NIST RM 8301 Boron Isotopes in Marine Carbonate (Simulated Coral and Foraminifera Solutions): Inter‐laboratory δ 11 B and Trace Element Ratio Value Assignment (original) (raw)
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Geostandards and Geoanalytical Research, 2020
Boron isotopes in marine carbonates are increasingly used to reconstruct seawater pH and atmospheric pCO2 through Earth’s history. While isotope ratio measurements from individual laboratories are often of high quality, it is important that records generated in different laboratories can equally be compared. Within this Boron Isotope Intercomparison Project (BIIP), we characterised the boron isotopic composition (commonly expressed in δ11B) of two marine carbonates: Geological Survey of Japan carbonate reference materials JCp‐1 (coral Porites) and JCt‐1 (giant clam Tridacna gigas). Our study has three foci: (a) to assess the extent to which oxidative pre‐treatment, aimed at removing organic material from carbonate, can influence the resulting δ11B; (b) to determine to what degree the chosen analytical approach may affect the resultant δ11B; and (c) to provide well‐constrained consensus δ11B values for JCp‐1 and JCt‐1. The resultant robust mean and associated robust standard deviatio...
Chemical Geology, 2009
The boron isotope composition of marine carbonates such as foraminiferal tests and coral skeletons is increasingly being used to reconstruct seawater pH values and atmospheric pCO 2 concentrations spanning hundreds of thousands or even millions of years. However, inter specific and small scale (microns) intra specific isotopic variation, either due to life processes of an organism or patchy recrystallisation and dissolution in fossilised material, can limit the use of the boron isotope ratio as palaeo-pH recorder. One approach to address this problem is the combined use of in situ and high spatial resolution mass spectrometry and high precision bulk analytical techniques. While much effort has been invested to establish reference material for silicates little attention has been devoted towards characterizing and using carbonate material allowing direct isotopic comparisons between B isotope data produced on carbonates by different techniques and laboratories. Hence, here we present data on the boron isotope composition of carbonate material determined by multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS), thermal ionization mass spectrometry (TIMS), and secondary ionization mass spectrometry (SIMS). The new reference material permits the B isotope analysis of single foraminiferal chambers using SIMS and to empirically relate between seawater pH, the B isotope composition of O. universa and the predicted foraminiferal vital effect.
Biogeosciences Discussions, 2018
Boron isotopes ( 11 B) records from tropical ocean corals have been used to reconstruct paleo-pH of ocean for the past several decades to few centuries which are comparable to the resolution of instrumental records. In most of the studies, attempts have been made to decipher the role of anthropogenic CO2 forcing to recent trend of ocean acidification based on 11 B derived paleo-pH records. However, such attempts in past were often hindered by limited knowledge of oceanographic factors that contributed to past pH variability and changes. In this study, we have evaluated pH records reconstructed using 11 B records from the Pacific and the Atlantic Oceans corals and investigated major forcing factors that contributed to sub annual-decadal scale pH variability and changes since the industrial era ~1850 AD. To the best of our knowledge, total eight 11 B records from the Pacific and two from the Atlantic Oceans are available in published literatures. The compilations of these records show large variability; range between 26.27-20.82 ‰ which corresponds to pH range 8.40-7.63 respectively. Our investigation of pH records from the Pacific ocean based on principal component analysis (PCA) reveals that atmospheric CO2 can explains maximum up to ~26% of the total pH variability during 1950-2004 AD, followed by the ocean-climate oscillations (i.e. ENSO and PDO) driven oceanographic factors up to ~17%. The remaining large variability (~57%) could not be explained by above forcing factors and hence we invoke possible influence of metabolic processes of corals and/or changes in micro-environments within the reefs which are often neglected in interpreting paleo-pH records. Therefore, we highlight the need for detailed investigation in future studies to understand about the exact
The isotopic composition of boron (δ 11 B) in marine carbonates is well established as a proxy for past ocean pH, however, its robust application to palaeo-environments relies on the generation of species-specific calibrations. Existing calibrations utilising the deep-sea coral (DSC) Desmophyllum dianthus highlight the potential application of this pervasive species to pH reconstructions of intermediate depth waters. Nevertheless, considerable uncertainty remains regarding the estimation of seawater pH from these bulk skeletal δ 11 B measurements, likely resulting from microstructural heterogeneities in δ 11 B of D. dianthus. To circumvent this problem, thus improving the reliability of the D. dianthus δ 11 B-pH calibration, we present a new δ 11 B calibration of micro-sampled fibrous aragonite from this species. Modern coral specimens recovered from the Atlantic, Pacific, and Southern Oceans, micro-sampled using microdrilling, micromilling, and laser cutting extraction, were analysed for trace element (B/Ca, Mg/Ca, Sr/Ca, and U/Ca) and boron isotopic composition. We find the best calibration against the δ 11 B of borate in local ambient seawater (a function of pH and taken from hydrographic data sets; pH range 7.57 to 8.05) utilises δ 11 B measurements of fibres with likely slow growth rates and minimal contamination from adjacent microstructures (identified by low Mg/Ca) for each coral specimen. This new calibration exhibits a stronger, and better-defined dependence on ambient seawater pH compared to bulk coral δ 11 B; δ 11 B fibre = (0.93 ± 0.17) × δ 11 B borate + (12.02 ± 2.63). We suggest that the majority of the variability in measured δ 11 B between replicate bands of fibrous arago-nite from a D. dianthus specimen can be explained by small incorporation of non-fibrous aragonite and surface impurities during microsampling and growth rate effects. This study confirms the utility of D. dianthus as an archive of precise palaeo-pH (±0.07 pH units), provided that suitable sampling strategies are applied. Published by Elsevier B.V.
Rapid, high-precision measurements of boron isotopic compositions in marine carbonates
Rapid Communications in Mass Spectrometry, 2014
The isotopic composition and elemental abundance of boron (B) in marine carbonates provides a powerful tool for tracking changes in seawater pH and carbonate chemistry. Progress in this field has however been hampered by the volatile nature of B, its persistent memory, and other uncertainties associated with conventional chemical extraction and mass spectrometric measurements. Here we show that for marine carbonates, these limitations can be overcome by using a simplified, low-blank, chemical extraction technique combined with robust MC-ICPMS methods. METHODS: Samples are dissolved in dilute HNO 3 and loaded firstly onto on a cation exchange column with the major cations (Ca, Mg, Sr, Na) being quantitatively retained while the B fraction is carried in the eluent. The eluent is then passed through an anion column ensuring that any residual anions, such as SO 4 2-, are removed. Isotopic measurements of 11 B/ 10 B ratios are undertaken by matching both the B concentration and isotopic compositions of the samples with the bracketing standard, thereby minimising corrections for cross-contamination. RESULTS: The veracity of the MC-ICPMS procedure is demonstrated using a gravimetrically prepared laboratory standard, UWA24.7, relative to the international reference standard NIST SRM 951 (δ 11 B = 0 ‰). This gives values consistent with gravimetry (δ 11 B = 24.7±0.3‰ 2sd) for solutions ranging in concentration from 50-500 ppb, equivalent to ~2-10 mg size coral samples. The overall integrity of the method for carbonate analysis is demonstrated by measurements of the international carbonate standard JCp-1 (δ 11 B = 24.3 ±0.34‰ 2sd). CONCLUSIONS: A streamlined, integrated approach is described here that enables rapid accurate, high precision measurements of boron isotopic compositions and elemental abundances in commonly analysed samples, such as corals, bivalves, and large benthic forams. The overall simplicity of this robust approach should greatly facilitate the wider application of boron isotope geochemistry, especially to marine carbonates.
Boron isotopes and B/Ca in benthic foraminifera: Proxies for the deep ocean carbonate system
Earth and Planetary Science Letters, 2011
Accurate records of the state of the ocean carbonate system are critical for understanding past changes in pCO2, ocean acidification and climate. The chemical principles underlying the proxy of oceanic pH provided by the boron isotope ratio of foraminiferal carbonate are relatively well understood, but the proxy's reliability has been questioned. We present 76 new Multi-Collector Inductively-Coupled Plasma Mass Spectrometry (MC-ICPMS) δ11B measurements on a range of benthic foraminifera from 23 late-Holocene samples from the Atlantic that reaffirm the utility of the δ11B-pH proxy. Our boron isotope measurements on ~ 10 benthic foraminifera tests typically yield a precision of ~ ± 0.25‰ at 2 s.d. (equivalent to ~ ± 0.03 pH units). δ11B values of epifaunal species are within analytical uncertainty of those predicted from a simple model assuming sole incorporation of B(OH)4− from seawater and no vital effects, using the independently determined fractionation factor of 1.0272 between 11B/10B of aqueous boron species. Infaunal foraminifera are consistent with this model, but record the combined effects of lower pore-water δ11B and pH. No influence of partial dissolution or shell size on δ11B is observed. We have also measured the B/Ca ratios of the same samples. For individual Cibicidoides species, B/Ca shows a good correlation with Δ[CO32−], but the B/Ca of different co-occurring species morphotypes varies considerably. These effects are not seen in δ11B, which may therefore provide a more robust proxy of the ocean carbonate system. Whilst in theory δ11B and B/Ca can be combined to provide a quantitative reconstruction of alkalinity and dissolved inorganic carbonate (DIC), in practice this is precluded by propagated uncertainties. δ11B data give significant constraints on foraminifera calcification mechanisms, and seem most simply explained by incorporation of B(OH)4− into a HCO3− pool, which is then completely incorporated in foraminiferal CaCO3. Our demonstration of the predictable variation of δ11B with pH, across a wide range of species and locations, provides confidence in the application of MC-ICPMS measurements of foraminiferal δ11B to reconstruct past changes in the ocean carbonate system.► Extensive core-top study of the δ11B of benthic foraminifera using MC-ICPMS. ► 11B of core-top epifaunal foraminifera matches calculated δ11B of seawater B(OH)4−. ► δ11B of infaunal foraminifera matches calculated δ11B of porewater B(OH)4−. ► Utility of δ11B-pH proxy reaffirmed.
Chemical Geology
High-latitude cold-water coral reefs are particularly vulnerable to climate change due to enhanced CO 2 uptake in these regions. To evaluate their physiological functioning and potential application as pH archives, we retrieved both recent and fossil samples of Lophelia pertusa along the Norwegian margin from Oslofjord (59°N), over to Trondheimsfjord, Sula and Lopphavet (70.6°N). Boron isotope analyses (δ 11 B) were undertaken using solutionbased and laser ablation multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS; LA-ICP-MS), and secondary ion mass spectrometry (SIMS). Epi-fluorescence microscopy was employed to provide a rapid pre-screening routine for structure-specific subsampling in the coral skeleton. This integrated approach enabled us to assess heterogeneities within single specimens, as well as to investigate the role of local environmental influences including recent and past variations. All three mass spectrometry methods show substantial differences in the δ 11 B of the theca wall (TW) and the centres of calcification (COC's). Micro-bulk subsamples milled from the theca wall of modern specimens originating from different habitats but with comparable seawater pH (8-8.16) gave consistent δ 11 B values averaging 26.7 (± 0.2‰, 2σ, n = 4), while COC subsamples systematically deviated towards lower B/Ca (by~40%) and depleted δ 11 B values (minimum 22.7 ± 0.3‰, 2σ), implying a difference of at least 4‰ between TW and COC. SIMS and LA-ICP-MS measurements identified much larger internal heterogeneities with maximum variation of~10‰ between the distinct skeletal structures; minimal SIMS δ 11 B values of~17.3 ± 1.2‰ (2σ) were associated with the pure COC material. Our findings may be interpreted in terms of the occurrence of two main, but likely different, biomineralisation mechanisms in L. pertusa, with the COC's generally exhibiting minimal pH up-regulation, potentially supporting the use of bicarbonate in the early stages of biomineralisation. Furthermore, we highlight the potential utility of L. pertusa for palaeo-proxy studies if targeting the compositionally homogenous TW zones devoid of COC admixtures, which appear to provide highly reproducible measurements.
Assessing scleractinian corals as recorders for paleo-pH: Empirical calibration and vital effects
Geochimica et Cosmochimica Acta, 2004
Laboratory experiments on the branching, symbiont-bearing coral genus Porites and Acropora have been carried out to determine the dependence of the skeletal boron isotopic composition (␦ 11 B) on the pH of seawater. The results show a clear relationship similar to previously established empirical calibrations for planktonic foraminifera and inorganic calcite. A Ϫ0.6‰ offset exists between P. cylindrica and A. nobilis which is systematic over the pH range of 7.7-8.2. To test whether the ␦ 11 B of coral skeletons changes with physiological processes such as photosynthesis and respiration, corals were grown along a depth transect in their natural environment and under controlled conditions in the laboratory at varying light intensities and food supply. Although we also observe an isotopic offset between P. compressa and Montipora verrucosa, neither experimental treatment systematically changed the ␦ 11 B of the two species. These findings are encouraging for using the boron isotope paleo-pH proxy in corals, because it appears that seawater pH is the dominant control on the boron isotopic composition in corals.
Earth and Planetary Science Letters, 2010
Reliable reconstructions of deep ocean carbonate ion concentration, [CO 3 2− ], and pH are crucial to understand mechanisms responsible for the past atmospheric CO 2 variations observed in ice cores. However, it is challenging to reconstruct past deep water [CO 3 2− ] and pH and literature results from different proxies conflict, warranting careful investigations on possible reasons for the existing inconsistencies. Here, we present the first down core B/Ca and δ 11 B records measured in an epifaunal benthic foraminifer Cibicidoides wuellerstorfi from the Caribbean Sea during the last 160 kyr. The two proxies yield quantitatively comparable deep water [CO 3 2− ] and pH results, showing high values during glacials relative to inter-glacials (differences in [CO 3 2− ] and pH are ∼ 35 μmol/kg and ∼ 0.15, respectively), consistent with past ocean circulation changes in the Caribbean Sea. Our data provide convincing evidence that both proxies serve as faithful proxies to estimate deep ocean [CO 3 2− ] and pH, despite our incomplete understanding of boron incorporation into foraminiferal carbonates.
2007
Stable isotopes of carbon (δ 13 C) and oxygen (δ 18 O) were analyzed in surface and subsurface sediments of modern carbonate platform and barrier reef (Belize), atoll (Maldives) and ramp (Kuwait) settings. The δ 13 C values ranged from -1.6 to +5.3‰ and δ 18 O values from -3.2 to +2.3‰. Among individual particle types, non-skeletal grains such as peloids and ooids exhibit highest values whereas coral fragments display relatively low δ 13 C and δ 18 O values. The highest statistically significant correlations between abundance of carbonate grains, mineralogy and geochemistry occur in the ramp setting, where facies types may be defined using carbon and oxygen isotopic composition. In the platform, barrier and atoll examples, correlations are poor and there are no clear spatial trends in the carbon and oxygen isotopic values of sediments or facies. In locations with comparably high amounts of non-skeletal grains, δ 13 C values correlate with the aragonite content of the samples. The difference between the ramp and other examples is probably a consequence of the continuous depositional energy gradient, which appears to be the major controlling factor of facies distribution in the ramp setting. In the atoll, barrier reef and platform examples, depositional energy gradients are more variable due to higher morphological and environmental variability. The δ 13 C and δ 18 O values of samples from Holocene cores also exhibit high total variability ranging from -1.9 to -0.5‰ in δ 13 C and from -0.2 to +5.2‰ in δ 18 O. Strong excursions in δ 13 C and δ 18 O in individual cores are seen near the base where values became more negative as a consequence of diagenesis, i.e., the influence of a subaerial exposure