early marine diagenesis of biogenic aragonite and mg calcite new constraints from high resolution stem and aem analyses of modern platform carbonates prior studies of porewater compositions from modern shallow marine carbonates have established that dissolution and recrystallization of metastable aragonite and mg calcites occur during the earliest stages of sedimentation yet significant microstructural and mineralogical changes in sediment allochems have not been observed in part this is due to the high resolution required to identify diagenetic changes in these finely crystalline materials herein we present ultrastructural and microgeochemical evidence for early marine diagenesis using scanning electron microscopy sem and high resolution scanning transmission analytical electron microscopy stem aem methods to characterize original biogenic materials and sediment boxcores from modern deposits on the floridan bahamas platform we selected the two most common sediment producers a mg calcite foraminifer peneropolid and an aragonitic green algae halimeda for study both are composed of submicron sized crystallites whose excess free energy could provide a thermodynamic driving force for recrystallization stem observations of grain mounts containing dispersed mg calcite and aragonite crystallites from gently disaggregated individual peneropolids and halimeda segments indicate that living specimens contain euhedral prismatic crystals with blunt terminations and smooth faces specimens from the sediment column show abundant evidence for alteration the most dramatic changes involve crystallite dissolution and precipitation of thin overgrowths causing the overall aspect ratio of crystallites to shorten and widen direct measurements of several hundred individual crystallites confirm that crystallite length and width distributions differ significantly between original and altered materials these changes are consistent with crystal growth processes that tend to minimize surface free energy by increasing overall crystal size and by producing more equant shape the precipitated material has a composition and structure which is grossly similar to the host crystallite as determined by aem and electron diffraction analyses aem analyses of hundreds of mg calcite crystallites from living specimens of peneropolid foraminifera indicate a composition of 13 14 mol mgco3 whereas crystallites from altered tests are 1 3 mole lower taken together these data suggest that early diagenesis in shallow marine carbonates is indeed manifested in the solids as well as the sediment pore waters producing significant changes in biogenic mg calcite and aragonite crystallite size and shape this alteration would not produce changes in the mineral assemblage because dissolution is accompanied by precipitation of compositionally similar overgrowths under major element conditions not drastically dissimilar from overlying seawater however crystallite recrystallization likely has implications for incorporation of minor elements which undergo cycling via organic matter decomposition or redox changes e g uranium cadmium manganese rare earth elements

tropical sea surface temperature reconstruction for the early paleogene using mg ca ratios of planktonic foraminifera 1 to understand the climate dynamics of hypothesized past greenhouse intervals it is essential to constrain tropical sea surface temperatures sst yet existing proxy records give conflicting results here we present the first mg ca based study of pre quaternary sst and investigate early paleogene late paleocene through late middle eocene 58 6 39 8 ma tropical temperatures using planktonic foraminifera belonging to the genus morozovella from ocean drilling program site 865 on allison guyot western central equatorial pacific ocean calcification temperatures similar to or warmer than modern tropical sst are calculated using a range of assumptions regarding diagenesis temperature calibration and seawater mg ca long term warming is observed into the early eocene 54 8 49 0 ma with peak sst between 51 and 48 ma and rapid cooling of 4 c beginning at 48 ma these findings are inconsistent with the 18o based sst previously estimated for this site

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

el cuchillo seismic sequence of october 2013 july 2014 in the burgos basin northeastern mexico hydraulic fracturing or reservoir induced seismicity

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

biogeography of neogene calcareous nannofossils in the caribbean and the eastern equatorial pacific floral response to the emergence of the isthmus of panama abstract principal components analysis of nannofossil assemblages in five odp sites in the caribbean and the eastern equatorial pacific was used to monitor neogene surface water circulation changes in 15 83 10 71 ma floral distributions clearly show the existence of the circum tropical current between the caribbean and the eastern equatorial pacific and no surface water communication between the northern and southern caribbean in 10 71 9 36 ma the circum tropical current weakened and the northward intra caribbean current had been initiated northern and southern caribbean surface waters again became separated in 8 35 3 65 ma and the circum tropical current was regenerated after 2 76 ma the northward intra caribbean current has completely been established and the circum tropical current disappeared this suggests that a barrier to the circum tropical current had formed indicating the final closure of the isthmus of panama

application of benthic foraminiferal mg ca ratios to questions of cenozoic climate change abstract we investigate the evolution of cenozoic climate and ice volume as evidenced by the oxygen isotopic composition of seawater 18osw derived from benthic foraminiferal mg ca ratios to constrain the temperature effect contained in foraminiferal 18o values we have constructed two benthic foraminiferal mg ca records from intermediate water depth sites ocean drilling program sites 757 and 689 from the subtropical indian ocean and the weddell sea respectively together with the previously published composite record of lear et al science 287 2002 269 272 and the neogene record from the southern ocean of billups and schrag paleoceanography 17 2002 10 1029 2000pa000567 we obtain three almost complete representations of the 18osw for the past 52 myr we discuss the sensitivity of early cenozoic mg ca derived paleotemperatures and hence the 18osw to assumptions about seawater mg ca ratios we find that during the middle eocene 49 40 ma modern seawater ratios yield mg ca derived temperatures that are in good agreement with the oxygen isotope paleothermometer assuming ice free conditions intermediate waters cooled during the middle eocene reaching minimum temperatures by 40 ma the corresponding 18osw reconstructions support ice growth on antarctica beginning by at least 40 ma at the eocene oligocene boundary mg ca ratios and hence temperatures from weddell sea site 689 display a well defined maximum we caution against a paleoclimatic significance of this result and put forth that the partitioning coefficient of mg in benthic foraminifera may be sensitive to factors other than temperature throughout the remainder of the cenozoic the temporal variability among 18osw records is similar and similar to longer term trends in the benthic foraminiferal 18o record an exception occurs during the pliocene when 18osw minima in two of the three records suggest reductions in global ice volume that are not apparent in foraminiferal 18o records which provides a new perspective to the ongoing debate about the stability of the antarctic ice sheet maximum 18osw values recorded during the pleistocene at southern ocean site 747 agree well with values derived from the geochemistry of pore waters schrag et al science 272 1996 1930 1932 further highlighting the value of the new mg ca calibrations of martin et al earth planet sci lett 198 2002 193 209 and lear et al geochim cosmochim acta 66 2002 3375 3387 applied in this study we conclude that the application of foraminiferal mg ca ratios allows a refined view of cenozoic ice volume history despite uncertainties related to the geochemical cycling of mg and ca on long time scales

taking the temperature of past ocean surfaces accurate reconstructions of past climatic conditions on earth are important for modeling future climate change researchers use climate proxies from deep sea sediments corals or ice cores to reconstruct these past climatic conditions but as nurnberg explains in this perspective different techniques often give different answers a relatively new technique mg ca paleothermometry is a particularly promising tool especially in conjunction with oxygen isotope measurements on the same planktonic foraminiferal specimens the power of this method is exemplified by the study by lea et al

questioning carbonate diagenetic paradigms evidence from the neogene of the bahamas carbonate diagenetic models have been heavily influenced by numerous studies of exposed quaternary limestones as a result meteoric diagenesis is often assumed to be the principle means of altering aragonite rich sediments into calcitic limestones however these models are limited by the scarcity of examples of aragonite rich sediments buried in seawater that have never been influenced by meteoric fluids the bahamas transect cores recovered originally aragonite rich sediments deposited in deep water beyond the easy reach of meteoric waters and provide an opportunity to test current diagenetic paradigms the bahamas transect consists of seven cores drilled in the prograding western margin of great bahama bank the two proximal cores clino and unda were drilled on the platform top and recovered shallow water platform to reef facies overlying deeper margin and proximal slope facies the five distal cores were drilled by odp leg 166 in up to 660 m of water and recovered carbonate slope facies all studied sections are neogene to pleistocene in age diagenetic environments were identified based on petrographic and scanning electron microscopy sem observations xrd mineralogy carbon and oxygen stable isotopic data and trace elements the upper 100 150 m of the two proximal cores were altered in meteoric to mixing zone diagenetic environments but all other intervals were altered exclusively in marine pore fluids during seafloor marineburial and deep burial diagenesis several of the findings of this study question current carbonate diagenetic paradigms these include 1 large scale sea level lowstands may not have chemically active meteoric lenses as we found no meteoric alteration at the 3120 m elevation of the latest pleistocene lowstand rather phreatic meteoric diagenesis appears restricted to within w10 m of the land surface 2 mixing zone diagenesis includes aragonite dissolution and minor lmc cementation but does not show the cavernous porosity or dolomitization predicted by mixing zone diagenetic models current models are based on coastal mixing zones which do not appear to be applicable to these more inland and perhaps more typical locations 3 marine burial diagenesis produces a mature limestone with fabrics formerly considered diagnostic for meteoric diagenesis such as moldic porosity aragonite neomorphism blocky calcite spar and calcite microspar however oxygen stable isotopic data average n 18 o 1x indicate alteration in marine pore fluids only the character of marine burial diagenesis is partially controlled by the nature of the sediment being altered we have identified two end member styles an open system style characterized by dissolution of aragonite without significant cementation and a more closed system style with aragonite dissolution

paleo sea surface temperature calculations in the equatorial east atlantic from mg ca ratios in planktic foraminifera a comparison to sea surface temperature estimates from u37k oxygen isotopes and foraminiferal transfer function we present two 270 kyr paleo sea surface temperature sst records from the equatorial divergence and the south equatorial current derived from mg ca ratios in the planktic foraminifer globigerinoides sacculifer the present study suggests that the magnesium signature of g sacculifer provides a seasonal sst estimate from the upper 50 m of the water column generated during upwelling in austral low latitude fall winter common to both down core records is a glacial interglacial amplitude of 3 3 5 c for the last climatic changes and lower holocene and glacial oxygen isotope stage 2 temperatures compared with interglacial stage 5 5 and glacial stage 6 temperatures respectively the comparison to published sst estimates from alkenones oxygen isotopes and foraminiferal transfer function from the same core material pinpoints discrepancies and conformities between methods

accuracy standardization and interlaboratory calibration standards for foraminiferal mg ca thermometry the use of liquid and solid standards for foraminiferal mg ca and sr ca determinations and interlaboratory calibration has been investigated preparation of single element standard solutions from primary solid standard material enables the preparation of mixed standard solutions with mg ca and sr ca ratios of known accuracy to better than 0 1 we also investigated commercial reference materials to determine whether existing carbonate standards could be used as reference material for mg ca determinations in foraminiferal calcite we propose that in the absence of a pure calcium carbonate standard certified for mg ca ecrm 752 1 a limestone crm containing mg ca within the range of typical foraminifera is a suitable solid standard for interlaboratory calibration replicate mg ca determinations showed that provided silicate phases are removed by centrifugation this material is homogenous within the precision of daily instrumental mg ca determinations over a range of sample weights from 10 to 1000 mg taken from two separate bottles of ecrm 752 1 results gave an average value of mg ca 3 75 mmol mol 0 015 s d 0 41 r s d on 118 determinations from the two bottles

comparison of atlantic and pacific paleochemical records for the last 215 000 years changes in deep ocean circulation and chemical inventories abstract detailed cd ca and 13 c data have been obtained for benthic foraminifera from western north atlantic and equatorial pacific sediment cores in the modern ocean both tracers are closely linked to nutrient distributions the sedimentary records for both tracers indicate that bottom waters overlying the atlantic site have been nutrient depleted relative to those at the pacific site over the last 215 000 years from this evidence it is reasonable to infer that there has been a continuous net flux of nutrient depleted water from the western north atlantic into the pacific this exchange has undergone significant fluctuations with the export of nutrient depleted atlantic water diminishing by about a factor of two relative to the inflow from southern ocean sources over the last 215 000 years carbon isotope fluctuations in both regions are dominated by variable storage of isotopically light carbon on continents with a lesser contribution from these deep ocean circulation changes the cadmium signal in the north atlantic is dominated by changes in deep ocean circulation patterns cadmium shows less variability in the pacific which may reflect changes in the global average cadmium content or minor changes in deep pacific circulation patterns using these records to estimate global averages it appears that glacial ocean water had 22 more cd and 0 46 less 13 c than the modern ocean these numbers are estimates which may be revised as more data become available although they are not likely to be as much as 20 in error for cd or 0 2 for 13 c relative north atlantic deep water nadw formation rates are modulated with a significant 41 kyr periodicity linked to obliquity induced variations in high latitude insolation nadw lags 8 2 kyr behind insolation however

final closure of panama and the onset of northern hemisphere glaciation abstract the greenland ice sheet is accepted as a key factor controlling the quaternary glacial scenario however the origin and mechanisms of major arctic glaciation starting at 3 15 ma and culminating at 2 74 ma are still controversial for this phase of intense cooling ravelo et al 1 a c ravelo d h andreasen m lyle a o lyle m w wara regional climate shifts caused by gradual global cooling in the pliocene epoch nature 429 2004 263 267 proposed a complex gradual forcing mechanism in contrast our new submillennial scale paleoceanographic records from the pliocene north atlantic suggest a far more precise timing and forcing for the initiation of northern hemisphere glaciation nhg since it was linked to a 2 3 c surface water warming during warm stages from 2 95 to 2 82 ma these records support previous models g h haug r tiedemann effect of the formation of the isthmus of panama on atlantic ocean thermohaline circulation nature 393 1998 673 676 2 claiming that the final closure of the panama isthmus 3 0 2 5 ma j groeneveld s steph r tiedemann d nurnberg d garbe schonberg the final closure of the central american seaway geology in prep 3 induced an increased poleward salt and heat transport associated strengthening of north atlantic thermohaline circulation and in turn an intensified moisture supply to northern high latitudes resulted in the build up of nhg finally culminating in the great irreversible climate crash at marine isotope stage g6 2 74 ma in summary there was a two step threshold mechanism that marked the onset of nhg with glacial to interglacial cycles quasi persistent until today

middle pliocene sea surface temperatures a global reconstruction identification and analyses of pliocene marine microfossils from 64 globally distributed stratigraphic sequences have been used to produce a middle pliocene sea surface temperature reconstruction of the earth this reconstruction shows little or no change from current conditions in low latitude regions and significant warming of the ocean surface at mid and higher latitudes of both hemispheres this pattern of warming is consistent with terrestrial records and suggests a combination of enhanced meridional ocean heat transport and enhanced greenhouse effect were responsible for the middle pliocene warmth

precessional forcing of nutricline dynamics in the equatorial atlantic climate control of nutricline depth in the equatorial atlantic can be monitored by variations in the abundance of the phytoplankton species florisphaera profunda a conceptual model based on in situ evidence associates high abundances of f profunda with a deep nutricline and low abundances with a shallow nutricline a 200 000 year record of f profunda relative abundances obtained from a deep sea core sited beneath the region of maximum equatorial divergence at 10 w has 52 percent of its variance centered on the 23 000 year precessional band cross spectral analysis between the signals of f profunda and sea surface temperature independently derived from zooplankton species shows their 23 000 year cycles to be coherent and nearly in phase abundance minima of f profunda coincide with times of december perihelion whereas abundance maxima coincide with june perihelion these relations indicate that nutricline dynamics in the divergence region of the equatorial atlantic are controlled by variations in the tropical easterlies forced by the precessional component of orbital insolation on time scales greater than 10 000 years

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

permanent el nino like conditions during the pliocene warm period during the warm early pliocene 4 5 to 3 0 million years ago the most recent interval with a climate warmer than today the eastern pacific thermocline was deep and the average west to east sea surface temperature difference across the equatorial pacific was only 1 5 0 9 c much like it is during a modern el nino event thus the modern strong sea surface temperature gradient across the equatorial pacific is not a stable and permanent feature sustained el nino like conditions including relatively weak zonal atmospheric walker circulation could be a consequence of and play an important role in determining global warmth

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

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

calibration of the mg ca of globorotalia truncatulinoides r for the reconstruction of marine temperature gradients 1 recent work has provided useful mg ca to water temperature calibrations for shallow dwelling planktonic foraminifer species globorotalia truncatulinoides right coiling r is a deep dwelling species that can serve as a source of information about the temporal variability in the water characteristics of the thermocline we present a temperature calibration for the mg ca in the shell of g truncatulinoides r and examine some of the practical issues associated with evaluating the usefulness of the technique the mg ca in the primary and the secondary calcite of individual g truncatulinoides r correlates exponentially with water column temperatures showing a change of 10 in the mg ca per 1 c r2 0 92 a limited comparison with plankton tow samples demonstrates that the average mg ca temperature was offset 1 c from the average temperature calculated using the 18o calibration of o neil et al 1969 and the mg ca temperatures have a range similar to the 18o temperatures comparisons of the mg in the core top samples to water depth of deposition indicates that dissolution does not alter the measured value of mg in the primary calcite

new digital magnetic anomaly database for north america the geological survey of canada gsc u s geological survey usgs and consejo de recursos minerales of mexico crm are compiling an upgraded digital magnetic anomaly database and map for north america this tri national project expected to be completed by late 2002 will replace the magnetic anomaly map of north america constructed as part of the geological society of america s decade of north american geology dnag program the u s component of the dnag map consists of a digitized version of the first analog magnetic map for the u s produced by zietz 1982 the canadian part is based on a 2 km grid that covers 70 of the country s landmass unfortunately no mexican data were included in the dnag map

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

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

lithologic controls on calcite recrystallization in cenozoic deep sea sediments abstract interpretations of calcite strontium calcium records in terms of ocean history and calcite diagenesis require distinguishing the effects on deep sea calcite sediments of changes in ocean chemistry of different mixes of calcite depositing organisms as sediment contributors through time and space and of the loss of sr during diagenetic calcite recrystallization in this paper sr ca and 18 o values of bulk calcium carbonate sediments are used to estimate the relative extent of calcite recrystallization in samples from four time points core tops 5 6 9 4 and 37 1 ma at eight ocean drilling program sites in the equatorial atlantic ceara rise and equatorial pacific ontong java plateau and two eastern equatorial pacific sites the possibility that site to site differences in calcite sr ca at a given time point originated from temporal variations in ocean chemistry was eliminated by careful age control of samples for each time point with sample ages differing by less than the oceanic residence times of sr and ca the sr ca and 18 o values of 5 6 and 9 4 ma samples from the less carbonate rich eastern equatorial pacific sites and ceara rise site 929 appear to be less diagenetically altered than the sr ca and 18 o values of contemporaneous samples from the more carbonate rich sites it is evident from these data that both sr ca and 18 o in bulk calcite have been diagenetically altered in some samples 5 6 ma and older these data indicate that noncarbonate sedimentary components like clay and biogenic silica have partially suppressed recrystallization at the lower carbonate sites sr ca data from the less altered carbonate poor sites indicate higher oceanic sr ca relative to today at 5 6 and 9 4 ma

a short circuit in thermohaline circulation a cause for northern hemisphere glaciation the cause of northern hemisphere glaciation about 3 million years ago remains uncertain closing the panamanian isthmus increased thermohaline circulation and enhanced moisture supply to high latitudes but the accompanying heat would have inhibited ice growth one possible solution is that enhanced moisture transported to eurasia also enhanced freshwater delivery to the arctic via siberian rivers freshwater input to the arctic would facilitate sea ice formation increase the albedo and isolate the high heat capacity of the ocean from the atmosphere it would also act as a negative feedback on the efficiency of the conveyor belt heat pump

vertical distribution and isotopic fractionation of living planktonic foraminifera from the panama basin a model1 2 which explains the vertical and seasonal distribution of planktonic foraminifera was developed using data from the western north atlantic and is comprised of three tenets 1 the conditions in the photic zone upper 80 100 m exclusively dictate planktonic foraminifera species composition and abundance throughout the water column 2 species are vertically stratified within the photic zone according to their temperature preference depth distribution according to temperature preference has been proposed by several authors3 based on isotope analyses of sediments due to seasonal temperature variations seasonal variations in the 18o composition of seawater and species specific isotope fractionation rigorous proof of this hypothesis cannot be provided from sediment analyses alone 3 the chlorophyll maximum is a major food source zone which is preferentially exploited by foraminifera our data from the panama basin which are presented here are confirmation of this model the panama basin in the eastern equatorial pacific which has a shallow and steep thermocline was sampled for living planktonic foraminifera a multiple opening closing net and environmental sensing system mocness 4 was used to collect 13 sets of eight vertically stratified oblique samples we report here the quantitative distribution and stable isotopic composition of planktonic foraminifera from four mocness tows taken over 5 days during august 1979 rv knorr cruise 73 at 5 20 n 8 50 w each tow consisted of eight samples which integrated 12 5 m intervals from 0 to 100 m for moc 126 25 m intervals from 0 to 200 m for moc 127 100 150 m intervals from 0 to 1 000 m on moc 128 and 250 m intervals from 0 to 2 000 m on moc 131

holocene climate evolution in the high latitude southern hemisphere simulated by a coupled atmosphere sea ice ocean vegetation model the holocene climate is simulated in a 9000 yr long transient experiment performed with the ecbilt clio vecode coupled atmosphere sea ice ocean vegetation model this experiment is forced with annually varying orbital parameters and atmospheric concentrations of co2 and ch4 the objective is to study the impact of these long term forcings on the surface temperature evolution during different seasons in the high latitude southern hemisphere we find in summer a thermal optimum in the mid holocene 6 3 ka bp with temperatures locally 3 degrees c above the preindustrial mean in autumn the temperatures experienced a long term increase particularly during the first few thousand years the opposite trend was simulated for winter and spring with a relatively warm southern ocean at 9 ka bp in inter up to 3 5 degrees c above the preindustrial mean and a warm continent in spring 3 degrees c followed by a gradual cooling towards the present these long term temperature trends can be explained by a combination of 1 a delayed response to orbital forcing with temperatures lagging insolation by i to months owing to the thermal inertia of the system and 2 the long memory of the southern ocean this long memory is related to the storage of the warm late winter spring anomaly below the shallower summer mixed layer until next winter sea ice plays an important role as an amplifying factor through the ice albedo and ice insulation feedbacks our experiments can help to improve our understanding of the holocene signal in proxies for instance the results suggest that in contrast to recent propositions teleconnections to the northern hemisphere appear not necessarily to explain the history of southern hemisphere temperature changes during the holocene

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

alteration of volcanic matter in deep sea sediments evidence from the chemical composition of interstitial waters from deep sea drilling cores six deep sea drilling project dsdp sites 252 285 315 317 336 386 were examined for the chemical composition of the dissolved salts in interstitial waters the oxygen isotopic composition of the interstitial waters and the major ion composition of the bulk solid sediments an examination of the concentration depth profiles of dissolved calcium magnesium potassium and h218o in conjunction with oxygen isotope mass balance calculations confirms the hypothesis that in dsdp pelagic drill sites concentration gradients in ca mg k and h218o are largely due to alteration reactions occurring in the basalts of layer 2 and to alteration reactions involving volcanic matter dispersed in the sediment column oxygen isotope mass balance calculations require substantial alteration of layer 2 up to 25 of the upper 1000 m but only minor exchange of ca mg and k occurs with the overlying ocean this implies that alteration reactions in layer 2 are almost isochemical

the use of paleoceanographic proxies in carbonate periplatform settings opportunities and pitfalls in a sediment core from the leeward side of the great bahama bank ocean drilling program odp leg 166 1006a 24h early pliocene several paleoceanographic proxies were compared with carbonate mineralogy the proxies measured on the planktonic foraminifera species globigerinoides sacculifer are mg ca and sr ca elemental ratios and 18o values these proxies are widely used in pelagic sediments to derive parameters of water masses such as paleo temperature and salinity to produce quantitative estimates it is necessary to verify that the primary shell mineralogy of the foraminifera was not altered diagenetically diagenetic alteration can be rapid in periplatform settings relative to pelagic deep sea sediments since the meta stable carbonate phases provide an additional driving force for recrystallisation we show that the sr ca ratio of foraminiferal calcite can be used to assess the degree of diagenetic alteration of their shell chemistry using this method we demonstrate that the primary signal in the oxygen isotope ratios is preserved in the studied core in the mg ca record the relative change of foraminiferal mg ca ratios seems to be preserved but absolute values are influenced by diagenesis the second set of proxies comprises 13c and c n ratios of organic carbon these are used in pelagic sediments in order to assess the origin of organic carbon terrestrial or marine phytoplankton it is demonstrated here that a simple two end mixing model cannot explain the observed co occurrence of relatively high 13corg and c n values as the 13corg values co vary with the aragonite content we attribute this signature to varying contribution of organic carbon from benthic algae which are also the major aragonite producers on the platform top

link between oceanic heat transport thermohaline circulation and the intertropical convergence zone in the early pliocene atlantic planktonic foraminiferal oxygen isotope records from the western and eastern tropical pacific and atlantic oceans suggest a southward shift in the intertropical convergence zone toward its modern location between 4 4 and 4 3 ma a concomitant shift in the carbon isotope compositions of atlantic benthic foraminifera provides strong evidence for an increased thermohaline overturn at this time we suggest that the southward shift of the intertropical convergence zone and associated change in trade wind circulation altered equatorial surface hydrography increased the advection of warmer and more saline surface waters into the subtropical and north atlantic and contributed to thermohaline overturn

microfaunal evidence for elevated pliocene temperatures in the arctic ocean the migration of thermophilic marine ostracoda into the arctic ocean during the pliocene indicates that winter and summer ocean temperatures around arctic margins were 0 c and 3 c respectively and that ice free conditions existed for most or all of the arctic by at least 3 5 3 0 ma probably earlier the opening of the bering strait allowed marine organisms to migrate through the arctic ocean mostly from the pacific ocean migrant taxa such as cythere hemicythere and neomonoceratina are known from pliocene deposits of alaska and canada as well as neogene deposits of the north pacific and atlantic oceans on the basis of ecological and zoogeographic information on ostracode species from more than 800 modern core top samples for the north atlantic north pacific and arctic oceans we determined winter and summer temperature tolerances for migrant taxa to be at or above about 0 c and 3 c this suggests ice free summers and probably a perennially ice free arctic ocean in some regions elevated water temperatures in the arctic ocean between 3 5 and 2 0 ma is supported by evidence for late pliocene increased meridional heat transport in the north atlantic ocean

climatic evolution of the southern ocean during the pliocene epoch from 4 8 to 2 6 million years ago abstract we studied the paleoclimatic history of the southern ocean during the pliocene before the intensification of northern hemisphere glaciation at 2 4 ma from isotopic and sedimentologic data from odp leg 114 sites subantarctic south atlantic relatively warm climatic conditions prevailed in the southern ocean during the early early pliocene between 4 6 and 4 2 ma as evidenced by benthic and planktonic 18 o values that were generally less than the holocene despite this warmth significant ice rafting episodes are recorded at several drill sites and piston core locations throughout the southern ocean this interval correlates with a eustatic highstand and represents a climatic optimum for the southern ocean when low and mid latitude species migrated into the antarctic and surface waters were warmer than at present although it is generally agreed that this interval was warm in the southern hemisphere divergent opinions exist as to whether this warming led to the partial decay or growth of the antarctic ice sheet a distinct mid pliocene cooling occurred between 3 5 and 3 2 ma as evidenced by an increase in 18 o values of planktonic and benthic foraminifers in hole 704a and by faunal changes indicative of progressive cooling of antarctic surface waters and development of biotic provinciality in the southern ocean during the late pliocene 3 25 2 6 ma planktonic and benthic 18 o values commonly exceeded those of the holocene and several distinct cooling and or ice volume events occurred during the late gauss chron most notably at 2 9 and 2 63 ma faunal studies suggest several northward advances of the polar front zone and expansion of sea ice in the antarctic during this period these events preceded the major climatic transition at 2 4 ma when the pfz moved to the north sea ice expanded in the antarctic and glaciation intensified in both hemispheres

early pliocene climate a perspective from the western equatorial atlantic warm pool high resolution 3 4 kyr planktonic stable isotope stratigraphies from site 925 drilled on ceara rise ocean drilling program leg 154 are used to investigate the role of the western equatorial atlantic sea surface hydrography in early pliocene 3 2 4 7 ma climate change oxygen isotope results from globigerinoides sacculifer a mixed layer dweller suggest that equatorial sea surface temperatures were cooler than today by 2 3 c consistent with relatively strong northward advection of heat away from the equator oxygen isotope results from neogloboquadrina dutertrei suggest that over the long term this thermocline dweller tracks global ice volume fluctuations stable isotope gradients between the two planktonic species throughout the entire interval imply a stable warm pool in the western equatorial atlantic we observe a rapid 3 4 kyr decrease in g sacculifer and the n dutertrei 18o values at 4 36 ma that may reflect a freshening of the sea surface a direct response to a southward displacement of the intertropical convergence zone and perhaps an indirect response to restricted flow through the central american seaway

the salinity contrast between the atlantic and pacific oceans during glacial time in today s ocean the salinity of low latitude surface waters in the pacific is on the average 1 per mil lower than in the atlantic oxygen isotope records for planktonic foraminifera suggest that an even larger salinity deficit may have existed for pacific surface water during glacial time if so the transport of water vapor from the atlantic to the pacific must have been as strong as or even stronger to balance the tendency toward salt buildup the atlantic would have had to export during glacial time waters saltier than it received from the other oceans

shallow burial diagenesis of deep water carbonates northern bahamas results from deep ocean drilling transects rates of burial diagenesis and subsurface distribution of chalk and limestone in modern deep water carbonate slopes were little known prior to 1985 when the ocean drilling program established two drill transects in the northern bahamas north of little bahama bank and in southwestern exuma sound from these transects different shallow burial along the accretionary north margin of little bahama bank the amount of lithified strata decreases seaward because of a decreasing volume of bank derived aragonite the rate of bulk carbonate calcitization increases seaward as the rate of diagenesis begins to match then exceed the rate of burial mineral controlled diagenesis is of little consequence below about 20 m subsurface only 30 km seaward of the bank margin along the bypass margin in exuma sound the extent of lithification increases downslope toward preferential accumulation of bank derived aragonite much higher accumulation rates and high percentages of aragonite along this margin sustain a still present mineral controlled diagenetic potential in limestone at 300 m from analogy of modern bahama slopes considerable diagenetic heterogeneity within the shallow burial realm may be expected along some ancient carbonate margins our results serve to illustrate carbonate mineral stabilization and early limestone formation with secondary porosity in a sea water mediated environment and they further highlight the high diagenetic potential of periplatform carbonates

insolation cycles as a major control of equatorial indian ocean primary production analysis of a continuous sedimentary record taken in the maldives indicates that strong primary production fluctuations 70 to 390 grams of carbon per square meter per year have occurred in the equatorial indian ocean during the past 910 000 years the record of primary production is coherent and in phase with the february equatorial insolation whereas it shows diverse phase behavior with 18o depending on the orbital frequency eccentricity obliquity or precession examined these observations imply a direct control of productivity in the equatorial oceanic system by insolation in the equatorial indian ocean productivity is driven by the wind intensity of westerlies which is related to the southern oscillation therefore it is suggested that a precession forcing on the southern oscillation is responsible for the observed paleoproductivity dynamics

determination of intratest variability of trace elements in foraminifera by laser ablation inductively coupled plasma mass spectrometry 1 we have developed a technique to determine the variability of trace elements including li b na mg mn cu zn sr and ba within foraminifera tests using laser ablation inductively coupled plasma mass spectrometry la icp ms this technique has a high spatial resolution width 40 80 m depth 0 5 m is reproducible 8 external reproducibility and has low detection limits generally 0 05 g g 1 we demonstrate that normalization of data to a calcite standard usually gives results that are more consistent with solution icp ms data than normalization to nist 612 rastering into the wall of the final chamber of globigerinoides sacculifer shows that the outermost 1 5 m of the test is enriched in trace elements including mn relative to the interior indicating the presence of a contaminant surface phase pustule calcite close to the aperture of globorotalia tumida has different sr ca and ba ca compared to other parts of the test sr ca and ba ca partition coefficients suggest that the pustule calcite is diagenetic and or formed in a more open system multiple analyses of orbulina universa tests recovered from a latitudinal transect in the north atlantic give a relationship between mg ca and sea surface temperature similar to that reported elsewhere in the literature these initial data demonstrate the validity of this technique and show that it is potentially an extremely powerful microanalytical tool for palaeoceanographic and palaeontological studies

an atlas of the distribution of calcium carbonate in sediments of the deep sea historical observations of the concentration of calcium carbonate in global deep sea sediments are compiled and compared with a new gridded field of seawater co3 concentration to reveal regional variations in the calcite lysocline the most obvious mode of variability of the calcite lysocline is the thickness of the lysocline defined here as the difference in overlying water carbonate saturation co3 between high and low calcite sediments with a thicker lysocline in the atlantic than in the pacific i attribute this variation to differences in the delivery rate of terriginous material a recent model for the lower glacial atmospheric pco2 proposed to change the relationship between the depth of the lysocline and the co3 of the water column by changing the rain rate ratio of organic carbon to calcite production the rain ratio model archer and maier reimer 1994 i search the data set for analogs to the proposed glacial world by looking for a link between the regional climate at the sea surface and the depth of the lysocline below the co3 at the carbonate compensation depth ccd in the tropics appears to be 10 20 mol kg 1 co3 more undersaturated than in high latitudes but this is smaller than the 40 mol kg 1 shift required by the model in addition the general resemblance of the glacial lysocline to the present day requires that the proposed shift in co3 at the ccd be globally uniform rather than locally variable as climate forcing would probably generate i conclude that the rain ratio model would probably require some globally uniform perturbation during glacial time such as a change in ocean si content if it is to explain the entire pco2 decrease observed in the glacial atmosphere finally i grid the sedimentary data to estimate that the inventory caco3 which is available to neutralize fossil fuel co2 is approximately 1600 gt carbon a quantity which may be exceeded by fossil fuel release in the next several centuries

microspar development during early marine burial diagenesis a comparison of pliocene carbonates from the bahamas with silurian limestones from gotland sweden comparison of ultrastructures in pliocene periplatform carbonates from the bahamas with silurian limestones from gotland sweden reveals that despite the differences in primary sediment composition and age they reflect a similar mechanism of lithification in both sequences calcite microspar was formed as a primary cement at an early stage of marine burial diagenesis neither significant compression nor meteoric influence are necessary for the formation of calcite microspar a model is proposed for the process of microsparitic cementation of fine grained aragonite needle muds comprising four stages 1 unconsolidated aragonite dominated carbonate mud 2 precipitation of microspar that engulfs aragonite needles 3 dissolution of aragonite resulting in pitted surfaces of the microspar crystals and 4 slight recrystallization our results contradict the widespread opinion that microspar necessarily is a product of secondary recrystallization of a previously lithified micrite

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

palaeoclimatology core data from the antarctic margin sediments at the edge of antarctica are a largely unexploited source of information about climate change they have now provided a valuable local record of sea surface temperatures for the past 12 000 years see letter p 250 the antarctic peninsula is currently one of the fastest warming locations on earth but its long term variability has remained unclear amelia shevenell and colleagues now use the tex86 proxy a palaeothermometer that tracks membrane lipids of the marine picoplankton crenarchaeota to show that a long term cooling of about 4 c occurred in waters near the tip of antarctic peninsula over the past 12 000 years this is consistent with orbitally controlled changes in insolation shorter term variability in temperature seems to have been strongly influenced by the position of the westerly winds this work suggests that the present influence of the el nino southern oscillation system on the antarctic peninsula is a relatively recent phenomenon dating to the late holocene

reconstructing past sea surface temperatures correcting for diagenesis of bulk marine carbonate abstract a numerical model which describes oxygen isotope exchange during burial and recrystallization of deep sea carbonate is used to obtain information on how sea surface temperatures have varied in the past by correcting measured 18o values of bulk carbonate for diagenetic overprinting comparison of bulk carbonate and planktonic foraminiferal 18o records from odp site 677a indicates that the oxygen isotopic composition of bulk carbonate does reflect changes in sea surface temperature and 18o at odp site 690 we calculate that diagenetic effects are small and that both bulk carbonate and planktonic foraminiferal 18o records accurately reflect paleogene warming of high latitude surface oceans biased from diagenesis by no more than 1 c the same is likely to be true for other high latitude sites where sedimentation rates are low at dsdp sites 516 and 525 the effects of diagenesis are more significant measured 18o values of eocene bulk carbonates are more than 2 lower at deeply buried site 516 than at site 525 consistent with the model prediction that the effects of diagenesis should be proportional to sedimentation rate model corrections reconcile the differences in the data between the two sites the resulting paleotemperature reconstruction indicates a 4 c cooling of mid latitude surface oceans since the eocene at low latitudes the contrast in temperature between the ocean surface and bottom makes the carbonate 180 values particularly sensitive to diagenetic effects most of the observed variations in measured 18o values are accounted for by diagenetic effects rather than by sea surface temperature variations we show that the data are consistent with constant equatorial sea surface temperatures through most of the cenozoic with the possible exception of the early eocene when slightly higher temperatures are indicated we suggest that the lower equatorial sea surface temperatures for the eocene and oligocene reported in other oxygen isotope studies are artifacts of diagenetic recrystallization and that it is impossible to reconstruct accurately equatorial sea surface temperatures without explicitly accounting for diagenetic overprinting

secular oscillations in the carbonate mineralogy of reef building and sediment producing organisms driven by tectonically forced shifts in seawater chemistry the primary mineralogy of oolites and early marine carbonate cements led sandberg nature 305 1983 19 22 to divide the phanerozoic eon into three intervals of aragonite seas and two intervals of calcite seas hardie geology 24 1996 279 283 has shown that these oscillations together with synchronous oscillations in the mineralogy of marine potash evaporites can be explained by secular shifts in the mg ca ratio of seawater driven by changes in spreading rates along mid ocean ridges the hardie model also predicts that high mg calcite should precipitate along with aragonite as it does in today s aragonite sea we have uncovered oscillations in the carbonate mineralogy of hypercalcifying organisms ones that have produced massive skeletons large reefs or voluminous bodies of sediment that correspond to sandberg s aragonite seas and calcite seas and that are predicted by the hardie model particular groups of corals sponges and algae appear to have been dominant reef builders only when favored by an appropriate mg ca ratio in seawater in early and middle paleozoic calcite seas calcite i reefs were dominated by calcitic tabulate heliolitid and rugose corals and calcitic stromatoporoids in contrast during the period of late paleozoic early mesozoic aragonite seas aragonite ii aragonitic groups of sponges scleractinian corals and phylloid algae as well as high mg calcitic red algae were principal reef builders during late cretaceous time at the acme of calcite ii massive rudists displaced aragonitic hermatypic corals in today s aragonite sea aragonite iii scleractinian corals are again dominant reef builders along with high mg calcitic coralline algae major sediment producing algae exhibit temporal patterns similar to those of reef builders calcitic receptaculitids flourished during calcite i whereas aragonitic dasycladaceans did not become dominant rock formers until aragonite ii during calcite ii calcitic nannoplankton formed massive coccolith chalks in warm shallow seas of the late cretaceous after the mg ca ratio of seawater had reached a very low value and calcium concentration a very high value as the mg ca ratio of seawater rose and calcium concentration fell during the cenozoic era individual coccoliths on average became less massive and encrusted cells less thickly by pliocene time during aragonite iii the prominent genus discoaster secreted only narrow rayed coccoliths that covered less than 25 of the cell surface also during aragonite iii the aragonitic green alga halimeda emerged as the dominant skeletal sediment producer in reef tracts the influence of seawater chemistry on skeletal secretion appears to have been especially strong for morphologically simple taxa that exert relatively weak control over their own calcification such groups include algae sponges corals and bryozoans morphological simplicity also permits these groups to adopt vegetative or colonial modes of growth that confer success in competition for space on reefs this linkage in addition to the basic chemical demands of hypercalcification has given the mg ca ratio of seawater strong control over the success of individual reef building taxa more generally this ratio appears to have strongly influenced evolutionary changes in the skeletal mineralogy of sponges and cheilostome bryozoans throughout their history we conclude that throughout phanerozoic time a chain of causation has extended from mid ocean ridge processes via seawater chemistry to the mineralogical and biological composition of reef communities and bioclastic carbonate deposits

isotopic signature of burial diagenesis and primary lithological contrasts in periplatform carbonates miocene great bahama bank the stable isotope geochemistry of miocene sediments from the leeward margin of the great bahama bank was examined to investigate burial diagenetic processes in periplatform carbonates data indicate that in addition to differences in bulk proportions of neritic and pelagic carbonate along the slope rhythmic variation in primary carbonate content has controlled patterns of burial diagenesis and associated geochemical signatures throughout much of the succession examined the present study focuses on ocean drilling program sites 1006 and 1007 the most distal of five sites drilled from marginal to deep basin environments during leg 166 these miocene sections are characterized by their cyclic appearance manifest as decimeter to meter scale alternations between light colored ooze chalk limestone and dark colored marl marlstone the section at site 1006 contains a high proportion of pelagic carbonate and is unlithified to a subbottom depth of 675 m fluctuations in 18 o and 13 c values at this site are independent of lithological variation and reflect primary conditions at site 1007 located at the toe of slope and composed of a mixture of bank derived and pelagic carbonate limestones are densely cemented show little evidence of compaction and have 18 o values up to 2 higher than coeval sediments at site 1006 marlstones at site 1007 are poorly cemented exhibit an increase in compaction related features with depth and have lower and more variable 18 o values that are similar to those of coeval sediments at site 1006 isotopic and petrographic characteristics of limestone interbeds result from cement precipitation from cold sea water during the first 100 m of burial higher proportions of insoluble materials and pelagic carbonate seem to have inhibited diagenetic alteration in adjacent marlstones in spite of significant compaction and pressure solution during burial original isoto pic compositions appear to be best preserved in these intervals at site 1007 the documented contrasts in petrographic and isotopic patterns illustrate the role of primary sediment composition in controlling lithification processes in periplatform carbonates and stress the importance of consid ering such factors when interpreting geochemical data from ancient shelf and slope limestones

manganese carbonate overgrowths on foraminifera tests below the zone where manganese is remobilized as mn2 aq reductively cleaned foraminifera in deep sea sediments have much higher mnca than those in core tops and sediment traps mnca ranges from less than 20 10 6 in and above the mno2 maximum to as high as 700 10 6 in reducing panama basin sediments the most plausible explanation for this enrichment is that the tests are coated with mn carbonate overgrowths these coatings can account for a significant proportion of the mn in reduced deep sea sediments uptake of manganous ion by carbonate may explain the absence of mn nodules in areas of high carbonate accumulation extreme degrees of overgrowth can alter foram trace element values but this artifact can be avoided by avoiding foraminifera with high mn ca

isotopic paleoceanography of the caribbean and east pacific role of panama uplift in late neogene time comparisons of carbon isotopic data on benthic foraminifera from deep sea drilling project sites 502 western caribbean and 503 eastern pacific indicate that the difference between the atlantic and the pacific in the per mil enrichment in carbon 13 of total dissolved carbon dioxide increased about 6 million years ago and again 3 million years ago when the difference reached the modern level 1 per mil comparisons of planktonic foraminiferal oxygen isotopic data for the caribbean and the pacific suggest that the salinity of caribbean surface waters began increasing 4 million years ago possibly in response to shoaling of the panama isthmus these results suggest that modern circulation patterns in the caribbean and eastern pacific developed by 3 million years ago in concert with changing tectonic climatic and biogeographic patterns

holocene southern ocean surface temperature variability west of the antarctic peninsula the antarctic peninsula is currently one of the fastest warming locations on earth but its long term variability has remained unclear amelia shevenell and colleagues now use the tex86 proxy a palaeothermometer that tracks membrane lipids of the marine picoplankton crenarchaeota to show that a long term cooling of about 4 c occurred in waters near the tip of antarctic peninsula over the past 12 000 years this is consistent with orbitally controlled changes in insolation shorter term variability in temperature seems to have been strongly influenced by the position of the westerly winds this work suggests that the present influence of the el nino southern oscillation system on the antarctic peninsula is a relatively recent phenomenon dating to the late holocene the antarctic peninsula is currently one of the fastest warming locations on earth but its long term variability has remained unclear this study uses tex86 sea surface temperature proxy evidence to show that a long term cooling of about 3 4 c occurred in waters near the tip of the antarctic peninsula over the past 12 000 years consistent with orbitally controlled changes in insolation shorter term variability in temperature at the antarctic peninsula appears to have been strongly influenced by the position of westerly winds the present influence of the el nino southern oscillation system on the antarctic peninsula may have arisen only during the late holocene the disintegration of ice shelves reduced sea ice and glacier extent and shifting ecological zones observed around antarctica1 2 highlight the impact of recent atmospheric3 and oceanic warming4 on the cryosphere observations1 2 and models5 6 suggest that oceanic and atmospheric temperature variations at antarctica s margins affect global cryosphere stability ocean circulation sea levels and carbon cycling in particular recent climate changes on the antarctic peninsula have been dramatic yet the holocene climate variability of this region is largely unknown limiting our ability to evaluate ongoing changes within the context of historical variability and underlying forcing mechanisms here we show that surface ocean temperatures at the continental margin of the western antarctic peninsula cooled by 3 4 c over the past 12 000 years tracking the holocene decline of local 65 s spring insolation our results based on tex86 sea surface temperature sst proxy evidence from a marine sediment core indicate the importance of regional summer duration as a driver of antarctic seasonal sea ice fluctuations7 on millennial timescales abrupt sst fluctuations of 2 4 c coincide with globally recognized climate variability8 similarities between our ssts southern hemisphere westerly wind reconstructions9 and el nino southern oscillation variability10 indicate that present climate teleconnections between the tropical pacific ocean and the western antarctic peninsula11 strengthened late in the holocene epoch we conclude that during the holocene southern ocean temperatures at the western antarctic peninsula margin were tied to changes in the position of the westerlies which have a critical role in global carbon cycling9 12

foraminiferal mg ca increase in the caribbean during the pliocene western atlantic warm pool formation salinity influence or diagenetic overprint we constructed a high resolution mg ca record on the planktonic foraminifer globigerinoides sacculifer in order to explore the change in sea surface temperature sst due to the shoaling of the isthmus of panama as well as the impact of secondary factors like diagenesis and large salinity fluctuations the study covers the latest miocene and the early pliocene 5 6 3 9 ma and was combined with 18o to isolate changes in sea surface salinity sss before 4 5 ma sstmg ca and sss show moderate fluctuations indicating a free exchange of surface ocean water masses between the pacific and the atlantic the increase in 18o after 4 5 ma represents increasing salinities in the caribbean due to the progressive closure of the panamanian gateway the increase in mg ca toward values of maximum 7 mmol mol suggests that secondary influences have played a significant role evidence of crystalline overgrowths on the foraminiferal tests in correlation with aragonite sr ca and productivity cyclicities indicates a diagenetic overprint on the foraminiferal tests laser ablation inductively coupled plasma mass spectrometry analyses however do not show significantly increased mg ca ratios in the crystalline overgrowths and neither do calculations based on pore water data conclusively result in significantly elevated mg ca ratios in the crystalline overgrowths alternatively the elevated mg ca ratios might have been caused by salinity as the 18o record of site 1000 has been interpreted to represent large fluctuations in sss and cultivating experiments have shown an increase in mg ca with increasing salinity we conclude that the mg ca record 4 5 ma can only reliably be considered for paleoceanographical purposes when the minimum values not showing any evidence of secondary influences are used resulting in a warming of central caribbean surface water masses after 4 5 ma of 2 c

interlaboratory comparison study of mg ca and sr ca measurements in planktonic foraminifera for paleoceanographic research thirteen laboratories from the usa and europe participated in an intercomparison study of mg ca and sr ca measurements in foraminifera the study included five planktonic species from surface sediments from different geographical regions and water depths each of the laboratories followed their own cleaning and analytical procedures and had no specific information about the samples analysis of solutions of known mg ca and sr ca ratios showed that the intralaboratory instrumental precision is better than 0 5 for both mg ca and sr ca measurements regardless whether icp oes or icp ms is used the interlaboratory precision on the analysis of standard solutions was about 1 5 and 0 9 for mg ca and sr ca measurements respectively these are equivalent to mg ca based temperature repeatability and reproducibility on the analysis of solutions of 0 2 c and 0 5 c respectively the analysis of foraminifera suggests an interlaboratory variance of about 8 rsd for mg ca measurements which translates to reproducibility of about 2 3 c the relatively large range in the reproducibility of foraminiferal analysis is primarily due to relatively poor intralaboratory repeatability about 1 2 c and a bias about 1 c due to the application of different cleaning methods by different laboratories improving the consistency of cleaning methods among laboratories will therefore likely lead to better reproducibility even more importantly the results of this study highlight the need for standards calibration among laboratories as a first step toward improving interlaboratory compatibility

high resolution holocene record in the southeastern bay of biscay global versus regional climate signals abstract core ks10b north east atlantic 43 50 n 2 03 w water depth 550 m was recovered at a location of high sediment deposition and hence includes a high resolution palaeoclimatic record for the southeastern bay of biscay over the last 9000 cal yr bp the effect of global and regional climatic forcing factors e g orbital forcing north atlantic oscillation nao and their subsequent control on water temperature sea level hydrology and continental influence were investigated by studying planktic and benthic foraminiferal faunas 150 m sedimentology and stable isotopes results indicate probable episodic long term incursions of the warm and salty iberian poleward current ipc into the bay of biscay during the holocene by the intermittent presence of subtropical globigerinoides ruber in the otherwise temperate fauna these incursions seem to be triggered by negative nao like conditions our data show five main climatic periods which are in general agreement with the literature data on the climatic variability in the north atlantic and the iberian peninsula the early holocene 9000 7400 cal yr bp is characterized by low sea level significant downslope transport eutrophic benthic settings and high surface water productivity these environmental characteristics are probably due to the general wet and warm climate under a prevailing negative nao increasing precipitation and river runoff and favouring the incursion of the ipc into the bay of biscay the climatic optimum appears between 7400 and 6000 cal yr bp under a generally positive nao index in the following 6000 3500 cal yr bp surface water cooling is matching a steep decline of the northern hemisphere summer insolation meanwhile benthic settings are changing progressively towards present day trophic conditions the time interval from 3500 to 1800 cal yr bp encompasses the iberian roman humid period characterized by warm and humid conditions and increasing primary production under a prevailing negative nao index the last 1800 years were characterized by stable cool conditions reflecting a change towards a positive nao state

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

millennial scale dynamics of the east asian winter monsoon during the last 200 000 years the primary productivity dynamics of the last 200 000 years in the sulu sea was reconstructed using the abundance of the coccolithophore florisphaera profunda in the images md97 2141 core we find that primary productivity was enhanced during glacial periods which we suggest is due to a stronger east asian winter monsoon during the last 80 kyr eight significant increases in primary productivity pp in the sulu sea are similar to east asian winter monsoon changes recorded in chinese loess the pp maxima are not linked with heinrich events he in the north atlantic although four pp peaks are synchronous with he the pp oscillations have frequencies near those of the dansgaard oeschger cycles in northern hemisphere ice records and indicate a teleconnection of the east asian winter monsoon with greenland climate in this sulu sea record the east asian winter monsoon oscillates with periodicities of6 4 2 3 4 2 3 and 1 5 kyr in particular the 1 5 kyr cycle exhibits a strong and pervasive signal from stage 6 to the holocene without any ice volume modulation this stationarity suggests that the 1 5 kyr cycle is not driven by some high latitude forcing

chronology of the palmer deep site antarctic peninsula a holocene palaeoenvironmental reference for the circum antarctic palmer deep sediment cores are used to produce the first high resolution continuous late pleistocene to holocene time series from the antarctic marine system the sedimentary record is dated using accelerator mass spectrometer radiocarbon methods on acid insoluble organic matter and foraminiferal calcite fifty four radiocarbon analyses are utilized in the dating which provides a calibrated timescale back to 13 ka bp reliability of resultant ages on organic matter is assured because duplicates produce a standard deviation from the surface age of less than laboratory error i e 50 years in addition surface organic matter ages at the site are in excellent agreement with living calcite ages at the accepted reservoir age of 1260 years for the antarctic peninsula spectral analyses of the magnetic susceptibility record against the age model reveal unusually strong periodicity in the 400 200 and 50 70 year frequency bands similar to other high resolution records from the holocene but so far unique f

effect of ambient mg ca ratio on mg fractionation in calcareous marine invertebrates a record of the oceanic mg ca ratio over the phanerozoic the mg ca ratio of seawater has changed significantly over the phanerozoic primarily as a function of the rate of ocean crust production echinoids crabs shrimps and calcareous serpulid worms grown in artificial seawaters encompassing the range of mg ca ratios that existed throughout the phanerozoic exhibit a direct nonlinear relationship between skeletal and ambient mg ca specimens grown in seawater with the lowest mg ca 1 changed their mineralogy to low mg calcite 4 mol mgco3 suggesting that these high mg calcareous organisms would have produced low mg calcite in the cretaceous when oceanic mg ca was lowest 1 these results support the empirical evidence that the skeletal chemistry of calcareous organisms has varied significantly over the phanerozoic as a function of the mg ca of seawater and that the mg ca of unaltered fossils of such organisms may be a record of oceanic mg ca throughout the phanerozoic mg fractionation algorithms which relate skeletal mg ca seawater mg ca and temperature were derived from these and other experiments they can be used to estimate paleoceanic mg ca ratios and temperatures from fossil skeletal mg ca of the organisms evaluated paleoceanic mg ca ratios recalculated by using the echinoderm mg fractionation algorithm from published fossil echinoid mg ca crinoid mg ca and paleotemperature data are consistent with other estimates and models of oceanic mg ca over the phanerozoic

distributional variations in marine crenarchaeotal membrane lipids a new tool for reconstructing ancient sea water temperatures it has recently been shown that membrane lipids of marine crenarchaeota a ubiquitous and abundant component of plankton occur in relatively high concentrations in recent and ancient sediments in this study we investigated the environmental controls on the relative distribution of these lipids in surface sediments we especially focussed on temperature as it is known from the thermophilic genetic relatives of marine crenarchaetoa that the composition of their membrane strongly depends on growth temperature indeed a significant linear correlation r2 0 92 is found between the number of cyclopentane rings in sedimentary membrane lipids derived from marine crenarchaeota and the annual mean sea surface temperatures this suggests that the mechanism of physical adaptation of their membrane compositions to temperature is identical to that of their thermophilic relatives in turn archaeal lipid distributions in sediments may thus allow the reconstruction of sea water temperatures of ancient marine environments

a cenozoic seawater sr ca record from benthic foraminiferal calcite and its application in determining global weathering fluxes a cenozoic multi species record of benthic foraminiferal calcite sr ca has been produced and is corrected for inter specific offsets typically less than 0 3 mmol mol and for the linear relationship between decreasing benthic foraminiferal sr ca and increasing water depth the water depth correction determined from holocene late glacial maximum and eocene paleowater depth transects is not vert similar0 1 mmol mol km the corrected cenozoic benthic foraminiferal sr ca record ranges from 1 2 to 2 0 mmol mol and has been interpreted in terms of long term changes in seawater sr ca enabling issues related to higher resolution variability in sr ca to be ignored we estimate that seawater sr ca was not vert similar1 5 times modern values in the late cretaceous but declined rapidly into the paleogene following a minimum in the eocene seawater sr ca increased gradually through to the present day with a minimum superimposed on this trend centered in the late miocene by assuming scenarios for changing seawater calcium concentration and using published carbonate accumulation rate data combined with suitable values for sr partition coefficients into carbonates the seawater sr ca record is used to estimate global average river sr fluxes these fluxes are used in conjunction with the seawater strontium isotope curve and estimates of hydrothermal activity tectonic outgassing to calculate changes in global average river 87sr 86sr through the cenozoic the absolute magnitude of sr fluxes and isotopic compositions calculated in this way are subject to relatively large uncertainties nevertheless our results suggest that river sr flux increased from 35 ma to the present day roughly two fold accompanied by an overall increase in 87sr 86sr by not vert similar0 to 0 001 between 75 and 35 ma river 87sr 86sr also increased by not vert similar0 001 to 0 002 but was accompanied by a decrease two to three fold in river sr flux

spherical prism magnetic effects by gauss legendre quadrature integration summary regional spherical coordinate observations of the earth s crustal magnetic field components are becoming increasingly available from shipborne airborne and satellite surveys in assessing the geological significance of these data theoretical anomalous magnetic fields from geologic models in spherical coordinates need to be evaluated this study explicitly develops the elegant gauss legendre quadrature formulation for numerically modelling the complete magnetic effects i e potential vector and tensor gradient fields of the spherical prism we also use these results to demonstrate the magnetic effects for the crustal prism and to investigate the crustal magnetic effects at satellite altitudes for a large region of the middle east centred on iran

formation of holocene sedimentary laminae in the black sea and the role of the benthic flocculent layer holocene black sea sediments recovered in 1988 and 1993 from box cores and gravity cores were analyzed geochemically microscopically and with backscattered electron imagery bsei in order to determine the temporal geochemical and sedimentological relationships between the benthic flocculent layer often referred to as the fluff layer and the formation of underlying laminated unit i sediments existence of a permanent benthic fluff layer in the black sea basin is suggested acting as a geochemical transition layer within which all sedimentary particles are hydraulically sorted and particles subject to dissolution or organic remineralization are altered prior to accumulation we propose that particle residence time within the benthic fluff layer is a key factor in determining sedimentary microfabric and geochemical composition of laminated unit i sediments we present a schematic model depicting the above relationships and use it to propose a paleoflux scenario for laminae formation in the unit ii sapropel

assessing the impact of diagenesis on foraminiferal geochemistry from a low latitude shallow water drift deposit abstract due to their large heat and moisture storage capabilities the tropics are fundamental in modulating both regional and global climate furthermore their thermal response during past extreme warming periods such as super interglacials is not fully resolved in this regard we present high resolution analytical foraminiferal geochemical 18 o and mg ca records for the last 1800 kyr from the shallow 487 m inner sea drift deposits of the maldives archipelago in the equatorial indian ocean considering the diagenetic susceptibility of these proxies in carbonate rich environments we assess the integrity of a suite of commonly used planktonic and benthic foraminifera geochemical datasets globigerinoides ruber white globigerinita glutinata with bulla pulleniatina obliquiloculata with cortex and cibicides mabahethi and their use for future paleoceanographic reconstructions using a combination of spot secondary ion mass spectrometer electron probe micro analyzer and scanning electron microscope image data it is evident that authigenic overgrowths are present on both the external and internal test shell surfaces yet the degree down core as well as the associated bias is shown to be variable across the investigated species and proxies given the elevated authigenic overgrowth mg ca 12 22 mmol mol and 18 o values closer to the benthic isotopic compositions the whole test planktonic g ruber w geochemical records are notably impacted beyond 627 4 ka 24 7 mcd yet considering the setting i e bottom water location for overgrowth formation the benthic foraminifera 18 o record is markedly less impacted with only minor diagenetic bias beyond 790 0 ka 28 7 mcd even though only the top of the g ruber w and c mabahethi records whole test data would be suitable for paleo reconstructions of absolute values i e sea surface temperature salinity seawater 18 o the long term cycles while dampened appear to be preserved furthermore planktonic species with thicker tests i e p obliquiloculata w c might be better suited in comparison to thinner test counter parts i e g glutinata w b g ruber w for traditional whole test geochemical studies in shallow carbonate rich environments a thicker test equates to a smaller overall bias from the authigenic overgrowth overall if the diagenetic impact is constrained as done in this study these types of diagenetically altered geochemical records can still significantly contribute to studies relating to past tropical seawater temperatures latitudinal scale ocean current shifts and south asian monsoon dynamics

hydrothermal circulation through mid ocean ridge flanks fluxes of heat and magnesium thermally driven convection of seawater occurs through oceanic crust of all ages at the seafloor spreading axis on mid ocean ridge flanks and in the ocean basins at the ridge axis and on the flanks circulating seawater produces a major chemical exchange between the oceans and the crust based on heat budget constraints and the composition of hot springs between 10 and 40 of the river flux of mg can be taken up during high temperature alteration of the basaltic crust along the ridge axis most of the hydrothermal heat loss however occurs on the mid ocean ridge flanks where the temperatures are lower and the seawater flux correspondingly larger the estimated heat loss on the flanks is so large that upwelling must occur over a large fraction 5 30 of the seafloor less than 65 ma in age if temperatures are 20 c and seepage velocities are on the order of 10 to 100 cm y the circulating seawater needs to lose on average less than 1 2 of its mg content in order to solve the mg mass balance for the oceans chemical fluxes through mid ocean ridge flanks are poorly known because of the wide range of crustal conditions that prevail there and the paucity of study to date the most critical parameter for characterizing crustal conditions is temperature in basement which is a function of crustal age basement topography and sediment thickness and permeability basement temperature which can usually be inferred from heat flow and seismic reflection surveys largely determines the change in the composition of seawater circulating through basement this change can be inferred in turn from profiles of sediment porewater chemistry all sites studied to date with temperatures at the sediment basement interface 25 c have a large component of advective heat loss and show only a small 80 mg loss both types of sites may be important for chemical fluxes whether the cooler sites are important depends on how much the seawater changes in composition as it circulates through the crust only small changes are needed whether the warmer sites are important depends on how much heat is lost by advection in this type of setting the warmer sites could produce significant chemical fluxes even if they are scarce they could account for the entire river input of mg to the oceans even if they represent only 8 20 of the total advective heat loss on ridge flanks

reconstruction of caribbean sea surface temperature and salinity fluctuations in response to the pliocene closure of the central american gateway and radiative forcing using δ44 40ca δ18o and mg ca ratios the 18o values of planktonic foraminifera increased in the caribbean by about 0 5 relative to the equatorial east pacific values between 4 6 and 4 2 ma as a consequence of the closure of the central american gateway cag this increase in 18o can be interpreted either as an increase in caribbean sea surface mixed layer salinity sss or as a decrease in sea surface temperatures sst this problem represents an ideal situation to apply the recently developed paleotemperature proxy 44 40ca together with mg ca and 18o on the planktic foraminifer globigerinoides sacculifer from odp site 999 although differences in absolute temperature calibration of 44 40ca and mg ca exist the general pattern is similar indicating a sst decrease of about 2 3 c between 4 4 and 4 3 ma followed by an increase in the same order of magnitude between 4 3 and 4 0 ma correcting the 18o record for this temperature change and assuming that changes in global ice volume are negligible the salinity induced planktonic 18o signal decreased by about 0 4 between 4 4 and 4 3 ma and increased by about 0 9 between 4 3 and 4 0 ma in the caribbean the observed temperature and salinity trends are interpreted to reflect the restricted exchange of surface water between the caribbean and the pacific in response to the shoaling of the panamanian seaway possibly accompanied by a southward shift of the intertropical convergence zone itcz between 4 4 and 4 3 ma differences in mg ca and 44 40ca derived temperatures can be reconciled by corrections for secular variations of the marine mg casw and 44 40ca a salinity effect on the mg ca ratio and a constant temperature offset of 2 5 c between both sst proxy calibrations

effect of the formation of the isthmus of panama on atlantic ocean thermohaline circulation the late cenozoic closure of the seaway between the north andsouth american continents is thought to have caused extensive changes in ocean circulation and northern hemisphere climate1 2 but the timing and consequences of the emergence of the isthmus of panama which closed the seaway remain controversial1 2 3 4 5 here we present stable isotope and carbonate sand fraction records from caribbean sediments which when compared to atlantic and pacific palaeoceanographic records indicate that the closure caused a marked reorganization of ocean circulation starting 4 6 million years ago shallowing of the seaway intensified the gulf stream and introduced warm and saline water masses to high northern latitudes these changes strengthened deep water formation in the labrador sea over the next million years as indicated by an increased deep water ventilation and carbonate preservation in the caribbean sea and favoured early pliocene warming of the northern hemisphere the evaporative cooling of surface waters during north atlantic deep water formation would have introduced moisture to the northern hemisphere although the pronounced intensification of northern hemisphere glaciation between 3 1 and 2 5 million years ago substantially lagged the full development of north atlantic deep water formation we propose that the increased atmospheric moisture content was a necessary precondition for ice sheet growth which was then triggered by the incremental changes in the earth s orbital obliquity

mechanisms of holocene palaeoenvironmental change in the antarctic peninsula region the antarctic peninsula is one of the three fastest warming regions on earth here we review holocene proxy records of marine and terrestrial palaeoclimate in the region and discuss possible forcing mechanisms underlying past change with a specific focus on past warm periods our aim is to critically evaluate the mechanisms by which palaeoclimate changes might have occurred in order to provide a longer term context for assessing the drivers of recent warming two warm events are well recorded in the holocene palaeoclimate record namely the early holocene warm period and the mid holocene hypsithermal mhh whereas there are fewer proxy data for the mediaeval warm period mwp and the recent rapid regional rrr warming we show that the early holocene warm period and mhh might be explained by relatively abrupt shifts in position of the southern westerlies superimposed on slower solar insolation changes a key finding of our synthesis is that the marine and terrestrial records in the ap appear to show markedly different behaviour during the mhh this might be partly explained by contrasts in the seasonal insolation forcing between these records circumpolar deep water cdw has been implicated in several of the prominent changes through the holocene but there are still differences in interpretation of the proxy record that make its influence difficult to assess further work is required to investigate contrasts between marine and terrestrial proxy records east west contrasts in palaeoclimate the history of cdw to retrieve a long onshore high resolution record of the holocene and determine the role of sea ice in driving or modulating palaeoclimate change along with further efforts to study the proxy record of the rrr and the mwp

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

cenozoic deep sea temperatures and global ice volumes from mg ca in benthic foraminiferal calcite a deep sea temperature record for the past 50 million years has been produced from the magnesium calcium ratio mg ca in benthic foraminiferal calcite the record is strikingly similar in form to the corresponding benthic oxygen isotope 18o record and defines an overall cooling of about 12 c in the deep oceans with four main cooling periods used in conjunction with the benthic 18o record the magnesium temperature record indicates that the first major accumulation of antarctic ice occurred rapidly in the earliest oligocene 34 million years ago and was not accompanied by a decrease in deep sea temperatures

role of panama uplift on oceanic freshwater balance comparison between planktic foraminiferal oxygen isotope records from the caribbean sea ocean drilling program odp site 999 and the equatorial east pacific odp site 851 suggests an increase in caribbean surface water salinity between 4 7 and 4 2 ma the modern atlantic pacific salinity contrast of about 1 became fully established at 4 2 ma as reflected by a 0 5 planktic foraminifera 18o enrichment in the caribbean sea this is interpreted as the result of restricted surface water exchange between the tropical atlantic and pacific in response to the shoaling of the central american seaway as a consequence the atlantic and pacific surface ocean circulation regime changed as did the freshwater balance between the major ocean basins simultaneous shifts in benthic carbon isotope records in the caribbean sea suggest an intensification in north atlantic thermohaline circulation these results indicate that the panamanian isthmus formation caused several new ocean atmosphere feedback mechanisms that have affected climate since the early pliocene

changes in caribbean surface hydrography during the pliocene shoaling of the central american seaway pliocene d18o records of shallow and deep dwelling planktonic foraminifers from the caribbean ocean drilling program sites 999 and 1000 the tropical east pacific sites 1241 and 851 and the atlantic site 925 ceara rise and site 1006 western great bahama bank were used to examine atlantic caribbean pacific atmospheric and oceanic linkages associated with the progressive closure of the central american seaway 5 5 3 ma comparisons indicate the development of an inner caribbean salinity gradient in the mixed layer and salinity changes on precessional periodicities after 4 4 ma site 1000 when the pacific caribbean throughflow became significantly restricted the high amplitude variability in salinity is also observed at site 1006 monitoring the caribbean outflow into the atlantic comparisons of caribbean and atlantic planktonic d18o records suggest the north atlantic subtropical gyre as a major source for high salinity surface waters precession induced variations in the volume transport of pacific surface water masses through the panamanian seaway are considered a main factor to explain the caribbean salinity minima results from a coupled climate model point to changes in the el nin o southern oscillation state as a potential trigger for changes in the amount of pacific inflow into the caribbean

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