Methodology:

Whole septa and attached theca were taken from cup corals samples using a rotary cutting tool. This tool was further used to remove surficial oxide coatings and any chalky white altered carbonate. Microstructures within cold-water corals are known to exhibit highly contrasting delta11B, therefore where sufficient sample material allowed, multiple sub-samples (typically duplicates) were measured to assess microstructural bias. Coral fragments were finely crushed using a pestle and mortar before a 2 to 4 mg aliquot of the homogenous powder was taken. A warm 1% H2O2 (buffered in NH4OH) oxidative clean and weak acid polish (0.0005 M HNO3) was performed on powders. Samples were then dissolved in distilled 0.5 M HNO3.

All analyses were carried out at the Univ. of Bristol and Univ. of St Andrews. An aliquot of the dissolved sample was analyzed by ICP-MS using well-characterised, matrix-matched, synthetic standard solutions to yield trace metal ratios to calcium. Repeat analysis of NIST RM 8301c (n=35) yielded analytical precision of <±2% for Li/Ca, B/Ca, Na/Ca, Mg/Ca, Sr/Ca, Cd/Ca, Ba/Ca, and U/Ca ratios; <±5% for Al/Ca, Mn/Ca, Ni/Ca, Nd/Ca, and W/Ca ratios; ±10% for Cu/Ca; ±16% for Fe/Ca and Zn/Ca; and >±25% for Sn/Ca and Pb/Ca.

A further aliquot of the dissolved sample containing ~65 ng B was separated from the carbonate matrix using 20 microliter micro-columns containing Amberlite IRA 743 boron-specific anionic exchange resin. The delta11B of purified boron samples were measured by (MC)-ICPMS against NIST SRM 951 at St Andrews and Bristol following identical protocols (Foster, 2008; Foster et al., 2013; Rae et al., 2011). Published and ongoing interlaboratory comparison studies reveal no systematic analytical offset between these institutions (Foster et al., 2013). Samples, blanks, and standards were introduced to the instrument in a 0.5 M HNO3 and 0.3 M HF acid matrix to aim B wash out (Misra et al., 2014; Rae et al., 2018). Full procedural uncertainty is assessed using repeat measurement of NIST 8301c consistency standard yielding average delta11B values of 24.19 ± 0.22per mille at Bristol (n=14) and 24.12 ± 0.12per mille at St Andrews (n=15). Total procedural blanks (n=21) were on average <0.25% of the sample boron loaded onto columns.

References:

Foster, G. L. (2008). Seawater pH, pCO2 and [CO^2-3] variations in the Caribbean Sea over the last 130 kyr: A boron isotope and B/Ca study of planktic foraminifera. Earth and Planetary Science Letters, 271(1-4), 254-266. DOI: 10.1016/j.epsl.2008.04.015

Foster, G. L., Hönisch, B., Paris, G., Dwyer, G. S., Rae, J. W. B., Elliott, T., ... Vengosh, A. (2013). Interlaboratory comparison of boron isotope analyses of boric acid, seawater and marine CaCO3 by MC-ICPMS and NTIMS. Chemical Geology, 358, 1-14. DOI: 10.1016/j.chemgeo.2013.08.027

Rae, JWB, Foster, GL, Schmidt, DN & Elliott, T 2011, 'Boron isotopes and B/Ca ratios in benthic foraminifera: proxies for the deep ocean carbonate system' Earth and Planetary Science Letters, vol. 302, no. 3-4, pp. 403-413. https://doi.org/10.1016/j.epsl.2010.12.034

Misra, S., Owen, R., Kerr, J. & Greaves, M. Determination of delta11B by HR-ICP-MS from mass limited samples: application to natural carbonates and water samples. Geochim. Cosmochim. Acta 140, 531-552 (2014).

Rae JWB, Burke A, Robinson LF, Adkins AJ, Chen T, Cole C, Greenop R, Li T,E. Littley E, Nita DC (2018) CO2 storage and release in the deep Southern Ocean on millennial to centennial timescales Nature 562 (7728), p.569

Data collection:

Multi-Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICPMS, Thermo Neptune and Neptune Plus)

Single Collector Mass Spectrometer (ICPMS, Thermo Element2; Agilent 7500)

Data quality:

Limits of detection for trace metal analyses by ICP-MS were calculated for each analytical batch using the average blank (in counts per second) plus 5 standard deviation of the blank. Sample results that returned below this threshold within each run are quoted as '<LOD'.