The boron isotopic ratio of 11B/10B (δ11BSRM951) and trace element composition of marine carbonates are key proxies for understanding carbon cycling (pH) and palaeoceanographic change. However, method validation and comparability of results between laboratories requires carbonate reference materials. Here, we report results of an inter‐laboratory comparison study to both assign δ11BSRM951 and trace element compositions to new synthetic marine carbonate reference materials (RMs), NIST RM 8301 (Coral) and NIST RM 8301 (Foram) and to assess the variance of data among laboratories. Non‐certified reference values and expanded 95% uncertainties for δ11BSRM951 in NIST RM 8301 (Coral) (+24.17‰ ± 0.18‰) and NIST RM 8301 (Foram) (+14.51‰ ± 0.17‰) solutions were assigned by consensus approach using inter‐laboratory data. Differences reported among laboratories were considerably smaller than some previous inter‐laboratory comparisons, yet discrepancies could still lead to large differences in calculated seawater pH. Similarly, variability in reported trace element information among laboratories (e.g., Mg/Ca ± 5% RSD) was often greater than within a single laboratory (e.g., Mg/Ca < 2%). Such differences potentially alter proxy‐reconstructed seawater temperature by more than 2 °C. These now well‐characterised solutions are useful reference materials to help the palaeoceanographic community build a comprehensive view of past ocean changes.

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&lt;p&gt;During the last glacial period atmospheric CO&lt;sub&gt;2&lt;/sub&gt; and temperature in Antarctica varied together on millennial timescales, with CO&lt;sub&gt;2&lt;/sub&gt; abruptly increasing by 10-20 ppm in &lt;1000 years in some cases. The exact causes of these rapid CO&lt;sub&gt;2&lt;/sub&gt; changes during a cold glacial climate remain unclear. Here we examine the role of ocean carbon storage and atmospheric exchange by applying the boron isotope-pH (CO&lt;sub&gt;2&lt;/sub&gt;) proxy to Globigerina bulloides from core site TAN110628 located in the Pacific Sector of the Southern Ocean.&amp;#160; By reconstructing the surface carbonate system at TAN110628 at high temporal resolution (1 sample every 1 kyr) from 30 to 64 kyr we are able to fully constrain the nature of carbon leakage from the Sub Antarctic Zone of the Southern Pacific Ocean associated with these millennial-scale changes in atmospheric CO&lt;sub&gt;2&lt;/sub&gt;.&amp;#160; This provides unique insights into the causes of abrupt changes in atmospheric CO&lt;sub&gt;2&lt;/sub&gt; during Marine Isotope Stage 3 and the last termination.&amp;#160;&lt;/p&gt;