Atmospheric C-14 variations derived from tree rings during the early Younger Dryas

Atmospheric radiocarbon variations over the Younger Dryas interval, from ∼13,000 to 11,600 cal yr BP, are of immense scientific interest because they reveal crucial information about the linkages between climate, ocean circulation and the carbon cycle. However, no direct and reliable atmospheric C records based on tree rings for the entire Younger Dryas have been available. In this paper, we present (1) high-precision C measurements on the extension of absolute tree-ring chronology from 12,400 to 12,560 cal yr BP and (2) high-precision, high-resolution atmospheric C record derived from a 617-yr-long tree-ring chronology of Huon pine from Tasmania, Australia, spanning the early Younger Dryas. The new tree-ring C records bridge the current gap in European tree-ring radiocarbon chronologies during the early Younger Dryas, linking the floating Lateglacial Pine record to the absolute tree-ring timescale. A\ua0continuous and reliable atmospheric C record for the past 14,000 cal yr BP including the Younger Dryas is now available. The new records indicate that the abrupt rise in atmospheric ΔC associated with the Younger Dryas onset occurs at ∼12,760 cal yr BP, ∼240 yrs later than that recorded in Cariaco varves, with a smaller magnitude of ∼40‰ followed by several centennial ΔC variations of 20-25‰. Comparing the tree-ring ΔC to marine-derived ΔC and modelled ΔC based on ice-core Be fluxes, we conclude that changes in ocean circulation were mainly responsible for the Younger Dryas onset, while a combination of changes in ocean circulation and C production rate were responsible for atmospheric ΔC variations for the remainder of the Younger Dryas