We present the first continuous records from 0 to 5 Ma (in 0.333 m.y. integrated time steps) of paired boron/calcium (B/Ca) ratios and boron isotopes (d11B) in the planktonic foraminifera Globogerinoides sacculifer (without sacc) from a site in the western equatorial Pacific Ocean (Ocean Drilling Program Site 806). These measurements, the first made in conjunction with calcification temperature (magnesium/calcium ratios) and average shell mass measurements, indicate that pH is not the sole environmental variable controlling B in planktonic foraminiferal calcite. Our data are consistent with calcification temperature exerting a primary control on B concentration and isotopic composition in planktonic foraminifera. If so, calcification temperature must be taken into account if pH for past oceans and atmospheric pCO2 are to be estimated from B isotope measurements in foraminiferal calcite. Doing so will substantially increase the uncertainty of pH estimates. Although this work was designed as a temporal study, its results define new aspects of calibrating the d11B paleo-pH tracer.

Sediment depth is given in mbsf. Measured on G. sacculifer (w/o sacc) size fraction 355-425 µm. Age assignments were made using the timescales of Berger et al. (1993) and Mayer et al. (1993).

Supplement to: Wara, Michael W; Delaney, Margaret Lois; Bullen, Thomas D; Ravelo, Ana Christina (2003): Possible roles of pH, temperature, and partial dissolution in determining boron concentration and isotopic composition in planktonic foraminifera. Paleoceanography, 18(4), 1100