Peak glacial 14C ventilation ages suggest major draw-down of carbon into the abyssal ocean

• Published in: Climate of the Past
• Main Authors: Sarnthein, M., Schneider, B., Grootes, P. M.
• Format: Text
• Language: English
• Published: 2018
• Subjects: Pacific; Southern Ocean; ice core
• Online Access: https://doi.org/10.5194/cp-9-2595-2013; https://cp.copernicus.org/articles/9/2595/2013/

Ice core records demonstrate a glacial–interglacial atmospheric CO 2 increase of ~ 100 ppm, while 14 C calibration efforts document a strong decrease in atmospheric 14 C concentration during this period. A calculated transfer of ~ 530 Gt of 14 C-depleted carbon is required to produce the deglacial coeval rise of carbon in the atmosphere and terrestrial biosphere. This amount is usually ascribed to oceanic carbon release, although the actual mechanisms remained elusive, since an adequately old and carbon-enriched deep-ocean reservoir seemed unlikely. Here we present a new, though still fragmentary, ocean-wide Δ 14 C data set showing that during the Last Glacial Maximum (LGM) and Heinrich Stadial 1 (HS-1) the maximum 14 C age difference between ocean deep waters and the atmosphere exceeded the modern values by up to 1500 14 C yr, in the extreme reaching 5100 14 C yr. Below 2000 m depth the 14 C ventilation age of modern ocean waters is directly linked to the concentration of dissolved inorganic carbon (DIC). We propose as a working hypothesis that the modern regression of DIC vs. Δ 14 C also applies for LGM times, which implies that a mean LGM aging of ~ 600 14 C yr corresponded to a global rise of ~ 85–115 μmol DIC kg −1 in the deep ocean. Thus, the prolonged residence time of ocean deep waters may indeed have made it possible to absorb an additional ~ 730–980 Gt DIC, one third of which possibly originated from intermediate waters. We also infer that LGM deep-water O 2 dropped to suboxic values of < 10 μmol kg −1 in the Atlantic sector of the Southern Ocean, possibly also in the subpolar North Pacific. The deglacial transfer of the extra-aged, deep-ocean carbon to the atmosphere via the dynamic ocean–atmosphere carbon exchange would be sufficient to account for two trends observed, (1) for the increase in atmospheric CO 2 and (2) for the 190‰ drop in atmospheric Δ 14 C during the so-called HS-1 "Mystery Interval", when atmospheric 14 C production rates were largely constant.