Seawater pH reconstruction using boron isotopes in multiple planktonic foraminifera species with different depth habitats and their potential to constrain pH and pCO2 gradients

• Published in: Biogeosciences
• Main Authors: Guillermic, Maxence, Misra, Sambuddha, Eagle, Robert, Villa, Alexandra, Chang, Fengming, Tripati, Aradhna
• Format: Text
• Language: English
• Published: 2020
• Subjects: Planktonic foraminifera
• Online Access: https://doi.org/10.5194/bg-17-3487-2020; https://www.biogeosciences.net/17/3487/2020/

Boron isotope systematics of planktonic foraminifera from core-top sediments and culture experiments have been studied to investigate the sensitivity of δ 11 B of calcite tests to seawater pH. However, our knowledge of the relationship between δ 11 B and pH remains incomplete for many taxa. Thus, to expand the potential scope of application of this proxy, we report δ 11 B data for seven different species of planktonic foraminifera from sediment core tops. We utilize a method for the measurement of small samples of foraminifera and calculate the δ 11 B -calcite sensitivity to pH for Globigerinoides ruber , Trilobus sacculifer (sacc or without sacc), Orbulina universa , Pulleniatina obliquiloculata , Neogloboquadrina dutertrei , Globorotalia menardii , and Globorotalia tumida, including for unstudied core tops and species. 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. The sensitivity of δ 11 B carbonate to δ 11 B borate (e.g., Δ δ 11 B carbonate ∕Δ δ 11 B borate ) in core tops is consistent with previous studies for T. sacculifer and G. ruber and close to unity for N. dutertrei , O. universa , and combined deep-dwelling species. Deep-dwelling species closely follow the core-top calibration for O. universa , which is attributed to respiration-driven microenvironments likely caused by light limitation and/or symbiont–host interactions. 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 p CO 2 at sites spanning different oceanic regimes, thereby constraining changes in vertical pH gradients and yielding insights into the past behavior of the oceanic carbon pumps.