190 / 2024-09-11 09:20:39
The mechanism of boron incorporation into foraminifera: Insights from numerical modeling
seawater and calcifying fluid chemistry, inorganic calcite, benthic foraminifera, vital effect, boron partition coefficient (λB), δ11B
Session 53 - Geological analogues for future warm ocean and climate
Abstract Accepted
Na Qian / China University of Geoscience (Beijing)
Shuo Zhang / Tsinghua University
Paleoceanographers use boron proxies (i.e., δ11B, B/Ca ratio) to reconstruct past seawater carbonate parameters and atmospheric pCO2. However, the mechanism for the boron incorporation into foraminifera is not fully understood. Here, we construct a model of boron isotope composition (δ11B) in calcifying fluid for foraminifera to explore the selective incorporation of boric acid (BOH)3, B3) and borate (B(OH)4-,B4) into foraminiferal calcite. PB3 and PB4 are defined as the membrane permeability coefficients for B3 and B4. The model results indicate that when the PB3/PB4 ratio varies among 0~0.01 and 0.01~+∞, the B(OH)4- δ11B in calcifying fluid is close to the value in seawater. Furthermore, the relationships between boron partitioning coefficient (λB) and carbonate saturation (Ω) in inorganic and foraminiferal calcite show a consistent pattern, i.e., λB increases with Ω, when PB3/PB4 ratio falls within 0 to 0.01. Thus, a PB3/PB4 ratio between 0 and 0.01 can account for both δ11B and λB values measured in the benthic foraminifera from the global ocean. This research firstly reports the modeled δ11B in the calcifying fluid and reveals the proportion of B3, B4 incorporated by foraminifera.