planktonic foraminiferal mg ca as a proxy for past oceanic temperatures a methodological overview and data compilation for the last glacial maximum as part of the multi proxy approach for the reconstruction of the glacial ocean margo incentive published and unpublished temperature reconstructions for the last glacial maximum lgm based on planktonic foraminiferal mg ca ratios have been synthesised and made available in an online database development and applications of mg ca thermometry are described in order to illustrate the current state of the method various attempts to calibrate foraminiferal mg ca ratios with temperature including culture trap and core top approaches have given very consistent results although differences in methodological techniques can produce offsets between laboratories which need to be assessed and accounted for where possible dissolution of foraminiferal calcite at the sea floor generally causes a lowering of mg ca ratios this effect requires further study in order to account and potentially correct for it if dissolution has occurred mg ca thermometry has advantages over other paleotemperature proxies including its use to investigate changes in the oxygen isotopic composition of seawater and the ability to reconstruct changes in the thermal structure of the water column by use of multiple species from different depth and or seasonal habitats presently available data are somewhat limited to low latitudes where they give fairly consistent values for the temperature difference between late holocene and the lgm 2 3 5 c data from higher latitudes are more sparse and suggest there may be complicating factors when comparing between multi proxy reconstructions

calibration of the planktonic foraminiferal mg ca paleothermometer sediment trap results from the guaymas basin gulf of california 1 the mg ca ratio has been measured in two surface dwelling species of planktonic foraminifera globigerinoides ruber and globigerina bulloides from biweekly sediment trap samples collected in guaymas basin gulf of california between august 1992 and november 1997 the guaymas basin experiences significant seasonal changes in sea surface temperature sst 16 33 c and thus is an ideal location for testing the temperature dependence of mg incorporation into foraminiferal calcite the planktonic foraminiferal mg ca ratios are directly compared with concurrent temperature measurements from the study site the results from the sediment trap study reveal a strong positive correlation between sst and the mg ca ratio in both g ruber r2 0 86 and g bulloides r2 0 90 the mg ca ratio increases exponentially by 7 per 1 c change in temperature for g ruber and by 6 for g bulloides these results indicate that the mg ca ratio in g ruber and g bulloides accurately records the measured seasonal surface temperature cycle and interannual variability in the guaymas basin within 1 c the greatest deviation between mg ca estimated sst and observed sst occurs in the spring and fall for both species this variability is attributed to rapidly changing hydrographic conditions and possible offset between the time of calcification and the temperature measurements in addition g ruber and g bulloides exhibit very high mg ca ratios during the strong el nino southern oscillation years of 1992 and 1997 verifying their potential to record sst up to 33 c and 28 c respectively the trace metal data are compared with foraminiferal oxygen isotope and alkenone measurements made on the same suite of sediment trap samples to assess the internal consistency of these temperature proxies strong correlations exist between the 18o and mg ca for g ruber r2 0 86 and g bulloides r2 0 79 similarly sea surface temperature estimates from mg ca ratios are in good agreement with alkenone derived temperature estimates r2 0 89 for g ruber and r2 0 81 for g bulloides

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

late glacial stage and holocene tropical ice core records from huascaran peru two ice cores from the col of huascaran in the north central andes of peru contain a paleoclimatic history extending well into the wisconsinan wurm glacial stage and include evidence of the younger dryas cool phase glacial stage conditions at high elevations in the tropics appear to have been as much as 8 to 12 c cooler than today the atmosphere contained about 200 times as much dust and the amazon basin forest cover may have been much less extensive differences in both the oxygen isotope ratio 18o 8 per mil and the deuterium excess 4 5 per mil from the late glacial stage to the holocene are comparable with polar ice core records these data imply that the tropical atlantic was possibly 5 to 6 c cooler during the late glacial stage that the climate was warmest from 8400 to 5200 years before present and that it cooled gradually culminating with the little ice age 200 to 500 years before present a strong warming has dominated the last two centuries

living planktonic foraminifera in the eastern south atlantic during spring indicators of water masses upwelling and the congo zaire river plume abstract planktonic foraminifera were collected from pumped surface water samples and net tows over the upper 150 m of the water column in the eastern south atlantic ocean during october and november 1989 of the 24 recorded species 12 occur abundantly and form 6 foraminiferal assemblages the assemblages correlate with the physico chemical properties of the 6 vapor surface water masses the correlation of species with low salinity is due to properties co variant with salinity at several locations high concentrations of planktonic foraminifera were observed caused by frontal mixing or reproduction the g sacculifer g ruber white assemblage marks the south equatorial under current minor contribution of g menardii and n dutertrei to this assemblage reflects the subsurface equatorial under current the n dutertrei g siphonifera assemblage reflects the south equatorial counter current and equatorial under current the n pachyderma g bulloides assemblage reflects the coastal upwelling over the shelf and the filaments of mixed oceanic and upwelled water in the coastal of the benguela current bc the angola benguela front at the interface of the warm currents and the bc is reflected by the g inflata g bulloides assemblage an unusual coincidence of g sacculifer g bulloides in one assemblage results from the interaction of the subtropical gyre and the oceanic branch of the bc the g rubber pink n dutertrei assemblage is attributed to the warm low saline plume in front of the congo zaire river

long chain alkenones and alkyl alkenoates as palaeotemperature indicators their production flux and early sedimentary diagenesis in the eastern north atlantic the production and fate of long chain alkenones and alkenoates was examined with regard to their use as palaeotemperature indicators alkenoate abundances were higher than previously reported for other regions and more strongly correlated with temperature than was alkenone unsaturation u37k suggesting biogeographical variability in alkenone and alkenoate production in surface waters we define the aa36 ratio to parameterize alkenoate abundance and present an empirical temperature calibration derived from our euphotic zone samples for use in the north atlantic t 17 35 25 12 u37k 26 73 aa36 93 90 u37k aa36 significant diagenetic losses of alkenones and alkenoates were found within the water column and near surface sediments in spite of diagenetic losses the temperature signal recorded by these compounds in the sediments remains largely unaltered and corresponds to the euphotic zone water temperature during the springtime period of maximum coccolithophorid production and flux rather than the average annual sea surface temperature

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

a tropical mechanism for northern hemisphere deglaciation 1 we investigate the role of the tropics in the melting and reforming of the laurentide ice sheet on glacial timescales using an atmospheric general circulation model it is found that warming of tropical sea surface temperatures ssts from glacial boundary conditions as observed at the end of glacial periods causes a large increase in summer temperatures centered over the ice sheet forming regions of canada this highlatitude response to tropical change is due to relatively small changes in the circulation of the extratropical atmosphere which lead to changes in the vertical profiles of temperature and moisture in the extratropical atmosphere the maximum perturbation in the summer radiative balance over the laurentide ice sheet 25 w m 2 due to the changes in the local atmospheric water vapor inventory is much larger than that induced by glacial to interglacial changes in atmospheric co2 these changes via an atmospheric bridge between the tropics and extratropics represent a mechanism for deglaciations which is consistent with timing constraints in contrast a cold perturbation to tropical sst for interglacial boundary conditions results in only very small changes in the delivery of water vapor to the laurentide region and therefore almost no cooling over the canadian region this implies that tropical ssts could play a more important role in melting ice sheets in the northern hemisphere than in reforming them possibly providing a mechanism which could help to explain the rapidity of deglaciation relative to glacial inception

sea surface temperatures of the western arabian sea during the last deglaciation 1 in this study we present a sea surface temperature sst record from the western arabian sea for the last 20 000 years we produced centennial scale d 18 o and mg ca sst time series of core niop929 with focus on the glacial interglacial transition the western arabian sea is influenced by the seasonal ne and sw monsoon wind systems lowest ssts occur during the sw monsoon season because of upwelling of cold water and highest ssts can be found in the low productivity intermonsoon season the mg ca based temperature record reflects the integrated sst of the sw and ne monsoon seasons the results show a glacial interglacial sst difference of 2c which is corroborated by findings from other arabian sea cores at 19 ka b p a yet undescribed warm event of several hundred years duration is found which is also reflected in the d 18 o record a second centennial scale high sst low d 18 o event is observed at 17 ka b p this event forms the onset of the stepwise yet persistent trend toward holocene temperatures highest mg ca derived ssts in the niop929 record occurred between 13 and 10 ka b p interglacial sst is 24c indicating influence of upwelling the onset of arabian sea warming occurs when the north atlantic is experiencing minimum temperatures the rapid temperature variations at 19 17 and 13 ka b p are difficult to explain with monsoon changes alone and are most likely also linked to regional hydrographic changes such as trade wind induced variations in warm water advection

the role of ocean atmosphere reorganizations in glacial cycles abstract a case is made that glacial to interglacial transitions involve major reorganizations of the ocean atmosphere system such reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere only in this way can the rapidity of glacial terminations the hemispheric synchroneity and symmetry of mountain glaciation and the large polar air temperature and dustiness variations be accounted for if these reorganizations are driven in some fashion by orbitally induced seasonal insolation changes then the connection between insolation and climate is most likely through impacts of fresh water transport on the ocean s salinity distribution

vanadium in foraminiferal calcite evaluation of a method to determine paleo seawater vanadium concentrations we assess the potential of using foraminiferal calcite as a paleoceanographic indicator of seawater v concentrations laboratory culture experiments show that living benthic and planktonic foraminifera incorporate v into their test in direct proportion to seawater concentrations distribution coefficients relative to the culture solution are d 2 1 10 3 and 2 8 10 3 for g calida and a lobifera respectively we use a cleaning procedure that effectively removes most v rich contaminant phases from foraminiferal calcite preserved in the fossil record including organic matter and mn fe oxyhydroxides mnco3 overgrowths cannot be eliminated since v is conservative in the ocean foraminiferal calcite recently accreted and found in surface sediment samples should have the same v content if this tracer accurately reflects seawater concentrations v ca values for the same species of foraminifera are constant for core top samples collected above the foraminiferal lysocline in different ocean basins the mean distribution coefficients relative to seawater are d 5 8 1 0 10 3 10 3 0 7 10 3 and 32 2 5 x 10 3 for g sacculifer g tumida and c wuellerstorfi respectively these differences suggest that v incorporation is species dependent core top analyses along two submarine rises in the equatorial atlantic and pacific oceans indicate significant dissolution effects with increasing depth of deposition and thus more extensive partial dissolution of the test vca decreases by a factor of three in g tumida increases by up to a factor of four in g sacculifer and increases by a factor of two in c wuellerstorfi no exchange between foraminiferal v and detrital v in sediments is observed over an interval of 200 kyr

factors controlling the fluoride content of planktonic foraminifera an evaluation of its paleoceanographic applicability abstract this work is an assessment of the effects of seawater salinity and temperature on the incorporation of fluoride into calcitic shells of planktonic foraminifera and of the subsequent modification of shell chemistry by postdepositional dissolution a strong correlation between the fluoride content of most planktonic species and their calcification depth was observed deeper calcifying foraminifera have lower fluoride content and heavier 18o composition perhaps suggesting a temperature control on the partition coefficient however species deviations from this general trend and the absence of correlation between fluoride and sea surface temperature within an individual species suggest that the coprecipitation of fluoride in foraminiferal calcite is more strongly controlled by biological processes rather than by simple chemical relationships foraminiferal fluoride shows weak or no correlation with sea surface salinity core top planktonic foraminifera from the eastern equatorial atlantic sierra leone rise show a substantial decrease of fluoride and to a lesser extent mg content with increasing water depth 2931 5104 m these decreasing trends with depth are attributed to selective dissolution i e removal of the more dissolution susceptible fraction with a different chemical composition than the residual a process which previously has been suggested to account for variations in the isotopic composition of planktonic foraminifera these findings indicate that foraminiferal fluoride cannot serve as a reliable tracer of oceanic paleo temperature or salinity it is possible however that fluoride may be useful for the study of dissolution in deep sea sediments

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

bayesian hierarchical regression analysis of variations in sea surface temperature change over the past million years statistical challenges often preclude comparisons among different sea surface temperature sst reconstructions over the past million years inadequate consideration of uncertainty can result in misinterpretation overconfidence and biased conclusions here i apply bayesian hierarchical regressions to analyze local sst responsiveness to climate changes for 54 sst reconstructions from across the globe over the past million years i develop methods to account for multiple sources of uncertainty including the quantification of uncertainty introduced from absolute dating into inter record comparisons the estimates of local sst responsiveness explain 64 62 to 77 95 interval of the total variation within each sst reconstruction with a single number there is remarkable agreement between sst proxy methods with the exception of mg ca proxy methods estimating muted responses at high latitudes the indian ocean exhibits a muted response in comparison to other oceans i find a stable estimate of the proposed universal curve of change in local sst responsiveness to climate changes as a function of sin2 latitude over the past 400 000 years sst change at 45 n s is larger than the average tropical response by a factor of 1 9 1 5 to 2 6 95 interval and explains 50 35 to 58 95 interval of the total variation between each sst reconstruction these uncertainty and statistical methods are well suited for application across paleoclimate and environmental data series inter comparisons

paleosecular variations of the geomagnetic field during the holocene from eastern asia abstract high resolution paleomagnetic secular variation psv records bear great information of dynamics processes of the earth s geomagnetic field and can be further used for inter profile correlation and for dating sediments however effects of changes in the depositional environment on psv records have not been fully determined this study constructed holocene psv records for the gravity piston core zsqd34 obtained from the northern south china sea rock magnetic and transmission electron microscope tem results indicate that single sd and psd domain magnetites are the main carrier of the natural remanent magnetization comparable to the records derived from the freshwater lakes and the modeling results we observed that direction curves from these two environments of contrasting salinity content are rather consistent the direction curves are independent of the constructed salinity however the gradual increasing trend of relative intensity since about 5 kyr might be related to the decreasing sea surface salinity furthermore on the centennial and millennial time scale the relative intensity and salinity show some positive relation suggesting a potential contribution of salinity to the paleomagnetic relative intensity recording processes

constraining past seawater δ18o and temperature records developed from foraminiferal geochemistry paired measurements of magnesium to calcium ratios mg ca and the stable oxygen isotopic composition 18o in foraminifera have significantly advanced our knowledge of the climate system by providing information on past temperature and seawater 18o 18osw a proxy for salinity and ice volume however multiple sources of uncertainty exist in transferring these downcore geochemical data into quantitative paleoclimate reconstructions here we develop a computational toolkit entitled paleo seawater uncertainty solver psu solver that performs bootstrap monte carlo simulations to constrain these various sources of uncertainty psu solver calculates temperature and 18osw and their respective confidence intervals using an iterative approach with user defined errors calibrations and sea level curves our probabilistic approach yields reduced uncertainty constraints compared to theoretical considerations and commonly used propagation exercises we demonstrate the applicability of psu solver for published records covering three timescales the late holocene the last deglaciation and the last glacial period we show that the influence of salinity on mg ca can considerably alter the structure and amplitude of change in the resulting reconstruction and can impact the interpretation of paleoceanographic time series we also highlight the sensitivity of the records to various inputs of sea level curves transfer functions and uncertainty constraints psu solver offers an expeditious yet rigorous approach to test the robustness of past climate variability inferred from paired mg ca 18o measurements

comparison of isotopic composition of planktonic foraminifera in plankton tows sediment traps and sediments planktonic foraminifera from plankton tows sediment traps and sediments in the central north atlantic were studied in order to understand what determines their oxygen and carbon isotope composition a clear separation of species and genera on a 18o vs 13c plot for all samples suggests that their isotopic composition is controlled to a certain degree by biological factors within a species population the globorotaliids show a positive linear correlation between 18o and 13c while the shallow dwelling spinose species mostly globigerinoides species do not show a definite trend the latter species when collected in plankton tows often show slight negative deviations from isotopic equilibrium with respect to oxygen all species deviate from carbon isotope equilibrium by 1 5 to 6 these deviations from equilibrium are probably caused by incorporation of isotopically light metabolic co2 into the skeleton which is enhanced by the activity of symbiotic algae during their ontogeny the average weight per individual of most species increases which indicates that calcification continues to a depth of about 100 m this additional skeleton roughly 50 by weight is isotopically heavier because temperatures are lower and photosynthesis of symbiotic algae stops below the photic zone therefore the skeleton of foraminifera collected in sediment traps below 400 m has an overall oxygen isotope composition that seems to be in equilibrium for caco3 deposited in the upper 100 m

evaluation of oxygen isotope and mg ca ratios in high magnesium calcite from benthic foraminifera as a proxy for water temperature oxygen isotope ratios 18o and mg ca ratios in organically produced calcium carbonate calcite and aragonite by marine species have been used as proxies for paleotemperature the relationship between the components of large benthic foraminiferal tests high magnesium calcite and seawater temperature has been little investigated yet we conducted culture experiments using two species of reef dwelling large benthic foraminifera under six temperature conditions 21 30 c we selected the perforate species calcarina gaudichaudii and the imperforate species amphisorus kudakajimensis both of which are host to algal symbionts for the experiments the results indicated the significant correlation of mg ca ratios c gaudichaudii and a kudakajimensis and 18o c gaudichaudii with temperature the test weight of both species showed temperature dependency with maxima at 27 c or 29 c and subsequent decline at 30 c after correction for the contribution of the initial tests which can be calculated from the weight ratios of the initial and cultured tests the relationships of the mg ca ratios and 18o to temperature were obtained with the least squares best fit method as follows c gaudichaudii t 18 5 4 52 18oc 18osw a kudakajimensis t 25 0 4 96 18oc 18osw and c gaudichaudii and a kudakajimensis mg ca 2 85 t 81 20 we concluded that species specific calibration is unnecessary for mg ca temperature relationship although it is necessary for 18o related to the different calcification mechanisms of imperforate a kudakajimensis and perforate c gaudichaudii species

oxygen isotope constraints on surface ocean temperatures published oxygen isotope results from benthic and planktonic foraminifera are used to constrain the extent to which surface ocean temperatures in the tropics changed between glacial and interglacial time the possible impacts of bioturbation and of the redistribution of 18o16o ratios within the sea putting aside the oxygen isotope results are consistent with the climap project conclusion that tropical ocean temperatures remained within 2 c of their present value

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

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

reconstructing sea surface temperature and salinity using δ 18 o and alkenone records the oxygen isotope 18o composition of foraminiferal tests from deep sea sediments is widely used as a palaeoclimate proxy but it includes contributions from sea surface temperature global ice volume and local salinity which are difficult to separate recently a new technique for deriving palaeotemperatures has been developed which is based on the abundance ratios of unsaturated alkenones in phytoplankton algae1 2 here we use a combination of oxygen isotope and alkenone records in a deep sea core from the juncture of the arabian sea and the bay of bengal to extract the salinity signal from the former record variations in salinity are related to the balance between evaporation and precipitation3 and are thus a sensitive indicator of climate change our 170 kyr salinity record enables us to reconstruct changes in the indian monsoon over this period considerably extending earlier studies which reached back to 18 kyr ago 4 8 like these previous studies we find that large variations in the monsoon occurred during the transition from the last glacial period to the present interglacial but our results also provide a view of the monsoon throughout the last glacial and demonstrate the potential of this approach for reconstructing palaeosalinity

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

the mean flow field of the tropical atlantic ocean the mean horizontal sow eld of the tropical atlantic ocean is described between 20in and 20is from observations and literature results for three layers of the upper ocean tropical surface water central water and antarctic intermediate water compared to the subtropical gyres the tropical circulation shows several zonal current and countercurrent bands of smaller meridional and vertical extent the wind driven ekman layer in the upper tens of meters of the ocean masks at some places the sow structure of the tropical surface water layer as is the case for the angola gyre in the eastern tropical south atlantic although there are regions with a strong seasonal cycle of the tropical surface water circulation such as the north equatorial countercurrent large regions of the tropics do not show a signi cant seasonal cycle in the central water layer below the eastward north and south equatorial undercurrents appear imbedded in the westward sowing south equatorial current the antarcic intermediate water layer contains several zonal current bands south of 3in but only weak sow exists north of 3in the sparse available data suggest that the equatorial intermediate current as well as the southern and northern intermediate countercurrents extend zonally across the entire equatorial basin due to the convergence of northern and southern water masses the western tropical atlantic north of the equator is an important site for the mixture of water masses but more work is needed to better understand the role of the various zonal under and countercurrents in cross equatorial water mass transfer 1999 elsevier science ltd all rights reserved

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

interglacials of the last 800 000 years interglacials including the present holocene period are warm low land ice extent high sea level end members of glacial cycles based on a sea level definition we identify eleven interglacials in the last 800 000 years a result that is robust to alternative definitions data compilations suggest that despite spatial heterogeneity marine isotope stages mis 5e last interglacial and 11c 400 ka ago were globally strong warm while mis 13a 500 ka ago was cool at many locations a step change in strength of interglacials at 450 ka is apparent only in atmospheric co2 and in antarctic and deep ocean temperature the onset of an interglacial glacial termination seems to require a reducing precession parameter increasing northern hemisphere summer insolation but this condition alone is insufficient terminations involve rapid nonlinear reactions of ice volume co2 and temperature to external astronomical forcing the precise timing of events may be modulated by millennial scale climate change that can lead to a contrasting timing of maximum interglacial intensity in each hemisphere a variety of temporal trends is observed such that maxima in the main records are observed either early or late in different interglacials the end of an interglacial glacial inception is a slower process involving a global sequence of changes interglacials have been typically 10 30 ka long the combination of minimal reduction in northern summer insolation over the next few orbital cycles owing to low eccentricity and high atmospheric greenhouse gas concentrations implies that the next glacial inception is many tens of millennia in the future

reassessing mg ca temperature calibrations of neogloboquadrina pachyderma sinistral using paired δ44 40ca and mg ca measurements the mg ca temperature calibration of the polar to subpolar planktonic foraminifera neogloboquadrina pachyderma sinistral sinistral indicates left coiling was refined by a multiproxy approach combining hydrographic temperature and salinity data with mg ca delta ca 44 40 and delta o 18 values from holocene nordic seas core top samples reliable mg ca based temperature estimates are limited to foraminiferal tests that calcified in water masses with temperatures above similar to 3 degrees c at habitat depth in these samples mg ca and delta ca 44 40 values are positively correlated mg ca mmol mol 0 77 0 22 x delta ca 44 40 parts per thousand srm 915a 0 52 0 12 n 20 r 2 0 76 both mg ca and delta ca 44 40 derived temperatures projected onto their corresponding depth intervals reveal that the apparent calcification depth of n pachyderma sinistral averaging the specimens whole life cycle is bound to an isopycnal layer defined by water densities sigma t between 27 7 and 27 8 this implies that n pachyderma sinistral prefers gradually deeper habitats with increasing sea surface temperatures thus counterbalancing absolute temperature variations consequently the total temperature range recorded in this foraminiferal species is restricted and only partly reflects environmental changes on the basis of the new mg ca delta ca 44 40 and delta o 18 multiproxy data set we propose a linear mg ca temperature relation for high latitude n pachyderma sinistral mg ca mmol mol 0 13 0 037 t degrees c 0 35 0 17 t 3 degrees c in core top samples from polar waters with peak summer temperatures below similar to 3 degrees c the temperature response in the mg ca and delta ca 44 40 proxy signal is inversed and poorly correlated both mg ca and delta ca 44 40 derived temperature estimates pretend significantly higher calcification temperatures than maximum summer sea surface temperatures of these water masses

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

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

paleo sea surface salinities in the low latitude atlantic the δ18o record of globigerinoides ruber white on the basis of the comparison of 18o values of globigerinoides ruber white 18og ruber from modern sediments and measured sea surface temperatures sst and salinity sss 18og ruber values most clearly record summer sst and sss of the uppermost 50 m of water in the low latitude atlantic a new transfer equation is presented for estimating local summer paleo sss at 0 50 m depth using 18og ruber paleo sst and the global 18o ice effect of sea water with the standard error reaching 0 72 0 77 sss the equation was applied to a 35 kyr long 18og ruber record and paleo sst estimates based on planktonic foraminiferal assemblages to reconstruct the paleo sss changes along the east atlantic margin off the northwest sahara the resulting local sss show a general increase by 0 3 1 4 during the last glacial maximum lgm and large parts of glacial termination i suggesting a general increase in the upwelling of the highly saline north atlantic central water and or a reduced lateral advection of less saline canary current water two short salinity lows up to 0 35 less than today during and after the lgm are coeval with the heinrich meltwater events 1 and 2 in the north atlantic indicating the breakdown of coastal upwelling and meltwater advection from the north both events are followed by an extreme sss maximum 38 15 along with the restoration of the salinity conveyor belt at 9 0 5 5 ka the salinity minimum up to 0 65 less than today reflects the continental runoff linked to the phase of strong north saharan humidity during the early holocene climatic optimum

seasonal and interannual variation in santa barbara basin water temperatures observed in sediment trap foraminiferal mg ca 1 we have generated a santa barbara basin sediment trap mg ca record to evaluate culture based calibration equations for the temperate subpolar planktonic foraminiferal species globigerina bulloides and neogloboquadrina pachyderma dextral g bulloides and n pachyderma mg ca are significantly correlated with seasonal variations in temperature of the near surface and subthermocline depths respectively the average deviation between mg based and 18o based temperature estimates is 0 6 c for g bulloides and 0 8 c for n pachyderma differences between mg derived temperatures and instrumental temperatures may be due to cleaning methods environmental factors such as seasonal variations in foraminiferal depth habitats or possible secondary effects on mg ca core top mg ca of both g bulloides and n pachyderma is in excellent agreement with average values from the sediment trap lending strong support for the interpretation of downcore mg ca from these species as annual average near surface and thermoclinal temperatures

comparison of terrestrial and marine temperature estimates for the past 135 kyr off southeast africa a test for gcm simulations of palaeoclimate a combined oxygen isotope planktonic foraminiferal and pollen record from the southwestern indian ocean makes possible a comparison between estimated lowland terrestrial temperatures and isotope and faunal sea surface temperatures the estimates of land and sea mean temperatures over the past 135 kyr are consistent to within 0 5 c and in all three records the maximum temperature changes between glacial and interglacial times are about 3 4 c

mg ca in the planktonic foraminifera globorotalia inflata and globigerinoides bulloides from western mediterranean plankton tow and core top samples abstract due to its strong gradient in salinity and small temperature gradient the mediterranean provides an ideal setting to study the impact of salinity on the incorporation of mg into foraminiferal tests we have investigated tests of globorotalia inflata and globigerina bulloides in plankton tow and core top samples from the western mediterranean using icp oes for bulk analyses and la icp ms for analyses of individual chambers in single specimens mg ca observed in g inflata are consistent with existing calibrations whereas g bulloides had significantly higher mg ca than predicted particularly in core top samples from the easterly stations scanning electron microscopy and laser ablation icp ms revealed secondary overgrowths on some tests which could explain the observed high core top mg ca we suggest that the mediterranean intermediate and deep water supersaturated with respect to calcite cause these overgrowths and therefore increased bulk mg ca however the different species are influenced by diagenesis to different degrees probably due to different test morphologies our results provide new perspectives on reported anomalously high mg ca in sedimentary foraminifera and the applicability of the mg ca paleothermometry in high salinity settings by showing that 1 part of the signal is generated by precipitation of inorganic calcite on the foraminifer test due to increased calcite saturation state of the water and 2 species with high surface to volume shell surfaces are potentially more affected by secondary mg rich calcite encrustation

cadmium zinc copper and barium in foraminifera tests the concentrations of cadmium zinc copper and barium have been determined on 2 mg samples of single species foraminifera populations cleaning techniques were tested using north atlantic core tops and followed by a detailed downcore study for the last 30 000 years in south atlantic core v22 174 raw foram tests cleaned by crushing followed by ultrasonic removal of fine grained material and dissolved in a ph 5 5 acetate buffer contain appreciable amounts of trace elements associated with ferromanganese and alumino silicate contaminants a reductive complexing cleaning treatment reduces ferromanganese contamination by 1 2 orders of magnitude acetate buffers at ph 5 5 complex iron and raise the solubility of ferromanganese oxides these buffers are unsuitable for separating carbonate lattice bound trace elements from the fraction associated with ferromanganese phases improved mechanical and ultrasonic reductive cleaning combined with a mild dissolution in distilled water under 1 atm pco2 reduces contaminant levels another order of magnitude the cd and zn concentrations order 10 8 mole cd mole ca and 10 5 mole zn mole ca of species with low surface area show an increase with decreasing isotopic temperatures this increase is consistent with the increasing concentrations of these metals from low values in surface waters to higher values at depth the variance of cd and zn over the last 30 000 years in the central south atlantic is consistent with the probable variability of the dissolved trace elements at the calcification levels of the species analyzed cu and ba are irreproducible and probably sensitive to residual contaminant phases the trace element content of the tests differs from levels observed in a recent coprecipitation study foraminifera may be a significant vector in zinc cycling in the ocean

pore fluid constraints on the temperature and oxygen isotopic composition of the glacial ocean pore fluids from the upper 60 meters of sediment 3000 meters below the surface of the tropical atlantic indicate that the oxygen isotopic composition 18 o of seawater at this site during the last glacial maximum was 0 8 0 1 per mil higher than it is today combined with the 18 o change in benthic foraminifera from this region the elevated ratio indicates that the temperature of deep water in the tropical atlantic ocean was 4 c colder during the last glacial maximum extrapolation from this site to a global average suggests that the ice volume contribution to the change in 18 o of foraminifera is 1 0 per mil which partially reconciles the foraminiferal oxygen isotope record of tropical sea surface temperatures with estimates from barbados corals and terrestrial climate proxies

glacial north atlantic sea surface conditions reconstructed by glamap 2000 the response of the tropical ocean to global climate change and the extent of sea ice in the glacial nordic seas belong to the great controversies in paleoclimatology our new reconstruction of peak glacial sea surface temperatures ssts in the atlantic is based on census counts of planktic foraminifera using the maximum similarity technique version 28 simmax 28 modern analog technique with 947 modern analog samples and 119 well dated sediment cores our study compares two slightly different scenarios of the last glacial maximum lgm the environmental processes of the ice age land oceans glaciers epilog and glacial atlantic ocean mapping glamap 2000 time slices the comparison shows that the maximum lgm cooling in the southern hemisphere slightly preceeded that in the north in both time slices sea ice was restricted to the north western margin of the nordic seas during glacial northern summer while the central and eastern parts were ice free during northern glacial winter sea ice advanced to the south of iceland and faeroe in the central northern north atlantic an anticyclonic gyre formed between 45degrees and 60degreesn with a cool water mass centered west of ireland where glacial cooling reached a maximum of 12degreesc in the subtropical ocean gyres the new reconstruction supports the glacial to interglacial stability of sst as shown by climap project members climap 1981 the zonal belt of minimum sst seasonality between 2degrees and 6degreesn suggests that the lgm caloric equator occupied the same latitude as today in contrast to the climap reconstruction the glacial cooling of the tropical east atlantic upwelling belt reached up to 6degrees 8degreesc during northern hemisphere summer differences between these simmax based and published u37 k and mg ca based equatorial sst records are ascribed to strong sst seasonalities and sst signals that were produced by different planktic species groups during different seasons

a new model for effects of impersistent joint sets on rock slope stability abstract joints often have profound effects on elastic properties and strength of rock masses and therefore on rock slope stability in surface mine slopes joints are usually too numerous to be taken into account individually so an equivalent properties approach is necessary previous work that treats a jointed rock mass as an equivalent composite material of joints and intact rock between resulted in excellent agreement between estimated and true rock mass elastic moduli in case of fully persistent joints for example pariseau wg an equivalent plasticity theory for jointed rock masses int j rock mech min sci 1999 36 7 907 18 rock mass failure mechanisms on joints and through intact rock were retained using influence functions obviating the need for an equivalent rock mass strength impersistent joints which are not continuous on a joint plane can be accommodated pariseau wg effects of joint persistence on jointed rock masses trans soc min metal explor 2003 314 121 8 however slope stability analysis of a large deep copper mine indicated a need for computational efficiency even in two dimensional analysis of vertical sections through pit walls puri s role of joint persistence in rock slope stability ms thesis department of mining engineering university of utah 2006 the analyses by the popular finite element method used small elements of bench size near the pit slopes and much larger elements away from the pit walls the reasons for the graded meshes were numerical accuracy small elements and computational economy large elements small elements contained only a few joints while the larger elements contained hundreds of joints and led to impractical computation run times on the order of days a new modeling procedure that recognizes sufficiently large elements as representative volume elements rves assists in overcoming this obstacle a companion improvement embeds a sufficient number of joints in rve size elements that then allows for recovery of joint failure mechanisms that are lost with the rve designation these innovations reduced pc pentium 4 run times by two orders of magnitude to a few hours

depth and seasonality of alkenone production along the california margin inferred from a core top transect alkenone unsaturation indices uk 37 of marine sediment could prove particularly useful on organic rich continental margins where carbonate dissolution hampers the use of other paleoclimatic proxies mccaffrey et al 1990 kennedy and brassell 1992 forty core top samples of recent sediment from a latitudinal transect 23 40 n along the california margin yield uk 37 values that correlate linearly with modern mean annual sea surface temperatures ssts in the range of 12 23 c reproducibility of the unsaturation value in closely spaced cores is near analytical error uk 37 data define a relationship to temperature nearly identical to the prahl et al 1988 laboratory cultures of emiliania huxleyi the close agreement is particularly significant in light of the nannofossil composition of the sediments where the abundance of the coccolith taxon gephyrocapsa oceanica known to synthesize alkenones equals or exceeds that of e huxleyi comparison with seasonal temperature variations at different depths indicates that little if any alkenone production occurs at depths 30 m along the continental margin water depths 2 km sediments in more pelagic locations exhibit small but consistent biases toward winter and or subsurface production similar to previously reported sediment trap and core top data from the oregon margin prahl et al 1993 doose et al 1997

sea surface temperature variability in the north atlantic during the last two glacial interglacial cycles comparison of faunal oxygen isotopic and mg ca derived records climate variability in the northeast atlantic was investigated on glacial interglacial and millennial time scales during the last 200 000 years using sea surface temperature sst records derived from planktonic foraminiferal diversities and from mg ca measurements on globigerina bulloides paleoceanographical interpretations are supported by species composition analyses benthic and planktonic isotopic data as well as records of iceberg rafted debris ird differences of climate development are recognized for both interglacial and glacial periods temperature estimates indicate slightly warmer conditions up to 2 c during marine oxygen isotope stage mis 5e than during the holocene in contrast to the last glaciation when the sst minimum coincided with a minimum in solar insolation immediately before termination i during the penultimate glaciation a long sst minimum occurred at times of intermediate solar insolation well preceding the onset of termination ii this discrepancy between two glacial terminations may be explained by an inherently different orbital configuration characteristic for each glacial interval despite these differences between the two glacial trends the superimposed shorter lived climatic events reveal the same order of principal steps implying their common causal nature a direct comparison of faunal ssts with those retrieved from mg ca analysis shows that mg ca derived temperatures follow the general glacial interglacial trend however the latter appear to be largely overestimated supported by 18o data in g bulloides which show little response to millennial scale variability there seems to be a need for species dependent calibration experiments that also consider the different oceanographic settings this particular species can live in

environmental processes of the ice age land oceans glaciers epilog knowledge of the state of the earth at the last glacial maximum lgm an interval around 21 000 years ago is an important benchmark for understanding the sensitivity of global environmental systems to change much progress in understanding climates of the lgm has occurred in the 20 years since the end of the climap project of the 1970s climate long range investigation mapping and prediction here we review this progress based on presentations and discussion at a rst open science meeting of the epilog project environmental processes of the ice age land oceans glaciers held in delmenhorst germany may 1999 we outline key controversies and document protocols for epilog contributions so that a new synthesis of the lgm earth can emerge as an open project of the world s community of scientists 2001 elsevier science ltd all rights reserved

rapid switches in subpolar north atlantic hydrography and climate during the last interglacial mis 5e plateauing just below early mis 5e values a planktonic d 18 o minimum during the cooling event indicates that marked freshening of the surface waters accompanied the cooling we suggest that switches in the subpolar gyre hydrography occurred during a warmer climate involving regional changes in freshwater fluxes balance and east greenland current influence in the study area the nature of these hydrographic transitions suggests that they are most likely related to large scale circulation dynamics potentially amplified by gis meltwater influences

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

high resolution sea surface temperature records derived from foraminiferal mg ca ratios during the last 260 ka in the northern south china sea abstract high resolution sea surface temperatures sst derived from mg ca ratios of globeriginoides sacculifer at odp site 1144 were reported to reveal the sst changes during the last 260 ka in the northern south china sea scs the results indicate an average holocene sst of about 26 7 c about 3 6 c increase from lgm to the holocene and higher temperature during mis 5 5 than the holocene these agree well with other foraminifer mg ca and uk37 sst records in this region the mg ca records suggest warmer ssts during mis 3 in the northern scs compared with those in the eastern pacific strong east asian summer monsoon during mis 3 indicated by paleoclimate records from nearby continents may account for it step wise increases during terminations are shown in our sst record and the beginning of deglacial warming occurs at about 19 ka which precedes the change of oxygen isotopes suggesting a tropical driven forcing for the sst change in the northern scs this is further supported by a robust semi precessional cycle centering at 9 1 ka in the spectra of the sst record which is absent in that of the oxygen isotopes however tropical driven forcing seems not to be indicated in another mg ca sst record in the northern scs oppo d w and sun y b 2005 amplitude and timing of sea surface temperature change in the northern south china sea dynamic link to the east asian monsoon geology 33 10 785 788 the discrepancy may be caused by different post deposition dissolutions of foraminifer tests at these two sites details about the modification of foraminifer mg ca ratios after burial however are not well known in this region and further studies are needed

scenarios regarding the lead of equatorial sea surface temperature over global ice volume 1 recent proxy evidences indicate that the equatorial sea surface temperature sst may have led global ice volume by 3 kyr during the late pleistocene glacial cycles given the short timescales of equatorial dynamics equatorial climate variability is characterized by a timescale of no more than a few years it would seem somewhat surprising therefore that the equatorial ocean and atmosphere can determine and lead the long timescale 100 kyr glacial cycles two scenarios are presented according to which such a lead may be observed even when the equatorial ocean and atmosphere are not necessarily responsible for leading the glacial cycles they may still act as a strong amplifier first it is shown that if the plankton based proxy reflects the warm season temperature rather than an annual temperature it may lead the global temperature although the dynamics of the glacial cycles may still be dominated by the northern hemisphere ice sheets it is noted that a present day seasonal bias of the equatorial proxy record is still inconclusive and the possibility of a proxy bias only during glacial times is considered as well a second scenario is suggested in which global sea level rises before equatorial sst yet the later evolution of factors such as the atmospheric co2 and equatorial sst is faster and takes the lead over global ice volume if the initial rise of sea level is masked by a sufficiently large proxy noise because of instrumental and natural noise it may not be seen and the lead may be attributed to the equatorial sst and co2

sea surface temperatures of southern midlatitudes 0 160 kyr b p 1 late quaternary climate fluctuated between extremes of glaciations lasting 90 kyr on average and interglacial episodes lasting 10 kyr still largely unknown are the spatial and temporal evolution of these global climate states with vigorous debate still underway on the mechanisms responsible for glacial inceptions and terminations though it is widely believed that the southern hemisphere oceans play a central role in global climate changes few paleoclimate records exist from there here we present three new alkenone derived sst records from the midlatitude southern hemisphere spanning the last 160 kyr a full glacial interglacial cycle our subtropical sst records from the last glacial period are characterized by 1 warming 47 23 kyr b p when high latitudes in both hemispheres cooled and 2 milder temperatures during the penultimate glacial period than during the last glacial interval these sst features are found to be of tropical to subtropical wide extent implying increased thermal gradients at times of high latitude ice sheet growth this has implications for the vigor of atmospheric and upper ocean circulation and the transport of heat and moisture to the poles that may have been instrumental in the growth and maintenance of polar ice sheets during glacial periods

diagenetic mg calcite overgrowths on foraminiferal tests in the vicinity of methane seeps methane is a potent greenhouse gas and some episodes of past global warming appear to coincide with its massive release from seafloor sediments as suggested by carbon isotope records of foraminifera here we present structural geochemical and stable carbon isotope data from single foraminiferal calcite tests and authigenic mg calcite overgrowths in a sediment core recovered from an area of active methane seepage in western svalbard at ca 340 m water depth the foraminifera are from intervals in the core where conventional bulk foraminiferal 13c 13c values are as low as 11 3 mg ca analyses of the foraminiferal tests reveal that even tests for which there is no morphological evidence for secondary authigenic carbonate can contain mg rich interlayers with mg ca up to 220 mmol mol transmission electron microscopy tem of the contact point between the biogenic calcite and authigenic mg calcite layers shows that the two phases are structurally indistinguishable and they have the same crystallographic orientation secondary ion mass spectrometry sims analyses reveal that the mg rich layers are strongly depleted in 13c 13c 13c as low as 34 1 these very low 13c 13c values indicate that the authigenic mg calcite precipitated from pore waters containing methane derived dissolved inorganic carbon at the depth of the sulfate methane transition zone smtz as the depth of the smtz can be located several meters below the sediment seawater interface interpretation of low foraminiferal 13c 13c values in ancient sediments in terms of the history of methane seepage at the seafloor must be undertaken with care

trace element cartography of globigerinoides ruber shells using particle induced x ray emission 1 micro particle induced x ray emission pixe is a nondestructive elemental analysis technique that can be used to map the distribution of elements with a spatial resolution of 4 m2 and a penetration depth of 2 m in a calcite matrix to test its potential to improve our understanding of trace element distribution in foraminifera shells we mapped the mg distribution across individual chambers of the planktonic species globigerinoides ruber g ruber shells were picked from equatorial atlantic surface sediments sierra leone rise they ranged from well preserved to heavily dissolved tests the mapping of trace elements across test chambers made it possible to discriminate between variability inherent to the shell material and heterogeneity linked to contaminant phases contaminating mineral phases were characterized by high mg concentrations mg ca 19 7 mmol mol and high levels of si al and fe mg ca values of well preserved shells ranged from 3 9 to 4 5 mmol mol the mg to ca ratios of partially dissolved shells varied between 1 8 and 3 4 mmol mol between outer and inner chambers low and homogeneous mg ca values of 2 0 and 2 3 mmol mol were determined for chambers of a severely dissolved test

reconciling strong slab pull and weak plate bending the plate motion constraint on the strength of mantle slabs although subducting slabs undergo a bending deformation that resists tectonic plate motions the magnitude of this resistance is not known because of poor constraints on slab strength however because slab bending slows the relatively rapid motions of oceanic plates observed plate motions constrain the importance of bending we estimated the slab pull force and the bending resistance globally for 207 subduction zone transects using new measurements of the bending curvature determined from slab seismicity predicting plate motions using a global mantle flow model we constrain the viscosity of the bending slab to be at most similar to 300 times more viscous than the upper mantle stronger slabs are intolerably slowed by the bending deformation weaker slabs however cannot transmit a pull force sufficient to explain rapid trenchward plate motions unless slabs stretch faster than seismically observed rates of similar to 10 15 s 1 the constrained bending viscosity similar to 2 x 10 23 pa s is larger than previous estimates that yielded similar or larger bending resistance here similar to 25 of forces this apparent discrepancy occurs because slabs bend more gently than previously thought with an average radius of curvature of 390 km that permits subduction of strong slabs this gentle bending may ultimately permit plate tectonics on earth c 2008 elsevier b v all rights reserved

comparing proxies for the reconstruction of lgm sea surface conditions in the northern north atlantic abstract within the frame of the multiproxy approach for the reconstruction of the glacial ocean margo project sea surface conditions of the last glacial maximum lgm 23 19 ka were reconstructed using different proxies which were calibrated to a standardized modern hydrography in the north atlantic the revised lgm margo data set provides a comprehensive coverage including the nordic seas the data set includes reconstruction based on planktonic foraminifer assemblages dinocyst assemblages alkenone coccolithophorid biomarkers and mg ca ratios in planktonic foraminifers several hydrological features of the lgm north atlantic can be identified that are supported by all four proxies they include an extensive perennial sea ice cover along the eastern canadian and greenland margins seasonally ice free central north atlantic and norwegian sea and the winter sea ice limit being located at about 55 n all proxies also suggest significantly colder than modern sea surface conditions in the southeastern part of the north atlantic and a more zonal temperature pattern than at present with a steep sst gradient of the order of 10 c between 40 n and 45 n however in the nordic seas large discrepancies remain well above the level of uncertainty of the sst reconstructions these discrepancies might be related to stratification of the upper water mass linked to large annual amplitude of temperature with contrasting winter and summer conditions high interannual interdecadal variability or taphonomic processes affecting some of the proxies the average lgm sst in the nordic seas cannot at present be assessed with confidence however the existing evidence suggests that highly variable sea surface conditions and at least occasional advection of north atlantic waters may have characterised the glacial nordic seas

planktonic foraminifers as tracers of ocean currents in the eastern south atlantic the standing stock of planktonic foraminifers collected at 16 stations by multinet plankton tow has been examined in five discrete depth intervals 0 25 m 25 50 m 50 100 m 100 150 m and 150 300 m the assemblages document the status of populations in the surface and subsurface waters of the southeast atlantic during february march 1988 standing crops document hydrographic conditions in the coastal and geostrophic branch of the benguela current the angola current the tropical cyclonic gyre and the south equatorial current standing stocks are highest when primary production is intermediate very high primary production reduces foraminiferal crops significantly eleven species occur abundantly average 10 of the total standing stock a few species g glutinata g quinqueloba g clarkei are abundant at each station whereas the occurrence of other species g ruber g sacculifer g scitula g menardii g crassaformis n incompta n dutertrei is spatially restricted g ruber g rubescens and g glutinata are abundant in high salinity surface water also g ruber is abundant within the equatorial undercurrent water when this water is brought to the surface high concentrations of n incompta and g bulloides are observed in the angola benguela front when nutrient concentration is moderately elevated in surface and subsurface water upper part of the thermocline g crassaformis becomes abundant in the subsurface water of the angola benguela front this species is restricted to lower oxygenated subsurface water and traces incursions of water transported by the angola current g menardii is considered as an indicator for the equatorial undercurrent below the mixed layer whereas g scitula most probably points to an admixture of water transported by the northward flowing benguela current high abundances of g quinqueloba g clarkei in the surface and subsurface waters reflect favorable nutrient conditions like those present in the geostrophic benguela current and in the equatorial divergence zone g falconensis n dutertrei and g siphonifera appear to trace the southern equatorial current

li sr mg and na in foraminiferal calcite shells from laboratory culture sediment traps and sediment cores abstract constant temperature laboratory culture experiments of the planktonic foraminiferal species globigerinoides sacculifer brady suggest that the ratios of li and sr to ca in the shells are a function of these ratios in the culture solutions mg ca and na ca in the shells did not vary with changes of these ratios in the culture solution these are the first direct determinations of the relationship between foraminiferal shell chemistry and solution composition the possibility of temperature dependence for the minor elemental composition of foraminiferal shells was also investigated in the laboratory and by analysis of several planktonic and one benthic foraminiferal species from sediment trap and sediment core samples the sr ca mg ca and na ca ratios in the natural samples roughly correlate with calcification temperature whereas differences in the li ca ratios are small and not systematically related to temperature however laboratory culture experiments at 20 c and 30 c showed no variation in the li ca sr ca mg ca and na ca ratios with calcification temperature for the planktonic foraminifera g sacculifer and orbulina universa therefore observed differences in the sr ca mg ca and na ca ratios for the sediment trap and core foraminiferal samples cannot be ascribed to direct effects of calcification temperature but may be due to some other environmental factor which is correlated with temperature

structure of the upper water column in the northwest north atlantic modern versus last glacial maximum conditions 1 during the last glacial maximum the northwestern north atlantic constituted a major conduit for labrador and greenland ice sheet meltwaters vertical density gradients in its upper water masses have been reconstructed by combining information from transfer functions based on dinocysts and from oxygen isotope measurements 18o in planktonic foraminifera transfer functions yield temperature and salinity and thus potential density for the warmest august and coldest february months in the photic zone the 18o values in different size fractions of epipelagic globigerina bulloides and mesopelagic neogloboquadrina pachyderma left coiled npl foraminifera allow us to assess gradients through the pycnocline between surface and intermediate waters based on the calibration of a versus 18o relationship from transfer function reconstructions the size and density of npl shells provide further constraints on these gradients the results show the development of a very strong pycnocline during the lgm with a difference of about 3 summer to 1 5 winter units between surface and underlying waters they indicate conditions unfavorable for vertical convection and support the hypothesis of the spreading of a shallow low salinity buoyant layer over the northern north atlantic this layer depicted a strong e w gradient with maximum seasonal contrast and minimum absolute values westward

synchronous tropical south china sea sst change and greenland warming during deglaciation the tropical ocean plays a major role in global climate it is therefore crucial to establish the precise phase between tropical and high latitude climate variability during past abrupt climate events in order to gain insight into the mechanisms of global climate change here we present alkenone sea surface temperature sst records from the tropical south china sea that show an abrupt temperature increase of at least 1 c at the end of the last glacial period within the recognized dating uncertainties this sst increase is synchronous with the bolling warming observed at 14 6 thousand years ago in the greenland ice sheet project 2 ice core

assessment of sea surface temperature variations in the central north atlantic using the alkenone unsaturation index u37k abstract a high resolution record of u37k derived sst estimations has been obtained in a core from the central north atlantic ocean su90 08 43 30 n 30 24 w spanning a time period of 280 ky the general trend of the u37k profile parallels closely the 180 signal and represent an independent confirmation that the sst variations in the glacial interglacial time scales are correlated with the northern ice sheets evolution in contrast to the climap 1984 conclusions based on the foraminiferal transfer function technique the sst during the last interglacial period lip isotopic stage 5 5 are 2 3 c warmer than during the holocene this result is in good agreement with many studies based in coastal and continental records that strongly suggest warmer climatic conditions over north america and europe finally the sst estimates during the last glacial maximum lgm 18 ky bp where 4 5 c cooler than during the previous glacial period pgp stage 6 we argue that this difference is caused by a northward position of the polar front during the pgp in the central north atlantic

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

a 5 million year comparison of mg ca and alkenone paleothermometers geochemical sea surface temperature sst proxies such as the magnesium to calcium ratio mg ca in foraminifera and the alkenone unsaturation index uk 37 are becoming widely used in pre pleistocene climate records this study quantitatively compares previously published mg ca and uk 37 data from ocean drilling program odp site 847 in the eastern equatorial pacific to assess the utility of these proxies to reconstruct tropical sst over the last 5 ma foraminiferal mg ca sst calibrations that include a dissolution correction are most appropriate at this location because they provide sst estimates for the youngest sample that are close to modern mean annual sst the long term trends in the two records are remarkably similar and confirm a 3 5 c cooling trend from the early pliocene warm period to the late pleistocene noted in previous work absolute temperature estimates are similar for both proxies when errors in the dissolution correction used to estimate sst from mg ca are taken into account comparing the two sst records at odp site 847 to other records in the region shows that the eastern equatorial pacific was 2 4 c warmer during the early pliocene compared to today

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

carbonate dissolution and abyssal hydrography in the atlantic ocean abstract surface sediment samples from two regions in the eastern atlantic angola basin and cape verde basin and two regions in the western atlantic brazil basin and vema channel were examined to evaluate the relationship among carbonate dissolution abyssal hydrography and carbonate chemistry of the water column at each of these locations the position of the lysocline was determined carbonate saturation 1 was calculated and major deep water mass boundaries were identified as previously observed the correlation among these variables is strikingly different between the eastern and western atlantic in the vema channel and the brazil basin there is a first order correlation among the position of the lysocline the benthic thermocline aabw nadw boundary and the transition from saturation to undersaturation with respect to carbonate this relationship breaks down in the eastern atlantic where there is no noticeable benthic thermocline and the lysocline occurs significantly deeper than the saturation undersaturation transition

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