A Record of Deglacial Ventilation from Foraminiferal Radiocarbon at Intermediate Depths in the Eastern Equatorial Pacific

Abstract:

Ice core records reveal episodes of rapid atmospheric CO₂ rise and Δ¹⁴C excursions during deglaciation. Recent evidence suggests that this CO₂ was sequestered in deep and intermediate waters during glacial periods and then released to the atmosphere due to changes in ocean circulation. Scenarios involving a more efficient biological pump and reduced ventilation of Southern Ocean deep waters have been cited as likely methods for glacial carbon storage (Sigman and Boyle, 2000). A more efficient biological pump calls on increased CaCO₃ compensation as a buffer for reduced deep ocean alkalinity along with increased nutrient supply and primary production as a method of sequestering carbon from the surface ocean to the deep ocean (Marchitto et al., 2005). Modeling studies suggest that reduced ventilation of Southern Ocean waters due to increased sea ice cover and reduced upwelling is the dominant mechanism for carbon storage with a smaller contribution from the biological pump (Joos et al., 2011; Toggweiler., 2006). This study further examines the issue of changes in ocean ventilation by providing records of paired benthic and planktonic foraminiferal ¹⁴C ages from the deglacial sections of Eastern Equatorial Pacific marine sediment cores TR163-23 and TR163-18 at 2730 and 2030 meters depth, respectively. An Antarctic Intermediate Water (AAIW) sourced record of ventilation aids in the constraint of carbon previously sequestered through the Southern Ocean during periods of enhanced brine rejection and increased sea-ice extent (Marchitto et al., 2007; Pahnke et al., 2008; Keeling and Stephens, 2001). North Pacific Intermediate Water (NPIW) production has also been found to vary on millennial time scales reaching as far south as 8°N during glacial periods (Leduc et al., 2010). However, both cores used in this study are sufficiently deep and far enough south (0.41°N, 92.16°W and 2.81°N, 89.85°W) to avoid intrusion of NPIW that might obscure the AAIW signal.