seasonal variation in the flux of planktonic foraminifera time series sediment trap results from the panama basin abstract a mooring array with three automated sediment traps capable of collecting time series samples was deployed in the panama basin for one year beginning in december 1979 a series of six consecutive two month long samples was collected at each of three depths 890 2590 and 3560 m in order to examine seasonal variation in the flux of planktonic foraminifera and evaluate the contribution of foraminifera to the total carbonate flux the flux of the larger planktonic foraminifera 250 500 m and 500 1000 m is greatest during february march when upwelling is most intense in the panama basin in contrast the maximum flux of the smaller foraminifera 125 250 m is associated with a phytoplankton bloom during the summer months june through september this size dependent flux pattern appears to be a species specific effect the flux of the larger foraminifera is dominated by non spinose forms i e neogloboquadrina dutertrei and globorotalia theyeri while the flux of the smaller foraminifera consists predominantly of spinose species i e globigerinoides ruber g sacculifer and g conglobatus although the magnitude of the flux varied throughout the year the average weight of individual foraminiferal tests in different size fractions showed no seasonal variability with the exception of the june july period when there was a major coccolith bloom planktonic foraminifera greater than 125 m account for between 28 and 34 of the total carbonate flux at this location during the coccolith bloom planktonic foraminifera accounted for less than 2 of the total carbonate flux planktonic foraminifera in the 250 500 m size range are the most significant contributors to the overall particulate flux accounting for roughly 70 80 of the total foraminiferal fluxes measured at the three trap depths

magnetic susceptibility as carrier of a climatic signal in chalk abstract the composition and the magnetic properties of the insoluble residue of maastrichtian chalk from the north sea have been investigated in order to get a better understanding of the cyclic signals in chalk carbonates and the depositional processes that have contributed to the pattern the insoluble residue of the maastrichtian north sea chalk contains quartz dolomite pyrite organic material ferrimagnetic minerals and clay minerals smectite illites the concentration and in particular the type of clay minerals determine the variations in the magnetic properties of the insoluble residue and the bulk magnetic susceptibility of the chalk the existence of a detrital component in the insoluble residue suggests that the cyclic variations in the bulk magnetic susceptibility and consequently in the composition of the chalk are controlled by changes in the runoff from land into the basin

high resolution rock magnetic variability in shallow marine sediment a sensitive paleoclimatic metronome abstract an outer shelf deposit in central japan centered on the olduvai normal polarity event in the reversed matuyama chron reveals a close correlation of both the magnetic susceptibility and remanent intensity with the sedimentary cyclicities apparent in lithologies and molluscan assemblages two sedimentary cycles are characterized by distinctly similar but double peaked magnetic cyclicities the rock magnetic variability is primarily attributed to the relative abundance of terrigenous magnetic minerals and the double peak of the variability is characterized by the concentration of finer grained magnetic minerals the concentration is suspected to be controlled by both climatic change and shifting proximity of the shoreline as a function of rise and fall of the sea level due to glacio eustasy rock magnetic study reveals the record of a 21 ka period of orbital precession cycles within the sedimentary cyclicity attributable to a 41 ka period of orbital obliquity forcing

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

mid holocene el nino southern oscillation enso attenuation revealed by individual foraminifera in eastern tropical pacific sediments holocene reconstructions of the el nino southern oscillation enso provide valuable perspective on its recent evolution and can be important for assessing its future optimal assessment of past enso variability requires observations from its center of action in the eastern equatorial pacific but these are limited due to paucity of high resolution paleoceanographic archives e g corals here we use a new approach to quantify past enso variance based on the oxygen isotopic composition 18 o of individual foraminifera globigerinoides ruber from deep sea sediments in the enso source region individual g ruber foraminifera behave as monthly recorders of sea surface conditions including enso extremes circumventing the lack of annual resolution in the sediments intrapopulation 18 o distributions derived with this method from a core near the galapagos islands reveal mid holocene reductions in variance of 50 requiring drastic attenuation of the enso amplitude furthermore mg ca thermometry indicates that mid holocene background conditions were accompanied by a stronger zonal temperature gradient that coincided with a northward displaced intertropical convergence zone itcz the results suggest that the position of the itcz is an important factor in the low frequency modulation of enso and could influence its future evolution

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

apparent correlation of palaeomagnetic intensity and climatic records in deep sea sediments most reports of a correlation between pleistocene climate and geomagnetic field intensity rely strongly on the assumption that sediment natural remanent magnetic nrm intensity provides a record of geomagnetic field strength and is not sensitive to local changes in properties of the sediment critical assessment of relevant data presented here and elsewhere1 2 from deep sea sediment cores shows that a pronounced dependence of nrm intensity on sediment composition can occur which implies that this assumption is unlikely to be generally valid as sediment composition often reflects varying depositional conditions induced by climatic change the significance of correlations proposed between pleistocene palaeomagnetism and climatic indicators in deep sea sediments may be less dramatic than sometimes supposed

robust multi proxy data integration using late cretaceous paleotemperature records as a case study abstract in paleoclimate studies multiple temperature records are often compared and combined to evaluate temperature trends yet no standardized approach for integrating proxy derived paleotemperature records exists in addition paleotemperature data are often reported without uncertainty estimates prediction errors and raw data are not always available this complicates the quantification of for example temperature trends and the magnitude of warming events here we propose a robust quantitative approach for multi proxy analysis in paleoclimate studies to demonstrate this we study the latest maastrichtian warming event lmwe in the odp 174ax bass river core new jersey and integrate five independent paleotemperature proxies covering the last million years of the cretaceous our integrated temperature reconstruction suggests that after a climatically stable period a latest cretaceous warming of 3 9 1 1 c occurred between 450 and 100 kyr before the k pg boundary the error on this reconstructed temperature should be considered the absolute minimum error as poorly constrained or unknown uncertainties cannot be fully propagated the warming event was followed by a gradual cooling to pre warming conditions towards the end of the cretaceous furthermore the record suggests multiple warming pulses during the lmwe the results of this integrated approach are consistent with other latest cretaceous temperature records suggesting that the trend described here represents a global signal

intratest oxygen isotope variability in the planktonic foraminifer n pachyderma real vs apparent vital effects by ion microprobe abstract intratest oxygen isotope variations in the planktonic foraminifer neogloboquadrina pachyderma sinistral left coiling from north atlantic core top and multi net samples were assessed by ion microprobe analysis from 2 to 6 m spots with precision and accuracy better than 0 7 in 18 o 2 sd within a single foraminiferal test from a core top sample comprising both ontogenetic calcite and outer crust 18 o values vary from 0 5 to 3 7 pdb exceeding the range of equilibrium 18 o in the specimens habitat by a factor of three the isotopic difference between the ontogenetic calcite and the crust averages 1 8 neither of the two types of foraminiferal calcite precipitates in equilibrium with ambient seawater the ontogenetic calcite exhibits a negative vital effect 18 o m e 18 o measured 18 o equilibrium ranging from 0 5 to 1 the largest negative fractionation is associated to the inner walls of juvenile chambers in contrast a positive vital effect of about 0 8 was observed in the crust with respect to the highest equilibrium 18 o values at water depths below 200 m hence two vital effects that are opposite in sign are effective within a single foraminiferal test indicating that whole test values of this species are highly sensitive to the degree of encrustation and amplify or attenuate environmental signals the negative vital effect of the ontogenetic calcite was verified by ion microprobe analysis of four nonencrusted net sampled specimens reflecting three different depth intervals intra ontogenetic oxygen isotope ratios in these juvenile tests range from 0 6 to 3 0 and exhibit a negative vital effect even larger than that observed in core top samples based on these data the large range of apparent vital effects reported for this foraminiferal species can be assessed by a mass balance calculation assuming that the degree of encrustation is variable

observations at terrestrial impact structures their utility in constraining crater formation hypervelocity impact involves the near instantaneous transfer of considerable energy from the impactor to a spatially limited near surface volume of the target body local geology of the target area tends to be of secondary importance and the net result is that impacts of similar size on a given planetary body produce similar results this is the essence of the utility of observations at impact craters particularly terrestrial craters in constraining impact processes unfortunately there are few well documented results from systematic contemporaneous campaigns to characterize specific terrestrial impact structures with the full spectrum of geoscientific tools available at the time nevertheless observations of the terrestrial impact record have contributed substantially to fundamental properties of impact there is a beginning of convergence and mutual testing of observations at terrestrial impact structures and the results of modeling in particular from recent hydrocode models the terrestrial impact record provides few constraints on models of ejecta processes beyond a confirmation of the involvement of the local substrate in ejecta lithologies and shows that z models are at best first order approximations observational evidence to date suggests that the formation of interior rings is an extension of the structural uplift process that occurs at smaller complex impact structures there are however major observational gaps and cases e g vredefort where current observations and hydrocode models are apparently inconsistent it is perhaps time that the impact community as a whole considers documenting the existing observational and modeling knowledge gaps that are required to be filled to make the intellectual breakthroughs equivalent to those of the 1970s and 1980s which were fueled by observations at terrestrial impact structures filling these knowledge gaps would likely be centered on the later stages of formation of complex and ring structures and on ejecta

assessing the impact of diagenesis on δ11b δ13c δ18o sr ca and b ca values in fossil planktic foraminiferal calcite the geochemical composition of foraminiferal tests is a valuable archive for the reconstruction of paleo climatic oceanographic and ecological changes however dissolution of biogenic calcite and precipitation of inorganic calcite overgrowth and recrystallization at the seafloor and in the sediment column can potentially alter the original geochemical composition of the foraminiferal test biasing any resulting paleoenvironmental reconstruction the 11b of planktic foraminiferal calcite is a promising ocean ph proxy but the effect of diagenesis is still poorly known here we present new 11b 13c 18o sr ca and b ca data from multiple species of planktic foraminifera from time equivalent samples for two low latitude sites clay rich tanzanian drilling project tdp site 18 from the indian ocean containing well preserved glassy foraminifera and carbonate rich ocean drilling program odp site 865 from the central pacific ocean hosting recrystallized frosty foraminifera our approach makes the assumption that environmental conditions were initially similar at both sites so most chemical differences are attributable to diagenesis planktic foraminiferal 18o and 13c records show offsets in both relative and absolute values between the two sites consistent with earlier findings that these isotopic ratios are strongly influenced by diagenetic alteration sr ca and b ca ratios in planktic foraminiferal calcite are also offset between the two sites but there is little change in the relative difference between surface and deep dwelling taxa in contrast 11b values indicate no large differences between well preserved and recrystallized foraminifera suggesting that despite extensive diagenetic alteration the 11b of biogenic calcite appears robust potentially indicative of a lack of free exchange of boron between pore fluids and the recrystallizing caco3 our finding may remove one potential source of uncertainty in 11b based ph reconstructions and provide us with greater confidence in our ability to reconstruct ph in the ancient oceans from at least some recrystallized foraminiferal calcite however further investigations should extend this approach to test the robustness of our findings across a range of taphonomies ages and burial settings

the late pleistocene palaeoclimatic record of north atlantic deep sea sediments revealed by mineral magnetic measurements eight cores of north atlantic deep sea sediment are correlated using simple rapid and non destructive measurements of magnetic susceptibility and isothermal remanence this stratigraphy is demonstrably related to late pleistocene palaeoclimatic variations by comparison with the oxygen isotope and microfossil records of these cores fluctuations in the concentration dependent magnetic properties of the cores largely reflect their lithological composition consisting of climatically modulated cycles of marl glacial horizons and nannofossil chalk interglacial horizons high magnetic concentration characterises glacial horizons which correspond to periods when carbonate productivity was severely restricted and ice rafted detrital inputs were prolific coincident with the migration south of the north atlantic polar front to within 3 of latitude north of the coring site in contrast interglacial horizons are characterised by low magnetic concentration and high carbonate content of the sediment consequent on the retreat of the polar front and the re establishment of coccolith floras in its wake during these periods ratios formed between individual magnetic parameters are independent of magnetic concentration and are thus free of any climatic influences wrought by carbonate oscillations in this study however such ratios exhibit a definite response to palaeoclimatic variations attributable to differences in the composition and grain size of the magnetic mineral assemblage of glacial vis a vis interglacial horizons of the cores these differences in mineral magnetic composition are substantially confirmed by mossbauer effect studies of selected samples representing peak glacial and interglacial horizons of one core such glacial interglacial contrasts in the concentration mineralogy and grain size of the magnetic assemblage most probably result from variations in the source and flux density of detritral inputs induced by changes in climate x ray diffraction studies of the same core indicate that variations in the mineralogy of the detrital fraction of the sediment are consistent with those of the magnetic assemblage together these data point to the conclusion that a subsidiary low latitude possibly aeolian detrital flux supplements high latitude ice rafted input in glacial horizons of the cores the low latitude flux however is also identifiable in interglacial horizons independent evidence suggests that this low latitude aeolian flux may be derived from the sahel region of north africa and transported to the coring site by harmattan winds associated with saharan dust outbreaks

influence of sedimentary setting on the use of magnetic susceptibility examples from the devonian of belgium bulk magnetic susceptibility measurements on sedimentological samples from all geological periods have been used widely in the last two decades for correlations and as a proxy for sea level variations this paper explores the link between magnetic susceptibility depositional setting and environmental parameters these environmental parameters include distal proximal transects microfacies successions and fourth order trends on different carbonate platform types platform ramp carbonate mound or atoll during different devonian stages eifelian givetian and frasnian average magnetic susceptibility values over a distal proximal trending facies succession vary markedly with depositional setting on carbonate platforms average magnetic susceptibility generally increases towards the top of shallowing upward sequences on a distal proximal transect average magnetic susceptibility is intermediate for the deepest facies decreases for the reef belts and increases to a maximum in the back reef zone in ramps and atolls magnetic susceptibility trends clearly differ average magnetic susceptibility generally decreases towards the top of shallowing upward sequences and is highest in the deepest facies the strong relationship between magnetic susceptibility facies and sequences implies a strong environmental influence however the different responses in the different platform types suggest that sea level changes leading to variation in detrital input is not the only parameter controlling average magnetic susceptibility values other primary or secondary processes also probably influenced magnetic mineral distribution primary processes such as carbonate production and water agitation during deposition are probably key factors when carbonate production is high the proportion of magnetic minerals is diluted and the magnetic susceptibility signal decreases high water agitation during deposition will also selectively remove magnetic minerals and will lead to low average magnetic susceptibility values these parameters explain the lowest values observed on the reef platform inner ramp and atoll crown which are all in areas characterized by higher carbonate production and greater water agitation during deposition the lowest values observed in the lagoon inside the atoll crown can be related to detrital isolation by the atoll crown however other parameters such as biogenic magnetite production or diagenesis can also influence the magnetic signal diagenesis can change magnetism by creating or destroying magnetic minerals however the influence of diagenesis probably is linked strongly to the primary facies permeability amount of clay or organic matter and probably enhanced the primary signal the complexity of the signal gives rise to correlation problems between different depositional settings thus while magnetic susceptibility has the potential to be an important correlation tool the results of this investigation indicate that it cannot be used without consideration of sedimentary processes and depositional environments and without strong biostratigraphical control

reevaluation of the oxygen isotopic composition of planktonic foraminifera experimental results and revised paleotemperature equations cultured planktonic foraminifera orbulina universa symbiotic and globigerina bulloides nonsymbiotic are used to reexamine temperature 18o relationships at 15 25 c relationships for both species can be described by linear equations equations for o universa grown under low light ll and high light hl share a slope of 4 80 0 21 c 1 with a hl ll offset of 0 33 due to symbiont photosynthetic activity the effect of co32 on o universa is 0 002 mol 1 kg 1 and is insensitive to temperature for g bulloides ontogenetic effects produce size related trends in temperature 18o whereby larger shells are enriched in 18o relative to smaller specimens the o universa temperature 18o relationships are more accurate than previously published equations for describing plankton tow data our equations do not explain planktonic core top data with the same precision but provide a good fit to benthic cibicidoides data below 10 c temperature 18o relationships for g bulloides provide good agreement with field data for this species from the northeast pacific

impacts of storms on recent planktic foraminiferal test production and caco3 flux in the north atlantic at 47 n 20 w jgofs planktic foraminiferal assemblages are well known to vary in accordance with seasonal fluctuations in ocean properties periodic reproduction cycles and variations between water masses here we report that storms also can significantly influence foraminiferal assemblages during the rv meteor cruise 21 to the northeast atlantic ocean biotrans area from march to may 1992 planktic foraminifera were sampled using a multiple opening closing net while sampling two storms with wind forces up to 12 beaufort caused intensified surface layer mixing with shifts in the depth of the upper ocean mixed layer from 20 40 m to 170 240 m subsequently planktic foraminiferal growth rates increased resulting in an elevated quantity of small 100 150 m tests phase 1 when the wind strength increased a second time the mixed layer deepened to a depth below the former position of the pycnocline and again the abundance of small tests increased phase 2 during phase 2 the weight of calcite in specimens of the productive zone reached its maximum in the export zone an associated increase in empty tests occurred with a lag time depending on the test sinking velocity in the upper export zone down to 700 m water depth caco3 flux increased from 9 3 to 49 8 mg caco3 m 2 d 1 after the first storm and from 8 9 to 19 9 mg caco3 m 2d 1 after the second storm in the 700 to 2500 m depth interval the flux increased from 5 1 mg caco3 m 2 d 1 to about 9 2 mg caco m 2 d 1 thus the standing stock of living foraminifera and export of empty tests from the productive zone increased after the storms leading to pulses of caco3 exported from the surface to deep water

microstructural and geochemical perspectives on planktic foraminiferal preservation glassy versus frosty in recent years it has become apparent that the cool tropic paradox of paleogene and cretaceous greenhouse climates arises because of the diagenetic alteration of tropical planktic foraminiferal calcite near the seafloor yielding artificially high 18o values because the mg ca compositions of foraminiferal and inorganic calcite are thought to be quite different mg ca measurements should be a sensitive way of monitoring diagenetic alteration here we examine the extent of diagenetic alteration of eocene planktic foraminiferal calcite using scanning electron microscope imaging of foraminiferal test microstructures and geochemical 18o and mg ca analyses we compare microstructural and geochemical characteristics between given species exhibiting two contrasting states of preservation those that appear frosty under reflected light and those that appear glassy microstructural evidence reveals extensive diagenetic alteration of frosty foraminiferal tests at the micron scale while 18o analyses document consistently higher 18o and therefore lower paleotemperatures in this material yet we find that 18o offsets between species in these frosty foraminiferal assemblages appear to be generally preserved suggesting that frosty foraminifera remain valuable for generating relatively short approximately 1 myr paleoceanographic time series that do not demand absolute estimates of paleotemperature we also find that the observed increase in mg ca for planktic foraminifera exhibiting diagenetic alteration compared to glassy taphonomies is far smaller than would be expected from the addition of inorganic calcite based on laboratory derived mg2 partition coefficients our findings imply that a much lower mg2 partition coefficient controls inorganic calcite formation in deep sea sedimentary sections in accordance with the findings of baker et al 1982

late pliocene early pleistocene paleoceanographic evolution of the sea of japan abstract the stratigraphic distribution and abundance of molluscs and planktonic foraminifera within a sixth order 41 kyr depositional sequence of the early pleistocene omma formation in central japan provide several important information on the sea of japan since 2 5 ma the sea possibly experienced three substages in the paleoceanographic history since then during substage i 2 5 1 71 ma oxygen isotope stage 60 59 cold northern surface water prevailed due to the closure of the sea s southern entrance during substage ii 1 71 1 52 ma stage 51 the warm tsushima current flowed into the sea from the south during interglacial highstands during substage iii 1 52 0 ma isolation of the sea of japan was reinforced by narrowing and or shallowing of the northern entrance these changes were caused by some local tectonic movements that affected topography of the southern and northern straits inflow of the tsushima current resulted in migration of warm water organisms into the sea of japan during interglacial stages and acted as a barrier to the migration of terrestrial organisms between east asia and japanese islands

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

oxygen isotopes versus climap 18 ka temperatures a comparison from the tropical atlantic glacial interglacial differences in 18 o values of globigerinoides sacculifer have been mapped in the western and central tropical atlantic using data from surface and core sediments glacial interglacial differences in the western tropical atlantic if attributed to temperature changes only are at odds with temperature reconstructions performed by climap in the ceara rise region delta 18 o values exceeding 2 are recorded they can only be partly attributed to changes in the precipitation evaporation regime i e higher salinities and 18 o enriched precipitation an additional cooling of 1 2 c as compared to climap9s results is required to balance the 18 o record thus temperature changes from glacial to modern times amount to 2 3 c in the tropical atlantic off the northern coast of brazil

paleoceanographic implications of the difference in deep sea sediment mixing between large and fine particles more and more paleoceanographic studies are performed on different size fractions of deep sea sediments although it has been a controversial issue for some time the bioturbation process depends on the particle size and can in principle decouple paleoceanographic records obtained in the same core this problem is studied by using a simple mixing model which allows the derivation of analytical equations for both the expected phase shift and relative attenuation of signals carried by different size fractions depending on several parameters the time shift and relative attenuation can be on the order of a few millenia and 50 respectively however high sedimentation rates 10 20 cm kyr minimize these potential complications allowing us to study millenium scale events in well chosen sedimentary environments

middle eocene regional climate instability evidence from the western north atlantic high resolution 3 k y d 18 o records from middle eocene mixed layer dwelling planktonic foraminifera from the western north atlantic show pronounced 1 variability the magnitude of change is greater than that seen in open ocean pleistocene records but could not have been caused by ice volume and or sea level fluctuations instead the oxygen isotope shifts resulted primarily from large oscillations in sea surface temperatures and indicate that the regional paleoceanography of the middle eocene western north atlantic was not consistently warm or stable the large shifts in sea surface temperatures could reflect variations in the position of the gulf stream relative to blake nose or variations in upwelling intensity

biomineralization in perforate foraminifera in this paper we review the current understanding of biomineralization in perforate foraminifera ideas on the mechanisms responsible for the flux of ca2 and inorganic carbon from seawater into the test were originally based on light and electron microscopic observations of calcifying foraminifera from the 1980s onward tracer experiments fluorescent microscopy and high resolution test geochemical analysis have added to existing calcification models despite recent insights no general consensus on the physiological basis of foraminiferal biomineralization exists current models include seawater vacuolization transmembrane ion transport involvement of organic matrices and or ph regulation although the magnitude of these controls remain to be quantified disagreement between currently available models may be caused by the use of different foraminiferal species as subject for biomineralization experiments and or lack of a more systematic approach to study dis similarities between taxa in order to understand foraminiferal controls on element incorporation and isotope fractionation and thereby improve the value of foraminifera as paleoceanographic proxies it is necessary to identify key processes in foraminiferal biomineralization and formulate hypotheses regarding the involved physiological pathways to provide directions for future research

history of the inflow of the warm tsushima current into the sea of japan between 3 5 and 0 8 ma abstract the stratigraphic distribution of warm water molluscs planktonic foraminifers and diatoms in plio pleistocene strata 3 5 0 8 ma of the sea of japan coast of japan is the basis for reconstructing the history of the tsushima current the results indicate 1 the tsushima current flowed at 3 5 3 2 2 9 2 4 and 1 9 ma in the 3 5 1 7 ma interval 2 the current flowed at every interglacial highstand except for mis 25 23 and 21 3 in the 1 71 0 8 ma interval 3 the salinity and volume of the tsushima current during the earlier interval may have been significantly lower and smaller respectively than in the latter interval 4 the late pliocene altitude of the southern part of the sea of japan was up to 50 m above present day sea level

forward modeling of carbonate proxy data from planktonic foraminifera using oxygen isotope tracers in a global ocean model the distribution and variation of oxygen isotopes in seawater are calculated using the goddard institute for space studies global ocean model simple ecological models are used to estimate the planktonic foraminiferal abundance as a function of depth column temperature season light intensity and density stratification these models are combined to forward model isotopic signals recorded in calcareous ocean sediment the sensitivity of the results to the changes in foraminiferal ecology secondary calcification and dissolution are also examined simulated present day isotopic values for ecology relevant for multiple species compare well with core top data hindcasts of sea surface temperature and salinity are made from time series of the modeled carbonate isotope values as the model climate changes paleoclimatic inferences from these carbonate isotope records are strongly affected by erroneous assumptions concerning the covariations of temperature salinity and 18ow habitat imposed biases are less important although errors due to temperature dependent abundances can be significant

a comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials some results from lake sediments abstract a new rapid method for identifying relative grain size variations in magnetic involves the parameter anhysteretic susceptibility arm i e specific arm obtained in a 1 oe steady field which is particularly sensitive to the single domain sd and small pseudo single domain psd grains of the finer magnetite fraction a second parameter low field susceptibility is relatively more sensitive to the coarser magnetite fraction larger psd and smaller multidomain md grains we can then obtain a measure of the ratio of coarse to fine grain magnetite for large numbers of samples by plotting arversus a simple idealized model based on sized magnetite samples is proposed to explain the use of the armversus plot for detecting relative grain size changes in the magnetic content of natural materials the sediments of three lakes that contain magnetite or a similar magnetic carrier and have a wide range of values of arm and are used to test the model the model is used to interpret the magnetic variations observed and the interpretations are supported by high field hysteresis measurements of the same sediments the combination of the high field hysteresis method of day et al 1 and the arm vs method is a powerful technique allowing the rapid identification of both the relative grain size and domain state for large numbers of samples containing magnetite the armvs method should be used as an intial means of identifying distinct groups of samples the high field hysteresis method should then be applied to a few representative samples from each group to confirm the initial interpretation

climate variations in europe over the past 140 kyr deduced from rock magnetism rapid shifts in climate during the last glacial are now well documented particularly from the oxygen isotope records of the two greenland ice cores grip1 2 and gisp23 in the grip record1 2 these climate events are also seen during the preceding eemian interglacial which may be an analogue for the future climate warmed by the greenhouse effect but these shifts are not found in the eemian section of the gisp2 core3 casting doubt on whether the rapid shifts in the grip oxygen isotope record really do represent a climate signal here we present magnetic susceptibility pollen and organic carbon records from maar lake deposits in the massif central france these data provide an independent record of past climate and we find that they correlate well with the ice core records during the last glacial during the eemian two rapid cooling events seen in our record also correlate with those seen in the grip ice core supporting the idea that rapid climate change did occur in the eemian interglacial and demonstrating that it extended to continental europe

a geomagnetic polarity time scale for the period 0 17 ma based on 40ar 39ar plateau ages for selected field reversals utilizing 40ar 39ar plateau ages for selected field reversals at 1 2 10 16 and 34 ma a geomagnetic polarity time scale gpts is constructed following the technique of cande and kent 1992 this differs markedly from previous gpts especially in middle late miocene time the ages for the chrons in post miocene time are in agreement with values derived by the astrochronological technique refinements in this gpts await acquisition of 40ar 39ar plateau ages for field reversals in the time frames 3 8 ma and 11 15 ma

paleoenvironmental implications of rock magnetic properties of late quaternary sediment cores from the eastern equatorial atlantic rapid and nondestructive rock magnetic measurements of late quaternary sediment cores from the senegal continental slope and the sierra leone rise in the eastern equatorial atlantic correlate strongly with the specmap oxygen isotope master curve and carbonate content the rock magnetic paleoclimatic relationship results from differences in the concentration accumulation rate grain size and composition of magnetic minerals between glacials and interglacials at both sites magnetic mineral assemblages of glacial episodes are characterized by higher concentrations and accumulation rates of magnetic minerals by coarser grained ferrimagnetic minerals e g magnetite and by a lower ratio of ferrimagnetic to antiferromagnetic e g goethite hematite minerals by serving as a sensitive tracer for various deep sea sedimentary components rock magnetic properties can provide insights into changing sediment sources and fluxes and therefore are a useful addition to more traditional chemically and mineralogically based paleoceanographic techniques

signal analysis of cyclicity in maastrichtian pelagic chalks from the danish north sea abstract low field bulk magnetic susceptibility has been determined on maastrichtian chalk samples from a drill core from the dan field in the danish north sea fast fourier transformations fft have been used to detect possible cycles in the magnetic susceptibility data power spectra from the complete section and from sub sections of the magnetic susceptibility reveal two cyclicities of ca 0 4 cycles m and ca 1 7 cycles m which are present on a 90 confidence level signal analysis of natural gamma ray wire line log data supports these findings sedimentation rate estimates place the cycles in the milankovitch frequency band artificial time series are used to study the applicability of the fft to identifying cyclicity in chalks expected geological distortions e g hiati and sedimentation rate variations are introduced into the time series to investigate the response of the frequency spectra different methods of handling missing data intervals are also examined

a new geomagnetic polarity time scale for the late cretaceous and cenozoic we have constructed a magnetic polarity time scale for the late cretaceous and cenozoic based on an analysis of marine magnetic profiles from the world s ocean basins this is the first time since heirtzler et al 1968 published their time scale that the relative widths of the magnetic polarity intervals for the entire late cretaceous and cenozoic have been systematically determined from magnetic profiles a composite geomagnetic polarity sequence was derived based primarily on data from the south atlantic anomaly spacings in the south atlantic were constrained by a combination of finite rotation poles and averages of stacked profiles fine scale information was derived from magnetic profiles on faster spreading ridges in the pacific and indian oceans and inserted into the south ariantic sequence based on the assumption that spreading rates in the south atlantic were smoothly varying but not necessarily constant a time scale was generated by using a spline function to fit a set of nine age calibration points

astronomic timescale for the pliocene atlantic δ18o and dust flux records of ocean drilling program site 659 high resolution benthic oxygen isotope and dust flux records from ocean drilling program site 659 have been analyzed to extend the astronomically calibrated isotope timescale for the atlantic from 2 85 ma back to 5 ma spectral analysis of the 18o record indicates that the 41 kyr period of earth s orbital obliquity dominates the pliocene record this is shown to be true regardless of fundamental changes in the earth s climate during the pliocene however the cycles of sahelian aridity fluctuations indicate a shift in spectral character near 3 ma from the early pliocene to 3 ma the periodicities were dominantly precessional 19 and 23 kyr and remained strong until 1 5 ma subsequent to 3 ma the variance at the obliquity period 41 kyr increased the timescale tuned to precession suggests that the pliocene was longer than previously estimated by more than 0 5 m y

magnetite diagenesis in marine sediments from the oregon continental margin the magnetochemistry of sediments from the oregon continental margin is examined to determine the effects of iron sulfur diagenesis on the paleomagnetic record magnetic mineral dissolution and transformation into iron sulfides are a common feature in these suboxic to anoxic lutites these processes are evidenced in rapid decreases in natural remanent magnetization intensities and stabilities systematic changes in other rock magnetic properties and increases in solid phase sulfur concentrations with depth hysteresis measurements are used to evaluate downcore changes in magnetite concentration and grain size magnetite abundances decrease downcore from initial values of about 0 1 and nominal grain diameters lie within a narrow pseudosingle domain range of 0 08 to 0 6 m a first order surface area reaction model da dt ka is proposed to explain the magnetite dissolution mechanism where a is the total magnetite surface area and k is the rate constant the solution of this equation predicts that the surface area and concentration decrease exponentially and the concentration in addition depends on grain size application of this model in two cores where grain size varies with depth successfully explains the downcore profiles of both concentration and surface area despite extensive magnetite destruction magnetic directions in such sediments appear to reliably record long wavelength trends of the geomagnetic field

evidence for a change in the periodicity of tropical climate cycles at 2 4 myr from whole core magnetic susceptibility measurements the earth s orbit about the sun is influenced by gravitational interactions with the moon and other planets the resulting orbital perturbations give rise to cyclical variations in orbital eccentricity obliquity and precession with periods of 100 41 19 and 23 kyr respectively1 these variations are climatically important because they affect the seasonal and latitudinal distribution of solar radiation magnetic susceptibility measurements in deep sea sediment cores can be used as a sensitive indicator of temporal variations in the concentration of terrigenous material supplied to the sea bed here we use this approach to study the evolution of cycles of terrigenous sedimentation at ocean drilling program sites in the arabian sea and the eastern tropical atlantic we show from spectral analyses of the two susceptibility time series spanning the past 3 2 3 5 myr that the records are driven strongly by orbital forcing before 2 4 myr before present bp both records are strongly influenced by the 23 and 19 kyr periodicities but after 2 4 myr they are both significantly influenced by the 41 kyr periodicity this shift coincides with the beginning of major northern hemisphere glaciation which indicates for the indian ocean site that the supply of terrigenous sediment carried by monsoonal winds has responded to the rapid increase in ice cover at this time we cannot however exclude possible effects of changes in bottom water circulation on the susceptibility record of the atlantic site

paleoceanographic changes across the latest danian event in the south atlantic ocean and planktic foraminiferal response abstract a number of short warming events occurred during paleocene and eocene of which the paleocene eocene thermal maximum petm 56 ma is the most severe and most investigated event the less known latest danian event lde at 62 2 ma represents a 200 ky lasting warming phase superimposed on a long term cooling trend after the early paleocene south atlantic odp site 1262 data covering 1 myr indicate a warming of the entire water column by 1 5 2 6 c accompanying a prominent negative carbon isotope excursion 0 9 1 1 and a long term re organization of the planktic foraminiferal fauna associated with the lde this study unravels a different paleoceanographic evolution of the upper ocean structure compared to results from pacific odp site 1210 unlike the pacific the atlantic site lacks an apparent change of stratification as well as an overall dominance of thermocline dwelling planktic foraminifera species and a low abundance of surface dwelling photosymbiotic foraminifera within the lde indications for a slightly enhanced stratification of the upper water column and transient warming were indicated when surface dwelling planktic foraminifera became temporarily more abundant the long term evolution in planktic foraminifera with the disappearance of praemurica at the lde onset and a contemporaneous rise in morozovella is similar to the trends reported from shatsky rise odp site 1210

a rock magnetic record from lake baikal siberia evidence for late quaternary climate change rock magnetic measurements of sediment cores from the academician ridge region of lake baikal siberia show variations related to late quaternary climate change based upon the well dated last glacial interglacial transition variations in magnetic concentration and mineralogy are related to glacial interglacial cycles using a conceptual model interglacial intervals are characterized by low magnetic concentrations and a composition that is dominated by low coercivity minerals glacial intervals are characterized by high magnetic concentrations and increased amounts of high coercivity minerals the variation in magnetic concentration is consistent with dilution by diatom opal during the more productive interglacial periods we also infer an increased contribution of eolian sediment during the colder windier and more arid glacial conditions when extensive loess deposits were formed throughout europe and asia eolian transport is inferred to deliver increased amounts of high coercivity minerals as staining on eolian grains during the glacial intervals variations in magnetic concentration and mineralogy of lake baikal sediment correlate to the specmap marine oxygen isotope record the high degree of correlation between baikal magnetic concentration mineralogy and the specmap oxygen isotope record indicates that lake baikal sediment preserves a history of climate change in central asia for the last 250 ka this correlation provides a method of estimating the age of sediment beyond the range of the radiocarbon method future work must include providing better age control and additional climate proxy data thereby strengthening the correlation of continental and marine climate records

direct assessment of stable isotope variability in planktonic foraminifera populations abstract a large number of tests of three species of planktonic foraminifera globigerinoides sacculifer orbulina universa and pulleniatina obliquiloculata were analyzed for stable oxygen and carbon isotopes in a western equatorial pacific box core estimates of population variance were calculated using a statistical technique known as the jackknife these estimates were used to generate sampling curves which provide the number of foraminiferal tests required in an isotopic analysis when precision and reliability criteria are specified the jackknife results have important sampling implications 1 a large number of foraminiferal tests are required to obtain statistically reliable isotope data for example given a machine precision standard deviation of 0 09in0 417 tests g sacculifer 355 420 m are required to obtain a 18 o precision of 0 1in0 with 90 reliability 2 variance is a function of test diameter with greater variance being found in larger size fractions 3 variance is dependent on foraminiferal species 4 variance differences between glacial and interglacial samples are not significant 5 in the size interval 600 900 m a systematic relationship is not seen between size and 18 o or 13 c 6 replicate analysis is a practical method of improving isotope data quality size and species related variance differences are probably related to a number of factors including depth habitat seasonal production of tests species vertical migrations and vital and or symbiosis caused effects knowledge of data variance permits error assessment in sediment unmixing analyses and optimization of spectral estimates

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

modes of eastern equatorial pacific thermocline variability implications for enso dynamics over the last glacial period 1 changes in el nino southern oscillation enso variability are difficult to extract from paleoceanographic reconstructions because they are superimposed on changes in seasonal variability that modulate the first order climate signal here we address this problem by reconstructing thermocline structure from a marine sediment core retrieved from the eastern equatorial pacific at the core location changes in hydrologic parameters within the thermocline are linked to enso activity with a reduced influence of seasonal variability compared to surface waters we performed repeated isotopic analyses 18o on single specimens of the thermocline dwelling planktonic foraminifera neogloboquadrina dutertrei at several targeted time periods over the last 50 ka to extract the total thermocline variance a parameter supposed to reveal changes in enso no fundamental changes in amplitude and frequency of the events were detected despite differences in climatic background however our data suggest that long term variations in the thermocline variability occurred over the last 50 ka with the highest and lowest enso activities occurring during the last glacial period and the last glacial maximum respectively

the cretaceous paleogene k p boundary at brazos texas sequence stratigraphy depositional events and the chicxulub impact abstract two cores from brazos texas spanning the cretaceous paleogene k p boundary are investigated by a multidisciplinary approach aiming at unraveling environmental changes and sequence stratigraphic setting in addition the sedimentology of the k p event deposit and its correlation with the k p boundary is studied foraminifera and nannofossil stratigraphy indicates that both cores include a latest maastrichtian zone cf1 cf2 and earliest danian p0 p and p1a shale sequence with a sandy and chicxulub ejecta bearing event deposit at the k p boundary a hiatus of unknown duration may be present by the unconformable base of the event deposit planktic foraminifera as well as calcareous nannofossil abundance and diversity both decline abruptly above the event deposit k p mass extinction whereas benthic foraminifera show a pronounced faunal change but no mass extinction mineralogical and geochemical proxies suggest that except for the sandwiched k p event deposit no facies change took place across the k p boundary and no evidence for adverse an or dysoxic sedimentary conditions following the chicxulub impact was observed therefore the interval bracketing the k p event deposit is considered as highstand systems tract increased coarse detritus input and low planktic benthic p b foraminifera ratios during the earliest paleocene p0 and p both suggest an increased coastal proximity or relative sea level lowering although the k p mass extinction of planktic foraminifera might have influenced the p b ratios as well consequently the sandy shales of the early paleocene are considered as late regressive highstand or as lowstand deposit during p1a shales assigned as transgressive systems tract overlie a pyrite and glauconite rich bioturbated transgressive surface or type 2 sequence boundary the smectite dominated clay assemblage with minor illite kaolinite and chlorite indicates semiarid humid climates with no obvious shifts across the k p boundary the magnetic susceptibility signature during the maastrichtian reveals a subtle cyclic or rhythmic pattern whereas a high amplitude cyclic pattern is present during the early danian the k p event deposit shows a succession of high energetic debris flows and turbidites derived from multiple source areas followed by a period of decreasing current energy deposition was likely triggered by multiple tsunami or tempestites followed by a prolonged period of reworking and settling the chicxulub ejecta at the base of the k p event deposit consists of mg rich smectite as well as fe mg rich chlorite spherules their mineralogical composition points to target rocks of mafic to intermediate composition presumably situated in the northwestern sector of the chicxulub impact structure besides these silicic phases the most prominent ejecta components are limestone clasts accretionary carbonate clasts and microspar suggesting that the texas area received ejecta also from shallow carbonate rich lithologies at the impact site on the yucatan carbonate platform the excellent correlation of chicxulub ejecta at brazos with ejecta found in the k p boundary layer worldwide along with the associated mass extinction provides no evidence that chicxulub predated the k p boundary and allows for unequivocal positioning of the k p boundary at the event deposit

origin of the sedimentary magnetic record at ocean drilling program sites on the owen ridge western arabian sea the 3 2 m y whole core magnetic susceptibility record obtained during ocean drilling program leg 117 from the owen ridge in the western arabian sea represents one of the most convincing demonstrations of the ability of rock magnetic measurements to yield paleoceanographically significant information the salient features of this record are that 1 it correlates strongly with variations in the concentration and flux of eolian dust 2 it is driven strongly at earth orbital periodicities and 3 there is a significant change in the spectral character at 2 4 m y which may reflect the effect of the initiation of major northern hemisphere glaciation on aridity cycles within the eolian source areas in view of its potential paleoclimatic significance we have examined the origin of the rock magnetic signal from the owen ridge in more detail we find that despite the strong relationship throughout the record between magnetic susceptibility and percent terrigenous content there has been significant postdepositional alteration of the magnetic minerals via the process of reductive diagenesis we ascribe two steplike shifts in magnetic properties in the uppermost part of the section to this process the first occurs at about 1 5 m depth and is characterized by a loss of fine grained ferrimagnetic material the second stepshift in magnetic properties occurs at a depth of 6 8 m and is characterized by changes in rock magnetic parameters which indicate significant loss of both low coercivity magnetite and high coercivity hematite and or goethite magnetic mineral components scanning electron microscope and energy dispersive xray analyses show that the bulk of the coarse grained strongly magnetic fraction is detrital titanomagnetite and that there is a significant reduction in the fe ti ratio of these grains across the lower diagenetic front this suggests that titanomagnetite grains with higher ti contents may be more resistant to the process of reductive diagenesis and this may provide a mechanism for the relative stability of the ferrimagnetic fraction below the second diagenetic front

multispecies approach to reconstructing eastern equatorial pacific thermocline hydrography during the past 360 kyr 1 stable isotope data from eastern equatorial pacific eep core tr163 19 2 15 n 90 57 w 2348 m are presented for the surface dwelling foraminifers globigerinoides ruber and g sacculifer and thermocline dwelling globorotalia menardii and neogloboquadrina dutertrei using species specific normalization factors derived from experimental and plankton tow data we reconstruct a 360 kyr record of water column hydrography across the past three glacial cycles we demonstrate that g ruber maintains a mixed layer habitat throughout the entire record while g sacculifer records a mixture of thermocline and mixed layer conditions and g menardii and n dutertrei record thermocline properties we conclude that g sacculifer is not appropriate for paleoceanographic applications in regions with steep vertical hydrographic gradients results suggest that this region of the eep had a thicker mixed layer and deeper 13cdic boundary between the surface and equatorial undercurrent during the last two glacial periods a shift in n dutertrei and g sacculifer geochemistry prior to 185 kyr suggests water column structure and chemocline gradients changed possibly due to a shift in the position of the undercurrent relative to this site the timing and magnitude of glacial interglacial 13c variations between species indicates that near surface carbon chemistry is controlled by changes in productivity atmospheric circulation and advected intermediate water sources north of the antarctic polar front these results demonstrate that when properly calibrated for species differences multispecies geochemical data sets can be invaluable for reconstructing water column structure and properties in the past

opening the carbon isotope vital effect black box 1 seasonal temperatures in the euphotic zone recent laboratory experiments with orbulina universa show that the carbon and oxygen isotope signals from this symbiont bearing planktonic foraminifera record distinct environmental parameters irradiance and temperature since light levels are correlated with depth in the marine environment the carbon isotopic composition of o universa can be utilized to differentiate individuals from different depth habitats by combining 18o and 13c data from individuals in an assemblage estimates of seasonal temperature ranges are possible for the upper and lower euphotic zone of the ocean reconstruction of seasonal temperatures using individual holocene o universa from western equatorial pacific ocean boxcore erdc 83 yields ranges of 23 5 to 29 9 c and 20 1 to 24 5 c for the shallow and deep euphotic zone respectively these values are in excellent agreement with recent temperature measurements from this region analyses of individual late glacial 12 000 13 000 years b p o universa from this site suggest the seasonal upper euphotic zone temperature range was approximately 2 5 c lower than it is today a function of cooler summers

seawater ph and isotopic paleotemperatures of cretaceous oceans abstract stable oxygen isotope ratios 18 o of foraminifera are widely used to reconstruct the climatic history of earth it is well known that temperature reconstructions based on 18 o are complicated by factors such as the unknown isotopic composition of the ocean in addition recent experimental and theoretical work has shown that the seawater ph has a marked effect on the 18 o of foraminifera here i employ this effect to demonstrate that reconstructions based on 18 o of foraminifera may underestimate sea surface temperatures in the geological past ocean surface temperatures for the mid cretaceous are estimated to have been 2 3 5 c higher than previously thought

opening the carbon isotope vital effect black box 2 quantitative model for interpreting foraminiferal carbon isotope data interpretation of carbon isotope records from late quaternary planktonic foraminifers are confounded due to the presence of a significant physiological component in the carbon isotopic signal a quantitative carbon isotope qc model is presented which relates the carbon isotopic composition of a foraminiferal shell to the physiological processes of respiration and symbiont photosynthesis and to the 13c value of seawater co2 the qc model is calibrated with physiological and stable isotopic data from laboratory experiments with living planktonic foraminifers model simulations of chamber and shell 13c values with the symbiont bearing foraminifers orbulina universa and globigerinoides sacculifer suggest 1 variations in symbiont density and photosynthetic rate light level or habitat depth are the primary physiological parameters controlling intraspecific carbon isotopic variability in these species 2 respiration has little effect on the 13c of o universa and 3 each chamber in a multichambered foraminiferal test will have a distinct 13c value depending on its position in the test whorl size 13c value relationships reported for g sacculifer from fossil assemblages can be explained as a function of increasing symbiont density during ontogenetic development

late pliocene climate change 3 4 2 3 ma paleoceanographic record from the yabuta formation sea of japan abstract late pliocene paleoceanographic changes in the sea of japan between 3 4 and2 3 ma were investigated through study of molluscs diatoms and ostracodes from the yabuta formation in toyama prefecture the period 3 4 2 7 ma was characterized by relatively high sea level and cool water benthic faunas a progressive paleoceanographic shift towards colder oceanic conditions and lower sea level occurred beginning near 2 7 ma intenifying about 2 5 ma when important changes in ostracode and molluscan faunas occurred between 2 7 and 2 3 ma eight glacial events can be inferred based on drops in sea level of 50 60 m and increasing proportions of cold shallow water ostracode species whose modern ecology and zoogeography indicate colder winter water temperatures 3 4 c the glacial events between 2 5 and 2 3 ma were the most intense preliminary interpretation of the faunal and oceanographic events of the yabuta formation suggests that they correspond to northern hemispheric cooling also known from north atlantic deep sea oxygen isotope ird and planktic foraminiferal records north pacific diatom and radiolarian record and the chinese loess sequences the eight glacial events may record a 41 000 yr obliquity cycle which characterized other late pliocene climate proxy records inferred sea level drops near 2 5 2 3 ma of about 50 60 m provide direct evidence from an ocean margin setting that supports deep sea oxygen isotopic evidence indicating major changes in global ice volume changes

sea level and deep sea temperature variability over the past 5 3 million years ice volume and hence sea level and deep sea temperature are key measures of global climate change sea level has been documented using several independent methods over the past 0 5 million years myr older periods however lack such independent validation all existing records are related to deep sea oxygen isotope 18o data that are influenced by processes unrelated to sea level for deep sea temperature only one continuous high resolution mg ca based record exists with related sea level estimates spanning the past 1 5 myr here we present a novel sea level reconstruction with associated estimates of deep sea temperature which independently validates the previous 0 1 5 myr reconstruction and extends it back to 5 3 myr ago we find that deep sea temperature and sea level generally decreased through time but distinctly out of synchrony which is remarkable given the importance of ice albedo feedbacks on the radiative forcing of climate in particular we observe a large temporal offset during the onset of plio pleistocene ice ages between a marked cooling step at 2 73 myr ago and the first major glaciation at 2 15 myr ago last we tentatively infer that ice sheets may have grown largest during glacials with more modest reductions in deep sea temperature a novel approach to the estimation of sea level and deep sea temperature has been used to determine these quantities over the past 5 3 million years this approach based on oxygen isotope records from the eastern mediterranean shows that temperature and sea level histories are broadly correlated but also show intriguing temporal offsets most records of past sea level variation and associated changes in ocean temperature rely on variations in oxygen isotopes recorded in deep sea marine microorganisms these signals unfortunately are confounded by other influences making it difficult to extract a clear climate related signal eelco rohling and colleagues now present a novel approach to estimating sea level and deep sea temperature variations for the past 5 3 million years the record based on oxygen isotope variations from the eastern mediterranean avoids the issues of the deep sea approach and generally corresponds to an independent record of the past 1 6 million years as expected temperature and sea level are broadly correlated but also show intriguing temporal discontinuities as at the initiation of plio pleistocene ice ages when a major sea level drop lagged a sharp temperature decline by several hundred thousand years

testing the impact of diagenesis on the δ18o and δ13c of benthic foraminiferal calcite from a sediment burial depth transect in the equatorial pacific stable oxygen and carbon isotope 18o and 13c values measured in foraminiferal calcite are one of the primary tools used in paleoceanography diagenetic recrystallisation of foraminiferal calcite can act to reset primary isotopic values but its effects are typically poorly quantified here we test the impact of early stage diagenesis on stable isotope records generated from a suite of drill sites in the equatorial pacific ocean recovered during ocean drilling program odp leg 199 and integrated ocean drilling program iodp expedition 320 our selected sites form paleowater and burial depth transects with excellent stratigraphic control allowing us to confidently correlate our records we observe large inter site differences in the preservation state of benthic foraminiferal calcite implying very different recrystallisation histories but negligible inter site offsets in benthic 18o and 13c values we infer that diagenetic alteration of benthic foraminiferal calcite in sedimentary oozes must predominantly occur at shallow burial depths 100 m where offsets in both the temperature and isotopic composition of waters in which the foraminifera calcified and pore waters in which diagenesis occurs are small our results suggest that even extensive recrystallisation of benthic foraminiferal calcite results in minimal shifts from primary 18o and 13c values this finding supports the long held suspicion that diagenetic alteration of foraminiferal calcite is less problematic in benthic than in planktic foraminifera and that in deep sea sediments routinely employed for palaeoceanographic studies benthic foraminifera are robust recorders of stable isotope values in the fossil record

recognition of cyclicity in the petrophysical properties of a maastrichtian pelagic chalk oil field reservoir from the danish north sea subdivision of the maastrichtian chalk from the danish north sea has proven difficult because of its homogenous composition which is caused by a fairly stable depositional environment nevertheless the chalk petrophysical properties show cyclic behavior that potentially can be used for subdivision petrophysical properties of a 23 m long succession of maastrichtian chalk from the dan field were examined for cyclicity by spectral analysis magnetic susceptibility values measured on plug samples together with the neutron porosity and natural gamma radiation well log data were analyzed both as complete data sets and in subsets to survey the general existence of cycles in the chalk all three properties contain consistent cycles at approximately 2 m wavelength as well as additional frequencies where the relative dominance of the different frequencies differs cross spectral analyses of subsets of the petrophysical parameters provide substantial evidence for the coexistence of the approximately 2 m cycles in the maastrichtian chalk furthermore the magnetic susceptibility carries spectral evidence for a higher frequency because most power spectra of the subsets from the magnetic susceptibility have a spectral peak in the 1 8 2 0 cycles m interval i e approximately 0 5 m cycle the cycles can be interpreted as resulting from the eccentricity 94 5 k y and the precession 22 5 k y of the milankovitch cycles assuming a sedimentation rate of 2 6 cm k y the existence and the understanding of cycles at a submeter scale yield possibilities for an advantageously precise subdivision of chalk reservoirs and correlation between wells begin page 2004

evidence for bacterial palaeoecological origin of mineral magnetic cycles in oxic and sub oxic tasman sea sediments abstract sediments from the tasman basin in the southwest pacific ocean show a cyclic pattern of variation in mineral magnetic properties including susceptibility and remanence over the brunhes chron the magnetic pattern is dominated by fluctuations in the concentration of a single domain ferrimagnetic component identified as bacterial magnetofossils by tem investigation of the magnetic fraction the intervals of low bacterial magnetite concentration occurring in glacial periods are accompanied by a change of the bacterial magnetosome morphology assemblage interpreted as recording a change in bacterial species assemblage there is no evidence of iron or sulphate reducing conditions during low bacterial magnetite intervals concentrations of bacterial magnetite are low when oxygen concentrations in surface sediment pore waters dropped either as the result of variation in bottom water oxygen concentration or sedimentation rate the variations in the magnetic signal are therefore interpreted as resulting primarily from bacterial palaeoecological control rather than dissolution or alteration the bacteria in this deep sea environment are apparently aerophilic and grow near the sediment surface within the oxic zone implying that magnetic remanence is also acquired near the surface but up to tens of centimetres below where the oxic zone is very thick

upper devonian carbonate platform correlations and sea level variations recorded in magnetic susceptibility abstract this paper concerns the analysis of four outcrops in the frasnian upper devonian of belgium we compare the results of a precise sedimentological analysis with magnetic susceptibility ms data this comparison allows us to improve stratigraphic correlations and to test the relationship between magnetic susceptibility and sea level changes considering the sedimentological study different microfacies have been identified from the external belt dominated by relatively argillaceous open marine facies with crinoids to the biostromal and the lagoonal belt dominated by algae rich muddy facies fourth and third order sequences have also been identified and are probably related to sea level variations magnetic susceptibility data provides us very good fourth order correlations and the link between magnetic susceptibility and different sedimentological parameters is obvious more precisely ms appears to be related to fourth and third order sequences and to microfacies

do planktic foraminifera accurately record shifts in the carbon isotopic composition of seawater σco2 abstract both the carbon isotopic composition of seawater and physiological vital effects such as respiration and symbiont photosynthesis influence the 13 c value of foraminiferal calcite the symbiont bearing planktic foraminifera orbulina universa was grown in a series of laboratory experiments to determine whether vital effects differentially obscure the 13 c signal such that changes in the 13 c of seawater co 2 cannot be quantitatively evaluated foraminifera were cultured under three different irradiance levels to elicit a full range of symbiont photosynthetic effects and in seawater with 13 c values ranging between 1 77 ambient and 5 76 power regression analysis of isotope data from individual shells plotted against culture irradiance yields three curves which are nearly parallel but are offset by the difference between the carbon isotopic composition of the culture waters when irradiance groups are combined and o universa 13 c values are plotted against seawater 13 c three parallel linear regressions are obtained with slopes ranging between 0 93 and 0 96 because the slopes are near unity it is concluded that the 13 c of o universa accurately tracks changes in the carbon isotopic composition of seawater regardless of the magnitude of its physiological vital effect o universa oxygen isotope data show that individuals maintained in the low and medium irradiance groups secrete their shells in isotopic equilibrium according to established paleotemperature equations in contrast individuals grown under high irradiance levels maximum symbiont photosynthetic rates are on average 0 35 depleted in 18 o relative to equilibrium symbiont enhanced calcification rates in the high light group may be responsible for the observed 18 o difference

early oligocene glaciation and productivity in the eastern equatorial pacific insights into global carbon cycling the onset of sustained antarctic glaciation across the eocene oligocene transition eot marks a pivotal change in earth s climate but our understanding of this event particularly the role of the

rock magnetic evidence for the dissolution and authigenic growth of magnetic minerals within anoxic marine sediments of the california continental borderland the rock magnetic properties of marine sediments from the california continental borderland san pedro santa catalina and san nicolas basins have been studied in order to quantitatively assess the effects of sediment diagenesis on magnetic minerals previous studies have noted that the natural remanent magnetization in these sediments primarily carried by detrital magnetite decays to 10 or less of its surface value soon after deposition this decrease is caused by magnetite dissolution related to sediment diagenesis and is unrelated to paleoclimatic variations or changes in the regional influx of detrital magnetic material detailed rock magnetic measurements show that shifts to softer remanent coercivity and differences in the rate and degree of magnetic intensity loss with depth can be related to the dissolution process the shift to softer remanent coercivity is related to a coarsening of the magnetic mineral grain sizes with depth due to preferential dissolution of the finest grained magnetic material the intensity decreases which are linearly proportional to magnetite concentration decreases indicate that dissolution occurs with rate constants ranging from 0 3 to 1 6 kyr 1 the rate constants sulfide concentrations and magnetite grain size estimates from the borderland are consistant with previous studies of magnetite dissolution our results demonstrate the importance of both sulfide and magnetite surface area in the dissolution process anomalous peaks in viscous remanence within the sediments suggest the authigenic growth of greigite and its subsequent transformation to pyrite

a test of different factors influencing the isotopic signal of planktonic foraminifera in surface sediments from the northern south china sea abstract the stable isotope composition of planktonic foraminifera is one of the most important proxies in paleoenvironmental research in this study three parameters affecting the stable isotope values of globigerinoides ruber from surface sediment from the northern south china sea were tested different cleaning methods different morphotypes and different size fractions our results show that in the small size fraction there is a small but significant effect on 13c by oxidizing the tests prior to measurement our data also confirm a small but significant difference between different morphotypes of g ruber however the variability caused by the seasonal effect stable isotope value is larger than the effect caused by different cleaning protocols or different morphotypes the large spread of the isotope values up to 2 have some implications to paleoceanographic reconstructions when measurements are performed on a small number of foraminiferal tests the isotope value does not necessarily reflect yearly average or a certain season but is a random value of the seasonal variability in that region

statistical constraints on el nino southern oscillation reconstructions using individual foraminifera a sensitivity analysis recent investigations of submillennial paleoceanographic variability have attempted to resolve high frequency climate signals such as the el nino southern oscillation enso using the population statistics of individual planktic foraminiferal 18o analyses this approach is complicated by the relatively short lifespan of individual foraminifers 2 4 weeks compared to the time represented by a typical marine sediment sample decades to millennia here we investigate the uncertainty associated with individual foraminiferal analyses ifa through simulations on forward modeled 18ocarbonate first focusing on the nino3 4 region of the tropical pacific ocean a bootstrap monte carlo algorithm is developed to constrain the uncertainty on ifa statistics subsequently to test the sensitivity of ifa to changes in seasonal cycle amplitude enso amplitude and enso frequency synthetic time series of 18ocarbonate with differing variability are constructed and tested with our algorithm the probabilities of the ifa technique in detecting changes in enso amplitude and seasonal cycle amplitude or a combination of both for the surface ocean and thermocline at different locations in the tropical pacific are quantified we find that the uncertainty in the standard deviation is smaller than the range that the ifa signal is insensitive to enso frequency and at certain locations the seasonal cycle may dominate enso ifa sensitivity towards enso is highest at the central equatorial pacific surface ocean and the eastern equatorial pacific eep thermocline whereas sensitivity towards the seasonal cycle is highest at the eep surface ocean our results suggest that rigorous uncertainty quantification should become standard practice for accurately interpreting ifa data

paleocurrent analysis for the late pleistocene holocene incised valley fill of the yangtze delta china by using anisotropy of magnetic susceptibility data abstract anisotropy of magnetic susceptibility ams analysis has been conducted on samples from borehole core cm 97 from the yangtze river changjiang incised valley fill china to determine the paleocurrent directions to help in reconstructing sedimentary paleoenvironments borehole cm 97 consists of fluvial unit 1 estuarine units 2 6 and deltaic units 7 9 sediments after the last glacial maximum in ascending order the ams results show that the paleocurrent directions for the tide dominated estuarine and deltaic sediments were westerly or northwesterly directed flood tide dominated but give no definite trend for the fluvial sediments comparison between the paleocurrent directions inferred from primary sedimentary structures and in situ ams data shows that they are in good agreement confirming the applicability of ams as a good paleocurrent indicator for sediments deposited in coastal tide dominated environments considering that these sediments were strongly tide influenced and the tidal pattern since 12 kyr bp has not changed significantly we think that the westerly or northwesterly current direction most probably resulted from flood tidal currents and the sedimentary paleoenvironment was a flood tide dominated estuary or delta additionally it has been found that downhole changes of some ams parameters including the mean magnetic susceptibility k the corrected anisotropy degree p j and the magnetic foliation f clearly mark the defined stratigraphic boundaries in the borehole this further extends the validity of ams as a good stratigraphic marker in addition to its long known credibility as a sensible paleocurrent recorder

defining uncertainty and error in planktic foraminiferal oxygen isotope measurements foraminifera are the backbone of paleoceanography planktic foraminifera are one of the leading tools for reconstructing water column structure however there are unconstrained variables when dealing with uncertainty in the reproducibility of oxygen isotope measurements this study presents the first results from a simple model of foraminiferal calcification foraminiferal isotope reproducibility model firm designed to estimate uncertainty in oxygen isotope measurements firm uses parameters including location depth habitat season number of individuals included in measurement diagenesis misidentification size variation and vital effects to produce synthetic isotope data in a manner reflecting natural processes reproducibility is then tested using monte carlo simulations importantly this is not an attempt to fully model the entire complicated process of foraminiferal calcification instead we are trying to include only enough parameters to estimate the uncertainty in foraminiferal 18o records two well constrained empirical datasets are simulated successfully demonstrating the validity of our model the results from a series of experiments with the model show that reproducibility is largely controlled by the number of individuals in each measurement but also strongly a function of local oceanography if the number of individuals is held constant parameters like diagenesis or misidentification have an impact on both the precision and the accuracy of the data firm is a tool to estimate isotopic uncertainty values and to explore the impact of myriad factors on the fidelity of paleoceanographic records particularly for the holocene

oxygen and carbon isotopes of individual shells of planktonic foraminifera from ontong java plateau equatorial pacific abstract analyses of single shells of orbulina universa and two other species show ranges of 2 in 18 o and 13 c at various levels in a box core from the western equatorial pacific seasonal and inter annual variations can account for only about half of this range variations in depths of calcification and in metabolic effects must account for the rest the large range must introduce considerable noise in multi shell analysis unless the number of shells in the sample is of the order of 50 or more we did not find a change in the range downcore nor did we find any evidence for the deglacial meltwater spike

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

an explanation of the effect of seawater carbonate concentration on foraminiferal oxygen isotopes abstract stable oxygen isotope ratios of foraminiferal calcite are widely used in paleoceanography to provide a chronology of temperature changes during ocean history it was recently demonstrated that the stable oxygen isotope ratios in planktonic foraminifera are affected by changes of the seawater chemistry carbonate system the 18 o of the foraminiferal calcite decreases with increasing co 3 2 concentration or p h this paper provides a simple explanation for seawater chemistry dependent stable oxygen isotope variations in the planktonic foraminifera orbulina universa which is derived from oxygen isotope partitioning during inorganic precipitation the oxygen isotope fractionation between water and the dissolved carbonate species s h 2 co 3 hco 3 co 3 2 decreases with increasing p h provided that calcium carbonate is formed from a mixture of the carbonate species in proportion to their relative contribution to s the oxygen isotopic composition of caco 3 also decreases with increasing p h the slope of shell 18 o vs co 3 2 of orbulina universa observed in culture experiments is 0 0022 mol kg 1 1 spero et al 1997 whereas the slope derived from inorganic precipitation is 0 0024 mol kg 1 the theory also provides an explanation of the nonequilibrium fractionation effects in synthetic carbonates described by kim and o neil 1997 which can be understood in terms of equilibrium fractionation at different p h the results presented here emphasize that the oxygen isotope fractionation between calcium carbonate and water does not only depend on the temperature but also on the p h of the solution from which it is formed

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