Simulated Last Glacial Maximum Δ 14 C atm and the Deep Glacial Ocean Carbon Reservoir

• Published in: Radiocarbon
• Main Authors: Mariotti, V, Paillard, D, Roche, D M, Bouttes, N, Bopp, L
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 2013
• Subjects: General Earth and Planetary Sciences; Archeology; Southern Ocean
• Online Access: http://dx.doi.org/10.1017/s0033822200048517; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0033822200048517

Δ 14 C atm has been estimated as 420 ± 80% (IntCal09) during the Last Glacial Maximum (LGM) compared to preindustrial times (0%), but mechanisms explaining this difference are not yet resolved. Δ 14 C atm is a function of both cosmogenic production in the high atmosphere and of carbon cycling and partitioning in the Earth system. 10 Be-based reconstructions show a contribution of the cosmogenic production term of only 200 ± 200% in the LGM. The remaining 220% have thus to be explained by changes in the carbon cycle. Recently, Bouttes et al. (2010, 2011) proposed to explain most of the difference in pCO 2atm and Δ 13 C between glacial and interglacial times as a result of brine-induced ocean stratification in the Southern Ocean. This mechanism involves the formation of very saline water masses that contribute to high carbon storage in the deep ocean. During glacial times, the sinking of brines is enhanced and more carbon is stored in the deep ocean, lowering pCO 2atm . Moreover, the sinking of brines induces increased stratification in the Southern Ocean, which keeps the deep ocean well isolated from the surface. Such an isolated ocean reservoir would be characterized by a low Δ 14 C signature. Evidence of such 14 C-depleted deep waters during the LGM has recently been found in the Southern Ocean (Skinner et al. 2010). The degassing of this carbon with low Δ 14 C would then reduce Δ 14 C atm throughout the deglaciation. We have further developed the CLIMBER-2 model to include a cosmogenic production of 14 C as well as an interactive atmospheric 14 C reservoir. We investigate the role of both the sinking of brine and cosmogenic production, alongside iron fertilization mechanisms, to explain changes in Δ 14 C atm during the last deglaciation. In our simulations, not only is the sinking of brine mechanism consistent with past Δ 14 C data, but it also explains most of the differences in pCO 2atm and Δ 14 C atm between the LGM and preindustrial times. Finally, this study represents the first time to our knowledge that ...