Calibration and application of B/Ca, Cd/Ca, and δ11B in Neogloboquadrina pachyderma (sinistral) to constrain CO2 uptake in the subpolar North Atlantic during the last deglaciation. (30th May 2013)

• Record Type: Journal Article
• Authors: Yu, Jimin; Thornalley, David J. R.; Rae, James W. B.; McCave, Nick I.
• Is Part Of: Paleoceanography. Volume 28:Number 2(2013:Jun.)
• Page Start: 237
• Page End: 252
• Publication Date: 2013-05-30
• Subjects: Neogloboquadrina pachyderma (s) -- B/Ca, Cd/Ca, d11B -- subsurface pH and pCO2 and nutrients; Paleoceanography -- Periodicals; 551.46
• DOI: 10.1002/palo.20024
• Languages: English
• ISSNs: 0883-8305

Abstract

Abstract : [1] The North Atlantic and Norwegian Sea are prominent sinks of atmospheric CO2 today, but their roles in the past remain poorly constrained. In this study, we attempt to use B/Ca and δ 11 B ratios in the planktonic foraminifera Neogloboquadrina pachyderma (sinistral variety) to reconstruct subsurface water pH and p CO2 changes in the polar North Atlantic during the last deglaciation. Comparison of core‐top results with nearby hydrographic data shows that B/Ca in N. pachyderma (s) is mainly controlled by seawater B(OH)4 − /HCO3 − with a roughly constant partition coefficient K D = B / Ca CaC O 3 B OH 4 − / HCO 3 ¯ seawater of 1.48 ± 0.15 × 10 −3 (2σ), and δ 11 B in this species is offset below δ 11 B of the borate in seawater by 3.38 ± 0.71‰ (2σ). These values represent our best estimates with the sparse available hydrographic data close to our core‐tops. More culturing and sediment trap work is needed to improve our understanding of boron incorporation into N. pachyderma (s). Application of a constant K D of 1.48 × 10 −3 to high resolution N. pachyderma (s) B/Ca records from two adjacent cores off Iceland shows that subsurface p CO2 at the habitat depth of N. pachyderma (s) (~50 m) generally followed the atmospheric CO2 trend but with negative offsets of ~10–50 ppmv during 19–10 ka. These B/Ca‐based reconstructions are supported by independent estimates from low‐resolution δ 11 B measurements in the same cores. We also calibrate and apply Cd/Ca in N. pachyderma (s) to reconstruct nutrient levels for the same down cores. Like today's North Atlantic, past subsurface p CO2 variability off Iceland was significantly correlated with nutrient changes that might be linked to surface nutrient utilization and mixing within the upper water column. Because surface p CO2 (at 0 m water depth) is always lower than at deeper depths and if the application of a constant K D is valid, our results suggest that the polar North Atlantic has remained a CO2 sink during the calcification seasons of N. pachyderma (s) over the last deglaciation. Key Points: Subsurface pCO2 and nutrient from B/Ca, Cd/Ca and d11B in N. pachyderma (s) B/Ca and d11B suggest a CO2 sink off Iceland at 19‐10 ka Nutrient utilization correlates with millennial‐scale pCO2 variations