Equilibria, kinetics, and boron isotope partitioning in the aqueous boric acid–hydrofluoric acid system

REZ is grateful to Lance Agavulin and Glen Morangie for their spiritual support. JWBR was supported by the European Research Council (ERC Grant 805246) and the Natural Environment Research Council (NERC grant NE/N011716/1).The aqueous boric, hydrofluoric, and fluoroboric acid systems are key to a variety of applications, including boron measurements in marine carbonates for CO2 system reconstructions, chemical analysis and synthesis, polymer science, sandstone acidizing, fluoroborate salt manufacturing, and more. Here we present a comprehensive study of chemical equilibria and boron isotope partitioning in the aqueous boric acid–hydrofluoric acid system. We work out the chemical speciation of the various dissolved compounds over a wide range of pH, total fluorine (FT), and total boron (BT) concentrations. We show that at low pH (0 ≤ pH ≤ 4) and FT ≫ BT, the dominant aqueous species is BF4−, a result relevant to recent advances in high precision measurements of boron concentration and isotopic composition. Using experimental data on kinetic rate constants, we provide estimates for the equilibration time of the slowest reaction in the system as a function of pH and [HF], assuming FT ≫ BT. Furthermore, we present the first quantum-chemical (QC) computations to determine boron isotope fractionation in the fluoroboric acid system. Our calculations suggest that the equilibrium boron isotope fractionation between BF3 and BF4− is slightly smaller than that calculated between B(OH)3 and B(OH)4−. Based on the QC methods X3LYP/6-311+G(d,p) (X3LYP+) and MP2/aug-cc-pVTZ (MP2TZ),  α(BF3−BF4−) ≃ 1.030 and 1.025, respectively. However, BF4− is enriched in 11B relative to B(OH)4−, i.e., α(BF4−−B(OH)4−) ≃ 1.010 (X3LYP+) and 1.020 (MP2TZ), respectively. Selection of the QC method (level of theory and basis set) represents the largest uncertainty in the calculations. The effect of hydration on the calculated boron isotope fractionation turned out to be minor in most cases, except for BF4− and B(OH)3. Finally, we provide suggestions on best practice for boric acid–hydrofluoric acid applications in geochemical boron analyses.PostprintPeer reviewe

What fraction of the Pacific and Indian oceans' deep water is formed in the Southern Ocean?

Wally Broecker acknowledges funding from the Comer Science and Education Foundation. James W. B. Rae acknowledges funding from NERC standard grants NE/N003861/1 and NE/N011716/1, and support from the School of Earth and Environmental Sciences at the University of St Andrews during Wally Broecker’s visit, which sparked the discussions that led to this paper.In this contribution we explore constraints on the fractions of deep water present in the Indian and Pacific oceans which originated in the northern Atlantic and in the Southern Ocean. Based on PO4* we show that if ventilated Antarctic shelf waters characterize the Southern contribution, then the proportions could be close to 50–50. If instead a Southern Ocean bottom water value is used, the Southern contribution is increased to 75 %. While this larger estimate may best characterize the volume of water entering the Indo-Pacific from the Southern Ocean, it contains a significant portion of entrained northern water. We also note that ventilation may be highly tracer dependent: for instance Southern Ocean waters may contribute only 35 % of the deep radiocarbon budget, even if their volumetric contribution is 75 %. In our estimation, the most promising approaches involve using CFC-11 to constrain the amount of deep water formed in the Southern Ocean. Finally, we highlight the broad utility of PO4* as a tracer of deep water masses, including descending plumes of Antarctic Bottom Water and large-scale patterns of deep ocean mixing, and as a tracer of the efficiency of the biological pump.Publisher PDFPeer reviewe

Calibration and application of B/Ca, Cd/Ca, and δ^(11)B in Neogloboquadrina pachyderma (sinistral) to constrain CO_2 uptake in the subpolar North Atlantic during the last deglaciation

The North Atlantic and Norwegian Sea are prominent sinks of atmospheric CO_2 today, but their roles in the past remain poorly constrained. In this study, we attempt to use B/Ca and δ^(11)B ratios in the planktonic foraminifera Neogloboquadrina pachyderma (sinistral variety) to reconstruct subsurface water pH and pCO_2 changes in the polar North Atlantic during the last deglaciation. Comparison of core-top results with nearby hydrographic data shows that B/Ca in N. pachyderma (s) is mainly controlled by seawater B(OH)_4−/HCO_3− with a roughly constant partition coefficient (K_D = [B/Ca]_(CaCO_3) / [B(OH)_4−/HCO_3− (seawater)) of 1.48 ± 0.15 × 10^(−3) (2σ), and δ^(11)B in this species is offset below δ^(11)B of the borate in seawater by 3.38 ± 0.71‰ (2σ). These values represent our best estimates with the sparse available hydrographic data close to our core-tops. More culturing and sediment trap work is needed to improve our understanding of boron incorporation into N. pachyderma (s). Application of a constant K_D of 1.48 × 10^(−3) to high resolution N. pachyderma (s) B/Ca records from two adjacent cores off Iceland shows that subsurface pCO_2 at the habitat depth of N. pachyderma (s) (~50 m) generally followed the atmospheric CO_2 trend but with negative offsets of ~10–50 ppmv during 19–10 ka. These B/Ca-based reconstructions are supported by independent estimates from low-resolution δ^(11)B measurements in the same cores. We also calibrate and apply Cd/Ca in N. pachyderma (s) to reconstruct nutrient levels for the same down cores. Like today's North Atlantic, past subsurface pCO_2 variability off Iceland was significantly correlated with nutrient changes that might be linked to surface nutrient utilization and mixing within the upper water column. Because surface pCO_2 (at 0 m water depth) is always lower than at deeper depths and if the application of a constant KD is valid, our results suggest that the polar North Atlantic has remained a CO_2 sink during the calcification seasons of N. pachyderma (s) over the last deglaciation

Calibration and application of B/Ca, Cd/Ca, and δ11B in Neogloboquadrina pachyderma (sinistral) to constrain CO2 uptake in the subpolar North Atlantic during the last deglaciation

[1] The North Atlantic and Norwegian Sea are prominent sinks of atmospheric CO2 today, but their roles in the past remain poorly constrained. In this study, we attempt to use B/Ca and δ11B ratios in the planktonic foraminifera Neogloboquadrina pachyderma (sinistral variety) to reconstruct subsurface water pH and pCO2 changes in the polar North Atlantic during the last deglaciation. Comparison of core-top results with nearby hydrographic data shows that B/Ca in N. pachyderma (s) is mainly controlled by seawater B(OH)4−/HCO3− with a roughly constant partition coefficient inline image of 1.48 ± 0.15 × 10−3 (2σ), and δ11B in this species is offset below δ11B of the borate in seawater by 3.38 ± 0.71‰ (2σ). These values represent our best estimates with the sparse available hydrographic data close to our core-tops. More culturing and sediment trap work is needed to improve our understanding of boron incorporation into N. pachyderma (s). Application of a constant KD of 1.48 × 10−3 to high resolution N. pachyderma (s) B/Ca records from two adjacent cores off Iceland shows that subsurface pCO2 at the habitat depth of N. pachyderma (s) (~50 m) generally followed the atmospheric CO2 trend but with negative offsets of ~10–50 ppmv during 19–10 ka. These B/Ca-based reconstructions are supported by independent estimates from low-resolution δ11B measurements in the same cores. We also calibrate and apply Cd/Ca in N. pachyderma (s) to reconstruct nutrient levels for the same down cores. Like today's North Atlantic, past subsurface pCO2 variability off Iceland was significantly correlated with nutrient changes that might be linked to surface nutrient utilization and mixing within the upper water column. Because surface pCO2 (at 0 m water depth) is always lower than at deeper depths and if the application of a constant KD is valid, our results suggest that the polar North Atlantic has remained a CO2 sink during the calcification seasons of N. pachyderma (s) over the last deglaciation

Calibration and application of B/Ca, Cd/Ca, and δ11B in Neogloboquadrina pachyderma (sinistral) to constrain CO2 uptake in the subpolar North Atlantic during the last deglaciation

Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 28 (2013): 237–252, doi:10.1002/palo.20024.The North Atlantic and Norwegian Sea are prominent sinks of atmospheric CO2 today, but their roles in the past remain poorly constrained. In this study, we attempt to use B/Ca and δ11B ratios in the planktonic foraminifera Neogloboquadrina pachyderma (sinistral variety) to reconstruct subsurface water pH and pCO2 changes in the polar North Atlantic during the last deglaciation. Comparison of core-top results with nearby hydrographic data shows that B/Ca in N. pachyderma (s) is mainly controlled by seawater B(OH)4−/HCO3− with a roughly constant partition coefficient of 1.48 ± 0.15 × 10−3 (2σ), and δ11B in this species is offset below δ11B of the borate in seawater by 3.38 ± 0.71‰ (2σ). These values represent our best estimates with the sparse available hydrographic data close to our core-tops. More culturing and sediment trap work is needed to improve our understanding of boron incorporation into N. pachyderma (s). Application of a constant KD of 1.48 × 10−3 to high resolution N. pachyderma (s) B/Ca records from two adjacent cores off Iceland shows that subsurface pCO2 at the habitat depth of N. pachyderma (s) (~50 m) generally followed the atmospheric CO2 trend but with negative offsets of ~10–50 ppmv during 19–10 ka. These B/Ca-based reconstructions are supported by independent estimates from low-resolution δ11B measurements in the same cores. We also calibrate and apply Cd/Ca in N. pachyderma (s) to reconstruct nutrient levels for the same down cores. Like today's North Atlantic, past subsurface pCO2 variability off Iceland was significantly correlated with nutrient changes that might be linked to surface nutrient utilization and mixing within the upper water column. Because surface pCO2 (at 0 m water depth) is always lower than at deeper depths and if the application of a constant KD is valid, our results suggest that the polar North Atlantic has remained a CO2 sink during the calcification seasons of N. pachyderma (s) over the last deglaciation.This research is funded by Lamont-Doherty Postdoctoral Fellowship, Lawrence Livermore Fellowship and the Australian National University (J.Y.), by NERC RAPID grant NER/T/S/2002/00436 (N. M. and D. T.), and by a NERC PhD studentship (J.R.).2013-11-3

Biogeochemical significance of pelagic ecosystem function:An end-cretaceous case study

This work was aided by a Nuffield Summer Studentship granted to MJH, a U.S. Science Support Program (USSSP) Post-Expedition Activity award for IODP Exp. 342 to PMH, a Flint Postdoctoral Fellowship to DEP, a NERC PhD Studentship granted to JWBR, and a URF and Wolfson merit award to DNS.Pelagic ecosystem function is integral to global biogeochemical cycling, and plays a major role in modulating atmospheric CO2 concentrations (pCO2). Uncertainty as to the effects of human activities on marine ecosystem function hinders projection of future atmospheric pCO2. To this end, events in the geological past can provide informative case studies in the response of ecosystem function to environmental and ecological changes. Around the Cretaceous–Palaeogene (K–Pg) boundary, two such events occurred: Deccan large igneous province (LIP) eruptions and massive bolide impact at the Yucatan Peninsula. Both perturbed the environment, but only the impact coincided with marine mass extinction. As such, we use these events to directly contrast the response of marine biogeochemical cycling to environmental perturbation with and without changes in global species richness. We measure this biogeochemical response using records of deep-sea carbonate preservation. We find that Late Cretaceous Deccan volcanism prompted transient deep-sea carbonate dissolution of a larger magnitude and timescale than predicted by geochemical models. Even so, the effect of volcanism on carbonate preservation was slight compared with bolide impact. Empirical records and geochemical models support a pronounced increase in carbonate saturation state for more than 500 000 years following the mass extinction of pelagic carbonate producers at the K–Pg boundary. These examples highlight the importance of pelagic ecosystems in moderating climate and ocean chemistry.PostprintPeer reviewe

Anthropogenic acidification of surface waters drives decreased biogenic calcification in the Mediterranean Sea

This work contributes to the ICTA-UAB “Unit of Excellence” (FPI/MDM-2015-0552- 16-2; CEX2019-000940-M) and was funded by the Spanish Ministry of Science and Innovation, BIOCAL Project (PID2020-113526RB-I00), the EU-FP7 “Mediterranean Sea Acidification in a Changing Climate” project (MedSeA; grant agreement 265103), and the Generalitat de Catalunya (MERS, 2021 SGR 00640). J.W.B.R. acknowledges the European Research Council under the European Union’s Horizon 2020 research and innovation program (grant agreement 805246) and B.M the Severo Ochoa grant CEX2018-000794-S and CSIC LINKA20102. G.L. acknowledges funding from the Spanish Ministry of Universities through a Maria Zambrano grant.Anthropogenic carbon dioxide emissions directly or indirectly drive ocean acidification, warming and enhanced stratification. The combined effects of these processes on marine planktic calcifiers at decadal to centennial timescales are poorly understood. Here, we analyze size normalized planktic foraminiferal shell weight, shell geochemistry, and supporting proxies from 3 sediment cores in the Mediterranean Sea spanning several centuries. Our results allow us to investigate the response of surface-dwelling planktic foraminifera to increases in atmospheric carbon dioxide. We find that increased anthropogenic carbon dioxide levels led to basin wide reductions in size normalized weights by modulating foraminiferal calcification. Carbon (δ13C) and boron (δ11B) isotopic compositions also indicate the increasing influence of fossil fuel derived carbon dioxide and decreasing pH, respectively. Alkenone concentrations and test accumulation rates indicate that warming and changes in biological productivity are insufficient to offset acidification effects. We suggest that further increases in atmospheric carbon dioxide will drive ongoing reductions in marine biogenic calcification in the Mediterranean Sea.Publisher PDFPeer reviewe

Arctic and Antarctic forcing of ocean interior warming during the last deglaciation

Funding was provided by an Antarctic Bursary awarded to J.A.S., ERC and NERC grants awarded to L.F.R. (278705, NE/S001743/1, NE/R005117/1) and L.F.R. and J.W.B.R. (NE/N003861/1).Subsurface water masses formed at high latitudes impact the latitudinal distribution of heat in the ocean. Yet uncertainty surrounding the timing of low-latitude warming during the last deglaciation (18–10 ka) means that controls on sub-surface temperature rise remain unclear. Here we present seawater temperature records on a precise common age-scale from East Equatorial Pacific (EEP), Equatorial Atlantic, and Southern Ocean intermediate waters using new Li/Mg records from cold water corals. We find coeval warming in the tropical EEP and Atlantic during Heinrich Stadial 1 (+ 6 °C) that closely resemble warming recorded in Antarctic ice cores, with more modest warming of the Southern Ocean (+ 3 °C). The magnitude and depth of low-latitude ocean warming implies that downward accumulation of heat following Atlantic Meridional Overturning Circulation (AMOC) slowdown played a key role in heating the ocean interior, with heat advection from southern-sourced intermediate waters playing an additional role.Publisher PDFPeer reviewe

A rapid, simple, and low-blank pumped ion-exchange column chromatography technique for boron purification from carbonate and seawater matrices

Funding: This work is supported by the European Research Council under the European Union's Horizon 2020 research and innovation program (Grant 805246) to J.W.B.R., H.J., a Natural Environmental Research Council (NERC)-IAPETUS2 Doctoral Training Programme (DTP) Studentship to NE/S007431/1 C.X., a NERC-IAPETUS DTP Studentship NE/RO12253/1 to M.T., a Leverhulme Trust Early Career Fellowship ECF-2023-199 to H.J., a NERC UK IODP grant NE/P000878/1 to S.B. and S.N., and a Taiwanese MOST Grant 111-2116M-002-032-MY3 to S.N.Boron isotope ratios (δ11B) are used across the Earth Sciences and are increasing analyzed by Multi-Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICPMS). Accurate δ11B MC-ICPMS analysis requires boron purification from the sample matrix using ion-exchange column chromatography. However, the traditional gravity-drip column method is time-consuming and prone to airborne contamination due to its long duration and open resin surface. To address these issues, we designed a novel, simple, and reliable column chromatography technique called “peri-columns.” This method uses a peristaltic pump to generate vacuum on a commonly used column set up. This method uses sealed collection beakers and does not require solutions to pass through pump tubing, minimizing contamination. The duration is reduced by eight-fold, processing 12 samples in just 1.5 hr. It also yields low and consistent total procedural blanks, averaging 11 pg. The efficiency and efficacy of this method were tested by repeated boron purification from calcium carbonate and high-sodium matrices with international and in-house reference materials. The results matched those obtained using the gravity column method and fell within our laboratory long-term and international certified values. The mean δ11B and 2SD (standard deviation) of repeatedly processed NIST 8301f were 14.57 ± 0.26‰ (n = 31), NIST 8301c was 24.19 ± 0.33‰ (n = 10), STAiG-F1 was 16.20 ± 0.26‰ (n = 13), and seawater was 39.52 ± 0.32‰ (n = 10). All the components of our techniques are commercially available, and it is easily adaptable to other laboratories and isotope systems.Publisher PDFPeer reviewe