Bomb radiocarbon in tree rings from northern New South Wales, Australia; implications for dendrochronology, atmospheric transport, and air-sea exchange of CO (sub 2) .

Abstract

We have analyzed by radiocarbon 27 consecutive single rings, starting from AD 1952, of a preliminarily cross-dated section (DFR 021) of Pinus radiata, which grew in Armidale, northern New South Wales, Australia. The bomb (super 14) C results suggested the possibility of 2 false rings, and, consequently, 2 misidentified rings in the preliminary count for this section. This possibility was supported by a better ring-width correlation between the revised DFR 021 count and other Pinus radiata chronologies in the study region. This indicated that bomb (super 14) C is a useful tool to complement the standard techniques of dendrochronology in tree species where annual rings are not always clearly defined. Our accelerator mass spectrometry (AMS) (super 14) C results for Armidale Pinus radiata, on a corrected timescale, can be compared with previously published atmospheric and oceanic (super 14) C data. The data show interesting features of atmospheric circulation and the regional air-sea exchange of CO (sub 2) for the bomb period. On average, the difference between Delta (super 14) C values for Armidale (30 degrees S) and those for Tasmania (42 degrees S) was negligible, implying a small latitudinal (super 14) C gradient in the Southern Hemisphere. However, small offsets between Armidale and Tasmania were observed for some periods. The variation of these offsets suggests some slight changes in the relative contributions of the 2 excess (super 14) C sources (the northern troposphere and southern stratosphere) to the southern troposphere. In the decay of bomb (super 14) C, atmospheric (super 14) C reached a global equilibrium at the end of the 1960s and decreased exponentially, halving every 16 years. The time for air-sea exchange of CO (sub 2) for southern Pacific mid-latitudes was found to be about 7.5 yr, which was equivalent to a CO (sub 2) flux from the atmosphere to the oceans of 21.5 moles m (super -2) y (super -1) for the 1970s.