Distinct roles of the Southern Ocean and North Atlantic in the deglacial atmospheric radiocarbon decline

In the context of the atmospheric CO2 C-14/C (Delta C-14(atm)) changes since the last ice age, two episodes of sharp Delta C-14(atm) decline have been related to either the venting of deeply sequestered low-C-14 CO2 through the Southern Ocean surface or the abrupt onset of North Atlantic Deep Water (NADW) formation. In model simulations using an improved reconstruction of C-14 production, Atlantic circulation change and Southern Ocean CO2 release both contribute to the overall deglacial Delta C-14(atm) decline, but only the onset of NADW can reproduce the sharp Delta C-14(atm) declines. To fully simulate Delta C-l4(atm) data requires an additional process that immediately precedes the onsets of NADW. We hypothesize that these early Delta C-14(atm) declines record the thickening of the ocean's thermocline in response to reconstructed transient shutdown of NADW and/or changes in the southern hemisphere westerly winds. Such thermocline thickening may have played a role in triggering the NADW onsets. (C) 2014 Elsevier B.V. All rights reserved.