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

on the stability of the atlantic meridional overturning circulation during the last deglaciation using a generalized stability indicator l we explore the stability of the atlantic meridional overturning circulation amoc during the last deglaciation based on a paleoclimate simulation from the last glacial maximum as forced by various external climate forcings notably the meltwater forcing the amoc experiences a collapse and a subsequent rapid recovery in the early stage of deglaciation this change of the amoc induces an anomalous freshwater divergence and later convergence across the atlantic and therefore leads to a positive l suggesting a negative basin scale salinity advection feedback and in turn a mono stable deglacial amoc further analyses show that most anomalous freshwater is induced by the amoc via the southern boundary of the atlantic at 34 s where the freshwater transport m ovs is about equally controlled by the upper branch of the amoc and the upper ocean salinity along 34 s from 19 to 17 ka as a result of multiple climate feedbacks associated with the amoc change the upper ocean at 34 s is largely salinified which helps to induce a switch in m ovs from import to export our study has important implications to the deglacial simulations by climate models a decomposition of l shows that the amoc stability is mostly determined by two terms the salinity stratification at 34 s and the change of stratification with the amoc both terms appear positive in model however the former is likely to be distorted towards positive as associated with a common bias existing over the south atlantic in climate models therefore the amoc is potentially biased towards mono stability in most paleoclimate simulations

confounding effects of coral growth and high sst variability on skeletal sr ca implications for coral paleothermometry massive corals offer continuous records of climate locked within their skeleton with the most commonly applied paleo thermometer being sr ca recently however problems with sr ca thermometry indicate that the intrinsic variance of single core sr ca time series differs between cores here we compare the sr ca records and growth parameters of two porites lutea colonies sampled from the same reef zone 0 72 km apart with two gridded sst datasets ersst and hadisst off ne madagascar specifically we address seasonal and interannual variability as well as trend differences between records over the same 43 year period the two gridded sst datasets showed strong seasonality and weak positive enso anomalies on a slow 43 year warming trend at significantly different rates both the coral sr ca records showed the same clear seasonality and similar amplitudes in sst however on interannual timescales they displayed diverging 43 year sr ca trends and opposite responses to weak enso anomalies moreover their growth response also differed as one coral showed increasing extension calcification rates and sr ca ratios cooling over the 43 years while the other coral showed decreasing extension calcification rates and sr ca ratios warming further during positive enso events the calcification rates of the two corals were negatively correlated while skeletal density anomalies were opposite possible explanations to why these corals are so different may be related to the corals growth response to sst changes the growth response of individual corals to increasing sst seems to be opposite which in turn are likely related to biological factors consequently coral growth responses explain much of the inter colony sr ca variability

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

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

a bayesian multivariate calibration for globigerinoides ruber mg ca the use of mg ca in marine carbonates as a paleothermometer has been challenged by observations that implicate salinity as a contributing influence on mg incorporation into biotic calcite and that dissolution at the sea floor alters the original mg ca yet these factors have not yet been incorporated into a single calibration model we introduce a new bayesian calibration for globigerinoides ruber mg ca based on 186 globally distributed core top samples which explicitly takes into account the effect of temperature salinity and dissolution on this proxy our reported temperature salinity and dissolution here expressed as deep water co32 sensitivities are 2 8 7 0 9 c 3 9 1 2 psu and 3 3 1 3 mol kg 1 below a critical threshold of 21 mol kg in good agreement with previous culturing and core top studies we then perform a sensitivity experiment on a published record from the western tropical pacific to investigate the bias introduced by these secondary influences on the interpretation of past temperature variability this experiment highlights the potential for misinterpretations of past oceanographic changes when the secondary influences of salinity and dissolution are not accounted for multiproxy approaches could potentially help deconvolve the contributing influences but this awaits better characterization of the spatio temporal relationship between salinity and 18osw over millennial and orbital timescales

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

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

salinity bias on the foraminifera mg ca thermometry correction procedure and implications for past ocean hydrographic reconstructions 1 mg ca in foraminiferal calcite has recently been extensively used to estimate past oceanic temperatures here we show however that the mg ca temperature relationship of the planktonic species globigerinoides ruber is significantly affected by seawater salinity with a 1 psu change in salinity resulting in a 1 6 c bias in mg ca temperature calculations if not accounted for such a bias could lead for instance to systematic overestimations of mg ca temperatures during glacial periods when global ocean salinity had significantly increased compared to today we present here a correction procedure to derive unbiased sea surface temperatures sst and 18osw from g ruber tmg ca and 18of measurements this correction procedure was applied to a sedimentary record to reconstruct hydrographic changes since the last glacial maximum lgm in the western pacific warm pool while uncorrected tmg ca data indicate a 3 c warming of the western pacific warm pool since the lgm the salinity corrected sst result in a stronger warming of 4 c

adaptation of a flow through leaching procedure for mg ca paleothermometry 1 mg ca ratios in planktonic foraminifera reflect calcification temperatures and are thus useful for sea surface temperature sst reconstructions despite the obvious utility of this paleoceanographic tracer problems of dissolution gametogenic calcification and contaminant phases have thus far limited confidence in mg ca based reconstructions here we show strong evidence of mg heterogeneity in foraminiferal calcite by sequentially measuring the composition of different forms of calcite ontogenetic gametogenic diagenetic in the same shells while monitoring and removing contaminant phases a new flow through method combines chromatographic technology and inductively coupled plasma mass spectrometry icp ms in a series of cleaning and dissolution reactions monitored continuously with time resolved analysis tra this combination of slow controlled dissolution and tra provides a complete elemental description of contaminant phases and sorts the cleaned calcium carbonate based on dissolution sensitivity examination of partially dissolved shells with electron microscopy suggests that the flow through method simulates the natural dissolution sequence and effectively separates the different calcite domains within a single foraminiferal shell heterogeneity of mg ca in foraminiferal calcite is clearly demonstrated in flow through analysis foraminiferal shells have initially high mg levels that decrease steadily throughout dissolution later dissolution yields lower mg ca which is likely due to a combination of subsurface calcification and biomineralization effects mg ca ratios from the most dissolution sensitive high mg portions of surface dwelling species in core tops are used to calculate calcification temperatures a comparison of late holocene core top data with world ocean atlas sst data indicates that the flow through method does yield viable sst estimates furthermore a depth transect in the eastern tropical pacific suggests that this approach provides the opportunity to extract initial calcification temperatures despite partial dissolution of foraminiferal shells

an intensity ratio calibration method for the accurate determination of mg ca and sr ca of marine carbonates by icp aes an inductively coupled plasma atomic emission spectroscopy icp aes method for the accurate and precise simultaneous measurement of the mg ca and sr ca content of carbonates was established while a precision of 0 3 1 standard deviation sd is easily obtainable for both mg ca and sr ca analysis a ca matrix effect complicates achieving similar levels of accuracy with conventional calibration procedures an alternative ratio calibration procedure is proposed which overcomes the ca matrix effects and ensures the accuracy of the mg ca and sr ca analysis of marine carbonates to 0 3 almost an order of magnitude better than conventional calibration methods the longer term precision is 0 1 if the batch run average values are corrected for longer term drift the method is suitable for analysis of foraminiferal calcite and coral aragonite and can easily be adjusted for the analysis of other carbonates or microsamples

rapid analysis of high precision sr ca ratios in corals and other marine carbonates a method for rapid determination of high precision sr ca ratios in scleractinian corals is presented using an inductively coupled plasma atomic emission spectrophotometer samples are corrected for instrument drift using a reference solution similar to the approach used for analysis of stable isotopes using gas source mass spectrometry further correction for variation of the sr ca ratio with ca concentration is accomplished using internal standards the precision once all corrections have been made is better than 0 1 relative standard deviation 1 for samples of similar ca concentration and better than 0 2 for samples with variable ca concentrations this method increases the sample throughput by approximately a factor of 20 relative to thermal ionization mass spectrometry and significantly reduces instrument and per sample costs comparison of sr ca data for a coral from the galapagos islands with an instrumental temperature record shows excellent agreement and demonstrates the potential for application of this technique to samples of modern and fossil scleractinian corals and other marine carbonates including foraminifera

further constraints on the diagenetic influences and salinity effect on globigerinoides ruber white mg ca thermometry implications in the mediterranean sea we analyzed mg ca ratios of the planktonic species globigerinoides ruber white picked from 49 box core samples covering the whole mediterranean sea and 2 core tops from the atlantic ocean over the entire data set we found no significant correlation between mg ca and 18o derived calcification temperatures this lack of correlation is chiefly due to the presence of an early diagenetic mg rich calcite coating which can constitute up to 20 of the total shell calcite in the central and eastern mediterranean basin and result in anomalously high mg ca values and a high scattering in the western mediterranean sea however g ruber mg ca scattering shows smaller amplitude and mg rich calcite remains under the xrd detection limit sem observations indicate that only a few samples are affected by trace amounts of post mortem calcite overgrowths most of this calcite being likely removed during the chemical cleaning for mg ca analyses using core top sediments from the western mediterranean sea we performed an empirical calibration exercise which confirms that g ruber mg ca is not only related to temperature but it is also significantly affected by sea surface salinity this salinity effect is not specific to high salinity environments such as the mediterranean sea since it appears to be coherent with recent results obtained on indo pacific and atlantic surface sediments which suggest that a 1 psu change in sss results in a 1 7 c mg ca temperature bias this sensitivity to salinity is significantly higher than those deduced from culture experiments

composition and timing of carbonate vein precipitation within the igneous basement of the early cretaceous shatsky rise nw pacific numerous calcium carbonate veins were recovered from the igneous basement of the early cretaceous shatsky rise during integrated ocean drilling program iodp expedition 324 the chemical sr ca mg ca and isotopic 87sr 86sr 143nd 144nd 18o 13c compositions of these veins were determined to constrain the timing of vein formation a dominant control by seawater chemistry on calcite composition is evident for most vein samples with variable contributions fromthe basaltic basement slightly elevated precipitation temperatures as inferred from oxygen isotope ratios indicative of hydrothermal vein formation are only observed at site u1350 in the central part of shatsky rise the highest 87sr 86sr ratios least basement influence of vein samples at each drill site range from 0 70726 to 0 70755 and are believed to reflect the contemporaneous seawater composition during the time of calcite precipitation in principle age information can be deduced by correlating these ratios with the global seawater sr isotope evolution since the sr isotopic composition of seawater has fluctuated three times between the early and mid cretaceous no unambiguous precipitation ages can be constrained by this method and vein precipitation could have occurred at any time between 80 and 140 ma however based on combined chemical and isotopic data and correlations of vein compositionwith formation depth and inferred temperature we argue for a rather early precipitation of the veins shortly after basement formation at each respective drill site

detection of silica mediated dissolution of magnetic grains in sediments using forc diagrams 1 recently silica mediated dissolution has been recognized as a potentially important factor influencing magnetic studies of marine and lacustrine sediments although direct evidence for the dissolution of magnetic particles in silica rich environments is lacking the process is expected to produce changes in the magnetic grain size distribution a hypothesis that is tested in this study on sediments from lake tanganyika east africa using first order reversal curves forcs results from different magnetic intensity zones within the studied samples clearly show changes in the grain size distribution of magnetic minerals in particular zones with high biogenic silica content bsi correlated with depletion in fine grained magnetic material whereas zones with lower bsi showed no depletion these results are consistent with the idea that silica mediated dissolution results in the preferential removal of fine grained magnetic material and indicate that forc diagrams are effective in characterizing silica mediated dissolution in sediments

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

environmental magnetism of pleistocene sediments in the north pacific and ontong java plateau temporal variations of detrital and biogenic components 1 an environmental magnetic study was conducted to investigate temporal variations of the sources of magnetic minerals in the pacific ocean using sediment cores of pleistocene age the proportion of interacting i to noninteracting n i single domain components was estimated from first order reversal curve diagrams and the proportion of middle m to low l coercivity components was determined from decomposition of isothermal remanent magnetization irm acquisition curves the i and m components are interpreted to be carried by terrigenous maghemite while the n i and l components represent biogenic magnetite an inverse correlation between the ratio of anhysteretic remanent magnetization susceptibility arm to saturation irm sirm and the i n i ratio was confirmed for sediments across wide expanses in the pacific ocean this implies that arm sirm can be used to estimate the relative abundances of biogenic and terrigenous components in sediments in the north pacific the relative abundance of the i and m components increases in glacial periods variations of arm sirm and s ratio s 0 1t resemble each other and decrease in the same time intervals these variations reflect increases of terrigenous input in glacial periods as eolian dust on the ontong java plateau in the western equatorial pacific on the other hand minima in arm sirm and s 0 1t occur at glacial to interglacial transitions and the relative abundance of the i and m components increases in these periods terrigenous material in this region is considered to be transported mainly from the new guinea and solomon islands by the equatorial undercurrent the higher proportion of the terrigenous component at glacial to interglacial transitions is coeval with carbonate preservation maxima reported from the ontong java plateau suggesting a linkage between the two

magnetic mineral diagenesis abstract reduction oxidation redox reactions occur during burial because sediments contain reactive mixtures of oxidised and reduced components diagenetic chemical reactions represent the approach of all sedimentary components toward equilibrium and control the long term stability of sedimentary iron bearing minerals magnetic minerals are sensitive indicators of sedimentary redox conditions and of changes in these conditions through time with diagenetic effects ranging from subtle to pervasive despite the importance of magnetic mineral diagenesis in paleomagnetism rock magnetism and environmental magnetism and the usefulness of these subjects in the earth and environmental sciences there is no systematic single published treatment of magnetic mineral diagenesis this paper is an attempt to provide such a treatment for the full range of diagenetic environments magnetic mineral diagenesis during early burial is driven largely by chemical changes associated with organic matter degradation in a succession of environments that range from oxic to nitrogenous to manganiferous to ferruginous to sulphidic to methanic where the free energy yielded by different oxidants decreases progressively in each environment in oxic environments the most important diagenetic processes involve surface oxidation of detrital minerals and precipitation of fe3 bearing minerals from solution in ferruginous environments the most reactive detrital and authigenic iron oxides undergo dissolution often mediated by dissimilatory iron reducing bacteria which releases fe2 that becomes available for other reactions the fe2 in solution can diffuse upward where it is oxidised to form new authigenic iron oxyhydr oxide minerals or it can become bioavailable to enable magnetotactic bacteria to biomineralise magnetite generally at the base of the overlying nitrogenous zone alternatively dissimilatory iron reducing bacteria can produce extracellular magnetite within ferruginous environments in sulphidic environments iron bearing detrital mineral assemblages undergo more radical alteration hydrogen sulphide which is a byproduct of bacterial sulphate reduction or of anaerobic oxidation of methane reacts with the fe2 released from iron mineral dissolution or directly with solid iron oxyhydr oxide minerals to form iron sulphide minerals mackinawite greigite and pyrite authigenic growth of ferrimagnetic greigite has important implications for paleomagnetic recording secondary iron sulphide formation can also occur as a result of anaerobic oxidation of methane methane migration through sediments in association with biogenic or thermogenic methane production or in association with gas hydrate dissociation can disrupt the diagenetic steady state and give rise to greigite and monoclinic pyrrhotite formation that remagnetises sediments most of the above described diagenetic processes occur below 50 c with continuing burial above 50 c but at sub metamorphic temperatures magnetic minerals can undergo further thermally induced chemical changes that give rise to a wide range of mineralogical transformations that affect the magnetic record of the host sediment these changes include remagnetisations magnetic analysis can provide much valuable information concerning diagenesis in environmental processes the range of processes discussed in this paper should assist researchers in analysing sediment magnetic properties for which the assessment of diagenetic effects has become a necessary component

mg ca variation in planktonic foraminifera tests implications for reconstructing palaeo seawater temperature and habitat migration the nature of compositional variability within the tiny calcitic shells tests that are precipitated by planktonic foraminifera has been investigated using laser ablation inductively coupled plasma mass spectrometry la icp ms systematic large and correlated variation of mg ca mn ca ba ca and zn ca but relatively uniform sr ca are observed through the test walls of analysed species globigerinoides sacculifer globigerinoides ruber neogloboquadrina pachyderma and neogloboquadrina dutertrei distinct chamber and chamber wall layer compositions can be resolved within individual tests and mg ca compositional differences observed in sequentially precipitated test components of the different species analysed are consistent with seawater temperature changes occurring with habitat migration during their adult life cycle stages estimated test calcification temperatures are in keeping with available seawater temperature constraints indicating the potential for accurate seawater temperature reconstruction using la icp ms mg rich 1 6 mol mg surface veneers that are also enriched in mn ba and zn have been found on all species and all fossil tests as well as on live sampled tests of g ruber with the latter suggesting a possible biogenic origin these mg rich surfaces bias bulk test compositions toward higher mg ca values by between 5 and 35

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

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

magnetite dissolution in siliceous sediments 1 magnetite dissolution and consequent loss of magnetization is widely observed in reducing sedimentary environments where the decrease in eh ph values with depth is driven by bacterially mediated degradation of organic carbon we have observed low magnetizations in sediments with elevated pore water silica concentrations that arise from diagenesis of biogenic silica and or silicic volcanic ash these depletions in magnetization are greater than can be accounted for by dilution with magnetite poor sediments and suggest that postdepositional destruction of magnetite has occurred biosiliceous sediments usually also contain elevated concentrations of organic carbon which makes it difficult to separate organic carbon related magnetite dissolution from other possible mechanisms for magnetite dissolution however the extent of magnetite dissolution in the sedimentary sequences that we have studied is not obviously related to the redox state of the environment this suggests that other mechanisms might have given rise to magnetite dissolution in these siliceous sediments thermodynamic calculations indicate that magnetite is unstable under conditions of elevated dissolved silica concentrations and appropriate eh ph conditions and predict that magnetite will break down to produce iron bearing smectite a survey of magnetic susceptibility and pore water geochemical data from widely distributed ocean drilling program sites supports this observed link between high dissolved silica concentrations and low magnetic susceptibilities this observed link also holds for environments with low biogenic silica productivity and low organic carbon content but with high interstitial silica concentrations due to dissolution of silicic volcanic ashes dissolution of magnetite is therefore predicted to be a common feature of siliceous sedimentary environments

paleolimnological evidence for the onset and termination of glacial aridity from lake tanganyika tropical east africa geochemical and sedimentological data in a continuous 60 000 year sediment core record from the kalya horst region of central lake tanganyika provide a detailed history of paleoclimate mediated weathering and overflow events from upstream lake kivu univariate elemental profiles bivariate elemental ratios and multivariate analyses of chemical trends show variations between the dry late pleistocene 32 18 ka cal yr bp and the wetter conditions that both preceded and post date that interval this record places important new constraints on the timing of aridity in east africa during the high latitude last glacial maximum lgm based on significant decreases in magnetic susceptibility and soluble cation concentrations coinciding with biogenic silica elemental indicatorsintheoldestportionofthesedimentaryrecord 60 50kacalyrbp characterizethisintervalasacomparatively wetperiod similar to modern conditions our record demonstrates that the ensuing transition toward arid conditions in tropical africa during high latitude glaciation was a two staged event with intermediate levels of aridity occurring from 50 32 ka cal yr bp followed by intense aridity from 32 18 ka cal yr bp the initiation of inflow from upstream lake kivu into lake tanganyika is evidenced at 10 6 ka cal yr bp through its influence on both elemental profiles mg ca and through its effect on 87 sr 86 sr increases in elemental mg ca sr concentrations coincide with the timing of the lake kivu overflow metal geochemistry suggests that the overflow from lake kivu into lake tanganyika may have ceased between 8 and 6 ka cal yr bp suggesting a period of middle holocene aridity in east africa 2007 elsevier b v all rights reserved

the source of ions for biomineralization in foraminifera and their implications for paleoceanographic proxies the global carbon cycle is strongly perturbed by fossil fuel burning leading to atmospheric co2 increase climatic warming followed by polar ice melting and global sea level rise are predicted due to the greenhouse effect of increasing co2 in the atmosphere houghton et al 1995 the ocean plays a major role in neutralizing the excess co2 because the amount of inorganic carbon available for exchange with the atmosphere in the ocean is approximately 50 60 times larger than in the atmosphere e g siegenthaler and sarmiento 1993 the bulk of the atmospheric co2 excess will eventually be neutralized by caco3 dissolution in the deep marine environment this is however is a relatively slow process that operates on the time scale of ocean circulation 1000 yrs and is therefore causing an accumulation of co2 in the atmosphere this phenomenon will result in potentially severe consequences to the well being of global ecological systems obviously the scientific attention of many biogeochemists is focused on processes controlling the response of the marine system to changes in atmospheric co2 concentrations e g archer and maier reimer 1994 broecker 1997 sigman and boyle 2000 berger 2002 foraminifera corals and coccolithophores in the global carbon cycle there are four dominant processes involved in neutralizing the excess atmospheric co2 in the ocean these are 1 gas exchange at the air sea interface and reaction with the carbonate ion to form bicarbonate 2 net primary productivity 3 caco3 production and dissolution and 4 ocean circulation most of these processes are biologically mediated and may have special importance in shallow tropical environments where the exchange with the atmosphere is more direct in this review we address the mechanism of biomineralization in one of the major groups that precipitates caco3 in the ocean the foraminifera as we will show this group

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

recent warming of mountain permafrost in svalbard and scandinavia 1 three deep boreholes 100 m in mountain permafrost were recently drilled in svalbard janssonhaugen and in scandinavia tarfalaryggen and juvvasshoe for long term permafrost monitoring these holes form part of a latitudinal transect of boreholes in permafrost through europe established by the permafrost and climate in europe pace project six year thermal time series data collected from the three boreholes are presented these data provide the first opportunity for temporal trends in permafrost temperatures in svalbard and scandinavia to be analyzed results show that the permafrost has warmed considerably at all three sites significant warming is detectable down to at least 60 m depth and present decadal warming rates at the permafrost surface are on the order of 0 04 0 07 c yr 1 with greatest warming in svalbard and in northern scandinavia the present regional trend shows accelerated warming during the last decade

deep subpermafrost thermal regime in the mackenzie delta basin northern canada analysis from petroleum bottom hole temperature data in our studies of the thermal regime of sediments of the young mackenzie delta in the southeastern part of the beaufort mackenzie basin of northern canada we used thermal data from the base of the permafrost layer together with temperature data from petroleum wells by analyzing bottom hole temperature bht data we found that the percentage correction i e the percentage difference between bht and equilibrium temperature is less than 10 with 67 probability for times exceeding 10 hours after circulation ended regardless of circulation time no correlation exists between the percentage correction and depths for the bht data theoretical temperature depth profiles were constructed from the individual heat flow q q q and q q values q is error of estimate of q the interval thermal conductivities and a permafrost base temperature of 0 c estimates of q were based on the maximum bhts from depths 2 7 km the measured and corrected bht values for depths less than 1 5 km lie outside the rang

neogloboquadrina pachyderma dex and sin mg ca and δ18o records from the norwegian sea magnesium calcium mg ca records based on n pachyderma dex and n pachyderma sin from the last 1200 years have been retrieved from high resolution cores in the norwegian sea comparing temperatures inferred from mg ca and the oxygen isotopic composition of calcite 18oc with instrumental temperature records from ocean weather ship mike suggests that n pachyderma calcifies during the summer season with an offset to oxygen isotope equilibrium of 0 6 in this region summer temperatures below the thermocline are related to the winter season ventilation and breakdown of the seasonal thermocline hence the deeper dwelling n pachyderma sin provides a winter season signal down core n pachyderma dex mg ca temperatures display larger variance than observed in 18oc temperatures record derived from the same morphotype the smaller variance in the 18ocn pachyderma dex temperatures is probably linked to salinity changes in the upper 50 m of the water column the mg ca temperature and 18oc records are used to reconstruct changes in the oxygen isotopic composition of water 18ow during the last 1200 years the reconstructed 18ow records show variation within a realistic range allowing the influence of other water masses than those present at the site today and suggest that the mg ca signal in morphotypes of n pachyderma in the norwegian sea responds to changes in climatic parameters

reconstruction of mid to late holocene winter temperatures in the skagerrak region using benthic foraminiferal mg ca and δ18o reconstruction of skagerrak deep water renewal is used to assess regional changes in winter thermal conditions over the past 6800 years changes in winter climate conditions from the skagerrak region are in turn linked to shifts in holocene large scale atmospheric circulation patterns prevailing over northern europe we use melonis barleeanus mg ca from two sediment cores in the central skagerrak to reconstruct temperature of skagerrak intermediate water representing the warm season temperature variability and deep water for monitoring skagerrak deep water renewal reflecting the winter temperature variability in addition m barleeanus 18o is used from the deeper core to reconstruct salinity also monitoring the deep water renewal our results show that the skagerrak deep water experienced phases of particularly enhanced renewal during the mid holocene reflecting severe winter conditions followed by a general shift to reduced renewal as a consequence of milder winter conditions over the north sea a

millennial scale variability of deep water temperature and δ18odw indicating deep water source variations in the northeast atlantic 0 34 cal ka bp 1 paired measurements of mg ca and 18occ calcite 18o in benthic foraminifera from a deep sea core recovered on the iberian margin md99 2334k 37 48 n 10 10 w 3 146 m have been performed in parallel with planktonic 18occ analyses and counts of ice rafted debris ird the synchrony of temperature changes recorded in the greenland ice cores and in north atlantic planktonic 18occ allows the proxy records from md99 2334k to be placed confidently on the gisp2 time scale this correlation is further corroborated by ams 14c dates benthic mg ca measurements in md99 2334k permit the reconstruction of past deep water temperature tdw changes since 34 cal ka bp calendar kiloyears before present using these tdw estimates and parallel benthic 18occ measurements a record of deep water 18o 18odw has been calculated results indicate greatly reduced tdw in the deep northeast atlantic during the last glaciation until 15 cal ka bp when tdw warmed abruptly to near modern values in parallel with the onset of the bolling allerod interstadial subsequently tdw reverted to cold glacial values between 13 4 and 11 4 cal ka bp in parallel with the younger dryas cold reversal and the h0 ice rafting event similar millennial scale tdw changes also occurred during the last glaciation indeed throughout the last 34 cal ka millennial 18odw and tdw changes have remained well coupled and are linked with ird pulses coincident with heinrich events 3 2 1 and the younger dryas when transitions to lower tdw and 18odw conditions occurred in general millennial tdw and 18odw variations recorded in md99 2334k describe an alternation between colder low 18odw and warmer high 18odw conditions which suggests the changing local dominance of northern sourced north atlantic deep water nadw versus southern sourced antarctic bottom water aabw the observed similarity of the tdw and gisp2 18oice records would therefore suggest a common component of variability resulting from the coupling of nadw formation and greenland climate a link between greenland stadials and the incursion of cold low 18odw aabw in the deep northeast atlantic is thus implied which contributes to the relationship between greenland climate and the millennial benthic 18occ signal since 34 cal ka bp

influence of test size water depth and ecology on mg ca sr ca δ18o and δ13c in nine modern species of planktic foraminifers abstract mg ca palaeothermometry in foraminiferal calcite is a widely applied tool in palaeoceanography however our understanding of the effects of planktic foraminiferal ecology and early diagenesis on test calcite mg ca is limited here we report results of a study designed to shed new light on ecological size related and very early water column diagenetic controls on mg ca in planktic foraminiferal calcite we analysed mg ca and stable isotopes of nine modern planktic foraminiferal species across fourteen mostly 50 m window sieve fractions in a core top sample from the north atlantic ocean we also analysed mg ca in four of these nine species from plankton tow samples collected from 0 to 2500 m water depth in the north atlantic ocean and arabian sea our core top study confirms that sensitivity of mg ca to change in test size is species specific but reveals an overall decrease in mg ca with increasing test size in all but one species orbulina universa for which mg ca increases with size these findings are broadly consistent with known ecological behaviour suggesting that the size related signal is largely environmentally rather than calcification rate controlled our results underscore the need to undertake mg ca palaeothermometry on narrow size fractions of planktic foraminifers particularly for shallow dwelling species such as g bulloides and g ruber where mg ca is most sensitive to test size across the size range of 200 350 m our plankton tow data from the arabian sea are in agreement with in situ temperatures in contrast our data from the north atlantic ocean reveal large variability and marked offsets to warmer values from in situ temperatures that are interpreted to reflect lateral advection from the south storm induced vertical mixing of the water column and or the influence of surface water salinity on the mg ca signal none of our plankton tow mg ca data shows any evidence of test dissolution in the water column our study provides important verification that the mg ca signal recorded during calcification does not undergo diagenetic degradation during test transport to the sea floor thereby satisfying an important precondition of its palaeo proxy utility

climate impact of late quaternary equatorial pacific sea surface temperature variations magnesium calcium data from planktonic foraminifera in equatorial pacific sediment cores demonstrate that tropical pacific sea surface temperatures ssts were 2 8 0 7 c colder than the present at the last glacial maximum glacial interglacial temperature differences as great as 5 c are observed over the last 450 thousand years changes in sst coincide with changes in antarctic air temperature and precede changes in continental ice volume by about 3 thousand years suggesting that tropical cooling played a major role in driving ice age climate comparison of sst estimates from eastern and western sites indicates that the equatorial pacific zonal sst gradient was similar or somewhat larger during glacial episodes extraction of a salinity proxy from the magnesium calcium and oxygen isotope data indicates that transport of water vapor into the western pacific was enhanced during glacial episodes

effects of quaternary sea level cycles on strontium in seawater abstract the effects of quaternary sea level changes on the sr budget of the ocean are investigated using coupled numerical models of the seawater sr and ca budgets glacial interglacial sea level cycles influence the sr concentration of seawater directly through the periodic exposure and weathering of aragonite on continental shelves and indirectly by modulating the location and extent of carbonate deposition in the ocean as sea level recedes brief pulses of sr are added to the ocean from recrystallization of shelf aragonite this flux at its maximum is nearly ten times larger than the combined riverine and hydrothermal influx the large shelf recrystallization fluxes during glacial maxima produce rapid increases in the sr ca ratio of seawater despite the long residence time of sr in the ocean variations in the ratio of aragonitic vs calcitic sedimentation also influence on the sr content of seawater because the sr partitioning coefficient is higher in aragonite however this effect is minor compared to shelf aragonite recrystallization based on a variety of sensitivity tests the amplitude of sr ca variations ranges from 1 to 3 and is maximized by constant rates of total carbonate deposition extensive aragonite recrystallization and carbonate budgets which include dissolution of shelf carbonates such variation is sufficient to produce up to 1 5 c errors in paleotemperatures calculated from coral sr ca ratios since the last glacial maximum

assessing influence of diagenetic carbonate dissolution on planktonic foraminiferal mg ca in the southeastern arabian sea over the past 450 ka comparison between globigerinoides ruber and globigerinoides sacculifer 1 the influence of supralysoclinal calcite dissolution on the mg ca thermometer over the last 450 ka is assessed using globigerinoides ruber and globigerinoides sacculifer from a core site in the eastern arabian sea the studied site is characterized by precession cycled paleoproductivity changes that have induced calcite dissolution in the sediments although the core still contains 40 80 caco3 during high productivity periods the narrow sized test weights of both foraminiferal species tend to decrease with increasing mn ca ratio indicating corrosive pore water conditions scanning electron microscope observations show that g sacculifer maintains a better preserved test ultrastructure than g ruber microprobe mapping reveals that mg rich bands in g ruber chamber walls are preserved despite reduced ca content assuming that the low test weight and offset in mg ca temperature between g sacculifer and g ruber are exclusively produced by calcite dissolution the bias in mg ca temperature determination can be estimated at around 1 c comparable to uncertainty of this thermometry despite the evidence for test dissolution foraminiferal mg ca seems to preserve initial temperature signals under the studied conditions

benthic foraminiferal mg ca paleothermometry a revised core top calibration core top samples from different ocean basins have been analyzed to refine our current understanding of the sensitivity of benthic foraminiferal calcite magnesium calcium mg ca to bottom water temperatures bwt benthic foraminifera collected from hawaii little bahama bank sea of okhotsk gulf of california ne atlantic ceara rise sierra leone rise the ontong java plateau and the southern ocean covering a temperature range of 0 8 to 18 c were used to revise the cibicidoides mg ca temperature calibration the mg ca bwt relationship of three common cibicidoides species is described by an exponential equation mg ca 0 867 0 049 exp 0 109 0 007 bwt stated errors are 95 ci the temperature sensitivity is very similar to a previously published calibration however the revised calibration has a significantly different preexponential constant resulting in different predicted absolute temperatures we attribute this difference in the preexponential constant to an analytical issue of accuracy some genera notably uvigerina show apparently lower temperature sensitivity than others suggesting that the use of constant offsets to account for vital effects in mg ca may not be appropriate downcore mg ca reproducibility as determined on replicate foraminiferal samples is typically better than 0 1 mmol mol 1 2 s e thus considering the errors associated with the cibicidoides calibration and the downcore reproducibility bwt may be estimated to within 1 c application of the revised core top mg ca bwt data to cenozoic foraminiferal mg ca suggests that seawater mg ca was not more than 35 lower than today in the ice free ocean at 50 ma

variation of foraminiferal sr ca over quaternary glacial interglacial cycles evidence for changes in mean ocean sr ca 1 records of sr ca changes in planktonic and benthic foraminifera from diverse hydrographic settings reveal coherent variability 5 1 between ocean basins and between surface and deep waters over the past 300 kyr there is a general increase in foraminiferal sr ca over the penultimate glaciation declining to minimum values during stage 5 and an increase in sr ca from stage 5 through stage 2 coincident changes in benthic foraminifera records from the atlantic and pacific basins imply that sr ca variations are not dominated by dissolution planktonic culturing data provide evidence that the downcore sr ca variations are not controlled by temperature changes and suggest only a small influence of salinity and ph variation common to the records is most readily explained by changes in mean ocean sr ca if fossil foraminifera reliably record higher glacial seawater sr ca coral sr paleothermometry would underestimate sea surface temperature during glacialepisodes

diagenetic mg rich calcite in mediterranean sediments quantification and impact on foraminiferal mg ca thermometry abstract mg ca ratios in planktonic foraminifera have been developed into a powerful tool in paleoceanography to reconstruct past sea surface temperatures sst however additional factors that might have an influence on mg ca like dissolution salinity diagenesis and carbonate ion effects have come into focus in this paper the occurrence of diagenetic calcification and its potential effects on mg ca have been studied using 20 well preserved core tops recovered from the mediterranean sea analyses were performed on two planktonic foraminifer species globigerinoides ruber and globigerina bulloides using icp aes mg ca measurements sem observations and x ray diffractometry analyses foraminiferal mg ca values are higher than those obtained in the open sea the highest values were found in the eastern mediterranean basin these anomalies cannot be simply explained by a salinity effect because mg ca ratios when corrected for temperature influence do not display any significant correlation with salinity our results seem to indicate that diagenesis can account for anomalously high mg ca values indeed sem observations show aggregates of rhombohedral crystals that could be interpreted as secondary calcite overgrowths we note also the occurrence of numerous coccoliths trapped in foraminifer walls and covered with a secondary mineral phase x ray diffraction diagrams of numerous foraminiferal samples exhibit peak of mg rich calcite 10 12 associated with the usual foraminifer calcite peak it has been demonstrated that this calcite highly rich in mg is compatible with an inorganic calcite precipitated directly from seawater the deconvolution of the main xrd peak 104 shows that the percentage of mg rich calcite can reach up to 21 of the total foraminiferal calcite in the eastern basin whereas in the western mediterranean sea proportions do not exceed 5 in addition we demonstrate that the diagenetic process is very heterogeneous even at the sample scale and is not simply a reflection of co 3 at the sea bottom thus the high mg ca ratios measured from mediterranean sea planktonic foraminifera does not appear to be caused by increased mg uptake in a high salinity setting but instead result chiefly from the presence of mg rich calcite 10 12 deposited during early diagenetic processes

repeat temperature measurements in borehole gc 1 northwestern utah towards isolating a climate change signal in borehole temperature profiles temperature depth profiles in borehole gc 1 northwestern utah were measured in 1978 1990 and 1992 borehole temperatures below 80 m depth are highly reproducible over the 14 year period indicating long term thermal stability a slowly changing temperature field above 80 m depth has similiar characteristics to synthetic temperature profiles computed from a 100 year record of air temperature changes at park valley weather station 50 km northeast of the borehole site

paleomagnetic secular variation records from holocene sediments of lake victoria 0 5 s 33 3 e we have conducted a paleomagnetic study of holocene sediments from lake victoria in order to develop a high resolution record of paleomagnetic secular variation psv this study has recovered psv

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

precise temperature monitoring in boreholes evidence for oscillatory convection part 1 experiments and field data temperature was monitored in two boreholes in kamchatka russia in years 2001 2003 ten min reading sampling interval was selected for the first half year run followed by shorter 12 days experiment with 5 s reading interval a similar experiment was repeated later in the test borehole sporilov prague czech republic where four temperature time series were performed with reading intervals varying from 1 to 20 s all temperature time series except the record from the bottom of the hole displayed intermittent non periodic oscillations of temperature of up to several hundredths of degree with sharp gradients and large fluctuations over all observed time intervals no such oscillation was detected at the bottom of the hole the spectral analysis revealed a high level of stochasticity in the measured signal calculated spectra showed band pass behavior without any definite peaks which might characterize certain periodicity local growth of the second moment technique revealed the presence of at least two distinct temperature forming processes one of them can be related to heat transfer in the structurally and compositionally complex subsurface the second process which presents the bulk of the measured signal probably reflects certain intra hole convection we hypothesized that the oscillatory regime of such convection is responsible for the stochastic nature of measured temperatures results of numerical modeling describing the fluctuation of water cells in a vertical slot support the idea of thermally unstable water column in a hole the instability of which produces a complex oscillation system model solutions and their discussion is presented in part ii of this work

biogeochemical controls on palaeoceanographic environmental proxies a review scientific observations of our oceans and climate go back no more than a couple of hundred years most of our information about the evolution of earth s ocean climate system relies instead on proxies primarily measurements of sediment components that respond to changes in environmental parameters this paper provides an overview of some of the most important biological and geochemical proxies and outlines their contribution to our understanding of the ocean climate system we also discuss some of the challenges that need to be overcome to obtain accurate records these include better understanding of the controls on the mechanisms of biomineralization the impacts of post depositional dissolution and diagenesis on primary proxy relationships proxy validation and analytical considerations

full vector paleomagnetic secular variation records from latest quaternary sediments of lake malawi 10 0 s 34 3 e abstract we have conducted a paleomagnetic study of late quaternary sediments from lake malawi east africa in order to develop a high resolution record of paleomagnetic secular variation psv this study has recovered psv records from two cores 3p 6p in northern lake malawi 10 0 s 34 3 e the psv appears to be recorded in fine grained detrital magnetite titanomagnetite grains detailed af demagnetization of the natural remanence nrm shows that a distinctive characteristic remanence chrm is demagnetized from 20 to 80 mt which decreases simply toward the origin the resulting directional psv records for 3p and 6p are easily correlatable with 29 distinct inclination features and 29 declination features the statistical character of the psv in both cores is consistent with holocene psv noted at other holocene equatorial sites radiocarbon dating of the cores is based on 18 independent radiocarbon dates and four dated stratigraphic horizons that can be correlated into each core the final directional psv time series cover the last 24 000 years with an average sediment accumulation rate of 30 cm kyr we have also developed a relative paleointensity estimate for these psv records based on normalizing the nrm after 20 mt af demagnetization by the sirm after 20 mt af demagnetization changing sedimentation patterns complicate any attempt to develop a single paleointensity record for the entire core lengths we have developed a relative paleointensity record for the last 6000 years that has 14 correlatable features including 5 notable peaks in intensity three of these peaks are synchronous with paleointensity highs farther north in se europe sw asia egypt but two of the peaks are at times of low paleointensity farther north we interpret this to indicate that lake malawi 10 s is at least partly under the influence of a different flux regeneration region of the outer core dynamo a relative paleointensity record was also developed for 11 000 24 000 ybp the general pattern appears to be consistent with other published records but our confidence in the correlations is more limited

magnesium and strontium compositions of recent benthic foraminifera from the coral sea australia and prydz bay antarctica analyses of the mg ca and sr ca ratios of the modern benthic foraminifera cibicides wuellerstorfi epifaunal and uvigerina species infaunal from the coral sea and cibicides refulgens epifaunal and trifarina angulosa infaunal from prydz bay antarctica revealed relationships with temperature that have possible applications for reconstructions of bottom water paleotemperatures a positive relationship exists between the mg ca and sr ca ratios of cibicides wuellerstorfi and cibicides refulgens and ambient temperatures at least within the range of 2 and 6 c for the correlation between mg ca compositions and temperature the r2 values range from 0 78 c wuellerstorfi alone to 0 88 c wuellerstorfi and c refulgens together at present the mg ca temperature relationship must be regarded as tentative because of significant overlap of standard error values the relationship between the sr ca compositions of c wuellerstorfi and bottom water temperature yields an r2 value of 0 95 these results indicate that sr ca and possibly mg ca ratios of cibicides wuellerstorfi may provide useful information for the assessment of paleotemperature single species data are presently insufficient to assess the influence of ambient temperature on trace element compositions of uvigerina species trifarina angulosa may have mg ca compositions which are positively related to temperature but sr ca values seem unaffected by temperature this may be due to pore water influences on infaunal tests or to vital effects although more modern data are needed our present results suggest that sr ca ratios and possibly mg ca ratios of some benthic foraminifera have the potential to be useful paleothermometers at least within a temperature range of 2 to 6 c

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

diagenesis of magnetic minerals in recent haemipelagic sediments rapidly deposited sediments from marine and lake environments are being used increasingly to study decadal to millennial fluctuations in the earth s magnetic field the objectives are to gain more fundamental understanding of the geodynamo and to establish a new dating technique for sediments while lacustrine sections are generally restricted to temperate latitude glacial lakes 20 000 yr old rapidly deposited marine sediments along continental margins potentially offer continuous high resolution yet long term records of geomagnetic secular variation however to interpret the sedimentary magnetic record accurately geochemical processes that affect the reliability of the magnetic signal must be understood we now report downcore magnetic profiles from undisturbed kasten cores taken in rapidly deposited laminated sediments from the gulf of california and in bioturbated haemipelagic muds on the oregon continental slope which give apparently reliable directions but show dramatic decreases in the intensities of natural nrm and artificial arm irm remanences with depth downcore porewater and solid sulphur analyses show concave down decreases in porewater sulphate and systematic increases in pyrite and metastable monosulphides the maximum curvature of the sulphide profile occurs directly below the high magnetization zone combined with other compositional and mineralogical analyses these data suggest that due to oxidative decomposition of organic matter magnetites and other iron oxides become progressively reduced and subsequently sulphidized and pyritized with depth iron reduction seems to occur before sulphide formation changes in magnetic stability parameters are consistent with selective dissolution of the finer sized grains causing downcore coarsening of the magnetic fraction

imprints of high salinity water plumes originating from the red sea during termination ii abstract the investigation of a core collected in the socotran area western indian ocean provides new insights into water mass exchanges between the red sea and the gulf of aden through the strait of bab el mandeb during the penultimate deglaciation the benthic oxygen isotope record documents the occurrence of stillstands and possibly reversals within the general trend of sea level rise plumes of warm and salty waters are recorded at the surface of the arabian sea and as far as the socotran coast for each increase in sea level these plumes disappeared whenever global sea level stopped rising or showed a brief lowering according to their high salinities these plumes can only originate in the red sea the sill of bab el mandeb becoming deeper and wider during the deglaciation allowed greater exchange between both seas and stronger flow out of the red sea at each episode of sea level rise isotopic and faunal evidence suggest a strengthening of coastal upwelling in the arabian sea during these periods this increase in upwelling activity may explain how plumes of highly saline waters were maintained at the surface moreover the high salinity surface plumes may have facilitated upwelling activity through the destabilisation of density stratification in the upper water column the occurrence of at least high salinity salty water outflows during termination ii confirms the step wise non linear structure of the penultimate deglaciation providing a perfect example of the threshold concept in rapid climate changes

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

return to thermal equilibrium of an intermittently drilled hole theory and experiment abstract in 1992 a 150 m deep borehole was drilled in ordovician shales in prague drilling lasted 1 month and was interrupted by frequent stoppages temperature recovery after drilling was observed until equilibrium was reached the maximum temperature disturbance in the upper part of the hole was 0 6 c 2 days after drilling and the temperature gradient was reduced to 14 1 mk m 1 at that time 17 8 0 6 mk m 1 in equilibrium to be able to appreciate the effect of stoppages in drilling the horner plot method was modified so that the discontinuity of drilling was respected it was demonstrated theoretically on two examples that neglect of discontinuity of the drilling might result in an error if the temperature undisturbed by drilling is estimated from non equilibrium temperature logs the horner plot method and the modified approach were applied to the non equilibrium temperature data estimates of the equilibrium temperature in the borehole were calculated and compared with the true measured equilibrium temperature if discontinuity of drilling was taken into account the deviation of the estimates from the equilibrium temperature was reduced more than twofold to less than 0 06 c in comparison with the horner plot method and the least squares temperature gradient determined from the estimates differed from the equilibrium gradient by less than its standar error we may conclude that the suggested method which includes the effect of discontinuous drilling and which was tested on measured data considerably improved the results in comparison with the horner plot technique

progressive dissolution of titanomagnetites at odp site 653 tyrrhenian sea abstract magnetic properties microscopy and ferrous ferric iron ratio document increasing down core alteration of titanomagnetite to iron sulfide at odp site 653 leg 107 tyrrhenian sea changes in magnetic properties are interpreted to indicate a grain size increase in titanomagnetite to 40 m below seafloor bsf and a grain size decrease from this level to about 150 m bsf as dissolution affects first the fine grained and then the coarser grained magnetite the availability of dissolved sulfate from underlying messinian evaporites may account for the sulfide supply at depth and hence for the prolonged dissolution process dissolution at leg 107 sites adjacent to site 653 is less pronounced possibly by the availability of organic matter that can be metabolised by sulfate reducing bacteria