holocene rainfall variability in southern chile a marine record of latitudinal shifts of the southern westerlies geochemical and clay mineral parameters of a high accumulation marine sediment core from the chilean continental slope 41 s provide a 7700 yr record of rainfall variability in southern chile related to the position of the southern westerlies we especially use the iron content measured with a time resolution of ca 10 yr on average of 14 caccelerator mass spectrometry dated marine sediments as a proxy for the relative input of iron poor coastal range and iron rich andean source rocks variations in this input are most likely induced by rainfall changes in the continental hinterland of the core position based on these interpretations we find a pronounced rainfall variability on multicentennial to millennial time scales superimposed on generally more arid conditions during the middle holocene 7700 to 4000 cal yr b p compared to the late holocene 4000 to present this variability and thus changes in the position of the southern westerlies are first compared to regional terrestrial paleoclimate data sets from central and southern chile in order to derive possible wider implications and forcing mechanisms of the holocene latitudinal shifts of the southern westerlies we then compare our data to ice core records from both tropical south america and coastal antarctica these records show similar bands of variability centered at ca 900 and 1500 yr comparisons of band pass filters suggest a close connection of shifts of the southern westerlies to changes within the tropical climate system the correlation to climate conditions in coastal antarctica shows a more complicated picture with a phase shift at the beginning of the late holocene coinciding with the onset of the modern state of el nin o southern oscillation system the presented data provide further evidence that the well known millennial scale climate variability during the last glacial continued throughout the holocene fl 2001 elsevier science b v all rights reserved

spatial productivity variations during formation of sapropels s5 and s6 in the mediterranean sea evidence from ba contents abstract we investigated five time equivalent core sections 180 110 kyr bp from the balearic sea menorca rise the easternmost levantine basin and southwest south and southeast of crete to reconstruct spatial patterns of productivity during deposition of sapropels s5 and s6 in the mediterranean sea our indicators are ba total organic carbon and carbonate contents we found no indications of ba remobilization within the investigated core intervals and used the accumulation rate of biogenic ba to compute paleoproductivity maximum surface water productivity up to 350 g c m2 yr was found during deposition of s5 isotope stage 5e but pronounced spatial variability is evident coeval sediment intervals in the balearic sea show very little productivity change suggesting that chemical and biological environments in the eastern and western mediterranean basins were decoupled in this interval we interpret the spatial variability as the result of two different modes of nutrient delivery to the photic zone river derived nutrient input and shoaling of the pycnocline nutricline to the photic zone the productivity increase during the formation of s6 was moderate compared to s5 and had a less marked spatial variability within the study area of the eastern mediterranean sea given that s6 formed during a glacial interval glacial boundary conditions such as high wind stress and or cooler surface water temperatures apparently favored lateral and vertical mixing and prevented the development of the spatial gradients within the eastern mediterranean sea ems observed for s5 a non sapropel sediment interval with elevated ba content and depleted 18o 16o ratios in planktonic foraminifer calcite was detected between s6 and s5 that corresponds to the weak northern hemisphere insolation maximum at 150 kyr at this time productivity apparently increased up to five times over surrounding intervals but abundant benthic fauna show that the deep water remained oxic following our interpretation the interval denotes a failed sapropel when a weaker monsoon did not force the ems into permanent stratification the comparison of interglacial and glacial sapropels illustrates the relevance of climatic boundary conditions in the northern catchment in determining the facies and spatial variability of sapropels within the ems

the oceanic mesoscale convective system and associated mesovortex observed 12 december 1992 during toga coare this study documents the precipitation and kinematic structure of a mature mature to decaying westward propagating near equatorial oceanic mesoscale convective system mcs observed by airborne doppler radars during toga coare the tropical ocean global atmosphere coupled ocean atmosphere response experiment this system occurred on 12 december 1992 during the convectively active phase of an intraseasonal oscillation and was followed at its dissipating stage by a redevelopment of convection that led to the mcs observed on 13 december 1992 these two successive mcss were associated with a two day atmospheric disturbance radar deduced airflows at two time periods reveal many similarities with other tropical oceanic cloud clusters in particular a marked rear inflow jet associated with a midlevel cyclonic mesovortex was observed within the rear of the stratiform region the mesovortex was better defined both in size and depth during the mature to decaying stage and was located more inside the system within a region of convergence due to the westward propagation of the rear inflow countergradient transports of momentum normal to the mean orientation of the system at midlevels and downgradient transports at lower and higher levels helped to intensify this rear inflow these transports were mostly accomplished by eddy structures cyclonic vorticity was concentrated at the rear of the mcs and peaked at the centre of the observed closed wind circulation as previously observed stretching of the pre existing vertical vorticity was the dominant dynamical mechanism which helped to amplify the mesovortex at mid to upper levels while tilting of the horizontal vorticity into the vertical was a lesser mechanism and had an opposite effect in most respects advective processes were negatively correlated with the stretching and tilting mechanisms but not sufficiently to be balanced the resulting tendency was an increase of cyclonic vorticity at low to mid levels and a net decrease above

unlocking the barite paleoproductivity proxy a new high throughput method for quantifying barite in marine sediments abstract the accumulation rate of barite baso4 in marine sediments is a powerful tracer of paleo export productivity due to the refractory nature of barite in sediments and its ability to record ecosystem wide productivity it has been used to reconstruct past export productivity and to infer the effects of ocean circulation and nutrient supply on ocean ecosystems however the difficulty in generating large datasets of reliable barite accumulation rates has limited the use of this proxy here we present a new method for quantifying barite in marine sediments that promises a dramatic increase in sample throughput while also improving recovery of barite in a wide variety of marine sediments this method relies on selective dissolution of barite using a chelating ligand that avoids liberating ba from silicate phases and it can therefore work reliably on small 250 mg sediment aliquots rigorous evaluation of the method reveals that it quantitatively extracts barite and is largely unaffected by other ba sources due to the relatively simple analytical requirements of this barite extraction method and the small sample amount needed it can also be used to rapidly generate paleoproductivity records both during and after coring expeditions altogether this new technique should expand the study of the marine biologic system in the past by dramatically increasing analytical efficiency and widening the range of questions that are accessible using barite accumulation rate as a paleoproductivity proxy

systematic biotic responses to palaeoenvironmental change in the late pleistocene southern south china sea a preliminary study oxygen and carbon isotopes from the planktonic foraminifer globigerinoides sacculifer trace element contents calcium carbonate biogenic silica grain size and abundances of diatoms radiolarians and foraminifera in a deep sea core from the southwestern south china sea were analysed to investigate the response of various marine ecological communities to environmental changes over the last 200 ka the synthesised results show that the quality of the palaeoecological environment for biological growth is primarily affected by nutrient supply and terrigenous disturbance ba and p are important nutrient elements for the growth of diatoms radiolarians and planktonic foraminifera together with dissolved silica and calcium carbonate in sea water these elements may control microbiotic development however variations in fe content appear to affect diatom and radiolarian abundance optimal biotic growth occurs when nutrients are abundant and when there is minimal terrigenous disturbance biotic growth decreases when sea water is highly oligotrophic and terrigenous input is high maximum biological growth occurred in the mid holocene but deteriorated soon afterwards owing to increased terrigenous input causing a decrease of biological abundance and productivity in the late holocene the results also indicate how the toba volcanic eruption ca 74 ka ago contributed to changing the ecological environment in the southern south china sea copyright c 2008 john wiley sons ltd

high resolution marine record of climatic change in mid latitude chile during the last 28 000 years based on terrigenous sediment parameters abstract marine sediment cores from the continental slope off mid latitude chile 33 s were studied with regard to grain size distributions and clay mineral composition the data provide a 28 000 yr14c accelerator mass spectrometry dated record of variations in the terrigenous sediment supply reflecting modifications of weathering conditions and sediment source areas in the continental hinterland these variations can be interpreted in terms of the paleoclimatic evolution of mid latitude chile and are compared to existing terrestrial records glacial climates 28 000 18 000 cal yr b p were generally cold humid with a cold semiarid interval between 26 000 and 22 000 cal yr b p the deglaciation was characterized by a trend toward more arid conditions during the middle holocene 8000 4000 cal yr b p comparatively stable climatic conditions prevailed with increased aridity in the coastal range the late holocene 4000 0 cal yr b p was marked by more variable paleoclimates with generally more humid conditions variations of rainfall in mid latitude chile are most likely controlled by shifts of the latitudinal position of the southern westerlies compared to the holocene the southern westerly wind belt was located significantly farther north during the last glacial maximum less important variations of the latitudinal position of the southern westerlies also occurred on shorter time scales

barium in sediments off northwest africa a tracer for paleoproductivity or meltwater events 1 high resolution down core analyses of the solid phase content of total barium batot and total organic carbon toc back to 25 kyr b p were performed on a gravity core from the upper continental slope off cape yubi morocco the observed discrepancy between the two potential paleoproductivity proxies batot and toc initiated supplementary examinations of the pore water the geochemistry of the clay fraction x ray diffraction analyses and the application of a sequential ba extraction method of selected samples additionally we analyzed down core samples of the planktonic foraminifera turborotalita quinqueloba and globorotalia inflata for their ba ca ratios these analyses which were performed for the first time on these species were used to reconstruct past oceanic ba concentrations we suggest that in the study area which is characterized by high accumulation rates the preserved toc content is a valuable proxy for past primary productivity whereas the solid phase batot contents appear to be affected by other mechanisms and factors peaks of total barium content in the clay fraction and of ba ca ratios in the planktonic foraminifera shells found during the younger dryas and the heinrich 1 event are likely to result from increased meltwater influx into the northern north atlantic we suggest that ba enriched meltwater was transmitted by the eastern boundary current system from higher latitudes to the region of the canary islands total barium contents of the clay fraction batot clay and ba ca in planktonic foraminifera shells seem to be reliable proxies for this discharge of meltwater

barium sio2 excess and p2o5 as proxies of biological productivity in the middle east during the palaeocene and the latest palaeocene benthic extinction event the distribution of barium and other elements related to biological productivity has been studied in two palaeocene sections from the middle east in the bathyal ben gurion section israel ba ba al2o3 15 concentrations are low in the range 0 04 to 0 3 in the lower palaeocene and very high 1 to 2 throughout most of the upper palaeocene in the neritic gebel aweina section in egypt ba values are low 0 1 throughout the entire palaeocene the ba enrichments at ben gurion and their correlations with increases in p2o5 and opaline silica and local and global 13c maxima indicate that upwelling and high productivity were important in this region during the late palaeocene the absence of ba enrichments in the shallower gebel aweina section probably reflects the strong depth dependence of biobarium deposition in the uppermost palaeocene at the level where the global benthic extinction event is registered ba concentrations in the ben gurion section increase to anomalous 6 which suggests that upwelling and possibly wind strengths intensified during this event the results speak against deep water formation in this region since downwelling and not upwelling is required

a numerical study of the along line variability of a frontal squall line during pre storm despite considerable progress in the understanding of two dimensional structures of squall lines little attention has been paid to the along line variability of these convective systems in this study the roles of meso and larger scale circulations in the generation of along line variability of squall lines are investigated using an 18 h prediction of a frontal squall line that occurred on 26 27 june 1985 during pre storm preliminary regional experiment for stormscale operational research meteorology it is shown that the canadian regional finiteelement rfe model reproduces reasonably well a number of surface and vertical circulation structures of the squall system as verified against available network observations these include the initiation propagation and dissipation of the squall system surface pressure perturbations and cold outflow boundaries a midlevel mesolow and an upper level mesohigh a front to rear ftr ascending flow overlying an intense rear to front rtf flow and a leading convective line followed by stratiform precipitation regions it is found that across line circulations at the northern segment of the squall line differ significantly from those at its southern segment including the different types of precipitation the absence of the rtf flow and midlevel mesolow and the early dissipation of organized convection in the northern part the along line variability of the squall s circulations results primarily from the interaction of convectively generated perturbations with a midlevel baroclinic trough the large scale trough provides an extensive rtf flow component in the southern portion of the squall system and an ftr flow component in the north whereas the midlevel mesolow tends to enhance the rtf flow to the south and the ftr flow to the north of the mesolow during the mature to decaying stages the along line variability of the squall s circulations appears to be partly responsible for the generation of different weather conditions along the line such as the development of an upper level stratiform region in the southern segment and a midlevel cloud region in the northern portion of the squall line

sources and modes of terrigenous sediment input to the chilean continental slope abstract physical chemical and mineralogical properties of a set of surface sediment samples collected along the chilean continental slope 21 44 s are used to characterise present day sedimentation patterns and sediment provenance on the chilean margin despite the presence of several exceptional latitudinal gradients in relief oceanography tectonic evolution volcanic activity and onshore geology the present day input of terrigenous sediments to the chilean continental margin appears to be mainly controlled by precipitation gradients and source rock composition in the hinterland general trends in grain size denote a southward decrease in median grain size of the terrigenous corganic caco3 and opal free fraction which is interpreted as a shift from aeolian to fluvial sedimentation this interpretation is supported by previous observations of southward increasing bulk sedimentation rates north south trends in sediment bulk chemistry are best recognised in the iron fe and titanium ti vs potassium k and aluminium al ratios of the sediments that most likely reflect the contribution of source rocks from the andean volcanic arc these ratios are high in the northernmost part abruptly decrease at 25 s and then more or less constantly increase southwards to a maximum at 40 s

geochemical characteristics of chilean upwelling sediments at 36 s abstract we examined the cycling of c s fe and the trace elements te ag cd mo mn re and se in chilean upwelling sediments from water depths of 127 2744 m at 36 s the sediments are clay rich with moderate total organic carbon toc and low biogenic caco3 contents for the shallow site within oxygen minimum zone omz which shows some thioploca biomass highest observed toc contents correspond to highest productivity induced toc flux and or enhanced preservation under o2 deficient conditions pyrite formation may be restricted by the concurrent presence of elemental s in thioploca and or the availability of reactive iron in the other sediments 370 m water depth pyrite formation is strongly restricted due to the low availability of metabolizable toc for sulfate reduction calculations of the degree of bacterially mediated remineralization suggest that more nitrogen than toc was remineralized by sulfate reduction than expected from redfield c n relationship manganese is significantly depleted due to reductive dissolution of mn hydr oxides within all sediments mo is only significantly enriched vs the lithogenic background in the shallow core implying anoxic conditions contents of re and mo as well as re mo ratios indicate suboxic conditions for the other cores cd and re contents decrease with increasing water depth reflecting decreasing reducing conditions in contrast authigenic ag contents increase with water depth suggesting enrichment controlled by seawater availability and or opaline input and not redox conditions elevated se contents in all cores may be either due to bio detrital input or diffusion from seawater accumulation rates of toc ts and te off chile are in the same order as those from the gulf of california and lower than those off peru distinct seasonality in upwelling and dilution of chilean sediments with terrigenous material lead to rather low metabolizable toc contents and lower te trapping capacity

ferromanganese nodules from manop sites h s and r control of mineralogical and chemical composition by multiple accretionary processes abstract the chemical composition of ferromanganese nodules from the three nodule bearing manop sites in the pacific can be accounted for in a qualitative way by variable contributions of distinct accretionary processes these accretionary modes are 1 1 hydrogenous i e direct precipitation or accumulation of colloidal metal oxides in seawater 2 2 oxic diagenesis which refers to a variety of ferromanganese accretion processes occurring in oxic sediments and 3 3 suboxic diagenesis which results from reduction of mn 4 by oxidation of organic matter in the sediments geochemical evidence suggests processes 1 and 2 occur at all three manop nodule bearing sites and process 3 occurs only at the hemipelagic site h which underlies the relatively productive waters of the eastern tropical pacific a normative model quantitatively accounts for the variability observed in nearly all elements zn and na however are not well explained by the three end member model and we suggest that an additional accretionary process results in greater variability in the abundances of these elements variable contributions from the three accretionary processes result in distinct top bottom compositional differences at the three sites nodule tops from h are enriched in ni cu and zn instead of the more typical enrichments of these elements in nodule bottoms in addition elemental correlations typical of most pelagic nodules are reversed at site h the three accretionary processes result in distinct mineralogies hydrogenous precipitation produces mno2 oxic diagenesis however produces cu ni rich todorokite and suboxic diagenesis results in an unstable todorokite which transforms to a 7 a phase birnessite upon dehydration the presence of cu and ni as charge balancing cations influence the stability of the todorokite structure in the bottoms of h nodules which accrete dominantly by suboxic diagenesis na and possibly mn 2 provide much of the charge balance for the todorokite structure limited growth rate data for h nodules suggest suboxic accretion is the fastest of the three processes with rates at least 200 mm 106 yr oxic accretion is probably 10 times slower and hydrogenous 100 times slower since these rates predict more suboxic component in bulk nodules than is calculated by the normative analysis we propose that suboxic accretion is a non steady state process variations in surface water productivity cause pulses of particulate flux to the sea floor which result in transient mn reduction in the surface sediments and reprecipitation on nodule surfaces

the sequence of events surrounding termination ii and their implications for the cause of glacial interglacial co2 changes events surrounding termination ii as preserved in the vostok ice core provide a number of clues about the mechanisms controlling glacial to interglacial climate change antarctic temperature and the atmosphere s co2 content increased together over a period of 8000 years this increase is bounded by a drop in dust flux at its onset and by a drop in the 18o of trapped air at its finish a similar lag between dust flux and foraminiferal 18o is seen in a southern ocean marine record suggesting that the 18o in air trapped in vostok ice is a valid proxy for ice volume the synchronous change of atmospheric co2 and southern hemisphere temperature thus preceded the melting of the northern hemisphere ice sheets this observation coupled with the fact that nutrient reorganization in the north atlantic occurs with or after the sea level rise eliminates many scenarios proposed to explain the co2 rise including those which rely on sea level change conveyor related nutrient redistribution or north atlantic cooling southern ocean scenarios become the front runners but the most popular mechanism iron fertilization has two problems in explaining the co2 rise before termination ii first much of the dust demise occurs prior to the change in co2 so if iron is the villain a threshold value of its supply must be called upon above which productivity does not continue to increase second the co2 rise continues for some 4 5 kyr after the dust flux has fallen to close to zero these problems may be solved if the increased iron supply in dust caused higher rates of nitrogen fixation during the glacial periods in this case the residence time of oceanic nitrate of a few thousand years would enable decreasing productivity to be a global rather than a local phenomenon and would explain the slow rampup of atmospheric co2

palaeoproductivity at the antarctic continental margin opal and barium records for the last 400 ka abstract records of biogenic opal and barium were measured in sediment cores at the antarctic continental margin in the area of the weddell lazarev and cosmonaut seas these records provide a qualitative and quantitative tool to estimate changes in palaeoproductivity over the last 400 ka the stratigraphy of the investigated cores is calibrated to a lithostratigraphy adjusted to a stable isotope record from the eastern weddell sea which is supported by a th dating method we present evidence that interglacial productivity along the antarctic continental margin is twice as high compared to subantarctic sites near south orkney a glacial interglacial pattern with high productivity during peak warm stages can be observed back to 400 ka high interglacial productivity is linked to a reduced sea ice coverage which is regulated by the heat flux introduced by north atlantic deep water nadw to the antarctic ocean generally good correlations between the barium and opal records of the sediment cores indicate that dissolution of opal in the water column and the sediment does not obscure the surface productivity signal therefore in this area biogenic opal in combination with other proxies can be used for palaeoproductivity estimates palaeoproductivity is also assessed quantitatively from the barium record using the approaches of dymond et al dymond j suess e lyle m 1992 barium in deep sea sediments a geochemical proxy for paleoproductivity paleoceanography 7 163 181 and francois et al francois r honjo s manganini s j ravizza g e 1995 biogenic barium fluxes to the deep sea implications for paleoproductivity reconstructions glob biochem cycles 9 2 289 303 palaeoproductivity rates obtained by both methods show a good temporal correspondence in peak warm stages higher values are computed with the approach of dymond et al 1992 though some barium may be provided by lateral advection of material as indicated by th data near south orkney both methods provide values which are representative of a high productivity area they are drastically reduced during glacial times the extent and duration of sea ice coverage and the persistence of coastal polynyas is considered to be of primary importance in controlling the flux of biogenic material to sediments of the antarctic continental margin

sedimentation in the chile trench petrofacies and provenance abstract the chile trench study area extends over 2 000 km along the andean continental margin from 23 s to 42 s latitude the qfl composition of chile trench sands encompasses the average compositions of modern sands from strike slip continental arc oceanic backarc and oceanic forearc types of active margins valloni and maynard 1981 and spans the complete spectrum from dissected to undissected magmatic arc settings dickinson et al 1983 trench sands along north chile central chile and the glaciated archipelago of south chile are derived from a more plutonic source region or dissected magmatic arc these sands exhibit abnormally low lithic and calcic plagioclase content but high quartz and alkali feldspar in central chile the plutonic provenance is correlated with an ab ence of quaternary volcanism along the chilean archipelago pleistocene glaciation has carved into the magmatic roots of the andes effecting arc dissection in spite of active volcanism in arid north chile the volcanic debris of the high cordillera is trapped onshore in longitudinal forearc basins allowing an exaggerated contribution from crystalline rocks of the coast range the light and heavy mineral and lithic composition of trench sands is described by four ideal petrologic assemblages isolated by q mode factor analysis the basic magmatic arc petrofacies volcanic lithics calcic plagioclase olivine clinopyroxene and orthopyroxene the most chemically unstable and least differentiated assemblage is derived exclusively from basalts and basaltic andesites in the quaternary volcanic arc of south chile the acidic magmatic arc petrofacies volcanic lithics alkali feldspar biotite hornblende and magnetite is derived from andesitic to rhyolitic volcanics and granodioritic plutons emplaced during various mesozoic and cenozoic magmatic episodes in the history of the andean margin the metamorphic magmatic arc petrofacies mica alkali feldspar hlorite actinolite epidote and blue green hornblende is derived from ferromagnesian rocks altered to the greenschist facies in the basal marine section of the andean eugeosyncline and in the paleozoic basement the cratonic block petrofacies quartz and the accessory minerals andalusite garnet and tourmaline is derived from mature platform sediments late stage granitic intrusions and high grade regional metamorphics associated with the south american craton it is most prominent along northern chile where the continental crust is thickest and presumably truncated by subduction erosion actual petrofacies in the chile trench are typically mixtures of the four ideal petrofacies their compositions can be related to 1 the lithology and erodibility of the source terranes 2 the distribution and composition of modern arc volcanism 3 the prevailing climate in the provenance region and 4 the structure and morphology of the continental margin and trench in many cases contemporary volcanism inundates and dominates the petrologic assemblage diluting contributions from all other source rock types and forming a low diversity petrofacies at high latitudes where glaciation was extensive a variety of source rock terranes were actively denuded and petrofacies of high diversity were deposited in the adjacent trench the linear frequency of sediment supply points along the base of the continental slope controls the spatial heterogeneity of petrofacies on the depositional surface in the trench basin the most homogenous petrofacies derived from major submarine canyon systems and extensive subaerial drainage basins may extend hundreds of kilometers along margin due to axial transport processes within the trench

late quaternary precessional cycles of terrigenous sediment input off the norte chico chile 27 5 s and palaeoclimatic implications abstract the palaeoclimatic conditions during the last glacial maximum lgm of southern south america and especially latitudinal shifts of the southern westerly wind belt are still discussed controversially longer palaeoclimatic records covering the late quaternary are rare a particularly sensitive area to late quaternary climatic changes is the norte chico northern chile because of its extreme climatic gradients small shifts of the present climatic zonation could cause significant variations of the terrestrial sedimentary environment which would be recorded in marine terrigenous sediments to unveil the history of shifting climatic zones in northern chile we present a sedimentological study of a marine sediment core geob 3375 1 from the continental slope off the norte chico 27 5 s sedimentological investigations include bulk and silt grain size determinations by sieving atterberg separation and detailed sedigraph analyses additionally clay mineralogical parameters were obtained by x ray diffraction methods the 14c dated core covering the time span from approximately 10 000 to 120 000 cal yr b p consists of hemipelagic sediments terrigenous sedimentological parameters reveal a strong cyclicity which is interpreted in terms of variations of sediment provenance modifications of the terrestrial weathering regimes and modes of sediment input to the ocean these interpretations imply cyclic variations between comparatively arid climates and more humid conditions with seasonal precipitation for northern chile 27 5 s through the late quaternary the cyclicity of the terrigenous sediment parameters is strongly dominated by precessional cycles for the palaeoclimatic signal this means that more humid conditions coincide with maxima of the precession index as e g during the lgm higher seasonal precipitation for this part of chile is most likely derived from frontal winter rain of the southern westerlies thus the data presented here favour not only an equatorward shift of this atmospheric circulation system during the lgm but also precession controlled latitudinal movements throughout the late quaternary precessional forcing of latitudinal movements of the westerly atmospheric circulation system may be conceivable through teleconnections to the northern hemisphere monsoonal system in the atlantic ocean region

surface sediment distribution along the chilean continental slope related to upwelling and productivity abstract the coastal upwelling system of the peru chile current belongs to the most productive regions in the world oceans in spite of this remarkable fact only very little is known about the sediment distribution in its southern part off the coast of chile to increase the knowledge about this region a multiparameter study of the surface sediment distribution along the chilean continental slope between 27 and 42 s has been carried out detailed analyses of sedimentary data toc and carbonate contents 13corg 15n of the species composition of planktic foraminifera and of the stable isotope composition of the two planktic foraminifera species neogloboquadrina pachyderma dex and globigerina bulloides reveal a close relation to environmental conditions in the region the pattern of a southward increase of surface water productivity known from satellite data is closely reflected in the organic carbon and 15n data information about the water mass distribution especially about varying influences of upwelling waters and warmer subtropical surface waters can be derived from the species composition of the planktic foraminifera while the stable isotope data provide additional clues about water mass characteristics high productivity along the chilean margin north of 40 s is sustained by coastal upwelling while further to the south advection of nutrients with the antarctic circumpolar current and a significant riverine input fuel the highest productivity found in the study area this data set will provide the base for future paleoclimatic and paleoceanographic reconstructions of the southeast pacific region

inorganic geochemical indicators of glacial interglacial changes in productivity and anoxia on the california continental margin abstract evidence from sediments in cores collected from within the present oxygen minimum zone omz 600 1200 m on the central and northern california margins record several episodes during the last interstadial ois 3 ca 60 24 ka of deposition of laminated sediments containing elevated concentrations of several trace elements indicative of anoxic conditions e g mo ni zn and cu the presence of abundant well preserved organic matter as well as lack of bioturbation and the presence of elevated concentrations of mo and other trace elements all support the theory that the omz in the northeastern pacific ocean was more intense possibly anoxic at several times during the late pleistocene sediments of all ages in cores from the southern california margin contain elevated concentrations of mo suggesting that this area has always had higher rates of sulfate reduction than either the central or northern california areas most of the ba in sediments in all cores collected on the upper continental slope 200 2700 m off california and southern oregon is derived from detrital clastic material and this source did not change much in time however the amount of biogenic ba did vary with time and these variations closely follow the temporal variations in organic c corg mass accumulation rate using ba and corg mass accumulation rates as proxy variables for productivity all cores show that organic productivity under the california current upwelling system was highest during ois 3 and the holocene and lowest during the last glacial interval lgi ca 24 10 ka all paleoproductivity proxy variables indicate that the southern california area has always experienced higher productivity than other areas under the california current at least over the last 50 ky

late quaternary rapid climate change in northern chile analyses of terrigenous sediments from the chilean continental slope off the southern border of the atacama desert 27 5 s focusing on illite crystallinity and the fe al ratio of the sediments reveal a high frequency variability of the position of the southern westerlies which is very similar to the coeval short term climatic events known from greenland ice cores and from north atlantic sediments besides showing dominantly precession driven variability in precipitation over the andes these analyses also reveal rapid changes in weathering intensity along the chilean coastal range during the last 80 000 years these rapid changes occur at much shorter timescales than the 19 100 kyr orbital forcing of the milankovitch cycles

a comparison between excess barium and barite as indicators of carbon export 1 since dymond et al 1992 proposed the paleoproductivity algorithm based on bio ba which relies on a strong correlation between ba and organic carbon fluxes in sediment traps this proxy has been applied in many paleoproductivity studies barite the main carrier of particulate barium in the water column and the phase associated with carbon export has also been suggested as a reliable paleoproductivity proxy in some locations we demonstrate that baexcess total barium minus the fraction associated with terrigenous material frequently overestimates babarite barium associated with the mineral barite most likely due to the inclusion of barium from phases other than barite and terrigenous silicates e g carbonate organic matter opal fe mn oxides and hydroxides a comparison between overlying oceanic carbon export and carbon export derived from baexcess shows that the dymond et al 1992 algorithm frequently underestimates carbon export but is still a useful carbon export indicator if all caveats are considered before the algorithm is applied babarite accumulation rates from a wide range of core top sediments from different oceanic settings are highly correlated to surface ocean 14 c and chlorophyll a measurements of primary production this relationship varies by ocean basin but with the application of the appropriate f ratio to 14 c and chlorophyll a primary production estimates the plot of babarite accumulation and carbon export for the equatorial pacific atlantic and southern ocean converges to a global relationship that can be used to reconstruct paleo carbon export index terms 3022 marine geology and geophysics marine sediments processes and transport 4267 oceanography general paleoceanography 4825 oceanography biological and chemical geochemistry keywords paleoproductivity barite export production excess barium marine sediments citation eagle m a paytan k r arrigo g van dijken and r w murray a comparison between excess barium and barite as indicators of carbon export paleoceanography 18 1 1021 doi 10 1029 2002pa000793 2003

water depth and diagenetic constraints on the use of barium as a palaeoproductivity indicator sediments underneath the high productivity areas of the coastal upwclling and equatorial divergence zones in the pacific and indian oceans are enriched in barium and on this basis the barium content of the sediments has long been suggested as a potential palaeoproductivity indicator analyses of sediments from the peru margin corroborate the pattern of enhanced barium accumulation in areas of high primary productivity in the deep ocean but also show that this pattern cannot be extended to shallow water deposits sediments from the peru shelf lack any barium enrichment whereas this element is significantly enriched in slope and basinal deposits in water columns deeper than 2000 m this depth effect is further illustrated at site 682 located in the rapidly subsiding lima basin the quaternary sequence deposited at water depths 3000 m is enriched in organic carbon opal and biogenic barium the miocene sediments although deposited under highly productive waters associated with a coastal upwclling centre do not show an enrichment in the barium record corresponding to the very high organic carbon and opal levels a pattern that is consistent with deposition in shallow basins in addition to the effect of water depth on the barium distribution overprinting of primary signals can be observed in sediments from upwclling areas undergoing strong anoxic diagenesis microcrystalline barite is partly dissolved in intervals depleted in interstitial sulphate as shown for sediments from the peru margin dissolution of barite in sulphate depleted intervals of deep water sections leads to high barium concentrations near the termination of the sulphate reducing zone where downward sulphate and upward barium diffusion foster local barite precipitation in diagenetic fronts the barium distribution in sedimentary oxic and suboxic environments at deep water depositional sites has a high potential as a palaeoproductivity indicator however barium accumulation as a proxy for ocean fertility should be used with caution in areas of varying water depths and in anoxic diagenetic environments where sulphate depletion undcrsatur ates the interstitial waters with respect to barite

barium and the late paleocene δ13c maximum evidence of increased marine surface productivity deep sea sediment ba ba al2o3 sample 15 ba aluminosilicate records show increasing values synchronous with the evolution of the late paleocene global 13c maximum reflecting an increase in marine surface primary production and biogenic barite formation at this time at two oligotrophic locations deep sea drilling project dsdp sites 384 and 527 in the north and south atlantic respectively ba increases from 160 360 ppm in the early paleocene to 1100 3000 ppm during the 13c maximum at equatorial dsdp site 577 positioned within or near the high productivity zone ba increases from 15 500 ppm in the early paleocene to 25 400 ppm in conjunction with late paleocene maximum 13c values linear fitted correlation plots of sediment ba content versus surface water 13c in all three regions support barite originating in the euphotic zone the early to late paleocene relative increase in ba illustrates how burial rates of corg relative to al2o3 accelerated by a factor of 1 8 and 6 0 in the eutrophic and oligotrophic areas respectively a tentative estimate weighing our result for the entire ocean suggests that accumulation rates of organic carbon increased by a factor of 2 during the late paleocene 13c maximum

the impact of sediment provenance on barium based productivity estimates abstract biogenic barium in marine sediments has been suggested to be a reliable proxy of export productivity from the surface ocean and algorithms have been developed to link these properties however problems arise when the proposed algorithms are applied to predominantly terrigenous sediments a major source of error is incorrect estimates of the terrigenous ba al ratio in normative calculations of the amount of biogenic barium in the sediment compared to an often used global average ba al ratio much better results can be obtained by estimating the terrigenous ba al ratio from exponential regression of the ba al ratios of surface sediments obtained from continental slope transects this method has been applied to surface sediments from the chilean continental slope the calculated regional terrigenous ba al ratios could be verified with purely terrigenous samples from chilean rivers the resulting accumulation rates of biogenic barium on the chilean continental slope reliably reproduce the regional pattern of primary productivity in the southern peru chile current indicating the potential of biogenic barium as a useful paleo productivity proxy

modelling the joint variability of grain size and chemical composition in sediments abstract the geochemical composition of siliciclastic sediments correlates strongly with grain size hence geochemical composition may serve as a grain size proxy in the absence of grain size variations geochemical data of siliciclastic sediments may be used to characterise size independent processes i e sediment provenance weathering mixing shape density sorting and diagenesis in general however geochemical data sets contain both types of information in order to formalise interpretation of geochemical data we propose a mathematical method to decompose the total geochemical variability of a series of genetically related specimens into a grain size dependent the shared signal and a grain size independent part the residual signal the former may serve as a proxy for grain size whereas the latter represents geochemical variability that would have been observed if all sediments would have had the same grain size distribution the two data sets are jointly decomposed by means of partial least squares pls and orthogonal projection subsequently the presence of significant grain size independent geochemical variability in the residual signal is determined in a statistically rigorous manner using a 2 test using a synthetic example we show that the residual record effectively reveals an imposed provenance signal which could not have been resolved from the geochemical or grain size data sets individually we analysed the relation between grain size and geochemical composition in three quaternary marine sediment cores located offshore west africa and south america geob7920 2 geob9508 5 and geob7139 2 both sites are characterised by biogenic sediment input in addition to fluvial and aeolian sediment input from the continent it was found that all cores show a strong but different correlation between the mean grain size and the bulk geochemical composition these results demonstrate that geochemical grain size proxies are empirical and site specific it was also found that the geochemical and grain size data in cores geob7920 2 and geob7139 2 do not contain unique information whereas in core geob9508 5 ti varies independently from the grain size this residual ti signal correlates with the transport mechanism as demonstrated by statistically different values of aeolian and fluvial dominated sediments however a unique interpretation of this residual signal in terms of the postulated grain size independent mechanisms could not be provided without additional information we conclude that the proposed model facilitates identification and validation of different element ratios as grain size proxies and more importantly as proxies for size independent processes for this reason the model paves the way for rigorous analysis of multi proxy data which are widely used in palaeoceanographic and palaeoclimatic research

upwelling and productivity along the peru chile current derived from faunal and isotopic compositions of planktic foraminifera in surface sediments abstract we report on the spatial distribution of isotopic compositions of the two planktic foraminifera species globigerina bulloides and neogloboquadrina pachyderma dex and the faunal assemblages of planktic foraminifera in 91 surface sediment samples along the chilean continental slope between 23 s and 44 s both 13c and 18o data of n pachyderma dex show little variability in the study area north of 39 s the isotopic values of n pachyderma dex are heavier than those of g bulloides whereas south of 39 s this relation inverses this is indicative for a change from a well mixed deep thermocline caused by coastal upwelling north of 39 s to well stratified water masses in a non upwelling environment south of 39 s in addition the faunal composition of planktic foraminifera marks this change by transition from an upwelling assemblage north of 39 s to a high nutrient non upwelling assemblage south of 39 s which is characterized by decreased contributions of upwelling indicators such as g bulloides n pachyderma sin and globigerinita glutinata in general we can conclude that food and light rather than temperature are the primary control of the planktic foraminiferal assemblage between 23 s and 44 s off chile our data point to higher marine productivity at upwelling centers north of 25 s and at 30 33 s south of 39 s significant supply of nutrients by fluvial input most likely boosts the productivity

chemical evidence for and implications of a primary fes phase in the ankarvattnet zn cu pb massive sulphide deposit central swedish caledonides the origin of the pyrrhotite in the ankarvattnet massive sulphide deposit is discussed based on chemical relations between the different mineralization types a metamorphic genesis is rejected and a premetamorphic origin is alternatively suggested which is in agreement with similar ideas for the origin of the pyrrhotite in other deposits the pyrrhotite is thought to have formed in the stringer zone to a massive pyritic layer with similar formation mechanisms as for volcanogenic massive sulphide deposits the recognition of a stringer zone mineralogy provides better possibilities to understand the physico chemical character of the ore forming environment

formative stage of a long lived mesoscale vortex observed by airborne doppler radar abstract the formative stage of a long lived mesoscale cyclonic vortex was captured by the noaa p 3 aircraft as it investigated a developing mesoscale convective system mcs near the southeastern coast of taiwan on 16 june 1987 during the taiwan area mesoscale experiment the supporting environment of the mesovortex was characterized by an exceptionally moist atmosphere and moderate ambient vertical shear through a deep layer from the near surface to 6 km with much weaker shear and winds aloft in addition a pronounced low level mesoscale shear convergence zone which resulted from the interaction of southeasterly flow with northeasterly flow confined to the near coast region existed in the vicinity of the observed mesovortex composite three dimensional wind fields derived via pseudo dual doppler synthesis show the vortex had a horizontal diameter expanding from 40 km to 70 km in the lower to midtroposphere respectively and exhibited considerable tilt through this layer contrary to previously d

biogenic silica and diatom thanatocoenosis in surface sediments below the peru chile current controlling mechanisms and relationship with productivity of surface waters abstract based on 76 surface sediment samples collected between ca 22 and 44 s along the chilean coast in the southeast pacific ocean we report on the north south distribution of opal content and diatom concentration and the quantitative and qualitative composition of the preserved diatom community latitudinal differences in the siliceous signal reflect the influence of two main mechanisms of surface water production coastal upwelling off northern and central chile till ca 38 s and nutrient enrichment by the input of cold southern non upwelling associated waters south of ca 38 s the poleward increase in biogenic opal and diatom values parallels well the north south increase of pigment concentration in surface waters as recorded by satellites between 22 and 33 s where low pigment concentrations are measured opal content and diatom concentration are mostly low except at 22 23 s in contrast both higher opal and diatom values at 34 38 s and 41 42 s correspond well with higher pigment estimations preserved diatom populations document the present day dominant hydrographical conditions nutrient enrichment of surface waters due to coastal upwelling results in intensive production of diatoms off northern and central chile reflected by the predominance of the richly composed association of chaetoceros spores north of ca 38 s the diatom association shows that the area between 35 and 38 s is transitional the abrupt decrease of chaetoceros spores south of 38 s off chile coupled with the enhanced contribution of thalassiosira spp representatives of high productivity low temperature waters points to the presumed high nutrient supply by the iron limited nutrient rich antarctic circumpolar water the contribution of benthic diatoms reflects some lateral transport from the near shore area into deeper positions south of 38 s

geostatistic recognition of genetically distinct shale facies in upper triassic chang 7 section the ordos basin north china abstract the ordos basin in north china may be one of the nonmarine basins with highest hydrocarbon generation per volume of sedimentary fill it has great potential for unconventional oil and gas exploration especially shale oil when evaluating and predicting shale oil resources the difference between different regions and different layers of shale is very obvious so it cannot be calculated simply by average a geostatistic decision tree was constructed based on a training set of 22 parameters geochemistry petrology and sedimentology for 110 shale samples from the basin which can be used to implement genetic classification of subsequently collected shale samples three shale facies are identified by the decision tree the properties of each facies are different such as toc kerogen type and sulfur content genetic properties indicate formation conditions and provide base for the geostatistic assignments the differential distribution of shale facies in the basin reflects their origins from different formation mechanism elements ratios isotopes and biomarkers can be used to infer the sedimentary environment for each shale facies facies 1 mainly occurs in the upper chang 7 section and shows evidence of quartz rich source rock deposited under suboxic anoxic condition facies 3 occurs at the lower chang 7 section and shows evidence of clay rich and pyrite rich shale deposited under reducing dysoxic conditions with numerous higher plants input facies 1 and 2 constitutes the upper chang 7 with interactive thick layers facies 2 and 3 constitute the lower chang 7 with interactive thin layers petrology geochemistry and sedimentology of the shale facies suggest facies 1 represents the suboxic anoxic upper chang 7 proximal quartz rich shale which has lower toc and sulfur content than other facies the organic lamina is straight but rare kerogen is type i and dominated by sapropel the content of saturated hydrocarbon in chloroform asphalt a extract is the highest facies 2 has higher toc value sulfur content and soluble hydrocarbon content than facies 1 it was formed in unstable hydrodynamic environment under weak anoxic condition it is characterized by abundant laminas with various deformation structures and more alginite and vitrinite in kerogen anoxic lower chang 7 distal sulfur rich shale source rock make up organic rich facies 3 7 0 17 0 wt toc this facies received more higher plant input than the other facies well preserved algae shells are common in numerous and flat laminas the content of chloroform asphalt of facies 3 is higher than that of other facies but among which the saturated hydrocarbon content is the lowest the aromatic non hydrocarbon and asphalt are the highest suggesting the fluidity of hydrocarbon is the worst compared to others this facies was formed in the environment where temperature is relative lower water is relative deeper productivity and salinity are relative higher and the reducibility is relative stronger a deeper understanding of shale classification and distribution is important for the accurate resource evaluation and optimal exploration planning of shale oil

barium accumulation in the atlantic sector of the southern ocean results from 190 000 year records extensive investigations of sedimentary barium were performed in the southern south atlantic in order to assess the reliability of the barium signal in antarctic sediments as a proxy for paleoproductivity maximum accumulation rates of excess barium were calculated for the antarctic zone south of the polar front where silica accumulates at high rates the correspondence between barium and opal supports the applicability of barium as a proxy for productivity within the antarctic zone north of today s average sea ice maximum interglacial vertical rain rates of excess barium are high with a maximum occurring during the last deglaciation and early holocene and during oxygen isotope chronozone 5 5 during these periods the maximum silica accumulation was supposedly located south of the polar front glacial paleoproductivity instead was low within the antarctic zone north of the polar front significantly higher barium accumulation occurs during glacial times the vertical rain rates however are as high as in the glacial antarctic zone therefore there was no evidence for an increased productivity in the glacial southern ocean

carbonate to biosilica transition at the norian rhaetian boundary controlled by rift related subsidence in the western tethyan lagonegro basin southern italy abstract the lagonegro basin located in the southern apennines italy records a transition from carbonate sediments of the calcari con selce fm cherty limestone to biosiliceous sediments of the scisti silicei fm siliceous shale around the norian rhaetian boundary nrb upper triassic sedimentologic and chemostratigraphic analysis of three sections pignola abriola monte volturino and madonna del sirino representing a proximal to distal transect across the basin document marine productivity redox and chemical weathering conditions the basin was characterized by low to moderate productivity and mainly oxic deep waters with no systematic secular variation throughout the 10 myr long study interval a weathering proxy the chemical index of alteration cia shifts toward higher values from 0 70 to 0 80 in all three study sections suggesting development of warmer and or more humid conditions just before the nrb the lack of evidence for changes in marine productivity or redox conditions and the time transgressive nature of the carbonate biosilica transition suggests that the latter was caused not by changes in planktonic communities but rather by a rise in the ccd the most likely cause of which was seafloor subsidence within the actively rifting ionian ocean i e the westernmost branch of the tethys ocean the tectonically active character of the lagonegro basin is also reflected in evidence of synsedimentary paleoseismic activity e g numerous debris flows around the basin margins the present study thus documents sedimentologic changes within a marginal basin in a geologically young ocean

geochemistry of surface sediments from the fjords of northern chilean patagonia 44 47 s spatial variability and implications for paleoclimate reconstructions abstract the patagonian fjords have a clear potential to provide high resolution sedimentary and geochemical records of past climate and environmental change in the southern andes to improve our ability to interpret these proxy records we investigated the processes that control fjord sediment inorganic geochemistry through a geochemical mineralogical and sedimentological analysis of surface sediment samples from the fjords of northern chilean patagonia a simple terrestrial index based on measurements of salinity and fraction of terrestrial carbon was used to estimate the terrestrial input river discharge at each site our results demonstrate that under the cold climate conditions of patagonia chemical weathering is weak and the inorganic geochemical composition of the fjord sediments is primarily controlled by hydrodynamic mineralogical sorting i e the intensity of river discharge our results suggest that the distribution of fe ti and zr in surface sediments is controlled by their association with heavy and or coarse minerals whereas al is independent of hydrodynamic processes the elemental ratios fe al ti al and zr al are therefore well suited for estimating changes in the energy of terrestrial sediment supply into the fjords through time zr al is particularly sensitive in proximal environments while fe al is most useful in the outer fjords and on the continental margin in the most proximal environments however fe al is inversely related to hydrodynamic conditions caution should therefore be exercised when interpreting fe al ratios in terms of past river discharge the application of these proxies to long sediment cores from quitralco fjord and golfo elefantes validates our interpretations our results also emphasize the need to measure al based elemental ratios at high precision which can be achieved using simultaneous acquisition icp aes technology this study therefore constitutes a strong basis for the interpretation of sedimentary records from the chilean fjords

terrigenous sediment supply along the chilean continental margin modern regional patterns of texture and composition the regional patterns of texture and composition of modern continental slope and pelagic sediments off chile between 25 s and 43 s reflect the latitudinal segmentation of geological morphological and climatic features of the continental hinterland grain size characteristics are controlled by the grain size of source rocks the weathering regime and mode of sediment input eolian off northern chile vs fluvial further south bulk mineral assemblages reveal a low grade of maturity regional variations are governed by the source rock composition of the different geological terranes and the relative source rock contribution of the coastal range and andes as controlled by the continental hydrology the relative abundance of clay minerals is also predominantly influenced by the source rock composition and partly by continental smectite neoformation latitudinal variations of illite crystallinities along the chilean continental slope and west of the peru chile trench clearly reflect modifications of the weathering regime which correspond to the strong climatic zonation of chile

a comparison of multiple proxies for export production in the equatorial pacific 1 several commonly used paleoproductivity proxies were compared to evaluate the validity of assumptions and limitations associated with each proxy export production fluxes cexport over glacial interglacial timescales were calculated from previously developed proxy specific algorithms at ttn013 pc72 and ttn013 pc114 both located in the equatorial pacific comparison of data from the same core intervals yields conflicting results despite calibrations based on the same core top samples the periodicity of marine barite excess ba and excess al based cexport records is similar the relative magnitude of cexport when calculated using excess ba and algorithms based on sediment trap data is significantly different than records based on core top calibrations particularly during glacial intervals at both sites bulk sedimentary al ti and ba ti ratios covary however these ratios do not correspond with the downcore records of their respective excess concentrations and their accumulation rates or with contemporaneous records based on marine barite excess ba and excess al accumulation although downcore records based on sediment mass accumulation rates may be compromised by sediment focusing this process cannot explain all the differences observed among the various data sets presented here this implies that some or all of these proxies do not exclusively respond to changes in export production the contradictions among these data highlight the importance of addressing inconsistencies among paleoproxies and re examining assumptions imbedded in proxy fundamentals prior to applying paleoproductivity proxies and interpreting paleoceanographic records

glacial to interglacial fluctuations in productivity in the equatorial pacific as indicated by marine barite an empirical correlation between marine barite baso4 accumulation rate in core top sediment samples from two equatorial pacific transects at 140 w and 110 w and the estimated primary productivity of the overlying water column were used to evaluate glacial to interglacial changes in productivity fluctuations in barite accumulation rates down core indicate that during glacial periods of the past 450 000 years the productivity in the central and eastern equatorial pacific was about two times that during intervening interglacial periods this result is consistent with other evidence that productivity was high in the eastern and central equatorial pacific during the last glacial