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

• Main Authors: Guillermic, Maxence, Misra, Sambuddha, Eagle, Robert, Villa, Alexandra, Chang, Fengming, Tripati, Aradhna
• Format: Text
• Language: English
• Published: 2019
• Subjects: Planktonic foraminifera
• Online Access: https://doi.org/10.5194/bg-2019-266; https://www.biogeosciences-discuss.net/bg-2019-266/

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 their calcite tests to seawater pH. However, our knowledge of the relationship between δ 11 B 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 δ 11 B-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 δ 11 B carbonate to δ 11 B borate (eg. Δδ 11 B carbonate /Δδ 11 B borate ) 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 pCO 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 pump.