Cenozoic boron isotope variations in benthic foraminifers

摘要

The boron isotopic composition of seawater (δ~(11)B_(sw)) is a prerequisite for reliably estimating past variation of seawater pH from boron isotopes in marine carbonates (δ~(11)Bc). Here we compose a 50 m.y. stack of δ~(11)B_c from Atlantic and Pacific Ocean deep-sea sediments, and discuss the potential effects of deep-sea pH and δ~(11)B_(sw) on our record. Using model-based Cenozoic pH values, the inferred δ~(11)B_(sw) values suggest an ~3‰ increase since the Late Eocene, superimposed on oscillating variations with amplitudes of up to 2‰. Our estimates match existing reconstructions of δ~(11)B_(sw), but call into question published fluid δ~(11)B in halite as a recorder of δ~(11)B_(sw).