Abstract
Abstract. Ice core records demonstrate a glacial–interglacial atmospheric CO2 increase of ~ 100 ppm, while 14C calibration efforts document a strong decrease in atmospheric 14C concentration during this period. A calculated transfer of ~ 530 Gt of 14C-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 Δ14C data set showing that during the Last Glacial Maximum (LGM) and Heinrich Stadial 1 (HS-1) the maximum 14C age difference between ocean deep waters and the atmosphere exceeded the modern values by up to 1500 14C yr, in the extreme reaching 5100 14C yr. Below 2000 m depth the 14C 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. Δ14C also applies for LGM times, which implies that a mean LGM aging of ~ 600 14C 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 O2 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 CO2 and (2) for the 190‰ drop in atmospheric Δ14C during the so-called HS-1 "Mystery Interval", when atmospheric 14C production rates were largely constant.
Highlights
Global climatic and oceanic conditions underwent a series of fundamental transitions after the Last Glacial Maximum (LGM) that ended near 19 ka (Mix et al, 2001)
We use the 14C concentrations of the atmosphere and deep ocean during that time, both expressed in a Modern Carbon (MC) fraction to translate ‰ 14C values for intra-LGM, intra-Heinrich Stadial 1 (HS-1), and intra-Bølling– Allerød (B/A) into apparent age differences between the atmosphere and deep water (= benthic ventilation ages; 14C yr)
Extrapolating the validity of the modern global distributions of apparent 14C ventilation ages and dissolved inorganic carbon (DIC), we propose a new working hypothesis to infer past changes in the carbon storage of ocean deep waters
Summary
Global climatic and oceanic conditions underwent a series of fundamental transitions after the Last Glacial Maximum (LGM) that ended near 19 ka (Mix et al, 2001). To test the various model postulates and to quantify past changes in the carbon budget of the global ocean, we combine modern oceanographic data with a set of modern and past apparent 14C ventilation ages for ocean deep waters below 1500 m/2000 m water depth (w.d.) (Bard, 1998; Sarnthein, 2011; data sources in Table 1b and Fig. S1) These ages mean the time needed for a sample with pristine atmospheric 14C concentration in surface waters to decay to the 14C concentration observed in shallow- and deep-ocean samples, depicted in 14C values of foraminifers. This process would provide both the amount of carbon and the 14C concentration for the early deglacial drop in atmospheric 14C by 190 ± 10 ‰ over HS-1 (Broecker and Barker, 2007)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
