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

mg ca ratios of single planktonic foraminifer shells and the potential to reconstruct the thermal seasonality of the water column mg ca ratios of surface and subsurface dwelling foraminifera provide valuable information about the past temperature of the water column planktonic foraminifera calcify over a period of weeks to months therefore the range of mg ca temperatures obtained from single specimens potentially records seasonal temperature changes we present solution derived mg ca ratios for single specimens of the planktonic foraminifera species globigerinoides ruber pink globigerinoides ruber white and globorotalia inflata from a sediment trap off northwest africa 20 45 6 n 18 41 9 w cleaning of single specimens was achieved using a flow through system in order to prevent sample loss mg ca ratios of surface dwelling g ruber pink show strong seasonality linked to sea surface temperature mg ca ratios of g ruber white do not show such seasonality subsurface dwelling g inflata flux is largest during the main upwelling season but mg ca ratios reflect annual temperatures at intermediate water depths the sediment trap time series suggests that changes in the range of mg ca ratios exhibited by single specimens of g ruber pink and g inflata from the sedimentary record should provide information on the past temperature range under which these species calcified statistical analysis suggests detectable changes in the mg ca range are 0 80 mmol mol g ruber pink and 0 34 mmol mol g inflata for g ruber pink such changes would indicate changes in the seasonal sea surface temperature range 4 c or a shift in the main calcification and reproductive period for g inflata such changes would indicate 1 7 c changes in the thermocline temperature or a change in the depth habitat

surface and subsurface seawater temperature reconstruction using mg ca microanalysis of planktonic foraminifera globigerinoides ruber globigerinoides sacculifer and pulleniatina obliquiloculata laser ablation inductively coupled plasma mass spectrometry microanalyses of mg ca across individual final chambers of three planktonic foraminifera species globigerinoides ruber g sacculifer and pulleniatina obliquiloculata reveal significant interspecies differences in test mg concentrations whereas these three species have similar mg ca values at low sea surface temperatures similar to 22 degrees c they diverge markedly at high sea surface temperatures similar to 29 degrees c explanations for these differences in species mg ca values based on detailed comparison of species intratest mg ca distributions suggest that compositional variability within tests cannot account for the observed deviation of species mg ca values in warm water equatorial regions multiple regression modeling and delta o 18 analysis of globigerinoides sacculifer tests indicate that interspecies differences in mg ca values result from different depth habitats the average mg ca values of g ruber final chambers reflect the temperature of the surface mixed layer 0 25 m whereas those of g sacculifer and pulleniatina obliquiloculata correlate best with subsurface temperatures at 50 75 m and 100 125 m water depths respectively mg ca calibration to the temperatures at these depths reveals a similar temperature control on mg test composition in all species combining our results with mg ca values from published culturing experiments we derive a generalized equation for the effect of temperature and seawater salinity on foraminiferal mg ca we also show that the mg ca composition of specific calcite layers within foraminiferal tests including the low mg ca layers of globigerinoides ruber and g sacculifer and the cortex layer of pulleniatina obliquiloculata correlates with seawater temperature and can be used as an additional proxy for seawater temperature

microdistribution of mg ca sr ca and ba ca ratios in pulleniatina obliquiloculata test by using a nanosims implication for the vital effect mechanism the mg ca ratio within foraminiferal calcareous tests shells is widely used to reconstruct past seawater temperature however recent studies reported that the organic components within a test affect the mg ca distribution in this study we have measured the mg ca sr ca and ba ca ratios within the planktonic foraminifera pulleniatina obliquiloculata by using a nanosims secondary ion mass spectrometer sims which has excellent spatial resolution 1 m and allows us to compare the distribution of chemical compositions with that of the organic components element compositions show banding distributions composed of alternately higher and lower values of those elemental ratios the mg ca ratios previously considered to be mainly controlled by calcification temperature show larger variations than the values expected from the seawater temperature at the habitat depth of p obliquiloculata comparison of the elemental distribution with the test microstructure reveals that the bands of high mg ca and sr ca ratios correspond with layers of the organic components such coincidence suggests that the organic components strongly affect the mg ca and sr ca ratios within a test in spite of the heterogeneous distribution temperature estimated from the averaged mg ca ratio within a test is consistent with seawater temperature at the habitat depth of p obliquiloculata indicating that whole mg ca ratio of foraminiferal test may be useful as paleotemperature proxy in contrast to the mg ca ratio the heterogenity in ba ca ratio which previously has been considered to be mainly controlled by the ambient seawater composition is not fully matched with the layers of the organic compositions although the organic components concentrate ba other unknown factors appear to also cause heterogenity in ba incorporation

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

novel observations on biomineralization processes in foraminifera and implications for mg ca ratio in the shells stable isotopes and trace elements in foraminifera shells are important for determining the paleochemistry of the ocean and mg ca ratios and 1 8 o values in foraminifera have recently been used to determine simultaneously the temperature and salinity of past oceans however large variations between species and significant mg intra shell heterogeneity indicate a major role for biological factors in determining the mg ca ratio in foraminifera our novel in vivo observations on the biomineralization process of perforate foraminifera show that their calcareous wall is composed of two different calcite types a thin high mg primary layer and low mg layers that cover the primary layer on both sides the data may suggest that two biomineralization pathways are employed in the formation of the different calcite types a new conceptual framework is provided to explain part of the mg heterogeneity in foraminiferal shells and the variable sensitivity of the mg ca ratio to temperature in different species

variability of mg ca and sr ca between and within the planktonic foraminifers globigerina bulloides and globorotalia truncatulinoides the variability in mg ca and sr ca within individual tests and chambers of tests and samples consisting of differing numbers of individuals was determined for globigerina bulloides and globorotalia truncatulinoides in a north atlantic core top sample 52 918 n 16 917 w the variability in mg ca and sr ca within individual tests and chambers was determined by electron microprobe and samples consisting of variable sample size were measured using inductively coupled plasma optical emission spectrometer icp oes large compositional heterogeneity was found within individual chambers and within the test as a whole of the two species and the presence of regions with up to 10 mmol mol mg ca especially in g bulloides mean mg ca decreases in successive chambers of g bulloides especially the 300 355 m fraction and is accompanied by decreasing variance but is not statistical significant sr ca is much more homogeneously distributed with a normal distribution and shows no differences from chamber to chamber the variability of mg ca and sr ca decreases with increasing sample size from single to five to twenty tests per sample approximately as for a normal distribution with greater variability for g bulloides than for g truncatulinoides equivalent to uncertainties in temperature n 20 of 1 1 c and 0 7 c for the two species within the whole of the sediment mixed layer

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

effects of seawater carbonate ion concentration and temperature on shell u mg and sr in cultured planktonic foraminifera we investigate the sensitivity of u ca mg ca and sr ca to changes in seawater co3 and temperature in calcite produced by the two planktonic foraminifera species orbulina universa and globige rina bulloides in laboratory culture experiments our results demonstrate that at constant temperature u ca in o universa decreases by 25 7 per 100 mol co3 k g 1 as seawater co3 increases from 110 to 470 mol kg 1 results from g bulloides suggest a similar relationship but u ca is consistently offset by 40 at the same environmental co3 in o universa u ca is insensitive to temperature between 15 c and 25 c applying the o universa relationship to three u ca records from a related species globigerinoides sacculifer we estimate that caribbean and tropical atlantic co3 was 110 70 mol kg 1 and 80 40 mol kg 1 higher respectively during the last glacial period relative to the holocene this result is consistent with estimates of the glacial interglacial change in surface water co3 based on both modeling and on boron isotope ph estimates in settings where the addition of u by diagenetic processes is not a factor down core records of foraminiferal u ca have potential to provide information about changes in the ocean s carbonate concentration below ambient ph ph 8 2 mg ca decreased by 7 5 o universa t o 16 6 g bulloides per 0 1 unit increase in ph above ambient ph the change in mg ca was not significant for either species this result suggests that mg ca based paleotemperature estimates for the quaternary during which surface ocean ph has been at or above modern levels have not been biased by variations in surface water ph sr ca increased linearly by 1 6 0 4 per 0 1 unit increase in ph shell mg ca increased exponentially with temperature in o universa where mg ca 0 85 exp 0 096 t whereas the change in sr ca with temperature was within the reproducibility of replicate measurements copyright 2004 elsevier ltd

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

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

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

ecological and temperature controls on mg ca ratios of globigerina bulloides from the southwest pacific ocean we present mg ca data for globigerina bulloides from 10 core top sites in the southwest pacific ocean analyzed by laser ablation inductively coupled plasma mass spectrometry la icpms mg ca values in g bulloides correlate with observed ocean temperatures 7 degrees c 19 degrees c and when combined with previously published data an integrated mg ca temperature calibration for 7 degrees c 31 degrees c is derived where mg ca mmol mol 0 955 x e 0 068 x t r 2 0 95 significant variability of mg ca values 20 30 was found for the four visible chambers of g bulloides with the final chamber consistently recording the lowest mg ca and is interpreted in part to reflect changes in the depth habitat with ontogeny incipient and variable dissolution of the thin and fragile final chamber and outermost layer concomitantly added to all chambers caused by different cleaning techniques prior to solution based icpms analyses may explain the minor differences in previously published mg ca temperature calibrations for this species if the lower mg ca of the final chamber reflects changes in depth habitat then la icpms of the penultimate or older chambers will most sensitively record past changes in near surface ocean temperatures mean size normalized g bulloides test weights correlate negatively with ocean temperature t 31 8 x e 30 5xwtn r 2 0 90 suggesting that in the southwest pacific ocean temperature is a prominent control on shell weight in addition to carbonate ion levels

exploring the dissolution effect on the intrashell mg ca variability of the planktic foraminifer globigerinoides ruber the mg ca ratio of the planktic foraminifer globigerinoides ruber is widely used for reconstructing past sea surface temperatures the shell mg ca ratio is also lowered by dissolution which results in lower sea surface temperature estimates in partially dissolved shells here we use an electron microprobe image mapping technique to map the intrashell variability of the mg ca ratio in g ruber white sensu stricto shells to explore changes in the intrashell mg ca ratio associated with dissolution we examine shells from shallow and deep cores ceara rise western tropical atlantic from the holocene and last glacial maximum that represent a preservational gradient image map results show that the mg ca ratio is highly variable both within a single shell and among samples obtained from the same sediment interval our results show that intrashell mg ca variability is retained in samples that have undergone dissolution quantitative analysis of the data from mg ca mapping suggests that preferential loss of high mg ca calcite alone cannot account for the difference in intrashell mg ca variability of shells from shallow and deep cores in both time periods rather the data imply that in g ruber analyzed in this study there is a loss of high mg ca ratios accompanied by a more uniform lowering of mg ca over the range of intershell mg ca variability of shells subjected to dissolution at the 1 m resolution of the microprobe analysis in this study

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

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

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

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

crustal scale seismic profiles across the manila subduction zone the transition from intraoceanic subduction to incipient collision 1 we use offshore multichannel seismic mcs reflection and wide angle seismic data sets to model the velocity structure of the incipient arc continent collision along two trench perpendicular transects in the bashi strait between taiwan and luzon this area represents a transition from a tectonic regime dominated by subduction of oceanic crust of the south china sea west of the philippines to one dominated by subduction and eventual collision of rifted chinese continental crust with the luzon volcanic arc culminating in the taiwan orogeny the new seismic velocity models show evidence for extended to hyperextended continental crust 10 15 km thick subducting along the manila trench at 20 5 n along transect t1 as well as evidence indicating that this thinned continental crust is being structurally underplated to the accretionary prism at 21 5 n along transect t2 but not along t1 to the south coincident mcs reflection imaging shows highly stretched and faulted crust west of the trench along both transects and what appears to be a midcrustal detachment along transect t2 a potential zone of weakness that may be exploited by accretionary processes during subduction an additional seismic reflection transect south of t1 shows subduction of normal ocean crust at the manila trench

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

timing and mechanism for intratest mg ca variability in a living planktic foraminifer abstract geochemical observations indicate that planktic foraminifer test mg ca is heterogeneous in many species thereby challenging its use as a paleotemperature proxy for paleoceanographic reconstructions we present mg ca and ba ca data collected by laser ablation icp ms from the shells of orbulina universa cultured in controlled laboratory experiments test calcite was labeled with ba spiked seawater for 12 h day or night calcification periods to quantify the timing of intratest mg banding across multiple diurnal cycles results demonstrate that high mg bands are precipitated during the night whereas low mg bands are precipitated during the day data obtained from specimens growing at 20 c and 25 c show that mg ca ratios in both high and low mg bands increase with temperature and average test mg ca ratios are in excellent agreement with previously published empirical calibrations based on bulk solution icp ms analyses in general mg band concentrations decrease with increasing ph and or co2 3 but this effect decreases as experimental temperatures increase from 20 c to 25 c we suggest that mitochondrial uptake of mg2 from the thin calcifying fluid beneath streaming rhizopodial filaments may provide the primary locus for mg2 removal during test calcification and that diurnal variations in either mitochondrial density or activity produce mg banding these results demonstrate that mg banding is an inherent component of test biomineralization in o universa and show that the mg ca paleothermometer remains a fundamental tool for reconstructing past ocean temperatures from fossil foraminifers

controls on shell mg ca and sr ca in cultured planktonic foraminiferan globigerinoides ruber white mg ca and sr ca ratios were determined on a single species of planktonic foraminiferan globigerinoides ruber white collected from the gulf of eilat and cultured in seawater at five different salinities 32 to 44 five temperatures 18 to 30 c and four ph values 7 9 to 8 4 the mg ca temperature calibration of cultured g ruber with an exponential slope of 8 3 c agrees well with previously published calibrations from core tops and sediment traps however the dependence of mg ca on salinity with an exponential slope of 5 3 psu is also significant and should be included in the calibration equation with this purpose we calculated a calibration equation for g ruber dependent on both temperature and salinity within the 95 confidence limits mg ca mmol mol exp 0 06 0 02 s psu 0 08 0 02 t c 2 8 1 0 r2 0 95 the influence of ph on mg ca ratios is negligible at ambient seawater ph 8 1 to 8 3 however we observe a dominating ph control on shell mg ca when the ph of seawater is lower than 8 0 sr ca in g ruber shows a significant positive correlation with average growth rate presumably part of the variability in shell sr ca in the geological record is linked to changes in growth rates of foraminifera as a response to changing environmental conditions

first spaceborne phase altimetry over sea ice using techdemosat 1 gnss r signals a track of sea ice reflected global navigation satellite system gnss signal collected by the techdemosat 1 mission is processed to perform phase altimetry over sea ice high precision carrier phase measurements are extracted from coherent gnss reflections at a high angle of elevation 57 the altimetric results show good consistency with a mean sea surface mss model and the root mean square difference is 4 7 cm with an along track sampling distance of 140 m and a spatial resolution of 400 m the difference observed between the altimetric results and the mss shows good correlation with the colocated sea ice thickness data from soil moisture and ocean salinity this is consistent with the reflecting surface aligned with the bottom of the ice water interface due to the penetration of the gnss signal into the sea ice therefore these high precision altimetric results have potential to be used for determination of sea ice thickness

micromapping of mg ca values in cultured specimens of the high magnesium benthic foraminifera 1 this study measured mg ca values in cross sections of the benthic foraminifer planoglabratella opercularis d orbigny using an electron probe microanalyzer epma spot size 2 m 1000 analyses we cultured clonal juveniles of this species under controlled temperatures this species precipitates high magnesium calcite as its test material mean mg ca values increased linearly with the culture temperature therefore mg ca values in walls of subsequently formed chambers reflected changes in temperature during the experiment foraminiferal specimens yielded variable mg ca values within their test walls which resulted from the pattern of chamber formation and from minor variations of mg ca within one chamber wall

calibration of mg ca thermometry in planktonic foraminifera from a sediment trap time series 1 paired mg ca and 18o measurements on planktonic foraminiferal species g ruber white g ruber pink g sacculifer g conglobatus g aequilateralis o universa n dutertrei p obliquiloculata g inflata g truncatulinoides g hirsuta and g crassaformis from a 6 year sediment trap time series in the sargasso sea were used to define the sensitivity of foraminiferal mg ca to calcification temperature habitat depths and calcification temperatures were estimated from comparison of 18o of foraminifera with equilibrium calcite based on historical temperature and salinity data when considered together mg ca mmol mol of all species except two show a significant r 0 93 relationship with temperature t c of the form mg ca 0 38 0 02 exp 0 090 0 003 t equivalent to a 9 0 0 3 change in mg ca for a 1 c change in temperature small differences exist in calibrations between species and between different size fractions of the same species o universa and g aequilateralis have higher mg ca than other species and in general data can be best described with the same temperature sensitivity for all species and pre exponential constants in the sequence o universa g aequilateralis g bulloides g ruber g sacculifer other species this approach gives an accuracy of 1 2 c in the estimation of calcification temperature the 9 sensitivity to temperature is similar to published studies from culture and core top calibrations but differences exist from some literature values of pre exponential constants different cleaning methodologies and artefacts of core top dissolution are probably implicated and perhaps environmental factors yet understood planktonic foraminiferal mg ca temperature estimates can be used for reconstructing surface temperatures and mixed and thermocline temperatures using g ruber pink g ruber white g sacculifer n dutertrei p obliquiloculata etc the existence of a single mg thermometry equation is valuable for extinct species although use of species specific equations will where statistically significant provide more accurate evaluation of mg ca paleotemperature

impact of biomineralization processes on the mg content of foraminiferal shells a biological perspective the mg ca ratio in foraminiferal shells is widely used as a proxy for paleotemperatures nevertheless it seems that the basic mg content of foraminifera is determined by biological factors as can be concluded from the large inter species and intrashell variability and the frequent deviations from inorganic behavior this paper discusses three possible ways by which foraminifera can control or modify the mg content in their shell 1 involvement of organic matrix in the precipitation process that may alter the partition coefficient of mg in biogenic calcite 2 controlled conversion of transient amorphous phases to calcite and 3 modification of the mg concentration in the parent solution from which the crystals precipitate the first two mechanisms are probably responsible for the precipitation of high mg calcite phases whole shell or sublayers while the third mechanism leads to the formation of low mg calcite phases we propose a model adapted from epithelial cells that allows massive mg2 removal from the biomineralization site this model is especially relevant to the planktonic and deep benthic low mg foraminifera that are frequently used for paleotemperature reconstructions we discuss the possible biological roles of mg in the shell in terms of the calcite polymorph conservation the in vivo chemical stability of the shell the functions of mg as a stabilizer of transient phases and as a controlling agent of the precipitation process several temperature sensitive biological processes that may influence the mg ca ratio of the shell are suggested and a model that combines biogenic and inorganic considerations is presented the model uses mg heterogeneity in the shell together with temperature response biologic and inorganic of biomineralization processes to account for the deviation of planktonic foraminifera from inorganic calcite at equilibrium with seawater

mapping of an ophiolite complex by high resolution visible infrared spectrometry the sumail massif of the oman peridotite has been surveyed by the high spectral resolution imager hymap the field measurements have been taken simultaneously to the hymap campaign with a ger 3700 spectrometer to compare the two data sets further calibration and atmospheric correction are made through empirical line corrections a continuum removal by a modified gaussian model on reflectance is then performed for each pixel to minimize atmospheric scattering and shadowing effects classification from spectral distance is established using field observations and comparisons at full spectral resolution to identify peridotite subunits harzburgites and dunites and to distinguish plagioclase wehrlites from gabbros detections of hydrothermal transformations of olivine in serpentines and their alteration in carbonates along fracture networks characterized by narrow spectral signatures validate the classification this demonstrates the utility of the high spectral resolution and the development of appropriate processing methods for geological identifications

mg ca of globorotalia inflata as a recorder of permanent thermocline temperatures in the south atlantic 1 we present a species specific mg ca calcification temperature calibration for globorotalia inflata from a suite of 38 core top samples from the south atlantic from 8 s to 49 s g inflata is a deep dwelling planktonic foraminifer commonly occurring in subtropical to subpolar conditions which qualifies it for reconstructions of the permanent thermocline apparent calcification depths and calcification temperatures were determined by comparing measured 18o with equilibrium 18o of calcite based on water column properties based on our core top samples g inflata apparent calcification depth is constant throughout the south atlantic midlatitudes with a depth of 350 400 m within the permanent thermocline the resulting mg ca calcification temperature calibration is mg ca 0 72 0 045 0 042 exp 0 076 0 006 calcification temperature r2 0 81 and covers the temperature range 3 1 c 16 5 c we applied our mg ca calibration to gravity core ps2495 3 from the mid atlantic ridge at 41 s to test its validity by reconstructing a low resolution record covering the last two glacial interglacial cycles our paleotemperature record reveals large changes in temperature for terminations i and ii when permanent thermocline temperature increased by as much as 8 c the g inflata paleotemperature record suggests that oceanic fronts repeatedly migrated over the location of core ps2495 3 during the last 160 kyr this study shows the potential of g inflata mg ca to reconstruct paleotemperatures in the permanent thermocline

a biomineralization model for the incorporation of trace elements into foraminiferal calcium carbonate measurements of srca of benthic foraminifera show a linear decrease with water depth which is superimposed upon significant variability identified by analyses of individual foraminifera new data for cdca support previous work in defining a contrast between waters shallower and deeper than 2500 m measured element partition coefficients in foraminiferal calcium carbonate relative to sea water d have been described by means of a one box model in which elements are extracted by rayleigh distillation from a biomineralization reservoir that serves for calcification with a constant fractionation factor such that d 1 f 1 f where f is the proportion of ca remaining after precipitation a modification to the model recognises differences in element speciation the model is consistent with differences between dsr dba and dcd in benthic but not planktonic foraminifera depth variations in d for sr and ba are consistent with the model as are differences in depth variation of dcd in calcitic and aragonitic benthic foraminifera the shallower depth variations may reflect increasing calcification rates with increasing water depth to an optimum of about 2500 m observations of unusually lower dcd for some deep waters not accompanied by similar dsr or dba may be because of dissolution or a calcification response to a lower carbonate saturation state