No signature of abyssal carbon in intermediate waters off Chile during deglaciation

At the end of the Last Glacial Maximum (19,000 to 11,000 years ago), atmospheric carbon dioxide concentrations rose while the Delta(14)C of atmospheric carbon dioxide declined(1,2). These changes have been attributed to an injection of carbon dioxide with low radiocarbon activity from an oceanic abyssal reservoir that was isolated from the atmosphere for several thousand years before deglaciation(3). The current understanding points to the Southern Ocean as the main area of exchange between these reservoirs(4). Intermediate water formed in the Southern Ocean surrounding Antarctica would have then carried the old carbon dioxide signature to the lower-latitude oceans(5,6). Here we reconstruct the Delta(14)C signature of Antarctic Intermediate Water off the coast of Chile for the past 20,000 years, using paired (14)C ages of benthic and planktonic foraminifera. In contrast to the above scenario, we find that the Delta(14)C signature of the Antarctic Intermediate Water closely matches the modelled surface ocean Delta(14)C, precluding the influence of an old carbon source. We suggest that if the abyssal ocean is indeed the source of the radiocarbon-depleted carbon dioxide, an alternative path for the mixing and propagation of its carbon dioxide may be required to explain the observed changes in atmospheric carbon dioxide concentration and radiocarbon activity.