abrupt changes in antarctic intermediate water circulation over the past 25 000 years the formation and circulation of antarctic intermediate water has varied over glacial interglacial timescales a neodymium record from the atlantic ocean basin suggests that changes in circulation may have been driven by changes both in antarctic intermediate water formation in the southern ocean and in the strength of north atlantic meridional overturning

a mid ordovician temperate carbonate shelf the black river and trenton limestone groups of southern ontario canada abstract mid ordovician limestones of southern ontario are usually considered to be tropical shelf limestones and interpreted using facies models derived from recent tropical carbonate environments nevertheless depositional rates grain types faunas erosion surfaces mineralogy and geochemistry are more compatible with a temperate or even cold shelf environment in view of the low latitudes 20 s indicated by paleomagnetism this suggests deposition in relatively cold seas deposition below a tropical thermocline or that the paleomagnetic data are wrong similar features in other caradocian limestones of eastern north america show that these inferred cooler conditions were widespread if deposition occurred below a tropical thermocline most shallow water caradocian limestones must be re interpreted as deeper water deposits more likely in view of the evidence for temperate conditions in shallow water is that the whole eastern seaboard of north america was affected by cold currents arising from southern polar ice caps and thus was a temperate shelf environment

a study of cleaning procedures used for foraminiferal mg ca paleothermometry the various cleaning steps required for preparation of foraminiferal samples for mg ca and sr ca analysis are evaluated for their relative importance and effects on measured elemental ratios it is shown that the removal of silicate contamination is the most important step for the measurement of mg ca ratios in an example bulk sample mg ca decreases from 10 5 to 2 5 mmol mol 1 during clay removal oxidation of organic material causes a lowering of sample mg ca in the order of 10 or approximately 1 c when converted to temperature use of dilute acid leaching to remove adsorbed contaminants causes partial dissolution of the sample carbonate and a corresponding decrease in mg ca reductive treatment also causes dissolution of the sample and a decrease in the mg ca ratio of up to 10 15 sample preparation for sr ca analysis does not require the same degree of rigor as is necessary for mg ca work the within run reproducibility of the method described here for g ruber in a core top sample from the arabian sea was 1 8 mean sample ratio was 4 72 mmol mol 1 when converted to temperature this becomes 28 0 2 c the equivalent result for sr ca was 0 5 mean ratio 1 44 mmol mol 1

the middle late cambrian reef transition and related geological events a review and new view abstract the reefs of the middle late cambrian cambrian epoch 3 furongian have long been simply considered as microbialites that flourished in the aftermath of the archaeocyath extinction thorough review of the reefs in these periods shows however that the cambrian epoch 3 and the furongian actually yield different types of reefs the cambrian epoch 3 reefs are dominated by thrombolites and dendrolites largely constructed by the calcified microbes epiphyton and renalcis on the other hand the furongian reefs consist mainly of maze like maceriate reefs and columnar stromatolites the maceriate reefs most likely formed by siliceous sponges and calcified microbes including girvanella and tarthinia whereas the columnar stromatolites were mainly constructed by girvanella tarthinia and minor siliceous sponges other microbial reefs e g non columnar stromatolites persisted during the cambrian epoch 3 and the furongian mainly as small patch reefs or reefal crusts lithistid sponge microbial reefs initially formed in the cambrian epoch 3 and occurred throughout the furongian but occupied only a minor portion during these periods several geological events occurred across the boundary between the cambrian epoch 3 and the furongian including positive carbon and sulfur isotope excursions a eustatic sea level drop major faunal turnover of trilobites and diversification of new organisms the coincidence of these events and the transition in reefal fabrics suggest that reef ecosystems were significantly influenced by at least some of these events among the events it is likely that sea level change would have affected reefs although further studies are required in order to test whether and how the other events influenced the reef transition epiphyton and renalcis and thrombolites and dendrolites formed by them declined greatly most likely due to sea level fall and thus decreased in shallow marine habitat at the end of cambrian epoch 3 the cambrian epoch 3 thrombolites and dendrolites were gradually replaced by a sponge microbial association of the maze like maceriate reefs and the columnar stromatolites in the furongian coincident with a sea level rise

upper water mass variability in the anegada jungfern passage ne caribbean during the last 11 100 cal yr using qualitative and quantitative analyses of planktonic foraminifera assemblages 18o measurements mg ca temperature relationship globigerinoides ruber pink sensu stricto data and sea surface temperatures ssts derived from artificial neural network ann transfer functions a reconstruction was made of upper water mass variability in the anegada jungfern passage ajp northeastern caribbean sea over the last c 11 100 years our record is based on the study of two marine sediment cores and reveals three main circulation stages during the holocene in the early holocene 11 100 6300 cal yr bp ann based sst estimations indicate moderately cooler than present winter condition in the ne caribbean with ssts of 25 5 c these conditions presumably reflect advection of well mixed upper water masses from the guyana upwelling area associated with a strong atlantic meridional overturning circulation amoc and enhanced trade wind activity linked to a more northerly location of the inter tropical convergence zone itcz between 6300 and 3700 cal yr bp a relative warming of winter ssts 26 5 c was probably related to a weaker circulation and upper water mass mixing because of less intense trade wind activity as the itcz moved southwards from 3700 cal yr bp to the present the region was characterised by small seasonal sst variations and generally stable winter and summer ssts the data suggest a minor shift in the sub surface inflow pattern during the last 2000 years possibly related to changes in northern hemisphere large scale atmospheric circulation also observed at higher latitude the ann based temperature pattern is supported by fluctuations in the mg ca derived temperature record although temperature maxima derived from the mg ca ratio appear anomalously high on a holocene timescale we conclude that the northeastern caribbean sst and circulation regime have been mainly dependent on the position of the itcz which in turn is controlled by changes in hemispheric solar insolation

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

fast teleconnections to the tropical atlantic sector from atlantic thermohaline adjustment 1 we examine the first decade of adjustment of the north atlantic climate following an abrupt freshening of the high north atlantic and resulting slowdown of the atlantic meridional overturning circulation amoc in a coupled model with reference to previously proposed teleconnection mechanisms after an initial ocean driven cooling at the subtropical subpolar gyre boundary subsequent equatorward progression is dominated by an atmosphere surface ocean mechanism driving evaporative cooling in the tropical north atlantic and resulting in an anomalous southward itcz displacement by year 2 the tropical cooling is countered by fast ocean baroclinic adjustment to the reduced overturning that increases the volume of tropical surface waters as well as ocean circulation changes to the increased northeasterly trades however it is the atmosphere surface ocean teleconnection that explains the hemispheric asymmetric nature of the tropical atlantic surface climate impact to amoc slowdown underlining its crucial importance in high to low latitude teleconnections

sequence sequence stratigraphy sea level changes and depositional systems in the cambro ordovician of the north china carbonate platform abstract the cambro ordovician strata in north china were deposited over a very extensive craton extending some 1500 km east west and 1000 km north south the dominantly shallow water carbonate succession reaches up to 2000 m in thickness and two megasequences transgressive regressive cycles can be distinguished lower cambrian through lower ordovician strata and middle through upper ordovician strata separated by a major palaeokarst the first megasequence consists of nine sequences which are generally 50 150 m in thickness the lower cambrian sediments consist of phosphorites and phosphatic sandstones deposited during the flooding of the craton carbonates mudrocks and evaporites were deposited in the early cambrian under an arid climate laying the foundation for the subsequent long period of shallow water carbonate deposition which lasted some 70 m y the middle and lower upper cambrian sequences consist predominantly of mudrocks and storm deposits tempestites in the lower part and oolitic grainstones and tidal flat lime mudstones in the upper part these represent outer mid and mid inner ramp depositional systems respectively of the transgressive and highstand systems tracts these sequences have strong similarities with the grand cycles in the cambro ordovician successions of north america in the upper cambrian there is a distinctive unit of glauconitic purple red mudstone several metres thick which is interpreted as the deposits of the maximum flooding of the first megasequence in the upper cambrian there was a phase of tilting of the north china carbonate platform to the north and storm deposits especially intraclastic conglomerates and hummocky cross stratified grainstones packstones were very common at this time also common in upper middle and lower upper cambrian strata are stromatolitic thrombolitic bioherms several metres in diameter the upper upper cambrian through lower ordovician strata are dominantly fine grained limestones and dolomites deposited in shallow subtidal and inter to supra tidal environments on a low energy epeiric sea platform this part of the succession is the regressive part of the first megasequence so that overall the platform shows an evolution from platform initiation to platform foundation to a ramp depositional system and then an extensive epeiric platform on a small scale the succession is composed of metre scale shallowing upward cycles parasequences arranged into cycle sets of 10 30 m thick the middle upper ordovician megasequence consists mostly of shallow water carbonates with several thick evaporite units minor palaeokarsts and palaeosoils separate the sequences which are composed of metre scale cycles regional uplift affected the north china platform in the ordovician and sedimentation did not resume until the carboniferous there is a good correlation of the two transgressive regressive megasequences described here with the global 2nd order relative sea level curve for the cambro ordovician

sequence stratigraphy of the taebaek group cambrian ordovician mideast korea abstract this study focuses on the sequence stratigraphic implications of the taebaek group cambrian ordovician a mixed carbonate siliciclastic sequence ca 1200 m thick in the mideastern part of the korean peninsula the group contains 11 lithologic units formations that can be partitioned into four packages supersequences i iv each package comprises alternation of siliciclastic and carbonate successions corresponding to the second order sequence supersequence formed in a period of 10 100 m y supersequence i jangsan myeonsan myobong and daegi fms represents the initial inundation and subsequent drowning during the late early to middle middle cambrian it experienced the drowning between the middle and late middle cambrian forming type 3 sequence boundary supersequence ii sesong and hwajeol fms was formed by prolonged marine flooding during the late middle and late cambrian it was terminated by a large supply of siliciclastics due to the rejuvenation of the drainage basin and the subsequent shallowing at the cambrian ordovician boundary type 2 sequence boundary supersequence iii dongjeom dumugol and makgol fms comprises the lowstand coarse grained siliciclastics transgressive shale by marine flooding and shallow platform carbonates by highstand progradation in the early ordovician following the large scale eustatic fall of sea level in the earliest middle ordovician supersequence iv jigunsan and duwibong fms formed on the subaerial exposure surface type 1 sequence boundary by resumed marine flooding in the middle ordovician this study provides basis for basin scale correlation with the coeval sequences in northeastern china

salar de atacama basin a record of compressional tectonics in the central andes since the mid cretaceous art no tc1008

bryozoan distribution and growth form associations as a tool in environmental interpretation tasmania australia abstract the cool temperate carbonate sediments of eastern and western tasmania and bass strait composed of 29 50 of bryozoan skeletal grains two hundred and eighty three bryozoan bulk sediments around tasmania were studied to determine the relationship between bryozoan zoarial growth form association and their depth zone bryozoans skeletons are grouped into 11 morphotypes according to architecture and style of disarticulation fragmentation encrusting forms erect flexible cellariiform and erect rigid robust branching adeoniform cheilostomes are consistently the most widespread with delicate branching cyclostomes the next most common growth form associations were grouped into four depth related settings strand line shallow shelf middle shelf and deep shelf this study demonstrates that bryozoan morphotype associations occupying different depth zones are valuable for providing fundamental paleo environmental information morphotype associations are related mainly to water depth water energy sedimentation rate and substrate in the strand line setting encrusting unilaminar and erect flexible articulated branching are abundant while in the shallow shelf erect flexible encrusting multilaminar erect rigid robust fenestrate and delicate branching are major growth forms the above associations indicate high to moderate energy levels moderate to high sedimentation rates and flexible to hard substrates in middle shelf areas erect rigid fenestrate robust and delicate branching cheilostomes and cyclostomes are the most common growth forms these associations indicate decreasing water energy lower sedimentation rate and presence of stable hard to soft substrates in the deep shelf setting the dominance of erect rigid robust fenestrate and foliose forms indicate deep quiet water low sedimentation rate and hard substrate

continental margin deformation along the andean subduction zone thermo mechanical models the chilean andes extend north south for about 3000 km over the subducting nazca plate and show evidence of local rheological controls on first order tectonic features here rheological parameters are tested with numerical models of a subduction zone incorporating slab pull and upper plate convergence which calculate the development of stress and strain over a typical period of 4 myr the models test the effects of subduction interface strength arc and fore arc crust rheology and arc temperature on the development of superficial near surface faulting as well as viscous shear zones in the mantle deformation geometries are controlled by the intersection of the subduction interface with continental rheological heterogeneities upper plate shortening and trench advance are both correlated and favored to a first order by upper plate weakness and to a second order by interface strength in cases of a strong interface a weak forearc crust is dragged downward by tectonic erosion a scenario for which indications are found along the northern chilean margin in contrast for a resistant forearc the slab pull force transmits to the surface and produces topographic subsidence this process may explain present day subsidence of the salar de atacama basin and or the persistence of a central depression specific conditions for northern chile produce a shear zone that propagates from the subduction zone in the mantle through the altiplano lower crust into the subandean crust as proposed by previous studies models with a weak interface in turn allow buoyant subducted material to rise into the continental arc in case of cessation of the slab pull this buoyant material may rise enough to change the stress state in the continental crust and lead to back arc opening in a case of young and hydrated oceanic plate forced by the slab pull to subduct under a resistant continent this plate is deviated and indented by the continental mantle and stretches horizontally at 100 km depth this situation might explain the flat wadati benioff zone of central chile

identification and removal of mn mg rich contaminant phases on foraminiferal tests implications for mg ca past temperature reconstructions 1 the geochemical composition of foraminifera shells from an ocean drilling program site in the panama basin has been analyzed by several analytical techniques la icp ms icp ms xrd sem edx in order to identify and evaluate the occurrence of contaminant phases which may bias paleoenvironmental reconstructions la icp ms results on uncleaned tests indicate the presence of mnmg rich contaminant phases at the inner surfaces of the foraminiferal shells which have mn ca ratios up to 400 mmol mol 1 and mg ca ratios up to 50 mmol mol 1 we have rigorously assessed the ability of different cleaning protocols to remove these contaminant phases and have obtained satisfactory results only when a reductive step is included the analysis of cleaning residuals collected after each of the different cleaning steps applied reveals that high mn values are associated with at least two different contaminant phases of which only one is linked to high mg values xrd analysis further reveals that the mn mg rich phase is the ca mn mg carbonate kutnahorite ca mn mg co3 2 our results demonstrate that the presence of kutnahorite like minerals can bias mg ca ratios toward higher values by 7 36 and lead to significant overestimation of past seawater temperatures by 0 9 up to 6 2 c in the case of these panama basin samples components 11 867 words 13 figures 3 tables

horizontal subduction zones convergence velocity and the building of the andes we discuss the relationships between andean shortening plate velocities at the trench and slab geometry beneath south america although some correlation exists between the convergence velocity and the westward motion of south america on the one hand and the shortening of the continental plate on the other hand plate kinematics neither gives a satisfactory explanation to the andean segmentation in general nor explains the development of the bolivian orocline in paleogene times we discuss the cenozoic history of horizontal slab segments below south america arguing that they result from the subduction of oceanic plateaus whose effect is to switch the buoyancy of the young subducting plate to positive we argue that the existence of horizontal slab segments below the central andes during eocene oligocene times and below peru and north central chile since pliocene resulted 1 in the shortening of the continental plate interiors at a large distance from the trench 2 in stronger interplate coupling and ultimately 3 in a decrease of the trenchward velocity of the oceanic plate present day horizontal slab segments may thus explain the diminution of the convergence velocity between the nazca and south american plates since late miocene

sea surface temperature anomalies associated with the 1997 1998 el nino recorded in the oxygen isotope composition of planktonic foraminifera anomalously warm sea surface temperatures and associated high rainfall propagated northward from the eastern equatorial pacific along the western margin of north america during the 1997 1998 el nino we present data from the guaymas basin gulf of california and the santa barbara basin southern california borderlands that clearly demonstrate that the oxygen isotope composition of planktonic foraminifera accurately records the local sea surface temperature changes related to the el nino phenomenon on the basis of this observation the varved sediments accumulating in these basins should contain a detailed history of both the occurrence and intensity of past el nino events

ordovician oxygen isotopes and paleotemperatures abstract valid marine 18o proxies have been defined from three ordovician units and with previously estimated sea water 18o values we have calculated paleotemperatures for low latitude settings during a greenhouse climatic era valid marine proxies include marine equant bladed and translucent fibrous calcite these cements are interpreted to be valid marine proxies based on cathodoluminescence minor element content abundance of microdolomite and stable isotopic both altered marine and non marine calcite phases values valid marine proxies from the chickamauga alabama holston tennessee and kullsberg sweden formations have an overall range of 18o values in each unit that is confined to within 1 unlike altered marine cements which exhibit significantly wider ranges of 18o values we suggest a likely non glacial ordovician sea water value of 2 1 smow from which paleotemperatures can be calculated calculated paleotemperatures are broadly consistent with crowley and baum s 1995 late ordovician paleoclimatic model

persistent summer expansion of the atlantic warm pool during glacial abrupt cold events palaeoclimate records and numerical model simulations indicate that changes in tropical and subtropical sea surface temperatures and in the annual average position of the intertropical convergence zone are linked to high latitude climate changes on millennial to glacial interglacial timescales it has recently been suggested that cooling in the high latitudes associated with abrupt climate change events is evident primarily during the northern hemisphere winter implying increased seasonality at these times8 however it is unclear whether such a seasonal bias also exists for the low latitudes here we analyse the mg ca ratios of surface dwelling foraminifera to reconstruct sea surface temperatures in the northeastern gulf of mexico for the past 300 000 years we suggest that sea surface temperatures are controlled by the migration of the northern boundary of the atlantic warm pool and hence the position of the intertropical convergence zone during boreal summer and are relatively insensitive to winter conditions our results suggest that summer atlantic warm pool expansion is primarily affected by glacial interglacial variability and low latitude summer insolation because a clear signature of rapid climate change events such as the younger dryas cold event is lacking in our record we conclude that high latitude events seem to influence only the winter caribbean climate conditions consistent with the hypothesis of extreme northern hemisphere seasonality during abrupt cooling events

mg ca and sr ca ratios in planktonic foraminifera proxies for upper water column temperature reconstruction reliable temperature estimates from both surface and subsurface ocean waters are needed to reconstructpast upper water column temperature gradients and past oceanic heat content this work examines therelationships between trace element ratios in fossil shells and seawater temperature for surface dwellingforaminifera species globigerinoides ruber white and globigerina bulloides and deep dwelling species globorotalia inflata globorotalia truncatulinoides dextral and sinistral and pulleniatina obliquiloculata mg ca and sr ca ratios in shells picked in 29 modern core tops from the north atlantic ocean are calibratedusing calculated isotopic temperatures mg ca ratios on g ruber and g bulloides agree with published dataand relationships for deep dwelling species mg ca calibration follows the equation mg ca 0 78 0 04 exp 0 051 0 003 t with a significant correlation coefficient of r

the great ordovician biodiversification event gobe the palaeoecological dimension abstract the great ordovician biodiversification event gobe saw a spectacular increase in marine biodiversity at all taxonomic levels largely within the phyla established much earlier during the so called cambrian explosion the diversification was probably the result of a combination of several geological and biological processes and the positive feedbacks resulting from them the present paper reviews the palaeoecological dimension of the gobe it involved major increases in s and biodiversity largely associated with the rise of the paleozoic evolutionary fauna dominated by suspension feeders and involving a greater occupation of ecospace and more complex ecological structures in the ecological evolutionary units p1 and p2 in the benthos these include more complex food webs than those of the cambrian greater tiering especially above the sediment water interface and the development of guild structures indicating increased competition between taxa for particular resources the ordovician is characterized by a profound change in reef composition with a switch from microbial dominated reefs in the early and middle ordovician to metazoan dominated reefs in the late ordovician increases in complexity of deep water trace fossil assemblages began in the early ordovician and mark the increasing exploitation in that environment and the development of hardgrounds permitted bioerosion and encrusting strategies together with the appearance of cryptic communities within the water column the gobe involved a significant increase in the diversity of the phytoplankton and the development of a diverse zooplankton including planktotrophic larvae from a range of invertebrate clades this revolution in the plankton enabled the establishment of a diverse fauna of pelagic vertebrates molluscs and arthropods and promoted the rise of suspension feeders in the benthos an escalation amongst predators and thus community evolution may also have been a major driver of biodiversification

glacial water mass geometry and the distribution of δ13c of σco2 in the western atlantic ocean 1 oxygen and carbon isotopic data were produced on the benthic foraminiferal taxa cibicidoides and planulina from 25 new piston cores gravity cores and multicores from the brazil margin the cores span water depths from about 400 to 3000 m and intersect the major water masses in this region these new data fill a critical gap in the south atlantic ocean and provide the motivation for updating the classic glacial western atlantic 13c transect of duplessy et al 1988 the distribution of 13c of co2 requires the presence of three distinct water masses in the glacial atlantic ocean a shallow 1000 m southern source water mass with an end member 13c value of about 0 3 0 5 vpdb a middepth 1500 m northern source water mass with an end member value of about 1 5 and a deep 2000 m southern source water with an end member value of less than 0 2 and perhaps as low as the 0 9 values observed in the south atlantic sector of the southern ocean ninnemann and charles 2002 the origins of the water masses are supported by the meridional gradients in benthic foraminiferal 18o a revised glacial section of deep water 13c documents the positions and gradients among these end member intermediate and deep water masses the large property gradients in the presence of strong vertical mixing can only be maintained by a vigorous overturning circulation

global ice volume fluctuations north atlantic ice rafting events and deep ocean circulation changes between 130 and 70 ka multiproxy data from north atlantic deep sea sediment core neap18k provide a detailed record of climate through oxygen isotope stage ois 5 seven distinct large scale episodes of ice rafting c25 c19 were identified between 126 and 70 ka global ice volume reconstructions based on high resolution benthic 18 o records indicate that major ice rafting events were not confined to ice volume maxima at ois 5d and 5b but also occurred during periods of ice sheet growth and disintegration however iceberg discharges were restricted to times when sea levels were 40 65 m below present values ice rafting episode c25 the first large scale cooling of mid atlantic surface waters after the last interglacial occurred during the gradual buildup of continental ice sheets at the ois 5e 5d transition major ice sheet collapses allied to ice rafting events c24 and c21 were associated with rapid sea level increases of 20 and 40 m respectively suborbital climatic fluctuations in the neap18k sedimentary record denoted by prominent 7 5 4 5 and 3 k y cyclicities appear to correlate with both greenland atmospheric temperatures and changes in thermohaline circulation patterns inferred from benthic 13 c values and hence provide clear evidence of a highly interconnected north atlantic climatic regime during ois 5

stable isotopes of planktonic foraminifera from tropical atlantic caribbean core tops implications for reconstructing upper ocean stratification abstract 18o values of nine tropical subtropical planktonic foraminiferal species with different preferential habitat depths collected from 62 core top samples along an east west transect across the tropical atlantic caribbean were used to test the applicability of interspecific 18o gradients for reconstructions of tropical upper ocean stratification in general the 18o difference 18o between intermediate and shallow dwelling species decreases and 18o between deep and intermediate dwellers increases with increasing thermocline depth towards the west the statistical significance of regional differences in 18o highlights 18o between the intermediate dwellers in particular globorotalia scitula and globorotalia tumida and the shallow dweller globigerinoides ruber pink as well as 18o between the deep dwellers globorotalia crassaformis or globorotalia truncatulinoides dextral and intermediate dwellers as most sensitive to changes in tropical atlantic thermocline depth based on the observed regional variations in interspecific 18o we propose a multispecies stratification index stratrop 18ointermediate 18oshallow 18odeep 18oshallow for the tropical ocean statistically significant differences in stratrop values between the e atlantic and the caribbean suggest that this index may be a useful tool to monitor variations in tropical upper ocean stratification in the geological record

surface and deep water changes in the subpolar north atlantic during termination ii and the last interglaciation to reconstruct the history of water mass exchange between the ne atlantic and the nordic seas sediment cores from 2 km water depth were studied across termination ii tii and through the last interglaciation mis5e during early tii the sudden appearance of the low latitude planktonic foraminifera beella megastoma is noted in both regions along with a steep decrease in benthic foraminiferal 18o since other proxies indicate that surface waters were cold and stratified because of meltwater conditions which prevented near surface thermohaline circulation and vertical convection in the nordic seas water mass exchange between the two areas occurred at the subsurface during later tii surface conditions changed and this subsurface circulation style was eventually replaced by vertical convection in the nordic seas b megastoma vanished from the record together with ice rafted debris ird at the end of tii while subpolar foraminiferal abundance rose peak interglacial conditions with intensive vertical convection now fully developed generating a bottom water temperature gradient of 4 c between the two areas however surface water temperatures deteriorated in the nordic seas already notably before ird recurred and 18o increased at the end of mis5e

comparison of glacial and interglacial conditions between the polar and subpolar north atlantic region over the last five climatic cycles a multiparameter based interpretation of sediment records from the northeast atlantic and the western nordic seas suggests that during the last 500 000 years only in marine isotopes stage mis 11 5e and 1 were there somewhat comparable interglacial boundary conditions in both regions i e strongly reduced occurrence of iceberg rafted debris ird and high carbonate bioproductivity although the northeast atlantic experienced such conditions during all peak interglaciations with the exception of mis 7 planktic foraminiferal 18o from this region would still indicate that significantly colder sea surface temperatures sst prevailed during mis 11 than during mis 9 5e and 1 this assumption is corroborated by a continuous input of ird into the western nordic seas during mis 11 implying a much steeper sst gradient between the polar and subpolar region and an overall reduced thermohaline activity in the polar latitudes the iceberg proxy also reveals that maximum ird discharge always happened during the final phase of glaciation and into early deglaciation terminations as these ird records from the two regions are characterized by a high time coherency it is concluded that short term variability is a persistent feature of the glacial climate system

calibration of mg ca thermometry in planktonic foraminifera from a sediment trap time series 1 paired mg ca and 18o measurements on planktonic foraminiferal species g ruber white g ruber pink g sacculifer g conglobatus g aequilateralis o universa n dutertrei p obliquiloculata g inflata g truncatulinoides g hirsuta and g crassaformis from a 6 year sediment trap time series in the sargasso sea were used to define the sensitivity of foraminiferal mg ca to calcification temperature habitat depths and calcification temperatures were estimated from comparison of 18o of foraminifera with equilibrium calcite based on historical temperature and salinity data when considered together mg ca mmol mol of all species except two show a significant r 0 93 relationship with temperature t c of the form mg ca 0 38 0 02 exp 0 090 0 003 t equivalent to a 9 0 0 3 change in mg ca for a 1 c change in temperature small differences exist in calibrations between species and between different size fractions of the same species o universa and g aequilateralis have higher mg ca than other species and in general data can be best described with the same temperature sensitivity for all species and pre exponential constants in the sequence o universa g aequilateralis g bulloides g ruber g sacculifer other species this approach gives an accuracy of 1 2 c in the estimation of calcification temperature the 9 sensitivity to temperature is similar to published studies from culture and core top calibrations but differences exist from some literature values of pre exponential constants different cleaning methodologies and artefacts of core top dissolution are probably implicated and perhaps environmental factors yet understood planktonic foraminiferal mg ca temperature estimates can be used for reconstructing surface temperatures and mixed and thermocline temperatures using g ruber pink g ruber white g sacculifer n dutertrei p obliquiloculata etc the existence of a single mg thermometry equation is valuable for extinct species although use of species specific equations will where statistically significant provide more accurate evaluation of mg ca paleotemperature

deglacial sea surface temperature and salinity increase in the western tropical atlantic in synchrony with high latitude climate instabilities a sediment core from the western tropical atlantic covering the last 21 000 yr has been analysed for centennial scale reconstruction of sea surface temperature sst and ice volume corrected oxygen isotopic composition of sea water delta 18 o ivc sw using mg ca and delta 18 o of the shallow dwelling planktonic foraminifer globigerinoides ruber white at a period between 15 5 and 17 5 kyrbp the mg ca sstand delta 18 o ivc sw a proxy for sea surface salinity sss reveals a warming of around 2 5 degrees c along with all increase in salinity a second period of pronounced warming and sss increase occurred between 11 6 and 13 5 kyr bp within age model uncertainties both warming intervals were synchronous with air temperature increase over antarctica and ice retreat in the southern south atlantic and terminated with abrupt centennial scale sss decrease and slight sst cooling in conjunction with interglacial reactivation of the meridional overturning circulation moc we suggest that during these warm intervals production of saline and warm water of the north brazil current resulted in pronounced heat and salt accumulation and was associated with warming in the southern atlantic southward displacement of the intertropical convergence zone and weakened moc at the termination of the younger dryas and heinrich event 1 intensification of cross equatorial heat and salt transport caused centennial scale cooling and freshening of the western tropical atlantic surface water this study shows that the western tropical atlantic served as a heat and salt reservoir during deglaciation the sudden release of accumulated heat and salt at the end of younger drays and heinrich event 1 may have contributed to the rapid reinvigoration of the atlantic moc c 2005 elsevier b v all rights reserved

oceanic link between abrupt changes in the north atlantic ocean and the african monsoon abrupt changes in the african monsoon which have been recorded throughout the late pleistocene and early holocene epochs tend to coincide with changes in north atlantic thermohaline circulation a numerical simulation shows that the interaction between thermohaline circulation in the north atlantic ocean and wind driven currents in the topical atlantic ocean contributes to the rapidity of african monsoon transitions during abrupt climate change events

construction of the earliest stromatoporoid framework labechiid reefs from the middle ordovician of korea abstract the great ordovician biodiversification event gobe involved a remarkable rise of skeletal reefs during the late middle ordovician a new type of skeletal patch reef built by labechiid stromatoporoids is reported from the yeongheung formation darriwilian of the korean peninsula part of the eastern north china block a hot spot for late middle ordovician diversification of early labechiids the attachment of laminar labechiids subordinate peloidal micritic crusts and spiculate sponges and minor bryozoans on peloidal intraclastic packstone to grainstone substrates and upward growth of these organisms by repeated encrustation resulted in the construction of centimeter scale domal tight frame structures these skeletal frames were in turn veneered by larger labechiids forming sub meter scale laminar skeletal reefs with primary cavities such skeletal reefs that formed by the encrustation and binding of labechiid stromatoporoids are analogous to the bindstone frameworks of coeval laurentian reef mounds and skeletal reefs though they differ markedly in composition as is apparent in the absence of tabulate corals and markedly lower contribution of bryozoans both of which were key elements of the chazy reefs of laurentia the yeongheung reefs described herein represent some of the oldest labechiid skeletal reefs known to date and formed mainly by the aggregation of early stromatoporoids prior to the arrival of corals and other robust constructors in the region this discovery provides new information on the evolutionary trends of early skeletal reefs in response to the appearance of new reef building organisms and their regional distributions during the ordovician radiation

random sampling of carbonate mounds an example from the upper ordovician of alabama abstract paleontological and lithological studies of a carbonate mound provide the necessary data from which characterizations for that mound or locality can be constructed these data based characterizations are a convenient mechanism for making qualitative comparisons with other mounds as has been done in some previous studies that discussed middle ordovician now considered upper ordovician mounds of the appalachian basin each of these studies had a different focus including the paleoecology of individual mound localities issues of ecological zonation and regional stratigraphical investigation quantitative comparisons are precluded among these studies because each mound was sampled using different procedures resulting in paleontological data sets of dissimilar density and depth two mound localities from carbonates of the upper ordovician chickamauga group stones river equivalent of jefferson and blount counties al were chosen for study to investigate the application of random sampling techniques to mound populations in outcrop one mound from each locality was completely censused to generate population compositional and structural data the location and higher level identification of each macrofossil on the surface of these mounds were recorded these bryozoan dominated data sets represent the best estimates available concerning the underlying population of mound constructors dwellers and occasional visitors rarefaction analysis was used to predict the number of randomly chosen fossils needed to detect the major taxonomic groups from each of these populations a computer program target was written to validate rarefaction predictions by conducting random sampling experiments using the census data sets the program prompts for input of three user defined variables that set the parameters of a sampling experiment and then throws randomly located sampling boxes at the mound data set recording the results statistical analysis of results from these sampling experiments validated the predictions of rarefaction analysis and led us to employ a conservative approach for sampling additional mounds at these localities

sea level and deep water temperature changes derived from benthic foraminifera isotopic records we show that robust regressions can be established between relative sea level rsl data and benthic foraminifera oxygen isotopic ratios from the north atlantic and equatorial pacific ocean over the last climatic cycle we then apply these regressions to long benthic isotopic records retrieved at one north atlantic and one equatorial pacific site to build a composite rsl curve as well as the associated confidence interval over the last four climatic cycles our proposed reconstruction of rsl is in good agreement with the sparse rsl data available prior to the last climatic cycle we compute bottom water temperature changes at the two sites and at one southern indian ocean site taking into account potential variations in north atlantic local deep water 18o our results indicate that a last glacial maximum lgm enrichment of the ocean mean oxygen isotopic ratio of 0 95 is the lowest value compatible with unfrozen deep waters in the southern indian ocean if local deep water 18o did not increase during glacials with respect to present such a value of the lgm mean ocean isotopic enrichment would impose a maximum decrease in local bottom water 18o at the north atlantic site of 0 30 during glacials

deglacial variability in the surface return flow of the atlantic meridional overturning circulation 1 benthic foraminiferal cd ca from a florida current sediment core documents the history of the northward penetration of southern source waters within the surface return flow of the atlantic meridional overturning circulation amoc cd seawater estimates cdw indicate that intermediate depth southern source waters crossed the equator and contributed to the florida current during the bolling allerod warm period of the last deglaciation consistent with evidence of only a modest amoc reduction compared to today the cdwestimates also provide the first paleoceanographic evidence of a reduction in the influence of intermediate depth southern source waters within the florida current during the younger dryas a deglacial cold event characterized by a weak north atlantic amoc our results reveal a close correspondence between the northward penetration of intermediate depth southern source waters and the influence of north atlantic deep water suggesting a possible link between intermediate depth southern source waters and the strength of the atlantic amoc

interlaboratory comparison study of calibration standards for foraminiferal mg ca thermometry an interlaboratory study of mg ca and sr ca ratios in three commercially available carbonate reference materials bam rs3 cmsi 1767 and ecrm 752 1 was performed with the participation of 25 laboratories that determine foraminiferal mg ca ratios worldwide these reference materials containing mg ca in the range of foraminiferal calcite 0 8 mmol mol to 6 mmol mol were circulated with a dissolution protocol for analysis participants were asked to make replicate dissolutions of the powdered samples and to analyze them using the instruments and calibration standards routinely used in their laboratories statistical analysis was performed in accordance with the international standardization organization standard 5725 which is based on the analysis of variance anova technique repeatability rsdr an indicator of intralaboratory precision for mg ca determinations in solutions after centrifuging increased with decreasing mg ca ranging from 0 78 at mg ca 5 56 mmol mol to 1 15 at mg ca 0 79 mmol mol reproducibility rsdr an indicator of the interlaboratory method precision for mg ca determinations in centrifuged solutions was noticeably worse than repeatability ranging from 4 5 at mg ca 5 56 mmol mol to 8 7 at mg ca 0 79 mmol mol results of this study show that interlaboratory variability is dominated by inconsistencies among instrument calibrations and highlight the need to improve interlaboratory compatibility additionally the study confirmed the suitability of these solid standards as reference materials for foraminiferal mg ca and sr ca determinations provided that appropriate procedures are adopted to minimize and to monitor possible contamination from silicate mineral phases

end member models for andean plateau uplift abstract diverse techniques have been applied over the past decade to quantify the uplift history of the central andean plateau ap in this study opposing models for surface uplift are evaluated including a rapid rise of 2 5 km 10 6 ma and a slow and steady rise since 40 ma these end member models are evaluated by synthesizing observations of the ap lithosphere and the history of deformation sedimentation exhumation magmatism uplift and fluvial incision structural and geophysical studies estimate variable shortening magnitudes 530 150 km involving cover to basement rocks an isostatically compensated thick crust 80 65 km high heat flow and zones of variable velocity and attenuation in the crust and mantle these observations have invoked interpretations such as a hot weak lithosphere partial melt crustal flow and perhaps current localized delamination but do not provide strong support for massive delamination required by the rapid uplift model deformation and associated exhumation began 60 40 ma and generally migrated eastward with consistent long term average shortening rates 12 8 mm yr in bolivia favoring the slow uplift model volcanic and helium isotope evidence show an ap wide zone of shallow mantle melting and thin lithosphere that has existed since 25 ma which is inconsistent with the rapid rise model that suggests lithospheric thinning occurred 10 6 ma paleoaltimetry data suggest a rapid 2 5 km elevation gain 10 to 6 ma but are equally consistent within error with a linear rise since 25 ma widespread fluvial incision 2 5 1 km occurred along the western flank since 11 8 ma and may be associated with surface uplift as proposed by the rapid rise model however the paleoaltimetry and incision data can also be explained by regional climate change associated with plateau uplift implications of these results for reconstructions of ap evolution are that 1 substantial deformation of a weak lithosphere is essential 2 ap growth has taken significantly longer 40 myr and was more uniform along strike 1500 km than previously appreciated and 3 the slow and steady uplift model is most consistent with available constraints we conclude that the rapid uplift model may be an overestimate and that a more protracted cenozoic uplift history is tenable

marine oxygenation lithistid sponges and the early history of paleozoic skeletal reefs abstract microbial carbonates were major components of early paleozoic reefs until coral stromatoporoid bryozoan reefs appeared in the mid ordovician microbial reefs were augmented by archaeocyath sponges for 15 myr in the early cambrian by lithistid sponges for the remaining 25 myr of the cambrian and then by lithistid calathiid and pulchrilaminid sponges for the first 25 myr of the ordovician the factors responsible for mid late cambrian microbial lithistid sponge reef dominance remain unclear although oxygen increase appears to have significantly contributed to the early cambrian explosion of marine animal life it was followed by a prolonged period dominated by greenhouse conditions as sea level rose and co2 increased the mid late cambrian was unusually warm and these elevated temperatures can be expected to have lowered oxygen solubility and to have promoted widespread thermal stratification resulting in marine dysoxia and hypoxia greenhouse conditions would also have stimulated carbonate platform development locally further limiting shallow water circulation low marine oxygenation has been linked to episodic extinctions of phytoplankton trilobites and other metazoans during the mid late cambrian we propose that this tendency to dysoxia hypoxia in shallow marine environments also limited many metazoan reef builders in contrast during the mid late cambrian the ability of lithistid sponges to withstand low oxygen levels allowed them to create a benthic association with microbial carbonates that dominated global reefs these conditions ameliorated during the ordovician as temperature decline promoted ocean ventilation the prolonged time gap occupied by low diversity reefs between the cambrian explosion and the great ordovician biodiversification event reflects elevated temperatures and reduced marine oxygenation that limited metazoan diversification in shallow marine environments

on the interpretation of caribbean paleo temperature reconstructions during the younger dryas 1 a conundrum exists regarding whether the sea surface temperatures decreased or increased over the southern caribbean and the western tropical atlantic region during the younger dryas when the north atlantic cooled substantially and the atlantic thermohaline circulation was weakened significantly despite the proximity of core locations some proxy reconstructions record a surface cooling while others indicate a warming we suggest that this seemingly paradoxical finding may at least partially be attributed to the competing physical processes that result in opposing signs of temperature change in the region in response to weakened north atlantic meridional overturning circulation our coupled ocean atmosphere model experiments indicate that the temperature response over the southern caribbean and western tropical atlantic regions is complex and can vary considerably in small spatial scales depending on the nature of physical processes that dominate

florida straits density structure and transport over the last 8000 years 1 the density structure across the florida straits is reconstructed for the last 8000 years from oxygen isotope measurements on foraminifera in sediment cores the oxygen isotope measurements suggest that the density contrast across the florida current increased over this time period the magnitude of this change corresponds to an increase in the geostrophic transport referenced to 800 m water depth of 4 sverdrups sv over the last 8000 years the spatial and seasonal distribution of incoming solar radiation due to changes in the earth s orbit has caused systematic changes in the atmospheric circulation including a southward migration of the intertropical convergence zone over the last 8000 years these changes in atmospheric circulation and the associated wind driven currents of the upper ocean could readily account for a 4 sv increase in the strength of the florida current we see no evidence in our data for dramatic changes in the strength of the atlantic meridional overturning circulation over this time period

depauperate skeletonized reef dwelling fauna of the early cambrian insights from archaeocyathan reef ecosystems of western mongolia abstract reef dwelling organisms in the early cambrian include typical members of the cambrian fauna such as trilobites chancelloriids and hyoliths however in comparison to later ordovician reefs cambrian reefs often do not appear as diverse here we investigate early cambrian microbial archaeocyathan reefs of the salaagol formation in the zavkhan basin of mongolia as well as perform a literature survey of 40 early paleozoic reefs to understand the timing of reef biodiversity by using point count analysis we can quantify the carbonate contribution of framework builders and reef dwelling organisms in these ecosystems we find that mongolian reefs contained several genera of framework building archaeocyaths 5 0 by volume and associated microbial forms 5 4 but are unevenly distributed through the formation archaeocyathan contribution increases are potentially concurrent with negative shifts in carbon isotopic composition similar to other localities in gondwana however reef dwelling biota was minimal 0 3 throughout the salaagol formation and did not correlate to changes in framework builders or geochemical proxies such as u v and carbon isotopes a literature survey of ediacaran through ordovician reefs suggests that there is a trend of increasing reef dweller abundance functional richness and skeletonization through time the changes in abundance 17 9 to 28 8 considered frequent and functional richness 3 7 to 6 0 functional groups could be due to an increase in productivity in the oceans during the cambrian thereby expanding the base of the food web during the lead up to the ordovician radiation the trend of increasing skeletonization could be due to the evolution of more robust skeletons among reef dwellers in order to protect themselves from increased predation in reef environments these trends suggest that at least during the early paleozoic increases in biological diversity are not necessarily concurrent with the establishment of a framework reef

rapid subtropical north atlantic salinity oscillations across dansgaard oeschger cycles geochemical and sedimentological evidence suggest that the rapid climate warming oscillations of the last ice age the dansgaard oeschger cycles were coupled to fluctuations in north atlantic meridional overturning circulation through its regulation of poleward heat flux the balance between cold meltwater from the north and warm salty subtropical gyre waters from the south influenced the strength and location of north atlantic overturning circulation during this period of highly variable climate here we investigate how rapid reorganizations of the ocean atmosphere system across these cycles are linked to salinity changes in the subtropical north atlantic gyre we combine mg ca palaeothermometry and oxygen isotope ratio measurements on planktonic foraminifera across four dansgaard oeschger cycles spanning 45 9 59 2 kyr ago to generate a seawater salinity proxy record from a subtropical gyre deep sea sediment core we show that north atlantic gyre surface salinities oscillated rapidly between saltier stadial conditions and fresher interstadials covarying with inferred shifts in the tropical atlantic hydrologic cycle and north atlantic overturning circulation these salinity oscillations suggest a reduction in precipitation into the north atlantic and or reduced export of deep salty thermohaline waters during stadials we hypothesize that increased stadial salinities preconditioned the north atlantic ocean for a rapid return to deep overturning circulation and high latitude warming by contributing to increased north atlantic surface water density on interstadial transitions

synchronous high frequency oscillations in tropical sea surface temperatures and north atlantic deep water production during the last glacial cycle stable isotopic measurements of g sacculifer and c wuellerstorfi in a core from the western equatorial atlantic imply that there are parallel suborbital oscillations in surface water hydrography and deep water circulation occurring during oxygen isotope stages 2 and 3 low values of g sacculifer 18o accompany high values of c wuellerstorfi 13c linking warmer sea surface temperatures ssts in the tropics with increased production of lower north atlantic deep water nadw the amplitude of the 18o oscillations is 0 6 or 2 3 c which is superimposed on a glacial interglacial amplitude of about 2 1 using the g sacculifer 18o data we calculate that surface waters were colder during stage 2 than calculated by climap 1976 1981 the longer period 2 kyr oscillations in air temperature recorded in the greenland and antarctic ice cores appear to correlate with oscillations in sea surface temperature in the equatorial atlantic the magnitude of these oscillations in tropical sst is too large to have resulted from changes in meridional heat transport caused by the global conveyor alone the apparent synchroneity of equatorial sst and polar air temperature changes as well as the amplitude of the sst changes at the equator are consistent with the climate effects expected from changes in the atmosphere s greenhouse gas content h2ovapor co2 and ch4

links between salinity variation in the caribbean and north atlantic thermohaline circulation variations in the strength of the north atlantic ocean thermohaline circulation have been linked to rapid climate changes1 during the last glacial cycle through oscillations in north atlantic deep water formation and northward oceanic heat flux2 3 4 the strength of the thermohaline circulation depends on the supply of warm salty water to the north atlantic which after losing heat to the atmosphere produces the dense water masses that sink to great depths and circulate back south2 here we analyse two caribbean sea sediment cores combining mg ca palaeothermometry with measurements of oxygen isotopes in foraminiferal calcite in order to reconstruct tropical atlantic surface salinity5 6 during the last glacial cycle we find that caribbean salinity oscillated between saltier conditions during the cold oxygen isotope stages 2 4 and 6 and lower salinities during the warm stages 3 and 5 covarying with the strength of north atlantic deep water formation7 at the initiation of the bolling allerod warm interval caribbean surface salinity decreased abruptly suggesting that the advection of salty tropical waters into the north atlantic amplified thermohaline circulation and contributed to high latitude warming

the earliest evolutionary link of metazoan bioconstruction laminar stromatoporoid bryozoan reefs from the middle ordovician of korea abstract sub metre scale patch reefs composed primarily of stromatoporoids and bryozoans are reported from the duwibong formation upper middle ordovician taebaeksan basin korea in the eastern margin of the sino korean block the reef framework is constructed of alternating thin laminae of the primitive labechiid stromatoporoid cystostroma the bryozoan nicholsonella subordinate solenopora and minor siliceous sponges alternating laminae of stromatoporoids and bryozoans are largely responsible for the formation of a globular framework composed of columnar branching bulbous to irregular masses solenopora sporadically occurring as tiny patches or thin laminae attached to the stromatoporoid bryozoan framework is considered to be subordinate encrusters siliceous sponges occur within the stromatoporoid bryozoan framework and within the growth framework and bored cavities interpreted as subordinate encrusters and cryptic dwellers the compact globular framework of the duwibong stromatoporoid bryozoan consortium represents a new type of ordovician skeletal bioconstruction but with a certain structural similarity to lower ordovician bryozoan reefs in the south china block together with coeval labechiid reefs occurring near the current study area the duwibong reefs suggest that incursion of the primitive stromatoporoids into the earliest bryozoan reefs resulted in the dominance of reef building stromatoporoids in peri gondwana in contrast to coeval reefs in laurentia which commonly contain tabulate corals

deepwater source variations during the last climatic cycle and their impact on the global deepwater circulation the degree of similarity of the 13c records of the planktonic foraminiferal species n pachyderma and of the benthic foraminiferal genus cibicides in the high latitude basins of the world ocean is used as an indicator of the presence of deepwater sources during the last climatic cycle whereas continuous formation of deep water is recognized in the southern ocean the norwegian sea stopped acting as a sink for surface water during isotope stage 4 and the remainder of the last glaciation however deep water formed in the north atlantic south of the norwegian sea during the last climatic cycle as early as isotope substage 5d and this area was also the only active northern source during stages 4 2 a detailed reconstruction of the geographic distribution of 13c in benthic foraminifera in the atlantic ocean during the last glacial maximum shows that the most important deepwater mass originated from the southern ocean whereas the glacial north atlantic deep water cannot be traced south of 40 n at shallower depth an oxygenated 13c rich intermediate water mass extended from 45 n to 15 s in the pacific ocean a ventilation higher than the modern one was also found in open ocean in the depth range 700 2600 m and is best explained by stronger formation of intermediate water in high northern latitudes

increasing coccolith calcification during co2 rise of the penultimate deglaciation termination ii abstract glacial to interglacial environmental changes have a strong impact on coccolithophore assemblage composition at the same time glacial terminations are characterised by an increase in atmospheric co 2 concentration in order to determine how these two processes influence the calcite production of coccolithophores we compared coccolith weight estimates obtained with the automated coccolith recognition system syraco with sem assemblage counts covering the penultimate glacial termination t ii from two sediment cores in the north atlantic ocean at the temperate rockall plateau odp site 980 mean coccolith weight peaks around heinrich event 11 this is paralleled by a shift within the coccolith assemblage related to the changes of the oceanic frontal system during termination ii in the tropical florida strait far from the influences of frontal zones mean noelaerhabdaceae coccolith weight doubles during termination ii this is partly due to an assemblage shift towards larger and heavier calcifying morphotypes but mainly an effect of increasing coccolithophore calcification this increase is exactly mirroring the rise in atmospheric co 2 contradicting previous findings from termination i reconstructions of dic alkalinity and calcite saturation at the florida strait during termination ii produce higher estimates of these parameters compared to previous studies for which coccolith weight estimates are available and therefore a change of the carbonate system is the most likely cause for the coccolithophore calcification increase during atmospheric co 2 rise our results illustrate that even during rising atmospheric co 2 the conditions of the seawater carbonate system can be favourable for coccolithophore calcification the total caco 3 production of a coccolithophore assemblage under increasing co 2 therefore depends on regional seawater carbonate system characteristics and the local assemblage composition

reply to the comment by r a astini and f m davila on the west andean thrust the san ramon fault and the seismic hazard for santiago chile 1 we have proposed earlier a new tectonic model for the evolution of the andes mountain belt as a bivergent orogen here to reply to a comment by astini and davila 2010 we discuss briefly the protracted diachronic evolution over tens of million years by propagating deformation at the large scale over 10 10 km its influence on basin formation in the back arc region retroarc foreland basin and the mechanical implications of the bivergence in the tectonics of the fore arc region particularly the possible effects of the underthrusting of the coastal crustal scale rigid block the marginal block beneath the west andean thrust 2 the comment by astini and davila 2010 criticizes our new model presented by armijo et al 2010 suggesting that theandes is a fundamentally bivergent or doubly vergent orogen and defends the conventional model of andean orogeny which we think obsolete involving crustal shortening only by development of retroarc thrusts in the back arc region e g as discussed among many others by isacks 1988 our model is based on the structural study of the san ramon fault system and the principal cordillera at the front of the western flank of the andes which is used to characterize the crustal scale west andean thrust wat a major fold thrust system in the fore arc region synthetic to the subduction zone astini and davila raise cursorily a large number of important questions which cannot be fully addressed in this reply 3 to summarize the main argument 1 astini and davila think that according to the critical taper wedge model e g davis et al 1983 the dominant thrusting of the andes cannot have shifted from an initial westward vergence to an eastward vergence as we propose 2 they claim that the well known eastward cratonward migration of thrusting associated with foreland basin formation in argentina cannot be explained if the initial dominant thrusting of the andes was in the fore arc with westward directed vergence and 3 astini and davila argue that no continental block in the fore arc region as the marginal or coastal block that we have defined can be considered as a western foreland of the andes because there is no well developed western foreland basin the miscellaneous final remarks by astini and davila express their doubts that our model may fit currently accepted models of mass transfer sediment flow across orogens and tectonic climatic forcing because according to our model a major topographic slope would have been created to the west of the andes a feature that as anyone can check is not hypothetical but a matter of fact last but not least the andes at 33 5 s latitude would not be in an early stage of its evolution as we claim because sediments in the argentinean foreland record its development since more than 20 ma our reply intended to identify first order conflicting issues is as follows

evidence for early warming and cooling in north atlantic surface waters during the last interglacial in depth analysis of planktic foraminiferal census data paired with 18o records of specific indicator species provides new insight into the surface ocean evolution of the northeast atlantic during the previous interglacial warm period oxygen isotope stage ois 5e full interglacial conditions existed at the study site for a maximum of only 8 kyr between 125 and 117 ka highest sea surface temperatures ssts occurred during early ois 5e concomitant with high summer insolation but after the main phase of ice sheet melting of the preceding glaciation saalian this early peak sst interval is marked by the appearance of tropical subtropical species and lasted for 4 kyr until 121 ka as corroborated by a major change in planktic 18o relative stability in global ice volume continued for another 3 4 kyr before ssts dropped further toward the next stadial during early ois 5e the situation of the surface water vertical structure appears to have been different from the early holocene for ois 5e it is therefore suggested that the particular melting history of late saalian ice had a long lasting and profound effect on both postdeglacial surface water mass configuration in the north atlantic and heat moisture transfer into europe

assessing the effect of dissolution on planktonic foraminiferal mg ca ratios evidence from caribbean core tops in order to assess the dissolution effect on foraminiferal mg ca ratios we analyzed mg ca of seven planktonic foraminiferal species and four of their varieties from caribbean core tops from 900 4700 m water depth depending on the foraminiferal species and variety mg ca start to decline linearly below co32 levels of 18 26 mol kg by 0 04 0 11 mmol mol per 1 mol kg co32 similar to decreases of 0 5 0 8 mmol mol per kilometer below 2500 3000 m water depth above these species specific critical levels mg ca remains stable with higher intraspecific mg ca variability than below we developed routines to correct mg ca from below these critical thresholds for dissolution effects which reduce the overall intraspecific variability by 24 64 and provide dissolution corrected mg ca appropriate to calculate holocene paleotemperatures when taking into account only dissolution unaffected mg ca from 2000 m the systematic succession of foraminiferal species according to their mg ca reflects expected calcification depths

geomorphic evidence for recent uplift of the fitzcarrald arch peru a response to the nazca ridge subduction abstract the 400 000 km 2 wide fitzcarrald arch constitutes a wide topographic high of the amazon basin against the central andes in order to constrain its formation mechanisms and in particular to test its relationships to the nazca ridge subduction a quantitative geomorphology analysis of the arch is performed using hypsometric integrals elongation and azimuths of 7th and 5th order catchments they all express a trend from high maturity to low maturity from nw towards se this maturity gradient coupled with the local drainage direction demonstrate that the fitzcarrald arch is not a classical alluvial fan since its apex is located 100 km east to the subandean thrust front and the corresponding sedimentary pile is lacking nor is the arch the superficial expression of an inherited transfer zone because its geomorphic shape is radial and it does not diverge from a symmetry axis moreover such a reactivated structure is not found at depth on seismic profiles in addition our data show that underlying geomorphic control on catchment initiation and development has progressed from nw to se which in combination with the observation of crustal doming by espurt et al espurt n baby p brusset s roddaz m hermoza w regard v antoine p o salas gismondi r bolanos r 2007 how does the nazca ridge subduction influence the modern amazonian foreland basin geology 35 515 518 suggests that this relief is caused by the eastward sliding of the buoyant nazca ridge beneath the south american lithosphere

facies geometry and geological significance of late ordovician early caradocian coral bioherms lourdes formation western newfoundland late ordovician coral bioherms in the lourdes formation of western newfoundland exhibit a complex mixing of architectural elements including framework boundstone and suspension deposits the bioherms occur within a narrow 16 m stratigraphic interval and a prominent unconformity truncates the interval of bioherm growth and tops of many of the bioherms the buildups developed along a carbonate ramp they occur isolated and in groups individuals in groups are aligned in parallel orientation the sizes of the bioherms range from small 50 100 cm coral piles to columnar and dome shaped masses 1 15 m however topographic relief was never more than 1 m bioherm construction reflects i stacking of the tabulate coral labyrinthites chidlensis and less common stromatoporoids ii accumulation of microbial stromatoporoid boundstone and suspension deposits within shelter cavities between corals and iii detrital bioherm flank skeletal grainstone beds trypanites borings are common in the tops of coral heads the bioherms exhibit three growth development stages i seafloor stabilization wherein rare abraded coral colonies lie scattered within pelmatozoan skeletal grainstone lenses ii colonization wherein corals l chidlensis rare stromatoporoids labechia sp and other biota bryozoans produced a bioherm overlying the basal sediment base and iii diversification which is marked by a more diverse range of fauna and flora as well as occurrence of shelter cavity deposits the diversification stage usually makes up more than 70 of a bioherm structure and in some defines multiple periods of start up and shut down of bioherm growth the latter is defined by bored omission surfaces and or deposition of inter bioherm sediment the lourdes bioherms have a similar ecological structure biotic diversity and depositional environment to patch reefs in the equivalent carters limestone in tennessee the mixture of coral stacking and boundstone as architectural elements identify an early palaeozoic transition of reef design development along shallow water platforms that began to displace the muddy boundstone bafflestone carbonate buildups more typical of the early and middle ordovician time

sedimentology and distinction of carbonate buildups middle ordovician east tennessee abstract investigation of extensive skeletal grainstone deposits that comprise much of the middle ordovician sequence in east tennessee has resulted in the recognition of two distinct carbonate buildup complexes the rockdell formation comprises abundant pelmatozoan bryozoan grainstones and packstones and lesser deposits of lime wackestone these deposits represent carbonate sand shoals consisting of a mixture of in situ and transported skeletal grains which surround relatively small isolated to anastomosing lime mud mounds the rockdell buildup was developed in shallow water high energy conditions on a relatively stable platform the holston formation is dominated by bryozoan pelmatozoan packstones that surround roughly elliptical masses of bryozoan wackestone boundstone the holston rep esents a series of lime mud bryozoan patch reefs that were surrounded by piles of in situ skeletal sand produced in pelmatozoan bryozoan thickets the holston buildup developed in deeper water on the outer platform or perhaps downslope recognition and distinction of these two buildups is based on consideration of a number of criteria including 1 color 2 overall composition and distribution of flora and fauna 3 composition and distribution of bryozoan fauna 4 types and distribution of component lithofacies and 5 character of associated lime mud deposits distinction of these buildups has major importance in the determination of east tennessee paleogeography during the middle ordovician and also has implications for possible hydrocarbon exploration in these deposits the criteria applied here may be useful in making distinctions among other carbonate buildups in the geologic record

southward migration of the intertropical convergence zone through the holocene titanium and iron concentration data from the anoxic cariaco basin off the venezuelan coast can be used to infer variations in the hydrological cycle over northern south america during the past 14 000 years with subdecadal resolution following a dry younger dryas a period of increased precipitation and riverine discharge occurred during the holocene thermal maximum since approximately 5400 years ago a trend toward drier conditions is evident from the data with high amplitude fluctuations and precipitation minima during the time interval 3800 to 2800 years ago and during the little ice age these regional changes in precipitation are best explained by shifts in the mean latitude of the atlantic intertropical convergence zone itcz potentially driven by pacific based climate variability the cariaco basin record exhibits strong correlations with climate records from distant regions including the high latitude northern hemisphere providing evidence for global teleconnections among regional climates

cavity dwelling biota in middle ordovician chazy bryozoan mounds from quebec bryozoan mounds dominated by batostoma chazyensis from the laval formation of the chazy group early middle ordovician near montreal quebec contain framework cavities that house a coelobiontic cavity dwelling biota reports of coelobionts of ordovician age are rare and this is the first report of chazy group mounds containing coelobionts algae sponges and bryozoa batostoma dominate the cavity biota and are found encrusting cavity walls and roofs the algae are represented by mammillary encrustations now micrite and solenpora sp on the roofs the sponges are not identified but occur both as isolated monaxial triaxial and six rayed spicules and as body fossils within the cavities coccoid cells of unknown affinities are also found these cavities provide the first evidence of coelobiontic biological erosion trypanites a compound morphogenus is the only macroborer and is found in cavity walls endolithic boring algae are present and indicate that as early as the middle ordovician b

post rift reactivation of the onshore margin of southeast brazil evidence from apatite u th he and fission track data abstract on the continental margin of southeast brazil there is good geological evidence for post rift tectonic reactivation in the form of onshore tertiary basins up to 800 m deep and cretaceous to paleocene alkaline intrusive bodies at the surface with the aim of constraining the mesozoic and cenozoic exhumation history of this region we present new apatite u th he ages on basement samples which one of us previously used for apatite fission track aft analysis the new he ages range from 115 5 2 2 ma to 47 0 6 4 ma whereas the aft ages range from 330 3 22 ma to 64 5 3 ma inverse thermal history modelling of all the data provides more detail on the post rift cooling history than do the aft data alone furthermore models incorporating radiation damage effects on he diffusion produce thermal histories that are more consistent with independent geological evidence than models without these effects the results imply that only a few samples record an early cooling phase around the time of opening of the south atlantic ocean the new u th he data also imply a late cretaceous phase of exhumation between 90 and 60 ma subsequently the region underwent slow cooling i e erosion rate two or three samples seem to indicate a period of rapid cooling during the neogene although this is at the limit of resolution of the methods the post rift cooling phases imply exhumation from depths between 2 and 5 km this activity we attribute to compression in the south american plate between the andean subduction zone and the mid atlantic ridge in southeast brazil compression acted on a crust that was thermally or mechanically susceptible to reactivation during the late cretaceous deformation in the study area was of regional extent whereas during the tertiary it concentrated along pre existing shear zones of the precambrian brasiliano orogeny

deposition of a muddy sediment drift in the southern straits of florida during the late quaternary abstract bottom currents associated with the florida current in large part control deposition of muddy biogenic sediments in the constricted deep sea passage of the southern straits of florida the unit is similar to muddy contourite drifts based on sediment structures changing thickness of biostratigraphic zones and distribution of biogenic sands in twenty piston cores current activity affected deposition more during the last glacial period than during the present and penultimate interglacial periods of the last 127 000 years based on the presence of an erosional regional unconformity that ended in the upper part of the glacial interval and on the change in pattern of silt and clay accumulation rates in the glacial interval relative to interglacial intervals

coupled tectonic evolution of andean orogeny and global climate abstract the largest tectonic relief breaking the earth s surface 13 km vertically is at the subduction margin of the andes which generates routinely megathrust earthquakes mw 8 5 and drives the paradigmatic andean orogen here we present key geologic evidence to reassess first order features of geomorphology and tectonics across the central andes where the orogen includes the altiplano plateau and attains its maximum integrated height and width the andean subduction margin has a stepped morphology dominated by the low relief atacama bench which is similar to a giant uplifted terrace slopes gently over a width of 60 100 km from the andes to the pacific and runs over more than 1000 km of coastal length we find that the genesis of stepped morphology at the andean seaboard is due to concomitant development of large west vergent thrusts parallel to the subduction interface and increasing aridity in the atacama desert which keeps an unprecedented large scale record of interplaying tectonics and cenozoic climate change incorporating our results with published geological knowledge demonstrates that andean orogeny is characterized by trench perpendicular bivergent and trench parallel bilateral growth over the past 50 myr associated with positive trench velocity toward the continent trench advance and subduction of a wide slab under south america we hypothesize that a global plate tectonic reorganization involving long lasting viscous mantle flow has probably forced both andean orogeny and global climate cooling since 50 ma in contrast two important stepwise pulses of increasing aridity and trench perpendicular andean growth appear to be results of changes in erosion rates due to global late eocene and middle miocene cooling events

sr ca in multiple species of planktonic foraminifera implications for reconstructions of seawater sr ca sr ca ratios were measured on eight species of planktonic foraminifera from a core top transect of the north atlantic five of the species globigerinoides ruber globigerina bulloides neogloboquadrina pachyderma globigerinoides sacculifer globigerinella siphonifera show remarkably little within species variability in sr ca 1 2 0 1 three globorotaliid species globorotalia hirsuta globorotalia inflata globorotalia truncatulinoides show somewhat greater variability 3 7 interspecies variations are of 10 the variability in globorotaliid sr ca is explained either by a greater temperature sensitivity than for other species or by depth dependent dissolution other than this effect the overwhelming control on foraminiferal sr ca appears to be seawater sr ca in contrast time series sr ca records of four species from a north atlantic sediment core over a glacial interglacial cycle show very significant differences n pachyderma shows large amplitude changes in sr ca 9 7 in phase with 18o whereas g ruber shows the smallest amplitude changes 2 6 out of phase with 18o and most similar to model predictions for temporal changes in seawater sr ca records of g inflata and g bulloides are intermediate amplitude changes of 3 3 4 7 and out of phase with 18o the lack of coherence in the time series records between the species shows that factors in additional to changing seawater sr ca must affect planktonic foraminiferal sr ca

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr

subtropical atlantic salinity variability and atlantic meridional circulation during the last deglaciation during the last deglaciation ca 21 10 ka freshening of the north atlantic surface likely caused reductions in atlantic meridional overturning circulation amoc the mechanisms related to amoc recovery remain poorly understood here we present three new deglacial surface temperature and 18oseawater 18osw reconstructions from the western subtropical north and south atlantic similarities to tropical caribbean and western atlantic 18osw records suggest that a salty surface water mass accumulated in the western atlantic from 27 s to 33 n during periods of reduced amoc however 18osw decreases led deep amoc resumption by hundreds of years we suggest that the northward export of salt previously trapped in the western atlantic resulted in the early establishment of a shallow overturning circulation that eventually culminated in deep amoc resumption implying that amoc may constitute a self limiting system

miocene quaternary structural evolution of the uyuni atacama region andes of chile and bolivia abstract we describe the miocene quaternary geological structural evolution of the region between the salar de uyuni and de atacama andes of chile and bolivia we recognized four main tectonic events based on fold geometry fault kinematics and stratigraphic data the oldest event of miocene age is characterized by folding and reverse faulting of the sedimentary successions with an e w direction of shortening in the northern part of the studied area and a wnw ese shortening in the southern part the following two events of pliocene age are characterized by lower shortening amounts they occurred first by reverse faulting with a nw se trending greatest principal stress 1 computed with striated fault planes and a vertical least principal stress 3 followed by pervasive strike slip faulting with the same nw se trending 1 and a horizontal ne sw 3 the fourth event dating to the late pliocene quaternary is characterized by normal faulting the 3 still trends ne sw whereas the intermediate principal stress 2 exchanged with 1 volcanism accompanied both the contractional transcurrent and extensional tectonic phases the mio pliocene compression appears directly linked to a rapid convergence and an apparently important coupling between the continental and oceanic plates the e w to wnw ese direction of shortening of the miocene structures and the nw se 1 of the pliocene structures seem to be more linked to an intra andean re orientation of structures following the wnw directed absolute motion of the south american plate the extensional deformations can be interpreted as related to gravity forces affecting the highest parts of the volcanic belt in a sort of asymmetrical sw ward collapse of the belt

an evaluation of controls on planktonic foraminiferal sr ca comparison of water column and core top data from a north atlantic transect sr ca in planktonic foraminifera recovered from the water column over 0 800 m along a meridional transect in the north atlantic ocean from 30 to 60 n were compared with data from core top samples on the same transect and with in situ temperatures determined from water column ctd profiles species belonging to the globorotaliid genus show significant variability in sr ca from place to place whereas non globorotaliid species show no significant variability this variability for the globorotaliid species in core top samples has already been shown to covary with calcification temperature derived from 18o but it also covaries with bottom depth symptomatic of a dissolution artifact these alternatives are distinguishable from the water column data for which the globorotaliid species show a small temperature dependence of 0 025 mmol mol c within the range 5 15 c however temperature dependence is not supported by glacial interglacial differences in sr ca for globorotaliid and non globorotaliid species and at least from this perspective a co3 2 influence seems more likely

decadal changes in water mass characteristics at 24 n in the subtropical north atlantic ocean abstract three transatlantic hydrographic sections across 24 n through the center of the subtropical gyre are analyzed for evidence of decadal changes in water mass characteristics in the main thermocline there has been a steady increase in salinity from 1957 to 1981 to 1992 the salinity at a given potential temperature between 12 c and 17 c has increased at a nearly constant rate of 0 010 per decade at constant potential density salinity and temperature both increased at rates of 0 018 per decade and 0 065 c per decade in the intermediate waters between 800 and 1500 dbar salinity has increased as well on average by as much as 0 025 from 1981 to 1992 either on constant potential temperature or constant density surfaces these changes cannot be due to vertical heaving of a constant water mass structure and they cannot be easily explained in terms of horizontal shifts in the subtropical gyre water mass structure throughout the water column down to 2000 dbar and across the zonal extent of the 24 n

causes of tropical atlantic paleo salinity variation during periods of reduced amoc 1 during periods of reduced atlantic meridional overturning circulation amoc associated with a freshening of northern north atlantic surface water paleo proxy records indicate a corresponding surface salinity increase over the entire tropical atlantic although latitudinal shifts in the mean position of the atlantic intertropical convergence zone itcz can explain certain features of the paleo salinity reconstructions this mechanism does not offer an explanation for the reconstructed basin wide paleo salinity response to amoc change here we present new results from general circulation model simulations that suggest the sea surface salinity sss increase in the tropical north atlantic during periods of weakened amoc is mainly controlled by the atmospheric response to the north atlantic cooling while the oceanic teleconnection contributes to increased sss over the equatorial and south tropical atlantic ocean

evidence for increased volume transport of the florida current in the pliocene and pleistocene abstract results from biostratigraphy and sedimentology of five cores from the yucatan channel indicate a possible minor increase in current winnowing 3 7 m y ago a large significant increase in winnowing 3 1 m y ago and numerous cycles in winnowing throughout the latest pliocene and pleistocene these episodes correlate with winnowing events on the blake plateau and are attributed to increased volume transport of the florida current due to closure of the mid america seaway and glacial cycles of the late pliocene and pleistocene epochs

geometry facies and development of middle ordovician carbonate buildups virginia appalachians large carbonate buildups from 1 to 60 km wide and 20 to 250 m thick in the lower part of the middle ordovician foreland basin sequence in virginia include shallow ramp and downslope types the buildups overlie peritidal and lagoonal carbonates shallow ramp buildups are overlain by deep ramp nodular limestone downslope buildups are overlain by slope and basin limestone and or shale lime wackestone and or mudstone commonly with stromatactoid structures occurs in cores of buildups and as abundant small pods enclosed in skeletal sand bindstone is rare but bryozoan bafflestone locally marine cemented is common in downslope cores and pods pelmatozoan ramose bryozoan sands and rudstone locally with abundant mud pods may form sheets beneath flanking and above core facies they are planar bedded or less commonly have large scale foresets black shaly skeletal limestone containing siliceous sponges brachiopods bryozoans and pelmatozoans forms deep flank beds surrounding downslope buildups and grades outward into basinal limestone and or shale the buildups are carbonate banks that developed in a transgressive setting involving sea level rise and subsidence of the foreland basin they formed as a result of high rates of skeletal production by bank biotas and by baffling action of stalked and branching organisms widespread marine cementation converted the loose bank sediments into rigid structures some downslope buildups were initiated on unconformity highs but most buildups overlie thick sequences of shallow water facies some shallow ramp buildups may be localized above a linear high tazewell arch shallow ramp buildups were killed by influxing mud following incipient drowning of the shallow ramp downslope buildups were killed following basin subsidence when they were covered by anoxic basin waters exploration models involving buildups on carbonate ramps should recognize the potential for both shallow ramp and downslope buildup trends such downslope buildups are particularly important because buildup facies are closely associated with potential reservoir rocks of the slope and basin

glacial interglacial differences in circulation and carbon cycling within the upper western north atlantic we investigated glacial interglacial changes in the circulation and carbon cycling in the western north atlantic subtropical gyre using hydrographic data and downcore records of the stable isotopic compositions of individual shells of bahamian benthic foraminifera potential temperature salinity depth relations show that modern thermocline 200 1000 m and deep 1000 2000 m waters in the providence channels bahamas originate in the sargasso sea and are typical of the subtropical gyre gradients in the stable isotopic compositions of late holocene planulina and cibicidoides species from the bank margins 400 to 1500 m depth reflect temperature nutrient and isotopic gradients of modern subtropical gyre waters the difference between the 18o of glacial maximum and late holocene foraminifera is 2 1 for the upper 900 m of the water column and 1 6 for deeper waters indicating that these waters were 4 c and 2 c cooler respectively during glacial time the glacial temperature gradient dt dz was similar to today while the base of the thermocline was 100 m shallower these results differ significantly from our earlier results from multiple shell 18o analyses which implied upper thermocline waters were only 1 c cooler and dt dz was greater during the glacial maximum the difference occurs because bioturbation adversely affects multiple shell analyses of glacial aged samples from shallow water depths at all depths above 1500 m foraminiferal 13c are greater during the glacial maximum than the late holocene by at least 0 1 to 0 2 as much as 0 6 in the lower thermocline indicating that nutrient concentrations throughout the thermocline were reduced and there was no oxygen minimum zone during the glacial maximum this suggests greater more uniform ventilation of the thermocline results of single and multiple shell 13c analyses of glacial age foraminifera compare favorably because samples most affected by mixing correspond to water depths where the glacial interglacial change of 13c was small cooler upper ocean waters during the glacial maximum reflect cooler temperatures at the ocean surface where isopycnal surfaces outcrop including large areas of the subtropical ocean a shallower thermocline base is consistent with southward migration of the northern edge of the subtropical gyre or increased mode water production enhanced thermocline ventilation is consistent with more vigorous winds and all isopycnal surfaces outcropping in the area of ekman downwelling

calibrating mg ca ratios of multiple planktonic foraminiferal species with δ 18 o calcification temperatures paleothermometry for the upper water column in order to consistently approximate the thermal vertical structure of past upper water columns mg ca ratios of eight planktonic foraminiferal species with different preferential calcification depths selected from 76 tropical atlantic and caribbean sediment surface samples were calibrated with 18o derived calcification temperatures with an overall range of 8 28 c extending the broad number of species specific calibrations which agree well especially with our shallow dweller calibrations this study presents new bulk calcite mg ca vs calcification temperature relationships for shallow dwelling globigerinoides ruber pink thermocline dwelling globorotalia menardii and deep dwelling globorotalia truncatulinoides dextral and globorotalia crassaformis not separately calibrated before the species specific temperature sensitivities are relatively similar 7 11 increase in mg ca per 1 c yet y axis intercepts vary from 0 23 0 65 for the shallow and thermocline dwellers to 0 83 1 32 for the deep dwellers based on these differences we established a warm water calibration for temperatures 19 c mg ca 0 29 exp 0 101 t r 0 90 shallow and thermocline dwellers and a cold water calibration for temperatures 15 c mg ca 0 84 exp 0 083 t r 0 85 deep dwellers these calibrations are offset by 8 c this may be significant for paleotemperature reconstructions which are afflicted with the problem that similar mg ca offsets are probably characteristic of extinct species used to calculate past temperatures

a geostrophic transport estimate for the florida current from the oxygen isotope composition of benthic foraminifera we present a new method for the quantitative reconstruction of upper ocean flows for during times in the past for the warm t 5 c surface ocean density can be accurately reconstructed from calcite precipitated in equilibrium with seawater as both of these properties increase with decreasing temperature and increasing salinity vertical density profiles can be reconstructed from the oxygen isotopic composition of benthic foraminifera the net volume transport between two vertical density profiles can be calculated using the geostrophic method using benthic foraminifera from surface sediment samples from either side of the florida straits florida keys and little bahama bank we reconstruct two vertical density profiles and calculate a volume transport of 32 sv using this method this agrees well with estimates from physical oceanographic methods of 30 32 sv for the mean annual volume transport we explore the sensitivity of this technique to various changes in the relationship between temperature and salinity as well as salinity and the oxygen isotopic composition of seawater

isotopic characterization of late neogene travertine deposits at barrancas blancas in the eastern atacama desert chile abstract here we explore the potential of spring related surface and subsurface carbonates as an archive of paleoenvironmental change at barrancas blancas located in the broadest and driest sector of the atacama desert at 24 5 s from these deposits we present a new stable isotopic record of paleoenvironmental conditions over portions of the past 11 5 ma u pb dates from the carbonates both surface and subsurface demonstrate that springs have discharged at this location over much of the last 11 5 ma attesting to the exceptional geomorphic stability of the central atacama many of the sampled vein systems line vertical fissures and formed within the aquifer before groundwater discharged at the surface carbonates in such circumstances should not undergo off gassing and kinetic fractionation prior to formation simplifying the interpretation of their isotopic composition oxygen isotopic compositions of carbonates are generally high 5 vpdb and using paleospring water temperatures of 3 13 c reconstructed from clumped isotopes point to strongly up to 50 evaporated water isotope values like those associated with the hyperarid core of the atacama desert today carbon isotopic compositions are also high 3 pdb reflecting a recharge area essentially devoid of plants and dominated by volcanic co 2 as is the case today our isotopic results are very similar to those from the calama basin to the north suggesting that the western face of the andes between 21 and 25 s has been highly evaporative and nearly plantless when these springs discharged over the last 11 5 ma the spring carbonates at barrancas blancas strongly resemble those found at devils hole and furnace creek in death valley usa and as such warrant further exploration as potential archives of climate change

gulf stream density structure and transport during the past millennium the gulf stream transports approximately 31 sv 1 sv 10 6 m 3 s 1 of water and 1 3 10 15 w of heat into the north atlantic ocean the possibility of abrupt changes in gulf stream heat transport is one of the key uncertainties in predictions of climate change for the coming centuries given the limited length of the instrumental record our knowledge of gulf stream behaviour on long timescales must rely heavily on information from geologic archives here we use foraminifera from a suite of high resolution sediment cores in the florida straits to show that the cross current density gradient and vertical current shear of the gulf stream were systematically lower during the little ice age ad 1200 to 1850 we also estimate that little ice age volume transport was ten per cent weaker than today s the timing of reduced flow is consistent with temperature minima in several palaeoclimate records implying that diminished oceanic heat transport may have contributed to little ice age cooling in the north atlantic the interval of low flow also coincides with anomalously high gulf stream surface salinity suggesting a tight linkage between the atlantic ocean circulation and hydrologic cycle during the past millennium

timing and nature of alluvial fan development along the chajnantor plateau northern chile abstract alluvial systems in the atacama desert provide a unique opportunity to elucidate the sedimentary response to climate variability particularly changes in precipitation in hyperarid environments alluvial fans along the eastern margin of the salar de atacama adjacent to the chajnantor plateau in the atacama desert of northern chile provide an archive of climate modulated sediment transfer and erosion at an extreme of earth s climate three regional alluvial fan surfaces qf1 oldest to qf3 youngest were mapped along the western flank of the chajnantor plateau the alluvial fans were examined with geomorphic and terrestrial cosmogenic 36 cl surface exposure dating methods to define the timing of alluvial fan formation and to determine the role of climatic processes on fan development in a hyperarid environment alluvial fans in the study area are comprised of hyperconcentrated flow and boulder rich debris flow deposits that reflect deposition transitioning between cohesive and noncohesive regimes alluvial fan surfaces yield exposure ages that range from 49 6 4 4 to 194 12 ka while debris flow boulders yield exposure ages ranging from 12 4 2 1 to 229 53 ka cosmogenic 36 cl exposure ages indicate that abandonment of alluvial fan surfaces qf1 qf2 and qf3 date to 175 22 6 ka mis 6 134 5 9 18 ka mis 6 and 20 07 6 26 ka mis 2 respectively a 36 cl concentration depth profile through alluvial fan qf1 suggests a simple depositional history with minimal nuclide inheritance implying relatively rapid aggradation 6 m in ca 25 kyr followed by surface abandonment ca 180 200 ka our data support a strong climatic control on alluvial fan evolution in the region and we propose that the alluvial fans along the margins of the salar de atacama form according to the humid model of fan formation

sensitivity of the atlantic intertropical convergence zone to last glacial maximum boundary conditions 1 recent paleoproxy records suggest that the mean latitude of the atlantic intertropical convergence zone itcz varied synchronously with north atlantic climate over a range of timescales throughout the holocene and last glacial maximum we show that the present day meridional mode of atmosphere ocean variability in the tropical atlantic is a potentially useful model for understanding these paleoclimate changes the tropical atlantic in a coupled atmospheric general circulation and slab ocean model responds to last glacial maximum conditions with a southward displacement of the itcz this response arises primarily through the land ice sheet that forces increased north atlantic trades analogous to the forcing on the present day meridional mode changes to sea ice coverage and to ocean heat transport associated with a weakened atlantic thermohaline circulation also cause a meridional mode response though through different mechanisms our results highlight the potential for tropical atlantic paleoclimate to be driven from the high latitude influences in particular land ice on glacial interglacial timescales

contemporary recent extension and compression in the central andes abstract although extension in the high andes vs compression in the lowlands has already been widely discussed in the literature for the first time we recognized both extensional and contractional structures that developed contemporaneously during late pliocene quaternary times in a wide area of the central andean chain about 90 000 km 2 where crustal earthquake data are missing this area comprises north eastern chile south western bolivia and north western argentina and extends from the puna plateau to the altiplano volcanic belt late pliocene quaternary folds with hinge lines trending nne ssw to n s are mostly located along the westernmost part of the volcanic belt and the eastern part of the western cordillera locally there are coeval reverse faults parallel to the folds which reach up to the surface particularly the miscanti ridge tolocha fault and la casualidad ridge may be the morphostructural expression of tens km long fault propagation folds which locally show topographic scarps hundreds of meters high north and east of the contractional structures we found evidence of late pliocene quaternary normal faults striking n s in the southern part of the study area and nw se in the northern part well developed grabens are present in the higher areas of the volcanic belt and in the transition zone with the puna plateau the surface rupture zones of normal fault swarms range 8 24 km in length with single fault strands up to 18 km long which are typical of tectonic structures the distribution in space and time of the studied contractional and extensional structures indicates that they originated in the same time period we thus address the challenging question regarding the possible origin of the stress sources by analysing possible causes such as volcanotectonics high topography orogeny collapse and gravitational spreading of the orogen in relation also with the role played by inherited structures we finally analyse the relations between the different structures and magma upwelling and the potential for seismic hazard

interacting loop current variability and mississippi river discharge over the past 400 kyr the loop current mediating the oceanic heat and salt flux from the caribbean sea into the atlantic ocean and its interference with the mississippi river discharge are critical for both the regional climate in the gulf of mexico area and the water vapor transport towards high northern latitudes we present a 400 kyr record of sea surface temperature and local surface salinity from the northeastern gulf of mexico images core md02 2575 approximated from combined planktonic foraminiferal 18o and mg ca which reflects the temporal dynamics of the loop current and its relationship to both varying mississippi discharge and evolution of the western hemisphere warm pool the reconstructed sea surface temperature and salinity reveal glacial interglacial amplitudes that are significantly larger than in the western hemisphere warm pool sea surface freshening is observed during the extreme cool periods of marine isotope stages 2 8 and 10 caused by the strengthened mississippi discharge which spread widely across the gulf favored by the less established loop current interglacial and interstadial sea surface conditions instead point to a strengthened northward flowing loop current in line with the northward position of the intertropical convergence zone allowing northeastern gulf of mexico surface hydrographic conditions to approach those of the caribbean at these times the mississippi discharge was low and deflected westward promoted by the extended loop current previously described deglacial megadischarge events further to the west did not affect the northeastern gulf of mexico hydrography implying that meltwater routing from the laurentide ice sheet via the mississippi river is unlikely to have affected atlantic meridional overturning circulation

weaker gulf stream in the florida straits during the last glacial maximum as it passes through the florida straits the gulf stream consists of two main components the western boundary flow of the wind driven subtropical gyre and the northward flowing surface and intermediate waters which are part of the global conveyor belt compensating for the deep water that is exported from the north atlantic ocean1 the mean flow through the straits is largely in geostrophic balance and is thus reflected in the contrast in seawater density across the straits2 here we use oxygen isotope ratios of benthic foraminifera which lived along the ocean margins on the boundaries of the florida current during the last glacial maximum to determine the density structure in the water and thereby reconstruct transport through the straits using the geostrophic method a technique which has been used successfully for estimating present day flow3 our data suggest that during the last glacial maximum the density contrast across the florida straits was reduced with the geostrophic flow referenced to the bottom of the channel at only about two thirds of the modern value if the wind driven western boundary flow was not lower during the last glacial maximum than today these results indicate a significantly weaker conveyor belt component of the gulf stream compared to present day values whereas previous studies based on tracers suggested that deep waters of north atlantic origin were not widespread during glacial times indicating either a relatively weak or a shallow overturning cell our results provide evidence that the overturning cell was indeed weaker during glacial times

relation of subtropical atlantic temperature high latitude ice rafting deep water formation and european climate 130 000 60 000 years ago abstract a new high resolution record of sea surface temperature from the subtropical western north atlantic documents a series of abrupt coolings within marine isotope stage 5 which can be objectively correlated with marine core evidence for increased ice sheet discharge at subpolar latitudes and reduced north atlantic deep water formation these results indicate that ice sheet forcing of deep ocean circulation influenced surface temperatures over much of the north atlantic a proposed correlation to the pollen record of grande pile france indicates that each cold event seen in the pollen sequence has a unique counterpart in the record of subtropical ocean temperature if this correlation is correct it suggests that the warmest part of the european eemian ended suddenly in response to oceanographic changes and that the subsequent post temperate phase of the eemian extended well into the interval of ice sheet growth corresponding to marine isotope substage 5d

coeval compressional deformation and volcanism in the central andes case studies from northern chile 23 s 24 s received 22 may 2009 revised 6 august 2009 accepted 24 august 2009 published 1 december 2009 1 in this contribution we examine the relationship between active compression and construction of pleistocene volcanoes in the present day magmatic arc of the central andes 23s 24s deformation producedseveraln sstriking 40kmlongsubparallel ridges these ridges formed by folding of pliocene ignimbrites and upper pliocene and pleistocene lavas they are asymmetrical in profile and have a gentle back limb and steeper frontal limb andesitic monogenetic volcanoes show a close spatial relationship with the ridges some volcanoes are on the hinge zone whereas others lay on the sides of the ridges we interpret this spatial pattern as a result of magma storage and migration along a system of subhorizontal reservoirs and reverse faults magma reservoirs probably formed along flat portions of reverse faults between ramp structures that serve as episodic magma transport

hydrological variability in florida straits during marine isotope stage 5 cold events modeling and proxy studies indicate that a reduction of atlantic meridional overturning circulation amoc strength profoundly impacts temperatures and salinities in the sub tropical atlantic especially on subsurface levels while previous studies focused on prominent periods of amoc reduction during the last deglaciation we aim to test whether similar reconfigurations of the subtropical hydrography occurred during the moderate climatic alterations punctuating the last interglacial marine isotope stage mis 5 here we present temperature and salinity records from a florida straits core by combining d18o and mg ca analyses on surface globigerinoides ruber white and deep dwelling globorotalia crassaformis foraminifera covering mis 5 in high resolution the data reveal increasing salinities at intermediate depths during interglacial cooling episodes decoupled from relatively stable surface conditions this probably indicates the spatial expansion of saline subtropical gyre waters due to enhanced ekman downwelling and might also point to a changed density structure and altered geostrophic balance in florida straits notably these oceanographic alterations are not consistently occurring during periods of amoc reduction the data suggest that the expansion of gyre waters into florida straits was impeded by the increasing influence of antarctic intermediate water aaiw from mis 5 5 to 107 kyr bp afterward increasingly positive benthic d13c values imply a recession of aaiw allowing the temporary expansion of gyre waters into florida straits we argue that the inferred transient subtropical salt accumulation and warm pool expansion might have played a pivotal role in reinvigorating meridional overturning and dampen the severity of interglacial cold phases

the relationship between shell size and mg ca sr ca δ18o and δ13c of species of planktonic foraminifera the relationship between shell size and mg ca sr ca 18o and 13c of planktonic foraminiferal calcite has been investigated using seventeen species in six different size fractions mg ca increases and sr ca decreases with increasing size except for two globorotaliid species which show the opposite trend the changes in mg ca broadly follow 18o calcification temperatures except that surface and near surface dwelling species show larger changes in mg ca than can be accounted for by differences in calcification temperature derived from 18o the increases in mg ca and decreases in sr ca vary linearly with the well established increase in 13c with size this is consistent with smaller individuals calcifying faster than larger individuals and larger individuals forming calcite that more closely reflects seawater temperature and composition it appears that variations in calcification rate affect mg and sr shell chemistry the observations may account for part of the temporal variability in foraminiferal sr ca within a single size fraction that has been attributed to changes in seawater sr ca