mg ca temperature calibration for costate bulimina species b costata b inflata b mexicana a paleothermometer for hypoxic environments abstract costate species of bulimina are cosmopolitan infaunal benthic foraminifers which are common in the fossil record since the paleogene in the present study we evaluate the temperature dependency of mg ca ratios in bulimina inflata b mexicana and b costata from an extensive set of core top samples from the atlantic pacific and indian oceans the results show no significant offset in mg ca values between costate morphospecies when present in the same sample the apparent lack of significant inter specific inter morphotype differences amongst the analyzed costate buliminids allows for the combined use of their data sets for our core top calibration over a bottom water temperature bwt range of 3 13 c the bulimina species show a sensitivity of 0 12 mmol mol c which is comparable to that of epifaunal cibicidoides species and higher than that of the shallow infaunal uvigerina spp the most commonly used taxon in mg ca based palaeotemperature reconstruction the reliability and accuracy of the new mg ca temperature calibration is corroborated in the fossil record by a case study in the timor sea which demonstrates the presence of southern sourced waters at intermediate depths for the past 26 000 years costate species of bulimina might thus provide a valuable alternative for bwt reconstruction in mesotrophic to eutrophic settings where many of the commonly used more oligotrophic species are rare or absent and be particularly useful in hypoxic settings such as permanent upwelling zones where costate buliminids often dominate foraminiferal assemblages the evaluation further reveals a mean positive offset of 0 2 mmol mol of the atlantic data set over the indo pacific data set which contributes to the scatter in our calibration although an explanation for this offset is not straightforward and further research is necessary we hypothesize that different levels of export production and carbonate ion concentrations in pore waters are likely reasons

the salinity temperature and δ18o of the glacial deep ocean we use pore fluid measurements of the chloride concentration and the oxygen isotopic composition from ocean drilling program cores to reconstruct salinity and temperature of the deep ocean during the last glacial maximum lgm our data show that the temperatures of the deep pacific southern and atlantic oceans during the lgm were relatively homogeneous and within error of the freezing point of seawater at the ocean s surface our chloride data show that the glacial stratification was dominated by salinity variations in contrast with the modern ocean for which temperature plays a primary role during the lgm the southern ocean contained the saltiest water in the deep ocean this reversal of the modern salinity contrast between the north and south atlantic implies that the freshwater budget at the poles must have been quite different a strict conversion of mean salinity at the lgm to equivalent sea level change yields a value in excess of 140 meters however the storage of fresh water in ice shelves and or groundwater reserves implies that glacial salinity is a poor predictor of mean sea level

momentum and heat balances in steady coastal currents abstract the momentum balance for coastal currents forced by a longshore wind stress and a longshore density gradient is examined for coastlines of various orientations we isolate the coastal circulation by requiring that the longshore wind stress and density gradient become uniform in the adjacent deep ocean in which the longshore bottom pressure gradient is assumed to be zero and derive a vorticity equation for the longshore current for a prescribed cross shelf variation of wind stress and density structure solutions of this equation are obtained for a uniform longshore wind stress along a coastline with an exponential shelf in two situations a for a uniform cross shelf density on the inner shelf and a zero longshore bottom pressure gradient on the outer shelf the division between the two regions occurring approximately at the depth of the main thermocline and b for a thermohaline structure which is independent of the cross shelf co ordinate such that the coastal current is barotropic it is shown that on a zonal coast the coastal transports due to the wind stress forcing are of o wl 0 and due to the density gradient forcing of o 0 gh t 2 0 l where wl and 0 0 l are respectively the longshore wind stress and surface density gradient 0 is a reference density for seawater g is the acceleration of gravity h t is the scale depth for the main thermocline d f d y where f 2 sin in which is the angular speed of rotation of earth and is the latitude and w t w is a shelf parameter in which w t is the exponential shelf scale depth and w is an eddy scale on eastern boundaries the transports are less especially in a and are identically zero on western boundaries on which the transport is determined by external non local processes the longshore velocity structure on the western boundary depends strongly on and incorporates a system of currents and counter currents the heat balance for the coastal circulation is investigated by considering the solution of the heat conservation equation for the surface temperature with the cross shelf boundary conditions of zero heat flux through the coast and into deep ocean it is found that the sea surface temperature anomaly is zero for wind stress forcing and positive for density gradient forcing at constant salinity mixed forcing however may lead to upwelling which is characterized by a negative sea surface anomaly upwelling occurs on non western boundaries on which there is a longshore wind stress of sufficient intensity or on western boundaries where there is an external transport of sufficient magnitude to generate a net transport up the longshore surface density gradient this occurs on eastern coasts where there is poleward advection of warm water and sufficiently strong equatorward meridional winds and on western coasts in a polar gyre where there is a strong equatorward external transport and a poleward temperature gradient the ekman circulation maintains the upwelling anomalies

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

mg ca temperature proxy in benthic foraminifera new calibrations from the florida straits and a hypothesis regarding mg li 1 over the past decade the ratio of mg to ca in foraminiferal tests has emerged as a valuable paleotemperature proxy however large uncertainties remain in the relationships between benthic foraminiferal mg ca and temperature mg ca was measured in benthic foraminifera from 31 high quality multicore tops collected in the florida straits spanning a temperature range of 5 8 to 18 6 c new calibrations are presented for uvigerina peregrina planulina ariminensis planulina foveolata and hoeglundina elegans the mg ca values and temperature sensitivities vary among species but all species exhibit a positive correlation that decreases in slope at higher temperatures the decrease in the sensitivity of mg ca to temperature may potentially be explained by mg ca suppression at high carbonate ion concentrations it is suggested that a carbonate ion influence on mg ca may be adjusted for by dividing mg ca by li ca the mg li ratio displays stronger correlations to temperature with up to 90 of variance explained than mg ca alone these new calibrations are tested on several last glacial maximum lgm samples from the florida straits lgm temperatures reconstructed from mg ca and mg li are generally more scattered than core top measurements and may be contaminated by high mg overgrowths the potential for mg ca and mg li as temperature proxies warrants further testing

improved oxygen isotope temperature calibrations for cosmopolitan benthic foraminifera abstract despite decades of use as a paleoceanographic proxy considerable uncertainty still surrounds the temperature dependence of benthic foraminiferal 18o widely applied paleotemperature equations may mix non equilibrium foraminifera with equilibrium synthetic calcite resulting in temperature sensitivities that are too large warm water foraminiferal calibrations may give temperature sensitivities that are too small for very cold waters here we combine new core top measurements from the florida straits and the arctic ocean with published data to derive new 18o temperature relationships for three groups of benthic foraminifera we derive a quadratic equation for cibicidoides and planulina that agrees well with equilibrium synthetic calcite and that should be applicable over all oceanographic temperatures we find that uvigerina is not at equilibrium and is isotopically heavier than cibicidoides and planulina by 0 47 in contrast to the historically used 0 64 hoeglundina elegans is further enriched and appears to be slightly heavier than equilibrium aragonite finally we discuss the implications of the florida straits observations for the hypothesis that benthic foraminifera precipitate their shells from a ph dependent mixture of bicarbonate and carbonate ions

western equatorial pacific deep water carbonate chemistry during the last glacial maximum and deglaciation using planktic foraminiferal mg ca to reconstruct sea surface temperature and seafloor dissolution 1 we present a reconstruction of deep water carbonate saturation state co32 in the western equatorial pacific for the last glacial maximum lgm and deglaciation based on changes in the mg ca ratio of planktic foraminifers with increased water depth our data suggest there have been changes in bottom water co32 over the past 25 000 years at water depths as shallow as 1 6 km the co32 reconstruction for the lgm suggests co32 was similar or slightly higher than modern values between 1 6 and 2 0 km shifting sharply to lower values an average 30 mol kg lower below 2 5 km the shift in chemistry between 2 0 and 2 5 km supports a hypothesis that pacific overturning circulation occurred deeper during the lgm with a slightly more ventilated water mass above 2 0 km the data are not consistent with enhanced preservation in this region of the deep pacific at depths greater than 2 5 km suggesting that the long held view of better preservation throughout the glacial deep pacific must be reevaluated for the deglaciation we have evidence of a co32 maximum that suggests enhanced deglacial preservation between 1 6 and 4 0 km in comparison to the holocene and the lgm the deglacial co32 was as much as 28 mol kg higher than modern between 1 6 and 4 0 km results suggest carbonate burial rates were 1 5 times greater during the deglacial than the over the past 5 kyr

ecological evidence from live dead comparisons of benthic foraminiferal faunas off cape blanc northwest africa abstract a comparison of live and dead benthic foraminiferal faunas in a five station sample transect off cape blanc suggests that interspecific differences in living dead l d ratios are to a large extent determined by seasonal differences in reproduction it is proposed that many epifaunal and superficial infaunal species show a highly opportunistic behaviour with a majority of the foraminifera being produced in a relatively short period of the year the density of deeper infaunal taxa on the contrary would be much more stable over time sites with large contrasts in l d ratios between deep intermediate infaunal and epifaunal shallow infaunal taxa should be subject to important seasonal variations in the downward flux of organic matter this study suggests that important ecological information can be gained from live dead comparisons

mg ca in the benthic foraminifera cibicidoides wuellerstorfi and cibicidoides mundulus temperature versus carbonate ion saturation magnesium calcium mg ca ratios in two widely used benthic foraminiferal species cibicidoides wuellerstorfi and cibicidoides mundulus cibicidoides kullenbergi picked from global ocean core tops and from six cores in the north atlantic ocean have been measured to investigate mg ca variability cleaning effect and influences from bottom water temperature bwt and deep water carbonate ion saturation co32 replicate measurements of the two species reveal mg ca variability of 0 07 0 07 mmol mol compared with mg ca in samples cleaned by oxidative cleaning mg ca ratios are significantly lowered by 0 10 0 09 mmol mol in samples cleaned by reductive cleaning likely due to preferential leaching during the reductive cleaning step the cleaning influence is large relative to glacial interglacial mg ca changes 0 05 0 31 mmol mol by this study regression of core top data from a wide range of locations show that c wuellerstorfi mg ca is strongly affected by deep water co32 with a sensitivity of 0 009 mmol mol per mol kg when bwt is included in regressions the correlation is slightly more significant with a weak bwt sensitivity on mg ca of between 0 03 0 01 and 0 07 0 02 mmol mol per c because co32 and bwt co vary for most core top samples an alternate method of separating the two effects was made by comparing glacial to interglacial changes in mg ca from a depth transect of north atlantic cores where the bwt and carbonate ion histories since the last glacial period have been well constrained results from this transect suggest that the bwt effect is 0 03 mmol mol per c weaker than inferred from the core top study therefore core top and down core data suggest that c wuellerstorfi mg ca is insensitive to bwt changes the weak bwt effect when compared with natural variability complicates the use of mg ca in this species to reconstruct past bwt taking all measured samples from various environments into account c mundulus mg ca ratios show no correlation with bwt or deep water co32

quaternary deep sea temperature histories derived from benthic foraminiferal mg ca abstract we have generated benthic foraminiferal mg ca records from eastern tropical atlantic core m16772 3 9 km and eastern tropical pacific core tr163 31p 3 2 km to assess the potential for using benthic mg paleothermometry to reconstruct quaternary bottom water temperature histories variations in mg ca records from both the atlantic and pacific show a significant correlation with climatic oscillations of the last 330 kyr shell mg ca peaks during interglacial episodes with marine isotope stage mis 5e mg ca nearly matching holocene values in both cores lower mg ca values occur during glacial intervals to estimate temperatures from downcore mg ca we have augmented the published cibicidoides sp mg ca temperature dataset rosenthal et al geochim cosmochim acta 61 1997 3633 3643 with new data to include the temperature range of deep waters applying the 10 9 change in mg ca per c defined by the expanded calibration to the deep atlantic data implies glacial interglacial shifts in deep water temperature of 2 4 c over the last 300 kyr temperature estimates are comparable to deep atlantic temperature changes proposed by labeyrie et al nature 327 1987 477 482 there is greater uncertainty in deriving temperatures from the tropical pacific core due to a limited uvigerina spp core top calibration set however glacial interglacial temperature oscillations appear to be on the order of 2 3 c in addition core tr163 31p records clear millennial scale mg ca and 18 o oscillations in mis 3 corresponding to temperature fluctuations of 0 5 c additional calibration studies are needed to address potential secondary effects on mg ca

late holocene variability of upper north atlantic deep water temperature and salinity 1 magnesium calcium ratios in benthic foraminifera cibicidoides pachyderma from a sediment core on the laurentian slope 1854 m exhibit strong millennial scale fluctuations during the past 4000 years we convert these data to seawater paleotemperatures using a new monospecific linear equation results suggest that the temperature of upper north atlantic deep water dominated by labrador seawater today has varied by at least 2 c during the late holocene millennial scale coolings coincide with previously identified periods of increased drift ice and regional glacier advances including the little ice age paired oxygen isotope measurements indicate that salinity and perhaps density were reduced during the cold periods we discuss possible mechanisms for transmitting this cold fresh signal from surface waters to intermediate depths our reconstructed late holocene ranges in upper north atlantic deep water properties greatly exceed those of the instrumental record and imply that large changes may be yet to come

refining benthic foraminiferal mg ca temperature calibrations using core tops from the western tropical atlantic implication for paleotemperature estimation benthic foraminiferal mg ca has been shown to have great potential as a proxy for reconstructing deep water temperatures however the exact relationship between mg uptake in benthic foraminifera and temperature is still ambiguous and further exploration and refinement is much needed to reduce uncertainties associated with the method here we present new core top mg ca data from benthic foraminiferal species from the lower part of the thermocline in the western tropical atlantic northern brazilian margin this area is unusual in that the changes in carbonate chemistry along the transect are very small making it an ideal region for isolating and studying the role of temperature in the incorporation of mg into the benthic shells our results show that benthic foraminiferal mg ca largely reflects temperature in this area our data are combined with previously published data to produce new and improved mg ca calibration equations for a number of benthic foraminiferal species within the atlantic ocean our study provides the first c wuellerstorfi mg ca data for the 46 degrees c temperature range and indicates that c wuellerstorfi mg ca is strongly controlled by temperature as a result the newly established c wuellerstorfi calibration over the entire 06 degrees c temperature range is significantly improved with respect to previously published c wuellerstorfi calibrations limited to the coldest part between 0 and 4 degrees c other benthic species cibicidoides kullenbergi globocassidulina subglobosa uvigerina peregrina and oridorsalis umbonatus have also been studied although these results are less conclusive

benthic foraminifera as bio indicators of drill cutting disposal in tropical east atlantic outer shelf environments we present a study of benthic foraminiferal faunas from the outer continental shelf off congo tropical west africa with the aim to determine the impact of the discharge of oily drill cuttings on the sea floor environment to judge the regenerating capacity of the benthic ecosystem and to investigate the possibility to develop an environmental monitoring method for open marine continental shelf environments based on benthic foraminifera we studied the spatial distribution and microhabitats of living and dead foraminiferal faunas sampled in april 2003 4 years after the end of disposal activities in the upper 3 cm of the sediment at 9 stations about 180 m depth offshore congo that were subject to various degrees of pollution by oily cuttings from 1993 until 1999 our results describe a zonation of foraminiferal faunas in the 750 m around the former disposal sites at the immediate vicinity of the discharge points within 70 m faunas are characterized by low foraminiferal densities faunas between 70 m and 250 m of the disposal sites have very high foraminiferal densities with high percentages about 80 of opportunistic taxa such as bulimina aculeata bulimina marginata textularia sagittula trifarina bradyi and bolivina spp between 250 and 750 m from the disposal site foraminiferal densities decrease and the percentages of opportunistic species are lower 40 60 of indicator species these results show that 4 years after the cessation of oily cutting disposal strong environmental impact is limited to the 250 m around the disposal sites we used these data to develop a quantitative pollution index values of which are strongly correlated to distance to the disposal site this foraminiferal index offers the possibility to quantify the impact of anthropogenic eutrophication in continental shelf environments but its validity must be tested in other continental shelf environments

a record of bottom water temperature and seawater δ18o for the southern ocean over the past 440 kyr based on mg ca of benthic foraminiferal uvigerina spp the sensitivity to temperature of mg ca ratios in the shallow infaunal benthic foraminifera uvigerina spp has been assessed core top calibrations over 1 20 c show a range in sensitivity of 0 065 0 084 mmol mol c but few data are available spanning the temperature range anticipated in deep sea records over glacial interglacial cycles in contrast to epibenthic foraminiferal species carbonate ion saturation appears not to affect mg ca significantly a method based on estimating the ratio of the temperature sensitivity of foraminiferal mg ca to that of 18ocalcite shows that sensitivity for mg ca at the high end of the observed core top range 0 1 mmol mol c is required for consistency with lgm holocene differences in each property as constrained by independent proxy data this is supported by a mg ca record for uvigerina spp generated for the southern ocean over the past 440 000 years from ocean drilling program site 1123 chatham rise new zealand the record shows variability that correlates with climate oscillations the lgm deep ocean temperature derived from the mg ca record is 1 1 0 3 c transformation to temperature allows estimates to be made of changes in bottom water temperature and seawater 18o and comparison made with literature records analysis reveals a 2 5 kyr lead in the record of temperature over calcite 18o and a longer lead over seawater 18o this is a reflection of larger phase offsets at eccentricity periods phase offsets at tilt and precession are within error zero

late holocene deep sea benthic foraminifera from the sea of marmara abstract the benthic foraminiferal assemblages of two cores from the late holocene organic carbon rich and carbonate poor deep sea sediments of the eastern depression of the sea of marmara have been studied they were deposited under high level of primary productivity and poorly oxygenated bottom water conditions they show low diversity and are dominated by a group of species adapted to an infaunal life style with wide bathymetric distribution ca 70 2000 m in the mediterranean sea oxygen deficiency down to about 0 5 ml l does not seem adversely to affect the rate of reproduction of the dominant species belonging to melonis chilostomella buliminids and bolivinitids their distribution is primarily controlled by substrate conditions faunal similarities with fossil assemblages in association with some late quaternary sapropels and related facies from the eastern mediterranean basins suggest that they were deposited under palaeo oceanographic conditions closely similar to those of the modern sea of marmara

new spatial mg ca temperature calibrations for three arctic benthic foraminifera and reconstruction of north iceland shelf temperature for the past 4000 years 1 we have developed cold end mg ca temperature calibrations for three common arctic benthic foraminifera islandiella norcrossi helenae melonis barleeanus and cassidulina neoteretis and compare the three calibrations in a late holocene downcore record 0 4000 cal yr b p the calibration and downcore trends for the three arctic species extend the observation that mg incorporation into benthic foraminifera is species specific for the calibration we use a set of ctd casts bottom water 18oseawater measurements and surface grab samples collected from the iceland margin cruise b997 and the greenland margin cruise bs1191 water depth of sites used ranges from 165 to 656 m while spatial bottom temperature ranges from 0 to 7 c mg ca values ranged from 1 02 to 1 47 for i norcrossi helenae 0 64 to 2 21 for m barleeanus and 0 93 to 1 38 mmol mol for c neoteretis we calibrated mg ca content against isotopic calcification temperature calculated using t 16 9 4 0 18ocalcite corrected for vital effect 18oseawater exponential calibrations for the three species are as follows i norcrossi helenae mg ca 1 051 0 03 exp 0 060 0 011 t m barleeanus mg ca 0 658 0 07 exp 0 137 0 020 t and c neoteretis mg ca 0 864 0 07 exp 0 082 0 020 t on the basis of mg ca in these benthic species the downcore record from core md99 2269 is reconstructed bottom temperature values are interpreted to reflect variable inflow of atlantic and arctic water to the north iceland shelf during the last 4000 cal yr b p all three reconstructions show a decline by 0 1 c per century from circa 1500 0 cal yr b p which coincides with an increase in arctic benthic foraminifera abundances and a rise in sea ice proxies in the same core intriguingly c neoteretis diverges periodically to higher average temperature atlantic water conditions than shown by m barleeanus or i norcrossi helenae which both show arctic water temperature circa 1500 4000 cal yr b p

upwelling intensity and ocean productivity changes off cape blanc northwest africa during the last 70 000 years geochemical and micropalaeontological evidence abstract the accumulation of biogeochemical organic carbon calcium carbonates molybdenum and iodine micropalaeontological benthic foraminifera and terrigenous markers grain size si al zr al k al over the last 70 000 years in one core sedorqua 11k on the northwest african margin off cap blanc has been used to reconstruct past variations of local upwelling intensity and oceanic productivity the study demonstrates that productivity in this area increased during stage 3 particularly between 40 000 and 50 000 yr b p and during the last deglaciation between 6000 and 15 000 yr b p during most of isotopic stage 2 and particularly during the last glacial maximum productivity was much lower these variations can be attributed to changes in local wind stress and seasonality that are related to variability in monsoon pressure intensity because of the establishment of upwelling cells over the shelf due to high sea level the conditions of sedimentation during the last 5 6 thousend years on the upper slope site 11k are largely dominated by advection from the shelf leading to strong sorting prior to deposition advection seems to have been minor during the other periods of enhanced productivity a conceptual model is proposed to link the productivity variations to atmospheric circulation in particular to the wind stress direction and seasonality

the mediterranean outflow splitting a comparison between theoretical models and canigo data abstract the mediterranean outflow in the atlantic is vertically subdivided into two main cores that are identified by temperature and salinity maxima hydrological data collected west of the strait of gibraltar and off the south and south west coasts of portugal in september 1997 have been used in two different models to shed some light on the mechanisms that cause a splitting of the mediterranean outflow these models are i a steady one dimensional streamtube model and ii a local time dependent model that includes cross stream variations the streamtube model applied at the northern respectively the southern part of the outflow appears capable of reproducing the observed density difference between the two cores the vertical separation however was underestimated the results from the local model suggest that a bump in the bottom topography may be a determining factor for the splitting tendency of the flow

stable oxygen and carbon isotopes of live benthic foraminifera from the bay of biscay microhabitat impact and seasonal variability we determined the stable oxygen and carbon isotopic composition of live rose bengal stained benthic foraminifera n150 am size fraction of seven taxa sampled along a downslope transect between 140 to 2000 m water depth in the bay of biscay at the five stations hoeglundina elegans cibicidoides pachydermus uvigerina peregrina uvigerina mediterranea preferentially occupy shallow infaunal niches whereas melonis barleeanus and uvigerina elongatastriata occupy an intermediate infaunal microhabitat and globobulimina spp live in a deep infaunal niche close to the zero oxygen boundary when compared with d 18 o values of calcite formed in equilibrium with bottom waters u peregrina forms its test in close equilibrium with bottom water d 18 o all other foraminiferal taxa calcify with a constant offset to calculated equilibrium calcite there is no systematic relationship between the foraminiferal microhabitat depth and the dd 18 o between foraminiferal and equilibrium calcite we calculated correcting factors for the various taxa which are needed for constructing multispecies based oxygen isotope records in paleoceanographic studies of the study area the d 13 c values of foraminiferal taxa investigated in this study do neither record bottom water d 13 cdic in a 1 1 relationship nor with a constant offset but appear to be mainly controlled by microhabitat effects the increase of d 13 c values of shallow infaunal taxa with increasing water depth reflects the decrease of the exported flux of organic carbon along the bathymetric transect and early diagenetic processes in the surface sediment this is particularly the case for the shallow infaunal u peregrina the d 13 c values of deep infaunal globobulimina spp are much less dependent on the exported organic matter flux we suggest that the dd 13 c between u peregrina and globobulimina spp can shed light on the various pathways of past degradation of organic detritus in the benthic environments at a station in 550 m water depth where periodic eutrophication of sediment surface niches was demonstrated previously we performed a two year seasonal survey of the isotopic composition of foraminiferal faunas no marked seasonal changes of the stable carbon isotopic composition of shallow intermediate and deep infaunal foraminiferal taxa were observed thus the d 13 c values of foraminiferal individuals belonging to the n150 am fraction may result from rather long term calcification processes lasting for several weeks or months which limit the impact of ephemeral 12 c enrichment of shallow infaunal niches on the isotope chemistry of adult individuals during eutrophic periods only highly opportunistic taxa reproducing or calcifying during

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

late holocene productivity and hydrographic variability in the eastern mediterranean inferred from benthic foraminiferal stable isotopes 1 the paleoproductivity paleo oxygenation and paleohydrographic configuration of the southeastern mediterranean during the late holocene was reconstructed on the basis of the isotopic composition of the epibenthic heterolepa floridana shallow endobenthic uvigerina mediterranea and the deeper endobenthic bulimina inflata from two high resolution cores ga 112 470 m and ga 110 670 m the 13c between h floridana and u mediterranea reveals four intervals of enhanced productivity from 3 3 2 6 2 3 1 9 1 5 1 1 and 0 8 0 4 kyr bp coinciding with increased nutrient supply by the nile river the entire basin was well aerated with oxygen consumption varying between 1 0 and 3 5 ml o2 l oxygen consumption increases toward present day probably because of higher accumulation of total organic carbon at 1 7 kyr bp coinciding with the appearance of the mesotropic benthic species the hydrographic configuration of the basin has changed during the course of the last 3 75 kyr the levantine intermediate water liw deepens below 470 m between 3 3 and 2 0 kyr and especially between 2 5 and 2 0 kyr during the last 1 5 kyr the liw becomes shallower than 470 m similar to the present day the change in the hydrographic configuration reflects changes in evaporation precipitation ratio and in temperature

temperature and carbonate ion effects on mg ca and sr ca ratios in benthic foraminifera aragonitic species hoeglundina elegans received 16 march 2005 revised 20 june 2005 accepted 3 november 2005 published 21 february 2006 1 core top samples from atlantic little bahama banks lbb and pacific hawaii and indonesia depth transects have been analyzed in order to assess the influence of bottom water temperature bwt and aragonite saturation levels on mg ca and sr ca ratios in the aragonitic benthic foraminifer hoeglundina elegans both the mg ca and sr ca ratios in h elegans tests show a general decrease with increasing water depth although at each site the decreasing trends are consistent with the in situ temperature profile mg ca and sr ca ratios in lbb are substantially higher than in indonesia and hawaii at comparable water depths with a greater difference observed with increasing water depth because we find no significant difference between results obtained on live and dead specimens we propose that these differences are due to primary effects on the metal uptake during test formation evaluation of the water column properties at each site suggests that in situ co3 ion concentrations play an important role in determining the h elegans mg ca and sr ca ratios the co3 ion effect is limited however only to aragonite saturation levels dco3 aragonite below 15 mmol kg 1 above this level temperature exerts a dominant effect accordingly we propose that mg ca and sr ca in h elegans tests can be used to reconstruct thermocline temperatures only in waters oversaturated with respect to the mineral aragonite using the following relationships mg ca 0 034 0 002 bwt 0 96 0 03 and sr ca 0 060 0 002 bwt 1 53 0 03 for dco3 aragonite 1 5mmol kg 1 the standard error associated with these equations is about 1 1 c reconstruction of deeper water temperatures is complicated because in undersaturated waters changes in mg ca and sr ca ratios reflect a combination of changes in co3 and bwt overall we find that sr ca rather than mg ca in h elegans may be a more accurate proxy for reconstructing paleotemperatures

uranium in foraminiferal calcite as a recorder of seawater uranium concentrations abstract we present results of an investigation of uranium calcium ratios in cleaned foraminiferal calcite as a recorder of seawater uranium concentrations for accurate reconstruction of past seawater uranium content shell calcite must incorporate uranium in proportion to seawater concentration and must preserve its original uranium composition over time laboratory culture experiments with live benthic amphistegina lobifera and live planktonic globigerinella calida foraminifera show that the u ca ratio of cleaned calcite tests is proportional to the concentration of uranium in solution after correcting results for the presence of initial calcite the apparent distribution coefficient d u ca calcite u ca solution 10 6 0 3 10 3 for a lobifera and d 7 9 0 1 10 3 for g calida u ca ratios in planktonic foraminifera from core tops collected above 3900 m in the equatorial atlantic and above 2100 m in the pacific ocean show no significant difference among the species analyzed d estimated from core top samples ranges from 7 6 0 4 10 3 for o universa to 8 4 0 5 10 3 for g ruber in benthic species c wuellerstorfi d 7 0 0 8 10 3 u ca and mg ca in g tumida and g sacculifer from core tops taken near and below the regional lysocline decrease with water depth smaller decreases in u ca and mg ca with depth were observed in c wuellerstorfi in the planktonic species we believe that u ca and mg ca are lower in the more dissolution resistant fraction of calcite leading to lower u ca in more highly dissolved samples

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

the impact of salinity on the mg ca and sr ca ratio in the benthic foraminifera ammonia tepida results from culture experiments abstract over the last decade sea surface temperature sst reconstructed from the mg ca ratio of foraminiferal calcite has increasingly been used in combination with the 18o signal measured on the same material to calculate the 18ow a proxy for sea surface salinity sss a number of studies however have shown that the mg ca ratio is also sensitive to other parameters such as ph or co 3 2 and salinity to increase the reliability of foraminiferal mg ca ratios as temperature proxies these effects should be quantified in isolation individuals of the benthic foraminifera ammonia tepida were cultured at three different salinities 20 33 and 40 psu and two temperatures 10 15 c the mg ca and sr ca ratios of newly formed calcite were analyzed by laser ablation icp ms and demonstrate that the mg concentration in a tepida is overall relatively low mean value per experimental condition between 0 5 and 1 3 mmol mol when compared to other foraminiferal species sr being similar to other foraminiferal species the mg and sr incorporation are both enhanced with increasing temperatures however the temperature dependency for sr disappears when the distribution factor dsr is plotted as a function of calcite saturation state this suggests that a kinetic process related to is responsible for the observed dependency of sr incorporation on sea water temperature the inferred relative increase in dmg per unit salinity is 2 8 at 10 c and 3 3 at 15 c for the salinity interval 20 40 psu this implies that a salinity increase of 2 psu results in enhanced mg incorporation equivalent to 1 c temperature increase the dsr increase per unit salinity is 0 8 at 10 c and 1 3 at 15 c for the salinity interval 20 40 psu

a secondary ionization mass spectrometry calibration of cibicidoides pachyderma mg ca with temperature an evaluation of c pachyderma mg ca using a new suite of warm water multicores from the florida straits shows that the slope of mg ca with temperature is shallower than previously thought using secondary ionization mass spectrometry we have documented that the distribution of magnesium within the polished walls of foraminiferal tests is gaussian suggesting that the mg ca in these samples is not affected by the addition of a secondary high magnesium calcite in the walls the mg ca within a typical c pachyderma test varies by about 20 1 100 and the variability increases slightly in tests with higher mg ca the regression of c pachyderma mg ca with temperature has a slope of 0 13 0 05 mmol mol 1 per c indistinguishable from the slope observed in inductively coupled plasma mass spectrometry measurements from a different subset of the same multicores but about one half the slope of previously published calibrations the largest differences between the calibrations comes at the warm water end of the regression where previously published c pachyderma mg ca values from little bahama bank are at least 3 mmol mol 1 higher than observed in these new cores the reasons for this difference are not fully known but are most likely related to diagenesis at little bahama bank

relationships between the stable isotopic signatures of living and fossil foraminifera in monterey bay california 1 fossil foraminifera are critical to paleoceanographic reconstructions including estimates of past episodes of methane venting these reconstructions rely on benthic foraminifera incorporating and retaining unaltered the ambient isotopic compositions of pore fluids and bottom waters comparisons are made here of isotopic compositions of abundant live and fossil foraminifera uvigerina peregrina epistominella pacifica bulimina mexicana and globobulimina pacifica collected in monterey bay ca from two cold seeps clam flats and extrovert cliffs and from sediments 5 m outside of the clam flats seep clam flats has steep d 13 cdic gradients to 45 but dic at extrovert cliffs is less enriched in 12 c to approximately 22 oxygen isotope values of fossil foraminifera at clam flats are 1 5 enriched in 18 o over the living foraminifera as well as those of both live and fossil foraminifera at extrovert cliffs suggesting they may have lived during the last glacial maximum statistical comparisons student s t and kolmogorov smirnov tests of d 13 c and d 18 o values indicate that live and fossil foraminifera come from different populations at both clam flats and extrovert cliffs at clam flats the difference appears to result from alteration enriching some fossil foraminifera in 12 c over live foraminifera at extrovert cliffs the fossil foraminifera are enriched in 13 c over the live foraminifera suggesting they lived prior to the onset of venting and thus that venting began recently the short time of venting at extrovert cliffs may be responsible for the less alteration there compared with clam flats these results indicate that preservation of foraminifera is likely to be poor within long lived cold seeps but that foraminifera living in the surrounding sediment may incorporate and preserve broad basin wide changes in isotopic compositions of the ambient water

expression of the bipolar see saw in antarctic climate records during the last deglaciation ice core records of climate from greenland and antarctica show asynchronous temperature variations on millennial timescales during the last glacial period 1 the warming during the transition from glacial to interglacial conditions was markedly different between the hemispheres a pattern attributed to the thermal bipolar see saw 2 however a record from the ross sea sector of east antarctica has been suggested to be synchronous with northern hemisphere climate change 3 here we present a temperature record from the talos dome ice core also located in the ross sea sector we compare our record with ice core analyses from greenland based on methane synchronization 4 and find clearly asynchronous temperature changes during the deglaciation we also find distinct differences in antarctic records pointing to differences in the climate evolution of the indo pacific and atlantic sectors of antarctica in the atlantic sector we find that the rate of warming slowed between 16 000 and 14 500 years ago parallel with the deceleration of the rise in atmospheric carbon dioxide concentrations and with a slight cooling over greenland in addition our chronology supports the hypothesis that the cooling of the antarctic cold reversal is synchronous with the bolling allerod warming in the northern hemisphere 14 700 years ago 5 the period from about 8 to 25kyr before present bp includes the climate transition from the last glacial to the holocene as documented from polar ice cores and other climate archives the pattern of climate changes throughout this transition is different between antarctica and the surrounding southern ocean and the northern hemisphere the steady antarctic deglacial warming reaches a first maximum antarctic isotopic maximum aim1 ref 1 followedbyaninterruptiontowardscoolerconditionsduring the antarctic cold reversal acr conversely greenland records show two rapid warming phases at the onset of the dansgaard oeschger 1 do1 event bllingaller dinterstadial b a andthe

seismic detection of marine methane hydrate as offshore petroleum exploration and development move into deeper water industry must contend increasingly with gas hydrate a solid compound that binds water and a low molecular weight gas usually methane gas hydrate has been long studied in industry from an engineering viewpoint due to its tendency to clog gas pipelines however hydrate also occurs naturally wherever there are high pressures low temperatures and sufficient concentrations of gas and water these conditions prevail in two natural environments both of which are sites of active exploration permafrost regions and marine sediments on continental slopes in this article we discuss seismic detection of gas hydrate in marine sediments gas hydrate in deepwater sediments poses both new opportunities and new hazards an enormous quantity of natural gas likely far exceeding the global inventory of conventional fossil fuels is locked up worldwide in hydrates ex traction of this unconventional resource presents unique exploration engineering and economic challenges and several countries including the united states japan canada india and korea have initiated joint industry academic governmental programs to begin studying those challenges hydrates also constitute a potential drilling hazard because hydrates are only stable in a restricted range of pressure and temperature any activity that sufficiently raises temperature or lowers pressure could destabilize them releasing potentially large volumes of gas and decreasing the shear strength of the host sediments assessment of the opportunities and hazards associated with hydrates requires reliable methods of detecting hydrate and accurate maps of their distribution and concentration hydrate may occur only within the upper few hundred meters of deepwater sediment at any depth between the seafloor and the base of the stability zone which is controlled by local pressure and temperature hydrate is occasionally exposed at the seafloor where it can be detected either visually or acoustically by strong seismic reflection amplitudes or high backscatter

the mg ca temperature relationship of benthic foraminiferal calcite new core top calibrations in the 4 c temperature range abstract calcite magnesium calcium ratios were determined for four species of benthic foraminifera cibicidoides wuellerstorfi cibicidoides mundulus oridorsalis umbonatus and pyrgo murrhina from core top samples collected from the atlantic indian and pacific oceans where modern bottom water temperatures are less than 4 c mg ca of all four species increase with increasing temperature and the mg ca temperature relationship does not appear to be necessarily exponential mg ca of c mundulus is consistently higher than c wuellerstorfi implying differences in the uptake of mg by different species within this genus the observed mg ca for c wuellerstorfi at temperatures less than 3 c is lower than those predicted from published mg ca temperature relationships derived for cibicidoides spp at higher temperatures previous studies have attributed this change in the mg ca temperature relationship of c wuellerstorfi to the effect of decreased carbonate ion saturation co32 on mg ca at low temperatures a relationship between the co32 and mg ca of 0 0083 0 002 mmol mol mol kg has been established for c wuellerstorfi from this study