Inferring surface water equilibrium calcite δ¹⁸O during the last deglacial period from benthic foraminiferal records: Implications for ocean circulation

The ocean circulation modifies mixed layer (ML) tracer signals as they are communicated to the deep ocean by advection and mixing. We develop and apply a procedure for using tracer signals observed "upstream" (by planktonic foraminifera) and "downstream" (by benthic foraminifera) to constrain how tracer signals are modified by the intervening circulation and, by extension, to constrain properties of that circulation. A history of ML equilibrium calcite δ¹⁸O (δ¹⁸O_c) spanning the last deglaciation is inferred from a least-squares fit of eight benthic foraminiferal δ¹⁸O_c records to Green's function estimated for the modern ocean circulation. Disagreements between this history and the ML history implied by planktonic records would indicate deviations from the modern circulation. No deviations are diagnosed because the two estimates of ML δ¹⁸O_c agree within their uncertainties, but we suggest data collection and modeling procedures useful for inferring circulation changes in future studies. Uncertainties of benthic-derived ML δ¹⁸O_c are lowest in the high-latitude regions chiefly responsible for ventilating the deep ocean; additional high-resolution planktonic records constraining these regions are of particular utility. Benthic records from the Southern Ocean, where data are sparse, appear to have the most power to reduce uncertainties in benthic-derived ML δ¹⁸O_c. Understanding the spatiotemporal covariance of deglacial ML δ¹⁸O_c will also improve abilities of δ¹⁸O_c records to constrain deglacial circulation.