Stable carbon and oxygen isotope ratios of Cibicidoides wuellerstorfi (Table 1)

Coretop samples from a water depth profile from 1000 to 4500 m on the northern flank of the Walvis Ridge are 4.4 per mil lower than the values expected, based on calculations of the delta 11B(borate) of ambient seawater. Similar values for this foraminifer species are presented from ODP site 668B at the Sierra Leone Rise, in the equatorial Atlantic.

The consistency between data of the same species suggests the offsets are primary, rather than diagenetic. Glacial C. wuellerstorfi from ODP 668B and Walvis Ridge have boron isotope compositions only slightly different to interglacial samples, that is no larger than +0.10 pH units, or +23 µmol/kg in [CO3[2-]] above the reconstructed glacial lysocline, and -0.07 pH units, or -14 µmol/kg in [CO3[2-]] below. We use these results to suggest that glacial deep water pH in the Atlantic was similar to interglacial pH.