Assessing transient changes in the ocean carbon cycle during the last deglaciation through carbon isotope modeling

• Published in: Climate of the Past
• Main Authors: Kobayashi, Hidetaka, Oka, Akira, Obase, Takashi, Abe-Ouchi, Ayako
• Format: Text
• Language: English
• Published: 2024
• Subjects: ice core
• Online Access: https://doi.org/10.5194/cp-20-769-2024; https://cp.copernicus.org/articles/20/769/2024/

Atmospheric carbon dioxide concentration ( p CO 2 ) has increased by approximately 80 ppm from the Last Glacial Maximum (LGM) to the early Holocene. The change in this atmospheric greenhouse gas is recognized as a climate system response to gradual change in insolation. Previous modeling studies suggested that the deglacial increase in atmospheric p CO 2 is primarily attributed to the release of CO 2 from the ocean. Additionally, it has been suggested that abrupt change in the Atlantic meridional overturning circulation (AMOC) and associated interhemispheric climate changes are involved in the release of CO 2 . However, understanding remains limited regarding oceanic circulation changes and the factors responsible for changes in chemical tracers in the ocean during the last deglaciation and their impact on atmospheric p CO 2 . In this study, we investigate the evolution of the ocean carbon cycle during the last deglaciation (21 to 11 ka BP) using three-dimensional ocean fields from the transient simulation of the MIROC 4m climate model, which exhibits abrupt AMOC changes similar to those observed in reconstructions. We investigate the reliability of simulated changes in the ocean carbon cycle by comparing the simulated carbon isotope ratios with sediment core data, and we examine potential biases and overlooked or underestimated processes in the model. Qualitatively, the modeled changes in atmospheric p CO 2 are consistent with ice core records. For example, during Heinrich Stadial 1 (HS1), atmospheric p CO 2 increases by 10.2 ppm, followed by a reduction of 7.0 ppm during the Bølling–Allerød (BA) period and then by an increase of 6.8 ppm during the Younger Dryas (YD) period. However, the model underestimates the changes in atmospheric p CO 2 during these events compared to values derived from ice core data. Radiocarbon and stable isotope signatures ( Δ 14 C and δ 13 C) indicate that the model underestimates both the activated deep-ocean ventilation and reduced efficiency of biological carbon export in the ...