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The Mg/Ca of planktic foraminifera is widely used to determine past surface ocean temperatures but temperature is not the only factor that controls test Mg/Ca. Here we quantify the combined influence of seawater temperature, carbon chemistry, and cation chemistry on Orbulina universa Mg/Ca, based on experimental cultures where these factors were varied independently and simultaneously. We fit a new empirical multi-parameter model that quantifies the effects of each of these variables on the Mg/Ca of O. universa: Mg/Ca O. universa = Mg/Ca sw A · DIC sw B · exp C · C a sw + D · T + E We extend our approach to published Mg/Ca from cultured and sediment trap collected Globigerinoides ruber, and show that a similar equation can be used to describe test Mg/Ca, using [CO32−]sw or pH in place of DIC. The cause of this difference is unknown, but the sensitivity of these two ecophysiologically similar species to different carbon chemistry parameters highlights the uncertainty inherent in applying modern Mg/Ca calibrations to uncalibrated and/or extinct species. In both O. universa and G. ruber, Mg/Casw, [Ca]sw and carbon chemistry (DIC, [CO32−]sw or pH) each modulate the sensitivity of Mg/Ca to temperature. These variables are not constant in the ocean over time-scales relevant to palaeotemperature reconstructions, and must be accounted for when deriving temperature from foraminiferal Mg/Ca. Over time-scales longer than the residence times of Mg and Ca, secular changes in Mg/Casw and [Ca]sw will exert a primary influence on foraminiferal Mg/Ca and its sensitivity to temperature. On shorter timescales, co-variance between temperature and seawater carbon chemistry will influence Mg/Ca-derived temperature estimates. This is particularly relevant to transient hyperthermal events, where the Mg/Ca palaeothermometer is used to evaluate the relationship between atmospheric CO2 and ocean temperature. We explore the potential impact of these effects in an illustrative re-interpretation of Mg/Ca records across the Paleocene-Eocene Thermal Maximum.

The Central Mountains Archaic began with the arrival of foraging populations in the Intermountain West about 6000 years ago. This migration coincided with the "extremely dramatic" winter-wet event of 4350 cal b.c. and the arrival of piñon pine forests in the central Great Basin. Human foragers likely played a significant role in the rapid spread of piñon across the central and northeastern Great Basin. Logistic hunters exploited local bighorn populations, sometimes serviced by hunting camps (the "man caves" such as Gatecliff Shelter, Triple T Shelter, and several others) and they staged communal pronghorn drives at lower elevations. As climate cooled and became more moist, logistic bighorn hunting gradually shifted downslope, then apparently faded away about 1000 cal b.c. Communal pronghorn driving persisted into the historic era in the central Great Basin. This volume, the first in the Alta Toquima trilogy, describes and analyzes more than 100 alpine hunting features on the Mt. Jefferson tablelands. High-elevation, logistical bighorn hunting virtually disappeared across the central Great Basin with the onset of the Late Holocene Dry Period (about 750-850 cal b.c.), giving way to an alpine residential pattern at Alta Toquima (26NY920) and elsewhere on Mt. Jefferson. Situated at almost exactly 11,000 ft (3352 m) above sea level, Alta Toquima was sited on the south summit of Mt. Jefferson (the third-highest spot in the state of Nevada), where at least 31 residential stone structures were emplaced along this steep, east-facing slope. When first recorded in 1978, Alta Toquima was the highest American Indian village site known in the Northern Hemisphere. This volume discusses the material culture, plant macrofossils, vertebrate fauna, and radiocarbon dating for Alta Toquima. Bayesian analysis of 95 14C dates documents an initial occupation of Alta Toquima at 1370-790 cal b.c., with the sporadic settlements persisting until immediately before European contact. These alpine residences are the most dramatic examples of the intensified provisioning strategies that began in the Central Mountains Archaic about 3000 years ago, broadening the diet breadth to include plant and animal resources previously considered too costly. The oldest summertime residence at Alta Toquima correlates with the onset of Late Holocene Dry Period (LHDP) aridity (~750 cal b.c.), and these houses were episodically occupied only during the driest intervals throughout the next 1500 dramatic years of abrupt climate change. During the intervening wetter stretches, Alta Toquima was abandoned in favor of subalpine basecamps. This sequenced intensification predated the arrival of bow technology in the central Great Basin by more than a millennium. Exactly the opposite sequencing took place a few miles to the north, when Gatecliff Shelter was abandoned during LHDP aridity--precisely when the first summertime settlements appeared at Alta Toquima. This pattern reversed again when lowland habitats became sufficiently well watered to again support summertime patches of seeds and geophytes (~150 cal b.c.-cal a.d. 100). Alta Toquima families responded by abandoning (temporarily) their alpine summertime camps to repurpose former "man caves" like Gatecliff and Triple T shelters into family settlements. The Monitor Valley sequence documents several syncopated lowland-alpine, wet-dry reversals, reflecting an adaptive diversity that spanned more than two millennia. The drought terminating cal a.d. 1150 devastated much of the western Great Basin and American Southwest, but its impact was less severe in central Nevada. Although subalpine sites were again abandoned during the drought buildup that peaked in the mid-12th century, summertime occupation of Alta Toquima became more commonplace, although it increased notably during the ~cal a.d. 1200-1400 aridity and persisted throughout the Little Ice Age.

© 2020 The Authors. Rapid Communications in Mass Spectrometry published by John Wiley & Sons Ltd Rationale: Oxygen (δ18O) and carbon (δ13C) isotope analysis of foraminifera and other CaCO3 samples has been a key technique for paleoceanographical and paleoclimatological research for more than 60 years. There is ongoing demand for the analysis of ever smaller CaCO3 samples, driven, for example, by the desire to analyse single specimen planktic foraminifera, or small samples of tooth enamel. Methods: We present a continuous-flow mass spectrometric technique that uses cryo-focusing of sample CO2 to analyse CaCO3 samples in a weight range between 10 and 3 μg. These are considerably lower sample weights than achievable on most currently available standard instrumentation. The technique is automated, so that sample throughput lies at >60 samples per day. The method involves an on-line vial-flushing routine designed to remove machine drift due to blank CO2 build-up in the sample vials. Results: In a series of experiments the effect of blank CO2 build-up is quantified, and outgassing from the chlorobutyl septa identified as the source. An improved flushing routine together with the use of a cryo-focusing step in the analysis is demonstrated to provide the analytical stability and sensitivity to analyse CaCO3 samples in a weight range between 10 and 3 μg at ≤0.1‰ precision (1σ) for both δ18O and δ13C values. The technique yields similarly precise results for the analysis of the structural carbonate fraction of small tooth enamel samples. Conclusions: This study demonstrates that high-precision oxygen and carbon isotope analysis is possible on CaCO3 samples smaller than 5 μg by use of a continuous-flow isotope technique. Of key importance are (1) the application of a cold trap that drastically reduces sample gas loss, and (2) a modified flushing regime that eliminates increasing background CO2 build-up in sample vials during longer automated sample runs., Rapid Communications in Mass Spectrometry, 34 (19), ISSN:1097-0231, ISSN:0951-4198

Neogloboquadrina pachyderma is the dominant species of planktonic foraminifera found in polar waters and is therefore invaluable for paleoceanographic studies of the high latitudes. However, the geochemistry of this species is complicated due to the development of a thick calcite crust in its final growth stage and at greater depths within the water column. We analyzed the in situ Mg/Ca and δ18O in discrete calcite zones using LA‐ICP‐MS, EPMA and SIMS within modern N. pachyderma shells from the highly dynamic Fram Strait and the seasonally isothermal/isohaline Irminger Sea. Here we compare shell geochemistry to the measured temperature, salinity and δ18Osw in which the shells calcified to better understand the controls on N. pachyderma geochemical heterogeneity. We present a relationship between Mg/Ca and temperature in N. pachyderma lamellar calcite that is significantly different than published equations for shells that contained both crust and lamellar calcite. We also document highly variable SIMS δ18O results (up to a 3.3‰ range in single shells) on plankton tow samples which we hypothesize is due to the granular texture of shell walls. Finally, we document that the δ18O of the crust and lamellar calcite of N. pachyderma from an isothermal/isohaline environment are indistinguishable from each other, indicating that shifts in N. pachyderma δ18O are primarily controlled by changes in environmental temperature and/or salinity rather than differences in the sensitivities of the two calcite types to environmental conditions.

The symbiotic planktonic foraminiferaOrbulina universainhabits open ocean oligotrophic ecosystems where dissolved nutrients are scarce and often limit biological productivity. It has previously been proposed thatO. universameets its nitrogen (N) requirements by preying on zooplankton, and that its symbiotic dinoflagellates recycle metabolic ‘waste ammonium’ for their N pool. However, these conclusions were derived from bulk15N-enrichment experiments and model calculations, and our understanding of N assimilation and exchange between the foraminifer host cell and its symbiotic dinoflagellates remains poorly constrained. Here, we present data from pulse-chase experiments with13C-enriched inorganic carbon,15N-nitrate, and15N-ammonium, as well as a13C- and15N- enriched heterotrophic food source, followed by TEM (transmission electron microscopy) coupled to NanoSIMS (nanoscale secondary ion mass spectrometry) isotopic imaging to visualize and quantify C and N assimilation and translocation in the symbiotic system. High levels of15N-labelling were observed in the dinoflagellates and in foraminiferal organelles and cytoplasm after incubation with15N-ammonium, indicating efficient ammonium assimilation. Only weak15N-assimilation was observed after incubation with15N-nitrate. Feeding foraminifers with13C- and15N-labelled food resulted in dinoflagellates that were labelled with15N, thereby confirming the transfer of15N-compounds from the digestive vacuoles of the foraminifer to the symbiotic dinoflagellates, likely through recycling of ammonium. These observations are important for N isotope-based palaeoceanographic reconstructions, as they show that δ15N values recorded in the organic matrix in symbiotic species likely reflect ammonium recycling rather than alternative N sources, such as nitrates.

Oxygen (δWe present a continuous-flow mass spectrometric technique that uses cryo-focusing of sample COIn a series of experiments the effect of blank COThis study demonstrates that high-precision oxygen and carbon isotope analysis is possible on CaCO

The Mg/Ca paleotemperature proxy in planktic foraminifera is one of the most widely-used proxies for sea surface temperature. However, this ratio is not constant throughout the test, varying systematically by several fold independent of temperature between faster and slower growing diurnal bands. This phenomenon has yet to be explained mechanistically, however, changing calcification rates may be a contributing factor. Observing the relationship between calcification rate and trace metal incorporation for multiple proxies at the scale of this banding will allow us to better understand the contribution of kinetic effects to heterogeneity. In this study, we examine Me/Ca ratios on a diurnal cycle in Orbulina universa, utilizing a novel approach based on multiple isotopic spikes that allows us to measure Sr/Ca, Li/Ca and Mg/Ca with the precision of isotope dilution while still maintaining the time resolution of microanalytical techniques. Using independently measured growth rates derived from NanoSIMS measurements of diurnal Mg/Ca heterogeneity, we examine the effect of crystal growth rate on foraminiferal Sr/Ca and Li/Ca. We observe that Sr/Ca ratios in foraminifera are ~3% higher during the night than during the day, which initially appears opposite to the expected signal based on growth rate. However, we also observe a positive correlation between Sr and Mg in foraminiferal calcite, which falls on the same mineralogical line as the Sr/Ca and Mg/Ca of other biogenic and inorganic calcites. We attribute offsets in calcite composition from this mineralogical relationship to kinetics. Interpreted within that framework, day Sr/Ca ratios appear more affected by kinetics than night Sr/Ca ratios, which is consistent with observed calcification rates. The difference between any given data point and the mineralogical line can be explained by kinetic processes, and correlates with oceanographic properties in cultured foraminifera, which could help separate temperature from growth rate effects in the paleorecord.

Author(s): Menicucci, AJ; Thunell, RC; Spero, HJ | Abstract: The removal of exchangeable oxygen from diatom opal prior to δ18Odiatom analysis is a crucial first step before analyzing frustule oxygen isotopes for paleoceanographic applications. We present the results of experiments that quantify the temperature-dependent reactivity of biogenic silica with water under laboratory conditions. We demonstrate that controlled exchange between rinse water and diatom opal at room temperature results in predictable alteration of δ18Odiatom, after vacuum dehydroxylation. Diatom samples equilibrated with an 18O-enriched δ18Oequil. water solution of +94.4‰ at ~21 °C for 70 hr prior to dehydroxylation yield δ18Odiatom data that can be directly interpreted with existing empirical δ18Odiatom versus temperature relationships. We compare sediment trap-based δ18Odiatom temperature data with modern δ18Oforam temperatures. Finally, we present an ~220 year record of δ18Odiatom data from an eastern Pacific Guaymas Basin boxcore, analyzed using the microfluorination technique, that indicates diatom chlorophyll maximum (Chlmax) temperatures have shifted from a period during the late eighteenth and nineteenth centuries that was 8 °C cooler during the fall bloom relative to mean annual alkenone Uk′37 sea surface temperature, to the late twentieth century when we observe no difference between alkenone sea surface temperature and diatom Chlmax. These data suggest a twentieth century seasonal shift in the timing of fall upwelling and Guaymas Basin stratification breakdown that could be due to reduced upwelling efficiency and/or increased summer mixed layer thermal stratification.

Stable isotope analysis of biogenic carbonates has remained one of the most important tools in paleoceanography since Emiliani (1955) first described the fluctuation of oxygen isotopes in planktic foraminifers over the Pleistocene. Many laboratories now possess equipment with the capability to analyse foraminifer specimens singularly, at least for larger planktic forms.Being able to run single specimens of planktic foraminifers is significant, because it yields entirely different information than when one would analyse multiple specimens from the same species. Planktic foraminifers have an average life span of about one month, so analysing single specimens, makes paleoceanographic data at seasonal resolution available (e.g. Ganssen et al., 2011; Metcalfe et al 2019, and references therein).Most modern equipment for stable isotope analysis of CaCO3 samples yields good precision down to 10 microgram sample size. The smallest samples are generally measured with a dual inlet technique, because that quantitatively collects the CO2 gas sample in a cold trap before analysis, leading to a more efficient use of the sample gas. Modern dual inlet equipment has a sample size limit somewhere between 10 and 6 microgram CaCO3 sample weight, and in that range usually operates at increased analytical uncertainty when compared to larger samples (e.g. Ganssen et al., 2011). Smaller samples are problematic, because at small amounts of sample gas, the dual inlet system is not able to maintain viscous flow conditions required for precise isotope analysis. To circumvent that barrier, one can use continuous-flow (CF) mass spectrometry because in CF systems the carrier gas ensures proper flow conditions even if there is (virtually) no sample gas produced. Doing so has previously allowed for the isotope analysis of CaCO3 samples in the 10 – 6 microgram range at an external precision (1SD) of ~0.12‰ for both δ18O and δ13C (e.g. Metcalfe et al 2019).To further improve the performance of CF mass spectrometry for small CaCO3 samples, we ran experiments on a Thermo GASBENCH system, equipped with a cold trap (cf. Fiebig et al 2005) and interfaced with a Delta-V mass spectrometer. The experiments consisted of replicate analysis of CaCO3 standards between 10 and 3 micrograms in weight, which is the weight range of many of the smaller specimens of planktic foraminifers.Several hardware modifications were implemented to improve system stability and remove observed effects of contribution of blank CO2 building up in the sample vials. With these modifications, external reproducibility of the set-up for carbonate standard aliquots between 10 and 4 microgram reached a precision of ~0.10 ‰ for both δ18O and δ13C (1SD). This is similar to precisions typically attained for routine analysis of much larger samples in standard operation on the same equipment, and demonstrates that precise stable isotope analysis of smaller single-specimen planktic foraminifers than we could achieve so far is within reach of CF mass spectrometry.References:Emiliani, C. 1955, DOI: 10.1086/626295Fiebig, J., et al. 2005, DOI: 10.1002/rcm.2060Ganssen, G.M., et al., 2011, DOI:10.5194/cp-7-1337-2011Metcalfe, B., et al., 2019, DOI: 10.1029/2018PA003475

Ba/Ca ratios in many non-spinose planktic foraminifera are markedly higher than those observed in spinose planktic species, but the cause for these high Ba/Ca ratios is not understood. A better understanding of this geochemical anomaly could provide insights into the habitat and/or controls over Ba incorporation in these species and expand their utility in paleoclimate research. In spinose species, shell Ba/Ca depends only on the Ba/Ca ratio of seawater. Proposed explanations for high non-spinose Ba/Ca include (1) the empirical partition coefficient, DBa, differs from the spinose species, (2) shell Ba varies with seawater temperature and pH, or (3) non-spinose foraminifers have a preference for prey that has elevated Ba. We performed laboratory culture experiments to determine DBa for the thermocline-dwelling non-spinose planktic foraminifer Neogloboquadrina dutertrei. We find that the Ba/Ca ratio of foraminiferal calcite secreted in the laboratory varies linearly with the Ba/Ca ratio of the seawater. The DBa for this species, 0.11 ± 0.008 (2SE; 95% CL), is similar to the DBa for spinose species (0.13 ± 0.004, 2SE; 95% CL). As in spinose species, the Ba/Ca ratio of cultured specimens of N. dutertrei is not influenced by culture temperature (12–22 °C) or seawater pHNBS (range 7.8–8.3). However, the Ba/Ca ratio of individual plankton-tow N. dutertrei specimens that completed their lifecycle in the ocean exceeds the Ba/Ca ratio of cultured specimens by up to three orders of magnitude. It is unlikely this difference between cultured specimens and ocean-grown specimens is due to seawater [Ba] variability, since seawater Ba/Ca ratios calculated using our DBa are much higher than exist in the ocean. Rather, we suggest that elevated shell Ba/Ca in plankton tow and fossil N. dutertrei is due to calcification in the microenvironment of marine organic aggregates such as marine snow, where [Ba] is elevated as a result of Ba release from biogenic particulates.

Modern observations of planktic foraminifera from sediment trap studies help to constrain the regional ecology of paleoceanographically valuable species. Results from a weekly-resolved sediment trap time series (2008–2014) in the northern Gulf of Mexico demonstrate that 92% of Globorotalia truncatulinoides flux occurs in winter (January, February, and March), and that encrusted and non-encrusted individuals represent calcification in distinct depth habitats. We use individual foraminiferal analysis (IFA) of G. truncatulinoides tests to investigate differences in the elemental (Mg/Ca) and isotopic composition (δ18O and δ13C) of the encrusted and non-encrusted ontogenetic forms of G. truncatulinoides, and to estimate their calcification depth in the northern Gulf of Mexico. We estimate that non-encrusted and encrusted G. truncatulinoides have mean calcification depths of 66 ± 9 m and 379 ± 76 m, respectively. We validate the Mg/Ca-calcification temperature relationship for G. truncatulinoides and demonstrate that the δ18O and Mg/Ca of the non-encrusted form is a suitable proxy for winter surface mixed layer conditions in the Gulf of Mexico. Care should be taken not to combine encrusted and non-encrusted individuals of G. truncatulinoides for down core paleoceanographic studies.

Mg/Ca ratio paleothermometry in foraminifera is an important tool for the reconstruction and interpretation of past environments. However, existing Mg/Ca:temperature relationships for planktic species inhabiting middle- and high-latitude environments are limited by a lack of information about the development and impact of low-Mg/Ca ratio “crusts” and the influence of the carbonate system on Mg/Ca ratios in these groups. To address this, we cultured individual specimens of Neogloboquadrina incompta and Neogloboquadrina pachyderma in seawater across a range of temperature (6°–12°C) and pH (7.4–8.2). We found by laser ablation inductively couple mass spectrometry analyses of shells that culture-grown crust calcite in N. incompta had a lower Mg/Ca ratio than ontogenetic calcite formed at the same temperature, suggesting that temperature is not responsible for the low-Mg/Ca ratio of neogloboquadrinid crusts. The Mg/Ca:temperature relationship for ontogenetic calcite in N. incompta was consistent with the previously published culture-based relationship, and no significant relationship was found between Mg/Ca ratios and pH in this species. However, the Mg/Ca ratio in laboratory-cultured N. pachyderma was much higher than that reported in previous core top and sediment trap samples, due to lack of crust formation in culture. Application of our ontogenetic calcite-specific Mg/Ca:temperature relationships to fossil N. pachyderma and N. incompta from five intervals in cores from the Santa Barbara Basin and the Bering Sea shows that excluding crust calcite in fossil specimens may improve Mg/Ca-based temperature estimates.

Application of biogenic opal oxygen isotope ratios from fossil and subfossil diatoms to paleoceanographic problems has been hampered by analytical and calibration issues in concert with a lack of experimental data to test fundamental assumptions about sample processing techniques. Here we present experiments where we react purified sediment trap and sediment core diatom samples to waters of different oxygen isotopic composition to quantify oxygen isotope exchange between laboratory processing solutions and δ18Odiatom values. We generate δ18Odiatom data using a microfluorination technique, and present FTIR data for samples both before and after vacuum dehydroxylation in order to investigate the mineralogic behavior of biogenic silica after dehydroxylation occurs. Our data demonstrate that exposure of diatoms to different δ18Oequil. water solutions during sample preparation alters final δ18Odiatom values and this alteration occurs during sample dehydroxylation prior to IRMS analysis. In addition, we present data that show structural diatom hydroxyl is persistent in sediment core samples, but the degree of equilibration with surrounding water decreases with sample age and/or core depth increase. Based on FTIR data, we propose that OH– loss from biogenic silica occurs post depositionally and may occur after heating in the laboratory, producing molecular scale reorganization of the silica tetrahedra within the biogenic opaline structure. Finally, we provide preliminary estimates of the time necessary for complete dehydroxylation of diatom silica, which would result in fully mature biogenic opal. These data suggest that high latitude marine sediments are slow to mature, and that the rate of exchangeable oxygen reduction varies exponentially at the locations we examined. Maturation time estimates require millions of years, and likely vary depending on core location.

This study utilizes a combined stable isotope and 14C dating approach to determine the radiocarbon reservoir age correction, ΔR, for the James River, Virginia estuary from 17th century Crassostrea virginica shells of known collection dates. ΔR, which can vary spatially and temporally, is a locality-specific adjustment applied to the global ocean reservoir, R, to further account for the offset between the atmospheric and marine 14C calibration curves. To assess the temporal variability in ΔR, continuous δ18O sampling along the oyster shell hinge provides a seasonal record throughout the oyster's life. This is then used to identify sampling locations for 14C measurements based on calcite precipitated during the Summer (>19 °C) and Fall through Spring (F-Sp

The calcite shells, or tests, of foraminifera provide a window into Earth history because they are archived in most marine sediments and contain useful geochemical proxies for paleoceanography. Previous observations of diurnal heterogeneity in proxies like Mg/Ca demonstrate a complex relationship between environmental conditions and test composition. The causes for this diurnal banding and the potential impact for proxy interpretation in systems other than Mg/Ca have yet to be determined. Recently, Mg and Na in shells of the planktic foraminifer species Orbulina universa have been observed to be high at the location of the primary organic sheet (POS), i.e. the organic template upon which the calcite test is formed. Here we use time-of-flight secondary ion mass spectrometry (ToF-SIMS), a chemical and isotope mapping technique with a spatial resolution of 300 nm, to show that Na banding is a consistent feature in the tests of 45 individual cultured O. universa. This banding occurs in two distinct forms: (1) sharp Na bands associated with organic sheets that are embedded in the calcite test after chamber formation; and (2) regular, thicker, but lower-amplitude Na bands that are found throughout the test. We use the pattern of the first type of banding to indicate the extent and sequence of calcite growth during chamber formation. Specifically, we show that new chamber formation involves growth over the previous chamber in Orbulina bilobata, a morphotype of O. universa that develops a second partial spherical chamber attached to the primary sphere. This is consistent with a bilamellar model of foraminiferal growth. However, a SIMS mapping survey of the morphologically more complex Globigerina bulloides and Neogloboquadrina dutertrei suggests that the pattern of growth during chamber formation and the prevalence of different types of Na bands may be species-specific. The wide, repeating Na bands that occur throughout the test of O. universa generally occur in an inverse pattern with respect to Mg banding for the first few days of the foraminifer's life, but this pattern changes as the organism ages. We use the magnitude, timing, and coherency between Na and Mg bands to put constraints on various proposed mechanisms for banding, including antiport Mg2+-2Na+ exchange and kinetic growth rate effects.

To explore relationships between water column hydrography and foraminiferal geochemistry in the Eastern Tropical North Pacific, we present δ O 18 and Mg/Ca records from three species of planktonic foraminifera, Globigerinoides ruber, Globigerina bulloides, and Globorotalia menardii, collected from a sediment trap mooring maintained in the Gulf of Tehuantepec from 2006–2012. Differences in δ O 18 between mixed-layer species G. ruber and G. bulloides and thermocline-dweller G. menardii track seasonal changes in upwelling. The records suggest an increase in upwelling during the peak positive phase of El Nino, and an overall reduction in stratification over the six-year period. For all three species, Mg/Ca ratios are higher than what has been reported in previous studies, and show poor correlations to calcification temperature. We suggest that low pH (7.6–8.0) and [ CO 3 2 − ] values (∼70–120 μmol/kg) in the mixed layer contribute to an overall trend of higher Mg/Ca ratios in this region. Laser Ablation Inductively Coupled Mass Spectrometry analyses of G. bulloides with high Mg/Ca ratios (>9 mmol/mol) reveal the presence of a secondary coating of inorganic calcite that has Mg/Ca and Mn/Ca ratios up to an order of magnitude higher than these elemental ratios in the primary calcite, along with elevated Sr/Ca and Ba/Ca ratios. Some of the samples with abnormally high Mg/Ca are found during periods of high primary productivity, suggesting the alteration may be related to changes in carbonate saturation resulting from remineralization of organic matter in oxygen-poor waters in the water column. Although similar shell layering has been observed on fossil foraminifera, this is the first time such alteration has been studied in shells collected from the water column. Our results suggest a role for seawater carbonate chemistry in influencing foraminiferal calcite trace element:calcium ratios prior to deposition on the seafloor, particularly in high-productivity, low-oxygen environments.

International audience; Planktonic foraminifer tests are major archives of environmental change and provide a multitude of proxies in paleoceanography and paleoclimatology. The application of such proxies is contingent upon a collaborative effort to better understand how the living organisms record the properties of their environment and how the resulting signals are recorded in marine sediments. In this contribution, we provide a review of the rapidly developing sub-fields of research, where new advances have been made possibleby technological developments, and by cross-disciplinary work of the scientific community. Following brief historical overviews of the sub-fields, we discuss the latest advances in planktonic foraminifer research and highlight the resulting new perspectives in ocean and climate research. Natural classification based on consistent species concepts forms the basis for analysis of any foraminifer-derived proxy. New approaches in taxonomy and phylogeny of Cenozoic planktonic foraminifers (Section 2) are presented, highlighting new perspectives on sensitivity and response of planktonic foraminifers to the changing climate and environment (Section 4). Calibration of foraminifer-specific data and environmental parameters is improving along with the technical development of probes and the access to samples from the natural environment (Section 3), enhancing our understanding of the ever-changing climate and ocean system. Comprehension of sedimentation and flux dynamics facilitates maximum gain of information from fossil assemblages (Section 5). Subtle changes in the physical (e.g., temperature), chemical (e.g., pH), and biological (e.g., food) conditions of ambient seawater affect the abundance of species and composition of assemblages as well as the chemical composition of the foraminifer shell and provide increasingly-detailed proxy data on paleoenvironments (Section 6).

The oxygen isotope (δ18O) compositions of final chamber fragments of individual shells of the planktic foraminifer Orbulina universa were measured in situ via secondary ion mass spectrometry (SIMS) and by traditional gas-source mass spectrometry (GSMS) entailing acid digestion of sampled calcite. The paired SIMS-GSMS analyses were performed on final chamber fragments of fossil shells taken from the top of a sediment core (Holocene) as well as shells grown in laboratory culture. Multiple iterations of SIMS-GSMS analyses were conducted on final chamber fragments treated with a variety of cleaning protocols. The series of paired analyses yielded an average SIMS-GSMS δ18O offset (Δ18OSIMS-GSMS) of −0.9 ± 0.1‰ (±2 SE). The volume of material analyzed in 10-μm SIMS spots is ~105 times smaller than that analyzed by GSMS; hence, the extent to which these Δ18OSIMS-GSMS values represent real differences in analyte vs. instrumental factors remains unclear. Possible contributing factors to the SIMS-GSMS δ18O difference include sample-standard mismatch by SIMS, differences in standardization of SIMS and GSMS, and non-calcite contaminants in samples. Although the two datasets are consistently offset, SIMS values reproduce inter-shell δ18O variability delineated by shell fragment GSMS values. This strong positive covariance proved useful for bringing the two datasets into agreement (i.e. Δ18OSIMS-GSMS = 0), and confirms that SIMS-based foraminifer δ18O values record changes in calcification temperature and/or δ18O of seawater. Whether shells of foraminifer taxa with differing microcrystalline structures, chemical composition, and/or preservation histories register a similar Δ18OSIMS-GSMS value is a subject of ongoing testing.

© 2015 Elsevier B.V. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is becoming a widespread technique for analyzing elemental ratios in foraminiferal calcite. Here we focus on optimizing LA-ICP-MS for high-resolution depth profiling of elemental ratios through shell walls. This application reveals intrashell variability and provides a unique opportunity to quantify trace element incorporation over short time scales of calcification by an individual foraminifer. High-resolution depth profiling requires careful consideration of both ablation and analytical conditions required to resolve differences in shell chemistry across sub-micron shell thickness. We present laser ablation profiles of NIST SRM 610 standard glass data (in cps) and elemental/Ca ratios (in mmol/mol) from foraminiferal calcite obtained over a range of operating conditions using a Photon Machines 193nm UV excimer laser-ablation system, equipped with a dual-volume ANU HelEx chamber, coupled to an Agilent 7700x quadrupole ICP-MS. Different combinations of energy density, repetition rate, and mass spectrometer cycle time can yield varying elemental profiles. This variability can mimic and/or mask real intrashell trace element heterogeneity in foraminifer shells. At low (2 or greater, resulting in reduced spatial resolution.

We present a new method that quantifies the oxygen isotope geochemistry of Laurentide ice-sheet (LIS) meltwater across the last deglaciation, and reconstruct decadal-scale variations in the δ18O of LIS meltwater entering the Gulf of Mexico between ∼18 and 11 ka. We employ a technique that combines laser ablation ICP-MS (LA-ICP-MS) and oxygen isotope analyses on individual shells of the planktic foraminifer Orbulina universa to quantify the instantaneous δ18Owater value of Mississippi River outflow, which was dominated by meltwater from the LIS. For each individual O. universa shell, we measure Mg/Ca (a proxy for temperature) and Ba/Ca (a proxy for salinity) with LA-ICP-MS, and then analyze the same O. universa for δ18O using the remaining material from the shell. From these proxies, we obtain δ18Owater and salinity estimates for each individual foraminifer. Regressions through data obtained from discrete core intervals yield δ18Ow vs. salinity relationships with a y-intercept that corresponds to the δ18Owater composition of the freshwater end-member. Our data suggest that from 15.5 through 14.6 ka, estimated δ18Ow values of Mississippi River discharge from discrete core intervals range from −11‰ to −21‰ VSMOW, which is consistent with δ18O values from both regional precipitation and the low-elevation, southern margin of the LIS. During the Bolling and Allerod (14.0 through 13.3 ka), estimated δ18Ow values of Mississippi River discharge from discrete core intervals range from −22‰ to −38‰ VSMOW. These values suggest a dynamic melting history of different parts of the LIS, with potential contributions to Mississippi River outflow from both the low-elevation, southern margin of the LIS and high-elevation, high-latitude domes in the LIS interior that were transported to the ablation zone. Prior to ∼15.5 ka, the δ18Owater value of the Mississippi River was similar to that of regional precipitation or low-latitude LIS meltwater, but the Ba concentration in the Mississippi basin was affected by changes in weathering within the watershed, complicating Ba-salinity relationships in the Gulf of Mexico. After 13 ka, our data suggest Mississippi River outflow did not influence surface salinity above our Gulf of Mexico Orca Basin core site. Rather, we hypothesize that open ocean conditions prevailed as sea level rose and the paleoshoreline at the southern edge of North America retreated northward.

The carbon isotope composition (δ13C) of seawater provides valuable insight on ocean circulation, air-sea exchange, the biological pump, and the global carbon cycle and is reflected by the δ13C of foraminifera tests. Here more than 1700 δ13C observations of the benthic foraminifera genus Cibicides from late Holocene sediments (δ13CCibnat) are compiled and compared with newly updated estimates of the natural (preindustrial) water column δ13C of dissolved inorganic carbon (δ13CDICnat) as part of the international Ocean Circulation and Carbon Cycling (OC3) project. Using selection criteria based on the spatial distance between samples, we find high correlation between δ13CCibnat and δ13CDICnat, confirming earlier work. Regression analyses indicate significant carbonate ion (−2.6±0.4)×10−3‰/(μmolkg−1) [CO32−] and pressure (−4.9±1.7)×10−5‰m−1 (depth) effects, which we use to propose a new global calibration for predicting δ13CDICnat from δ13CCibnat. This calibration is shown to remove some systematic regional biases and decrease errors compared with the one-to-one relationship (δ13CDICnat=δ13CCibnat). However, these effects and the error reductions are relatively small, which suggests that most conclusions from previous studies using a one-to-one relationship remain robust. The remaining standard error of the regression is generally σ≅0.25‰, with larger values found in the southeast Atlantic and Antarctic (σ≅0.4‰) and for species other than Cibicides wuellerstorfi. Discussion of species effects and possible sources of the remaining errors may aid future attempts to improve the use of the benthic δ13C record.

The relationship between seawater temperature and the average Mg/Ca ratios in planktic foraminifera is well established, providing an essential tool for reconstructing past ocean temperatures. However, many species display alternating high and low Mg-bands within their shell walls that cannot be explained by temperature alone. Recent experiments demonstrate that intrashell Mg variability in Orbulina universa, which forms a spherical terminal shell, is paced by the diurnal light/dark cycle. Whether Mg-heterogeneity is also diurnally paced in species with more complex shell morphologies is unknown. Here we show that high Mg/Ca-calcite forms at night in cultured specimens of the multi-chambered species Neogloboquadrina dutertrei. Our results demonstrate that N. dutertrei adds a significant amount of calcite, and nearly all Mg-bands, after the final chamber forms. These results have implications for interpreting patterns of calcification in N. dutertrei and suggest that diurnal Mg-banding is an intrinsic component of biomineralization in planktic foraminifera., The degree to which the diurnal light/dark cycle influences Mg-heterogeneity in foraminifera with complex shell morphologies remains unknown. Here, using highly spatially resolved analytical techniques, the authors investigate Mg-banding and calcification in isotope-labelled Neogloboquadrina dutertrei specimens.

Deep-sea bamboo corals (order Gorgonacea, family Isididae) are known to record changes in water mass chemistry over decades to centuries. These corals are composed of a two-part skeleton of calcite internodes segmented by gorgonin organic nodes. We examine the spatial variability of bamboo coral organic node 13C/12C and 15N/14N from 13 bamboo coral specimens sampled along the California margin (37–32° N, 792–2136 m depth). Radiocarbon analyses of the organic nodes show the presence of the anthropogenic bomb spike, indicating the corals utilize a surface-derived food source (pre-bomb D14C values of ∼−100‰, post-bomb values up to 82‰). Carbon and nitrogen isotope data from the organic nodes (δ13C = −15.9‰ to −19.2‰; δ15N = 13.8‰ to 19.4‰) suggest selective feeding on surface-derived organic matter or zooplankton. A strong relationship between coral δ15N and habitat depth indicates a potential archive of changing carbon export, with decreased δ15N values reflecting reduced microbial degradation (increased carbon flux) at shallower depths. Using four multi-centennial-length coral records, we interpret long-term δ15N stability in the California Current. Organic node δ15C values record differences in carbon isotope fractionation dictated by nearshore vs. offshore primary production. These findings imply strong coupling between primary production, pelagic food webs, and deep-sea benthic communities.

Dansgaard–Oeschger (D–O) cycles had far-reaching effects on Northern Hemisphere and tropical climate systems during the last glacial period, yet the climatic response to D–O cycles in western North America is controversial, especially prior to 55 ka. We document changes in precipitation along the western slope of the central Sierra Nevada during early Marine Oxygen Isotope Stages (MIS) 3 and 4 (55–67 ka) from a U-series dated speleothem record from McLean's Cave. The timing of our multi-proxy geochemical dataset is coeval with D–O interstadials (15–18) and stadials, including Heinrich Event 6. The McLean's Cave stalagmite indicates warmer and drier conditions during Greenland interstadials (GISs 15–18), signified by elevated δ18O, δ13C, reflectance, and trace element concentrations, and less radiogenic 87Sr/86Sr. Our record extends evidence of a strong linkage between high-latitude warming and reduced precipitation in western North America to early MIS 3 and MIS 4. This record shows that the linkage persists in diverse global climate states, and documents the nature of the climatic response in central California to Heinrich Event 6.

Using oxygen isotope ratios in terminal growth rings, we estimate the month of harvest of 32 Macoma nasuta shells from a single component Late Phase II (450–200 cal BP) assemblage from CA-CCO-297. Results suggest that clamming occurred throughout the year, but was most pronounced during two pulses in early summer and early winter. We relate the former to longer daylight in early summer that facilitated access to tidal flats and clamming, while the latter may relate more to a lack of other foraging opportunities. We compare the results to Macoma seasonality studies at two other Late Period sites (CA-SFR-171 and CA-SMA-6) and one Middle Period site (CA-ALA-17) on San Francisco Bay. The patterns at all four sites are similar in many regards, but differ in the details and highlight new information on ancient settlement patterns in the region.

[1] Measurements of trace metal ratios in foraminiferal calcite are routinely used to reconstruct paleoceanographic conditions. Analyses using solution-based inductively coupled plasma mass spectrometry (ICP-MS) require dissolution of the entire foraminifer shell. The potential exists for contamination from adherent clays, mineralized coatings, and other diagenetic components that confound the biogenic trace metal signal. We present results from a cleaning experiment on fossil specimens of the planktic foraminifer Orbulina universa that were cracked into several shell fragments and subjected to different cleaning protocols. We use laser ablation ICP-MS (LA-ICP-MS) depth profiling to evaluate the effects of reductive, oxidative, and chelating (diethylene-triamine pentaacetic acid) cleaning protocols on shell Mg/Ca and Ba/Ca ratios. Using the natural pattern of intrashell Mg/Ca heterogeneity exhibited by O. universa, we demonstrate that reductive and oxidative cleaning can dissolve shell calcite from available surfaces, although intrashell Mg/Ca minima and maxima are unaffected. High-resolution depth profiles can be used to identify areas of heterogeneous intrashell Ba/Ca, which can be excluded from computations of whole-shell Ba/Ca. The size and density of shell pores plays a major role in the degree of contamination from sedimentary material. We demonstrate an approach for computing whole-shell Me/Ca ratios from LA-ICP-MS depth profiles that accounts for potential contamination and diagenetic overprinting.

RATIONALE Measuring δ(18)O values in silicates is difficult and hazardous in comparison with measurements of carbonate minerals due to the difficulty in breaking Si-O-Si bonds. A novel method for measurement of δ(18)O values from quartz and biogenic silica utilizing high-temperature pyrolysis with continuous-flow isotope ratio mass spectrometry (CF-IRMS) is presented. METHODS Samples were prepared by offline dehydroxylation/dehydration under vacuum at 1060°C. The dehydroxylated samples are mixed with polytetrafluoroethylene (PTFE) powder (2.3:1 PTFE/Si) and graphite in silver foil capsules and reacted in a vario PYRO cube TC/EA system in a glassy carbon reaction tube. Quartz and biogenic opal samples react with available carbon in a microfluorination environment upon decomposition of the PTFE, producing CO for analysis via CF-IRMS. RESULTS Silicate samples reacted quantitatively, producing data with yields ≥88% from ~400 µg samples. Multiple analyses with international standards demonstrated accuracy for replicate measurements (1σ range ±0.3-0.6‰), comparing favorably with previously published techniques. CONCLUSIONS New data produced with the microfluorination technique are comparable with data from studies using existing methodologies. The microfluorination technique has the potential to greatly increase the number of laboratories producing silicate oxygen isotope data for mineralogic, paleoclimatic and biogeochemical applications.

Although substantial turnovers of planktonic foraminiferal species occurred during Cretaceous oceanic anoxic events (OAEs), the direct effects of dissolved oxygen (DO) concentration on planktonic foraminifera remain obscure. Culture experiments can quantify the relationship between planktonic foraminiferal ecology and environmental parameters, but experiments controlling DO have yet to be conducted because it is difficult to maintain a stable oxygen concentration. In this study, we cultured two planktonic foraminifer species ( Orbulina universa and Globigerina bulloides ) at six different DO levels between 10% and 100% saturation. Both species showed a high tolerance to low DO, suggesting that “dysoxic” conditions (> 0.7 mg O 2 l − 1 ) were not a direct cause of planktonic foraminiferal extinction at OAEs. The high tolerance of these species to extremely low DO might be attributable to their evolutionary descent from benthic foraminifera. Final shell weight increased with increasing DO, suggesting that fossil foraminiferal shell weight could vary with past DO conditions. Our results suggest that the extinction of many planktonic foraminiferal species during OAEs may have been due to anoxic or euxinic conditions in the euphotic zone. The occurrence of these conditions can be explained either by the oxygen minimum layer model or by the stagnant ocean model combined with elevated riverine P input.

Seasonality estimates based on stable isotope analyses of shellfish remains has been an important thrust of settlement pattern reconstruction, allowing researchers to place people on the landscape at points in space at different times of the year. In exposed coastal settings seasonality reconstructions are typically dependent on annual changes in water temperature. This paper has two goals. First, we continue development of a method for determining shellfish harvest seasonality in estuarine environments where annual salinity changes, not temperature, drive isotopic variation. Second, we contribute to settlement pattern studies by showing how small and large sites can be linked into a single system by examining different site types and shellfish species. Our case study focuses on the Late Prehistoric period of the San Francisco Peninsula, includes a large shellmound (CA-SMA-6) and an ephemeral camp (CA-SFR-171), and examines clam (Macoma spp.) and mussel (Mytilus spp.) harvesting. In this case, data support a fission-fusion settlement pattern, with periods of dispersal during late winter through early summer and aggregation in late summer through early winter.

The boron isotopic composition of biogenic carbonates has been used to reconstruct seawater pH and atmospheric pCO 2 on Pleistocene and Cenozoic timescales. Because of their excellent preservation and extensive fossil record throughout the Phanerozoic, brachiopods are a promising candidate for extending the boron isotope record as far back as the Cambrian. Here we present stable carbon, oxygen, and boron isotopic measurements of modern Terebratulid brachiopod calcite in comparison with environmental pH estimates calculated from oceanographic data. Geochemical transects along the length and depth of single shells confirm previously published trends in carbon and oxygen isotopic composition. In the outer surface (primary and outermost secondary layers), δ 11 B covaries with δ 13 C and δ 18 O, with more negative values in the outer and more positive values in the middle of the shell. However, δ 11 B deviates from δ 13 C and δ 18 O in the inner part of the secondary layer, where the δ 13 C and δ 18 O values are more positive and near equilibrium, whereas δ 11 B returns to more negative values. A comparison of different specimens of the species Terebratalia transversa (Sowerby, 1846) and Laqueus californianus (Kuster, 1844) microsampled from the middle part of the fibrous secondary layer demonstrates a clear correlation to ambient pH with a sensitivity similar to other empirical calibration curves for cultured planktic foraminifers, corals, and inorganic calcite. The relationship in other species is less clear and significantly offset, necessitating the use of a single species or a cross-calibration method with other species in paleo-pH reconstructions.

Plankton, corals, and other organisms produce calcium carbonate skeletons that are integral to their survival, form a key component of the global carbon cycle, and record an archive of past oceanographic conditions in their geochemistry. A key aspect of the formation of these biominerals is the interaction between organic templating structures and mineral precipitation processes. Laboratory-based studies have shown that these atomic-scale processes can profoundly influence the architecture and composition of minerals, but their importance in calcifying organisms is poorly understood because it is difficult to measure the chemistry of in vivo biomineral interfaces at spatially relevant scales. Understanding the role of templates in biomineral nucleation, and their importance in skeletal geochemistry requires an integrated, multiscale approach, which can place atom-scale observations of organic-mineral interfaces within a broader structural and geochemical context. Here we map the chemistry of an embedded organic template structure within a carbonate skeleton of the foraminifera Orbulina universa using both atom probe tomography (APT), a 3D chemical imaging technique with à ngström-level spatial resolution, and time-of-flight secondary ionization mass spectrometry (ToF-SIMS), a 2D chemical imaging technique with submicron resolution. We quantitatively link these observations, revealing that the organic template in O. universa is uniquely enriched in both Na and Mg, and contributes to intraskeletal chemical heterogeneity. Our APT analyses reveal the cation composition of the organic surface, offering evidence to suggest that cations other than Ca(2+), previously considered passive spectator ions in biomineral templating, may be important in defining the energetics of carbonate nucleation on organic templates.

Shells are a visible component of archaeological middens in Central California. While coastal and bay shore sites are often dominated by shells, these food items were sometimes hauled many kilometers from their collection points and are found in appreciable numbers in inland sites as well. Using oxygen and carbon stable isotope data from 44 Mytilus sp. (mussel) shells, we reconstruct shellfish seasonality harvesting at one inland site dating to the Middle Period (ca. 2500-1000 cal yrs BP), CA-SOL-364. Data show that shells were collected from nearby Suisun Marsh and were harvested almost exclusively during winter, a pattern that contrasts with coastal and bay shore sites. Such a harvesting signature is unlike that expected for a food staple or a feasting resource. We suggest mussels were harvested as a fallback food, as a source of protein or micronutrient to complement carbohydrate-rich foods that were stored and consumed during winter, or perhaps were only exploited as opportunity costs relaxed during winter, making sessile mussels an attractive subsistence pursuit.

© 2016 Elsevier B.V. Scattered data interpolation and approximation techniques allow for the reconstruction of a scalar field based upon a finite number of scattered samples of the field. In general, the fidelity of the reconstruction with respect to the original scalar field tends to deteriorate as the number of samples decreases. For the situation of very sparse sampling, the results may not be acceptable at all. However, if it is known that the scalar field of interest is correlated with a known flow field - as is the case when the scalar field represents the value of an oceanographic tracer that propagates under the influence of the ocean's flow - then this knowledge can be exploited to enhance the scattered data reconstruction method. One way to exploit flow field information is to use it to construct a modified notion of distance between points. Replacing the standard Euclidean distance metric with a flow-field-aware notion of distance provides a method for extending standard scattered data interpolation methods into flow-based methods that produce superior results for very sparse data. The resulting reconstructions typically have lower root-mean-square errors than reconstructions that do not use the flow information, and qualitatively they often appear physically more realistic.

Author(s): Gebbie, G; Streletz, GJ; Spero, HJ | Abstract: Compilations of paleoceanographic observations for the deep sea now contain a few hundred points along the oceanic margins, mid-ocean ridges, and bathymetric highs, where seawater conditions are indirectly recorded in the chemistry of buried benthic foraminiferal shells. Here we design an idealized experiment to test our predictive ability to reconstruct modern-day seawater properties by considering paleoceanographic-like data. We attempt to reconstruct the known, modern-day global distributions by using a state estimation method that combines a kinematic tracer transport model with observations that have paleoceanographic characteristics. When a modern-like suite of observations (Θ, practical salinity, seawater δ18O, δ13CDIC, PO4, NO3, and O2) is used from the sparse paleolocations, the state estimate is consistent with the withheld data at all depths below 1500 m, suggesting that the observational sparsity can be overcome. Physical features, such as the interbasin gradients in deep δ13CDIC and the vertical structure of Atlantic δ13CDIC, are accurately reconstructed. The state estimation method extracts useful information from the pointwise observations to infer distributions at the largest oceanic scales (at least 10,000 km horizontally and 1500 m vertically) and outperforms a standard optimal interpolation technique even though neither dynamical constraints nor constraints from surface boundary fluxes are used. When the sparse observations are more realistically restricted to the paleoceanographic proxy observations of δ13C, δ18O, and Cd/Ca, however, the large-scale property distributions are no longer recovered coherently. At least three more water mass tracers are likely needed at the core sites in order to accurately reconstruct the large-scale property distributions of the Last Glacial Maximum.

It is poorly understood how intermediate water masses are affected by decadal scale climate via biogeochemical cycling, export production, and changes in circulation/ventilation. To this end, a geochemical nutrient proxy from deep-sea bamboo corals would provide decadal to centennial scale records of deep and intermediate-water nutrient dynamics. Seawater barium (BaSW) has a nutrient-like distribution in the water-column (similar to silicate), so Ba/Ca records in foraminifera, shallow water surface corals, and other deep-sea corals have been used to trace refractory nutrients. Here we present the first calibration of a nutrient proxy from skeletal barium preserved in the calcitic internodes of deep-sea bamboo corals, collected from intermediate water depths. A calibration was calculated from a broadly distributed suite of Isidella and Keratoisis corals spanning a silicate and BaSW gradient (n = 33 corals; 300–2800 m): Ba / Ca b a m b o o c o r a l μmol/mol = 0.079 ± 0.008 ∗ Ba SW nmol/kg + 4.205 ± 0.870 r 2 = 0.77 ; n = 33 The strong linear correlation between Ba/Cabamboo coral and BaSW suggests that coral Ba/Ca is a reliable recorder of seawater barium (and, therefore, silicate). We find a distribution coefficient (DBa) for Ba/Cabamboo coral of 1.3 ± 0.2, similar to that of other corals (surface and deep-sea dwelling) and inorganic calcium carbonate precipitation experiments (DBa = 1.2–1.5). This suggests that Ba incorporation is primarily driven by cationic substitution in bamboo corals and holds promise as a globally applicable refractory nutrient proxy. We find interannual–decadal scale variability in a Ba/Cabamboo coral timeseries from a California Margin coral (San Juan Seamount; 1295 m). These data suggest that additional high-resolution Ba/Cabamboo coral records may reveal a connection between regional-scale intermediate water biogeochemistry and low-latitude surface ocean/atmospheric climate.

Culture experiments with living planktic foraminifers reveal that the ratio of boron to calcium (B/Ca) in Orbulina universa increases from 56 to 92 μmol mol− 1 when pH is raised from 7.61 +/– 0.02 to 8.67 +/– 0.03 (total scale). Across this pH range, the abundances of carbonate, bicarbonate, and borate ions also change (+ 530, − 500, and + 170 μmol kg− 1, respectively). Thus specific carbonate system control(s) on B/Ca remain unclear, complicating interpretation of paleorecords. B/Ca in cultured O. universa also increases with salinity (55–72 μmol mol− 1 from 29.9–35.4‰) and seawater boron concentration (62–899 μmol mol− 1 from 4–40 ppm B), suggesting that these parameters may need to be taken into account for paleorecords spanning large salinity changes (~ 2‰) and for samples grown in seawater whose boron concentration ([B]SW) differs from modern by more than 0.25 ppm. While our results are consistent with the predominant incorporation of the charged borate species BOH4−into foraminiferal calcite, the behavior of the partition coefficient KD (defined as [B/Ca]calcite/BOH4−/HCO3−seawater) cannot be explained by borate incorporation alone, and suggests the involvement of other pH-sensitive ions such as CO32 − For a given increase in seawater BOH4−, the corresponding increase in B/Ca is stronger when BOH4− is raised by increasing [B]SW than when it is raised by increasing pH. These results suggest that B incorporation controls should be reconsidered. Additional insight is gained from laser-ablation ICP-MS profiles, which reveal variable B/Ca distributions within individual shells.

Oysters ( Crassostrea virginica ) were a central component of the Chesapeake Bay ecosystem in 1607 when European settlers established Jamestown, VA, the first permanent English settlement in North America. These estuarine bivalves were an important food resource during the early years of the James Fort (Jamestown) settlement while the colonists were struggling to survive in the face of inadequate supplies and a severe regional drought. Although oyster shells were discarded as trash after the oysters were eaten, the environmental and ecological data recorded in the bivalve geochemistry during shell deposition remain intact over centuries, thereby providing a unique window into conditions during the earliest Jamestown years. We compare oxygen isotope data from these 17th century oyster shells with modern shells to quantify and contrast estuarine salinity, season of oyster collection, and shell provenance during Jamestown colonization (1609–1616) and the 21st century. Data show that oysters were collected during an extended drought between fall 1611 and summer 1612. The drought shifted the 14 psu isohaline above Jamestown Island, facilitating individual oyster growth and extension of oyster habitat upriver toward the colony, thereby enhancing local oyster food resources. Data from distinct well layers suggest that the colonists also obtained oysters from reefs near Chesapeake Bay to augment oyster resources near Jamestown Island. The oyster shell season of harvest reconstructions suggest that these data come from either a 1611 well with a very short useful period or an undocumented older well abandoned by late 1611.

Production of marine shell beads in island and coastal settings was an important activity in prehistory, with important political and economic ties. Currently, there are few methods to track beads to their locus of production. Examining the spatial distribution of bead types provides one method of doing so. Chemical and stable isotopic methods provide an additional and independent means of testing hypotheses generated by spatial distributions. We use stable oxygen, carbon, and strontium isotope data to reconstruct provenance zones for 18 Olivella biplicata beads from the Los Angeles Basin and San Nicolas Island, California. We compare the results to isotopic data from modern and radiocarbon-dated whole shells collected along the Pacific Coast. Results indicate that all 18 beads were manufactured from shells growing in open coast locations south of Point Conception. Differences in isotopic composition between bead types suggest that not all were produced in the same location. Some, such as callus ...

Accurate and efficient measurement of the oxygen isotope composition of carbonates (delta(C) (18)O) based on the mass spectrometric analysis of CO(2) produced by reacting carbonate samples with H(3)PO(4) is compromised by: (1) uncertainties associated with fractionation factors (alpha(CO)(2)C) used to correct measured oxygen isotope values of CO(2)(delta(CO(2)(18)O) to delta(C) (18)O; and (2) the slow reaction rates of many carbonates of geological and environmental interest with H(3)PO(4). In contrast, determination of delta(C) (18)O from analysis of CO produced by high-temperature (1400 degrees C) pyrolytic reduction, using an elemental analyser coupled to continuous-flow isotope-ratio mass spectrometry (TC/EA CF-IRMS), offers a potentially efficient alternative that measures the isotopic composition of total carbonate oxygen and should, therefore, theoretically be free of fractionation effects. The utility of the TC/EA CF-IRMS technique was tested by analysis of carbonates in the calcite-dolomite-magnesite solid-solution and comparing the results with delta(C) (18)O measured by conventional thermal decomposition/fluorination (TDF) on the same materials. Initial results show that CO yields are dependent on both the chemical composition of the carbonate and the specific pyrolysis conditions. Low gas yields (100% of predicted yield) are associated with positive (+0.2 per thousand) deviations in delta(C(TC/EA) (18)O compared with delta(C(TDF) (18)O. At a pyrolysis temperature of 1420 degrees C the difference between delta(C) (18)O measured by TC/EA CF-IRMS and TDF (Delta(C(TC/EA,TDF) (18)O) was found to be negatively correlated with gas yield (r = -0.785) and this suggests that delta(C) (18)O values (with an estimated combined standard uncertainty of +/-0.38 per thousand) could be derived by applying a yield-dependent correction. Increasing the pyrolysis temperature to 1500 degrees C also resulted in a statistically significant correlation with gas yield (r = -0.601), indicating that delta(C) (18)O values (with an estimated uncertainty of +/-0.43 per thousand) could again be corrected using a yield-dependent procedure. Despite significant uncertainty associated with TC/EA CF-IRMS analysis, the magnitude of the uncertainty is similar to that associated with the application of poorly defined values of alpha(CO)(2), (C) used to derive delta(C) (18)O from delta(CO(2) (18)O measured by the H(3)PO(4) method for most common carbonate phases. Consequently, TC/EA CF-IRMS could provide a rapid alternative for the analysis of these phases without any effective deterioration in relative accuracy, while analytical precision could be improved by increasing the number of replicate analyses for both calibration standards and samples. Although automated gas preparation techniques based on the H(3)PO(4) method (ISOCARB, Kiel device, Gas-Bench systems) have the potential to measure delta(CO)(2) (18)O efficiently for specific, slowly reacting phases (e.g. dolomite), problems associated with poorly defined alpha(CO)(2), (C) remain. The application of the Principle of Identical Treatment is not a solution to the analysis of these phases because it assumes that a single fractionation factor may be defined for each phase within a solid-solution regardless of its precise chemical composition. This assumption has yet to be tested adequately.

This paper primarily reviews our recent work on the biology and geochemistry of foraminifera with respect to their use as paleoceanographic proxies. Our approach to proxy validation and development is described, primarily from a modeler’s point of view. The approach is based on complementary steps in understanding the inorganic chemistry, inorganic isotope fractionation, and biological controls that determine paleo-tracer signals in organisms used in climate reconstructions. Integration of laboratory experiments, field and culture studies, theoretical considerations, and numerical modeling holds the key to the method’s success. We describe effects of life-processes in foraminifera on stable carbon, oxygen, and boron isotopes as well as Mg incorporation into foraminiferal calcite shells. Stable boron isotopes will be used to illustrate our approach. We show that a mechanism-based understanding is often required before primary climate signals can be extracted from the geologic record because the signals can be heavily overprinted by secondary, non-climate related phenomena. Moreover, for some of the proxies, fundamental knowledge on the thermodynamic, inorganic basis is still lacking. One example is stable boron isotopes, a paleo-pH proxy, for which the boron isotope fractionation between the dissolved boron compounds in seawater was not precisely known until recently. Attempts to overcome such hurdles are described and implications of our work for paleoceanographic reconstructions are discussed.