Mega-14C Plateau Provides Global Age Tie Point for Pre-Boelling DO Event 1

Between 12,400 and 12,750 "atmospheric" 14C yr B.P. occurs an exceptionally broad 14C plateau that in total spans more than 800 calendar (cal.) years, from 15,250 to 14,420 cal. yr B.P. The plateau was first identified in Swiss lake sediments by Lotter et al. (1992) and more narrow-ly constrained on the basis of spline-interpolated coral and varve dates by Stuiver et al. (1998). A slight 14C age reversal by more than 200 years at the end of the plateau culminates near 14,500 cal. yr B.P., coeval with the Boelling peak warming in the GISP2 ice record and subsequent to the prominent DO warming event 1 at 14,680-14,665 cal. yr B.P. The start of the age reversal lies near 15,000 cal. yr, that is during the most recent part of the Heinrich 1 stadial (sensu lato). The plateau and its final 14C age increase were also identified in sediment cores from the South China Sea and the far northwestern Pacific, and possibly also in the Santa Barbara Basin (Hendy et al., 2002). Accordingly, the plateau helps to pin down for the time of the early Boelling the local paleo-14C reservoir ages to 800 years (compared to approx. 500 yr in the modern South China Sea and 800 yr in the northern North Pacific today) and thus provides a high-precision tool for global age correlations of regional paleoclimate events with the Greenland ice core record. Most significantly, the early onset of the 14C age reversal at about 15,000 cal. yr B.P. is equal to a drop in atmospheric 14C of about 120 per mil. In part, this shift may reflect a short-term but large-scale outgassing of "old" CO2 from the deep ocean to the atmosphere. Since the drop in 14C slightly preceded the abrupt climatic amelioration over Greenland, the outgassing may have its origin in early deglacial sea ice reduction that occurred in the Southern Ocean. In part, the extended 14C plateau may be linked to a short-term strong increase in geomagnetic intensity that was found both in the North Pacific and South Atlantic right during this time and may have induced a marked reduction in atmospheric 14C production.