon age of 317 4 ma is interpreted to closely date initial crystallization of the deformed edge field granite and confirms a record of late paleozoic penetrative deformation in the kiokee belt of south carolina u pb isotope data for the lake murray orthogneiss and clouds creek granite are discordant and suggest that the magmas of these plutons were derived by partial melting of a sialic precam brian source and then emplaced in the eastern piedmont at ca 315 ma prior to or during the early stages of the alleghanian orogeny the thermal maximum of alleghanian regional metamorphism amphibolite facies in the kiokee belt greenschist facies in the southeastern part of the carolina slate belt occurred during ca 295 315 ma during the late carboniferous and early permian the eastern piedmont experienced differential uplift erosion and relatively rapid postmeta morphic cooling isothermal surfaces were folded into an antiform synform antiform configuration corresponding to the kiokee carolina slate and charlotte belts respectively the geochronological data provide the following calibration for the late paleozoic deformational chronology recorded in the kiokee and carolina slate belts d2 lake murray deformation ca 295 315 ma d3 clarks hill deformation ca 285 295 ma and d4 irmo deformation ca 268 290 ma

geometry classification and kinematics of s c and s c fabrics in the mushandike area zimbabwe planar fabrics in small dextral shear zones in the mushandike area of the zimbabwe archaean craton consist of a sigmoidal primary foliation s displaced by discrete shears c or c these planar fabrics can be divided into porphyroclastic megacrystic and banded types depending mainly on the values of the angles between s and c or c surfaces the structures that define s surfaces and the spacing of c or c surfaces the values of the angles between the foliations are proposed as the basis for a general classification of planar fabrics in shear zones the values of the angles depend on microstructures and strain microstructural evidence shows that slip did not occur on s surfaces but only on c or c surfaces a model for the development of the fabrics proposes that s surfaces lie parallel to the xy plane of the local finite strain ellipsoid in domains of simple shear between c or c surfaces c surfaces may form in the orientation of a coulomb failure surface the field evidence suggests that an increase in bulk strain is at least partly accommodated by an increase in local strain in domains between c or c surfaces as the s surfaces rotate with the local finite strain ellipsoid

quaternary paleo oceanography pteropod preservation and stable isotope record of the red sea abstract an abundance of pteropod species their mode of preservation and stable isotope ratios of carbon and oxygen in benthic and planktic foraminifera have been determined in core md76 140 from the northern red sea isotopic data and benthic foraminiferal species indicate changes in o2 concentration in the bottom sediments the glacial stages are characterized by an almost anoxic bottom while the interglacial bottom was generally well ventilated in general very well preserved pteropod shells occur in glacial oxygen depleted intervals and also on recent well ventilated bottoms in the interglacial stages the preservation deteriorates and in the most extreme cases there is a complete dissolution of the aragonitic shells in these cases most of the assemblage is lost and the only traces of the original shells are their internal molds these are cemented with high magnesium calcite hmc which is a more stable carbonate phase in bottom sediments of the interglacial dissolution of aragonite discriminates between large and small shells the latter tend to be removed completely while the larger ones may be preserved as internal hmc molds limacina inflata is more readily molded than l trochiformis and thus its relative abundance increases in poorly preserved assemblages the state of aragonitic shell preservation depends on the degree of organic matter combustion in the sediments well preserved shells occur in sediments where the supply of organic matter is limited and o2 levels are high preservation deteriorates with increasing supply of organic carbon o2 consumption and increasing production of co2 in this case the dissolved carbonate is reprecipitated as hmc cement with further increase in organic matter supply and reduced ventilation nearly all oxygen is consumed and no3 and subsequently so42 become the oxidizing agents this is followed by an increasing carbonate alkalinity and excellent aragonitic shell preservation

the deformation matrix for simultaneous simple shearing pure shearing and volume change and its application to transpression transtension tectonics simultaneous simple shearing and pure shearing with or without additional volume change can be combined into a single upper triangular deformation matrix the off diagonal term is named the effective shear strain and is a simple function of the pure shearing and simple shearing components a three dimensional deformation matrix for the simultaneous combination of coaxial deformation with or without additional volume change and up to three simple shearing systems with mutually orthogonal shear planes is also presented by using this matrix one can easily extract the various properties of incremental as well as finite strain and the progressive as well as finite rotation of passive markers during deformation the case of transpression transtension is revised using the unified deformation matrix the orientation of the major axis of the strain ellipsoid 1 is always horizontal if the deformation is transtensional switches from horizontal to vertical during transpressional wrenching 1 wk 0 81 for constant vorticity deformations and is always vertical for highly transpressional deformations wk 0 81 for transpression material lines initially rotate towards the horizontal shearing direction but generally turn to rotate towards the vertical axis after a certain strain for transtension all material lines rotate towards a direction in the horizontal plane which is oblique to the shearing direction

character of the alleghanian orogeny in the southern appalachians part i alleghanian deformation in the eastern piedmont of south carolina the eastern piedmont province in south carolina contains a sequence of cambrian volcanic and sedimentary rocks that was penetratively deformed d1 and regionally metamorphosed m1 to the greenschist facies during the early and or middle paleozoic the eastern piedmont was subsequently affected by late paleozoic alleghanian polyphase deformation d2 d4 and regional metamorphism the earliest alleghanian event d2 is associated with amphibolite facies regional metamorphism and felsic plutonism in a mid crustal infrastructure at ca 295 315 ma the gradational interface between infrastructure and overlying suprastructure contained a steep m2 metamorphic gradient between amphibolite facies below and greenschist facies above numerous sheets of felsic orthogneiss and a deformation front marking the upper limit of intense d2 penetrative deformation d3 is represented by northwestward vergent folding of s1 and s2 foliations and m2 isothermal surfaces the kiokee belt in south carolina is interpreted as a d2 infrastructure exposed within the core of a d3 antiform this interpretation suggests that an alleghanian infrastructure may be present in the subsurface beneath much of the piedmont and coastal plain the polygenetic modoc zone forms the northwest boundary of the kiokee belt it is interpreted to represent an interface between d2 infrastructure and suprastructure which was rotated into a steep northwest dipping attitude during development of the kiokee belt antiform between ca 267 and 290 ma portions of the kiokee belt modoz zone and carolina slate belt were overprinted by ductile deformation d4 along steeply dipping northeast trending dextral shear zones

vorticity analysis in a metachert from the sanbagawa belt sw japan abstract common tectonic features of deformed metachert include both sets of extended and shortened veins and quartz c axis preferred orientation patterns in such rocks information is also commonly available on the orientation and magnitude of the finite strain these features can be used to derive two independent estimates of the degree of non coaxiality during deformation in an example from the sanbagawa belt sw japan the two methods give consistent results and show that deformation was intermediate between simple and pure shear such types of progressive deformation distributed over a broad region could cause substantial subvertical thinning and be a significant factor in the exhumation of high p t rocks in the region

laminar flow in shear zones the pernambuco shear zone ne brazil abstract the pernambuco shear zone psz is a 700 km long branch of one of the largest and best exposed precambrian strike slip shear zone systems in the world the shear zones are part of the eroded record of a large scale collision zone foliation and lineation orientations along the shear zone indicate that local deformation perturbations have produced variable fabric orientations with up to 40 change in dip and strike however the dominant flow pattern is consistently horizontal strike slip across a vertical shear plane well developed dextral shear sense criteria are observed at most localities although oblate strain fabrics are common and lineations are frequently absent very few small folds were found to refold the shear fabric developed in late precambrian granites which intrude along most of the shear zone but sheath folds are common in mylonitized pre shear gneisses this geometrical evidence indicates that steady laminar shear flow took place in the initially isotropic granites and more irregular but not turbulent flow preferentially developed in rocks with a pre existing fabric the deformation pattern is similar to many other deep crustal shear zones laminar shear flow is thought to be common in granites and coarse crystalline gneisses deformed in upper amphibolite to granulite facies conditions the dramatic weakening of the middle crust produced by syn shear injection of granites and mafic intrusions into vertical shear zones may cause the predominant movement pattern in collision zones to be strike slip lateral extrusion rather than compressional thrusting

the fate of coccoliths at 48 n 21 w northeastern atlantic abstract as part of the joint global ocean flux study program jgofs north atlantic bloom experiment nabe coccolithophore fluxes were recorded over one year period from april 1989 to april 1990 three vertically moored sediment traps synchronized on a 14 day interval were deployed at 48 n 21 w at three water depths at 1 2 and 3 7 km sea floor at 4 4 km we present the results on the vertical variability of coccolith and coccosphere fluxes through the water column calcium carbonate was the largest component of the total mass flux followed by particulate organic matter and opal coccolith and coccosphere seasonal fluxes followed the seasonality of the biogeochemical particle fluxes at all three depths with maxima occurring during the spring particle bloom the decrease in correlation between coccosphere and coccolith fluxes with depth from r 0 98 at 1 km depth to 0 60 at 3 7 km depth documents that disaggregation of the coccospheres occurs during settling in the deeper part of the water column between 1 and 3 7 km water depth annual coccosphere and coccolith fluxes were 1 5 108 and 0 9 10 11 m 2 year 1 respectively at 1 km depth or 3 1 108 and 1 4 10 11 m 2 year 1 including the spring 1990 episode for the 3 7 km trap the corresponding values were 0 5 108 and 1 1 1011 0 6 108 and 1 1 1011 including the partially recorded spring 1990 episode the slight increase in coccolith numbers with water depth can be explained by coccosphere disintegration and lateral influx nevertheless selective dissolution of delicate coccolith species from 1 to 3 7 km water depth occurs e g relative abundances of oolithothus fragilis coccoliths decrease from 3 at 1 km to less than 0 5 at 3 7 km water depth emiliania huxleyi gephyrocapsa muellerae calcidiscus leptoporus and coccolithus pelagicus constitute from 65 at 1 km depth to 95 at 3 7 km depth of the total coccolith assemblages the same four coccolith taxa dominate the fossil assemblages in the underlying surface sediments selective dissolution continues in the sediments most notably the abundance of the solution resistant species c leptoporus increases from 10 to 15 in the trap samples to 15 40 in the sediments annual flux of calcium carbonate in sediment trap samples accounts for about 60 of the total annual mass flux with the coccolith fraction m being about 45 of the annual carbonate flux mean value of 41 at 1 km and 50 at 3 7 km water depth the correlation between the m caco 3 and the calculated coccolithophore and calcisphere caco3 fluxes decreases with depth r 0 92 at 1 km and r 0 86 at 3 7 km indicating that partial dissolution and fragmentation of the delicate less calcified coccolithophore and planktic foraminifera species occurs during settling this fine fragmentation of biogenic caco3 can contribute to the m fraction causing the decrease of correlation with the calculated caco3 fluxes being based only on the flux of intact coccoliths and calcispheres

40ar 39ar constraints on chronology of augusta fault zone movement and late alleghanian extension southern appalachian piedmont south carolina and georgia

muted climate variations in continental siberia during the mid pleistocene epoch the large difference in carbon and oxygen isotope data from the marine record between marine oxygen isotope stage 12 mis 12 and mis 11 spanning the interval between about 480 and 380 kyr ago has been interpreted as a transition between an extremely cold glacial period and an unusually warm interglacial period with consequences for global ice volume sea level and the global carbon cycle1 2 3 4 the extent of the change is intriguing because orbital forcing is predicted to have been relatively weak at that time5 here we analyse a continuous sediment record from lake baikal siberia which reveals a virtually continuous interglacial diatom assemblage a stable littoral benthic diatom assemblage and lithogenic sediments with interglacial characteristics for the period from mis 15a to mis 11 from about 580 to 380 kyr ago from these data we infer significantly weaker climate contrasts between mis 12 and 11 than during more recent glacial interglacial transitions in the late pleistocene epoch about 130 to 10 kyr ago for the period from mis 15a to mis 11 we also infer an apparent lack of extensive mountain glaciation

florisphaera profunda a possible nannoplankton indicator of late quaternary changes in sea water turbidity at the northwestern margin of the pacific three piston cores from the ryukyu trench slope northwestern margin of the pacific ocean contain nearly continuous paleoceanographic records of the last 320 165 and 105 kyr ages of the cores are constrained by planktic 18o stratigraphy and roughly substantiated by the presence of two calcareous nannofossil events spectral analysis of the changes in relative abundance offlorisphaera profunda a nannoplankton species presently living in the lower euphotic zone reveals a maximum power at 0 01 cycles kyr corresponding to the 100 kyr cycle of orbital eccentricity much lower power is observed at the 23 kyr precessional band this differs from the equatorial atlantic ocean variations which show dominant power in the 23 kyr precessional band in the changes off profunda abundances molfino and mcintyre 1990a besides our cores were taken outside the equatorial divergence zone we also show a rather close relationship betweenf profunda abundance and sea water transparency secchi depth in the present northwest pacific based on data from 204 sites of surface sediment samples because sea water transparency is primarily affected by bio productivity change in open ocean stratigraphic changes off profunda abundances in our cores seem to have been caused by productivity change as well pointed out by molfino and mcintyre 1990a b a mechanism proposed by them for its change however is not applied to our cases due to differences in spectral analysis results and in geographic situation alternatively we suggest that geographic change of the northwestern margin of the pacific during the late quaternary causedf profunda abundance change through the sea water turbidity change which has been affected not only by bio productivity but also by land origin particles supply

annual and interannual variability in the kuroshio current system abstract individual seasonal 300 m temperature maps were constructed over the kuroshio current system from 130 e to 170 w for a 4 year period from summer 1976 through spring 1980 using transpac xbt data and jodc temperature depth data quasi stationary meanders in the kuroshic current system occurred at 137 c i e kuroshio meander at 144 e and 150 e i e lee wave meanders and near 160 e i e meander over the shatsky rise a composite of the paths of the kuroshio i e the 12 c isotherm from the individual seasonal maps and the total variance map finds nodes i e minima and anti nodes i e maxima of variability to have existed along the mean kuroshio path the anti nodes coincided with the location of the quasi stationary meanders the nodes in between zonal propagation of temperature anomalies accounted for 20 30 of the total interannual variance these temperature anomalies propagated eastward at 0 5 1 5 cm s 1 in the region 140 155 e and westward at 1 to 2 cm s 1 in the re

strain and kinematic analysis in general shear zones we present a unifying theory for the development and distribution of strain markers and kinematic indicators in zones of general shear and thus provide a framework in which data previously considered contradictory may be understood rigid and deformable porphyroclast systems including and complex grains are potential indicators of both strain and flow the shapes and distribution of such porphyroclast systems may be used to distinguish among different tectonic regimes general shear is divided into two fields sub simple shear in which the rotational component of the strain is less than that for simple shear and super simple shear in which the rotational component is greater than for simple shear sub simple shear may involve narrowing or broadening of shear zones super simple shear regimes are possible in local regions such as the vicinities of deformable porphyroclasts but must be enclosed by regimes of sub simple shear the polar mohr constructions for finite deformation and flow are useful to analyze general shear in theory the hyperbolic net is employed for practical plotting of real data and derivation of the kinematic vorticity number wn this number represents the relative contributions of pure and simple shear in steady flow in nature deformation is thought to build up and decay by processes that may invalidate the assumption of constant flow regime we therefore introduce the concept of accelerating deformation and analyze the implications of non steady flow for the shearing histories of deformed objects

coccolithophore export production species composition and coccolith caco3 fluxes in the ne atlantic and abstract coccolithophores were examined in two sediment traps deployed for one year april 1989 to april 1990 at approximately 1 km water depth in the subtropical ne atlantic at 34 n 21 w station nabe 34 and in the temperate ne atlantic 48 n 21 w station nabe 48 as part of the jgofs north atlantic bloom experiment nabe at both stations maximum coccolith and coccosphere fluxes were recorded during local spring bloom periods the average coccolith and coccosphere fluxes at nabe 34 were 1 12 10 9 m 2 d 1 and 4 90 10 6 m 2 d 1 respectively at this station coccoliths from 51 taxa were identified a marked seasonal change was noticed in relative abundances of emiliania huxleyi and deep photic zone species e huxleyi dominated during spring while in late autumn the coccolith assemblage was dominated by florisphaera profunda and the coccosphere assemblage by g flabellatus and algirosphaera spp emiliania huxleyi was the most abundant species in the overall coccolith and coccosphere assemblages with 69 and 64 respectively at nabe 48 the average daily fluxes were significantly lower with 3 88 10 8 coccoliths m 2 d 1 and 8 45 10 5 coccospheres m 2 d 1 and only 36 taxa were recorded in the trap samples emiliania huxleyi was the dominant species in the coccolith assemblage throughout the year with 72 and showed maximum fluxes during spring 1990 coccolithus pelagicus exhibited a distinct seasonal pattern with maximum fluxes in early june 1989 probably related to the development of a mesoscale cyclonic eddy in the vicinity of the trap site holococcolithophore fluxes were highest during maximum sea surface temperatures in summer the coccosphere assemblage was dominated by gephyrocapsa spp syracosphaera spp and e huxleyi estimated caco3 fluxes of coccoliths coccospheres and calcareous dinophytes were compared with the caco3 content in the fine m fraction the annual mass estimated caco3 flux of coccoliths and coccospheres was 5 1 g m 2 yr at nabe 34 and 2 7 g m 2 yr at nabe 48 and that of calcareous dinophytes 0 9 and 0 1 g m 2 yr respectively these summed mass estimated values contributed on average only 55 at nabe 34 and 60 at nabe 48 to the fine fraction caco3

sedimentation in the western arabian sea the role of coastal and open ocean upwelling monsoon induced coastal and open ocean upwelling explain 84 of the variations of the organic carbon fluxes measured in the deep western arabian sea in this paper sea level measurements satellite derived wind speeds sea surface temperatures and nutrient profiles are used to discern the relative importance of these factors on fluxes measured during nine years of continuous sediment trap deployments this exercise shows i the increase in fluxes observed during the initial stages of the sw monsoons are caused by open ocean upwelling which develops faster than the coastal upwelling ii coastal upwelling triggers diatom blooms from nutrients from subsurface water and sediment resuspension and more importantly by injecting resting stages of diatoms back into the euphotic zone iii silica depletion resulting from diatom blooms in laterally advecting water masses leads to a replacement of diatoms by other nitrate limited organisms iv organic carbon fluxes to the deep arabian sea increase in response to an intensification of both coastal and open ocean upwelling weak coastal upwelling and strong open ocean upwelling also increase organic carbon fluxes the varying dominance of their influence is reflected in the timing and the composition of the peak fluxes v the link between organic carbon flux and monsoon strength is non linear probably due to changes in the surface currents and to vigorous turbulence in the surface water during strong sw monsoons these processes could reduce the organic carbon flux in the western arabian sea by about 65

kinematics of ductile shearing from outcrop to crustal scale in the monte rosa nappe western alps significant ductile deformation has produced widespread mylonitic structures in the basement orthogneisses and the mesozoic cover quartzites and marbles of the monte rosa nappe in the inner part of the western alps we summarize here the results of a detailed microstructural study at several scales of observation in the northern part of the nappe and discuss the kinematic significance and compatibility of such results most of the observed deformations can be accounted for by progressive wnw vergent shearing during and after the late eocene within a ductile shear zone of crustal scale the displacement of the hanging wall may have been in excess of several tens of kilometers however some ese vergent shear criteria cannot be reconciled with this general picture and suggest that local backthrusting occurred later near the toe of the monte rosa nappe

structural analysis of the carolina inner piedmont terrane boundary implications for the age and kinematics of the central piedmont suture a terrane boundary that records paleozoic laurentia gondwana interactions new field mapping along the carolina inner piedmont terrane boundary in south carolina and eastern georgia reveals preaccretionary synaccretionary and postaccretionary faults the dextral strike slip lowndesville shear zone is adjacent to a 50 km long segment of the terrane boundary however the lowndesville shear zone is correlated eastward with the dextral strike slip beaver creek shear zone which is within the carolina terrane and predates 415 ma the lowndesville shear zone is overprinted by a dextral strike slip phyllonite zone named the deal creek shear zone the deal creek shear zone is correlated eastward with the gold hill silver hill shear zone which is also within the carolina terrane and records dextral strike slip motion between 400 and 325 ma the cross anchor and mulberry creek faults both truncate the lowndesville and the deal creek shear zones and form the terrane boundary the mulberry creek fault probably of triassic jurassic age juxtaposes the lowndesville shear zone adjacent to the carolina inner piedmont terrane boundary west of waterloo south carolina the cross anchor fault is the terrane boundary east of waterloo south carolina and forms the southeastern boundary of the whitmire reentrant crosscutting relationships indicate that the cross anchor fault is the oldest fault which juxtaposes the carolina and inner piedmont terranes in the study area these structural interpretations and available geochronological data indicate that the cross anchor fault is a 325 ma thrust fault and may be the central piedmont suture an early alleghanian suture resolves the problem of inserting the carolina terrane into the western iapetus ocean

development of a shear band cleavage as a result of strain partitioning abstract microstructural analyses of shear band cleavages in a centimeter scale shear zone within a metasomatic biotite band in the teshima granite ryoke metamorphic belt southwest japan show that strain partitioning occurred between quartz and biotite feldspar domains within the shear zone pre tectonic hydrothermal alteration within the granite caused biotite replacement of both plagioclase and k feldspar resulting in the development of biotite feldspar domains where k feldspar mantles dominantly biotite plagioclase aggregates subsequently the altered granite was plastically deformed in simple shear so that intra layer shear band cleavages were passively developed within the biotite feldspar domains whereas intense dynamic recrystallization occurred in the quartz domains the rotation and orientation of the intra layer shear band cleavages can be explained by a finite strain ellipse model which shows that strain in the biotite feldspar domain requires only 10 20 of the bulk simple shear strain for the development of such cleavages so that most of strain could be accommodated by deformation in the quartz domain consequently the model suggests that the development of the shear zone resulted in strain partitioning between the quartz and the biotite feldspar domains due to compositional variations via hydrothermal alteration within the granite

on resolving shear direction in foliated rocks deformed by simple shear we present a three dimensional model for the formation of crenulations in ductile shear zones based on compatibility conditions infinitesimal displacement equations and our own field observations in many shear zones at least two and probably three mesoscopic slip systems are active crenulation slip is interpreted to compensate for the displacement component of foliation slip normal to the shear zone wall in zones in which foliation slip is an important mode of deformation foliation and crenulation slip vectors do not necessarily lie in the same plane nor are they necessarily perpendicular to crenulation axes solutions for the orientation of the crenulation plane crenulation slip vector and magnitude of the crenulation slip shear strain belong to one of two possible solution sets given the orientation of slipping foliation the foliation slip vector and the magnitude of slip on foliation hence shear sense may be reliably interpreted from composite planar fabrics in ductile shear zones but more specifically shear direction cannot these results have broad implications in the interpretation of the kinematic significance of mineral lineations oblique to crenulation axes and in the deduction of shear strain from angular relations between planar fabric elements

nutricline variation in the equatorial atlantic coincident with the younger dryas variations in nutricline depth during the last deglaciation are recorded by the phytoplankton species florisphaera profunda a stacked record of six deep sea cores shows that across the entire equatorial atlantic there was a brief shallowing of the nutricline centered on 11 ka coincident with the younger dryas this shallowing is linked with high latitude north atlantic deglacial events we invoke high albedo and cool sea surface temperatures in the northern latitudes during 11 ka which steepened an already higher than expected winter insolation and hence temperature gradient for a time of june perihelion we postulate that the resultant increased pressure gradient caused an intensification of the northern hemisphere winter tropical easterlies which in turn caused equatorial divergence to occur in boreal winter