NOAA/WDS Paleoclimatology - Global Ocean Planktonic Foraminifera Boron Isotope Seawater pH Reconstruction

Boron isotope systematics of planktonic foraminifera from core-top sediments and culture experiments have been studied to investigate the sensitivity of d11B of their calcite tests to seawater pH. However, our knowledge of the relationship between d11B and pH remains incomplete for several taxa. Thus, to expand the potential scope of application of this proxy, we report data for 7 different species of planktonic foraminifera from sediment core-tops. We utilize a method for the measurement of small samples of foraminifera and calculate the d11B-calcite sensitivity to pH for Globigerinoides ruber, Trilobus sacculifer (sacc or w/o sacc), Orbulina universa, Pulleniatina obliquiloculata, Neogloboquadrina dutertrei, Globorotalia menardii and Globorotalia tumida, including for unstudied coretops and species. The sensitivity of d11Bcarbonate to d11Bborate (eg. Dd11Bcarbonate/Dd11Bborate) in core-tops is close to unity. Deep-dwelling species closely follow the core-top calibration for O. universa, which is attributed to respiration-driven microenvironments, likely caused by light limitation for symbiont-bearing foraminifera. These taxa have diverse ecological preferences and are from sites that span a range of oceanographic regimes, including some that are in regions of air-sea equilibrium and others that are out of equilibrium with the atmosphere. Our data support the premise that utilizing boron isotope measurements of multiple species within a sediment core can be utilized to constrain vertical profiles of pH and pCO2 at sites spanning different oceanic regimes, thereby constraining changes in vertical pH gradients and yielding insights into the past behavior of the oceanic carbon pump.