intraseasonal modulation of south american summer precipitation intraseasonal variation of convection over south america is examined using singular spectrum analysis ssa the dipole convection pattern with centers of action over the sacz and the subtropical plains is modulated by modes of different timescales both oscillatory modes with periods of 36 40 days mode 40 and 22 28 days mode 22 influence convection over the sacz with the faster mode mode 22 leading the variability over the subtropical plains mode 40 is related to the madden julian oscillation outgoing longwave radiation anomalies olra propagate eastward from the western pacific to the central pacific with a period of 40 48 days the 200 hpa streamfunction composites show a wavenumber 1 structure in the tropics and a wave train propagating downstream from the convective area in the tropical pacific the development of the dipole pattern is also contributed by mode 22 which features the meridional propagation of olra over south america from midlatitudes to the tropics the streamfunction composites for mode 22 show a wave train extending from the central pacific eastward to about 608s and curving toward the northeast over south america when the sacz is enhanced these two modes become meridionally aligned locally such episodes are characterized by a wave train propagating northeastward from southern south america toward the tropics composites based on the ssa decomposition indicate that the dominant periods of variability 22 and 40 days cancel out over the pacific region and reinforce each other over the sacz for times close to onset of the enhanced sacz episodes

stationary rossby wave propagation in a baroclinic atmosphere observational studies of teleconnections in both soisticial seasons have suggested various patterns of behaviour linked mainly to westerly jets and equatorial westerlies these have been interpreted using barotropic rossby wave theory and simulated using stationary forcing in barotropic models linearized about 300 hpa flows in this paper the relevant propagation behaviour is investigated using a baroclinic model with three dimensional climatological basic states time integrations are performed using localized thermal forcing as a wavemaker the propagation results are qualitatively very similar to those obtained with the barotropic model though there are quantitative differences the westerly jets still act as strong waveguides the shorter wavelengths and smaller wave activity speeds found with the baroclinic model are generally in better agreement with observation propagation into and from the upper tropospheric equatorial westerlies in the east pacific propagation across north america and propagation from europe across the arabian gulf are all found the extent to which upper tropospheric westerlies reach towards the equator influences the propagation into those regions barotropic models can only represent such behaviour if the basic state reflects the near equatorial upper tropospheric zonal wind structure

assessing the reliability of magnesium in foraminiferal calcite as a proxy for water mass temperatures though many studies on the mg contents in the calcitic tests of foraminifers exist the processes controlling its uptake are still a matter of debate laboratory cultures offer an excellent opportunity to reveal these mechanisms the mg concentrations within single chambers of the planktic foraminifer globigerinoides sacculifer brady maintained under controlled laboratory conditions were measured 1 at variable temperatures 19 5 29 5 c and constant salinity and 2 at variable salinity 22 45 and constant temperature the experimental results suggest that under natural conditions temperature is the leading mechanism controlling the mg ca ratio temperature and magnesium are related proportionally a temperature increase of ca 10 c gives rise to an increase of the magnesium concentrations of ca 130 drastic unnatural salinity changes dominate the effects of temperature a 110 change in the mg ca ratio was observed when salinity was elevated or reduced by more than ca 10 specimens which underwent gametogenesis reveal significantly higher mg concentrations than specimens that did not release gametes partition coefficients for mg in foraminiferal calcite are orders of magnitude lower than values from inorganically precipitated calcite when comparing observed mg ca ratios of foraminiferal tests with predicted mg ca ratios calculated according to empirical equations it becomes evident that foraminiferal tests are undersaturated with respect to mg for the water temperature they have experienced apparently foraminifers are capable of controlling their mg concentration the physiological processes presumably responsible for such depressed mg ca ratios appear to be temperature controlled as deduced from the close relationship of the observed mg ca ratios and water temperature this study demonstrates that variations in temperature and salinity are definitely reflected in the mg content of foraminiferal tests magnesium may thus serve as a paleo proxy for past surface water temperatures as long as postdepositional changes and salinity variations are of subordinate importance or can be excluded

active and break phases in the south american monsoon system the south american monsoon system sams refers to the austral summer season features of deep convective activity and large scale circulation this study examines intraseasonal variations in the low level wind circulation in the amazon and their modulating effects on active and break phases in sams daily averages of outgoing longwave radiation olr ncep ncar reanalysis and gridded rainfall station data in brazil are used from 1 november to 28 february 1980 99 the direction of wind anomalies 10 70 days in the rondonia state brazil is used to classify periods of westerly w and easterly e low level wind regimes composites of w regime show low level wind anomalies crossing the equator southward and closing in a cyclonic anomalous circulation off the coast of argentina and uruguay broad areas of enhanced convection and rainfall are observed in central and southeast brazil suppressed convection is observed over the bolivian altiplano and in northern south america in contrast in the e regime opposite patterns are observed in the low level circulation con vection and rainfall anomalies the duration of active w regimes and break e regimes periods are quite similar with median values of 4 and 5 days respectively further investigation showed that the region of convection and rainfall anomalies over venezuela and northwest brazil is observed only in the 10 30 day band comparison of the results shown here with previous studies indicates the importance of intraseasonal variations in the activity of sams

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

oxygen isotopic composition of multiple species of planktonic foraminifera recorders of the modern photic zone temperature gradient abundances of 12 species of planktonic foraminifera collected in two plankton tows from the east tropical atlantic are compared to the chlorophyll content and the temperature of the sea water from which they were collected as expected from previous work in the tropics all dominant tropical species occur in greatest abundance within the photic zone many species occur in greatest abundances in the seasonal thermocline in association with the maximum chlorophyll concentration while a few algal symbiont bearing species occur in greatest abundance in the mixed layer the 18o measurements of planktonic foraminifera shells from core top sediment samples confirm the vertical stratification within the photic zone that is suggested by the relationship between hydrography and abundances found in the plankton tows and found in the statistical study by ravelo et al 1990 comparison between the measured 18o values of planktonic foraminifera with the predicted 18o profiles of the overlying water column at three core locations indicate that species abundances in the sediment record the seasonally integrated conditions of the photic zone and suggests that the abundance of a species in the sediment depends on whether the preferred ecological conditions of that species may be found within the photic zone of the overlying water column sometime during the year species which calcify below the photic zone have only trace relative abundances finally it appears that the total range of 18o values of the dominant species approximates the predicted annual 18o of calcite range in the upper 80 m of the water column

deep pacific caco 3 compensation and glacial interglacial atmospheric co 2 abstract benthic foraminiferal 13c suggests that there was a net shift of isotopically light metabolic co2 from the upper ocean into the deep ocean during the last glacial period according to the caco3 compensation hypothesis this should have caused a transient drop in deep ocean co32 that was eventually reversed by seafloor dissolution of caco3 the resulting increase in whole ocean ph may have had a significant impact on atmospheric co2 compounding any decrease that was due to the initial vertical co2 shift the opposite hypothetically occurred during deglaciation when co2 was returned to the upper ocean and atmosphere and deep ocean co32 temporarily increased followed by excess burial of caco3 and a drop in whole ocean ph the deep sea record of caco3 preservation appears to reflect these processes with the largest excursion during deglaciation as expected but various factors make quantification of deep sea paleo co32 difficult here we reconstruct deep equatorial pacific co32 over the last glacial interglacial cycle using benthic foraminiferal zn ca which is strongly affected by saturation state during calcite precipitation our data are in agreement with the caco3 compensation theory including glacial co32 concentrations similar to or slightly lower than today and a termination i co32 peak of 25 30 mol kg 1 the deglacial co32 rise precedes ice sheet melting consistent with the timing of the atmospheric co2 rise a later portion of the peak could reflect removal of co2 from the atmosphere ocean system due to boreal forest regrowth caco3 compensation alone may explain more than one third of the atmospheric co2 lowering during glacial times

cleaning method impact on the mg ca of three planktonic foraminifer species a downcore study along a depth transect abstract we performed a downcore comparison of mg ca ratios obtained using reductive and non reductive cleaning methods applied to globigerinoides ruber pulleniatina obliquiloculata and globorotalia menardii picked along two nearby sediment cores retrieved at 2100 m and 3875 m in the eastern equatorial indian ocean at the shallower site our results show statistically significant discrepancies in averaged relative mg ca loss induced by the reductive cleaning compared to non reductive cleaning g menardii 8 5 g ruber 6 2 p obliquiloculata 4 4 suggesting that reductive cleaning impact on relative mg ca loss is species specific at the deeper site differences between the relative mg ca losses for the three species are smaller g menardii 3 7 g ruber 4 1 and p obliquiloculata 6 3 suggesting the clear impact of in situ preservation state on the cleaning related mg ca loss the mg ca loss in both relative and absolute mmol mol value of species g ruber and g menardii are significantly smaller at the deeper site than the shallower site implying that these two species which have experienced intense dissolution on the sea floor are less prone to lose further mg during the reductive cleaning p obliquiloculata however show non significant difference in mg ca loss between the two sites indicating that the cleaning related mg ca loss in this species is somewhat insensitive to the preservation state at our two sites our data reveal that mg ca loss results from partial dissolution induced by the reductive step we conclude that the non reductive cleaning approach should be preferred for building inter laboratory homogeneous datasets of mg ca derived temperatures whereas the reductive step should be only included when severe oxide coating is observed

circulation anomalies associated with tropical convection during northern winter abstract lagged cross correlations between outgoing longwave radiation olr and national meteorological center global analyses are utilized to isolate the preferred upper level and surface circulation anomalies associated with tropical convection during northern winter three intraseasonal time scales are studied 30 70 14 30 and 6 14 days in the 30 70 day band the upper level circulation signals are zonally elongated with zonal wavenumbers 0 2 dominant higher frequency signals are dominated by zonal wavenumbers 5 and 6 in the 14 30 day band convection over the eastern hemisphere is associated with upper level anticyclones in the subtropics and appears to be linked in some cases to midlatitude wave trains the strongest signals are for convection over africa australia and the eastern indian ocean only weak signals are seen for convection over indonesia in these regions of upper level easterlies olr anomalies peak prior to the maximum anomalies in wind suggesting forcing of the circulation b

improving temperature estimates derived from mg ca of planktonic foraminifera using x ray computed tomography based dissolution index xdx 1 temperatures derived from mg ca ratios of the calcite tests of planktonic foraminifera are distorted when samples are partially dissolved and methods are required to quantify this source of inaccuracy here we compare a dissolution index xdx based on x ray computed tomography scans to mg ca of four species of foraminifera g ruber white g sacculifer without sac n dutertrei and p obliquiloculata from core top sediments from the tropical pacific atlantic and western indian ocean deepwater calcite saturation values co32 at the sites ranged from 55 to 23 mol kg an estimate of mg ca reduction in mg ca due to dissolution was made for each sample mg ca decreased linearly from deepwater co32 values of between 10 4 and 15 5 mol kg these values are minimum estimates of the threshold below which mg ca is affected by dissolution as they are limited by assumptions made in calculating mg ca sensitivity of mg ca to co32 was greatest for g ruber where mg ca decreased by 0 102 0 036 mmol mol per mol kg sensitivity was similar for g sacculifer 0 047 0 015 mmol mol per mol kg n dutertrei 0 037 0 010 mmol mol per mol kg and p obliquiloculata 0 040 0 008 mmol mol per mol kg sensitivity was similar at all sites for each species excepting an apparently greater response for n dutertrei from the caribbean compared to other sites calibrations between xdx and mg ca provide a means to estimate dissolution bias on mg ca poor correlation between xdx and 18o suggests that for the small sample size typical for analysis variability in initial 18o overwhelms dissolution effects

depth profiles of δ13c in bottom water and core top c wuellerstorfi on the ontong java plateau and emperor seamounts we have measured the carbon isotopic composition of dissolved inorganic carbon in bottom waters of the ontong java plateau western equatorial pacific and on the northern emperor seamounts northwest pacific each of these locations is several hundred miles from the nearest geochemical ocean sections study geosecs stations and the observed 13c values at each site differ substantially from regionally averaged geosecs 13c profiles we discuss the possible causes of these differences including horizontal variability near bottom effects and problems with the pacific geosecs 13c data we also measured the isotopic composition c and o of core top c wuellerstorfi from a depth transect of cores at each location the 18o data are used to verify that our samples are holocene comparison of foraminiferal and bottom water 13c values shows that this species faithfully records bottom water 13c at both sites and demonstrates that there is no depth related artifact in the dissolved inorganic carbon c wuellerstorfi 13c relationship at these sites

carbonate dissolution fluctuations in the western equatorial pacific during the late quaternary planktonic foraminiferal test fragmentation in three cores along a depth transect from the western equatorial pacific erdc 93p 1619 m rc17 177 2600 m v28 238 3120 m thompson 1976 were examined for the last 500 kyr at sample intervals from 2 5 to 5 kyr to study the fluctuations of dissolution in the western equatorial pacific the age models were constructed by correlating the 18o records with the specmap stack imbrie et al 1984 results showed that intermediate and deep waters experienced the same patterns of dissolution through climatic cycles fragmentation varied with a greater amplitude and the carbonate ion concentration changed less in the deep than in the intermediate water dissolution has significant variance distributions and coherencies with 18o over the 100 41 and 23 kyr periods of orbital variations dissolution maxima lag ice volume minima by 6 to 20 kyr the dissolution variability was consistent with recent geochemical models which seek to explain the reduction of atmospheric co2 concentration at the last glacial maximum broecker 1982 boyle 1988

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

long term vegetation climate and ocean dynamics inferred from a 73 500 years old marine sediment core geob2107 3 off southern brazil abstract long term changes in vegetation and climate of southern brazil as well as ocean dynamics of the adjacent south atlantic were studied by analyses of pollen spores and organic walled dinoflagellate cysts dinocysts in marine sediment core geob2107 3 collected offshore southern brazil covering the last 73 5 cal kyr bp the pollen record indicates that grasslands were much more frequent in the landscapes of southern brazil during the last glacial period if compared to the late holocene reflecting relatively colder and or less humid climatic conditions patches of forest occurred in the lowlands and probably also on the exposed continental shelf that was mainly covered by salt marshes interestingly drought susceptible araucaria trees were frequent in the highlands with a similar abundance as during the late holocene until 65 cal kyr bp but were rare during the following glacial period atlantic rainforest was present in the northern lowlands of southern brazil during the recorded last glacial period but was strongly reduced from 38 5 until 13 0 cal kyr bp the reduction was probably controlled by colder and or less humid climatic conditions atlantic rainforest expanded to the south since the lateglacial period while araucaria forests advanced in the highlands only during the late holocene dinocysts data indicate that the brazil current bc with its warm salty and nutrient poor waters influenced the study area throughout the investigated period however variations in the proportion of dinocyst taxa indicating an eutrophic environment reflect the input of nutrients transported mainly by the brazilian coastal current bcc and partly discharged by the rio itajai the major river closest to the core site this was strongly related to changes in sea level a stronger influence of the bcc with nutrient rich waters occurred during marine isotope stage mis 4 and in particular during the late mis 3 and mis 2 under low sea level evidence of nothofagus pollen grains from the southern andes during late mis 3 and mis 2 suggests an efficient transport by the southern westerlies and argentinean rivers then by the malvinas current and finally by the bcc to the study site major changes in the pollen spore and dinocyst assemblages occur with similar pacing indicating strongly interlinked continental and marine environmental changes proxy comparisons suggest that the changes were driven by similar overarching factors of which the most important was orbital obliquity

impact of the madden julian oscillation on the summer west african monsoon in amip simulations at intraseasonal timescales convection over west africa is modulated by the madden julian oscillation mjo in this work we investigate the simulation of such relationship by 11 state of the art atmospheric general circulation models runs with prescribed observed sea surface temperatures in general the atmospheric model intercomparison project simulations show good skill in capturing the main characteristics of the summer mjo as well as its influence on convection and rainfall over west africa most models simulate an eastward spatiotemporal propagation of enhanced and suppressed convection similar to the observed mjo although their signal over west africa is weaker in some models in addition the ensemble average of models composites gives a better performance in reproducing the main features and timing of the mjo and its impact over west africa the influence on rainfall is well captured in both sahel and guinea regions thereby adequately producing the transition between positive and negative rainfall anomalies through the different phases as in the observations furthermore the results show that a strong active convection phase is clearly associated with a stronger african easterly jet aej but the weak convective phase is associated with a much weaker aej our analysis of the equatorial waves suggests that the main impact over west africa is established by the propagation of low frequency waves within the mjo and rossby spectral peaks results from the simulations confirm that it may be possible to predict anomalous convection over west africa with a time lead of 15 20 day

modulation of convection in the southwestern amazon basin by extratropical stationary fronts 1 regimes of lower tropospheric northwesterly wind observed in southwestern amazonia during the tropical rainfall measuring mission large scale biosphere atmosphere trmm lba field campaign were shown to be local manifestations of stationary frontal systems that extended into the deep tropics along the south atlantic convergence zone sacz regime frontal systems were transient and were confined to the subtropics during the interim periods of easterly and weak westerly flow non sacz regime observations from surface based radar in trmm lba suggested that mesoscale convective systems in the sacz regime were significantly larger in areal coverage with weaker rainfall intensity and weaker vertical development of the convective cells the diurnal variation of rain intensity and rain areal coverage generally showed afternoon maxima for both regimes but with important differences suggesting explosive convective cell growth in the non sacz regime and the dominance of nocturnal stratiform rain processes in the sacz regime these results had implications for the parameterization in general circulation models of subgrid scale convective processes in amazonia in terms of the large scale flow and for improving precipitation and latent heating retrieval from spaceborne platforms such as the trmm satellite

pleistocene δ18o records from ontong java plateau effects of winnowing and dissolution abstract sedimentation processes on ontong java plateau in the western equatorial pacific are reflected in oxygen isotope grain size and carbonate records processes recorded are dissolution of carbonate particles winnowing of fines and to some degree the gradient of productivity away from the equator carbonate dissolution begins to affect sediments significantly at about 3 km water depth winnowing is important on the top of the plateau and down the flanks to about 2 5 km water depth winnowing appears to have been greatly intensified during the ice age intervals

late pleistocene evolution of the ocean s carbonate system abstract we demonstrate that the carbonate record from a single site ocean drilling program site 1089 in the deep south atlantic represents a qualitative high resolution record of the temporal evolution of the carbonate saturation state of the deep sea the record is especially notable because it is free from many of the complications that limit other records low sedimentation rates blurring by chemical erosion bioturbation etc the pattern of carbonate variability is characteristic of indo pacific cores with high carbonate glacials and low carbonate interglacials wt carbonate lags changes in benthic 18 o by an average of 7 6 kyr and carbonate variations are in phase with the rate of change first derivative of benthic 18 o intense dissolution occurs at the transition from interglacial to glacial periods and increased preservation occurs during deglaciations these observations represent two fundamentally different responses of the marine carbonate system the lagged response of carbonate to 18 o reflects a steady state mass balance process whereby the lysocline adjusts to maintain alkalinity balance between riverine input and marine burial the site 1089 carbonate signal is remarkably similar to inferred changes in the sr ca of seawater for the past 250 kyr which implies that both carbonate dissolution and seawater sr ca may be controlled by sea level induced changes in the location of carbonate deposition shelf basin fractionation during glacial to interglacial cycles the transient change in preservation during the transitions into and out of glacial stages reflects a response of the carbonate system to a redistribution of alkalinity and dic in the ocean i e carbonate compensation comparison of the site 1089 carbonate and vostok p co 2 records suggests a role of deep sea co 3 2 variations for governing at least some second order features of the atmospheric p co 2 signal in order to quantify this role however measurement of indices of dissolution along a true depth transect will be required to estimate the magnitudes of changes in deep sea co 3 2

distinct responses of planktonic foraminiferal b ca to dissolution on seafloor we have measured b ca in four core top planktonic foraminiferal species globigerinoides ruber white globigerinoides sacculifer without final sac like chamber neogloboquadrina dutertrei and pulleniatina obliquiloculata from three depth transects the caribbean sea the southwestern indian ocean and the ontong java plateau to evaluate the effect of dissolution on planktonic foraminiferal b ca at each transect g ruber w and g sacculifer w o sac show decreasing b ca with increasing water depth this decrease in b ca is accompanied with decreases in shell weights mg ca and bottom water calcite saturation state this indicates a postdepositional dissolution effect on b ca in these two species the strong correlation observed between changes in b ca and bottom water calcite saturation state offers an approach to correcting for the dissolution bias by contrast b ca in n dutertrei and p obliquiloculata remains unchanged along depth transects although shell weights and mg ca display significant declines overall our core top results suggest species specific dissolution effects on b ca in different planktonic foraminiferal species

accurate estimation of sea surface temperatures using dissolution corrected calibrations for mg ca paleothermometry 1 paired 18o and mg ca measurements on the same foraminiferal shells offer the ability to independently estimate sea surface temperature sst changes and assess their temporal relationship to the growth and decay of continental ice sheets the accuracy of this method is confounded however by the absence of a quantitative method to correct mg ca records for alteration by dissolution here we describe dissolution corrected calibrations for mg ca paleothermometry in which the preexponent constant is a function of size normalized shell weight 1 for g ruber 212 300 m mg ca ruber 0 025 wt 0 11 e0 095t and b for g sacculifer 355 425 m mg ca sacc 0 0032 wt 0 181 e0 095t the new calibrations improve the accuracy of sst estimates and are globally applicable with this correction eastern equatorial atlantic sst during the last glacial maximum is estimated to be 2 9 0 4 c colder than today

variability of the south atlantic convergence zone simulated by an atmospheric general circulation model interannual and decadal variability of the south atlantic convergence zone sacz during austral summer season january february march jfm is investigated an attempt is made to separate the forced variability from the internal variability this is accomplished by applying a signal to noise optimization procedure to an ensemble of multidecadal integrations of the latest version of the ncar community climate model ccm3 forced with observed sst the result yields two dominant forced atmospheric responses a local response to atlantic sst anomalies with interannual decadal timescales and a remote response to pacific sst anomalies at interannual timescales the former is localized within the south atlantic ocean with almost no signal over land consisting of a dipolelike structure in precipitation close to the coast of south america accompanied by a clockwise anomalous circulation of surface winds the latter manifests itself mainly in the upper level circulation consisting of a northeastward shift of the sacz with associated rainfall anomalies during warm enso events

environmental controls on mg ca in neogloboquadrina incompta a core top study from the subpolar north atlantic magnesium calcium paleothermometry is an established tool for reconstructing past surface and deep sea temperatures however our understanding of non thermal environmental controls on the uptake of mg into the calcitic lattice of foraminiferal tests remains limited here we present a combined analysis of multiple trace element calcium ratios and stable isotope 18o and 13c geochemistry on the subpolar planktonic foraminifera neogloboquadrina incompta to assess the validity of mg ca as a proxy for surface ocean temperature we identify small size specific offsets in mg ca and 18oc values for n incompta that are consistent with depth habitat migration patterns throughout the life cycle of this species additionally an assessment of non thermal controls on mg ca values reveals that 1 the presence of volcanic ash 2 the addition of high mg abiotic overgrowths and 3 ambient seawater carbonate chemistry can have a significant impact on the mg ca to temperature relationship for carbonate ion concentrations of values 200 mol kg 1 we find that temperature exerts the dominant control on mg ca values while at values 200 mol kg 1 the carbonate ion concentration of seawater increases the uptake of mg thereby resulting in higher than expected mg ca values at low temperatures we propose two independent correction schemes to remove the effects of volcanic ash and carbonate ion concentration on mg ca values in n incompta within the calibration data set applying the corrections improves the fidelity of past ocean temperature reconstructions

seasonal changes in the isotopic composition of planktonic foraminifera collected in panama basin sediment traps abstract isotopic analyses have been made on five species of planktonic foraminifera collected in two deployments of parflux mark ii time series sediment traps in the panama basin the automated sampling system on the traps provided 4 one month samples from 29 july to 16 november 1979 and 6 two month samples from december 1979 to november 1980 the 18o values of globigerinoides ruber and globigerinoides sacculifer in this region are primarily affected by a low salinity surface layer that forms during the early winter these species each show a 1 total range in 18o the 18o values of the colder water species globorotalia menardii neogloboquadrina dutertrei and globorotalia theyeri show smaller seasonal changes in 18o the 13c values of g ruber and g sacculifer exhibit small seasonal changes 0 35 and 0 4 respectively despite large seasonal changes in surface water productivity the colder water species exhibit only slightly larger changes in 13c up to 0 55 throughout the year all colder water species exhibit minimum or near minimum 13c values during february and march which is the period of maximum upwelling and primary productivity seasonal variations in the flux of foraminifera in the water column at this location will have only a small effect on the isotopic composition of the sediment assemblage extreme values of 18o and 13c do not occur during the periods which are associated with the high flux of foraminiferal tests

paleoclimate history of galapagos surface waters over the last 135 000 yr abstract records of planktonic and benthic foraminiferal 18 o and planktonic mg ca from core tr163 22 just northwest of the galapagos islands reveal a detailed 250 450 year resolution climate history of the region over the last 135 thousand years kyr sea surface temperatures ssts reconstructed from g ruber mg ca averaged 24 3 0 4 c during the holocene 22 6 0 6 c during marine isotope stage mis 2 3 and 4 and 26 0 0 9 c during mis 5e changes in sst lead changes in both planktonic and benthic 18 o by an average 3 kyr suggesting that sst changes in this region predated continental ice volume changes changes in sst display clear millennial scale variability especially in marine isotope stage 3 with behavior somewhat similar to antarctic proxy air temperature and south pacific sst records removal of the temperature component from the planktonic 18 o record demonstrates that glacial interglacial 18 o water changes at this site were 1 0 0 2 similar to estimates for mean ocean shifts implying that salinity changes due to regional hydrological variation between the last glacial maximum and holocene in the galapagos region were minimal comparison between the tr163 22 sst record and an sst record from core tr163 19 north of the equatorial front reveals a largely similar broad scale climate history suggesting that changes in the galapagos region were caused by large scale forcing rather than by local or regional dynamical changes changes in atmospheric greenhouse forcing are the most plausible explanation for the observed large scale climate changes in the eastern equatorial pacific

interannual and interdecadal variability of the south atlantic convergence zone interannual variations of the summertime january march atmospheric circulation over subtropical south america are examined during the period 1958 97 using the national centers for environmental prediction national center for atmospheric research reanalysis data it is found from an empirical orthogonal function analysis that an anomalous upper tropospheric large scale stationary eddy in the lee of the andes tends to accompany a dipole in anomalous vertical motion an anomalous cyclonic anticyclonic eddy accompanies an intensified diffuse south atlantic convergence zone sacz with anomalous descent ascent to the southwest the cold core equivalent barotropic vertical structure of the anomalous cyclonic eddy and the 200 hpa vorticity balance are both characteristic of a stationary rossby wave the tendency for the eddy to be advected downstream by the mean westerlies is compensated by meridional advection of planetary vorticity and stretching associated with vertical motion the anomalous cyclonic flow at low levels reinforces the thermally direct circulation associated with the sacz a weak funneling of submonthly rossby wave activity into this descent region is also identified the interannual time series of the eddy is significantly correlated with north south dipolar sea surface temperature sst anomalies over the southwest atlantic one standard deviation 200 hpa wind speed anomalies of up to 5 m s21 are accompanied by sst anomalies of up to 0 38c a near cyclic 15 yr component is identified which the authors corroborate from independent analyses of southwest atlantic ssts and river flows both are

calcite saturation foraminiferal test mass and mg ca based temperatures dissolution corrected using xdx a 150 ka record from the western indian ocean a record of deep sea calcite saturation inline image derived from x ray computed tomography based foraminifer dissolution index xdx was constructed for the past 150 ka for a core from the deep 4157 m tropical western indian ocean g sacculifer and n dutertrei recorded a similar dissolution history consistent with the process of calcite compensation peaks in calcite saturation 15 mol kg higher than the present day value occurred during deglaciations and early in mis 3 dissolution maxima coincided with transitions to colder stages the mass record of g sacculifer better indicated preservation than did that of n dutertrei or g ruber dissolution corrected mg ca derived sst records like other sst records from marginal indian ocean sites showed coolest temperatures of the last 150 ka in early mis 3 when mixed layer temperatures were 4 c lower than present sst temperatures recorded by n dutertrei showed the thermocline to be 4 c colder in mis 3 compared to the holocene 8 ka b p

does a monsoon climate exist over south america the climatology and the basic state of the summertime circulation and rainfall over south america are studied using assimilation products from the data assimilation system of goddard earth observing system 1 geos1 and satellite derived rainfall results indicate the existence of a regional summer monsoon circulation regime induced by strong diabatic heating over the subtropical south american highland centered at the altiplano plateau sensitivity of the results to the assimilation scheme is tested by comparing that with the national centers for environmental prediction ncep reanalysis and with satellite rainfall estimates results show general agreement between the model produced rainfall anomaly and the satellite estimates as well as consistency between the basic circulation features in the geos 1 and the ncep reanalyses a case study of 1989 90 south american summer monsoon sasm reveals the following characteristics 1 in late spring the onset of sasm is signaled by an abrupt merging of the upper tropospheric double westerly jets one in the subtropics and the other in the subpolar region into a single jet in the midlatitudes this is followed by the establishment of a vortex to the southeast of altiplano and occurrence of heavy precipitation over subtropical eastern brazil 2 during the mature phase of sasm the heavy rainfall zone moves over the altiplano plateau and the southernmost brazilian highland the fully established sasm features are the following a an enhancement of equatorial north atlantic trade wind which emanates from the sahara high and crosses the equator over the south american continent b a buildup of strong northwesterlies along the eastern side of the tropical andes and c development of the south atlantic convergence zone in the southernmost position with strong convective activity meanwhile the upper tropospheric return flow emerges from an anticyclone formed over the altiplano plateau crosses the equator and sinks over northwestern africa 3 the withdrawal of sasm in late summer is signaled by the resplitting of the midlatitude westerly jet at the same time the low level northwest monsoon flow diminishes reducing the moisture supply and leading to the termination of heavy precipitation over the subtropical highland results also show that the above mentioned characteristics of sasm are clearly linked to the tropospheric temperature changes over the central south american highland sensible versus latent heating over the highland are bound to play an important role in the evolution of sasm to provide further support of presence of a monsoon climate over south america sasm is compared and contrasted to the classic east asian summer monsoon easm many similar features including evolution characteristics between the two systems have been identified contrasting aspects of the sasm from the easm are also discussed it is pointed out that a number of monsoonal characteristics of the climate of south america such as the seasonal reversal of the low level wind become apparent only when the strong annual mean wind is removed based on the characteristic features and their evolution the authors conclude that a monsoon climate does exist over south america

influence of south america orography on summertime precipitation in southeastern south america impacts of the main south american orographic structures the andes the brazilian plateau and the guiana shield on the regional climate and associated global teleconnection are investigated through numerical experiments in which some of these features are suppressed simulations are performed with a two way nesting system coupling interactively the regional and global versions of the lmdz4 atmospheric general circulation model at regional scale the simulations confirm previous studies showing that both the andes and the brazilian plateau exert a control on the position and strength of the south atlantic convergence zone sacz mainly through their impact on the low level jet and the coastal branch of the subtropical anticyclones the northern topography of south america appears to be crucial to determine the leading mode of rainfall variability in eastern south america which manifests itself as a dipole like pattern between southeastern south america and the sacz region the suppression of south america orography also shows global scale effects corresponding to an adjustment of the global circulation system changes in atmospheric circulation and precipitation are found in remote areas on the globe being the consequences of various teleconnection mechanisms when the brazilian plateau and the andes are suppressed there is a decrease of precipitation in the sacz region associated with a weakening of the large scale ascendance changes are described in terms of anomalies in the walker circulation meridional displacements of the mid latitude jet stream southern annular mode anomalies and modifications of rossby wave train teleconnection processes

incorporation and preservation of mg in globigerinoides sacculifer implications for reconstructing the temperature and 18o 16o of seawater using bathymetric transects of surface sediments underlying similar sea surface temperatures but exposed to increasing dissolution we examined the processes which affect the relationship between foraminiferal mg ca and 18o we found that globigerinoides saccculifer calcifies over a relatively large range of water depth and that this is apparent in their mg content on the seafloor foraminiferal mg ca is substantially altered by dissolution with the degree of alteration increasing with water depth selective dissolution of the chamber calcite formed in surface waters shifts the shell s bulk mg ca and 18o toward the chemistries of the secondary crust acquired in colder thermocline waters the magnitude of this shift depends on both the range of temperatures over which the shell calcified and the degree to which it is subsequently dissolved in spite of this shift the initial relationship between mg ca and 18o determined by their temperature dependence is maintained we conclude that paired measurements of 18o and mg ca can be used for reconstructing 18owater though care must be taken to determine where in the water column the reconstruction applies

exploring the dissolution effect on the intrashell mg ca variability of the planktic foraminifer globigerinoides ruber the mg ca ratio of the planktic foraminifer globigerinoides ruber is widely used for reconstructing past sea surface temperatures the shell mg ca ratio is also lowered by dissolution which results in lower sea surface temperature estimates in partially dissolved shells here we use an electron microprobe image mapping technique to map the intrashell variability of the mg ca ratio in g ruber white sensu stricto shells to explore changes in the intrashell mg ca ratio associated with dissolution we examine shells from shallow and deep cores ceara rise western tropical atlantic from the holocene and last glacial maximum that represent a preservational gradient image map results show that the mg ca ratio is highly variable both within a single shell and among samples obtained from the same sediment interval our results show that intrashell mg ca variability is retained in samples that have undergone dissolution quantitative analysis of the data from mg ca mapping suggests that preferential loss of high mg ca calcite alone cannot account for the difference in intrashell mg ca variability of shells from shallow and deep cores in both time periods rather the data imply that in g ruber analyzed in this study there is a loss of high mg ca ratios accompanied by a more uniform lowering of mg ca over the range of intershell mg ca variability of shells subjected to dissolution at the 1 m resolution of the microprobe analysis in this study

effect of preservation state of planktonic foraminifera tests on the decrease in mg ca due to reductive cleaning and on sample loss during cleaning four species of planktic foraminifera from core tops spanning a depth transect on the ontong java plateau were prepared for mg ca analysis both with cd cleaning and without mg cleaning a reductive cleaning step reductive cleaning caused etching of foraminiferal calcite focused on mg rich inner calcite even on tests which had already been partially dissolved at the seafloor despite corrosion there was no difference in mg ca of pulleniatina obliquiloculata between cleaning methods reductive cleaning decreased mg ca by an average all depths of 4 for globigerinoides ruber white and 10 for neogloboquadrina dutertrei mg ca of globigerinoides sacculifer above the calcite saturation horizon only was 5 lower after reductive cleaning the decrease in mg ca due to reductive cleaning appeared insensitive to preservation state for g ruber n dutertrei and p obliquiloculata mg ca of cd cleaned g sacculifer appeared less sensitive to dissolution than that of mg cleaned mg cleaning is adequate but sem and contaminants al ca fe ca and mn ca show that cd cleaning is more effective for porous species a second aspect of the study addressed sample loss during cleaning lower yield after cd cleaning for g ruber g sacculifer and n dutertrei confirmed this to be the more aggressive method strongest correlations between yield and co32 in core top samples were for cd cleaned g ruber r 0 88 p 0 020 and cd cleaned p obliquiloculata r 0 68 p 0 030 in a down core record wind28k correlation r between yield values 30 and dissolution index xdx was 0 61 p 0 002 where cleaning yield 30 most mg cleaned mg ca values were biased by dissolution

inside story an x ray computed tomography method for assessing dissolution in the tests of planktonic foraminifera x ray computed tomography ct provides an insight into the progression of dissolution in the tests of planktonic foraminifera four species of foraminifera g ruber white g sacculifer n dutertrei and p obliquiloculata from pacific atlantic and indian ocean core top samples were examined by ct and sem inner chamber walls began to dissolve at co32 values of 12 14 mol kg close to the calcite saturation horizon dissolution and precipitation of calcite may occur simultaneously inner calcite of g sacculifer n dutertrei and p obliquiloculata from such sites appeared altered or replaced whereas outer crust calcite was dense with no pores unlike the other species there was no distinction between inner and outer calcite in ct scans of g ruber empty calcite crusts of n dutertrei and p obliquiloculata were most resistant to dissolution and were present in samples where co32 20 mol kg five stages of preservation were identified in ct scans and an empirical dissolution index xdx was established xdx appears to be insensitive to initial test mass mass loss in response to dissolution was similar between species and sites at 0 4 g mol kg we provide calibrations to estimate co32 and initial test mass from xdx

variations in mg ca and sr ca ratios of planktonic foraminifera caused by postdepositional dissolution evidence of shallow mg dependent dissolution a comparative study has been made of two species of planktonic foraminifera g tumida and g sacculifer in a depth transect on the ontong java plateau western equatorial pacific g tumida tests from core top sediments showed decreasing mg ca 2 65 1 25 mmol mol and sr ca 1 50 1 16 mmol mol ratios with increasing water depth 1600 4400 m while no such variation was found in g sacculifer tests in excess of 355 m average mg ca 3 6 mmol mol sr ca 1 4 mmol mol artificial dissolution of g tumida tests led to a decrease in both mg ca and sr ca but in g sacculifer there was no significant change in the ratios analyses by electron microprobe revealed that mg ca of the inner chamber calcite in g tumida tests was much higher than that of the calcite crust keel whereas sr ca was only slightly elevated there were no consistent spatial differences in either mg ca or sr ca for g sacculifer tests dissolution in the oceans gives rise to the removal of the chamber calcite in g tumida about 30 of the total calcite leaving the keel calcite although g tumida is thought of as a dissolution resistant form the majority of mg ca and sr ca depletion and chamber loss occurs above the lysocline it is also possible that much of the mg enriched gametogenic calcite has been lost by dissolution from g sacculifer above 1600 m mg content has a significant effect on the dissolution susceptibility of planktonic foraminifera calculations show that the saturation horizon for mg rich parts of tests may be elevated by several hundred meters compared with normal calcite

preferential dissolution of benthic foraminiferal calcite during laboratory reductive cleaning we have investigated the effect of cleaning procedures on eight element ca ratios in three widely used benthic foraminifera species from core top and down core sediments two cleaning techniques were employed 1 comparison between mg cleaning and cd cleaning methods and 2 comparison between the various constituent reagents li ca b ca and sr ca ratios remained unchanged for samples subjected to different treatments but mg ca mn ca zn ca cd ca and u ca were substantially decreased when foraminifera shells were cleaned with reagents containing citrate in contrast no significant decreases in element ca ratios were observed for samples cleaned in n2h4 without citrate indicating that the role of n2h4 was insignificant during reductive cleaning and that citrate is responsible for decreases of mg ca mn ca zn ca cd ca and u ca decreases in these ratios are most likely due to 1 removal of contaminant particles enriched in mg mn zn cd and u and or 2 preferential leaching of caco3 by the formation of stable metal complexes through chelation between citrate and metals heterogeneously distributed in foraminiferal shells due to the negligible effect of n2h4 and preferential dissolution of caco3 during reductive cleaning it is suggested that the reductive cleaning step should be omitted and the mg cleaning method barker et al 2003 could be employed to clean foraminiferal shells for trace element measurements

core top calibration of mg ca in tropical foraminifera refining paleotemperature estimation 1 optimal use of mg ca as a paleotemperature proxy requires establishing calibrations for different species of foraminifera and quantifying the influence of dissolution to achieve this goal we have measured mg ca and 18o in a series of tropical and subtropical core tops including four depth transects the ceara rise the sierra leone rise and the rio grande plateau in the atlantic and the ontong java plateau in the pacific focusing on spinose mixed layer dwelling species globigerinoides ruber and globigerinoides sacculifer and nonspinose thermocline dwelling neogloboquadrina dutertrei shell mg ca in g sacculifer is 5 15 lower than in g ruber while n dutertrei mg ca is 49 55 lower than in g ruber this statistically significant offset has allowed us to establish different calibrations for each species multilinear regression analysis was used to develop calibration equations that include a correction term for the dissolution effect on mg ca in foraminiferal calcite presented in this paper are two sets of calibrations one set using core depth as a dissolution correction and another using co32 as a dissolution parameter the calibrations suggest that g ruber is the most accurate recorder of surface temperature while g sacculifer records temperatures below the surface at 20 30 m the depth habitat of n dutertrei is more uncertain owing to the wide range in habitat depths depending on hydrographic conditions but on average mg ca and 18o data suggest it is at 50 m of the three species n dutertrei is the most sensitive to dissolution up to 23 decrease in shell mg ca per km while g sacculifer is the most resistant

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

the south atlantic convergence zone intensity form persistence and relationships with intraseasonal to interannual activity and extreme rainfall abstract the characteristics of intensity geographical location and persistence of the south atlantic convergence zone sacz during the austral summer are investigated intensity and spatial features of the sacz are identified by performing a factor analysis of structural properties of outgoing longwave radiation olr data the first two leading factors explain 65 of the total variance of structural properties and characterize the sacz according to intensity and location oceanic versus continental an index is constructed based on the magnitude of the factor scores to identify intense weak and oceanic continental sacz the intense sacz category is associated with negative olr anomalies over a large area of tropical south america extending from the western amazon to the atlantic ocean the weak sacz category is observed with positive olr anomalies over tropical south america and negative olr anomalies over southeastern south america oceanic and continental aspects of the sacz are related to a

origin of convectively coupled kelvin waves over south america convectively coupled kelvin waves over the south american continent are examined through the use of temporal and spatial filtering of reanalysis satellite and gridded rainfall data they are most prominent from november to april the season analyzed herein the following two types of events are isolated those that result from preexisting kelvin waves over the eastern pacific ocean propagating into the continent and those that apparently originate over amazonia forced by disturbances propagating equatorward from central and southern south america the events with precursors in the pacific are mainly upper level disturbances with almost no signal at the surface those events with precursors over south america on the other hand originate as upper level synoptic wave trains that pass over the continent and resemble the cold surges documented by garreaud and wallace as the wave train propagates over the andes it induces a southerly low level wind that advects cold air to the north precipitation associated with a cold front reaches the equator a few days later and subsequently propagates eastward with the characteristics of a kelvin wave the structures of those waves originating over the pacific are quite similar to those originating over south america as they propagate to eastern south america and into the atlantic south america kelvin waves that originate over neither the pacific nor the midlatitudes of south america can also be identified in a composite sense these form over the eastern slope of the andes mountains close to the equator there are also cases of cold surges that reach the equator yet do not form kelvin waves the interannual variability of the pacific originating events is related to sea surface temperatures in the central eastern pacific ocean when equatorial oceanic conditions are warm there tends to be an increase in the number of disturbances that reach south america from the pacific

crystallinity of foraminifera shells a proxy to reconstruct past bottom water co3 changes 1 the reconstruction of past changes in bottom water co3 is central to evaluating competing oceanic scenarios that deal with long term variations in atmospheric pco2 in search of a quantitative bottom water co3 proxy we analyzed the variations of calcite crystallinity of planktonic foraminifera globigerinoides ruber shells picked from core top samples along three depth transects ontong java plateau and the northeast margin of irian jaya in the western equatorial pacific and the sierra leone rise in the eastern tropical atlantic the strong empirical relationship between calcite crystallinity inferred from the full width at half maximum fwhm of calcite 104 x ray diffraction peak and bottom water saturation relative to calcite co3 shows that foraminifera calcite crystallinity could be a promising proxy for the reconstruction of upper pleistocene bottom water carbonate ion concentration

reconstructing the upper water column thermal structure in the atlantic ocean 1 the thermal structure of the upper ocean 0 1000m is set by surface heat fluxes shallow wind driven circulation and the deeper thermohaline circulation its long term variability can be reconstructed using deep dwelling planktonic foraminifera that record subsurface conditions here we used six species neogloboquadrina dutertrei globorotalia tumida globorotalia inflata globorotalia truncatulinoides globorotalia hirsuta and globorotalia crassaformis from 66 core tops along a meridional transect spanning the mid atlantic 42 n to 25 s to develop a method for reconstructing past thermocline conditions we estimated the calcification depths from 18 o measurements and the mg ca temperature relationships for each species this systematic strategy over this large latitudinal section reveals distinct populations with different mg ca temperature relationships for g inflata g truncatulinoides and g hirsuta in different areas the calcification depths do not differ among the different populations except for g hirsuta where the northern population calcifies much shallower than the southern population n dutertrei and g tumida show a remarkably constant calcification depth independent of oceanographic conditions the deepest dweller g crassaformis apparently calcifies in the oxygen depleted zone where it may find refuge from predators and abundant aggregated matter to feed on we found a good match between its calcification depth and the 3 2ml l oxygen level the results of this multispecies multiproxy study can now be applied down core to facilitate the reconstruction of open ocean thermocline changes in the past

subpolar high anomaly preconditioning precipitation over south america abstract the mechanisms associated with the intraseasonal variability of precipitation over south america during the spring season are investigated with emphasis on the influence of a quasi stationary anomalous circulation over the southeastern south pacific ocean sep a spectral analysis performed to the bandpass filtered time series of daily precipitation anomalies for the la plata basin lpb and the south atlantic convergence zone sacz regions revealed several statistically relevant peaks corresponding to periods of roughly 23 days and 14 16 days with the lower higher frequency peaks more prevalent for the sacz lpb the large scale circulation patterns preconditioning precipitation variability over both regions were explored by means of a regression analysis performed on the daily 500 hpa geopotential anomaly field provided by the ncep ncar reanalysis dataset the most prominent feature of the regression fields is the presence of a quasi stationary anomalous anticyclonic cyclonic circulation

a homogeneous stochastic model of the madden julian oscillation abstract this paper presents a new empirical model to simulate the madden julian oscillation mjo which is the most prominent mode of tropical intraseasonal variability zonal wind components at 850 and 200 hpa from reanalysis 1948 2007 and outgoing longwave radiation from satellites 1979 2007 are used to identify mjos and characterize their statistical properties the temporal variability of the mjo is represented with a nine state first order markov chain in which state 0 represents quiescent days and states 1 8 are phases of the mjo when it is active transition probabilities are estimated based on the historical record of mjo events and sensitivity tests were performed to evaluate the best estimates for a homogeneous model once the model simulates time series of phase transitions composites of convective and circulation anomalies determine the spatial structure of the events the amplitudes of the mjos are stochastically generated with an amplitude factor that has a gaussian frequency distrib

large scale circulation patterns and related rainfall in the amazon basin a neuronal networks approach this study describes the main circulation patterns cp in the amazonian basin over the 1975 2002 period and their relationship with rainfall variability cps in the amazonian basin have been computed for each season from the era 40 daily 850 hpa winds using an approach combining artificial neural network self organizing maps and hierarchical ascendant classification a 6 to 8 cluster solutions depending on the season considered is shown to yield an integrated view of the complex regional circulation variability for austral fall winter and spring the temporal evolution between the different cps shows a clear tendency to describe a cycle with southern wind anomalies and their convergence with the trade winds progressing northward from the la plata basin to the amazon basin this sequence is strongly related to eastward moving extra tropical perturbations and their incursion toward low latitude that modulate the geopotential and winds over south america and its adjoining oceans during austral summer cps are less spatially and temporally organized compared to other seasons principally due to weaker extra tropical perturbations and more frequent shallow low situations each of these cps is shown to be associated with coherent northward moving regional rainfall patterns both in in situ data and era 40 reanalysis and convective activity however our results reveals that precipitation variability is better reproduced by era 40 in the southern part of the amazonian basin than in the northern part where rainfall variability is likely to be more constrained by local and subdaily processes e g squall lines that could be misrepresented in the reanalysis dataset this analysis clearly illustrates the existing connections between the southern and northern part of the amazonian basin in terms of regional circulation rainfall patterns the identification of these cps provide useful information to understand local rainfall variability and could hence be used to better understand the influence of these cps on the hydrological variability in the amazonian basin

revisiting diagenesis on the ontong java plateau evidence for authigenic crust precipitation in globorotalia tumida the calcite tests of foraminifera lie in marine sediments for thousands to millions of years before being analysed to generate trace element and isotope palaeoproxy records these sediments constitute a distinct physio chemical environment from the conditions in which the tests formed storage in sediments can modify the trace element and isotopic content of foraminiferal calcite through diagenetic alteration which has the potential to confound their palaeoceanographic interpretation a previous study of g tumida from the ontong java plateau western equatorial pacific found that preferential dissolution of higher mg chamber calcite and the preservation of a low mg crust on the tests significantly reduced whole test mg ca and sr ca brown and elderfield 1996 here we revisit these specimens with a combination of synchrotron x ray computed tomography sxct and electron probe micro analyses epma to re evaluate the nature of their diagenetic alteration the dissolution of higher mg calcite with depth was directly observed in the sxct data confirming the inference of the previous study the sxct data further reveal a thickening of the chemically and structurally distinct calcite crust with depth we propose that these crusts have a diagenetic origin driven by the simultaneous dissolution of high mg chamber calcite and precipitation of low mg crust from the resulting modified pore water solution while the breadth of the study is limited by the nature of the techniques the observation of both dissolution and re precipitation of foraminiferal calcite serves to demonstrate the action of two simultaneous diagenetic alteration processes with significant impacts on the resulting palaeoproxy signals

glacial deep water carbonate chemistry inferred from foraminiferal mg ca a case study from the western tropical atlantic we explore using changes in planktonic foraminiferal mg ca with water depth in a single region to infer relative changes in deep water carbonate chemistry the mg ca ratio in foraminiferal calcite is quantitatively lowered by dissolution we exploit this dissolution effect to generate a profile of carbonate ion concentration co32 for the deep waters of the tropical atlantic during the last glacial maximum we generated mg ca data for three species g ruber g sacculifer and n dutertrei from three cores located along a depth transect 2 8 to 4 0 km on the ceara rise in the western equatorial atlantic we attribute lower mg ca in glacial intervals from the shallow core to changes in sea surface temperature sst the even lower glacial mg ca values in the deeper cores are attributed to dissolution and are used to reconstruct a paleo co32 profile our down core mg ca data for g ruber and g sacculifer confirm that these species are more resistant to mg loss due to dissolution than n dutertrei the greater susceptibility of n dutertrei s mg content to dissolution limits the utility of this species in thermocline temperature reconstructions to cores above the lysocline but significant to this study makes n dutertrei useful in quantifying changes in deep water co32 our paleo co32 reconstruction based on n dutertrei suggests the last glacial maximum co32 gradient in the atlantic was much steeper than today implying that the boundary between deepwater masses in the atlantic was shallower during the last glacial maximum our results suggest comparison of mg ca from multiple cores from one region could similarly provide constraints on changes in carbonate chemistry in other basins and other time periods

a multi proxy evidence for the transition from estuarine mangroves to deltaic freshwater marshes southeastern brazil due to climatic and sea level changes during the late holocene abstract the present study investigates a paleo estuary at the doce river delta southeastern brazil through a multi proxy approach that links palynology diatoms sedimentology and geochemistry analyses i e total c total n 13 c and 15 n these analyses temporally synchronized with five radiocarbon ages revealed environmental changes from marine to continental over the last 7550 years the studied sedimentary succession recorded the upward transition from estuarine channel until 7550 cal yr bp to estuarine central basin 7550 to 5250 cal yr bp deposits the latter containing increased mangrove vegetation marine and marine brackish water diatoms the range of geochemical values 13 c 30 10 15 n 2 8 and c n 4 40 also indicate marine estuarine organic matter and c 3 terrestrial plants to that time interval a following period recorded two phases lake ria 5250 to 400 cal yr bp and fluvial channel 400 cal yr bp until modern age during this stage mangroves were replaced by trees shrubs and herbs grasses due to the disconnection with the marine realm as a result the corresponding sediments contain only organic matter sourced from freshwater and c 3 terrestrial plants 13 c 29 26 15 n 0 8 and c n 10 45 the equilibrium between fluvial sediment supply and relative sea level changes during the holocene controlled the morphologic and vegetation changes in the studied littoral the estuary became established during the early holocene as a resulted of a eustatic sea level rise when the fluvial sediment supply to the coast was relatively lower due to a dry period however during the late holocene the climatic force was more significant to the development of coastal morphology due to a wet period that caused an increase in sandy sediment supply to coastal system then the increase of fluvial discharge associated to a relative sea level fall caused a marine regression and shrinkage of mangroves during the late holocene the evaluation of mangrove dynamics according to climatic and sea level changes mainly during the late holocene is essential for the understanding of their survival ability under future scenarios with a probable accelerated sea level rise and intensification of extreme climatic events in southeastern brazil for the next century

paleolimnological record of the pampean plains argentina as a natural archive of south american hydroclimatic variability since the lgm to the current warm period abstract laguna mar chiquita lmc 30 54 s 62 51 w is a highly variable and shallow saline lake located in the pampean plains of argentina the paleolimnological record of lmc contains information on the environmental variability that occurred in a large area of southern south america since the last glacial maximum lgm until the present as inferred from the diatom assemblages sedimentary features and geochemical proxies prolonged intervals of high and lowstands have caused variations in water salinity trophic state and sedimentary processes this is the first paleolimnological reconstruction covering the hydroclimatic variability that occurred over the last 25 000 cal yr bp in the argentinean pampean region results are in accordance with well known global climatic phases the late pleistocene record is characterized by a scenario dominated by lowstands hypersaline and oligotrophic lake conditions radiocarbon ages 25 000 19 000 cal yr bp indicate that the onset of the record is coeval with the lgm later a progressive lake water level increase was registered at 17 000 cal yr bp which can be assigned to the heinrich stadial 1 a shift toward comparatively drier conditions identified in the record between 14 700 and 13 000 cal yr bp can be chronologically related to the antarctic cold reversal the transition from the late pleistocene to the holocene 13 500 10 500 cal yr bp is recorded by highstand phases while the early holocene record is characterized by high to intermediate water levels the hydrological reconstruction corresponding to the mid holocene is characterized by alternating phases of high lowstands the onset of the late holocene record is marked by the development of dry conditions and thus lowstand phases while around 1300 cal yr bp a distinct water lake level increase is recognized this humid phase ascribed to the medieval climatic anomaly is followed by the record of lowstands between 500 and 1000 cal yr bp being coeval with the little ice age the uppermost part of the record of lmc encompasses the current warm period showing a marked shift towards high lake water level conditions the hydrological variability registered in the paleolimnological record highlights the importance of laguna mar chiquita as an outstanding paleoclimate sensor of hydroclimatic variations for a large area of south eastern south america

planktonic foraminifera differential dissolution and the quaternary stable isotope record in the west equatorial pacific differential dissolution affects the isotopic composition of different species of planktonic foraminifera in different ways in the two species studied here in cores from ontong java plateau the less resistant species globigerinoides sacculifer is more readily affected at a shallower depth than the more resistant species pulleniatina obliquiloculata 2 9 versus 3 4 km but shows a smaller and less predictable response to partial dissolution 0 2 to 0 3 per mil versus 0 6 to 0 7 per mil comparison of isotopic values from the last glacial period with those from the late holocene indicates that the apparent dissolution effect is considerably reduced during the last glacial presumably due to reduced dissolution intensity during glacial time a change in the level of the lysocline of about 400 m is suggested in the published isotope records from pacific cores v28 238 and v28 239 the dissolution generated difference in 18o noted previously by shackleton and opdyke 1976 is seen to describe a mid brunhes dissolution maximum between 300 and 500 thousand years ago this mid brunhes dissolution excursion is well known from the pacific and the indian ocean

global dissolution effects on planktonic foraminiferal mg ca ratios controlled by the calcite saturation state of bottom waters mg ca ratios of planktonic foraminiferal tests are important tools for reconstructing past ocean temperatures at different levels of the upper water column yet numerous studies suggest a significant influence of calcite dissolution on mg ca ratios lowering their initial signal recorded within a planktonic foraminiferal habitat to determine the effect of dissolution this study presents mg ca ratios of eight planktonic foraminiferal species from the south china sea sediment surface continuously decreasing with increasing water depth the mg ca ratios also decrease with calcite saturation states close to and below saturation bottom water delta co32 40 mu mol kg 1 this preservation pattern compares well with examples of mg ca dissolution from the tropical atlantic ocean and is independent of the foraminiferal species merging a global data set by separate normalization of 79 mg ca data sets from the pacific atlantic and indian oceans which removes thermal differences between the ocean regions and foraminiferal species enabled us to quantify a global decrease in planktonic foraminiferal mg ca ratios of 0 054 0 019 mu mol mol 1 per mol kg 1 below a critical threshold for dissolution of 21 3 6 6 mu mol kg 1 the absolute decline in mg ca ratios which is similar for all species affects temperature estimates from sub thermocline species more strongly than those from shallow dwellers the water depth of this critical threshold in the global oceans shoals from 3 5 km in the north atlantic to 0 5 km in the north pacific based on calculations of the global calcite saturation state from 6321 hydrographic stations above this critical threshold mg ca ratios are well preserved and paleotemperature estimates are broadly unaffected by dissolution

horizontal structure and seasonality of large scale circulations associated with submonthly tropical convection the relationship between deep tropical convection and large scale atmospheric circulation in the 6 30 day period range is examined regression relationships between filtered outgoing longwave radiation at various locations in the tropics and 200 and 850 mb circulation are mapped for the standard seasons and the spatial structure and seasonal dependence of the results are interpreted in view of the basic state circulation in regions where the convection is embedded in upper level easterlies anomalous equatorial easterly flow is typically present at 200 mb within and to the west of the convective signal along with patterns of meridional outflow into subtropical anticyclonic perturbations lagged relationships suggest that the convection is forcing the circulation in many of these cases the outflow and subtropical circulations are strongest into the winter hemisphere during the solstitial seasons with more symmetric signals about the equator seen in the equinoctial seasons the longitudinal positioning of the subtropical features with respect to the convection varies but is generally located due poleward or just to the east of the convection there tends to be a first baroclinic mode vertical structure to these circulations such that equatorial westerlies are present at 850 mb within the convection with closed circulations on either side of the equator resembling equatorial rossby modes especially common over the atlantic and pacific sectors as a contrast in regions located within upper level westerlies or along the margin of influence of upper westerly disturbances convection appears to be forced by upper level wave energy propagating into the deep tropics with the heating located in the upward motion region ahead of upper level troughs this occurs over the atlantic and eastern pacific sectors during northern winter and spring and over australia the south pacific and south america during southern summer when upper westerlies are at relatively low latitudes where they can interact with deep tropical convection the results confirm theoretical and modeling ideas that suggest that rossby wave energy is able to propagate into the deep tropics in regions where upper level westerlies exist in the tropics

the el nino impact on the summer monsoon in brazil regional processes versus remote influences the el nino impact on brazil s summer monsoon has not been adequately assessed through seasonal analysis because it shows significant subseasonal variations in this study the el nino influence on the summer monsoon circulation rainfall and temperature is analyzed with monthly resolution using data from a dense network of stations the expected precipitation percentiles during the monsoon season of el nino en events are calculated as well as anomalies of surface temperature and thermodynamic parameters this information is analyzed jointly with anomaly composites of several circulation parameters the analysis shows that some precipitation and circulation anomalies which are consistent and important during part of the season are smoothed out in a seasonal analysis there are abrupt changes of anomalies within the summer monsoon season suggesting the prevalence of regional processes over remote influences during part of the season the probable role of remote influences and regional processes is assessed the anomalous heat sources associated with el nino perturb the walker and hadley circulations over south america and generate rossby wave trains that produce important effects in the subtropics and extratropics in the early summer monsoon season remotely produced atmospheric perturbations prevail over brazil anticyclonic low level anomalies predominate over central east brazil in the tropics and subtropics due to the subsidence over the amazon and to rossby waves in the subtropics easterly moisture inflow from the atlantic is favored but diverted toward northern south america sa and south brazil there are negative precipitation anomalies in north and central east brazil and positive ones in south brazil these precipitation anomalies are favored by the perturbation in the walker and hadley circulation over the east pacific and south america and by a rossby wave train over southern sa that originates in the eastern pacific in january with the enhancement of the continental subtropical heat low by anomalous surface heating during the spring there is anomalous low level convergence and cyclonic circulation over southeast brazil while at the upper levels anomalies of divergence and anticyclonic circulation prevail this anomalous circulation directs moisture flux toward central east brazil causing moisture convergence in this region a favorable thermodynamic structure enhances precipitation over central east brazil the dry anomalies in north brazil are displaced northward and the anomalies in south brazil almost disappear in february after the above normal precipitation of january the surface temperature anomalies turn negative and the precipitation diminishes in central east brazil there are negative rainfall anomalies in north brazil and in the south atlantic convergence zone sacz and positive ones in south brazil influence function analysis shows that while the anomalies of circulation over southeast brazil in the spring of el nino years are mostly due to remote influences from the tropical east pacific those in january are probably due to local influence during this month the monsoonlike circulation is enhanced simultaneous and lagged correlation analysis of sst and rainfall in central east brazil shows that sst anomalies in the atlantic ocean off the southeastern coast of brazil fluctuate on the same timescale as the circulation and precipitation anomalies

rainfall variability and trends of the past six decades 1950 2014 in the subtropical nw argentine andes the eastern flanks of the central andes are characterized by deep convection exposing them to hydrometeorological extreme events often resulting in floods and a variety of mass movements we assessed the spatiotemporal pattern of rainfall trends and the changes in the magnitude and frequency of extreme events 95th percentile along an e w traverse across the southern central andes using rain gauge and high resolution gridded datasets cpc uni and trmm 3b42 v7 we generated different climate indices and made three key observations 1 an increase of the annual rainfall has occurred at the transition between low 3 km areas respond differently to changing climate conditions and the transition zone between low and intermediate elevations is characterized by the most significant changes

alkenone paleothermometry biological lessons from marine sediment records off western south america an empirical global core top calibration that relates the alkenone unsaturation index u k 0 37 to mean annual sst masst is statistically the same as that defined for a subarctic pacific strain of emiliania huxleyi ccmp1742 grown exponentially in batch culture under isothermal conditions although both equations have been applied widely for paleosst reconstruction uncertainty still stems from two key ecological factors variability in the details of biosynthesis among genetically distinct alkenone producing strains and impacts of nonthermal physiological growth factors on u k 0 37 new batch culture experiments with ccmp1742 here reveal that u k 0 37 diverge systematically from the core top calibration in response to nutrient depletion and light deprivation two physiological stresses experienced by phytoplankton populations in the real ocean other aspects of alkenone alkenoate composition also respond to these stresses and may serve as signatures of such effects providing an opportunity to detect understand and potentially correct for such impacts on the geologic record a test case documents that sediments from the southeast pacific display the alkenone alkenoate compositional signature characteristic of cells physiologically stressed by light deprivation such an observation could be explained if marine snow provided a major vector of sedimentation for these biomarkers late pleistocene u k 0 37 records in the southeast pacific yield plausible paleotemperature histories of ice age cooling but ice age alkenone alkenoate signatures fall outside the range of modern calibration samples of similar u k 0 37 they better match core top samples deposited beneath waters characterized by much cooler masst suggesting key features of ice age ecology for alkenone producing haptophytes were different from today and that the u k 0 37 index taken alone may misgauge the total range of ice age cooling at these locations analysis of the full spectrum of alkenone alkenoate compositions preserved in sediments opens up a new opportunity that may improve the accuracy of paleotemperature estimates based on simple u k 0

the 3d microscopic signature of strain within glacial sediments revealed using x ray computed microtomography abstract x ray computed microtomography ct a non destructive analytical technique was used to create volumetric three dimensional 3d models representing the internal composition and structure of undisturbed pro and subglacial soft sediment sample plugs for the purposes of identifying and analysing kinematic indicators the technique is introduced and a methodology is presented addressing specific issues relating to the investigation of unlithified polymineralic sediments six samples were selected based on their proximity to type brittle and ductile deformation structures or because of their perceived suitability for successful application of the technique analysis of a proglacial ideal specimen permitted the 3d geometry of a suite of micro faults and folds to be investigated and the strain history of the sample reconstructed the poor contrast achieved in scanning a diamicton of glaciomarine origin is attributable to overconsolidation under normal loading the sediment demonstrated to have undergone subsequent subglacial deformation another overconsolidated diamicton contains an extensive small scale the subglacial sample evidence indicates that complex polyphase brittle ductile deformation histories are common in such diamictic soft sediments and that the local micro scale environment composition structure shear forces and effective pressure controls rheology the sediment void ratio is a key indicator of strain three of the samples are tentatively placed at different points on the strain cycle for subglacially deforming soft sediment based on their void ratio characteristics and distribution it has been demonstrated that ct offers significant potential for elucidating glacial soft sediment kinematics the ability of the technique to both test a variety of hypotheses pertaining to mechanisms operating within the subglacial environment and evaluate efforts to replicate those processes under controlled laboratory conditions is therefore discussed along with solutions to the problems encountered within this project ct also permits the seamless linking of analytical techniques applied at the hand specimen mm micromorphological m mm scanning electron microscopy and x ray diffraction fluorescence nm m scales and the archiving duplication and dissemination of sample volumetric 3d data

sub sea surface temperatures in the polar north atlantic during the holocene planktic foraminiferal mg ca temperature reconstructions holocene sea surface temperatures in the eastern fram strait are reconstructed based on mg ca ratios measured on the planktic foraminifer neogloboquadrina pachyderma sin the reconstructed sub sea surface temperatures ssstmg ca fluctuate markedly during the earliest holocene at 11 7 and 10 5 kyr bp this is probably in response to the varying presence of sea ice and deglacial meltwater between 10 5 7 9 kyr bp the ssstmg ca values are relatively high 4 c and more stable reflecting high insolation and intensified poleward advection of atlantic water after 7 9 kyr bp the ssstmg ca values decline to an average of 3 c throughout the mid holocene these changes can be attributed to a combined effect of reduced poleward oceanic heat advection and a decline in insolation as well as a gradually increased influence of eastward migrating arctic water the ssstmg ca values increase and vary between 2 1 c and 5 8 c from 2 7 kyr bp to the present this warming is in contrast to declining late holocene in

temperature δ18o relationships of planktonic foraminifera collected from surface waters abstract most of the isotopic paleotemperature equations used for paleoceanographic reconstructions have been derived from culture experiments or inorganic precipitates of calcium carbonate to test these equations in the modern ocean we measured the oxygen isotope composition of planktonic foraminifera globigerinoides ruber globigerinoides sacculifer globigerina bulloides and neogloboquadrina pachyderma collected from atlantic and southern ocean surface waters and added published plankton tow data from the pacific indian and arctic oceans the resulting species specific regression equations of the temperature 18o relationships for g ruber g sacculifer and g bulloides are statistically indistinguishable the equations derived for g sacculifer and g bulloides agree with relationships obtained from laboratory experiments in which these species were cultured at ph values close to modern surface waters the equation derived from n pachyderma has a significantly lower slope and offset than the other three species but produces a regression equation that is nearly identical to the one for the epifaunal benthic foraminifer cibicides sp our work on plankton tow and pumped samples indicates that culture derived equations appear to be more appropriate for predicting the absolute 18o of the species examined compared to equations derived from inorganic precipitates however over the oceanic temperature range the slopes of the equations we derive for living species agree with the slopes obtained from inorganic precipitates

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

frictional moisture convergence in a composite life cycle of the madden julian oscillation abstract a composite life cycle of the madden julian oscillation mjo is constructed using an index based on the first two eofs of the bandpass filtered 20 80 days 850 mb zonal wind averaged from 5 n to 5 s every 2 5 around the equator precipitation 1000 mb convergence 850 mb wind and 200 mb wind are composited for the period 1979 95 water vapor integrated from the surface to 300 mb is composited for the period 1988 92 frictional moisture convergence at the equator is shown to play an important role in the life cycle of the madden julian oscillation mjo regions of boundary layer convergence foster growth of positive water vapor anomalies to the east of convection this convergence coincides with 850 mb easterly wind anomalies as is consistent with kelvin wave dynamics drying of the atmosphere occurs rapidly after the passage of convection with the onset of 850 mb westerly perturbations possible mechanisms for this drying include boundary layer divergence and subsidence or horizontal advect

benthic foraminiferal b ca ratios reflect deep water carbonate saturation state boron calcium ratios were measured in four benthic foraminiferal species three calcitic cibicidoides wuellerstorfi cibicidoides mundulus and uvigerina spp and one aragonitic hoeglundina elegans from 108 core top samples located globally comparison of coexisting species shows b ca of c wuellerstorfi c mundulus h elegans uvigerina spp suggestive of strong vital effects on benthic foraminiferal b ca a dissolution effect on benthic b ca is not observed core top data show large intra species variations 50 130 mol mol in b ca within a single species benthic foraminiferal b ca show a simple linear correlation with deep water co32 providing a proxy for past deep water co32 reconstructions empirical sensitivities of co32 on b ca have been established to be 1 14 0 048 and 0 69 0 072 mol mol per mol kg for c wuellerstorfi and c mundulus respectively the uncertainties associated with reconstructing bottom water co32 using b ca in c wuellerstorfi and c mundulus are about 10 mol kg a preliminary application shows that the last glacial maximum lgm b ca ratios were increased by 12 at 1 2 km and decreased by 12 at 3 5 4 0 km relative to holocene values in the north atlantic ocean this implies that the lgm co32 was higher by not vert similar 25 30 mol kg at intermediate depths and lower by not vert similar 20 mol kg in deeper waters consistent with glacial water mass reorganization in the north atlantic ocean inferred from other paleochemical proxies

summertime precipitation variability over south america role of the large scale circulation abstract the observed large scale circulation mechanisms associated with summertime precipitation variability over south america are investigated particular attention is paid to the altiplano where a close relationship has been observed between rainfall and the position and intensity of the bolivian high empirical orthogonal function eof correlation and composite analyses suggest that on intraseasonal timescales typically 5 20 days rainy periods on the altiplano are associated with at least three types of circulation anomalies involving either extratropical cyclones cold core lows or the westward enhancement of the south atlantic high in each instance the primary support for high rainfall rates is a moist poleward flow at low levels along the eastern flank of the central andes in association with the south atlantic convergence zone sacz the warm low level flow along the sacz also inflates the overlying atmospheric column resulting in an intensification and southward shift of the bolivi

radiocarbon age offsets of foraminifera resulting from differential dissolution and fragmentation within the sedimentary bioturbated zone 1 shells of coexisting species of planktonic foraminifera from the ontong java plateau reveal radiocarbon age offsets of up to 2200 years similar offsets are found between fragments and whole shells of single species steady state modelling of dissolution and bioturbation within the sedimentary mixed layer predicts age differences of up to several kiloyears due to the interplay between differential dissolution and fragmentation of foraminifer shells and bioturbation the observation that fragile foraminiferal shells are systematically older than those of more robust species is more difficult to explain mechanisms of chemical erosion interface dissolution and sediment redistribution are all apparently unable to explain this phenomenon a possible solution is presented in which a particular species may be represented by two distinct classes of shells which are more or less robust in this case differential dissolution and fragmentation causes an increase in the mean age as the fragile class contributes less to the remaining intact shells this study highlights the vulnerability of low sedimentation rate cores to the effects of dissolution and bioturbation

temperature control on the incorporation of magnesium strontium fluorine and cadmium into benthic foraminiferal shells from little bahama bank prospects for thermocline paleoceanography surface sediments from little bahama bank lbb intersecting the subtropical thermocline were used to assess the influence of temperature on the incorporation of mg sr f and cd into shells of benthic foraminifera samples were obtained from twelve cores along the southern slope of lbb covering a temperature range of 18 4 5 c between 301 and 1585 m we studied the composition of ten calcitic and one aragonitic species which are often used in paleochemical reconstructions mg ca ratios decrease with increasing water depth in all benthic species both with calcitic and aragonitic mineralogy showing a strong correlation with water temperature similar decrease is seen in sr ca but with no correlation with temperature none of the benthic species studied here exhibits a depth or temperature related change in f ca similar trends are observed when using an ocean wide dataset which includes shallow and deep core tops 300 5000 m we suggest that temperature is the primary control on the mg content of benthic foraminifera based on inorganic precipitation experiments and thermodynamic considerations presented here a 30 40 decrease in the mg distribution coefficient in calcite may be expected as a result of a temperature change from 25 c to 5 c which is about half the observed change in lbb a calibration curve applied to c pachyderma data from core tops along the slope of little bahama bank suggests that water temperature may be inferred from mg ca ratios with an uncertainty of about 0 8 c therefore the mg content of benthic foraminifera may provide a new independent temperature proxy for studying shallow waters paleoceanography the linear decrease in sr ca with increasing depth is not correlated with temperature the trend is constant from the ocean surface down to 5 km suggesting that pressure related effects on the calcification process are a more likely explanation than post depositional dissolution mg ca ratios in aragonitic shells of h elegans covary with temperature in accord with recent observations from corals in contrast the sr and f chemistry of h elegans is very different than that of corals and inorganically precipitated aragonites the disparities between the elemental composition of biogenic and inorganic phases and the large intergeneric and interspecific differences observed both in planktonic and benthic foraminifera implicate temperature related physiological processes in regulating the coprecipitation of elements in foraminiferal shells our work demonstrates that cd ca ratios of shallow calcitic species reflect the vertical distribution of nutrients no significant influence of temperature on the partitioning of cd into the shells was found our data extend the previous deep water calibration boyle 1992 thereby allowing for the reconstruction of the nutrient chemistry of shallow thermocline waters

glacial interglacial changes in subantarctic sea surface temperature and δ18o water using foraminiferal mg laboratory culturing experiments with living globigerina bulloides indicate that mg ca is primarily a function of seawater temperature and suggest that mg ca of fossil specimens is an effective paleotemperature proxy using culturing results and a core top neogloboquadrina pachyderma calibration we have estimated glacial interglacial changes in sea surface temperature sst using planktonic mg ca records from core rc11 120 in the subantarctic indian ocean 43 s 80 e and core e11 2 in the subantarctic pacific ocean 56 s 115 w our results suggest that glacial sst was about 4 c cooler in the subantarctic indian ocean and 2 5 c cooler in the subantarctic pacific comparison of sst and planktonic 18o records indicates that changes in sst lead changes in 18o by on average 1 3 kyr the glacial interglacial temperature change indicated by the subantarctic mg ca records suggests that temperature accounts for 40 60 of the foraminiferal 18o change we have used the mg ca based sst estimates and 18o determinations to generate site specific seawater 18o records which suggest that seawater 18o was on average 1 more positive during glacial episodes compared with interglacial episodes

analysis of tropical extratropical interactions with influence functions of a barotropic model abstract influence functions ifs of a linear barotropic vorticity equation model are computed in order to determine the regions in which anomalous divergence at upper levels related to tropical heating anomalies has the largest impact on certain prominent low frequency anomalies the present computation differs from that of branstator in two aspects a the model includes the effects of the basic flow divergence and the advection by anomalous divergent wind and b the influence functions directly assess the influence of upper level divergence anomalies rather than sources of vorticity the ifs are applied to the study of low frequency tropical extratropical interactions at the interannual enso and intraseasonal 30 60 day oscillation timescales the origin of well known teleconnection patterns is explored through the identification of comma influence regions in the tropics and subtropics for their main action centers the subtropical west and central east pacific north of the equator is an impo

planktic foraminiferal dissolution in the twilight zone abstract calcite dissolution of planktic foraminifers that settle from the surface ocean to depths has been assessed using the weight size relationship of tests and correlated to carbonate ion concentration co 3 2 of ambient sea water globigerina bulloides and globigerinita glutinata were sampled from the north atlantic and the arabian sea during different seasons spring and fall and the monsoons respectively test weight has been determined for single tests from narrow size classes 250 8 m and 300 7 m minimum test diameter initial test weight of both species in surface waters differs between regions and seasons weight loss of settling tests in the twilight zone between 100 and 1000 m water depths averaged 19 below the twilight zone 1000 2500 m no weight loss occurs on average and tests may even gain weight remineralization of settling planktic foraminiferal tests is most pronounced at maximum co 3 2 accordingly strong dissolution occurs in the twilight zone at the depth of maximum decrease in co 3 2 it is assumed that dissolution of planktic foraminiferal calcite is caused by co 3 2 under saturation inside the test buffered by diffusive exchange of co 3 2 ions with the ambient sea water through the pores and aperture consequently reconstruction of small scale differences in seawater co 3 2 from test weight alone is not feasible and systematic correlation between test weight and co 3 2 of the ambient sea water is statistically not significant at constant co 3 2 remineralization cannot be deduced from test weight neither at high nor low co 3 2 saturation in total our data suggest that the global vertical planktic foraminiferal caco 3 flux is about 19 lower than calculated by schiebel 2002 planktic foraminiferal sedimentation and the marine calcite budget global biogeochemical cycles 16 4 1065 doi 10 1029 2001gb001459

global climatologies of fronts airmass boundaries and airstream boundaries why the definition of front matters abstractclimatologies of fronts airmass boundaries and airstream boundaries can be calculated using automated approaches on gridded data such approaches may require choices to define a front in

dissolution effects on the crystallography and mg ca content of planktonic foraminifera globorotalia tumida rotaliina revealed by x ray diffractometry several authors suggested that the thinning with increasing depth of deposition of calcite x ray diffractometry xrd peaks obtained on planktonic foraminifera tests resulted from the preferential removal of their poorly crystallized parts as dissolution increases by deconvolving xrd peak 104 from globorotalia tumida surface sediments sierra leone rise depth transect we show that the full width at midheight does not depend only upon crystallinity but reflects also the chemical and structural heterogeneity of foraminifera tests which results in closely spaced individual 104 diffraction peaks corresponding to phases with slightly different mg contents g tumida contains two calcite phases a well crystallized mg poor calcite and a poorly crystallized mg richer calcite increasing dissolution results in the preferential removal of the mg richer calcite and the improvement of its crystallinity whereas the mg poor calcite does not seem to be affected by dissolution between 2750 m and 4950 m of water depth on sierra leone rise

foraminiferal magnesium in globeriginoides sacculifer as a paleotemperature proxy foraminiferal magnesium shows increasing promise as a paleothermometer but the accuracy and precision are limited by biases introduced by partial dissolution salinity variations mg rich gametogenic calcite and contaminant phases we improved cleaning methods and reduced errors introduced by partial dissolution by sampling from well preserved cores in the equatorial atlantic and the caribbean sea with different dissolution histories all cores reveal a synchronous 25 increase in mg ca from the stage 2 3 boundary to the holocene core top indicating that dissolution is not a controlling factor modern temperatures estimated from core top mg ca are 24 5 25 0 c equal to mean annual water temperatures at 50 100 m we estimate that sea surface temperature increased by 2 6 c 1 3 from the last glacial maximum to the holocene holocene values were comparable to those during isotope stage 5e our data indicate that biases from contaminant phases and partial dissolution can be reduced this paleothermometer holds promise if uncertainties introduced by salinity variations and gametogenic calcite can be constrained

impact of mjo on the intraseasonal variation of summer monsoon rainfall over india the summer monsoon rainfall over india exhibits strong intraseasonal variability earlier studies have identified madden julian oscillation mjo as one of the most influencing factors of the intraseasonal variability of the monsoon rainfall in this study using india meteorological department imd high resolution daily gridded rainfall data and wheeler hendon mjo indices the intra seasonal variation of daily rainfall distribution over india associated with various phases of eastward propagating mjo life cycle was examined to understand the mechanism linking the mjo to the intraseasonal variability during mjo phases of 1 and 2 formation of mjo associated positive convective anomaly over the equatorial indian ocean activated the oceanic tropical convergence zone otcz and the resultant changes in the monsoon circulation caused break monsoon type rainfall distribution associated with this negative convective anomalies over monsoon trough zone region extended eastwards to date line indicating weaker than normal northern hemisphere inter tropical convergence zone itcz the positive convective anomalies over otcz and negative convective anomalies over itcz formed a dipole like pattern subsequently as the mjo propagated eastwards to west equatorial pacific through the maritime continent a gradual northward shift of the otcz was observed and negative convective anomalies started appearing over equatorial indian ocean during phase 4 while the eastwards propagating mjo linked positive convective anomalies activated the eastern part of the itcz the northward propagating otcz merged with monsoon trough western part of the itcz and induced positive convective anomalies over the region during phases 5 and 6 the dipole pattern in convective anomalies was reversed compared to that during phases 1 and 2 this resulted active monsoon type rainfall distribution over india during the subsequent phases 7 and 8 the convective and lower tropospheric anomaly patterns were very similar to that during phase 1 and 2 except for above normal convective anomalies over equatorial indian ocean a general decrease in the rainfall was also observed over most parts of the country the associated dry conditions extended up to northwest pacific thus the impact of the mjo on the monsoon was not limited to the indian region the impact was rather felt over larger spatial scale extending up to pacific this study also revealed that the onset of break and active events over india and the duration of these events are strongly related to the phase and strength of the mjo the break events were relatively better associated with the strong mjo phases than the active events about 83 of the break events were found to be set in during the phases 7 8 1 and 2 of mjo with maximum during phase 1 40 on the other hand about 70 of the active events were set in during the mjo phases of 3 to 6 with maximum during phase 4 21 the results of this study indicate an opportunity for using the real time information and skillful prediction of mjo phases for the prediction of break and active conditions which are very crucial for agriculture decisions

interactions between synoptic intraseasonal and interannual convective variability over southern africa after removing the annual cycle a principal component analysis is applied to the daily outgoing longwave radiation anomaly field used here as a proxy for atmospheric convection the analysis is carried out over the southern african region 7 5 e 70 e 10 s 40 s for austral summer november through february for the period 1979 1980 to 2006 2007 the first five principal components pc are retained the first two pcs describe spatial patterns oriented north west to south east from tropical southern africa sa to the mid latitudes they are interpreted to be different possible locations for synoptic scale tropical temperate troughs ttt one dominant rainfall producing synoptic system in the region the phase relationship between these two pcs describes a tendency for these ttt to propagate eastwards from sa to the mozambique channel and southern madagascar the next three pcs describe convective fluctuations respectively located over the north west the south and the centre of sa their time series are significantly associated with madden julian oscillation mjo activity in the tropics however we find that ttt systems are statistically independent of the mjo i e they are equally liable to occur during any phase of the mjo three pcs out of five also show a significant association with el nino southern oscillation confirming that el nino years mostly coincide with suppressed convection at the intraseasonal time scales a result consistent with its impact on seasonal averages diagnosed in previous studies

tracing deep sea calcite dissolution agreement between the globorotalia menardii fragmentation index and elemental ratios mg ca and mg sr in planktonic foraminifers 1 accurately quantifying deep sea calcite dissolution is crucial for understanding the role of the marine carbonate system in regulating atmospheric pco2 over millennia we compare a foraminifer fragmentation based calcite dissolution proxy globorotalia menardii fragmentation index mfi to mg ca sr ca and mg sr in several species of deep dwelling planktonic foraminifers we conducted microfossil and geochemical analyses on the same core top samples taken at different depths on the ontong java plateau to maximize the dissolution signal and minimize the temperature overprint on our data we also compare elemental ratios from planktonic foraminifer tests to modern bottom water co3 undersaturation and model derived estimates of percent calcite dissolved in deep sea sediments we find clear linear decreases in mg ca or mg sr in g menardii and pulleniatina obliquiloculata with increasing 1 bottom water co3 undersaturation 2 percent calcite dissolved in sediments calculated with biogeochemical modeling 3 mfi and 4 percent calcite dissolved derived from mfi these findings lend further support to mfi as a calcite dissolution proxy for deep sea sediments in contrast we find no significant correlation between sr ca and independent dissolution indicators our results suggest that mg ca and mg sr from deep dwelling foraminifers could potentially be used as calcite dissolution proxies in combination with independent water temperature estimates likewise establishing the relationship between mfi and dissolution induced changes in the mg ca of surface dwelling foraminifers could provide a tool to correct mg ca derived sea surface temperature reconstructions for calcite dissolution

determination of multiple element calcium ratios in foraminiferal calcite by quadrupole icp ms a method has been developed for rapid and precise simultaneous determination of nine element ca ratios in foraminiferal tests directly from intensity ratios using external matrix matched standards on a quadrupole inductively coupled plasma mass spectrometer icp ms all quantification isotopes are determined in pulse mode to avoid cross calibration small argide 40ar26mg interferences on 66zn are corrected by using two additional mg and zn standards a stable signal conducive for high precision measurements is obtained by cone conditioning variable calcium concentration has negligible effect on li al mn and sr but ca concentrations for standards and samples need to be constrained at a similar level for precise measurements of zn cd and u aliquots of samples are first analyzed for ca concentrations on an inductively coupled plasma atomic emission spectrometer icp aes and the remaining solutions are diluted to ca concentration of 100 ppm for ratio measurements to assure data quality the long term reproducibility of the method yielded precisions of li ca 2 4 b ca 4 2 mg ca 1 4 al ca 14 mn ca 0 9 zn ca 2 8 1 2 7 8 mol mol and 5 1 0 5 1 2 mol mol sr ca 0 9 cd ca 2 4 0 07 0 24 mol mol and 4 8 0 01 0 07 mol mol and u ca 2 5 for foraminiferal samples as small as 60 g

characterization of mg ca distributions in planktonic foraminifera species by electron microprobe mapping 1 the distribution of mg ca within the tests of eight modern planktonic foraminifer species has been characterized using electron microprobe mapping species include several that are commonly used for estimation of past seawater temperatures globigerinoides ruber g sacculifer neogloboquadrina incompta synonym of n pachyderma dex n dutertrei and g truncatulinoides each of the investigated species displays large variations in mg ca composition within individual tests however the pattern of mg ca variation is notably different between symbiont bearing and symbiont free species in symbiotic species cyclic mg ca compositional banding occurs that is characterized by narrow 1 3 m high mg ca typically 8 11 mmol mol bands intercalated between broader low mg ca typically 1 5 mmol mol bands this factor of 2 3 difference equates to an apparent calcification temperature change of 10 c or more such temperature changes are considered highly improbable and suggest vital effects significantly modify the incorporation of mg ca into the tests of symbiont bearing species these vital effects remain poorly understood and demand further careful evaluation as they may need to be accounted for when making reliable reconstructions of past oceanic temperatures symbiont free species typically have fewer and broader compositional bands that may reflect more closely changes in calcification temperature as these species migrate within a water column