Enhanced ocean-atmosphere carbon partitioning via the carbonate counter pump during the last deglacial

Stéphanie Duchamp-Alphonse (1) , Giuseppe Siani (1) , Elisabeth Michel (2, 3) , Luc L Beaufort (4) , Yves Gally (4) , Samuel Jaccard (5, 6)

1 GEOPS - Géosciences Paris Sud
2 LSCE - Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette]
3 PALEOCEAN - Paléocéanographie
4 CEREGE - Centre européen de recherche et d'enseignement des géosciences de l'environnement
5 Institute of Geological Sciences [Bern]
6 OCCR - Oeschger Centre for Climate Change Research

Several synergistic mechanisms were likely involved in the last deglacial atmospheric pCO$_2$ rise. Leading hypotheses invoke a release of deep-ocean carbon through enhanced convection in the Southern Ocean (SO) and concomitant decreased efficiency of the global soft-tissue pump (STP). However, the temporal evolution of both the STP and the carbonate counter pump (CCP) remains unclear, thus preventing the evaluation of their contributions to the pCO$_2$ rise. Here we present sedimentary coccolith records combined with export production reconstructions from the Subantarctic Pacific to document the leverage the SO biological carbon pump (BCP) has imposed on deglacial pCO$_2$. Our data suggest a weakening of BCP during the phases of carbon outgassing, due in part to an increased CCP along with higher surface ocean fertility and elevated [CO$_{2aq}$]. We propose that reduced BCP efficiency combined with enhanced SO ventilation played a major role in propelling the Earth out of the last ice age.

Mots clés: NATURAL IRON FERTILIZATION; DEEP SOUTHERN-OCEAN; ICE-AGE; COCCOLITHOPHORE CALCIFICATION; CO2 CONCENTRATION; EXPORT PRODUCTION; ORGANIC-MATTER; PHYTOPLANKTON; PRESERVATION; VENTILATION

Domaines: Planète et Univers [physics]; Sciences de la Terre

Stéphanie Duchamp-Alphonse, Giuseppe Siani, Elisabeth Michel, Luc L Beaufort, Yves Gally, et al.. Enhanced ocean-atmosphere carbon partitioning via the carbonate counter pump during the last deglacial. Nature Communications, 2018, 9, pp.2396. ⟨10.1038/s41467-018-04625-7⟩. ⟨hal-01819587⟩